The Marine Life Information Network

Modelling studies have shown temperature to be an important driver behind deep-sea sponge distribution (Howell et al., 2016; Knudby et al., 2013), while direct measurements have shown stable, low bottom temperatures in Arctic sponge communities (Roberts et al., 2018).  The area of the Faroe-Shetland Channel where the biotope is observed in the UK experiences natural fluctuations in temperature from <0°C to >8°C (Parry et al., 2015). The characterizing species Geodia barretti normally lives in deep-sea waters where temperatures are 8-9°C (Leys et al., 2018), however, Henry & Roberts (2014) mention that boreal ‘ostur’ occurs in sub-zero temperatures on the northern side of the Wyville-Thomson Ridge.

Geodia barretti also occurs in the Barents Sea where bottom temperatures average 4.8°C (Kędra et al., 2017).  Specimens were found in the Mediterranean Sea, at a depth of 167 m, where the water temperature was around 13°C (Cárdenas et al., 2013). In the Faroe-Shetland Channel, Kazanidis et al. (2019) observed that the transects with the highest densities of sponges had temperatures that ranged from 6.52 to 8.98°C. Kazanidis et al. (2019) also found that temperature was a significant variable in explaining variations in sponge density.

There have been concerns that real-world temperature increases can be deleterious.  Mass mortality of Geodia barretti in 2006 and 2008 at the Tisler reef, Norway was concurrent with ~4^°C bottom temperature increases over 24 hr periods, for up to two weeks (Guihen et al., 2012). However, in vitro experiments were carried out to replicate this event and no visible signs of stress were found (Strand et al., 2017). Although increased respiration rate was noted, the sponge’s microbiome remained stable, no mortality was observed and respiration rates returned to normal on return to control temperatures (Strand et al., 2017). This could suggest that Geodia barretti is resistant to a temperature increase at benchmark level and that other factors must have been complicit in the mass mortality seen at the Tisler reef (Strand et al., 2017). However, the confidence in the degree of concordance for this assessment has been recorded as ‘Low’ to reflect this uncertainty.  

The study by Strand et al. (2017) is not alone in suggesting that temperature, along with other stressors, may create an additive effect that may be more deleterious to the characterizing species. Scanes et al. (2018) found that the multiple stressors of increased temperature (+5°C) and suspended sediment (simulated inert mine tailings, at 10 mg/l) on Geodia atlantica interacted to cause an increase in the release of nitrogen, indicating a higher energy demand. The temperature increase itself also caused increased respiration and a greater percentage of unstable lysosomes (reduced cellular health), which may also be a result of an increase in energetic demand, as well as stress (Scanes et al., 2018). Furthermore, an increase in silicate uptake (used for biomineralization to produce their skeletons) was observed with elevated temperature (13°C) after 33 days (Scanes et al., 2018). However, this is opposite to previous and subsequent observations.  For example, Strand et al. (2017) found no effect on silicate uptake with warming.  The result of the multiple stressors (warming and suspended sediments) must be interpreted carefully. The authors found that there were complex interactive effects on the species under study. Unpicking these relationships to evaluate temperature change effects is not straightforward.

Overall, if the biotopes occur in areas corresponding to the lower limit or middle of their temperature range, then they are probably able to tolerate a long-term increase in temperature of 2°C. However, if the biotopes occur at the upper limit of their temperature range (i.e. 8.98°C; Kazanidis et al., 2019), then they probably cannot tolerate an increase in temperature of 2°C. Although specimens of Geodia barretti have been found in the Mediterranean at temperatures of 13°C (Cárdenas et al., 2013), these records do not represent the biotopes of interest (i.e. Geodia and other massive sponges on Atlanto-Arctic upper bathyal coarse or mixed sediment), so it cannot be assumed that the biotopes would survive at these temperatures. It is likely that only biotopes at the lowest limit of their temperature range will tolerate a short-term increase in temperature of 5°C, and the above studies have shown potentially deleterious effects caused by 4 or 5°C increases in temperature. It is important to note that an increase in temperature may also cause a decrease in water oxygen concentration, however, this pressure is addressed separately (see the ‘De-oxygenation’ pressure).

Sensitivity assessment. The biotopes are associated with a range of bottom water temperatures, however increasing temperature may have an effect on Geodia and other sponge species making up the biotopes, particularly when in combination with other stressors. Therefore, resistance is assessed as ‘Medium’, resilience as ‘Low’ and the sensitivity is assessed as ‘Medium’.

There is a range of evidence surrounding the effect of temperature change on the characterizing species and on sponge aggregations in other regions. Modelling studies have shown temperature to be an important driver behind deep-sea sponge distribution (Howell et al., 2016; Knudby et al., 2013) while direct measurements have shown stable, low bottom temperatures in Arctic sponge communities (Roberts et al., 2018). The area of the Faroe-Shetland Channel where the biotope is observed in the UK experiences natural fluctuations in temperature from <0°C to >8°C (Parry et al., 2015). The characterizing species Geodia barretti normally lives in deep-sea waters where temperatures are 8-9°C (Leys et al., 2018), however, Henry & Roberts (2014) also mention that boreal ‘ostur’ occurs in sub-zero temperatures on the northern side of the Wyville-Thomson Ridge. Geodia barretti also occurs in the Barents Sea where bottom temperatures average 4.8°C (Kędra et al., 2017). Specimens were found in the Mediterranean Sea, at a depth of 167 m, where the water temperature was around 13°C (Cárdenas et al., 2013). In the Faroe-Shetland Channel, Kazanidis et al. (2019) observed that the transects with the highest densities of sponges had temperatures that ranged from 6.52 to 8.98°C. Kazanidis et al. (2019) also found that temperature was a significant variable in explaining variations in sponge density.

Direct laboratory experiments on deep-sea representatives of the genera Polymastia and Radiella found that a decrease from 6°C to 0 and 3°C had no significant effect on feeding rates, although there was a decrease in filtration rates for Polymastia but not at a significant level (Robertson et al., 2017). They concluded that naturally occurring temperature shifts (such as those caused by the Labrador current in Newfoundland where their study was located) were well tolerated by sponges (Robertson et al., 2017). The study by Robertson et al. (2017) supports earlier conclusions that sponge communities could tolerate changes in thermal regime better than other groups, such as cold-water corals during El Niño Southern Oscillation (ENSO) events  (Kelmo et al., 2013).

Overall, if the biotopes occur in an area corresponding to the upper limit or middle of their temperature range, then they are probably able to tolerate a long-term decrease in temperature of 2°C. However, if the biotopes occur at the lower limit of their temperature range, then they probably cannot tolerate a decrease in temperature of 2°C. At the upper limit of their temperature range (8.98°C; Kazanidis et al., 2019) the biotopes are likely to tolerate a short-term decrease in temperature of 5°C, as this falls within the know temperature range of the biotopes.

Sensitivity assessment: Geodia barretti occurs at a range of temperatures in deep-sea waters from sub-zero to around 8.98°C (Henry & Roberts, 2014; Kazanidis et al., 2019) and direct laboratory experiments on other deep-sea species have shown that a decrease in temperature at the benchmark level would not have a significant effect. Therefore, resistance is assessed as ‘High’, resilience as ‘High’, and the biotope is assessed as ‘Not sensitive’ at the benchmark level.

Changes in salinity are unlikely due to the depth at which the biotopes are found, combined with the distance from shore and the low potential for brine or freshwater discharge. However, salinity (along with other factors) is an important controller of modelled deep-sea sponge distribution (Howell et al., 2016; Knudby et al., 2013). Many studies examining the distribution of deep-sea sponges are limited to recording the conditions present at natural sponge aggregations. For example, Geodia spp., Stelletta normani and Stryphnus ponderosus occur in full salinity, typically 34-35 psu (Klitgaard & Tendal, 2004; Kutti et al., 2013; Murillo et al., 2012). In modelling work undertaken by Knudby et al. (2013), Geodia sp. was hypothesized to have a minimum bottom salinity tolerance threshold within the range of 34.3-34.8 psu, but they acknowledged that further investigation was needed. Howell et al. (2016) similarly quote a narrow salinity range of 34.8-35.5 ppt for 'ostur' habitat.  In the Faroe-Shetland Channel, Kazanidis et al. (2019) observed that the transects with the highest densities of sponges had salinity values that ranged from 34.91 to 35.13 psu. Kazanidis et al. (2019) also found that salinity was a significant variable in explaining variations in sponge density. Beazley et al. (2013) similarly noted that salinity played a significant role in structure-forming sponge abundance. Evidence of direct salinity experimentation on deep-sea sponges is scarce but changes in salinity are not thought to induce spawning (Spetland et al., 2007).

Sensitivity assessment. Although changes in salinity are unlikely, the highly stable nature of water masses found at upper bathyal depths and the salinity range that the characterising species occur in suggests that the biotopes are likely to be intolerant of salinity changes. Therefore, if exposed to increased salinity, resistance is likely to be ‘Medium’, resilience is likely to be ‘Low’ and sensitivity would be considered as ‘Medium’. Please note that this assessment is made with low confidence due to the limited evidence on the effects.  

Changes in salinity are unlikely due to the depth at which the biotopes are found, combined with the distance from shore and the low potential for brine or freshwater discharge. However, salinity (along with other factors) is an important controller of modelled deep-sea sponge distribution (Howell et al., 2016; Knudby et al., 2013). Many studies examining the distribution of deep-sea sponges are limited to recording the conditions present at natural sponge aggregations. For example, Geodia spp., Stelletta normani and Stryphnus ponderosus occur in full salinity, typically 34-35 psu (Klitgaard & Tendal, 2004; Kutti et al., 2013; Murillo et al., 2012). In modelling work undertaken by Knudby et al. (2013), Geodia sp. was hypothesized to have a minimum bottom salinity tolerance threshold within the range of 34.3-34.8 psu, but they acknowledged that further investigation was needed. In the Faroe-Shetland Channel, Kazanidis et al. (2019) observed that the transects with the highest densities of sponges had salinity values that ranged from 34.91 to 35.13 psu. Kazanidis et al. (2019) also found that salinity was a significant variable in explaining variations in sponge density.  Evidence of direct salinity experimentation on deep-sea sponges is scarce but changes in salinity are not thought to induce spawning (Spetland et al., 2007).

Sensitivity assessment. Although changes in salinity are unlikely, the highly stable nature of water masses found at upper bathyal depths and the salinity range that the characterising species occur in suggests that the biotopes are likely to be intolerant of salinity changes. Therefore, if exposed to reduced salinity, resistance is likely to be ‘Medium’, resilience is likely to be ‘Low’ and sensitivity would be considered as ‘Medium’. Please note that this assessment is made with low confidence due to the limited evidence on the effects.     

As filter feeders, water flow (e.g., deep-sea bottom current) is important to the characterizing species for the supply of food and removal of metabolic waste. Studies into a range of deep-sea sponge species, including Pheronema carpenteri, Asconema sp. and the Geodiidae, have concluded that distribution and current flow may be linked, whether through supply of larval recruits, food, favourable dissolved oxygen conditions or removal of sediment (Beazley et al., 2013; Rice et al., 1990; White, 2003). For example, Roberts et al. (2018) stated that enhanced currents benefit sponge grounds in the Arctic (dominated by Geodia parva, Geodia hentscheli and Stelletta rhaphidiophora) by improving food and larval supply, as well as preventing smothering by the settling of suspended sediments.

The resistance of the characterizing species to changes in water flow regime is poorly understood. Results from modelling studies suggest that changes in water flow regime may not have a significant impact in some areas but have a larger impact on others. Modelling results from the north-west Atlantic suggested that deep-sea sponge grounds were found primarily in areas of high (>0.1 m/s) maximum bottom current flow and that minimum current speed was also an important variable in the model output, especially in slope waters (Knudby et al., 2013). In high-energy environments, Geodia barretti is found attached to stable substrata, while in areas with lower energy it is not attached but incorporates small stones in order to maintain negative buoyancy (Tjensvoll et al., 2013). This observation suggests that the species would not be negatively impacted by any changes in water flow.

Water flow conditions are vitally important for filter feeders, and to prevent excess sedimentation. While the characterizing sponge species are less likely to suffer damage in elevated currents due to their massive morphology, variable flow may reduce the flux of food. This, in turn, may reduce growth and increase metabolic demand through the additional pumping or restriction of larval dispersal. Provided there are no long-term physiological changes, the characterizing species should be able to revert to baseline levels of activity if changing water flow pressure was to cease.

Sensitivity assessment. A decrease at the benchmark level (0.1-0.2 m/s) is unlikely to have a significant effect on the normal high flow rates that this biotope experiences, and as the characterizing species normally occur in areas of higher flow rates (such as in the Faroe Shetland Channel; Masson et al., 2004), then an increase is unlikely to be detrimental. Therefore, resistance is assessed as ‘High’, resilience as ‘High’ and the biotope is considered ‘Not sensitive’ at the benchmark level.

The Geodia and other massive sponges biotopes are found at upper bathyal depths. Therefore, they will not be affected by changes in emergence regime and the biotopes are assessed as ‘Not relevant’.

The Geodia and other massive sponges biotopes are found at upper bathyal depths. Therefore, they will not be affected by changes in nearshore wave exposure and the biotopes are assessed as ‘Not relevant’.

This pressure is ‘Not assessed’, but any evidence is presented where available.

A study on the effects of trace metals (copper, iron, zinc, magnesium) on the shallow-water congeneric species Geodia cydonium in the Mediterranean, showed altered cell functions and effects on the immune system (Saby et al., 2009). Furthermore, all metals studied inhibited enzyme activity (Saby et al., 2009).  The congeneric shallow-water species Stelletta anancora was found to selectively accumulate the toxin arsenic, even if it was at normal environmental levels (Araújo et al., 2003, cited in Schoenberg, 2016).

Barite (BaSO₄), a solid primary particulate compound in water-based drilling muds, can contain low concentrations of heavy metals and metalloid impurities (such as arsenic, chromium, copper, lead, nickel and zinc) (Neff, 2008, 2010). After Geodia barretti was exposed to barite for 14 days, the concentrations of the metals copper and strontium were not significantly different from that of sponges exposed to seawater (Edge et al., 2016). Total concentrations of lead, however, were significantly higher in sponges exposed to 30 mg/L of barite for 14 days, compared to those exposed to seawater. Nevertheless, the levels of lead were below those known to cause adverse effects in other sponge species (Cebrian et al., 2003).

Laboratory experiments were carried out to assess the impact of heavy metal contamination on the larval settlement and survival of the shallow-water sponge species Crambe crambe in the Mediterranean (Cebrian and Uriz, 2007). The results showed no negative effects of short term (1 week) exposure to copper and cadmium at concentrations of 30 µg/l and 5 µg/l, respectively. This study also concluded that the synergetic negative effect of copper and hydrocarbons on Crambe crambe decreases settlement further, which may cause a decline in sponge populations.

Fang et al. (2018) investigated the effects of suspended barite on Geodia barretti and Stryphnus fortis (similar to the characterizing species Stryphnus ponderosus). This study also looked at suspended natural sediment effects and bentonite (see ‘Change in suspended solids’ and ‘Introduction of other substances’ pressures). No sponge mortality was observed over the 33-day exposure periods, during which concentrations of ≤15.2 mg/l of barite were used. However, the sponges were covered by deposited particles. Spicule protrusion, one mechanism to reduce smothering by sediment, was observed for Geodia barretti, however, it was apparently not effective. Stryphnus fortis showed reduced tissue oxygenation upon exposure to barite, likely to be caused by reduced pumping, another mechanism to reduce smothering by sediment (Bell et al., 2015; Fang et al., 2018). Exposure to fine particles caused reduced oxygen consumption, plus correlated with reduced nitrite and nitrate release by the sponges. Geodia barretti recovered its oxygen-nitrogen metabolism (back to control levels) following abatement of bentonite after 33 days. After 33-days following abatement of barite, recovery did not occur for either of the barite impacted sponge species. Stryphnus fortis indicated possible long-term damage from barite, whereby the net ammonium flux displayed strong delayed responses during the recovery period (Fang et al., 2018).

Exposure to barite also induces cellular stress (lysosomal instability) in Geodia barretti (Edge et al., 2016). Lysosomal membrane stability (LMS) in Geodia barretti decreased with an increase in the concentration of suspended barite following 12-hour exposure, and levels of LMS were significantly lower with higher concentrations (50 mg and 100 mg per litre of total suspended solids (TSS/L); Edge et al., 2016). Longer-term and continuous exposure to barite for 14 days caused a decrease in LMS with increasing total suspended solids and length of exposure. Intermittent exposure to barite again resulted in lowered LMS with increases in TSS. Sponges exposed to barite at 30 mg TSS/L after six days had lower LMS than those exposed to reference sediment, but at 14 days the difference was not significant. LMS in sponges exposed to intermittent barite at 10 mg TSS/L was similar to reference sediments and seawater, indicating that no cellular stress is caused at this concentration of barite. Intermittent exposures, with 12-hour recovery periods, did not allow full recovery from cellular toxicity, indicating that longer recovery is required. However, the long-term effect of barite on LMS was reduced with this intermittent exposure. Overall, LMS levels in Geodia barretti were lowered by up to 30% with exposure to barite (Edge et al., 2016).

This pressure is ‘Not assessed’, but any evidence is presented where available.

Stévenne (2018) exposed Geodia barretti to a weathered blend of crude oil for eight days, at varying concentrations (33, 100 and 300 µg/l) to mimic conditions experienced after an oil-spill event. No sponge mortality, necrosis, tissue loss or colour change occurred during the experiment. Furthermore, no significant changes in respiration rates occurred, although a decrease of up to 52% was observed after 24 hours of exposure to oil compared to control sponges. Varying patterns of increased and decreased rates of respiration were observed over the exposure time and compared to the control. A higher mean abundance in destabilised lysosomal cells occurred with the increase in oil concentration. Respiration rates and lysosomal stability of all sponges from all treatments returned to levels comparable to the control after the recovery period of 30 days (Stévenne, 2018).

Laboratory experiments were carried out to assess the impact of polycyclic aromatic hydrocarbon (PAH) contamination on the larval settlement of the shallow-water sponge species Crambe crambe in the Mediterranean (Cebrian & Uriz, 2007). The results showed that exposure for 10 days inhibited the settlement of sponge larvae to a certain extent (25% and 30% in 500 and 1000 mg/l, compared to 65% in control). This study also showed that the synergetic negative effect of copper and hydrocarbons on Crambe crambe decreases settlement further, which may cause a decline in sponge populations.

Vad et al. (2017b) investigated the effect of hydrocarbons and dispersants on the shallow-water sponge species Halichondria panicea. During exposure to hydrocarbon contaminated seawater, the filtration behaviour of the sponge was diminished, and no recovery occurred during the 48-hour period after exposure.

This pressure is ‘Not assessed’, and no evidence was available regarding the effect of synthetic compound contamination on the Geodia and other massive sponges biotopes.

No evidence

This pressure is ‘Not assessed’, but any evidence is presented where available.

Fang et al. (2018) investigated the effects of suspended bentonite (mineralised volcanic ash) on Geodia barretti and Stryphnus fortis (similar to the characterizing species Stryphnus ponderosus). This study also looked suspended natural sediment and barite effects (see ‘Change in suspended solids’ and ‘Transition elements & organo-metal (e.g. TBT) contamination’ pressures). No sponge mortality was observed over the 33-day exposure periods, during which concentrations of ≤15.2 mg/l of bentonite were used, however, the sponges were covered by deposited particles. Spicule protrusion, one mechanism to reduce smothering by sediment, was observed for Geodia barretti, however, it was apparently not effective. The reduced tissue oxygenation in Geodia barretti and Stryphnus fortis upon exposure to bentonite was likely to be caused by reduced pumping, another mechanism to reduce smothering by sediment (Bell et al., 2015; Fang et al., 2018). Exposure to fine particles caused reduced oxygen consumption, plus correlated with reduced nitrite and nitrate release by the sponges. Geodia barretti recovered its oxygen-nitrogen metabolism (back to control levels) following abatement of bentonite after 33 days. Stryphnus fortis indicated possible long-term damage from bentonite, whereby the net ammonium flux displayed strong delayed responses during the recovery period (Fang et al., 2018). Exposure of Geodia barretti to suspended bentonite up to a total suspended solids (TSS) concentration of 100 mg TSS/L for 12 hours caused no significant change to lysosomal membrane stability (LMS) (Edge et al., 2016).

Deoxygenation is known to cause mortality in a range of benthic organisms, especially sessile taxa that cannot escape unfavourable conditions. For the characterizing species Geodia barretti, there is some evidence of behavioural adaptations (reduced pumping and respiration rates) that allow the sponges to restrict oxygen consumption as a protective mechanism when exposed to increased sediment load, which can cause short-term depletion of oxygen (Kutti et al., 2015; Schoenberg, 2016; Tjensvoll et al., 2013). There is also evidence of natural hypoxia and suboxia in some Demospongiae taxa, related to internal microbial conditions (Lavy et al., 2016). However, Leys et al. (2018) suggested that changes in oxygenation may negatively affect Geodia barretti.  Leys et al. (2004) found that Hexactinellida (glass sponges) were rare (fewer than eight live sponges per 10 m²) in regions of fjords in British Columbia where dissolved oxygen levels fell below 2 ml/l. It may be possible that Demospongiae share a similar pattern, however, no evidence for this class could be found. As there is no direct evidence on the resistance or resilience of the characterizing species in a reduced oxygen scenario at benchmark pressure, this pressure is assessed as ‘No evidence’.

There is some evidence to suggest that nutrient enrichment may be beneficial to sponges by providing additional food resources. Leys et al. (2018) provided the first direct in vivo measurement of nutrient flux in Geodia barretti. Ammonium and nitrite are taken up by Geodia barretti, and nitrate is produced (Leys et al., 2018). Silicate is also required by demosponges (including Geodia sp., Stryphnus ponderosus and Stelletta normani) for biomineralization of spicules to produce their skeletons, which shapes the sponge growth, and allows cell organization and development of the aquiferous system (Scanes et al., 2018; Uriz et al., 2003). However, there is no evidence available to assess the effect of nutrient enrichment on the characterizing species at benchmark pressure. Nevertheless, by definition, the biotopes are considered to be 'Not sensitive' at the pressure benchmark, which assumes compliance with good status as defined by the WFD.

It is possible that a deposit of organic matter will provide additional food resources for the filter-feeding characterizing species, although Leys et al. (2018) found that little of the carbon in Geodia barretti comes from detritus, despite requiring it for energy. Howell et al. (2016) further suggest that the amount of particulate organic carbon, on which sponges feed, is a key driver of 'ostur' sponge distribution. In two Scandinavian fjords, the reproduction of Geodia barretti is known to be linked to the sedimentation of particulate organic matter (Spetland et al., 2007).  Gamete release occurs in early summer and October when sedimentation of particulate organic matter is at its highest, after the phytoplankton blooms in spring and autumn (Spetland et al., 2007). This suggests that the reproduction of Geodia barretti is highly dependent on the seasonality of food supplies (Hogg et al., 2010).

Sensitivity assessment. Geodia barretti requires organic matter in suspension to filter feed (Howell et al., 2016) and the seasonality of particulate organic matter is known to play a role in the reproduction pattern of the species (Hogg et al., 2010; Spetland et al., 2007). Therefore, the species would likely benefit from any organic enrichment, so long as it does not negatively disrupt the normal reproduction cycle of the species. Therefore, resistance for the organic enrichment pressure is assessed as ‘High’, resilience as ‘High’, and the biotopes are considered ‘Not sensitive’ at the benchmark level.

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of available habitat (resilience is ‘Very low’). The Geodia and other massive sponges biotopes are therefore considered to have ‘High’ sensitivity to this pressure.

In the Faroe-Shetland Channel, Kazanidis et al. (2019) found that the highest densities of Category 3 sponges (i.e., massive, spherical or papillate, including Geodia spp.) were associated with substrata consisting of cobbles with boulders. Kazanidis et al. (2019) also found that the substratum (specifically cobbles with boulders) was a significant variable in explaining variations in sponge density. Furthermore, there is some evidence suggesting that Geodia spp. larvae can settle/grow on hard substrata (cobbles and boulders) (Freese, 2001; Henry and Roberts, 2014). However, previous surveys found the characterizing species associated with sedimentary habitats only (Klitgaard & Tendal, 2004).

Sensitivity assessment. Nonetheless, a change from sedimentary to hard rock substratum is likely to impact the characterizing species and the physical habitat. As a specific sediment type defines biotopes, a change in sediment type will result in a change in the biotope classification and therefore the loss of the original biotope. Hence, resistance is assessed as 'None'. As this pressure is considered as a permanent change, resilience is assessed as 'Very Low', and sensitivity is, therefore, assessed as 'High'.

Although the Geodia and other massive sponges biotopes are found in both coarse and mixed sediment habitats (Parry et al., 2015) it is possible that changes in the Folk classification may have a small impact on the characterizing species. While a change to mixed sediment or coarse sediment may not have significant implications for the characterizing species, there is some evidence that changes to finer substrata i.e. sand or muddy sand will be detrimental. The distribution of this sponge community is strongly connected with the presence of pebbles and cobbles within the substratum (e.g. Kazanidis et al., 2019). Therefore, the species would not have a cobble to “hold on” to for anchorage on sandy substrata. Furthermore, on muddy sediment with strong bottom currents, the resuspension of the sediment fine fraction could clog the feeding capability of the filter feeder sponges. Klitgaard & Tendal (2004) found that silty or muddy sediments of volcanic origin were not suitable substrata for deep-sea sponges. Boreal ‘ostur’ assemblages have also been shown to increase the physical heterogeneity of the bottom, changing the local sediment structure over time through the release of spicules after death, resulting in muddy spicule mats covering the bottom (Klitgaard & Tendal, 2004).

Sensitivity assessment. A change in sediment type will result in a change in the biotope classification and, therefore, the loss of the original biotope. Although Geodia can survive in mixed or coarse sediments, sand or muddy-sand is not suitable, so resistance is assessed as ‘None’. As this pressure is considered as a permanent change, resilience is assessed as 'Very Low', and the biotope is considered to have ‘High’ sensitivity to a change in seabed type by one Folk class.

As the Geodia and other massive sponges biotopes are characterized by sessile invertebrates, removal of the substratum at the benchmark level would cause the destruction of the biotopes within the affected area. Recovery would be severely impacted given the slow growth rate of the characteristic species, and as Geodia barretti is an annual spawner with only a short-range larval dispersal and high larval retention (Mariani et al., 2006), resulting in low connectivity (Knudby et al., 2013).

Sensitivity assessment.  As the upper 30 cm of sediment is the most important fraction for accompanying fauna, nutrient recycling, etc., resistance is assessed as 'None'. Resilience is likely to be 'Very low’ based upon the slow growth rates of Geodia sp. (i.e., several decades; Klitgaard and Tendal, 2004), likely extreme lifespans (Fallon et al., 2010; Leys and Lauzon, 1998), and low connectivity (i.e., short-range larval dispersal and high larval retention; Knudby et al., 2013). Therefore, sensitivity is assessed as ‘High’.

Species of Demospongiae may be more resistant to surface abrasion than Hexactinellid species (glass sponges) due to their proteinaceous skeletons that make their structure more flexible (Serpetti et al., 2014). However, Freese (2001) found that Geodia sp. broke or were turned over when nudged by a submersible in their study. Observations from northern Norway show that trawl gear can transport whole sponge individuals (such as Geodia spp. and Stelletta sp.) and deposit them in lines when the gear is recovered, or in dips in seabed topography (Buhl-Mortensen et al., 2016). Kędra et al. (2017) mentioned that some large sponges were observed in old trawling tracks in the Barents Sea, and suggested that these were likely dislocated and moved by fishing activities.

In the Barents Sea, Kędra et al. (2017) found that, in a location where both Geodia barretti and Geodia macandrewii occur, the mean individual sponge biomass was higher in untrawled areas. In trawled areas, sponges were more than five times less frequent (and 18 times less frequent in one study area) compared to untrawled areas. Geodia barretti and Geodia macandrewii were found at both the trawled and untrawled sites in one study area with low fishing pressure. However, in the other two study areas, at higher fishing intensity, a strong reduction in the biomass of Geodia barretti was recorded compared to untrawled sites in the same areas. For example, in one area, sponge mean individual biomass was 32.2 g m^-2 (± 57.0) in untrawled sites, and 19.1 g m^-2 (± 54.7) in trawled sites. It is important, however, to note the very high variability in biomass recorded. In the Faroe-Shetland Channel, Kazanidis et al. (2019) found that demersal fisheries pressure was the most significant variable in explaining variations in sponge density. The higher densities of sponges were found in the area with the lowest values of demersal landings. Densities in the areas with higher demersal landings were significantly lower.

Geodia spp. are noted to be able to survive damage from physical contact with trawl gear, as well as to survive being handled on ships, and they can re-establish on the seabed once returned (Jørgensen et al., 2016). Sponges left damaged by trawls are vulnerable, however, particularly as their filter-feeding systems may be clogged by non-food particles (Løkkeborg and Fosså, 2011, cited in Jørgensen et al., 2016). Geodia barretti explants are able to continue their reproductive cycle following manipulation (Hoffmann et al., 2003), and tissue regeneration is known to occur in sponges (albeit not specifically Geodia sp.), so Jørgensen et al. (2016) suggest that trawl-induced mortality is equivocal.

Teixidó et al. (2004) conducted an assessment in the Weddell Sea, looking at the re-colonization of the benthic ecosystem, including Demospongiae, after iceberg disturbance. Re-colonization was assessed over three stages based on qualitative criteria (e.g., faunal composition, categorical abundance and seabed relief features). Although no quantitative studies have been carried out to characterize the time frame of these patterns, Demospongiae species appeared to be quicker at recolonizing impacted mobile substrata than Hexactinellid species (glass sponges), but massive sponges defined the late stages of recovery.

Freese (2001) assessed the recovery of Geodia sp. (later re-identified as likely Poecillastra tenuilaminaris of the same sub-order, Astrophorina; Malecha & Heifetz, 2017) in the Gulf of Alaska (at 206-209 m depth) following experimental trawling (one trawl per area). Furrows in the substratum from the trawling activity, and gouges from the dragging of boulders, were found to still be prominent after one year, with little evidence of backfilling. No new colonization was evident one year after the trawling and, of the surviving Geodia sp. individuals, 56.3% were found lying on the bottom either torn or intact, and 40.6% were undamaged. The remaining 3.1% were upright but torn. Geodia spp. did not show any sign of necrosis and, although damaged sponges did not show signs of repair or regrowth, most of the knocked over sponges or pieces of sponge that had been torn off still appeared viable (Freese, 2001).

In a follow-up study, 13 years post-trawling, Malecha & Heifetz (2017) found that the average density of Poecillastra tenuilaminaris (re-identified from Geodia sp.) was nearly equal between trawl and reference transects.  However, video analysis showed that 19.3% of the sponges in trawl transects were damaged (either lying on the bottom or torn). This was twice the rate of that in reference transects, and this species had the highest percentage of missing tissue compared to other species. On detailed observation, 57.1% were damaged in trawled areas versus 16.7% in reference transects. Seafloor gouging, boulder displacement and damaged sponges were still visible on some trawl transects after 13-years.    

A modelling study also found that if a sponge community in the Aleutian Islands, Alaska, which included Geodiidae, was subjected to bottom trawling, it would likely only recover to 80% of its original biomass within a 20-year timeframe, in the absence of further damage/removal (Rooper et al., 2011). Care should be taken however when using the results of models outside of a proper validation (Rooper et al., 2018). 

As mixed sediment biotopes can contain fractions of muddy-sand, surface abrasion can also cause resuspension of these sediments, in addition to mechanical damage, which may remove the top layer of sediment. Abrasion pressure can, therefore, cause the release of anoxic sediments or nutrients, and potentially siltation of benthic fauna (Schoenberg, 2016).  These pressures are assessed separately (see ‘Changes in suspended solids’, ‘Smothering and siltation changes’ and ‘Nutrient enrichment’). 

Sensitivity assessment. Although some Geodia spp. are reported to survive damage from physical contact with trawl gear, the benchmark level of pressure states ‘damage to seabed surface features’. At this benchmark level, there is significant evidence to support effects occurring, and the top layer of the sediment is likely to be removed. As such, the community and associated habitat of the biotopes will be impacted, so resistance is assessed as ‘None’, resilience as ‘Very low’ and overall sensitivity as ‘High’. 

Penetration and or disturbance of the substratum would result in similar, if not identical effects as the Abrasion pressure.

Sensitivity assessment. Although some Geodia spp. are noted to be able to survive damage from physical impacts, since the biotopes are characterized by sessile invertebrates that live on the surface of the sediment, damage to the sub-surface seabed would likely mean that most of the population will be killed, damaged or removed by the pressure. This would result in the loss of the biotopes, and re-colonization will have to come from other areas (Serpetti et al., 2014). Furthermore, penetration is likely to cause the removal of the top layer of sediment. As such, the community and associated habitat of the biotopes will be impacted, so resistance is assessed as ‘None’, resilience as ‘Very low’ and sensitivity as ‘High’.

Laboratory studies have shown severe reductions in respiration rates of Geodia barretti when subjected to high levels of suspended sediments for four hours (Tjensvoll et al., 2013). The study found decreases of 52% (at 50 mg/l), 86% (at 100 mg/l) and 67% (at 500 mg/l). However,  specimens returned to a baseline metabolic rate four hours after exposure (Tjensvoll et al., 2013). In the higher sediment loads, sponges were noted to be actively pumping one hour after the exposure period ended. In another study of four-hour exposure to suspended crushed rock particles at 500 mg/l, Kutti et al. (2015) similarly found that the oxygen consumption of Geodia barretti decreased significantly (50%) from pre-exposure consumption. However, all sponges recovered within the 30-minute flushing cycle, and oxygen consumption did not differ significantly from the pre-exposure rates.

In long-term exposure (50 days) of Geodia barretti to high (50 mg/l) and low (10 mg/l) concentrations, oxygen consumption was 50% lower in sponges exposed to crushed rock compared to those exposed to natural bottom sediments (Kutti et al., 2015). However, after 29 days of cyclic exposure, the sponges’ respiration rates did not return to that of unexposed sponges and were reduced by >60% during the daily 12-hour recovery interval (Kutti et al., 2015). This suggested that a recovery time of more than 12 hours is required. The reductions in oxygen consumption were a result of a decrease or arrest in pumping, which was a response to high suspended solid concentrations (Tjensvoll et al., 2013). Bell et al. (2015) also suggested that the suppression of oxygen consumption may be a defence mechanism to prevent the internal sponge tissue being exposed to sediment. These studies, therefore, indicate that Geodia barretti has well developed responses to cope with short periods of elevated concentrations of suspended natural bottom sediments. Tjensvoll et al. (2013) also found that exposure of Geodia barretti to low sediment concentrations of 10 mg/l had little or no effect, although there were some variations in respiration rate during the recovery period.

Fang et al. (2018) investigated the effects of suspended natural sediment (and barite and bentonite) on Geodia barretti and Stryphnus fortis (similar to the characterizing species Stryphnus ponderosus). No sponge mortality was observed over the 33-day exposure periods, at concentrations of ≤15.2 mg/l, however, the sponges were covered by deposited particles. Reduced tissue oxygenation occurred in Stryphnus fortis on exposure to suspended natural sediments and this was likely to be caused by reduced pumping (Bell et al., 2015; Fang et al., 2018). Exposure to fine particles caused reduced oxygen consumption. It is suggested that finer particles (<63 µm) may have greater effects than larger particles (Kutti et al., 2015) on the metabolism in Geodia barretti, even at 10 mg/l (Fang et al., 2018), but Stryphnus fortis samples were less sensitive. However, Geodia barretti recovered its oxygen-nitrogen metabolism (to control levels) following abatement of suspended natural sediment after 33 days. However, net ammonium flux displayed strong delayed responses during the recovery period in Stryphnus fortis, which indicates possible long-term damage from suspended natural sediment.

In a further study, exposure of Geodia barretti to suspended natural (reference) sediment up to a total suspended solids concentration of 100 mg/l for 12 hours caused no significant change to lysosomal membrane stability (LMS) (an indication of cellular stress) (Edge et al., 2016). Furthermore, there was no significant difference in LMS in sponges exposed to seawater compared to suspended reference sediments at 10, 50 or 100 mg/l for 12 hours. Over a slightly longer exposure, sponges exposed to reference sediment at 30 mg/l after six days did show lower LMS and lower total organic energy than those exposed to seawater, but at 14 days there were no significant differences. The increase in lysosomal stability with length of exposure suggested possible acclimatisation in Geodia barretti at <30 mg/l (Edge et al., 2016 cited in Scanes et al., 2018). A decrease in respiration levels was also recorded when Geodia atlantica was exposed to suspended sediments at 10 mg/l over a period of 40 days (Scanes et al., 2018). Furthermore, lower silicate uptake (used for biomineralization to produce their skeletons) occurred after 33 and 40 days of exposure to suspended sediments (Scanes et al., 2018). After 26 days of exposure, lysosomal membrane instability was increased in comparison to the control, but this effect was not observed again at 33 or 40 days, which again suggests that Geodia atlantica can acclimatise after 26 days of exposure to low levels of suspended sediment (Scanes et al., 2018).

Sensitivity assessment. At the benchmark level of change in one rank on the WFD scale for one year (i.e. from 10 to 100 mg/l), suspended solids may reduce the survivability of the characterizing species in the long term, despite there being some evidence of acclimatisation (Scanes et al., 2018). The effects also vary with the type and particle size of the suspended sediment. Higher levels of sediment exposure are likely to also increase the recovery period (Pineda et al., 2017b). Therefore, resistance is assessed as ‘Medium’, resilience as ‘Low’ and overall sensitivity is assessed as ‘Medium’.

Deep-sea sponge aggregations occur in high water flow environments, which will affect how long any sedimentation deposits remain, and whether this is long enough to have any significant effect. Roberts et al. (2018) mention that enhanced currents at sponge grounds prevent smothering by settling suspended sediments. Jones et al. (2012) noted that drill cuttings were removed over time in the Faroe-Shetland Channel by lateral advection during high current events of velocities up to 1 m/s (Masson et al., 2004) and from bioturbation resulting in vertical redistribution in the sediments. Deposition of up to 1.5 m of drill cuttings in the Faroe-Shetland Channel resulted in a reduction of Geodia spp. from 13.3 individuals per 100 m² before the impact, to 0.3 individuals per 100 m² 10 years later (Jones et al., 2012). After three years, Jones et al. (2012) noted that a significant amount of drill cuttings had been removed, particularly in areas of lower initial deposition. The pressure used in this study, however (up to 1.5 m of sediment cover) far exceeds the benchmark level (up to 5 cm of fine material). Drill cuttings changed the sediment median grain size from coarse to fine. They are also known to contain compounds that cause ecotoxicological effects, e.g. from added mud chemicals or from impurities in the weight material (Trannum et al., 2010).  Therefore, the contaminants may have increased the impact and/or delayed the recovery of Geodia spp. For more information on the effects of specific drilling mud substances (bentonite and barite), please see the ‘Introduction of other substances’ pressure.

Fang et al. (2018) observed that Geodia barretti and Stryphnus fortis (similar to the characterizing species Stryphnus ponderosus) were covered by deposited particles following a 33-day exposure to suspended solids (≤15.2 mg/l). Spicule protrusion, one mechanism to reduce smothering by sediment, was observed for Geodia barretti, however, it was apparently not effective to the intensive sediment deposition the sponges were subject to in the study.  Another mechanism to reduce smothering by sediment in sponges is to reduce pumping and, therefore, reduce tissue oxygenation. Reduced pumping was observed in Stryphnus fortis on exposure to suspended natural sediments (Bell et al., 2015; Fang et al., 2018). In another experiment on Geodia barretti, images of the sponges before and after the exposure to suspended particles showed ‘light’ deposition of sediment on the sponge surface (Kutti et al., 2015).

The effects of burial on sponges, in general, were discussed by Schoenberg (2016), who suggested that resistance may be influenced by the nature of the deposited sediment and duration of burial. It was hypothesised that coarse material may reduce the amount of deoxygenation that the sponge experiences from burial. It is also expected that sponges may be able to survive temporary burial (Hoffmann et al., 2008) but would commonly die if left buried (Schoenberg, 2016). Resistance may vary by species and be dependent on the morphology and where individuals survive, there is likely to be a large metabolic cost in clearing the sponge’s respiratory channels (Schoenberg, 2016). In addition, Schoenberg (2016) reported a range of concerns surrounding siltation on sponges in general, including behavioural adaptations, mucus production, and phagocytosis of ingested material.

Sensitivity assessment. While discrete siltation events may not be detrimental to the characterizing species, the nature of the deposited material and the duration of burial may influence the sensitivity of the biotope. Geodia barretti and Stryphnus fortis (similar to the characterizing species Stryphnus ponderosus) both exhibit mechanisms to reduce smothering by sediments. However, high rates of sediment deposition (e.g. Fang et al., 2018; Jones et al., 2012) will cause the porous sponges to become clogged with sediment, resulting in reduced feeding capability (Klitgaard & Tendal, 2004). Mortality and low recovery rates (>10 years; Jones et al., 2017) can then occur, even after a significant amount of the sediment is removed (e.g. after three years, due to the high energy environments associated with the biotopes; Jones et al., 2017). Therefore, resistance is assessed as ‘Medium’, resilience as ‘Low’, and sensitivity as ‘Medium’. Any abrasion effects associated with the removal of this pressure are covered under the specific abrasion pressure.

Deep-sea sponge aggregations occur in high water flow environments, which will affect how long any sedimentation deposits remain, and whether this is long enough to have any significant effect. Roberts et al. (2018) mention that enhanced currents at sponge grounds prevent smothering by settling suspended sediments. Jones et al. (2012) noted that drill cuttings were removed over time in the Faroe-Shetland Channel by lateral advection during high current events of velocities up to 1 m/s (Masson et al., 2004) and from bioturbation resulting in vertical redistribution in the sediments. Deposition of up to 1.5 m of drill cuttings in the Faroe-Shetland Channel resulted in a reduction of Geodia spp. from 13.3 individuals per 100 m² before the impact, to 0.3 individuals per 100 m² 10 years later (Jones et al., 2012). After three years, Jones et al. (2012) noted that a significant amount of drill cuttings had been removed, particularly in areas of lower initial deposition. The pressure used in this study, however (up to 1.5 m of sediment cover) far exceeds the benchmark level (up to 5 cm of fine material). Drill cuttings changed the sediment median grain size from coarse to fine. They are also known to contain compounds that cause ecotoxicological effects, e.g. from added mud chemicals or from impurities in the weight material (Trannum et al., 2010).  Therefore, the contaminants may have increased the impact and/or delayed the recovery of Geodia spp. For more information on the effects of specific drilling mud substances (bentonite and barite), please see the ‘Introduction of other substances’ pressure.

Fang et al. (2018) observed that Geodia barretti and Stryphnus fortis (similar to the characterizing species Stryphnus ponderosus) were covered by deposited particles following a 33-day exposure to suspended solids (≤15.2 mg/l). Spicule protrusion, one mechanism to reduce smothering by sediment, was observed for Geodia barretti, however, it was apparently not effective to the intensive sediment deposition the sponges were subject to in the study.  Another mechanism to reduce smothering by sediment in sponges is to reduce pumping and, therefore, reduce tissue oxygenation. Reduced pumping was observed in Stryphnus fortis on exposure to suspended natural sediments (Bell et al., 2015; Fang et al., 2018). In another experiment on Geodia barretti, images of the sponges before and after the exposure to suspended particles showed ‘light’ deposition of sediment on the sponge surface (Kutti et al., 2015).

The effects of burial on sponges, in general, were discussed by Schoenberg (2016), who suggested that resistance may be influenced by the nature of the deposited sediment and duration of burial. It was hypothesised that coarse material may reduce the amount of deoxygenation that the sponge experiences from burial. It is also expected that sponges may be able to survive temporary burial (Hoffmann et al., 2008) but would commonly die if left buried (Schoenberg, 2016). Resistance may vary by species and be dependent on the morphology and where individuals survive, there is likely to be a large metabolic cost in clearing the sponge’s respiratory channels (Schoenberg, 2016). In addition, Schoenberg (2016) reported a range of concerns surrounding siltation on sponges in general, including behavioural adaptations, mucus production, and phagocytosis of ingested material.

It is worth considering that currents and water flow will vary by location and as such, it is difficult to generalise about the effect of burial on the biotope. Nevertheless, benchmark levels of deposition are likely to represent a significant pressure to the biotope.

Sensitivity assessment. While discrete siltation events may not be detrimental to the characterizing species, the nature of the deposited material and the duration of burial may influence the sensitivity of the biotopes. Geodia barretti and Stryphnus fortis (similar to the characterizing species Stryphnus ponderosus) both exhibit mechanisms to reduce smothering by sediments. However, high rates of sediment deposition (e.g. Fang et al., 2018; Jones et al., 2012) will cause the porous sponges to become clogged with sediment, resulting in reduced feeding capability (Klitgaard & Tendal, 2004). Mortality and low recovery rates (>10 years; Jones et al., 2017) can then occur, even after a significant amount of the sediment is removed (e.g., after three years, due to the high energy environments associated with the biotopes; Jones et al., 2017). In areas of higher deposition, the removal of sediment, and therefore recovery, will take longer. As such, resistance is assessed as ‘Low’, resilience as ‘Very low’, and sensitivity is assessed as ‘High’. Any abrasion effects associated with the removal of this pressure are covered under the specific Abrasion pressure.

Although a number of studies (e.g., Chapron et al., 2018; Courtene-Jones et al., 2019, 2017; La Beur et al., 2019) have shown that microplastics are ingested by deep-sea invertebrates, the effects of the pressure are poorly understood, and no evidence could be found on the effects of litter on the characterizing species or other deep-sea sponges. This pressure is, therefore ‘Not assessed’.

No evidence could be found on the effects of Electromagnetic changes on the characterizing species. Therefore, this pressure is assessed as ‘No evidence’.

The Geodia and other massive sponges biotopes are characterized by invertebrates with no means to detect noise or vibration and, therefore, it is unlikely to be affected by changes in underwater noise. This pressure is assessed as ‘Not relevant’.

The Geodia and other massive sponges biotopes are characterized by invertebrates with no means to detect light, and they occur at considerable depth where little or no incident light penetrates from the surface. As such, the biotopes will not be affected by changes in light regime and this pressure is assessed as ‘Not relevant’.

The Geodia and other massive sponges biotopes are characterized by sessile invertebrates, which are not dependent on larvae from outside the population due to their short-range larval dispersal and high larval retention (Mariani et al., 2006), resulting in low connectivity (Knudby et al., 2013). Hence, these biotopes are unlikely to be affected by 'Barriers to species movement'. This pressure is assessed as ‘Not relevant’.

The Geodia and other massive sponges biotopes are characterized by sessile invertebrates and are unlikely to be affected by an increased risk of collision defined under the pressure. This pressure is assessed as ‘Not relevant’.

The Geodia and other massive sponges biotopes are characterized by invertebrates that are not reliant on vision, and as such will not be affected by Visual disturbance. This pressure is assessed as ‘Not relevant’.

None of the characterizing species associated with the Geodia and other massive sponges biotopes are subject to cultivation or translocation, so this pressure is considered ‘Not relevant’.

No evidence could be found regarding the effect the 'Introduction or spread of non-indigenous species' on the Geodia and other massive sponges biotopes. Hence, the pressure is assessed as ‘No evidence’.

While there is published evidence on immunity and the spread of diseases in sponges (Pita et al., 2018), evidence of disease in deep-sea sponges is scant. Evidence of natural defences against Vibrio harveyi (Isnansetyo et al., 2009) and natural antifoulants (Sjögren et al., 2011) has been shown in Geodia spp.. Luter et al. (2017) assessed the prevalence of disease affecting Geodia barretti in Norway. Within a total area of 534 m² at depths from 100-220 m, 0-20% of the Geodia barretti community showed signs of disease, evident by brown/black discolouration on the surface of the sponge and extensive tissue integration and fouling. On investigation, distinctly different microbial communities were present in diseased sponges compared to healthy and non-diseased sponges. However, as the effects of this disease on the sponge function is not clear, this pressure is assessed as ‘No evidence’.

The characterizing species associated with the Geodia and other massive sponges biotopes are not commercially targeted, hence this pressure is assessed as ‘Not relevant’.

This pressure only assesses the biological effects of the removal of species. For evidence on the effects of the removal itself, please see the 'Physical damage' pressures.

Specimens of Geodia barretti, Geodia macandrewii, Geodia atlantica and Stryphnus ponderosus have been reported to exceed 70 cm in diameter and 24 kg wet weight (Klitgaard & Tendal, 2004), with other specimens of Geodia barretti having a wet weight of 36.7 kg (Leys et al., 2018). These large sizes and the massive sponge morphology of these characterizing species means that they sit raised off the seafloor, putting them at higher risk of being removed as incidental by-catch (Jørgensen et al., 2016). In northern Norway, whole sponge individuals (such as Geodia spp. and Stelletta sp.) were found deposited in lines (i.e. from when trawl gear is recovered) or in dips in the seabed topography (Buhl-Mortensen et al., 2016). Kędra et al. (2017) also observed large sponges in old trawling tracks in the Barents Sea, suggesting that these were likely dislocated and moved by fishing activities. If a significant proportion of the Geodia species are removed, the biological structure will be altered, and the habitat complexity reduced.

The degree of recovery would be reliant upon surviving sponges providing a nucleus for population recovery, as Geodia barretti only has a short-range larval dispersal and high larval retention (Mariani et al., 2006), resulting in low connectivity (Knudby et al., 2013). Freese (2001) noted that most knocked over Geodia sp., or pieces of Geodia sp. that had been torn off (following an experimental trawl) still appeared viable after one year, showing that even dislodged individuals can survive and support the recovery of the biotopes. After 13 years, the average density of Poecillastra tenuilaminaris (re-identified from Geodia sp.) was nearly equal between trawl and reference transects, despite sponges in the trawled areas still showing damage (twice that of sponges in reference transects) and having the highest percentage of tissue missing (Malecha & Heifetz, 2017). After eight months of cultivation in the field and adaptation in a laboratory, explants of Geodia barretti, which started at 4 x 4 x 4 cm in size, have pumping and respiration rates similar to that of full-grown individuals (Kutti et al., 2015). This time-period allowed cortex regeneration to take place (Hoffmann et al., 2003), although the survival rate during cultivation was only 50% (Kutti et al., 2015).

Sensitivity assessment. Removal of a large percentage of the characterizing species would alter the character of the biotope. The resistance to removal is assessed as ‘Low’ due to the inability of these species to evade collection. The resilience is assessed as ‘Low’, with recovery only being able to begin when the pressure is removed altogether. Therefore, the sensitivity is assessed as ‘High’.