Biodiversity & Conservation

IR.SIR.EstFa.CorEle

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Removal of the substratum would result in the loss of Cordylophora caspia colonies, their hydrorhizae and any resting stages, together with Electra crustulenta and Balanus species. Therefore, an intolerance of high has been recorded. Recoverability is likely to be high (see additional information below).
Smothering
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At low salinities Cordylophora caspia forms short, un-branched colonies and smothering by 5 cm of sediment for one month (see benchmark) is likely to cover a large proportion of the colony, preventing feeding and hence reducing growth and reproduction in the hydroid, while local hypoxic conditions are also likely to inhibit growth (Fulton, 1961, 1963). For instance the hydroid Melicertum octocostatum annually over-summers as stolons in anoxic conditions in Abereiddy Quarry, growing back in autumn (Hiscock & Hoare, 1975). Smothering will also prevent feeding and growth in both Electra crustulenta and Balanus crenatus. The encrusting bryozoan grows rapidly and may be adversely affected, while Balanus crenatus was considered to be highly intolerant (see review). However, the hydroid colony is likely to become dormant, or otherwise survive for a period of at least a month, and recover rapidly once the sediment is removed. Therefore, a biotope intolerance of intermediate has been recorded to represent the potential loss of some members of the community. Recovery is likely to be very high (see additional information below).
Increase in suspended sediment
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Cordylophora caspia and Electra crustulenta are found in estuarine and sheltered lagoonal habitats, which are characterized by relatively high suspended sediment loads. Cordylophora caspia was also reported in saltmarsh pools (JNCC, 1999) and salt marshes are a depositional environment characterized by siltation. Therefore, Cordylophora caspia and Electra crustulenta are probably not sensitive to increases in suspended sediment loads at the benchmark level. Balanus crenatus is found a wide variety of habitats including estuaries and on the back of crustaceans in sedimentary habitats, although increased sediment loads may reduce growth rates. The biotope probably experiences marked changes in sedimentary loads between the winter and summer months, as is probably not sensitive to increases in suspended sediment at the benchmark level, while the moderately strong to strong tidal streams in this habitat minimize siltation.
Decrease in suspended sediment
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This biotope probably experiences marked changes in suspended sediment loads between winter and summer. A reduction in suspended sediment is unlikely to directly affect the biotope. A decrease in suspended sediment may reduce the availability of organic particulates and hence reduce food availability. Arndt (1986, 1989) suggested that Cordylophora caspia had a high food requirement for growth and reproduction. It is therefore, likely to be intolerant of any reduction in food availability. Overall, a reduction in suspended sediment may reduce food availability and hence growth and reproduction in all the species in the biotope and an intolerance of low has been recorded. Recovery is likely to be immediate.
Desiccation
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Intertidal populations of Cordylophora caspia are restricted to damp habitats such as under-boulders and overhangs. The branched growth form of this species is likely to retain water on emersion (see review). However, an increase in desiccation at the benchmark level is likely to result in drying and death of the uprights. Increased desiccation may result in the formation of resistant, dormant stages, however, no information on their desiccation tolerance was found.
Electra crustulenta is probably intolerant of desiccation and is limited to damp underboulder habitats or the relative humidity found between the frond of brackish water fucoids in the intertidal. Balanus crenatus is exclusively subtidal and intolerant of desiccation, as adults were reported to withstand 17 hours and 40 hours of aerial exposure depending on size, or a mean survival time of 14.4 hours in dry air (Barnes et al., 1963; Foster, 1971a,b). Therefore, an increase in desiccation at the benchmark level is likely to result in loss of the intertidal extent of the population and an intolerance of intermediate has been recorded.
If hydrorhizae or dormant stages survive, recovery is likely to be very rapid and colonies may appear rapidly once conditions return to their prior state. If resting stages are destroyed then recovery will depend on recruitment from nearby subtidal colonies, and is likely to be rapid (see additional information below).
Increase in emergence regime
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An increase in emergence is likely to adversely affect the biotope. While Cordylophora caspia would probably survive the extremes of temperature resulting from increased emergence (see below), the biotope is likely to succumb to increased desiccation (see above) if increased emergence exposes it to mid shore (or higher) conditions. Therefore, the upper shore proportion of the biotope is likely to be lost and an intolerance of intermediate has been recorded. Recoverability is likely to be very high (see additional information below).
Decrease in emergence regime
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A decrease in emergence is likely to increase the availability of suitable habitats for all members of the community but especially Cordylophora caspia and may allow the biotope to extend its range. Therefore, not sensitive* has been recorded.
Increase in water flow rate
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Water movement is essential for suspension feeding species to supply adequate food, remove metabolic waste products, prevent accumulation of sediment and disperse larvae. Hydroids are expected to be abundant where water movement is sufficient to supply adequate food but not cause damage (Hiscock, 1983; Gili & Hughes, 1995). This biotope occurs in moderately strong to strong tidal streams. Cordylophora caspia tolerates strong water flow and annulations at the base of branches provide flexibility to the colony, although water flow rates affect feeding efficiency. Similarly, Electra pilosa (and by inference Electra crustulenta) was able to grow in strong water flows (e.g. Menai Strait and Lough Ine rapids) (Ryland, 1970; Hermansen et al., 2001). Balanus crenatus is found in a wide range of water flow rates is often dominant in very strong tidal streams. A further increase in water flow to very strong is likely to reduce feeding efficiency and hence growth and reproduction and may even remove or damage hydroid colonies. But damaged hydroid colonies may survive as resting stages until water flow rates return to prior condition. Therefore, intolerance has been assessed as intermediate and recoverability as very high (see additional information below).
Decrease in water flow rate
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Water movement is essential for suspension feeding species to supply adequate food, remove metabolic waste products, prevent accumulation of sediment and disperse larvae. Member of this biotope have been recorded from a wide range of water flow rates, e.g. Cordylophora caspia was recorded from areas of weak or negligible water flow and Electra crustulenta was present in weak to very weak water flow in Poole Harbour and Loch Stenness, Orkney respectively (JNCC, 1999). Therefore, a reduction in water flow from e.g. strong to weak will probably not adversely affect the species directly, although food capture rates and growth may be reduced. In the high suspended sediment loads characteristic of estuaries a decrease of water flow from strong to weak would result in a dramatic increase in siltation, eventually resulting in smothering of the bedrock and the biotope. The biotope is unlikely to survive smothering for a protracted period (see benchmark) and would probably be lost. Therefore an intolerance of high has been recorded. The fragments of the biotope may persist under overhangs and on vertical surfaces, providing Cordylophora caspia larvae for recolonization and enhancing recovery. Therefore, a recoverability of high has been recorded.
Increase in temperature
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Growth rates were reported to increase with temperature in several bryozoans species, however, zooid size decreased, which may be due to increased metabolic costs at higher temperature (Menon, 1972; Ryland, 1976; Hunter & Hughes, 1994). Temperature is also a critical factor stimulating or inhibiting reproduction in hydroids, most of which have an optimum temperature range for reproduction (Gili & Hughes, 1995). Cordylophora caspia was regarded as a warm water, thermophilic species by Arndt (1989) and occurs in subtropical areas. It is unlikely to be adversely affected by long term chronic or short term acute increases in temperature at the benchmark level. The recorded distribution of Electra crustulenta is limited from southern England to Orkney but may be more widespread (Hayward & Ryland, 1998; JNCC, 1999).
Overall, the important characterizing species Cordylophora caspia and hence the biotope will probably survive an increase in temperature at the benchmark level. Therefore, not sensitive has been recorded. Balanus crenatus, however, is a boreal species and may be lost due to long term increases in temperature at the benchmark level, causing a minor decline in species richness.
Decrease in temperature
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Arndt (1989) reported that colonies of Cordylophora caspia died back in autumn when the temperature fell to about 10 °C only to germinate in spring when the temperature exceeded 5 °C. Arndt (1989) concluded that Cordylophora caspia was thermophilic but that low temperature had an important influence on growth and reproduction. Electra pilosa was reported to survive below freezing temperatures (Menon, 1972) although colonies are probably more tolerant of low temperatures in winter than summer (see review for details). Electra crustulenta may exhibit a similar response. Brault & Bourget (1985) noted that recruitment was delayed until spring on settlement plates deployed in winter. However, all the dominant species within the biotope are boreal or recorded from north of the British Isles. Therefore, although growth and reproduction may be reduced, they are unlikely to be adversely affected by reductions in temperature in British waters and an intolerance of low has been recorded. In addition, Cordylophora caspia is probably tolerant of acute short term changes in temperature, and can survive as resting, dormant stages down to -10 °C (Arndt, 1989).
Increase in turbidity
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A decrease in light penetration may decrease competition for space with macroalgae. But increased turbidity is likely to result in a decrease in phytoplankton and macroalgal primary production, which may reduce food available to the suspension feeders within the community. Therefore, an intolerance of low has been recorded.
Decrease in turbidity
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An decrease in turbidity may increase competition with macroalgae but also increase phytoplankton and hence zooplankton productivity and potentially increase food availability. Arndt (1986, 1989) suggested that Cordylophora caspia had a high food requirement for growth and reproduction. It is, therefore, likely to be intolerant of any change in food availability and may benefit from decrease in turbidity. Therefore, not sensitive has been recorded.
Increase in wave exposure
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The very sheltered situations in which this biotope occurs are unlikely to experience an increase in wave exposure at the benchmark level due to natural causes, except perhaps extreme storm conditions. However, an increase in large or fast boat traffic and the resultant wash may have a similar effect to an increase in wave exposure. Balanus crenatus is tolerant of a wide range of wave exposures. However, Cordylophora caspia and Electra crustulenta have only been recorded from very or extremely wave sheltered habitats, and this biotope has only been recorded in very to extremely wave sheltered conditions. Therefore, it is likely than an increase in wave exposure at the benchmark level (e.g. from 'very sheltered' to 'moderately exposed') is likely to result in loss or damage of the their colonies. Populations occupying small rocks, cobbles or pebbles are likely to be more intolerant, and the resultant movement of the substratum and sediment scour may also remove attached hydrorhizae, the resting stages of the hydroid, and encrusting bryozoan colonies. Therefore, an intolerance of high has been recorded.
Recovery of the biotope will depend on recruitment of Cordylophora caspia from other areas. However, any resting stages and fragments of colonies remaining may contribute to the recovery. Therefore, a recoverability of high has been suggested.
Decrease in wave exposure
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This biotope has only been recorded in very to extremely wave sheltered conditions. A decrease in wave exposure to ultra sheltered is unlikely to have any adverse effects since there is adequate water movement caused by strong tidal streams. Therefore, not sensitive has been recorded.
Noise
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Hydroids, bryozoans or barnacles are unlikely to be sensitive to noise or vibration at the benchmark level.
Visual Presence
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Hydroid and bryozoan polyps or barnacle cirri may retract when shaded by potential predators, however the community is unlikely to be affected by visual presence.
Abrasion & physical disturbance
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Abrasion by an anchor or fishing gear is likely to remove relatively delicate uprights of hydroids, damage bryozoan colonies and crush barnacles. However, in hydroids the surface covering of hydrorhizae may remain largely intact, from which new uprights are likely to grow. In addition, the resultant fragments of hydroid colonies may be able to develop into new colonies (see displacement). Populations on small hard substrata (e.g. cobbles, pebbles or stones) may be removed by fishing gear, constituting substratum loss (see above). Overall, a proportion of the hydroid and bryozoan colonies or barnacles are likely to be destroyed and an intolerance of intermediate has been recorded. However, recovery from surviving hydrorhizae and occasional fragments is likely to be rapid (see additional information below).
Displacement
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Removal of a bryozoan colony from its substratum would probably be fatal, and encrusting bryozoans are not known to be able to reattach. Similarly, Balanus crenatus is permanently attached to the substratum and could not survive if it was removed. However, fragmentation is thought to be a possible mode of asexual reproduction in hydroids (Gili & Hughes, 1995). Cordylophora caspia colonies have been cultured by securing cut uprights to slides to which they subsequently attach. Therefore, it is possible that a proportion of displaced hydroid colonies (or fragments thereof) may attach to new substrata, although, the encrusting bryozoans and barnacles are likely to be lost. Therefore, an intolerance of intermediate has been recorded. A recoverability of very high has been recorded (see additional information below).

Chemical Factors

Synthetic compound contamination
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Stebbing (1981) reported that Cu, Cd, and tributyl tin fluoride affected growth regulators in Laomedea (as Campanularia) flexuosa resulting in increased growth. Bryan & Gibbs (1991) reported that virtually no hydroids were present on hard bottom communities in TBT contaminated sites and suggested that some hydroids were intolerant of TBT levels between 100 and 500 ng/l.
Bryozoans are common members of the fouling community, and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints (Soule & Soule, 1977; Holt et al., 1995). Bryan & Gibbs (1991) reported that there was little evidence regarding TBT toxicity in bryozoans with the exception of the encrusting Schizoporella errata, which suffered 50% mortality when exposed for 63 days to 100ng/l TBT. However, Hoare & Hiscock (1974) suggested that Polyzoa (Bryozoa) were amongst the most intolerant species to acidified halogenated effluents in Amlwch Bay, Anglesey. Hoare & Hiscock (1974) found that Balanus crenatus survived near to an acidified halogenated effluent discharge where many other species were killed, suggesting a high tolerance to chemical contamination. However, barnacles have a low resilience to chemicals such as dispersants, dependant on the concentration and type of chemical involved and Holt et al. (1995) concluded that barnacles were fairly intolerant of chemical pollution.

Therefore, hydroids are probably intolerant of TBT contamination (which may be highest in estuarine environments) and bryozoans and barnacles are probably intolerant of chemical pollution. Cordylophora caspia was also a dominant species on settlement plates placed on a floating shipyard dock in Warnock river (Sandrock et al., 1991). Floating docks are likely to result in local contamination with heavy metals and antifouling agents from ship paints, as well as oils and other chemicals used in ship maintenance. Hydroid species adapted to a wide variation in environmental factors and with cosmopolitan distributions tend to be more tolerant of polluted waters (Boero, 1984; Gili & Hughes, 1995). Therefore, Cordylophora caspia is probably more tolerant of pollution than most hydroid species, and an intolerance of intermediate has been recorded to represent the potential loss of Balanus crenatus and Electra crustulenta, albeit at low confidence. A recoverability of very high has been recorded (see additional information below).

Heavy metal contamination
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Various heavy metals have been show to have sublethal effects on growth in the few hydroids studied experimentally (Stebbing, 1981; Bryan, 1984; Ringelband, 2001). Bryozoans are common members of the fouling community and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints. Bryozoans were also shown to bioaccumulate heavy metals to a certain extent (Soule & Soule, 1977; Holt et al., 1995). Barnacles may tolerate fairly high levels of heavy metals in nature, accumulate heavy metals and store them as insoluble granules, for example, they are found in Dulas Bay, Anglesey, where copper reaches concentrations of 24.5 µg/l due to acid mine waste (Foster et al., 1978; Rainbow, 1987).
Therefore, the community may tolerate a degree of heavy metal contamination and an intolerance of low has been recorded.
Hydrocarbon contamination
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Although subtidal, this biotope is relatively shallow and may be exposed to oils and hydrocarbons adsorbed onto particulates and ingested or through the water soluble fractions of oils and hydrocarbons. The water soluble fractions of Monterey crude oil and drilling muds were reported to cause polyp shedding and other sublethal effects in the athecate Tubularia crocea in laboratory tests (Michel & Case, 1984; Michel et al., 1986; Holt et al., 1995). The athecate Cordylophora caspia may show similar sublethal effects assuming similar physiology. Species of the encrusting bryozoan Membranipora and the erect bryozoan Bugula were reported to be lost or excluded from areas subject to oil spills (Mohammad, 1974; Soule & Soule, 1979). Houghton et al. (1996) reported a reduction in the abundance of intertidal encrusting bryozoans (no species given) at oiled sites after the Exxon Valdez oil spill. Littoral populations of encrusting bryozoans and hydroids are also probably intolerant of the smothering effects of oil pollution, resulting in suffocation of colonies. Littoral barnacles generally have a high tolerance to oil (Holt et al., 1995) and were little impacted by the Torrey Canyon oil spill (Smith, 1968) so Balanus crenatus is probably fairly resistant to oil.
Therefore, encrusting bryozoans are probably intolerant of hydrocarbon contamination while only sublethal effects have been observed in hydroids. However, the intertidal extent of the biotope is likely to be smothered a killed by exposure to oil and, therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be very high (see additional information below).
Radionuclide contamination
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Insufficient information
Changes in nutrient levels
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Estuarine habitats are generally higher in nutrient levels than coastal waters. A moderate increase in nutrients may increase food availability for suspension feeders, in the form of organic particulates. Eutrophication may result in local hypoxic conditions (see below) and /or blooms of ephemeral algae. However, in this turbid environment, ephemeral algae are likely to be limited to the very shallow water near the top of the shore, and unlikely to adversely affect the biotope. Therefore, not sensitive has been recorded.
Increase in salinity
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The hydroids and bryozoans present in the biotope are characteristic of brackish waters. Whilst Balanus crenatus also occurs on the open coast and therefore at full salinity. Electra crustulenta and Balanus crenatus are probably at the lower limit of their salinity tolerance within this biotope, and restricted to the deeper areas of the habitat. Cordylophora caspia is euryhaline, forming well developed colonies in water of 2 -12psu where tidal influence is considerable or between 2 -6psu where conditions are constant (Arndt, 1989) but it may also occur at full salinities and fast flowing, well oxygenated freshwater containing Ca, Mg, Na, Cl and K ions (Fulton, 1962; Arndt, 1989). However, Arndt (1989) suggested that the marine distribution of the brackish water hydroid Cordylophora caspia was probably limited by food availability, competition from Clava spp. or Laomedea spp. and predation e.g. from the nudibranch Tenellia adspersa (as Embletonia pallida). Therefore, the dominance of hydroid in this biotope is probably due to the exclusion of predators and competitors (con-specifics and ascidians). An increase in salinity at the benchmark level is likely to allow more marine species to colonize the biotope and potentially out-compete Cordylophora caspia. In the Tamar estuary this biotope is replaced by the biotope £SIR.HarCon£ at higher average salinities, with a greater number of species of encrusting bryozoan and hydroids. Therefore, the biotope would probably survive a short term, acute increase in salinity. But a long term increase in salinity will probably result in loss of the community at the marine limit of its range. However, it may be able to colonize new space at the upper estuarine limit of its range. Therefore, an intolerance of intermediate has been recorded to represent a loss of the extent of the biotope. Recoverability has been recorded as very high (see additional information below).
Decrease in salinity
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This biotope was described from the riverine/estuarine transition in the Tamar estuary, where the salinity was always below 20psu and could drop to zero. Electra crustulenta and Balanus crenatus are probably at the lower limit of their salinity tolerance within this biotope, and restricted to the deeper areas of the habitat. A further reduction to freshwater conditions would exclude Balanus crenatus and Electra crustulenta. Cordylophora caspia may survive and grow in freshwater conditions as long as Ca, Mg, Na, Cl and K ions are present, probably adopting a short growth form (see review; Fulton, 1962; Arndt, 1989). The biotope would probably survive a short term, acute decrease in salinity. In the long term, the habitat would probably be invaded by freshwater species, e.g. chironomids, amphipods, pondweeds and Phragmites sp. and the biotope would no longer be described as SIR.CorEle being effectively lost in the upper most reaches of the estuary. However, a decrease in salinity would allow Cordylophora caspia to colonize further down the estuary. Therefore, an intolerance of intermediate has been recorded to represent the reduction in the extent of the biotope. Recoverability is likely to be very high.
Changes in oxygenation
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Fulton (1962) found that some polyps of Cordylophora caspia fell off or were reabsorbed after 7 days in the complete absence of oxygen but remaining polyps began feeding shortly after the re-introduction of oxygen and Fulton (1962) concluded that Cordylophora caspia had a low oxygen requirement for growth and was able to grow at oxygen levels of >2mg/l (ca 1.4ml/l). Similarly, the hydroid Melicertum octocostatum annually over-summers as stolons in anoxic conditions in Abereiddy Quarry, growing back in autumn (Hiscock & Hoare, 1975).

Sagasti et al. (2000) reported that epifauna communities, including dominant species such as the bryozoans Conopeum tenuissimum and Membranipora tenuis, and the hydroid Obelia bicuspidata were unaffected by periods of moderate hypoxia (ca 0.35 -1.4 ml/l) and short periods of hypoxia (<0.35 ml/l) in the York River, Chesapeake Bay. Their study suggests that estuarine epifaunal communities are relatively tolerant of hypoxia. However, Balanus crenatus was reported to survive an average of 3.2 days in the absence of oxygen (Barnes et al., 1963), and it is probable that a proportion of the Balanus crenatus population would be lost, resulting in a loss of species richness.
Overall, Cordylophora caspia is probably tolerant of low oxygen levels and a biotope intolerance of low has been recorded.

Biological Factors

Introduction of microbial pathogens/parasites
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Insufficient information
Introduction of non-native species
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Cordylophora caspia is a non-native species (Allman, 1871-1872). But has not been reported to compete with other species, including other non-native species, in British or Irish waters.
Extraction
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It is extremely unlikely that any of the species indicative of sensitivity would be targeted for extraction and we have no evidence for the indirect effects of extraction of other species on this biotope.

Additional information icon Additional information

Intolerance assessment
Cordylophora caspia and other hydroids has the ability to produce dormant resting stages (menonts) that are far more resistant to environmental change than the colony itself. Therefore, although colonies may be removed or destroyed, the resting stages may survive in remnants of the hydrorhizae attached to the substratum. For the sake of assessment, the intolerance of the branched colonies themselves ( the clearly visible component) has been recorded. The resting stages provide a mechanism for rapid recovery.

Recoverability
Hydroids are often initial colonizing organisms in settlement experiments and fouling communities (see recruitment). It is likely that Cordylophora caspia will recruit to available space rapidly in its growing season, in the vicinity of other populations. Once colonized the hydroids ability to grow rapidly and reproduce asexually is likely to allow it to occupy space and sexually reproduce quickly, possibly recruiting to additional space before dying back in winter. Therefore, where colonies or dormant resting stages are present in the habitat, or within isolated habitats (e.g. lagoons), recovery is likely to be rapid and occur within less than a year.

Balanus crenatus and Electra crustulenta are also probably rapid colonizing species (see recruitment) that exhibit rapid growth and reproduction, with other population present is the Tamar estuary, so that recruitment and recovery of these species is also probably rapid.

Long distance dispersal in Cordylophora caspia is probably limited. Cordylophora caspia is found only in isolated, brackish water habitats, so that long distance dispersal is probably dependant on passive dispersal on floating debris or shipping. Although Cordylophora caspia has probably been introduced to the coasts of several countries, possibly including Britain (Allman, 1871-1872) and the Baltic Sea (Olenin et al., 2000), passive transportation is a sporadic and un-predictable event.

Therefore, if the population was destroyed but some fragments or resting stages of hydroids remain, or other populations were nearby, recovery would be rapid, probably taking a few years. But if the population of hydroids was completely destroyed, and resting stages or fragments removed, for example by severe chemical spills, recolonization rates would depend on distance from nearby colonies, and may take many years in isolated habitats such as lagoons and coastal lakes, where recovery would probably be very low.


This review can be cited as follows:

Tyler-Walters, H. 2002. Cordylophora caspia and Electra crustulenta on reduced salinity infralittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 21/08/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=27&code=1997>