Biodiversity & Conservation

The characterizing and other species in this biotope occupy space in the habitat but their presence is most likely primarily determined by the occurrence of a suitable substratum rather than by interspecific interactions. Ampharete falcata and Parvicardium ovale are functionally dissimilar and are not normally associated with each other but do occur in the same muddy sediment habitats. There is no information regarding possible interactions between any species in the biotope. In addition to Ampharete falcata and Parvicardium ovale the biotope supports several bivalve species and a fauna of burrowing species such as Amphiura filiformis, Amphiura chiajei, Nephrops norvegicus and smaller less conspicuous species such as errant polychaetes, nematodes etc.

The burrowing and feeding activities of Amphiura filiformis can modify the fabric and increase the mean particle size of the upper layers of the substrata by aggregation of fine particles into faecal pellets. Such actions create a more open fabric with a higher water content which affects the rigidity of the seabed (Rowden et al., 1998). Such destabilisation of the seabed can affect rates of particle resuspension.

The hydrodynamic regime, which in turn controls sediment type, is the primary physical environmental factor structuring benthic communities such as COS.AmpPar. The hydrography also affects the water characteristics in terms of salinity, temperature and dissolved oxygen. It is also widely accepted that food availability (see Rosenberg, 1995) and disturbance, such as that created by storms, (see Hall, 1994) are also important factors determining the distribution of species in benthic habitats.

One of the key factors affecting benthic habitats is disturbance which in deep sediment habitats such as COS.AmpPar is minimal and so communities are often relatively stable. However, there may be some seasonal changes in the biotope such as recruitment of young, growth rates and abundance of adults. For example, growth rates of Parvicardium ovale are greatest in August (Rasmussen, 1973). The abundance of Ampharete acutifrons was observed to have seasonal variation with a peak in April, which had fallen by October to be followed by a new recruitment in spring of the next year (Price & Warwick, 1980).

The biotope has very little structural complexity. On the surface of the sediment, the polychaete Ampharete falcata creates a turf of small tubes on the surface of muddy sediments in which some species, such as Macropodia spp. spider crabs, are able to live by clinging to the polychaete tubes. Within the sediment, burrowing species (for instance, Nephrops norvegicus) create habitats that cryptic species can use. Otherwise, the fauna uses the sediment for shelter without increasing structural complexity.

Productivity in subtidal sediments is often quite low. Macroalgae are absent from COS.AmpPar and so productivity is mostly secondary, derived from detritus and organic material. Allochthonous organic material is derived from anthropogenic activity (e.g. sewerage) and natural sources (e.g. plankton, detritus). Autochthonous organic material is formed by benthic microalgae (microphytobenthos e.g. diatoms and euglenoids) and heterotrophic micro-organism production. Organic material is degraded by micro-organisms and the nutrients are recycled. The high surface area of fine particles provides surface for microflora. Being confined to mud, the polychaete Ampharete falcata is probably susceptible to predation. A related species Ampharete acutifrons is the principal food of flounders in spring and summer so Ampharete falcata may be an important food source.

Recruitment and settlement of Parvicardium ovale normally takes place in July-August (Rasmussen, 1973). Ampharete falcata is thought to have a benthic larvae (Connor et al., 1997(a)) so that its dispersive capability is severely reduced. Time of recruitment is unknown although in a similar species, Ampharete acutifrons, recruitment of young takes place in the spring (Price & Warwick, 1980). In a study of Amphiura filiformis populations in Galway Bay over a period of 2 years O'Conner & McGrath (1980) were not able to identify discrete periods of recruitment. However, other studies suggest autumn recruitment (Buchanan, 1964) and spring and autumn (Glmarec, 1979). Using a 265µm mesh size Muus (1981) identified a peak settlement period in the autumn with a maximum of 6800 recruits per m².

An Ampharete biotope is likely to reach maturity very rapidly because the key species are short lived and reach maturity within a few months. Parvicardium ovale has a life span of less than a year (Lastra et al., 1993). There was no information found on the life-history characteristics of Ampharete falcata, however a related species Ampharete acutifrons was found to be an annual species (Price & Warwick, 1980). At a sub-littoral site in Swansea Bay Warwick & George (1980) observed three cohorts of Ampharete acutifrons co-existing so reproduction probably takes place over a protracted period. Recruitment of a similar species Ampharete acutifrons varied between 46 and 8996 individuals per m² over a five year period (Price & Warwick, 1980) suggesting irregular recruitment and therefore time for the community to reach maturity.