Search

The development of offshore wind farms and marine renewable energy devices in the Mediterranean is central to both national, and international, energy strategies for countries bordering the Mediterranean Sea. The ecological impacts of marine renewable energy development in the Mediterranean region, although essential for policy makers, are as yet unknown. The Northern Adriatic is identified as a plausible site for offshore wind farm development. Using the wider region (Adriatic and Northern Ionian) as a case study, this thesis examines the likely impact to the marine environment if an offshore wind farm is established. Site suitability, based on wind speed, bathymetry, and larvae connectivity levels are investigated along with the plausibility of the turbines operating as artificial reefs in the area. As offshore wind farms may alter the larval connectivity and supply dynamics of benthic populations, a connectivity map was constructed to identify areas of high and low connectivity in the Adriatic Sea. The Puglia coast of Italy is a likely larval sink, and displays some of the highest connectivity within the region, suggesting potential inputs of genetic materials from surrounding populations. Considering offshore wind farms could operate as artificial reefs, an in-situ pilot project was established to simulate the presence of wind turbines. Macroinvertebrates colonized the new substrata within the first few months but were lower in abundance when compared to a natural hard substrata environment. Time, turbine location, and the material used for turbine construction all affected the macro-invertebrate communities. In addition, fish abundances, and diversity were lower around the simulated OWF foundations in comparison to a natural hard substrata environment, and no increases in fish abundance occurred around the simulated turbines when compared to reference sites of soft substrata. This observation was validated with the use of an ecosystem modelling software (Ecopath with Ecosim), which simulated the overall ecosystem level impacts that would occur if 50 offshore monopile wind turbines were introduced to the Northern Ionian and colonized by macroinvertebrate communities. When compared to the baseline scenario (no simulated introduction of an OWF), the introduction of new habitat had no discernible impacts to the structure or functioning of the marine ecosystem. Noticeable changes to the ecosystem were only apparent if fishing restrictions were enforced in parallel with the simulated offshore wind farm; the ecosystem appears to become more structured by top down predation. In addition seabirds are also impacted by the reduction of fishing discards as a food source. These results are the first attempt to quantify the suspected benefits of offshore wind farms operating as de-facto marine protected areas.

Zooplanktivorous fishes are an essential trophic link transferring planktonic production to coastal ecosystems. Reef-associated or pelagic, their fast growth and high abundance are also crucial to supporting fisheries. I examined environmental drivers of their distribution across three levels of scale. Analysis of a decade of citizen science data off eastern Australia revealed that the proportion of community biomass for zooplanktivorous fishes peaked around the transition from sub-tropical to temperate latitudes, while the proportion of herbivores declined. This transition was attributed to high sub-tropical benthic productivity and low temperate planktonic productivity in winter. As temperatures declined in autumn, zooplanktivores migrated away from reefs, likely seeking warmer waters offshore. This was supported in a related bioacoustics survey around Montague Island, southern NSW, which showed the coast-to-shelf distribution of pelagic zooplanktivores in early spring was closely correlated with temperature, with schools seeking warmer waters of the East Australian Current at the shelf edge. Some zooplanktivores may select warm water to improve physiological performance and may also avoid shallow coastal areas, where vertically constrained distribution increases predation risk. To examine spatiotemporal dynamics of zooplanktivores around coastal reefs a non-scientific portable multibeam echosounder was deployed. As calibration of such instruments is impracticable, I assessed a novel metric of school thickness, delineating the spatial boundaries of schools rather than quantifying backscatter. These methods were applied to study school distribution around natural and artificial reefs, and variability attributed to current exposure and time of day. Schools regularly distributed upstream of structure, as fish competed for access to un-grazed prey. Schools blanketed the seafloor at night and rose high in the water column during the day to feed, particularly around high vertical relief artificial structures. These observations can inform the design of artificial reefs to include high vertical relief to facilitate foraging in the water column. These findings also agree with observations of dense schools associated with offshore oil and gas infrastructure and provide support for leave-in-place decommissioning. These distribution patterns have important implications for fisheries and for the predators which depend on regular and predictable access to prey.

Two widely-recognised hypotheses propose that increases in fish abundance at artificial reefs are caused by: (a) the attraction and redistribution of existing individuals; and/or (b) the addition of new individuals by production. Inadequate experimental designs compromised by a lack of sufficient replication and/or spatial interspersion of reefs with controls have prevented researchers from distinguishing between attraction and production. Infrequent sampling has also led to insufficient temporal coverage of life history-driven variations in fish abundance and biomass at reefs. Detection and resolution of these trends, together with incorporation of fish age/length data, and the use of techniques such as stable isotope analysis to infer trophic link(s) between reef residents and potential sources of epibenthic nutrition at reefs should help demonstrate mechanisms underlying attraction and/or production. Given that fish numbers tend to increase after artificial reef deployments, artificial reefs have been proposed as a means by which fish stocks could be enhanced by providing new habitat in areas where natural habitat vital for feeding, shelter and reproduction have been removed, such as residential canals. The purpose of my study was to investigate whether or not artificial reefs could be used to enhance fish production within residential canals. Five reefs were deployed into Lake Rumrunner on the Gold Coast in southeast Queensland, Australia (28°02’59”S, 153°25’19”E). Reefs were interspersed among five soft sediment (control) sites of similar depth. Fish assemblages at reefs, controls and shoreline jetties were quantitatively sampled using a modified seine pop net. Very few fish were recorded at controls, but fish abundance and biomass increased dramatically at reefs shortly after deployment, stabilising at levels above that of shoreline jetties. Reefs and jetties accommodated different fish assemblages and assemblage structure varied through time. Multivariate analyses indicated that the fish assemblage at jetties within Lake Rumrunner differed from assemblages at jetties in adjacent lakes in terms of biomass composition, accommodating numerous individuals of small-bodied species. The fish assemblage at reefs featured individuals of large-bodied species and occasional, itinerant individuals of species typical of offshore subtidal reefs. Among co-occurring (reef and jetty) fish species, strong differences in the distribution of Monodactylus argenteus (Monodactylidae) between reefs, jetties and controls suggested possible new production driven by reef deployment. Abundance and biomass of M. argenteus was significantly greater at reefs relative to controls (where no fish were caught) and jetties at all times after deployment. Individuals were consistently larger on reefs than on jetties. Analyses of length-frequency distributions through time indicated the size of individuals differed from one sampling time to the next for most sampling times at reefs, possibly representing cohort growth and movement through time...