Julie Bremner

A bioturbation classification of European marine infaunal invertebrates

Bioturbation, the biogenic modification of sediments through particle reworking and burrow ventilation, is a key mediator of many important geochemical processes in marine systems. In situ quantification of bioturbation can be achieved in a myriad of ways, requiring expert knowledge, technology, and resources not always available, and not feasible in some settings. Where dedicated research programmes do not exist, a practical alternative is the adoption of a trait-based approach to estimate community bioturbation potential (BPc). This index can be calculated from inventories of species, abundance and biomass data (routinely available for many systems), and a functional classification of organism traits associated with sediment mixing (less available). Presently, however, there is no agreed standard categorization for the reworking mode and mobility of benthic species. Based on information from the literature and expert opinion, we provide a functional classification for 1033 benthic invertebrate species from the northwest European continental shelf, as a tool to enable the standardized calculation of BPc in the region. Future uses of this classification table will increase the comparability and utility of large-scale assessments of ecosystem processes and functioning influenced by bioturbation (e.g., to support legislation). The key strengths, assumptions, and limitations of BPc as a metric are critically reviewed, offering guidelines for its calculation and application.

Incorporating ecological functioning into the designation and management of marine protected areas

Marine protected areas are generally designed and managed on the basis of the presence and extent of specific habitat types or the habitats of important species. However, it has become clear that in addition to including these ‘structural’ elements of marine systems, management strategies should incorporate a consideration of the functional aspects of the ecosystems. Biological traits analysis (BTA) has been successfully used to describe ecological functioning in marine benthic systems. BTA uses a number of biological characteristics expressed by the taxa present as indicators of key ecosystem functions. Two expert workshops were used to examine the potential for the application of BTA in the designation and management of MPAs. They concluded that BTA represented the best tool currently available for quantifying ecological functioning and agreed on 10-key ecological functions delivered by marine benthic communities. Twenty-four biological traits were also identified by the workshops as indices of these ten functions. In order to demonstrate the practical utility of the approach, BTA using these traits, was applied to a dataset covering benthos from within and around the proposed Eddystone Special Area of Conservation (SW England). The case study demonstrated that with the type of data normally available from conservation assessment type surveys, and a knowledge of the relevant biological traits, it is possible to use a consideration of ecological functioning to set boundaries for the MPA and to inform the site management objectives. The use of structure and function information to inform the designation process and subsequent management of marine protected areas is discussed.

Assessing Marine Ecosystem Health: The Long-Term Effects of Fishing on Functional Biodiversity in North Sea Benthos

Assessments based on the taxonomic composition and relative abundance of taxa provide valuable information about the effects of anthropogenic activities on benthic systems. However, international agreements also require active conservation of ecosystem functioning as well as biological assemblages. We must therefore learn more about how ecosystems function and why changes occur within them in order to fully understand the implications of human activities. Biological traits analysis allows systems to be described in terms of the characteristics of member taxa, describing functional diversity whilst retaining information on taxa distributions. This study used biological traits analysis to investigate the long-term effects of fishing on benthic infaunal communities. Infaunal abundance was recorded over three decades at two stations, one within and one outside a fishing ground in the central western North Sea. Each taxon present was categorised for the degree to which it exhibited certain biological traits. The distribution of these traits within a sample produced a picture of functional diversity. Multivariate analyses were used to compare trait composition at the stations over time, thus depicting how community functioning responded to physical disturbance. The assemblages at the two stations were functionally distinct at the onset of the study; with differences in size, feeding type and reproductive method. The functional structure changed over time at the station within the fishing ground as the level of exploitation varied. Large animals, predators, scavengers and those eating invertebrates or carrion dominated years of light effort in the fishing ground but were less represented when effort increased. No such changes occurred at the station outside the fishing ground. Fishing seems to have some effect on benthic functional biodiversity and this effect is most obvious when moving from low to moderate levels. The differences between stations at the start of the timeseries may reflect variations in the physical environment or may result from effects of fishing that predate the timeseries.

A Field Test of the Intermediate Disturbance Hypothesis in the Soft‐Bottom Intertidal

The intermediate disturbance hypothesis has had success in explaining changes in local diversity in many habitats. Recent laboratory work has shown that disturbance may act to increase diversity in soft-bottom marine communities as predicted by the hypothesis. In this paper, we present the results of a field experiment which tested the impacts of physical disturbance on soft-bottom, intertidal macrobenthic communities. Five disturbance treatments were used, differing in the frequency of applied disturbance events: the highest frequency treatments were dug every week, lowest every eight weeks. The experiment was run for a total of 25 weeks over the winter of 1997/98. Our experiment controlled for differences in recovery time after disturbances. Abundances of Pygospio elegans, Macoma balthica, Hydrobia ulvae and Streblospio benedicti were all significantly reduced in high disturbance treatments, as was the total number of species. No species showed significant increases in abundance in disturbed treatments, and there was no evidence of an increase in diversity in any treatments. These results are discussed in the context of the intermediate disturbance hypothesis. Our results suggest that the interspecific competitive effects postulated by the hypothesis are not important in structuring this low diversity, intertidal community. However. unequivocally rejecting the hypothesis is difficult because it contains many ambiguities, and acts more as a conceptual model than as a falsifiable hypothesis.

Biological Responses at Supraindividual Levels

The effects of pollutants on marine fauna and flora cover many direct and indirect effects at supraindividual levels, from populations to ecosystems. In recent times, hundreds of indicators, metrics, and assessment methods have been developed to determine the impacts of those pollutants on different components of the ecosystem. This development is generally included in the framework of national and international legislation, approved in different continents. Pollution effects on organisms can imply consequences at the population level to different degrees, from changes in population dynamics or genetic diversity, to the local extinction of a population. In turn, ecological integrity assessment requires the study of structure (e.g., richness, diversity), function (e.g., response of sensitive and opportunistic species or biological traits to pollution), and processes at the community level. However, the most important challenge is to understand the response of the complete ecosystem to interactions between multiple stressors (i.e., cumulative, synergistic, antagonistic) and to assess marine health in an integrative way at regional or global scales.

Challenges to quantifying glass eel abundance from large and dynamic estuaries

European eel Anguilla anguilla recruitment into the rivers of the northeastern Atlantic has declined substantially since the 1980s. Monitoring of recruiting juveniles, or glass eels, is usually undertaken in small estuaries and rivers. Sampling of large-scale estuaries is rare, due to the size of the sampling area and the resources needed to provide adequate sampling levels. Here we describe surveys for glass eels in the UK’s largest estuarine system, the Severn Estuary/Bristol Channel. We sampled across a 20 km-wide stretch of the estuary in 2012 and 2013, using a smallmeshed net deployed from a commercial fishing trawler, and the surveys yielded over 2500 glass eels. Eels were more abundant in the surface layer (0–1.4 m depth) than at depth (down to 8.4 m depth), were more abundant close to the south shore than along the north shore or middle of the estuary, and were more abundant in lower salinity water. Numbers were higher in the second year than in the first and eels were more abundant in February than April. The difficulties and logistics of sampling in such a large estuary are discussed, along with the level of resources required to provide robust estimates of glass eel abundance.