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

Gobius couchi lives and forages on a variety of substrata. It requires rockpools in the intertidal to survive at low tide. Therefore, loss of rockpools (for instance, by infilling) or rocky substrata (for instance, by spoil dumping or land claim) will most likely cause a proportion of the species population to die. However, at high tide adults are sufficiently mobile and will be able to recolonize areas which contain suitable substrata. Intolerance to substratum loss is assessed as intermediate. Recoverability is likely to be high (see Additional Information section 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

Gobius couchi will not be affected by smothering as they are mobile and able to swim away. However, destruction of habitat is important. Cordone & Kelley (1961) reported that (in a freshwater habitat) deposition of sediment on the bottom of the substratum would destroy needed shelter, reduce the availability of food, impair growth and lower the survival rate of eggs and larvae of fish. It is likely that Gobius couchi would be more intolerant if smothering occurred during the breeding season due to the probable destruction of broods of eggs. Materials such as concrete, oil or tar are likely to have a greater negative impact on the population. Intolerance due to smothering is assessed as intermediate. Recoverability is likely to be high (see Additional Information section 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

Moore (1977) indicated that an increase in siltation can have a negative effect on the growth of adult fish, survival of eggs and larvae and pathological effects on gill epithelia. Bottom-dwelling species are generally found to be tolerant of suspended solids (Moore, 1977). Juveniles have been reported as being more intolerant of siltation than adults (Moore, 1977). Therefore, intolerance has been recorded as low. Recoverability is likely to be high (see Additional Information section 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

Gobius couchi is likely to be tolerant of a decrease in suspended sediment.

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

Gobius couchi is found intertidally, in shallow rock pools. It can shelter in rock crevices and under boulders or weed, where the risk of desiccation is minimized. The animal is soft-bodied, so stranding of the individual, and subsequent exposure to sunshine and air for an hour would more than likely result in a proportion of the population dying. Intolerance to desiccation is therefore recorded as high. Recoverability is likely to be moderate (see Additional Information section 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

It is unlikely that Gobius couchi would be affected by a change in the emergence regime as at high tide it forages near the shore and at low tide it inhabits rock pools.

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

It is unlikely that Gobius couchi would be affected by a change in the emergence regime as at high tide it forages near the shore and at low tide it inhabits rock pools.

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

The ability of Gobius couchi to shelter in crevices between large boulders would be able to shield them from a moderate increase in the water flow rate. However, it is unlikely that they could withstand a large increase in water flow rate, as this would decrease the goby's ability to forage. Intolerance is assessed as low. Recoverability is likely to be high (see Additional Information section 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

Gobius couchi is likely to be tolerant of a decrease in water flow rate.

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

Insufficient
information was available to assess the sensitivity of Gobius couchi to an increase in temperature.

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

Temperature and oxygen levels change drastically over a tidal cycle in a rockpool. Couch's goby is capable of tolerating temperatures less than 6 °C by falling into a torpid state underneath stones (Minchin, 1988). By falling into this torpid state its ability to forage for food and reproduce is reduced.
The geographical distribution of Gobius couchi is restricted to the south-west of England and the Mediterranean Sea. A temperature decrease is likely to have an impact on Gobius couchi. During the severe winter period in 1962-63 the south-west coast of Britain experienced temperatures 5 and 6 °C below the long-term average for about 2 months. During this period there was heavy mortality of observed populations of Gobius paganellus, Gobius minutus, and Gobius flavens (Crisp (ed.), 1964). Therefore a decrease in temperature may affect populations in the British Isles, by either shifting the geographical distribution further southwards towards warmer waters, or killing a proportion of the northern-most population. Intolerance has been assessed as intermediate. Recoverability is likely to be high (see Additional Information section below).

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

An increase in turbidity would lead to a reduction in the amount of light penetration and, subsequently, a decrease in algal growth. Algae is the preferred food source of Gobius couchi, but other food sources (such as crustaceans and polychaetes) would still be readily available. The minimum light intensity needed for the detection and recognition of food are of great importance in many species of fish (Kinne, 1970). For instance if the organism needs to spend more time foraging for food, its energy expenditure will increase and could possibly lead to growth and reproductive problems. In heavily turbid waters fish larvae have been noted to show a greater than normal mortality. It is probable that Gobius couchi would be intolerant of changes in turbidity on a large scale, but probably not with changes of approximately 50 mg/l over a month. Therefore the species intolerance to turbidity is recorded as low. Recoverability is likely to be high (see Additional Information section below).

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

Decreases in turbidity benefit algal growth and therefore more food (algae and associated crustaceans) would be readily available. This would be beneficial to the population and tolerant* has been suggested.

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

Faria & Almada (1999) found that when rocky intertidal fish were removed or added to pools which had been disturbed by storms (which move large quantities of sand and reshape their contents) the negative effects on populations were variable. However, storms are an extreme event and couch's goby is sufficiently mobile and able to shelter in rock crevices or move to deeper water. Therefore, a change of two ranks on the wave exposure scale is unlikely to affect the goby.

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

A reduction of two ranks on the wave exposure scale is unlikely to affect the goby.

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

Insufficient
information.

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

Fish generally forage for food using visual methods and can detect differing levels of light and shade. It is therefore probable that Gobius couchi can also detect these changes and would be slightly affected by activity on the shore, more so in the breeding season. However, periods of time when activity might be reduced due to hiding would most likely be slight. Intolerance to visual presence is recorded as low. Recoverability is likely to be high (see Additional Information section below).

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

Gobius couchi is sufficiently mobile to avoid abrasive contact and to shelter from it, therefore it is unlikely to suffer from abrasion.

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

If displaced onto other suitable substrata no effects on the population are expected. Faria & Almada (1999) reported that experiments on removal and addition of individuals of Gobius cobitis show that the number of fish in the pools return to normal after a few weeks. It is likely that this would follow for Gobius couchi. However, if this occurs during the breeding season negative effects could be noted. Furthermore, if a male that is protecting fertilized eggs is displaced, the eggs are not likely to survive. Therefore, a low intolerance has been recorded. Recoverability is likely to be high (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

The population decline of Gobius couchi in the Helford area was suggested to possibly be due to TBT pollution (Potts & Swaby, 1991) or other man-made sources. Lindane is likely to bioaccumulate significantly and is considered to be highly toxic to fish (Cole et al., 1999). Ebere & Akintonwa (1992) conducted experiments on the toxicity of various pesticides to Gobius sp. They found Lindane and Diazinon to be very toxic, with 96 hr LC_50s of 0.25 µg/l and 0.04 µg/l respectively. TBT is very toxic to algae and fish. However, toxicity of TBT is highly variable with 96-hr LC₅₀ ranging from 1.5 to 36 µg/l, with larval stages being more intolerant than adults (Cole et al., 1999). PCBs are highly persistent in the water column and sediments, have the potential to bioaccumulate significantly and can be very toxic to marine invertebrates. However their toxicity to fish is not clear (Cole et al., 1999). Therefore, an intermediate intolerance has been recorded. Recoverability is likely to be high (see Additional Information section below).

Heavy metal contamination

Evidence

Cadmium, mercury, lead, zinc and copper are highly persistent, have the potential to bioaccumulate significantly and are all considered to be very toxic to fish (Cole et al., 1999). Mueller (1979) found that in Pomatoschistus sp., a different species of goby, very low concentrations of cadmium, copper and lead (0.5 g/l Cd²⁺; 5 g/l Cu²⁺; 20 g/l Pb²⁺) brought about changes in activity and an obstruction to the gill epithelia by mucus. This may also be true for Gobius couchi.
Inorganic mercury concentrations as low as 30 µg/l (96-h LC₅₀) are considered to be toxic to fish, whereas organic mercury concentrations are more toxic to marine organisms (World Health Organisation, 1989, 1991). Therefore, a high intolerance to heavy metals has been recorded. Recoverability is likely to be high (see Additional Section below).

Hydrocarbon contamination

Evidence

Toxicity of low molecular weight poly-aromatic hydrocarbons (PAH) to organisms in the water column is moderate (Cole et al., 1999). They have the potential to accumulate in sediments and, depending on individual PAH, to be toxic to sediment dwellers at levels between 6 and 150 µg/l (Cole et al., 1999). The toxicity of oil and petrochemicals to fish ranges from moderate to high (Cole et al., 1999). The main problem is due to smothering of the intertidal habitat.
Bowling et al. (1983) found that anthracene, a PAH, had a photo-induced toxicity to the bluegill sunfish. In fact, they reported that when exposed to sunlight anthracene was at least 400 times more toxic than when no sunlight was present. According to Ankley et al. (1997) only a subset of PAH's are phototoxic (fluranthene, anthracene, pyrene etc.). Effects of these compounds are destruction of gill epithelia, erosion of skin layers, hypoxia and asphyxiation (Bowling et al., 1983). It is possible that Gobius couchi could be similarly intolerant of hydrocarbons, however this is not known. An intermediate intolerance to hydrocarbons has been recorded. Recoverability is likely to be high (see Additional Information section below).

Radionuclide contamination

Evidence

Kinne (1984) reported that for the marine goby, Chasmichthys glosus, doses of as little as 100 rad (type not known) produced a readily observable response, causing severe damage to gonads of both males and females. The testes showed slightly greater intolerance. It is probable that Gobius couchi would respond similarly to sublethal irradiation at levels indicated above. Therefore an intermediate intolerance to radionuclides has been recorded. Recoverability is likely to be high (see Additional Information section below).

Changes in nutrient levels

Evidence

Higher nutrient levels may encourage the growth of algae such as Ulva spp., which is an important food source for Gobius couchi. In comparison, a decrease in nutrient levels may lead to a decrease in the availability of green algae. However, this is likely to exert a slight effect on the couch's goby as it is able to ingest other types of food (such as crustaceans and polychaetes). Therefore, a low intolerance to nutrients has been recorded. Recoverability is likely to be high (see Additional Information section 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

No information is available for salinity effects on Couch's goby. However they do inhabit a wide range of habitats, with varying salinities. This implies that they are able to adapt reasonably well to various salinities.

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

No information is available for salinity effects on Couch's goby. However they do inhabit a wide range of habitats, with varying salinities. This implies that they are able to adapt reasonably well to various salinities.

Changes in oxygenation

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

Evidence

Temperature and oxygen levels change drastically over a tidal cycle in a rockpool. It is likely that Gobius couchi is adapted to these changes, but that a drastic long term decrease in oxygen levels would be expected to have a slight negative impact on the population. Oxygenation intolerance is assessed as low. Recoverability is likely to be high (see Additional Information section below).

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 Gobius couchi 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

Gobius couchi has a restricted distribution, and is a rare and protected species. Therefore extraction of this species would have a great impact on the population density and viability. Intolerance is recorded as high, and recoverability is recorded as moderate (see Additional Information section 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

Gobius couchi is not known to depend on any other species. Therefore, it is likely to be not sensitive to the extraction of other species.