Biodiversity & Conservation

The biotope is characterized by tube-building or burrow-living polychaetes and by oligochaetes, with errant polychaetes foraging in the surrounding and underlying sediment.

Mobile, carnivorous polychaetes, including Nephtys hombergi, Anaitides spp, Eteone longa, and Pholoe spp., predate the smaller annelids and crustaceans.

The dominant tube-builders are the deposit feeding polychaetes Polydora ciliata and Lanice conchilega. In areas of mud, the tubes built by Polydora ciliata can agglomerate and form layers of mud an average of 20 cm thick, occasionally up to 50 cm (Daro & Polk, 1973).

The feeding activities of high densities of Polydora ciliata may inhibit the establishment of other benthic species by removing settling and developing larvae (Daro & Polk, 1973).

In some examples of the biotope, the tube-building, suspension feeding amphipod Ampelisca sp. and the burrowing Corophium volutator are present

The amphipods and the infaunal annelid species in the biotope probably interfere strongly with each other. Adult worms probably reduce amphipod numbers by disturbing their burrows and tubes, while high densities of amphipods can prevent establishment of worms by consuming larvae and juveniles (Olafsson & Persson, 1986).

Some examples of the biotope contain a number of infaunal bivalve species, including Abra alba, Abra nitida and Mysella bidentata, which probably both deposit feed and suspension feed depending on local environmental conditions.

Foraging species such as Carcinus maenas and Crangon crangon may feed selectively and influence the composition of the biotope.

The biotope is present throughout the year with the possibility of some seasonal variation in numbers of each species. Hall & Frid (1998) found that colonization by many of the polychaetes associated with this biotope did not vary significantly with season although recruitment of Tubificoides benedii and Ophyrotrocha hartmanni did vary significantly with season.

• Structural complexity is provided by the many tube building species in the biotope. The tubes built by Polydora ciliata for example are embedded in the sediment and the ends extend a few millimetres above the substratum surface. The mats of agglomerated sediment may be up to 50 cm thick.
• Additional structural complexity is provided by the burrows of infauna although these are generally simple. Most species living within the sediment are limited to the area above the anoxic layer, the depth of which will vary depending on sediment particle size and organic content. Underlying sediments may also become oxygenated by the activities of amphipods within their tubes (Mills, 1967), burrowing bivalves and polychaetes.

Production in IMU.Aph.Tub is mostly secondary, derived from detritus and organic material. Where the biotope occurs in shallow subtidal waters, some primary production comes from benthic microalgae (microphytobenthos e.g. diatoms, flagellates and euglenoides) and water column phytoplankton. In all cases, the benthos is supported predominantly by pelagic production and by detrital materials emanating from the coastal fringe (Barnes & Hughes, 1992). The amount of planktonic food reaching the benthos is related to:

• depth of water through which the material must travel;
• magnitude of pelagic production;
• proximity of additional sources of detritus, and the
• extent of water movement near the sea bed, bringing about the renewal of suspended supplies (Barnes & Hughes, 1992).

Food becomes available to deposit feeders by sedimentation on the substratum surface and by translocation from the water column to the substratum through production of pseudofaeces by suspension feeders.
Productivity in the biotope is expected to be high. Many of the characterizing species are likely to have a short life span, grow to maturity quickly and have multiple generations per year.
The sediment in the biotope may be nutrient enriched due to proximity to anthropogenic nutrient sources such as sewage outfalls or eutrophicated rivers.

Limited information has been found on species in the biotope and only characterizing species have been specifically researched.

• The lifecycle of Aphelochaeta marioni varies according to environmental conditions. In Stonehouse Pool, Plymouth, Aphelochaeta marioni (studied as Tharyx marioni) spawned in October and November (Gibbs, 1971) whereas in the Wadden Sea, Netherlands, spawning occurred from May to July (Farke, 1979). The embryos developed lecithotrophically and hatched in about 10 days (Farke, 1979). Under stable conditions, adult and juvenile Aphelochaeta marioni will disperse by burrowing (Farke, 1979).
• The spawning period for Polydora ciliata in northern England is from February until June and three or four generations succeed one another during the spawning period (Gudmundsson, 1985). After a week, the larvae emerge and are believed to have a pelagic life from two to six weeks before settling (Fish & Fish, 1996). The larvae settle preferentially on substrates covered with mud (Lagadeuc, 1991).
• Nephtys hombergi exhibits variable spawning success with failures in some years (Olive et al., 1997).
• The mating system of amphipods is polygynous and several broods of offspring are produced, each potentially fertilized by a different male. There is no larval stage and embryos are brooded in a marsupium, beneath the thorax. Embryos are released as sub-juveniles with incompletely developed eighth thoracopods and certain differences in body proportions and pigmentation. Dispersal is limited to local movements of these sub-juveniles and migration of the adults and hence recruitment is limited by the presence of local, unperturbed source populations (Poggiale & Dauvin, 2001). Dispersal of subjuveniles may be enhanced by the brooding females leaving their tubes and swimming to uncolonized areas of substratum before the eggs hatch (Mills, 1967).
• The tube building polychaetes, e.g. Pygospio elegans, generally disperse via a pelagic larval stage (Fish & Fish, 1996) and therefore recruitment may occur from distant populations (Boström & Bonsdorff, 2000). However, dispersal of some of the infaunal deposit feeders, such as Scoloplos armiger, occurs through burrowing of the benthic larvae and adults (Beukema & de Vlas, 1979; Fish & Fish, 1996). Recruitment must therefore occur from local populations or by longer distance dispersal during periods of bedload transport. Recruitment is therefore likely to be predictable if local populations exist but patchy and sporadic otherwise.

The community is dominated by fast growing opportunistic species and the community most likely reaches maturity within one year of space becoming available. In an experimental study investigating recovery of a range of species characteristically found in this biotope after copper contamination, Hall & Frid (1995) found that recovery took up to a year. However, Hall & Frid (1998) found that colonization by many of the polychaetes associated with this biotope did not vary significantly with season although recruitment of Tubificoides benedii and Ophyrotrocha hartmanni did vary significantly with season.

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