The role of fronts, eddies and bubbles on the distribution, abundance and advection of gelatinous zooplankton: new insights for finfish aquaculture
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Date
2018
Authors
Haberlin, Damien
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University College Cork
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Abstract
The past three decades, from 1990 to the present, have seen a considerable increase in the number of studies investigating the ecology of gelatinous zooplankton, driven in no small part by the negative socio-economic impacts of gelatinous zooplankton. Despites some exciting progress, some important gaps remain, particularly with regard to how physical and oceanographic processes influence the distribution and abundance of gelatinous zooplankton. It is well established that these are central processes in the formation of the patchy distribution of phytoplankton and large vertebrate pelagic predators, however, few studies have elucidated the role of such processes on gelatinous zooplankton. Therefore, the central theme of this thesis was to investigate the influence of mesoscale processes (fronts and eddies) on gelatinous zooplankton ecology. In addition, two strategies with the potential to reduce the impact of harmful jellyfish species at finfish farms were investigated: 1) the use of an artificial front as a barrier and; 2) the efficacy of a non-toxic antifouling coating to reduce hydroid biofouling. Temporal sampling in southwest Ireland and a compilation of historic observations revealed a low siphonophore diversity in Irish waters, with Muggiaea atlantica being the most abundant species by an order of magnitude. The occurrence of siphonophores in the southwest of Ireland indicated the influence of physical drivers and shared trends with the Western English Channel suggested a physical link between both regions. The Celtic Sea Front was the most likely physical link between both regions and its annual formation had a profound impact on gelatinous zooplankton distribution in the region for a period each year. Sampling carried out during July 2015 revealed two distinct gelatinous communities separated by the Celtic Sea Front; a cold mixed water community in the Irish Sea and a warm water stratified community in the Celtic Sea. The gelatinous abundance (656 indiv. m-3 ) and biomass (2085 mg C 1000 m-3 ) was higher in the Celtic Sea. The mean gelatinous contribution to the total zooplankton biomass was 4 - 6%, reaching a maximum of 16% in the Celtic Sea. There was no evidence that the front enhanced the abundance of biomass of gelatinous taxa, however, it is likely that the front influenced the community and biomass through broader scale advective processes. A survey in the northwest Atlantic also showed that a mesoscale warm core eddy had a profound influence on the gelatinous zooplankton, with a 12-fold decline in gelatinous zooplankton inside the eddy. Some larger calycophoran genera were present in the eddy, along with several large crustacean genera, nonetheless, most zooplankton taxa were poorly represented, suggesting an oligotrophic eddy core. An investigation of mitigation strategies for finfish aquaculture demonstrated that a bubble curtain may be of limited use due to the ability of small objects to pass through the bubble plume. Tests also showed, the potential rate of ‘jellyfish’ transmission through the bubble curtain is affected by wave height and frequency, meaning sites which experience high wave energy would negatively impact the bubble curtain. Experimental trials of a novel nontoxic coating applied to nylon netting typical to salmon farm cages showed no effect on the ubiquitous fouling hydroid Ectopleura larynx. Although the coating was effective at reducing microscopic fouling and enhanced clean-ability of nets, the stolon system of the macrofouling hydroids was extremely adaptable and the complex surface topography of the multi-stranded nylon provides a surface which is physically easy for the hydroids to anchor to.
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Keywords
Gelatinous zooplankton , Jellyfish , Hydromedusae , Oceanographic fronts , Salmon farming , Finfish aquaculture
Citation
Haberlin, M. D. 2018. The role of fronts, eddies and bubbles on the distribution, abundance and advection of gelatinous zooplankton: new insights for finfish aquaculture. PhD Thesis, University College Cork.