The ecology of the benthos in Liverpool Docks.

Brian. Wilkinson, Stephen
(1995) The ecology of the benthos in Liverpool Docks. PhD thesis, University of Liverpool.

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A broadscale survey of the benthos was carried out in the docks around Liverpool and the results indicated that the walls of the majority of the South Docks were dominated by Mytilus edulis. This species tended to be less abundant in docks close to the intake from the Mersey while Molgula manmattensis tended to be more abundant at these sites. These differences may be due to a combination of either increased suspended solids or decreased phytoplankton. The walls of Albert, Queens and Princes Docks were surveyed over a three year period. The results indicated that the abundance of Mytilus was relatively constant between years. Other more ephemeral species, such as Ciona, showed considerable variation both within and between years. Closer examination of the Mytilus population structure has indicated that it was dominated by one or two cohorts which had settled in 1988 - 1989. Much less recruitment has occurred subsequently. Reasons for this lack of recruitment are examined, however, the most likely explanations are increased predation from Carcinus and/or intraspecific interactions from the adult bed, either filtering out Mytilus larvae or reducing food supply to new settlers. Monitoring of the zooplankton indicated considerable temporal and spatial variation, despite the fact that the docks are effectively a closed ecosystem. The observed variations are attributed to either adult or larval behaviour or changes in primary production affecting secondary production. Tiles have been used to follow the pattern of annual succession and the effect of timing of available space on this pattern of succession. Results were integrated with changes observed in the wall benthos and variations in larval supply. Considerable differences were observed in the community that developed on suspended tiles, tiles fixed to the dock wall and cleared areas of the dock wall. One of the primary factors affecting this was thought to be reduced food supply on the wall due to the dense filter feeding assemblage there. No evidence was found of any strong interspecific interactions in the successional sequence. Rather, the community composition was typical for the time of year. The community development is described with regard to the life-history strategies of the species in the fouling assemblage. Tiles were also used to look at the annual pattern of algal settlement. This indicated that diatoms were the principal settlers early in the year, brown ephemerals such as Giffordia and Punctaria during spring and green ephemerals such as Enteromorpha and Cladophora over the summer period. Amphipods were the dominant grazers of this assemblage. Tiles left in place for two to three months initially developed dense algal growth but this was subsequently replaced by a cover of Botryllus. This change was thought to be accelerated by the grazing amphipods. No perennial algae were recorded in the docks; reasons for this are proposed. Finally, an assessment is made of the overall stability of the benthic ecosystem found in the docks around Liverpool and a number of possible management options, which could be used to improve the stability, are suggested.

Item Type: Thesis (PhD)
Depositing User: Symplectic Admin
Date Deposited: 23 Oct 2023 10:19
Last Modified: 23 Oct 2023 10:25
DOI: 10.17638/03176049
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