Fish utilisation of saltmarshes and managed relignment areas in SE England
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Saltmarshes in SE England are eroding rapidly and one potential impact is the loss of habitat for fishes. Saltmarshes have been created by setting back the existing line of flood defence through managed realignment. The use by fishes of natural and managed realignment habitats at Tollesbury, Abbotts Hall and Orplands was examined (2005-07). Three seasonal groups were apparent in the fish assemblages of the managed realignment sites: February-April (Pomatoschistus microps and Sprattus sprattus), May-September (Dicentrarchus labrax and Atherina presbyter) and October-January (Liza aurata and Liza ramada). The sites were used mainly by 0- and 1-group fishes and adult P. microps. The mean abundance (July - August 2007) was 558 0.1 ha' (range 76 - 2699 0.1 ha'). In summer, small (<30 mm) zooplanktivorous D. labrax fed successfully at all sites. Larger (30-59 mm) D. labrax consumed more macroinvertebrates in the Tollesbury managed realignment and two established marshes than at Abbotts Hall and Orplands. By autumn there were no site-specific differences in gut fullness of D. labrax. Stable isotope ratio analysis and gut contents analysis revealed that small (<50 mm) D. labrax, S. sprattus and A. presbyter assimilated zooplankton which eat detritus, resuspended microphytobenthos and some phytoplankton. L. aurata assimilated zooplankton and microphytobenthos. P. microps (20-50 mm) and A. presbyter (80-99 mm) assimilated benthic meiofauna. Larger (50-230 mm) D. labrax assimilated macroinvertebrates which eat microphytobenthos, Ulva spp., C3 plants and detritus. Some recommendations for saltmarsh restoration are provided with an estimate of the economic value of bass in saltmarshes,to highlight further areas of research.
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