Capitella capitata in enriched sublittoral muddy sediments
Ecological and functional relationships
Capitella capitata represents a complex (Grassle & Grassle, 1976) of over ten sibling species (Gemenick & Giere, 1997) which are likely to be present in the biotope. While the species of this complex show only slight differences in adult morphology, they differ widely in ontogenetic, ecological and genetic features (Gamenick & Giere, 1997) and have distinct reproductive modes (Grassle & Grassle, 1976).
Capitella capitata has been recorded in high numbers in areas of organic enrichment, where sewage inputs (Bridges, 1996; Holte & Oug, 1996; Cardell et al., 1998, Thom & Chew, 1979) and fish farms (Karakassis et al., 2000) were present. It has also been recorded in areas where sediments contain high concentrations of metals and hydrocarbons (Ward & Young, 1982; Olsgard, 1999; Petrich & Reish, 1979). The species is commonly cited as an indicator of organic enrichment, although members of the species complex vary in their response to disturbance and environmental change.
The conditions in which Capitella capitata flourishes are not tolerated by many other organisms. Thus, when members of the species complex occur in high densities few other species will be present.
Capitella capitata is also found in organically poor areas (Eagle & Rees, 1973) although it is unlikely to be present in such high abundance in these habitats because of competition from other species. Capitella capitata is a complex of opportunistic species with life history traits that enable them to rapidly colonize vacant and disturbed habitats. Thus, in areas of high disturbance, by regular dredging for instance, Capitella capitata may be present.
Lugworms have been found to have a strongly negative effect on the juvenile densities of Capitella capitata (Flach, 1991).
Seasonal and longer term change
- Although annual variations in the composition of cryptic species within the Capitella capitata complex have been documented (Grassle & Grassle, 1976), very little information has been found on seasonal or temporal changes in overall Capitella capitata populations.
- Differences, sometimes distinctly seasonal, may be observed in the breeding period of Capitella capitata according to variation in local conditions, especially temperature, organic enrichment of the sediment and population density. For example, Mendez et al. (1997) suggest that Capitella capitata is able to produce many individuals when organic supply is high enough to feed all the population. However, variation in reproductive output is also likely to be determined by differences in composition of the Capitella capitata species complex, as members are known to differ in fecundity, larval dispersal ability and general abundance (Grassle & Grassle, 1978).
- In the sheltered conditions in which the biotope is found it is unlikely that winter weather disturbance is likely to have an impact on population demographics.
Habitat structure and complexity
- The biotope has very little structural complexity with Capitella capitata, and the few other species that may be present, living in or on the sediment.
- Deposit feeders manipulate, sort and process sediment particles and may result in destabilization and bioturbation of the sediment which inhibits survival of suspension feeders.
Productivity in IMS.Cap is mostly secondary, derived from detritus and organic material. Macroalgae are absent from the biotope. The biotope occurs in nutrient rich areas, for example, close to sewage outfalls. 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. 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. Mendez et al. (1997) suggested that Capitella capitata is able to produce many individuals when organic supply is high enough to feed all the population, although the ability and timescale of response varies among members of the species complex (Grassle & Grassle, 1978).
- Warren (1976) noted that spawning of Capitella capitata occurred throughout the year in Plymouth, with all oocytes being released at a single spawning. Warren (1976) also noted that oocytes are not released into the coelomic fluid until almost fully developed and that larval development may have been completely benthonic. However, in the USA another variant of the Capitella capitata complex, Capitella species 1, has been shown to have planktonic larval development for a short time (hours to days) before settlement (Grassle & Grassle, 1974). Generally speaking, this species is considered to be iteroparous, and the larvae are brooded during part of their development within the adult tube.
- Planas & Mora (1989) have calculated that individuals from the northwest of Spain spend 2-4 weeks to change from eggs to the juvenile stage and about 3 months from juveniles to adults.
- Studies on natural populations of Capitella capitata in England show that sexual maturity is reached at about 4 months (Warren, 1976). However, in other geographical locations, sexual maturity may be reached at 3.5 months (Qian & Chia, 1994).
- Capitella species 1 larvae were attracted by a sulphide concentration of 0.1mm to 1.0mm, yielding higher settlement, subsequent metamorphosis and survival of settled polychaetes compared with non-sulphidic controls (Cuomo, 1985).
Time for community to reach maturity
A Capitella capitata biotope is likely to reach maturity very rapidly because the species of the complex are short lived, reaching maturity within about four months. Capitella capitata has an opportunistic life history and year round breeding. Bolam & Fernandes (2002) and Shull (1997) noted that Capitella capitata can colonize azoic sediments rapidly in relatively high numbers. Shull (1997) also demonstrated that this occurs by larval settlement, bedload transport and by burrowing. Thus, when conditions are suitable, the time for the community to reach maturity is likely to be less than six months.
This review can be cited as follows:
Hill, J. & Bilewitch, J.
Capitella capitata in enriched sublittoral muddy sediments.
Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line].
Plymouth: Marine Biological Association of the United Kingdom.
Available from: <http://www.marlin.ac.uk/habitatecology.php?habitatid=106&code=1997>