The Marine Life Information Network

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail

Evidence

Pheronema carpenteri fields are unlikely to be exposed to significant fluctuations in temperature, due to the relatively stable nature of habitats at such depths. However, modelling studies have indicated that temperature is a key factor driving deep-sea sponge distribution (Howell et al., 2016). There is no direct evidence on the effect of temperature changes on Pheronema carpenteri, but the species is predicted to live in areas with temperatures ranging from 2.73 to 20.9°C, with a mean of 5.17°C (Howell et al., 2016).  At the Porcupine Seabight, in UK waters, Pheronema carpenteri has been recorded at temperatures of 6.5 -7.1°C (Hendry et al., 2019); at Rosemary Bank Seamount between 4.82 - 6.67°C (Eerkes-Medrano et al., 2020); and at Le Danois Bank in the Bay of Biscay at a mean temperature of 10.19°C (Sánchez et al., 2008).

It has been suggested that the upper temperature limits of glass sponges may be related to their ability to arrest their feeding current when irritated by silt or sediment in the water (Leys et al., 1999, 2004). Recovery from a stimulated arrest of pumping (tested experimentally on the Hexactinellid deep-sea sponge Rhabdocalyptus dawsoni using an electric shock to mimic the effects of particulates irritating the sponge tissue) was found to be temperature dependent (Leys et al., 1999, 2004).  This indicates that glass sponges may be particularly sensitive to increased temperatures when combined with changes in suspended solids (water clarity) or smothering and siltation rate changes. However, it cannot be assumed that Pheronema carpenteri would respond in the same way as Rhabdocalyptus dawsoni.

Sensitivity assessment: Pheronema carpenteri has been predicted to occur between 2.73 to 20.9 °C, but with a mean value of 5.17°C (Howell et al., 2016). Therefore, in areas where the temperature is closer to the lower end of the associated range, the species is likely to have some degree of resistance to temperature increases as this would remain within its predicted range. However, in areas towards the higher end of the associated range, the characterizing species is unlikely to be able to tolerate changes in temperature at the benchmark level (an increase of 5°C), particularly if associated with other pressures. As Pheronema carpenteri adults are sessile, they are unable to escape unfavourable conditions.  Resistance is therefore assessed as ‘Medium’, resilience as ‘Low’, and overall sensitivity is assessed as ‘Medium’.

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail

Evidence

Pheronema carpenteri fields are unlikely to be exposed to significant fluctuations in temperature, due to the relatively stable nature of habitats at such depths. However, modelling studies have indicated that temperature is a key factor in driving the range of the species (Howell et al., 2016). There is no direct evidence on the effect of temperature changes  on Pheronema carpenteri, but the species is predicted to live in areas with temperatures ranging from 2.73 to 20.9°C, with a mean of 5.17°C (Howell et al., 2016). At the Porcupine Seabight, in UK waters, Pheronema carpenteri has been recorded at temperatures of 6.5 - 7.1°C (Hendry et al., 2019); at Rosemary Bank Seamount between 4.82 -6.67°C (Eerkes-Medrano et al., 2020); and at Le Danois Bank in the Bay of Biscay at a mean temperature of 10.19°C (Sánchez et al., 2008).

Sensitivity assessment: Pheronema carpenteri has been predicted to occur between 2.73 to 20.9°C, but with a mean value of 5.17°C (Howell et al., 2016). Therefore, in areas where the temperature is closer to the higher end of the associated range, the species is likely to have some degree of resistance to a temperature decrease as this would remain within its predicted range.  However, in areas towards the lower end of the range, the characterizing species is unlikely to able to tolerate changes in temperature at the benchmark level (a decrease of 5°C).  As Pheronema carpenteri are sessile as adults, they are unable to escape unfavourable conditions.  Resistance is therefore assessed as ‘Medium’, resilience as ‘Low’, and overall sensitivity is assessed as ‘Medium’.

Salinity increase (local)

Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

Pheronema carpenteri fields are unlikely to encounter changes in salinity, due to the depths at which they are found, their distance from the shore and therefore the extremely low potential for brine or freshwater discharge to enter their environment.  Pheronema carpenteri records generally occur in areas of full salinity, for instance at Porcupine Seabight in the North East Atlantic (35.2-35.4) and at Le Danois Bank in the Bay of Biscay (mean value recorded at 35.77) (Hendry et al., 2019; Sánchez et al., 2008).  Pheronema carpenteri sponges have been recorded at both Le Danois Bank and at mud volcano fields in the Gulf of Cádiz (Spanish waters), which are located in the area of transition between the highly saline Mediterranean Outflow Water (MOW, 36.1 – 36.9 psu) and the less saline waters of the North Atlantic Deep Water (NADW, at Gulf of Cádiz, 34.9-35.2 psu) or North Atlantic Central Water (NACW, at Le Danois Bank) (Rueda et al., 2012; Sánchez et al., 2008).

Sensitivity assessment: Pheronema carpenteri fields are unlikely to be exposed to significant changes in salinity, due to the highly stable nature of water masses at the depths these habitats are found.  However, as a result of living in such stable conditions, 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 overall sensitivity would be considered as ‘Medium’.  Please note that this assessment is made with low confidence due to the lack of available evidence. 

Salinity decrease (local)

Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

Pheronema carpenteri fields are unlikely to encounter changes in salinity, due to the depths at which they are found, their distance from the shore and therefore the extremely low potential for brine or freshwater discharge to enter their environment.  Pheronema carpenteri records generally occur in areas of full salinity, for instance at Porcupine Seabight in the North East Atlantic (35.2-35.4) and at Le Danois Bank in the Bay of Biscay (mean value recorded at 35.77) (Hendry et al., 2019; Sánchez et al., 2008). 

Pheronema carpenteri sponges have been recorded at both Le Danois Bank and at mud volcano fields in the Gulf of Cádiz (Spanish waters) which are located in the area of transition between the highly saline Mediterranean Outflow Water (MOW, 36.1 – 36.9 psu) and the less saline waters of the North Atlantic Deep Water (NADW, at Gulf of Cádiz, 34.9-35.2 psu) or North Atlantic Central Water (NACW, at Le Danois Bank) (Rueda et al., 2012; Sánchez et al., 2008). 

Sensitivity assessment: Pheronema carpenteri fields are unlikely to be exposed to significant changes in salinity, due to the highly stable nature of water masses at the depths these habitats are found at, as well as their significant distance from the shore and any freshwater input.  However, as a result of living in such stable conditions, 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 lack of available evidence.

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

As suspension feeders, water flow plays a key role in determining suitable areas for colonization by Pheronema carpenteri. Rice et al. (1990) proposed that sponge distribution was controlled by local hydrography and Howell et al. (2016) suggest that large suspension feeders may aggregate in areas where internal tidal waves propagate, such as the shelf break. These internal waves result in the resuspension of particulate organic matter on which sponges feed ( McIntyre et al., 2016).

It is thought that the depth range and distribution of Pheronema carpenteri at the Porcupine Seabight in the North East Atlantic, is heavily influenced by the magnitude of seabed currents, where the sponges may rely on currents for the provision of re-suspended organic sediments (Rice et al., 1990). One study found the highest sponge biomass to be at depths of between 1,000 and 1,300 m, where currents occasionally exceeded 15 cm/s (0.15 m/s) but generally remained between 1 and 3 cm/s (Rice et al., 1990). This indicates that Pheronema carpenteri is able to tolerate changes in water flow of up to 0.1 m/s, however, it is not clear for how long.  A study in the same area by Lampitt (1986) suggested that near-bed currents in excess of 7 cm/s kept organic matter in suspension, which might drive the distribution of suspension feeders such as Pheronema carpenteri. Based on this hypothesis, Rice et al., (1990) predicted that areas of the steepest topography on the eastern flank of the Seabight would have the highest tidal currents (estimated at 15 –20 cm/s) and the highest levels of re-suspended organic matter, which might therefore also host high densities of suspension feeders. However, their study found higher densities outside the regions of expected current enhancement. They suggest the species may not be able to withstand direct exposure to high current speeds, but, instead, may be dependent on organic matter being deposited down or along the slope (Rice et al., 1990).

A later study in the Porcupine Seabight by White (2003) found that Pheronema carpenteri were absent from sites with daily mean currents generally in excess of 10 cm/s, with 45% of measured currents exceeding 15 cm/s. In contrast, in the ‘sponge belt’ region (at similar depths to absence areas), daily mean currents were between 5 and 10 cm/s, with only 12% of measured currents exceeding 15 cm/s. This might again indicate that the species has lower tolerance to higher (>10 cm/s) current speeds. However, mean daily current velocity was also less stable in the ‘sponge belt’, with large variability in velocity and reversals in the direction of flow occurring, as a result of baroclinic motions of the diurnal period, indicating they may have some degree of resistance to changes in water flow (White, 2003). 

In contrast to the studies discussed above, observations at the Goban Spur, in the North East Atlantic, found that Pheronema carpenteri occurred at high densities at a sampling station at a depth of 1,470 m.  This station experienced water flow velocities of approximately 35 cm/s during Autumn and Winter, but in Spring and Summer, flow velocities did not exceed 10 cm/s (Flach et al., 1998). These findings indicate that Pheronema carpenteri found at this location are more resistant to changes in water flow than those populations at the Porcupine Seabight. 

Pheronema carpenteri was found to dominate sponge communities at the Condor seamount south-west of the Azores in the North East Atlantic, an area where mixing due to tidal currents interacting with sloping topography likely creates favourable conditions for filter feeders (van Haren et al., 2017).

Sensitivity assessment: As a suspension feeder, Pheronema carpenteri can only survive in areas where tidal flow is high enough to re-suspend solids (Rice et al., 1990; Roberts et al., 2018; White, 2003). Flow rates where Pheronema carpenteri occurs in the Porcupine Seabight generally range from 1 cm/s to 10 cm/s, indicating the species has some tolerance to changes in flow rate (Rice et al., 1990; White, 2003). However, the species was notably absent from nearby areas where flow rates are 15 – 20 cm/s (Rice et al., 1990; Roberts et al., 2018; White, 2003).  This suggests that Pheronema carpenteri would be unlikely to survive an increase in water flow rate of between 0.1m/s to 0.2m/s for more than 1 year. Contradicting evidence from Flach et al. (1998) however, states that dense aggregations of Pheronema carptenteri occur at the Goban Spur, in the North East Atlantic, where flow rates can be 35 cm/s for around six months. A precautionary assessment with low confidence is therefore given, where resistance is assessed as ‘Low’, resilience as ‘Low’, and overall sensitivity is assessed as ‘High’.

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

Pheronema carpenteri fields are found at mid and lower bathyal depths.  They will therefore not be impacted by changes in emergence regimes and the pressure is, therefore, assessed as ‘Not relevant’.

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

Pheronema carpenteri fields are found at mid and lower bathyal depths.  They will therefore not be impacted by changes in wave exposure and this pressure is, therefore, assessed as ‘Not relevant’.

Transition elements & organo-metal contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

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

Hydrocarbon & PAH contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

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

Synthetic compound contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

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

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. Further detail

Evidence

No evidence was found. 

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

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

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

Many marine organisms are unable to tolerate oxygen levels lower than approximately 2 mg/l, at which point it can affect either their growth or their survival (Gray et al., 2002). However, there is limited evidence on the impacts of oxygen supply and concentration on sponges (Whitney et al., 2005). 

Glass sponge reefs off the coast of British Columbia, Canada, inhabit areas with oxygen levels of 64-152 μm (equivalent to approx. 2-5 mg/l), but they have also been found deeper in oxygen levels down to 30μm (approx. 1mg/l) (Whitney et al., 2005). Leys et al. (2004) found that in the Saanich Inlet, off British Columbia, there was a relative scarcity of Hexactinellid sponges (Aphrocallistes vastus, Heterochone calyx, Farrea occa, Rhabdocalyptus dawsoni, Staurocalyptus dowlingi and Acanthascus cf. platei) below 60 m depth. They hypothesised that dissolved oxygen levels of below 1 ml/l may pose a physiological limitation to these sponges. 

There is, however, no direct evidence for the deepwater Pheronema carpenteri species and the glass sponge reefs mentioned above are unique to the northeastern Pacific, so cannot be used as a proxy for the deepwater Pheronema carpenteri field biotopes.

Sensitivity assessment. 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.

Nutrient enrichment

Benchmark. Compliance with WFD criteria for good status. Further detail

Evidence

Whitney et al. (2005) suggested that shelf canyon areas off the coast of British Columbia, Canada, provide access to upwelled nutrient-rich water and enhance the concentration and supply of particulate organic matter for the glass sponge reefs occurring there. Deep-sea sponge aggregations are thought to play a vital role in nutrient recycling as they filter large volumes of water, forming a link between suspended solids and the benthos (Howell et al., 2016).

A study modelling the predictive distribution of sponge aggregations across the north-east Atlantic found that depth (likely acting as a proxy for other factors) was the most important environmental variable to explain distribution of Pheronema carpenteri, with temperature, current speed and particulate organic carbon (POC) flux also playing important roles (Howell et al., 2016). Silicate was found to have a smaller effect; but  dissolved silicate is required by all Hexactinellid sponges (Howell et al., 2016). The data used in the study showed an average silicate level of 15 μM where Pheronema carpenteri occurred, and glass sponge reefs in British Columbia have been found to occur at much higher silicate levels of 43-75 μM (Whitney et al., 2005). In the predictive models, Howell et al. (2016) also found silicate was correlated with nitrate, phosphate and depth, indicating all variables play a part in sponge distribution. However, since depth was found to be the most important explanatory variable, it is difficult to determine the role these nutrients may play in driving Pheronema carpenteri distribution.

Since Hexactinellid sponges are thought to be dependent to some degree on dissolved silicate, and in some areas are found to occur in fairly high concentrations of silicate (Whitney et al., 2005), it is possible that the biotope would not be affected by an increase in nutrients. However, the evidence is very limited.  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.  

Organic enrichment

Benchmark. A deposit of 100 gC/m²/yr. Further detail

Evidence

Resuspension of particulate organic matter within the water column is an important food source for dense glass sponge aggregations in the northern Atlantic (Flach et al., 1998; Rice et al., 1990) and Howell et al. (2016) found that particulate organic carbon (POC) flux at the seabed was an important explanatory variable when modelling the distribution of Pheronema carpenteri in North Atlantic deep-sea areas. It is therefore likely that an increase in organic matter will benefit sponge grounds through the provision of additional food sources. 

The environments in which Pheronema carpenteri are found are generally in close proximity to relatively high current speeds, allowing for both the distribution of suspended matter and suitable food residency times (Roberts et al., 2018; Whitney et al., 2005).  This may also prevent organic matter from reaching levels that Pheronema carpenteri cannot tolerate.

Sensitivity assessment:  Pheronema carpenteri requires suspended organic matter in order to filter feed. The species is therefore likely to benefit from organic enrichment, meaning that resistance is assessed as ‘High’, resilience is ‘High’, and the biotopes are considered ‘Not sensitive’ at the benchmark level. However, due to very limited evidence, confidence in this assessment is low.

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

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 Pheronema carpenteri fields biotopes are, therefore, considered to have ‘High’ sensitivity to this pressure. 

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

Pheronema carpenteri aggregations predominantly occur on soft substrata or existing spicule mats (Bett & Rice, 1992).  On Ireland’s continental shelf margin there are multiple records of aggregations being present on soft sediment (Rice et al., 1990; O’Sullivan et al., 2017; Vieira et al., 2020) and in the Gulf of Cádiz, Pheronema carpenteri individuals were found widely distributed on soft-bottomed sediment around mud volcanos (Rueda et al., 2012).  In addition, there have been recent records of high densities of Pheronema sponges in the Azores, Portugal, growing on softer sediments surrounded by rock, and on existing spicule beds, some of which cover rocky substrata (Creemers et al., 2018).

The species has also been recorded on mixed substrata at stations across the North East Atlantic. However, these were individuals associated with aggregations of Caryophyllia sp. cup coral, as opposed to aggregations of the sponge itself (Howell et al., 2014).  Observations at George Bligh Bank, in the North East Atlantic, have recorded individuals attached to boulders and in patches of shelly substratum amongst the boulders, as well as in patches of softer sediment surrounded by mixed substrata (Narayanaswamy et al., 2013).  

Sensitivity assessment. Although the characterizing species has been recorded in areas with mixed substrata and boulders, it is typically found on soft substrata. Therefore, it is likely that a change from sediment to soft or hard rock will cause an impact.  Furthermore, as a specific sediment type defines the biotope, a change in sediment type will result in a change of biotope classification and therefore loss of original biotope.  Therefore, resistance is assessed as ‘None.’  As this pressure is considered a permanent change resilience is assessed as ‘Very low,’ and, therefore, sensitivity is assessed as ‘High.

Physical change (to another sediment type)

Benchmark. Permanent change in one Folk class (based on UK SeaMap simplified classification). Further detail

Evidence

Pheronema carpenteri aggregations are typically found on soft sediments or overgrowing existing spicule mats (Bett & Rice, 1992), with records of aggregations on Ireland’s continental shelf all existing on softer substrata  (Rice et al., 1990; O’Sullivan et al., 2017; Vieira et al., 2020).  Records of the species growing on boulders (Narayanaswamy et al., 2013) are of individuals as opposed to aggregations, and those on mixed substrata (Howell et al., 2014) are of Pheronema carpenteri associated with cup coral aggregations, rather than aggregations of the sponge itself.

Therefore, a change in Folk classification from mud to either sand and muddy sand or mixed sediment could impact the aggregations of characterizing species if pockets of softer sediment do not remain. Furthermore, as a specific sediment type defines the biotope, a change in sediment type will result in a change in the biotope classification and therefore the loss of the original biotope. 

Sensitivity assessment. Hence, resistance is assessed as ‘None’, resilience as ‘Very low’, and overall sensitivity is assessed as ‘High’.   

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

No specific evidence is available on the effects of extraction at the benchmark level on Pheronema carpenteri aggregations. Removal of sponges has, however, been documented from scientific trawling. For example, McIntyre et al. (2016) recorded Pheronema carpenteri individuals from Agassiz trawl samples on Rosemary Bank Seamount in the North East Atlantic and Sánchez et al. (2008) recorded the species in beam trawl and baca otter trawl samples from Le Danois Bank in the Bay of Biscay. Since the biotope is characterized by sessile invertebrates, removal of the substratum at the benchmark level would likely destroy the biotope within the impacted area.

Sensitivity assessment: As Pheronema carpenteri are epifaunal species, living on the surface of the sediment, the extraction of the substratum at the benchmark level to 30cm would result in removal and resultant mortality of the species. Therefore, the resistance is assessed as ‘None.’  Resilience is likely to be ‘Very low’ due to the assumed slow growth rates (Leys and Lauzon, 1998) and low connectivity (Ross et al., 2019)  of Pheronema carpenteri.  Sensitivity is, therefore, assessed as ‘High’

Abrasion / disturbance of the surface of the substratum or seabed

Benchmark. Damage to surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Viera et al. (2020) assessed the presence of Pheronema carpenteri at the Porcupine Seabight in the North East Atlantic in 2011, following studies undertaken by Rice et al. (1990) in 1983/4. Between the two studies, Viera et al. (2020) found that Pheronema carpenteri were still present in the same areas, but there was a decline in population density. The maximum density recorded by Rice et al. (1990) in the area assessed was 1.6 ind/m², at 1210 m depth, with the most comparable estimate of numerical density at that depth recorded in 2011 being 0.03 ind/m². Furthermore, average sponge density in the 1210-1250 m depth range (where Rice et al. (1990) recorded the highest overall sponge density) had declined by a factor of 36 between surveys. There was, however, a peak in numerical sponge density in the 2011 study at 1180-1200 m depth, at 0.80 ind/m². Vessel monitoring system (VMS) data suggested that between 2009 and 2017, commercial bottom trawling had occurred in the area, and trawl marks were recorded within the sponge’s bathymetric range. Although this does not provide direct evidence of the impacts of bottom trawl fishing on Pheronema carpenteri aggregations, it suggests a possible relationship (Vieira et al., 2020). However, the authors also note that the change in density could be due to a successional shift in populations of Pheronema carpenteri upslope, as hypothesised by Barthel et al. (1996).

It is thought that Hexactinellid sponges are susceptible to breakage by trawling due to their fragile nature and high profiles, as demonstrated by Aphrocallistes vastus (Austin et al., 2007).  Observations of Aphrocallistes vastus in-situ indicated that the species cannot survive the removal of significant portions of its body, and it is likely that if individuals are knocked over, they would be subject to the accumulation of sediment on one side. Although this species is in the same class as Pheronema carpenteri (Hexactinelida), they are otherwise taxonomically separate, so this evidence should be interpreted cautiously. Furthermore, the arrangement of siliceous spicules in Pheronema carpenteri means it may be more flexible than other glass sponges and therefore may also be more tolerant to surface abrasion than other hexactinellid species (Serpetti et al., 2014).

Sensitivity assessment: No direct experimental studies on the effects of abrasion on Pheronema carpenteri are available, however a significant reduction in the peak abundance of the species has been observed in an area of the Porcupine Seabight subject to demersal trawling (Vieira et al., 2020).  Although the cause of this decline cannot be clearly attributed to trawling, it highlights the need for a precautionary sensitivity assessment for the abrasion pressure. Therefore, resistance is assessed as ‘None’, resilience as ‘Very low’, and overall sensitivity is assessed as ‘High.’ 

Penetration or disturbance of the substratum subsurface

Benchmark. Damage to sub-surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Penetration or disturbance of the substratum surface would result in similar, if not identical, effects as the abrasion pressure (see above). Sensitivity assessment. As the biotopes are characterized by sessile invertebrates living on the surface of the sediment, damage to the sub-surface would likely result in a significant proportion of the population being killed, damaged or removed by this pressure.  Penetration is also likely to remove the top layer of sediment, further impacting the community and associated habitat of the biotopes.  Resistance is assessed as ‘None’, resilience as ‘Very low’, and sensitivity is, therefore, assessed as ‘High.’

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

Resuspended particulate organic matter within the water column is an important food source for dense glass sponge aggregations in the northern Atlantic, where internal waves may cause resuspension.  Food availability, as a result of local hydrographic conditions, has been considered a primary factor in controlling the distribution of Pheronema carpenteri at the Goban Spur and Porcupine Seabight in the North East Atlantic (Flach et al., 1998; Rice et al., 1990). However, high levels of suspended sediments may irritate sponges, causing them to arrest their feeding currents (Grant, 2018; Kahn et al., 2018). Grant (2018) highlighted that suspended sediments are a common factor to affect sponges, and whilst they may excrete some inorganic material, large quantities could be detrimental (Yahel et al., 2007; Kahn et al., 2015 in Grant, 2018).

Although no evidence was available for Pheronema carpenteri, the impact of increased suspended sediment concentrations (SSCs) has been studied in other deep-sea Hexactinellid sponge species (Aphrocallistes vastus, Heterochone calyx, Rhabdocalyptus dawsoni and Farrea occa) (Grant, 2018), through both in situ and laboratory studies.  These species form rare glass sponge reefs, specifically in the north eastern Pacific (Kahn et al., 2018). It should be noted that Pheronema carpenteri do not form such reefs, and therefore results from these studies may not be directly applicable to this biotope.

Studies were carried out in situ at two reefs in British Columbia, one dominated by Aphrocallistes vastus and a second dominated by Heterochone calyx and Farrea occa. Aphrocallistes vastus responded to SSC increases of 10 – 80 mg/litre with reduced excurrent flow, arresting feeding currents both through short, single arrests (up to five minutes) and prolonged ‘coughing’ arrests (up to 30 minutes), decreasing feeding by up to 70% (Grant, 2018).  Heterone calyx and Rhabdocalyptus dawsoni arrested feeding currents in response to small sediment disturbances of < 5 -10 mg/litre, with Rhabdocalyptus dawsoni ceasing all pumping activity after prolonged exposure to SSCs of <1mg/litre (Grant, 2018).  No arrests were observed in Farrea occa, however, it was noted that the comparatively lower normal pumping rate of this species made it more challenging to measure excurrent flow (Grant, 2018).

Laboratory based studies on Rhabdocalyptus dawsoni and Aphrocallistes vastus found both species arrested feeding currents immediately in response to the introduction of fine sediment (<25 μm) to incurrent water flow (Tompkins-MacDonald & Leys, 2008).  Larger amounts of sediment provoked repeated arrests, and exposure lasting over four hours resulted in a gradual decline in pumping activity, with scanning electron microscopy revealing that chambers had become clogged (Tompkins-MacDonald & Leys, 2008).  Recovery took up to 25 hours, with both species periodically arresting activity during this time (Tompkins-MacDonald & Leys, 2008).  These findings are supported by additional laboratory-based experiments on Rhabdocalyptus dawsoni, in which sponges responded to increased intake of suspended particulates by cessation of their feeding currents until the suspended matter had cleared from the water (Leys et al., 1999). Although none of these studies looked at Pheronema carpenteri, the results indicate that some glass sponges are impacted by exposure to high levels of suspended solids. However, the threshold sensitivity was shown to vary by species (Grant, 2018; Tompkins-MacDonald & Leys, 2008).

Sensitivity assessment: Pheronema carpenteri fields are likely to have some degree of resistance to changes in suspended solids due to the reliance of the characterizing species on suspended particulate matter as a food source, and the potential for the cessation of pumping in response to increased levels of suspended solids.  However, the prolonged exposure to a change in suspended solids at the benchmark level may reduce the survivability of individuals, as a result of clogged feeding and respiratory apparatus.  Recovery time is also likely to increase with the duration of exposure.  Therefore, resistance is assessed as ‘Medium’, resilience as ‘Low,’ and overall sensitivity is assessed as ‘Medium.’

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

There is no direct evidence of the effect of smothering and siltation changes on Pheronema carpenteri. However, it is known that deep-sea sponge grounds occur in areas of relatively high water flow, where detrital material may be moved over the sediment surface by bottom currents (Flach et al., 1998). Lampitt (1986) suggested that when currents are above 7 cm/s (at one metre above the seabed) material is resuspended.  It is thought that this enhanced water flow prevents sponges from being smothered by the settling of suspended solids (Roberts et al., 2018; Whitney et al., 2005).

Benthic sponges can tolerate smothering to some degree, however, the associated raised energetic costs impair regeneration abilities (Hogg et al., 2010). Bell et al. (2015) report that sponges can be adversely affected by sedimentation through ingestion of fine particles, causing clogging of inhalant canals and the aquiferous system, resulting in reductions in feeding efficiency, or blockage to filtering apparatus. Furthermore, the presence of sediments together with local water movements can cause abrasion to sponges, removing tissue or entire sponges (Bell et al., 2015). They conclude that most species are likely to have some ability to tolerate settled sediment, with some having adapted to sedimented habitats, although these are poorly understood (Bell et al., 2015). However, these studies have mostly been undertaken on shallow-water demospongiae species so it is difficult to know if they would apply to Pheronema carpenteri.

In the Squamish River, Howe Sound, British Columbia, there are reports of “graveyards” of glass sponges (Aphrocallistes vastus, Heterochone calyx, Farrea occa, Rhabdocalyptus dawsoni, Staurocalyptus dowlingi and Acanthascus cf. platei) at the base of the river, where sediments accumulate, likely as a result of mining activities upstream (Leys et al., 2004).  This extensive mortality is potentially related to smothering, oxygen deficits, toxic chemical effects, or a combination of all factors (Leys et al., 2004).  As smothering cannot be solely attributed to mortality, this evidence should be interpreted cautiously.  

At a glacial-fed river in British Columbia, Canada, Leys et al. (2004) also reported that areas with the highest sediment accumulation had sponges that were “small and sediment-covered”. In the areas where sediment accumulation was reduced, glass sponges (Aphrocallistes vastus, Heterochone calyx, Farrea occa, Rhabdocalyptus dawsoni, Staurocalyptus dowlingi and Acanthascus cf. platei) were present in their greatest abundance (Leys et al., 2004).  These patterns of glass sponge distribution suggest that high rates of sedimentation prevent sponges from becoming established (Leys et al., 2004).

Sensitivity assessment:  Discrete sediment deposition events may be detrimental to the characterizing species, however, the sensitivity will depend on the volume of sediment deposited, the duration of the event and the nature of the sediment involved.  Higher rates of sediment deposition are likely to result in reduced resistance and resilience, leading to an overall higher sensitivity of Pheronema carpenteri.  As it is thought that benthic sponges can tolerate some degree of smothering (Hogg et al., 2010; Leys et al., 2004), resistance is assessed as ‘Medium’ to ‘light smothering by 5 cm of fine sediment.  Hence, resilience is assessed as ‘Low’,’ and sensitivity as ‘Medium.’  Any impacts relating to changes in suspended solids or abrasion are covered under the specific pressure sections.

Smothering and siltation rate changes (heavy)

Benchmark. ‘Heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

There is no direct evidence of the effect of smothering and siltation changes on Pheronema carpenteri. However, it is known that deep-sea sponge grounds occur in areas of relatively high water flow, where detrital material may be moved over the sediment surface by bottom currents (Flach et al., 1998).  Lampitt (1986) suggest that when currents are above 7 cm/s (at one metre above the seabed) material is resuspended.  It is thought that this enhanced water flow prevents sponges from being smothered by the settling of suspended solids (Roberts et al., 2018; Whitney et al., 2005).

Benthic sponges are able to tolerate smothering to some degree, however, the associated raised energetic costs impair regeneration abilities (Hogg et al., 2010).  Bell et al. (2015) report that sponges can be adversely affected by sedimentation through ingestion of fine particles, causing clogging of inhalant canals and the aquiferous system, resulting in reductions in feeding efficiency, or blockage to filtering apparatus. Furthermore, the presence of sediments together with local water movements can cause abrasion to sponges, removing tissue or entire sponges (Bell et al., 2015). They conclude that most species are likely to have some ability to tolerate settled sediment, with some having adapted to sedimented habitats, although these are poorly understood (Bell et al., 2015). However, these studies have mostly been undertaken on shallow-water demospongiae species so it is difficult to know if they would apply to Pheronema carpenteri.

 In the Squamish River, Howe Sound, British Columbia, there are reports of “graveyards” of glass sponges (Aphrocallistes vastus, Heterochone calyx, Farrea occa, Rhabdocalyptus dawsoni, Staurocalyptus dowlingi and Acanthascus cf. platei) at the base of the river, where sediments accumulate, likely as a result of mining activities occurring upstream (Leys et al., 2004).   This extensive mortality is potentially related to smothering, oxygen deficits, toxic chemical effects, or a combination of all factors. As smothering cannot be solely attributed to mortality, this evidence should be interpreted cautiously.  

At a glacial-fed river in British Columbia, Canada, Leys et al. (2004) also reported that areas with the highest sediment accumulation had sponges that were “small and sediment-covered”. In the areas where sediment accumulation was reduced, glass sponges (Aphrocallistes vastus, Heterochone calyx, Farrea occa, Rhabdocalyptus dawsoni, Staurocalyptus dowlingi and Acanthascus cf. platei) were present in their greatest abundance (Leys et al., 2004).  These patterns of glass sponge distribution suggest that high rates of sedimentation prevent sponges from becoming established (Leys et al., 2004).

Sensitivity assessment:  Discrete sediment deposition events may be detrimental to the characterizing species, however, the sensitivity will depend on the volume of sediment deposited, the duration of the event and the nature of the sediment involved. Heavy siltation events are likely to be detrimental to the characterizing species, as Pheronema carpenteri are sessile organisms and are therefore unable to move to escape unfavourable conditions.  Individuals are likely to suffer mortality due to smothering and the clogging of feeding and respiratory apparatus, resulting in oxygen deficits and starvation (Leys et al., 2004).  If sediment accumulation persists it is likely to restrict recovery of the population, as high rates of sedimentation are thought to prevent sponges from becoming established (Leys et al., 2004). Recovery may only be possible upon cessation of sediment deposition and would likely depend on recruitment from populations outside the impacted area (Serpetti et al., 2014).  Therefore, resistance is assessed as ‘Low’ to deposition of 30 cm of fine sediment, Hence, resilience is assessed as ‘Very low’, and sensitivity as ‘High.’  Any impacts relating to changes in suspended solids, abrasion or contaminants are covered under the specific pressure sections.

Litter

Benchmark. The introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline). Further detail

Evidence

A number of studies (e.g. Chapron et al., 2018; Courtene-Jones et al., 2017, 2019; La Beur et al., 2019) have shown that microplastics are ingested by deep-sea invertebrates. Bergmann & Klages (2012) reported that tissue abrasion and resultant mortality of shallow-water Demospongiae species was caused by lost fishing gear, based on a study by Chiappone et al. (2005). They also conjected that as plastics can smother sponges; this may reduce particle uptake and, in the long term, could impact growth and reproductive output, water exchange and respiration (Bergmann & Klages, 2012).

However, the effects of the pressure are poorly understood, and no direct evidence could be found on the effects of litter on Pheronema carpenteri specifically. This pressure is, therefore ‘Not assessed’.

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT. Further detail

Evidence

No evidence could be found on the effects of electromagnetic changes on the characterizing species. However, hexactinellids can propagate electrical signals through their tissues for the co-ordination of cessation of their feeding current (Leys et al., 1999) and, therefore, there is the potential that they may be sensitive to such changes but in the absence of further evidence, this pressure is assessed as ‘No evidence’.

Underwater noise changes

Benchmark. MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year. Further detail

Evidence

No evidence could be found on the effects of noise changes on the characterizing species.  Laboratory experiments on other hexactinellid sponges (Rhabdocalyptus dawsoni and Aphrocallistes vastus) indicated that some species may arrest their feeding currents in response to mechanical stimuli, including the introduction of vibrations (Tompkins-MacDonald & Leys, 2008).  However, in the absence of further evidence, this pressure is assessed as ‘No evidence.’

Introduction of light or shading

Benchmark. A change in incident light via anthropogenic means. Further detail

Evidence

Pheronema carpenteri field biotopes occur at mid and lower bathyal depths, at which no light penetrates from the surface, and therefore they are unlikely to be impacted by the introduction of light. As such, the biotopes will not be affected by changes in the light regime and this pressure is assessed as ‘Not relevant’.  

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

Hexactinellids are assumed to have a short (<24 hour) planktonic larval duration, but this assumption is based on observations from just one shallow-water species (Ross et al., 2019) and is, therefore, not likely to be representative of Pheronema carpenteri, as deep-water species are believed to have comparatively longer larval durations than similar shallow-water species (Hilário et al., 2015). A successional upslope movement of Pheronema carpenteri on the Continental Slope off Morocco, identified by Barthel et al., (1996), found juveniles on the edges of patches that suggested a limited potential for dispersion. However, solitary individuals have also been observed away from other known populations and, therefore, dispersal over greater distances may also be possible (Ross et al., 2019).  Due to the lack of consistent and conclusive evidence, this pressure has been assessed as ‘No evidence.

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

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

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

The Pheronema carpenteri field 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’

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

Pheronema carpenteri is not subject to cultivation or translocation, therefore this pressure is ‘Not relevant.’

Introduction or spread of invasive non-indigenous species

Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail

Evidence

No evidence could be found regarding the effect of the 'Introduction or spread of invasive non-indigenous species' on the characterizing species.

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

No evidence could be found regarding the effect of the 'Introduction of microbial pathogens' on the characterizing species. This pressure is assessed as ‘No evidence’.

Removal of target species

Benchmark. Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

The characterizing species associated with Pheronema carpenteri fields on Atlantic mid and lower bathyal mud are not commercially targeted, therefore this pressure is assessed as ‘Not relevant’.

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

It is thought that bottom trawling could pose the biggest threat to Pheronema carpenteri fields (Ross et al., 2019).  Specimens of Pheronema carpenteri have been reported from photos of by-catch of bottom longline fisheries in the Azores, demonstrating that sponge fields are vulnerable to mortalities as a result of the removal of species (Cyr, 2018).

Records of Pheronema carpenteri observed on surveys at the Porcupine Seabight, North East Atlantic, indicated a 50% drop in individual body mass between 1983/4 and 2011, with sponge equatorial diameter also decreasing between these years (Vieira et al., 2020). In addition, there was a reduction in the geometric mean density of Pheronema carpenteri at all sites visited. Available fishing intensity data, coupled with evidence of trawl marks at study sites, suggested that bottom trawling was highly likely to have occurred in the wider study area in the years before and after the 2011 study, with a significant concentration of effort around the 1000 m bathymetric contour, where Pheronema carpenteri were previously found in high densities (Rice et al., 1990). While the authors noted that direct evidence cannot be provided, it is thought that bottom trawl fishing activity was a likely cause of the observed impacts on the Pheronema carpenteri aggregations at this location (Vieira et al., 2020).   

Sensitivity assessment: The removal of a significant proportion of the characterizing species would alter the character of the biotope.  Due to the fact that Pheronema carpenteri is sessile and, therefore, cannot avoid the pressure, the resistance is assessed as ‘None’.  The resilience is assessed as ‘Very Low’, as recovery will only be possible if the pressure is fully removed, and growth rates are likely to be slow (Leys and Lauzon, 1998).  Therefore, the sensitivity of the Pheronema carpenteri field biotopes is assessed as ‘High.