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No description available.

With the marine environment subjected to ever increasing anthropogenic pressures resulting in biodiversity and habitat losses, there is an urgent need to implement effective management and conservation strategies to limit these losses. One such strategy is the designation of Marine Protected Area (MPA) networks, with the central concept that individual MPAs are connected to its neighbours within the network However, determining scales of connectivity in an environment that varies considerably both spatially and temporally is inherently difficult. Larval dispersal is a main driver of population connectivity, and planktonic larval duration (PLD) is frequently used to infer dispersal distance. Thus far studies have predominantly focused on fish and tropical species, using approaches such as larval dispersal modelling, otolith microchemistry or genetic estimates of connectivity. This thesis aimed to assess the levels of connectivity in a range of benthic invertebrates characteristic of offshore shelf seas of the Northeast Atlantic, at a range of spatial and temporal scales. This was achieved by: (1) examining the variation in PLDs of a typical benthic assemblage, then using this information to examine the variation in realised dispersal at multiple locations using particle tracking software; (2) assessing habitat preferences for the same species, and exploring how the distribution of broad habitats would affect connectivity of species; and (3) using microsatellite markers to determine the genetic structure of the exploited scallop Pecten maximus at both a localised scale (Isle of Man) and a regional scale covering over half its range. While biological variation, in the form of PLD, did affect dispersal potential of common benthic invertebrates, it was the physical factors of hydrographic regime and substrate type within a species given dispersal range that played the most important role in determining ultimate dispersal distance and location. Additionally, the scale of genetic structure of the scallop Pecten maximus, with Norway genetically distinct from Scotland, Ireland and Isle of Man but weaker or no structure within those regions, highlighted the interaction of biological and physical factors. Ultimately, this thesis has provided valuable insight into the drivers of connectivity in the marine benthos, but further work, particularly more collaborative studies across multiple fields, is required if MPAs are to achieve their aims in the face of a changing environment.

The deep demersal community of the bathyal Porcupine Seabight is subject to environmental forcing on diel, seasonal and annual scales, in addition to the stochastic and transient influence of nutritional windfalls from the photic zone. The current regime at bathyal depth in the Porcupine Seabight is characterised by oscillations in current flow with periods of 12.4h and 14.8d. Increased current velocity and particle suspension in summer months synchronises well with the seasonal input of phytoplankton to the seafloor. These physical characteristics may constitute time signals in the deep ocean environment. Consumption and succession processes at bathyal food falls in the North Atlantic are suggestive of a fundamental difference in the community response between the North Atlantic and North Pacific oceans. The sinking of small cetacean carcasses constitutes a transient environmental impact on the local community structure which is not limited to the scavenging fauna. There is limited evidence of a response to the seasonal increase in available organic carbon in the white muscle of North Atlantic macrourids. This is in accordance with results from Pacific macrourids and suggests that the seasonal food pulse, experienced by the deep benthos under productive surface waters, is not greatly manifested at higher trophic levels. The successful adaptation of existing baited camera technology to incorporate an autonomous periodic bait-release system has enabled long-term high frequency time-series observations of deep-sea scavenging demersal fish and crustaceans to be made for the first time. An understanding of temporal environmental cues, and of the resultant interactions between organisms and their environment, effectively pervades the study of any aspect of organismal or population ecology.

This work represents an holistic study of the benthic environment. This research comprises Quaternary, hydrodynamic modelling, contaminant particle transport simulation and species-centric predictive habitat mapping. Understanding the formation processes of a Quaternary feature and the potential for modification of the seabed by prevailing currents creates a basis for comprehensive ecological studies of the benthos. Subsequently, the method described in this study offers a new strategy for marine habitat mapping. The formation mechanism of Beaufort's Dyke explains the geomorphology and substrata type of the area which are important variables for faunal assemblages and detailed hydrodynamic information from simulations increases the strength of subsequent ecological investigation. Using simulation results, differences in epifaunal community structure and abundance between sample regions can be attributed to enhancement of colonisation by near- bed currents and life history response to hydrodynamics rather than substratum composition alone. Also, the potential for modification of bedforms by prevailing currents can be tested by comparing hydrodynamic and sedimentological data. An observed increase in the concentration of heavy metals within Beaufort's Dyke sediments may be the first evidence of the legacy of ordnance disposal around the Dyke. Further increase in contaminant levels within Beaufort's Dyke sediments will negatively impact resident fauna and the ecology of the region. Particle transport simulations demonstrate that dispersal of heavy metals from Beaufort's Dyke is possible and that disposed ordnance may also contribute to pollution of surrounding areas. Habitat conservation is often initiated because of resident fauna that are deemed vulnerable but these fauna are subsequently omitted in the map creation process. By utilising hydrodynamic, acoustic and faunal data to objectively determine assemblage relationships and combining faunal distribution data to produce species- centric habitat maps, management of vulnerable species can be based upon the target species, its associated community and habitat rather than abiotic surrogates.

Backscatter imagery from multibeam echosounders (MBES) is increasingly used for benthic habitat mapping. This research explores MBES backscatter classification using QTC-Multiview on data from Stanton Banks (UK) and Cashes Ledge (USA). Image-processing algorithms are used to extract values from samples of backscatter data, which are reduced by principal components analysis and are objectively clustered. This process is initially evaluated using 2005 data from Stanton Banks and compared with ground-truth data to determine their biological validity. Low-levels of agreement are observed between acoustic class and ground- truth data «35%); video is determined to be the most spatially appropriate method for comparison. Subsequently, the area was resurveyed in 2006 using the same MBES with different operational parameters, acquiring low- and high-density data coverage. Percentage agreement between classifications was 78%, determined to be due to operational parameters as opposed to environmental change. Agreement with ground truth data improved from 71 % to 77% with increased data density. In 2008, a 2 km2 area was resurveyed at two different orientations and vessel speeds within the same 24 hr period. Classification revealed 53% similarity at 4 rns-1 and 49% at 2 rns-1 from opposing orientations. The same orientations surveyed at different speeds were between 68% (k=0.583) and 53% (k=0.384) similar. These results suggest that both orientation and speed are significant considerations in image-based classification. Finally, the significance of water-column biomass in backscatter classification was examined at Cashes Ledge using MBES data from kelp beds. Two approaches were examined for detecting the presence of macrophytes; image-based and manual picking. Comparison with video data revealed comparable success, with both methods most successful at predicting Laminaria sp. (77.3%-82.6% correct) in shallow water «30m). This research demonstrates the significance of MBES backscatter and image-based classification as potential tools for the emergent discipline of benthic habitat mapping.

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Disturbances are one of the most important factors in maintaining the coexistence of species, and their frequency, intensity and timing are all thought to be increasing as a direct consequence of anthropogenic global change. Therefore many species may not be able to adapt and may subsequently be lost from an ecosystem. The aim of this thesis is to focus on the local scale processes in benthic subtidal habitats that are thought to drive the co-existence of species within communities. The primary goal was to investigate disturbances and their impacts upon temperate marine benthic communities, and secondary aims explored the interactions between disturbances, productivity and habitat complexity. In order to test the intermediate disturbance hypothesis and a model of disturbance-productivity interactions, communities of two different successional stages were manipulated with a range of disturbance frequencies and varying levels of nutrient availability. The effect of temporal variation around the disturbance regime which caused the greatest effect, as well as the sequence of these disturbances, was then investigated. Finally the role of natural surface heterogeneities in creating refuges in the face of a suite of different disturbances was investigated, and used to discover the value of increasing habitat complexity in maintaining or promoting diversity. Results from all experiments have shown that disturbances are important structuring forces for benthic marine communities. Disturbance-productivity interactions do not support the intermediate disturbance hypothesis or the disturbance-productivity model and the temporal variability of disturbance regimes appears to be an unimportant factor in the structuring of these temperate communities, whereas increased habitat complexity provides important refuges in the presence of abiotic disturbances.