Spatial variability of marine climate change impacts in the North Atlantic

There is an accumulating body of evidence to suggest that many marine ecosystems in the North Atlantic, both physically and biologically are responding to changes in regional climate caused predominately by the warming of air and sea surface temperatures (SST) and to a varying degree by the modification of oceanic currents, precipitation regimes and wind patterns. The biological manifestations of rising SST and oceanographic changes have variously taken the form of biogeographical, phenological, physiological and community changes. For example, during the last 40 years there has been a northerly movement of warmer water plankton by 10 degree latitude in the north-east Atlantic and a similar retreat of colder water plankton to the north. This geographical movement is much more pronounced than any documented terrestrial study, presumably due to advective processes playing an important role. Other research has shown that the plankton community in the North Sea has responded to changes in SST by adjusting their seasonality (in some cases a shift in seasonal cycles of over six weeks has been detected), but more importantly the response to climate warming varied between different functional groups and trophic levels, leading to mismatch. Therefore, while it has been documented that marine ecosystems in certain regions of the Atlantic have undergone some conspicuous changes over the last few decades it is not known whether this is a pan-oceanic homogenous response. Using these two most prominent responses and/or indicative signals of pelagic ecosystems to hydro-climatic change, changes in species phenology and the biogeographical movement of populations, we attempt to identify vulnerable regional areas in terms of particularly rapid and marked change.

Transregional linkages in the North-Eastern Atlantic - An ‘end-to-end ’ analysis of pelagic ecosystems

This review examines interregional linkages and gives an overview perspective on marine ecosystem functioning in the north-eastern Atlantic. It is based on three of the 'systems' considered by the European Network of Excellence for Ocean Ecosystems Analysis (EUR-OC EANS was established in 2004 under the European Framework VI funding programme to promote integration of marine ecological research within Europe), the Arctic and Nordic Seas, North Atlantic shelf seas and North Atlantic. The three systems share common open boundaries and the transport of water, heat, nutrients and particulates across these boundaries modifies local processes. Consistent with the EUR-OC EANS concept of 'end-to-end' analyses of marine food webs, the review takes an integrated approach linking ocean physics, lower trophic levels and working up the food web to top predators such as marine mammals. We begin with an overview of the regions focusing on the major physical patterns and their implications for the microbial community, phytoplankton, zooplankton, fish and top predators. Human-induced links between the regional systems are then considered and finally possible changes in the regional linkages over the next century are discussed. Because of the scale of potential impacts of climate change, this issue is considered in a separate section. The review demonstrates that the functioning of the ecosystems in each of the regions cannot be considered in isolation and the role of the atmosphere and ocean currents in linking the North Atlantic Ocean, North Atlantic shelf seas and the Arctic and Nordic Seas must be taken into account. Studying the North Atlantic and associated shelf seas as an integrated 'basin-scale' system will be a key challenge for the early twenty-first century. This requires a multinational approach that should lead to improved ecosystem-based approaches to conservation of natural resources, the maintenance of biodiversity, and a better understanding of the key role of the north-eastern Atlantic in the global carbon cycle.

Macroalgal blooms alter community structure and primary productivity in marine ecosystems

Eutrophication, coupled with loss of herbivory due to habitat degradation and overharvesting, has increased the frequency and severity of macroalgal blooms worldwide. Macroalgal blooms interfere with human activities in coastal areas, and sometimes necessitate costly algal removal programs. They also have many detrimental effects on marine and estuarine ecosystems, including induction of hypoxia, release of toxic hydrogen sulfide into the sediments and atmosphere, and the loss of ecologically and economically important species. However, macroalgal blooms can also increase habitat complexity, provide organisms with food and shelter, and reduce other problems associated with eutrophication. These contrasting effects make their overall ecological impacts unclear. We conducted a systematic review and meta-analysis to estimate the overall effects of macroalgal blooms on several key measures of ecosystem structure and functioning in marine ecosystems. We also evaluated some of the ecological and methodological factors that might explain the highly variable effects observed in different studies. Averaged across all studies, macroalgal blooms had negative effects on the abundance and species richness of marine organisms, but blooms by different algal taxa had different consequences, ranging from strong negative to strong positive effects. Blooms' effects on species richness also depended on the habitat where they occurred, with the strongest negative effects seen in sandy or muddy subtidal habitats and in the rocky intertidal. Invertebrate communities also appeared to be particularly sensitive to blooms, suffering reductions in their abundance, species richness, and diversity. The total net primary productivity, gross primary productivity, and respiration of benthic ecosystems were higher during macroalgal blooms, but blooms had negative effects on the productivity and respiration of other organisms. These results suggest that, in addition to their direct social and economic costs, macroalgal blooms have ecological effects that may alter their capacity to deliver important ecosystem services.

Frequent locations of oceanic fronts as an indicator of pelagic diversity: application to marine protected areas and renewables

Frequent locations of thermal fronts in UK shelf seas were identified using an archive of 30,000 satellite images acquired between 1999 and 2008, and applied as a proxy for pelagic diversity in the designation of Marine Protected Areas (MPAs). Networks of MPAs are required for conservation of critical marine habitats within Europe, and there are similar initiatives worldwide. Many pelagic biodiversity hotspots are related to fronts, for example cetaceans and basking sharks around the Isle of Man, Hebrides and Cornwall, and hence remote sensing can address this policy need in regions with insufficient species distribution data. This is the first study of UK Continental Shelf front locations to use a 10-year archive of full-resolution (1.1 km) AVHRR data, revealing new aspects of their spatial and seasonal variability. Frontal locations determined at sea or predicted by ocean models agreed closely with the new frequent front maps, which also identified many additional frontal zones. These front maps were among the most widely used datasets in the recommendation of UK MPAs, and would be applicable to other geographic regions and to other policy drivers such as facilitating the deployment of offshore renewable energy devices with minimal environmental impact.

The effect of the North Atlantic Subpolar Front as a boundary in pelagic biogeography decreases with increasing depth and organism size

Broad-scale patterns in the distribution of deep-sea pelagic species and communities are poorly known. An important question is whether biogeographic boundaries identified from surface features are important in the deep mesopelagic and bathypelagic. We present community analyses of discrete-depth samples of mesozooplankton and micronekton to full-ocean depth collected in the area where the Mid-Atlantic Ridge is crossed by the Subpolar Front. The results show that the distributional discontinuity associated with the front, which is strong near the surface, decreases with increasing depth. Both the frontal separation near the surface and the community convergence at increasing depths were clearer for mesozooplankton than for micronekton.

The effect of the North Atlantic Subpolar Front as a boundary in pelagic biogeography decreases with increasing depth and organism size

Broad-scale patterns in the distribution of deep-sea pelagic species and communities are poorly known. An important question is whether biogeographic boundaries identified from surface features are important in the deep mesopelagic and bathypelagic. We present community analyses of discrete-depth samples of mesozooplankton and micronekton to full-ocean depth collected in the area where the Mid-Atlantic Ridge is crossed by the Subpolar Front. The results show that the distributional discontinuity associated with the front, which is strong near the surface, decreases with increasing depth. Both the frontal separation near the surface and the community convergence at increasing depths were clearer for mesozooplankton than for micronekton.