The Marine Life Information Network

Substratum loss

Benchmark. All of the substratum occupied by the species or biotope under consideration is removed. A single event is assumed for sensitivity assessment. Once the activity or event has stopped (or between regular events) suitable substratum remains or is deposited. Species or community recovery assumes that the substratum within the habitat preferences of the original species or community is present. Further details

Evidence

Removal of the substratum would also remove the entire population of Furcellaria lumbricalis growing on it. A small proportion of the population may grow epiphytically on other algal species, e.g. Phyllophora sp. (Sharp et al., 1993), and these would also be removed by substratum loss. Intolerance is therefore assessed as high. Recovery is recorded as moderate (see additional information below). The free living Furcellaria lumbricalis forma aegagropila is not attached to the substratum and therefore would not be affected by substratum loss. However, the free living form is not widely distributed (Levring et al., 1969) and so is not considered to represent the typical intolerance of the species.

Smothering

Benchmark. All of the population of a species or an area of a biotope is smothered by sediment to a depth of 5 cm above the substratum for one month. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. Further details.

Evidence

Furcellaria lumbricalis is an erect species which grows up to 300mm in length and is often found with the holdfast buried in coarse sediment (Dixon & Irvine, 1977). Furthermore, Johansson et al. (1998) reported that Furcellaria lumbricalis persisted in areas of the Baltic Sea where eutrophication resulted in high sediment loads. It is likely therefore that mature individuals would be tolerant of smothering with 5cm of sediment. However, recently settled propagules and small developing plants would be buried by 5cm of sediment and be unable to photosynthesize. For example, Vadas et al. (1992) stated that algal spores and propagules are adversely affected by a layer of sediment, which can exclude up to 98% of light. There is therefore likely to be mortality of some portion of the population and so intolerance is assessed as intermediate. Recoverability is recorded as moderate (see additional information below).

Increase in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Furcellaria lumbricalis is not likely to be affected directly by an increase in suspended sediment. However, increased suspended sediment will have knock on effects in terms of light attenuation (considered in 'turbidity') and siltation. As discussed above in 'smothering', increased rate of siltation may inhibit development of algal spores and propagules resulting in some mortality. Intolerance is therefore assessed as intermediate. Recoverability is recorded as moderate (see additional information below).

Decrease in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Furcellaria lumbricalis is not likely to be affected directly by a decrease in suspended sediment and the consequent decrease in siltation. However, the species is tolerant of a certain amount of siltation as demonstrated by the fact that it is often found with its holdfast buried in coarse sediment. If siltation decreased, Furcellaria lumbricalis may become open to competition from algal species which are less sediment tolerant and would otherwise be excluded.

Desiccation

1. A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour.
2. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details.

Evidence

Like many sublittoral algae, Furcellaria lumbricalis is very intolerant of desiccation. Gessner & Schramm (1971) (reviewed by Bird et al., 1991) recorded that at 18-20°C, the critical saturation deficit for the species was 60-70% of total water content, as contrasted with 10% for the intertidal species Fucus vesiculosus. On desiccation to 65% total water content, photosynthetic rate was depressed to 60% of the norm and recovery following re-immersion took 7 hours. Desiccation to 42% resulted in only 50% recovery in 7 hours and there was no recovery of photosynthesis in thalli dried to 7% of their original water content. Growth experiments by Indergaard et al. (1986) revealed that growth in a continuous spray regime was over 3 times faster (227µm/day vs. 61µm/day) than growth in an intermittent spray regime. The benchmark level of desiccation is exposure to air and sun for one hour. It is difficult to determine how this level relates to the recorded reactions, but it is likely that desiccation would cause mass mortality and so an intolerance of high is recorded. Recovery is recorded as moderate (see additional information below).

Increase in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Furcellaria lumbricalis is essentially a subtidal algae, but also occurs in rockpools in the intertidal (Dixon & Irvine, 1977) and occasionally at the extreme low water springs level on exposed shores (Austin, 1960b). An increase in emergence of 1 hour every tidal cycle for a year would place the portion of the population furthest up the shore in a zone where it would be vulnerable to desiccation. The effects of desiccation are detailed in the relevant section. Mortality of this portion of the population would be likely so intolerance is assessed as intermediate. Recoverability is recorded as moderate (see additional information below).

Decrease in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Furcellaria lumbricalis is a subtidal species (Dixon & Irvine, 1977) and so would not be affected by a decrease in emergence regime.

Increase in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

Furcellaria lumbricalis appears to be able to tolerate a wide range of water flow rates. It occurs from extremely sheltered areas with "very weak" tidal streams (Connor et al., 1997a) to exposed coasts (Austin, 1960b) where presumably it experiences much greater water flow rates. Moderate water movement is beneficial to seaweeds as it carries a supply of nutrients and gases to the plants, removes waste products, and prevents settling of silt. However, if flow becomes too strong, plants may be damaged and growth stunted. For example, Austin (1960b) recorded loss of fronds and restricted growth in Furcellaria lumbricalis specimens from an exposed shore in Wales. Additionally, an increase to very strong flows may inhibit settlement of spores and may remove adults or germlings. It is likely therefore that an increase in water flow rate would place the populations originally at the limit of their tolerance into a zone of intolerance and some mortality would result. Intolerance is therefore assessed as intermediate. Recoverability is recorded as moderate.

Decrease in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

Furcellaria lumbricalis occurs in areas of "very weak" water flow (Connor et al., 1997a) and therefore is likely to be tolerant of decreases in water flow. Gessner (1955) (cited in Schwenke, 1971) stated that deeper growing species of the benthos near Helgoland, including Furcellaria lumbricalis, had a smaller stagnation-caused respiratory inhibition than surface living species, which enabled them to thrive in low flow conditions. Furthermore, Austin (1960b) noted that Furcellaria lumbricalis in areas of low water flow lived longer and grew larger than specimens from areas with high flow. The species is therefore assessed as being tolerant.

Increase in temperature

1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

Furcellaria lumbricalis has a wide geographic range, occurring in Europe from northern Norway to the Bay of Biscay. Novaczek & Breeman (1990) recorded that specimens of Furcellaria lumbricalis grew well in the laboratory from 0-25°C with optimal growth between 10 and 15°C. Growth ceased at 25°C and 100% mortality resulted after 3 months exposure to 27°C. Similarly, Bird et al. (1979) recorded optimum growth at 15°C and cessation of growth at 25°C with associated necrosis of apical segments. Considering that maximum sea surface temperatures around the British Isles rarely exceed 20°C (Hiscock, 1998), it is unlikely that Furcellaria lumbricalis would suffer mortality due to the benchmark increase in temperature. However, elevated temperatures would probably result in inhibition of growth and hence intolerance is recorded as low. Growth should quickly return to normal when temperatures return to their original levels so recoverability is assessed as very high.

Decrease in temperature

1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

Furcellaria lumbricalis has a wide geographic range, occurring in Europe from northern Norway to the Bay of Biscay. Novaczek & Breeman (1990) recorded that specimens of Furcellaria lumbricalis grew well in the laboratory from 0-25°C with optimal growth between 10 and 15°C. The species tolerated -5°C for 3 months with no mortality. Bird et al. (1979) extrapolated from a growth curve they calculated for Furcellaria lumbricalis and concluded that growth would not be inhibited at 0°C. Minimum surface seawater temperatures rarely fall below 5°C around the British Isles so Furcellaria lumbricalis is likely to tolerate the benchmark decrease in temperature.

Increase in turbidity

1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

Furcellaria lumbricalis often occurs in relatively turbid waters. Laboratory experiments by Bird et al. (1979) revealed that Furcellaria lumbricalis was growth saturated at very low light levels (ca 20µE/m²/s) compared to other algae such as Chondrus crispus (50-60µE/m²/s) and Fucus serratus (100µE/m²/s). They suggest that this may be an explanation why Furcellaria lumbricalis is able to proliferate in relatively deep and turbid waters. Similarly, in their review, Bird et al. (1999) comment that in all studies, saturation and inhibition radiances were low for Furcellaria lumbricalis compared to other macroalgae indicating good competitive ability in the attenuated light of deeper or more turbid waters. In light of its tolerance of turbid conditions it is expected that the majority of the Furcellaria lumbricalis population would be unaffected by increases in turbidity, indeed, such changes may even provide the species with a competitive advantage over other macroalgae.

Decrease in turbidity

1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

Furcellaria lumbricalis is unlikely to be affected by a decrease in turbidity as it is growth saturated at very low light levels compared to other macroalgae (Bird et al., 1979; Bird et al., 1991).

Increase in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

Furcellaria lumbricalis typically occurs in a wide range of exposure categories, from "extremely sheltered" (Connor et al., 1997a) to exposed (Austin, 1960b). Increases in wave exposure may result in compromised growth and damage to or removal of the plants due to physical abrasion by sediments mobilized by wave action. Austin (1960b) noted that Furcellaria lumbricalis from extremely exposed sites have smaller dimensions than individuals from semi-exposed sites and that fronds may be lost due to storm action. Furthermore, Sharp et al. (1993) reported Furcellaria lumbricalis found cast ashore following storms. It is likely therefore that some mortality would occur due to increases in wave action and so intolerance is assessed as intermediate. Recoverability is recorded as moderate (see additional information below). It should be noted that the free living form Furcellaria lumbricalis forma aegagropila only occurs in sheltered habitats (Levring et al., 1969) and is likely to be more susceptible to being cast ashore by increased wave action.

Decrease in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

Furcellaria lumbricalis occurs in "extremely sheltered" habitats (Connor et al., 1997a) and is likely to tolerate decreases in wave exposure. Gessner (1955) (cited in Schwenke, 1971) noted that deep living species such as Furcellaria lumbricalis had a relatively high tolerance of stagnation. However, Austin (1960b) commented that Furcellaria lumbricalis from extremely sheltered habitats achieved smaller dimensions than individuals from moderately exposed habitats.

Noise

1. Underwater noise levels e.g., the regular passing of a 30-metre trawler at 100 metres or a working cutter-suction transfer dredge at 100 metres for one month during important feeding or breeding periods.
2. Atmospheric noise levels e.g., the regular passing of a Boeing 737 passenger jet 300 metres overhead for one month during important feeding or breeding periods. Further details

Evidence

Algae have no mechanisms for detection of sound and therefore would not be sensitive to disturbance by noise.

Visual presence

Benchmark. The continuous presence for one month of moving objects not naturally found in the marine environment (e.g., boats, machinery, and humans) within the visual envelope of the species or community under consideration. Further details

Evidence

Algae have no visual acuity and therefore would not be affected by visual disturbance.

Abrasion & physical disturbance

Benchmark. Force equivalent to a standard scallop dredge landing on or being dragged across the organism. A single event is assumed for assessment. This factor includes mechanical interference, crushing, physical blows against, or rubbing and erosion of the organism or habitat of interest. Where trampling is relevant, the evidence and trampling intensity will be reported in the rationale. Further details.

Evidence

The fronds of Furcellaria lumbricalis are cartilaginous and flexible and are therefore likely to be reasonably resistant to physical abrasion. However, Austin (1960b) noted that fronds are detached by storm action. The plant's point of attachment to the substratum, the holdfast, is a potential point of weakness. For example, Taylor (1970) (cited in Sharp et al., 1993) stated that clumps of fronds were easily removed from the substratum by drag-raking, but only where the plant had a sufficient number of dichotomies (usually more than 3) to snag in the rake. It is likely therefore that the benchmark level of abrasion, for instance the impact of an anchor and dragging of a chain, would cause some detachment and/or damage. It is unlikely that detached plants would find suitable substrata for reattachment and so mortality is likely to result. Intolerance is therefore assessed as intermediate. Recoverability is recorded as moderate (see additional information below). The free living Furcellaria lumbricalis forma aegagropila would prevent no mechanical resistance to abrasion and so would be unlikely to be damaged.

Displacement

Benchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details

Evidence

Sharp et al. (1993) noted that, following detachment, Furcellaria lumbricalis plants were capable of reattachment. During this process, growth may be compromised as energy would need to be diverted to the reattachment process. Intolerance is therefore assessed as low. Growth should quickly return to normal once the holdfast has become re-established so recoverability is recorded as very high. It should be noted that reattachment would only be possible if the plant was displaced to a suitable substratum.

Synthetic compound contamination

Sensitivity is assessed against the available evidence for the effects of contaminants on the species (or closely related species at low confidence) or community of interest. For example:

• evidence of mass mortality of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as high sensitivity;
• evidence of reduced abundance, or extent of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as intermediate sensitivity;
• evidence of sub-lethal effects or reduced reproductive potential of a population of the species or community of interest will be assessed as low sensitivity.

The evidence used is stated in the rationale. Where the assessment can be based on a known activity then this is stated. The tolerance to contaminants of species of interest will be included in the rationale when available; together with relevant supporting material. Further details.

Evidence

No evidence was found specifically relating to the intolerance of Furcellaria lumbricalis to synthetic chemicals. However, inferences may be drawn from the sensitivities of red algal species generally. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination, possibly due to the susceptibility of phycoerythrins to destruction. They also report that red algae are effective indicators of detergent damage since they undergo colour changes when exposed to relatively low concentration of detergent. Smith (1968) reported that 10 ppm of the detergent BP 1002 killed the majority of specimens in 24hrs in toxicity tests. Laboratory studies of the effects of oil and dispersants on several red algal species, including Plocamium cartilagineum (order Gigartinales), concluded that they were all sensitive to oil/ dispersant mixtures, with little difference between adults, sporelings, diploid or haploid life stages (Grandy, 1984) (cited in Holt et al., 1995). Cole et al. (1999) suggested that herbicides , such as simazina and atrazine were very toxic to macrophytes. Hoare & Hiscock (1974) noted that all red algae except Phyllophora sp. were excluded from Amlwch Bay, Anglesey, by acidified halogenated effluent discharge. The evidence suggests that in general red algae are very sensitive to synthetic chemicals. Intolerance of Furcellaria lumbricalis is therefore recorded as high. Recoverability is recorded as moderate (see additional information below).

Heavy metal contamination

Evidence

Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al. (1999) reported that Hg was very toxic to macrophytes. The sub-lethal effects of Hg (organic and inorganic) on the sporelings of another intertidal red algae, Plumaria elegans, were reported by Boney (1971). 100% growth inhibition was caused by 1 ppm Hg. No information was found concerning the effects of heavy metals on Furcellaria lumbricalis specifically, and therefore an intolerance assessment has not been attempted.

Hydrocarbon contamination

Evidence

No evidence was found specifically relating to the intolerance of Furcellaria lumbricalis to hydrocarbon contamination. However, inferences may be drawn from the sensitivities of red algal species generally. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination, possibly due to the susceptibility of phycoerythrins to destruction. Laboratory studies of the effects of oil and dispersants on several red algal species, including Plocamium cartilagineum (order Gigartinales), concluded that they were all sensitive to oil/ dispersant mixtures, with little difference between adults, sporelings, diploid or haploid life stages (Grandy, 1984) (cited in Holt et al., 1995). Intolerance is therefore assessed as high. Recoverability is recorded as moderate (see additional information below).

Radionuclide contamination

Evidence

No information was found concerning the intolerance of Furcellaria lumbricalis to radionuclides.

Changes in nutrient levels

Evidence

Bird et al. (1991) commented that productivity by Furcellaria lumbricalis was low, uptake of nutrients was slow and the species was not nutrient limited under normal conditions. This suggests that the species would not be greatly affected by an increase in nutrient concentration. However, eutrophication may have other knock-on effects. Johansson et al. (1998) suggested that one of the symptoms of large scale eutrophication is the deterioration of benthic algal vegetation in areas not directly affected by land-runoff or a point source of nutrient discharge. Altered depth distributions of algal species caused by decreased light penetration and/or increased sedimentation through higher pelagic production have been reported in the Baltic Sea (Kautsky et al., 1986; Vogt & Schramm, 1991). Johansson et al. (1998) studied changes in the benthic algal community of the Skagerrak coast in the Baltic Sea, an area heavily affected by eutrophication, between 1960 and 1997. They noted the disappearance of the red alga, Polyides rotundus, but commented that problems existed in their sampling method. They also noted the increase of delicate red algae with foliaceous thalli, e.g. Delesseria sanguinea and Phycodrys rubens, and tougher red algae with foliaceous thalli, e.g. Phyllophora sp. Increases in the delicate algae were most pronounced at the more wave exposed sites, while increases in the tougher algae occurred at the more sheltered sites with high sedimentation. They commented that these results suggest that the increase of delicate species with large growth potential may have been caused by eutrophication, but that the effect is counteracted when eutrophication results in high sedimentation, in which case the tougher Phyllophora sp. thrive. Additionally, Chondrus crispus and Furcellaria lumbricalis, both species with tough thalli, decreased at the wave exposed sites, possibly due to competition from the more vigorous Phycodrys rubens and Delesseria sanguinea, but persisted at the sites with high sedimentation. This study suggests that, although Furcellaria lumbricalis may be tolerant of eutrophication per se, populations may suffer as result of the reactions of other algal species. Intolerance is therefore recorded as intermediate, and recoverability as moderate (see additional information below).

Increase in salinity

1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

Furcellaria lumbricalis is a euryhaline species which occurs in a wide range of salinity conditions down to 6-8 psu (Bird et al., 1991). In the Kattegat and the Gulf of St Lawrence, it is reported to compete well with other species at salinities ranging from 25-32 psu (see review by Bird et al., 1991). Growth experiments in the laboratory revealed that optimum growth occurred at 20 psu, the species grew well at 10 psu and 30 psu, but that growth declined above 30 psu to negligible levels at 50 psu (Bird et al., 1979). It is expected that an increase in salinity may cause reduced growth and fecundity, but that mortality is unlikely. Intolerance is therefore assessed as low. Once salinities return to original levels, growth should quickly return to normal so recoverability is recorded as very high. The reason for the alga's euryhalinity may lie in its betaine content. Although these substances are present in insufficient quantity to act as osmotic solutes, they may have a complimentary osmoregulatory function in modifying membrane behaviour or in transporting ions (Blunden et al., 1989).

Decrease in salinity

1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

Furcellaria lumbricalis occurs in the lowest category on the salinity scale (Connor et al., 1997a) and therefore probably relatively tolerant of decreases in salinity. The species forms extensive populations in the main basin of the Baltic Sea where salinity is 6-8 psu in the upper 60-70 m and its extension into the Gulfs of Bothnia and Finland is limited by the 4 psu isohaline (see review by Bird et al., 1991). The reason for the alga's euryhalinity may lie in its betaine content. Although these substances are present in insufficient quantity to act as osmotic solutes, they may have a complimentary osmoregulatory function in modifying membrane behaviour or in transporting ions (Blunden et al., 1989).

Changes in oxygenation

Benchmark.  Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details.

Evidence

The effects of reduced oxygenation on algae are not well studied. Plants require oxygen for respiration, but this may be provided by production of oxygen during periods of photosynthesis. Lack of oxygen may impair both respiration and photosynthesis (see review by Vidaver, 1972). A study of the effects of anoxia on another red alga, Delesseria sanguinea, revealed that specimens died after 24 hours at 15°C but that some survived at 5°C (Hammer, 1972). Insufficient
information is available to make an intolerance assessment for Furcellaria lumbricalis.

Introduction of microbial pathogens/parasites

Benchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details.

Evidence

Little evidence exists concerning the infection of red algae by microbial pathogens. Barton (1901) noted that Furcellaria lumbricalis may become infested with nematode worms and reacts by gall formation. Insufficient
information exists to make an intolerance assessment.

Introduction of non-native species

Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details.

Evidence

Johansson et al. (1998) identified a number of algal species introduced to the Baltic Sea which could potentially compete with the native flora. Of these, only Bonnemaissonia hamifera and Sargassum muticum were observed to proliferate. The habitat preferences of Sargassum muticum and Furcellaria lumbricalis are likely to overlap and competition could potentially occur, with the vigorous Sargassum muticum likely to proliferate.

Extraction of this species

Benchmark. Extraction removes 50% of the species or community from the area under consideration. Sensitivity will be assessed as 'intermediate'. The habitat remains intact or recovers rapidly. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

Commercial utilization of Furcellaria lumbricalis is based on the gelling properties of its extracted structural polysaccharide, furcellaran (Bird et al., 1991). Extraction of Furcellaria lumbricalis was reviewed by Guiry & Blunden (1991). Commercial beds of Furcellaria lumbricalis occur in Denmark where the algae are harvested with purpose built trawl nets, whereas in the rest of Europe, the biomass is not sufficient for harvesting. In Denmark, harvesting reached its highest level of 31,000 t p.a. in 1962, but over-exploitation has led to a fall in production and the current harvest is about 10,000 t p.a. Christensen (1971) (cited in Bird et al., 1991) and Plinski & Florczyk (1984) noted that over-exploitation of Furcellaria lumbricalis has resulted in severe depletion of stocks. A sustainable harvest of Furcellaria lumbricalis occurs in Canada on the shores of the Gulf of St Lawrence where the harvest is sustainable as dredging and raking are prohibited and only storm cast plants may be gathered. In view of the potential impact that harvesting may have on the population, intolerance is assessed as high, however, no commercial harvest as yet occurs in Britain or Ireland. Recoverability is recorded as moderate (see additional information below).

Extraction of other species

Benchmark. A species that is a required host or prey for the species under consideration (and assuming that no alternative host exists) or a keystone species in a biotope is removed. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

Around Prince Edward Island, Canada, Furcellaria lumbricalis is gathered as bycatch along with the target species, Chondrus crispus. Intolerance is therefore assessed as intermediate and recoverability is recorded as high (see additional information below). However, Furcellaria lumbricalis is unwanted and areas with high proportions of the species are abandoned. Furcellaria lumbricalis may therefore potentially proliferate due to selective exploitation of Chondrus crispus (Sharp et al., 1993).