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

Clavelina lepadiformis is permanently attached to the substratum. Removal of substratum will result in loss of the population. Adults are unlikely to be able to reattach, therefore recovery depends upon dispersal of larvae during the breeding season. Intolerance to substratum loss is assessed as high. Recoverability is likely to be moderate (see Additional Information below).

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

Clavelina lepadiformis reaches up to 20 mm in height and often colonizes vertical surfaces and overhangs. Smothering by 5 cm depth of sediment will completely cover the majority of the population, with only those colonizing overhangs and vertical surfaces not being affected. Therefore, intolerance is assessed as high. Recoverability is likely to be 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

Increased siltation can cause clogging of ascidians respiratory organs (Bakus, 1968). Although Clavelina lepadiformis has relatively wide apertures which help prevent clogging from particles (Naranjo et al., 1996), the structure of its branchial sac is in its simplest form; a gill sheet is formed by a single screen with slits (Fiala-Medioni, 1978). This means that they are less efficient in expelling particles, and more likely to suffer from clogging of feeding apparatus than other forms of sea squirts, such as Ciona intestinalis. Nevertheless, Naranjo et al. (1996) found that Clavelina lepadiformis was dominant in a low rate of water renewal, excess silting and high suspended solid concentrations Therefore, intolerance to siltation is assessed as intermediate. Recoverability is likely to be high (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

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

The sea squirt is a delicate animal, so exposure to desiccating influences for one hour will probably result in death of a proportion of the population. Therefore, intolerance is assessed as high. Recoverability is likely to be 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

Clavelina lepadiformis is a sublittoral species. Changes in the emergence regime, where the lower shore becomes exposed for longer, are likely to result in a proportion of the population dying. Intolerance to the emergence regime is assessed as high. Recoverability is likely to be 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

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

Clavelina lepadiformis thrives in areas where there is very little, if any, water movement (for instance, Abereiddy Quarry, Pembrokeshire (Hiscock & Hoare, 1975) as it is an active suspension feeder. Naranjo et al. (1996) found that the species was dominant in a low rate of water renewal, excess silting and high suspended solid concentrations. High water flow rates may be detrimental to feeding ability and posture but are unlikely to cause detachment. On resumption of normal energy expenditure, condition should be restored rapidly. Intolerance is assessed as low. Recoverability is likely to be very high (see Additional Information below).

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

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

As the breeding season is temperature dependant (Berrill, 1975; Millar, 1970), a change in temperature is likely to result in a change in its time and duration. The distribution of the light bulb sea squirt extends to waters which lie to the north and south of Britain, and therefore to lower and higher temperatures. Long term changes in temperature can probably be accommodated, whereas acute short term changes may cause a proportion of the population to die. During the severe winter of 1962-63, although no significant mortality was noted, Crisp et al. (1964) found that many compound ascidians were retarded in renewal of the colony after 'winter budding', and some individuals may have been killed. Intolerance is assessed as intermediate. Recoverability is likely to be high (see Additional Information below).

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

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

The species is frequently dominant in areas such as harbours with high levels of suspended solids and low light penetration. Naranjo et al. (1996) found that the species was dominant in a low rate of water renewal, excess silting and high suspended solid concentrations. However, Moore (1977) found populations of Clavelina lepadiformis replacing Botryllus schlosseri in clear water creeks near West Mersea. It is therefore likely that Clavelina lepadiformis is tolerant to changes in turbidity. A number of ascidians have been shown to spawn in response to a sharp increase in light (Berrill, 1975; Whittingham, 1967). Therefore, it is possible that spawning in Clavelina lepadiformis could be triggered by low turbidity.

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

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

Clavelina lepadiformis is tolerant of a wide range of exposure, but is most abundant in moderately exposed sites (Picton, 1997). Therefore, changes in wave exposure are not likely to have any significant effect. However, increases above moderately exposed are likely to have adverse effects on the population resulting in loss of colonies, therefore, intolerance is assessed as intermediate. Recoverability is likely to be high (see additional Information below).

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

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

It is unlikely that sea squirts can detect noise vibrations.

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

It is unlikely that sea squirts are able to detect visual presence or lower light intensities due to shading.

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 light bulb tunicate is permanently attached to the substratum and is unable to move out of the way from abrasive objects. The body of the species is soft and delicate, so abrasion is likely to cause physical damage and possibly death. Intolerance is assessed as high. Recoverability is likely to be moderate (see additional information below).

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

After displacement, adults may not be able to reattach to the substratum. Intolerance is assessed as high. Recoverability is likely to be moderate (see Additional Information section below).

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

TBT and PCBs are generally considered to be toxic to marine invertebrates (Cole et al., 1999). However, there is insufficient information with respect to effects on Clavelina lepadiformis.

Heavy metal contamination

Evidence

Several species of tunicate are known to accumulate high concentrations of trace metals. De Caralt et al. (2002) studied differences in certain aspects of the biology of Clavelina lepadiformis between harbour and open rocky littoral populations in the Mediterranean. They reported that Clavelina lepadiformis accumulated copper, lead and vanadium (vanadium is used in ascidian metabolism). The harbour population contained significantly more copper and lead than open littoral population despite its abundance being an order of magnitude higher in the harbour, suggesting that both adults and larvae are tolerant to this kind of contamination. Tolerant has been suggested.

Hydrocarbon contamination

Evidence

Cole et al. (1999) stated that polycyclic aromatic hydrocarbons are of moderate toxicity to marine organisms. However there is insufficient information with regard to effects of hydrocarbons on Clavelina lepadiformis.

Radionuclide contamination

Evidence

Insufficient Information.

Changes in nutrient levels

Evidence

There is some suggestion that there are possible benefits to the adults from increased organic content of water (Naranjo et al. 1996).

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

Clavelina lepadiformis is tolerant of a wide range of salinities; Fish & Fish (1996) found that they could tolerate salinities as low as 14 psu. However, colonies in areas of full salinity are likely to be adversely affected by a short term acute change in salinity. Intolerance to salinity is assessed as low. Recoverability is likely to be immediate (see Additional Information below), when conditions return to normal or the sea squirt has adapted to the new levels.

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

Changes in oxygenation

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

Evidence

Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l. No information was found concerning the tolerance of Clavelina lepadiformis to changes in oxygenation. However, the species lives in extremely sheltered conditions where oxygen depletion may occur. Therefore, intolerance has been assessed as low. Recoverability is likely to be immediate (see Additional Information below), once conditions return to normal or the species has adapted to the new oxygen concentration levels.

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

Insufficient Information.

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

No alien or non-native species are known to affect Clavelina lepadiformis in Britain and Ireland.

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

It is extremely unlikely that Clavelina lepadiformis will be subject to extraction.

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

Adult Clavelina lepadiformis are not known to depend on other species. Therefore, the species is assessed as not sensitive.