The role of coastal defence structures in channeling production in coastal ecosystems

This study assessed the interaction of coastal defence structures (CDSs), namely shore-parallel<br/>‘low crested breakwater structures’ (LCSs), design features and hydrodynamic regime on the<br/>quantity and timings of macroalgae deposition. The employed sampling strategy comprised a<br/>spatially and temporally stratitified approach of time-lapse photography of macroalgae<br/>deposition, verified with field observations. Field surveys determined the associated ecological<br/>assemblages of the sediment infauna and rocky shore epifauna associated with the breakwater<br/>scheme, as well as for two nearby beaches with groynes. Further analysis determined decay<br/>rates, decay processes, changes in C and N stable isotope values of dominant macroalgal species<br/>and the dependence of the faunal assemblages on the decaying macroalgae deposits. Temporal<br/>analysis highlights the main factors driving macroalgal deposition were differences in spring<br/>and neap tidal range, wave height and sea temperature. Greatest deposition occurred during<br/>months of lower wave height and fewer storms, when filamentous red algae and ephemeral<br/>green algal species dominated. Results indicated to greater amounts of macroalgae deposits<br/>around LCSs than around wooden or granite groynes. Beach elevation best explained the spatial<br/>variation, both vertically and horizontally, in the benthic assemblages within the breakwater<br/>scheme, with the abundance of detritivorous deposit feeders being significantly correlated with<br/>abundance of macroalgae deposits. Orientation of LCSs, relative to wave action, was an<br/>important driver of epifaunal assemblages on the CDSs, with the eastward ends of the<br/>breakwaters providing the optimum intermediate environment with regards to wave action,<br/>exhibiting the greatest abundances of epifauna. Stable isotope analysis showed that the carbon<br/>and nitrogen isotopic values of macroalgae changed during the decomposition and were both<br/>species and time dependent. Isotope analysis illustrated that decaying macroalgae deposits were<br/>of greater trophic importance to species within the LCS ecosystem where there was large<br/>macroalgal deposition, than to species within the groyne ecosystem where macroalgal<br/>deposition was lower. Key findings of the study illustrate the importance of decaying<br/>macroalgae deposits for the local ecosystem via modification of food chain energy flows.<br/>Though the ecosystem benefits from this allochthonous resource, deposits may be a nuisance<br/>requiring controlled human intervention.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2008

Author dc:creator

• Jolley, Elizabeth Charlotte