The Marine Life Information Network

Removal of the substratum would entail removal of the plants themselves, germlings and gametophytes. They can not re-attach once removed and would be swept away. Evidence from storm damage and experimental removal of adult Laminaria species in Australia indicates that kelp forest can re-grow within 14 months. These experiments did not remove the gametophyte 'seed' bank. New individuals of Alaria esculenta colonized within 10 m of the parent plants in Norway. However, given the potentially large number of spores and gametophytes it is likely that recolonization would occur rapidly and sporophytes may grow up to 20 cm/month under optimal conditions in the field and up to 10 cm/day in rope culture systems (Birkett et al., 1998b; Kain & Dawes, 1987).

Although smothering of the adult sporophyte may reduce photosynthetic activity it is unlikely to cause damage. However, juvenile sporophytes may be smothered and their growth inhibited. The germlings, zoospores and gametophytes are likely to be intolerant of smothering.

Increased sedimentation may result in smothering of adults (sporophytes), germlings and gametophytes (see above). Increased sediment deposition may increase sediment scour which may damage sporelings in particular. However, the most likely effect of increased siltation will be increased light attenuation and turbidity (see below).

Kelps are normally subtidal species and are likely to be intolerant of desiccation. Alaria esculenta may extend into the lower eulittoral in very exposed conditions. However, these marginal populations have a reduced age range in comparison to the subtidal populations due to the loss of plants resulting from sunshine at low tide. An increase in desiccation by 25% over a period of a year is likely to remove the population.

The lower limit of Alaria esculenta populations is probably controlled by competition from other kelp species such as Laminaria hyperborea, Laminaria digitata and foliose red algae. A decrease in emergence is likely to extend the population up shore. However, an increase is emergence is likely to result in loss of plants at the upper limit of its distribution. Lost individuals are replaced by recruitment. However, the loss of plants will open the canopy and allow slow growing germling to replace adult sporophytes or the maturation of gametophytes.

The presence of Alaria esculenta is associated with strong wave action and tidal flow. Therefore, it is likely to be intolerant of any reduction in wave exposure and flow rate, which is likely to subject it to competition from other Laminarians e.g. Laminaria digitata.

Alaria esculenta germlings tolerate up to 16 °C, above which growth is inhibited (Sundene, 1962). Sundene (1962) reported that Alaria esculenta was only found on shores where the August mean seawater surface temperature is 16 °C or lower (except in areas of extreme exposure). Munda & Lüning (1977) reported that temperatures of 16 -17 °C for a few weeks were lethal to Alaria esculenta sporophytes based on field experiments with specimens transplanted to Helgoland from north Iceland. They suggested that sporophytes were likely to survive above 16 °C for some days, but that longer duration was lethal. Temperature was, therefore, considered to be the main factor controlling its distribution in Europe (Sundene, 1962; Munda & Lüning, 1977; Widdowson, 1971; Lüning, 1990). Birkett et al. (1998b) further suggest that kelp are stenothermal (intolerant of temperature change) and that upper and lower lethal limits of kelp would be between 1-2 °C above or below the normal temperature tolerances. Given its distribution in the North Atlantic and Arctic Sea is associated with the -2 °C February winter isotherm (Kraan pers. comm.). This species is likely to be intolerant of change in temperature equivalent to either benchmark. Its southern distribution is likely to be affected by the position of the mean surface temperature isotherm in Europe and therefore climatic change. The temperature tolerances of the gametophyte stages are different to those of the adult.

The light penetration influences the maximum depth at which kelps species can grow. Dring (1982) reported that laminarians grow at depths at which the light levels are reduced to 1% of incident light at the surface. This varies with the turbidity of the sea water from 100 m in the Mediterranean to only 6-7 m in the silt laden German Bight. Increased turbidity due to coastal engineering, dredging, cooling water plumes been reported to result in the loss of local kelp forest. Suspended material in vicinity of sewage outfalls have been reported to result in reduced the depth range and the fewer new plants under the canopy. However, Alaria esculenta is excluded from deep waters by competition from other kelp species and is unlikely to be light limited (except Rockall populations). Although likely to be intolerant of extreme increase of light attenuation it is unlikely to be affected by a long term change of turbidity of one level on the water clarity scale.

Alaria esculenta is characteristic of wave exposed coasts and favoured by increasing exposure. However, a decrease in wave exposure is likely to subject it to competition with Laminaria spp., which are likely to replace it as the dominant species as exposure decreases

Plants have no known sound or vibration receptors

Macroalgae are not known to react to the rapid changes in light and shade that would be associated with movement and have no known visual receptors.

Alaria esculenta is adapted to exposed and very wave exposed coasts. The force of wave action in these habitats is significant source of physical abrasion, which is mitigated by the flexibility of the frond. However, abrasion, for instance from a vessel stranding or equivalent disturbance, is likely to snag, damage, and remove fronds. Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be high.

Alaria esculenta is permanently attached to the substratum. If removed if can not re-attach (except in experimental conditions) and will be lost from the population. However, the population will recover fairly rapidly from the losses due the presence of germlings, large number of spores and gametophytes.

Atrazine was lethal to young sporophytes of Laminaria hyperborea at 1 mg/l and caused growth suppression at 10 µg/l (Hopkin & Kain, 1978). Mixed detergents, herbicides (dalapon 2,4-D) were not toxic at the levels tested. Cole et al. (1999) report the following as very toxic to macrophytes: atrazine; simazine; diuron; and linuron (herbicides). It is likely therefore that Laminariales such as Alaria esculenta are intolerant of atrazine and some other herbicides. PCBs inhibited growth, gametogenesis and sporophyte recruitment in Macrocystis pyrifera at 5 µg/litre and, therefore, may have similar sub-lethal effects on Alaria esculenta
Overall, herbicides and atrazine are likely to result in loss of a proportion of the population, and an intolerance of intermediate has been recorded.

Mercury and copper were found to be lethal at 50 µg/l and 100 µg/l respectively and toxic at 50 and 10 µg/ l respectively in Laminaria hyperborea. Zinc and cadmium were lethal at 5 mg/l and 10 mg/l respectively. Therefore, it is likely that Laminariales such as Alaria esculenta are intolerant of copper at benchmark level and so intolerance is assessed as intermediate. Zinc, cadmium and mercury especially are likely to cause sub-lethal effects.

Mucilaginous slime coating on kelp fronds is thought to protect them from coatings of oil. Hydrocarbons in solution reduce photosynthesis and may be algicidal. Reduction in photosynthesis depends on the type of oil, its concentration, length of exposure, method used to prepare oil-water mixture and irradiance in experimental trials (Lobban & Harrison, 1994). The sublittoral fringe and lower eulittoral populations of Alaria esculenta would be most vulnerable to oiling. Subtidal populations being only exposed to oil emulsions or oil adsorbed to particles. Kelps are relatively insensitive to dispersants (Birkett et al. 1998). Three days exposure to 1% diesel emulsion reduced photosynthesis completely in young Macrocytsis plants. Laminaria digitata exposed to diesel oil at 130 µg/litre reduced growth by 50% in a two year experiment. No growth inhibition was noted at 30 µg/l and the plants recovered completed in oil-free conditions. Overall, laminarians such as Alaria esculenta are probably relatively tolerant of oiling and an intolerance of low has been recorded.

No information found.

All kelp species are efficient absorbers of nutrients (nitrates and phosphates) and can take up and store excess nutrients. In exposed sites the turnover of fresh seawater suggests that nutrients are continuously replenished. Eutrophication is associated with loss of perennial macrophytes, a reduction in the depth range and replacement by mussels or opportunistic algae species (Fletcher, 1996; Birkett et al., 1998). Increased nutrients may increase growth of epiphytes and plankton, resulting in reduced light penetration for photosynthesis and a subsequent reduction in the depth at which kelp could grow. However, nutrients are often added to macrophyte cultures to increase productivity. Therefore a rank of intermediate intolerance has been given to represent the likely indirect effects on turbidity and competition.

Kelps are found in full salinity and thought to be stenohaline, i.e. intolerant of salinity change. Alaria esculenta sporophytes grew poorly at salinities below 25 psu (Sundene 1961). Although its may penetrate into the lower eulittoral in is probably highly intolerant of long term reductions in salinity (Birkett et al., 1998).

No information was found concerning on the effects of de-oxygenation in macrophytes.

Galls on the blade of Laminaria hyperborea and spot disease are associated with the endophyte Streblonema sp. although the causal agent is unknown (bacteria, virus or endophyte). Resultant damage to the blade and stipe may increase losses in storms. The endophyte inhibits spore production and therefore recruitment and recoverability. Streblonema sp. has been reported growing on Alaria esculenta but no further information was found (Lein et al., 1991).

The Japanese kelp Undaria pinnatifida (wakame) has recently spread to the south coast of England from Brittany where it was introduced for aquaculture. It is presently restricted to man made structures but could spread in the ballast water of commercial or recreational boats and shipping. Its potential competition with other kelps in the UK, including Alaria esculenta requires further study (Birkett et al., 1998).

There is considerable material on the effects of harvesting kelp species (Birkett et al. 1998; Guiry & Blunden, 1991) but little evidence concerning the effects of harvesting on Alaria esculenta populations. However, evidence from other kelp species suggest that the macrophytes can recover within 3-4 years, although the effects on the rest of the community is poorly studied. In canopy clearance experiments, Alaria esculenta may appear early in the succession suggesting that it would recover more rapidly.

Extraction of sea urchin predators such as lobsters and sea otters in Nova Scotia was suggested as a possible cause of catastrophic sea urchin infestation and loss of kelp forest. Removal of grazing species may reduce competition with urchins leading to a increase in their population and subsequent loss of kelp species. However, present evidence indicates that periodic good recruitment to the urchin population may have a greater effect. It seem likely that each of these factors influences urchin populations to different extents in different areas. These effects are poorly studied in UK populations of kelp. An increased urchin or other grazer population may increase time taken for the population to recover, since they are likely to remove young sporophytes.