Abstract
A rapidly expanding human population and technological advances in fisheries have driven a marked decline in wild fish stocks over the past century. In response to such issues, aquaculture practices are ascendency globally. Historically, bivalve cultivation was considered to be a benign practice with negligible effects to the surrounding environment, however following on going intensification, concerns have been raised about the cumulative ecological effects of coastal aquaculture development. The aim of this thesis was to determine the potential impact of bivalve aquaculture practices, particularly Mytilus edulis (blue mussel) cultivation, on coastal biodiversity.Firstly, orientation (upward facing, downward facing and vertical) of artificial substrata commonly associated with aquaculture practices was manipulated under laboratory conditions, and the settlement of scyphozoan jellyfish planulae was recorded. Scyphozoan planulae settled in greater numbers on vertically facing settlement plates, as opposed to those with upward or downward facing orientations. This finding suggests that the increased frequency of vertical substrata associated with aquaculture and further anthropogenic urbanisation may be facilitating the settlement of benthic scyphozoan life-stages.
As a logical extension to the first experiment an outdoor mesocosm platform was used to investigate the settlement of scyphozoan planulae onto artificial substratum in the presence of potential competitors for space in varying densities (alive M. edulis, dead M.edulis, and macroalgae). Planulae settlement was lowest within the high-density alive mussel treatment, with the presence of macroalgae contributing further towards reduced settlement. These findings suggest that bivalves provide an effective solution to planulae settlement on artificial structures associated with aquaculture platforms.
To gain a further insight on the impact of coastal bivalve aquaculture to the surrounding environment, the second half of the thesis (Chapters 4 and 5) focussed on the influence of aquaculture platforms on seagrass meadows. Initially, the effect of on-bottom M. edulis size class and density on intertidal seagrass was investigated in situ across two sites within Strangford Lough, Northern Ireland. No detectable impacts of M. edulis size class or density could be determined based on measures of seagrass (Zostera marina van. angustifolia) meadow productivity or organic matter content; suggesting that small-scale intensive bivalve cultivation (if well managed) shows significant promise as a sustainable practice. Following on from Chapter 4, physical disturbance associated with manual harvest was simulated within a seagrass meadow (again Z. marina var. angustifolia) to assess whether it altered top-down control mechanisms. Predation by mesopredators was greatest in regions of the meadow were structural complexity was reduced; suggesting that physical damage can set up a positive feedback mechanism within coastal food-webs that warrants further attention. Although presented as stand-alone studies these chapters combine ultimately in the form of management recommendations for the sustainable expansion of aquaculture practices around the island of Ireland.
| Date of Award | Dec 2019 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Department of Agriculture, Environment and Rural Affairs & Queen's University Belfast |
| Supervisor | Jonathan Houghton (Supervisor), Nessa O'Connor (Supervisor) & Philippe Archambault (Supervisor) |