The role of fronts, eddies and bubbles on the distribution, abundance and advection of gelatinous zooplankton: new insights for finfish aquaculture

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

Distinct gelatinous zooplankton communities across a dynamic shelf sea

Abstract: Understanding how gelatinous zooplankton communities are structured by local hydrography and physical forcing has important implications for fisheries and higher trophic predators. Although a large body of research has described how fronts, hydrographic boundaries, and different water masses (e.g., mixed vs. stratified) influence phytoplankton and zooplankton communities, comparatively few studies have investigated their influence on gelatinous zooplankton communities. In July 2015, 49 plankton samples were collected from 50 m depth to the surface, across five transects in the Celtic Sea, of which, four crossed the Celtic Sea Front. Two distinct gelatinous communities were found in this dynamic shelf sea: a cold water community in the cooler mixed water that mainly contained neritic taxa and a warm water community in the warmer stratified water that contained a mixture of neritic and oceanic taxa. The gelatinous biomass was 40% greater in the warm water community (∼ 2 mg C m−3) compared with the cold water community (∼ 1.3 mg C m−3). The warm water community was dominated by Aglantha digitale, Lizzia blondina, and Nanomia bijuga, whereas the cold water community was dominated by Clytia hemisphaerica and ctenophores. Physonect siphonophores contributed > 36% to the gelatinous biomass in the warm water community, and their widespread distribution suggests they are ecologically more important than previously thought. A distinct oceanic influence was also recorded in the wider warm water zooplankton community, accounting for a ∼ 20 mg C m−3 increase in biomass in that region

Ecosystem benefits of floating offshore wind

Report produced for Simply Blue GroupThe offshore renewable energy (ORE) sector is at a crucial moment with multiple governments enacting policies and legislation that will decisively accelerate the expansion of offshore renewable energy globally. Floating offshore wind energy will become increasingly important over the next decade and this report seeks to elucidate the potential ecosystem benefits of floating offshore wind energy developments

Bioinspired aryldiazonium carbohydrate coatings: reduced adhesion of foulants at polymer and stainless steel surfaces in a marine environment

Surface treatments that minimize biofouling in marine environments are of interest for a variety of applications such as environmental monitoring and aquaculture. We report on the effect of saccharide coatings on biomass accumulation at the surface of three materials that find applications in marine settings: stainless steel 316 (SS316), Nylon-6 (N-6), and poly(ether sulfone) (PES). Saccharides were immobilized via aryldiazonium chemistry; SS316 and N-6 samples were subjected to oxidative surface pretreatments prior to saccharide immobilization, whereas PES was modified via direct reaction of pristine surfaces with the aryldiazonium cations. Functionalization was confirmed by a combination of X-ray photoelectron spectroscopy, contact angle experiments, and fluorescence imaging of lectin–saccharide binding. Saccharide immobilization was found to increase surface hydrophilicity of all materials tested, while laboratory tests demonstrate that the saccharide coating results in reduced protein adsorption in the absence of specific protein–saccharide interactions. The performance of all three materials after modification with aryldiazonium saccharide films was tested in the field via immersion of modified coupons in coastal waters over a 20 day time period. Results from combined infrared spectroscopy, light microscopy, scanning electron and He-ion microscopy, and adenosine-triphosphate content assays show that the density of retained biomass at surfaces is significantly lower on carbohydrate modified samples with respect to unmodified controls. Therefore, functionalization and field test results suggest that carbohydrate aryldiazonium layers could find applications as fouling resistant coatings in marine environments

Localised residency and inter-annual fidelity to coastal foraging areas may place sea bass at risk to local depletion

For many marine migratory fish, comparatively little is known about the movement of individuals rather than the population. Yet, such individual-based movement data is vitally important to understand variability in migratory strategies and fidelity to foraging locations. A case in point is the economically important European sea bass (Dicentrarchus labrax L.) that inhabits coastal waters during the summer months before migrating offshore to spawn and overwinter. Beyond this broad generalisation we have very limited information on the movements of individuals at coastal foraging grounds. We used acoustic telemetry to track the summer movements and seasonal migrations of individual sea bass in a large tidally and estuarine influenced coastal environment. We found that the vast majority of tagged sea bass displayed long-term residency (mean, 167 days) and inter-annual fidelity (93% return rate) to specific areas. We describe individual fish home ranges of 3 km or less, and while fish clearly had core resident areas, there was movement of fish between closely located receivers. The combination of interannual fidelity to localised foraging areas makes sea bass very susceptible to local depletion; however, the designation of protected areas for sea bass may go a long way to ensuring the sustainability of this species

Diversity and occurrence of siphonophores in irish coastal waters

Siphonophores are at times amongst the most abundant invertebrate zooplankton predators in the oceans. Historically, siphonophores have been under-sampled and of the studies conducted there has been a bias towards oceanic oligotrophic waters where they are considered to be more important. In temperate coastal regions, comparatively less is known about the diversity and abundance of siphonophores, where periodic blooms can restructure the plankton communities and have been correlated with high mortalities in the salmon aquaculture industry. To address this lack of knowledge, plankton samples were collected during two periods (March 2009-March 2011 and April 2014-November 2015) from a coastal embayment in the southwest of Ireland. In total, three siphonophore species were found, the calycophoran Muggiaea atlantica, and the physonects, Nanomia bijuga and Agalma elegans. Muggiaea atlantica was the most abundant species (250 colonies m(-3)), with densities an order of magnitude higher than either physonect. Muggiaea atlantica displayed a distinct seasonality, whereas the physonect species were sporadic in occurrence. Comparing siphonophores in Bantry Bay and the Western English Channel (Plymouth Marine Laboratory\u27s L4 station) indicates both regions share a similar pattern of inter-annual occurrence and provides novel information on the seasonality and occurrence of siphonophores in Irish coastal waters

First observations of the freshwater jellyfish craspedacusta sowerbii lankester, 1880 in ireland coincides with unusually high water temperatures

The freshwater hydrozoan Craspedacusta sowerbii was observed for the first time in Ireland at five localities in two separate river catchments (Shannon and Eme) during the summer of 2013. All collected medusae from Lough Derg on the Shannon catchment were female. Analysis of water temperature data for the period 2001-2015 found that water temperatures greater than 21 degrees C were only recorded in 2013. The occurrence of medusae in three distinct areas during this unusually warm summer suggests that it may have been present in its polyp form for some years, or even decades. While it is not known when the species arrived in Ireland, the spread of this species may have involved different pathways. With climate warming, further appearances of the medusa-stage may be expected

Large-scale sampling reveals the spatio-temporal distributions of the jellyfish Aurelia aurita and Cyanea capillata in the Irish Sea

At-sea distributions of large scyphozoan jellyfish across the Irish Sea were studied using visual surface counts from ships of opportunity. Thirty-seven surveys were conducted along two >100 km long transects between Ireland and the UK from April to September in 2009 and 2010. Five species were recorded but only Aurelia aurita and Cyanea capillata were frequently observed. The first formal description of the seasonal changes in the abundances and distributions of these two species in the study area is provided. The highest densities of these species were more likely to be found ~30 km offshore, but large aggregations were present both in coastal and offshore waters. Evidence for aggregations of medusae along physical discontinuities was provided by coupling jellyfish observations with simultaneous records of environmental parameters. The value of surveys from ships of opportunity as cost-effective semi-quantitative tools, to develop local knowledge on jellyfish abundance, distribution, and phenology is discussed