Melanie C. Austen

The Role of Biodiversity in the Functioning of Freshwater and Marine Benthic Ecosystems

Abstract Empirical studies investigating the role of species diversity in sustaining ecosystem processes have focused primarily on terrestrial plant and soil communities. Eighteen representative studies drawn from post-1999 literature specifically examined how changes in biodiversity affect benthic ecosystem processes. Results from these small-scale, low-diversity manipulative studies indicate that the effects of changes in biodiversity (mostly synonymous with local species richness) are highly variable over space and time and frequently depend on specific biological traits or functional roles of individual species. Future studies of freshwater and marine ecosystems will require the development of new experimental designs at larger spatial and temporal scales. Furthermore, to successfully integrate field and laboratory studies, the derivation of realistic models and appropriate experiments will require approaches different from those already used in terrestrial systems.

Economic valuation for the conservation of marine biodiversity

Policy makers are increasingly recognising the role of environmental valuation to guide and support the management and conservation of biodiversity. This paper presents a goods and services approach to determine the economic value of marine biodiversity in the UK, with the aim of clarifying the role of valuation in the management of marine biodiversity. The goods and services resulting from UK marine biodiversity are detailed, and 8 of the 13 services are valued in monetary terms. It is found that a decline in UK marine biodiversity could result in a varying, and at present unpredictable, change in the provision of goods and services, including reduced resilience and resistance to change, declining marine environmental health, reduced fisheries potential, and loss of recreational opportunities. The results suggest that this approach can facilitate biodiversity management by enabling the optimal allocation of limited management resources and through raising awareness of the importance of marine biodiversity.

The specificity of meiobenthic community responses to different pollutants: Results from microcosm experiments☆

In preliminary microcosm experiments we have been able to demonstrate a clear differential response of meiobenthic assemblages to zinc, copper and cadmium contamination. Sediment and natural meiobenthic communities were collected from two estuaries, the Lynher (mud with a high organic content) and Exe (sand with a low organic content). The sediments were dosed separately with zinc, copper and cadmium at three different dose levels. The meiobenthic community structure from both sites was unaffected by cadmium at any of the dose levels. The communities in the zinc and copper treatments were significantly different (ANOSIM p < 0.05) from each other and from the controls (and cadmium treatments). Although the differential response occurred in both sediment types, its intensity was greater in the sand than the mud. The Exe sand communities were much more strongly affected by the contaminants, even at the lowest dose, copper having a more severe effect than zinc. The Lynher mud meiobenthos was most strongly affected by the zinc treatment and there was a graded response to both zinc and copper with significant differences in the communities at different doses (ANOSIM p < 0.05). These differences between sediments could be due to the binding of metals onto organic material, thus reducing their availability to the fauna.

Meiobenthic and macrobenthic community structure along a putative pollution gradient in southern Portugal

Macro- and meiobenthos were sampled from Ria Formosa, Portugal along putative sewage pollution gradients in summer 1987 and winter 1988. The status of the benthos was assessed using multidimensional scaling ordination, ABC plots, and a variety of univariate indices of community structure. Meiobenthos in both seasons and macrobenthos in winter appeared to respond to sewage enrichment only in the immediate vicinity of the sewage outfalls and channels but ABC plots indicated that macrobenthic communities were moderately stressed throughout the area in summer. In the summer, human digging for shellfish results in considerable sediment turnover. Since meiofauna may be less affected by physical sediment disturbance than macrofauna this may explain why the macrofauna communities were apparently disturbed relative to the meiofauna even beyond the influence of the sewage. Sampling meiofauna with the macrofauna significantly increased our understanding of mans impact in this area. There was little correlation between macro- and meiobenthos in diversity, abundances, number of taxa and biomass and these indices gave no indication of an organic enrichment gradient.

The use of offshore meiobenthic communities in laboratory microcosm experiments: response to heavy metal contamination

Abstract A microcosm, originally developed for intertidal, estuarine meiobenthic communities, has been used to determine the effects of the heavy metals copper, zinc, cadmium and lead on offshore meiobenthic nematode communities. Significant differences were observed in community structure between controls and all metals except cadmium. The dose response of the offshore meiofauna to experimental contamination was rather confusing as copper and zinc low doses appeared to have much more drastic effects than the high doses. We speculate that at the highest copper and zinc dose levels the metals acted as preservatives such that animals died but did not decompose. This indicates that metals will affect the microbial component of the sediment as well as the meiobenthos in this type of experimental design. The response to the contaminants of offshore sediment biota differed from that previously observed in intertidal estuarine biota. This may be because fauna in the estuarine environment are subjected to greater levels of natural physicochemical stress and are therefore more generally tolerant. This suggests that environmental impact assessments should bioassay communities which naturally inhabit the environment to be assessed. The methods used have potential in the development of a community level bioassay particularly since it appears that the dominant nematode component of meiobenthic communities, from a wide range of habitats, can be easily maintained in simple microcosms.

Experimental evidence for the role of Brissopsis lyrifera (Forbes, 1841) as a critical species in the maintenance of benthic diversity and the modification of sediment chemistry

Abstract The effects on infaunal diversity and sediment chemistry of bioturbation/feeding activity by different densities of the heart urchin Brissopsis lyrifera are quantified in an experiment conducted in the benthic mesocosm facility of the Norwegian Institute for Water Research at Solbergstrand, Norway. Using sediment from Bjornhordenbukta, a small, sheltered bay in Oslofjord, areas were subjected to 20 weeks of continuous disturbance from urchins at densities equivalent to 28 and 71 individuals m −2 , whilst other areas remained undisturbed. Low density treatments, reflecting the natural field densities observed during collection of the sediment, produced higher infaunal β diversity than the heavily disturbed or control treatments and this could be attributed to a decrease in competitive exclusion. This is consistent with the predictions of the intermediate disturbance hypothesis ( Connell, 1978 ). Bioturbation also caused a significant change in the chemistry of the surface sediment increasing oxygenation, decreasing the rates of denitrification and increasing the precipitation of phosphate. It is concluded that the disturbance activity of Brissopsis lyrifera may play a vital role in the maintenance of regional diversity and in the mediation of geochemical processes.

A community level sediment bioassay applied to an estuarine heavy metal gradient

Abstract A simple laboratory microcosm system, previously used as a community level sediment bioassay for laboratory contaminated sediments, has been used for testing contaminated field sediments. Meiobenthic communities from the Lynher Estuary were incubated with defaunated sediment collected from the Fal Estuary system where a gradient of heavy metal concentrations is reflected in meiofaunal community structure. In the microcosms changes in nematode community structure were related to sediment metal concentrations. These changes in community structure were similar to those previously observed between creeks in the Fal Estuary system indicating that an experimental microcosm approach can be useful both as a sediment bioassay and in the validation of conclusions drawn from field surveys.

Comparison Of Long-Term Trends In Benthic And Pelagic Communities Of The North-Sea

Species abundance data for benthic communities, collected during 1971–1988 off Northumberland on the north-east coast of England (western North Sea) and the Skagerrak (eastern North Sea), and pelagic data collected in corresponding areas during 1958–1988 by the Continuous Plankton Recorder (CPR) survey have been subjected tomulti-dimensional scaling ordination. Changes in community structure at the two benthic stations show a high degree of similarity, characterised by a transition in the late 70s. Similarly, there is a less marked transition between the 70s and 80s in pelagic community structure from the eastern North Sea but pelagic data from the western North Sea shows no discernible patterns. Benthic community biomass data, available only for the Skagerrak station, enabled abundance/biomass comparison curves to be constructed which demonstrated a change from un-disturbed communities in the early and mid 70s to moderately disturbed communities in the late 70s and 80s. North Sea macrofaunal abundance, and, in the Skagerrak, macrofaunal biomass appear to co-vary with phytoplankton colour and total zooplankton abundance, although there are insufficient data for statistical testing. A number of factors including eutrophication and/or pollution may be responsible for these changes in community structure.

Comparison of univariate and multivariate aspects of estuarine meiobenthic community structure

In a survey of ten sites in the Tamar estuary in January 1984, spatial variability in the species composition and structure of nematode and copepod species assemblages was greater between sites over a range of 1–3 km than between replicates at the same site. Two aspects of meiofauna community structure were studied: (1) the multivariate information: the identities of the species or nematode feeding types are retained and used integrally with data on abundances during comparison of assemblages using multivariate analyses [multidimensional scaling ordination (MDS)] and (2) the univariate information: taxonomic identity is not retained during comparisons of assemblage structure; data analyzed includes numberical abundances, species counts and diversity. Multivariate aspects of species assemblage structure were closely correlated with salinity for both copepods and nematodes. For nematode assemblages sediment disturbance may also have been important and other unidentified factors have clear secondary effects on multivariate copepod assemblage structure. Univariate aspects of nematode assemblage structure did not appear to be correlated with the salinity gradient in the Tamar, sites at the mouth and head of the estuary had a more even nematode species distribution than those in the middle reaches. Nematode univariate assemblage structure may have been more strongly influenced by sediment disturbance caused by hydrographic processes, macrofauna, food resource availability or some combination of all three. Copepod abundances and species numbers were variable but assemblages became more dominated and less diverse with increasing distance away from the mouth of the estuary. Data from 1984 were compared with data from 1982 collected at three of the sites by Warwick and Gee (1984). Persistence of assemblage structure varied from site to site and according to the attribute of community structure under consideration.

Bioturbation as a mechanism for setting and maintaining levels of diversity in subtidal macrobenthic communities

Over 2 years, experiments were conducted tocompare the effects of sediment disturbance by different bioturbating, macrofaunal organisms on the diversity and structure of the associated infaunal community. The four species investigated were the bivalves Nuculoma tenuis (Montagu, 1808) and Abra alba (Wood, 1802), the heart urchin Brissopsis lyrifera (Forbes, 1841), and the burrowing decapod Calocaris macandreae (Bell, 1846). These organisms were chosen to allow assessment of the effects of contrasting feeding activities and body sizes of the bioturbating species on the diversity of the macrobenthic communities. Bioturbation by the sub-surface deposit feeders N. tenuis and B. lyrifera promoted higher levels of α and β diversity in treatments exposed to intermediate levels of disturbance. Whilst no such ‘intermediate response’ was demonstrated for A. alba or C. macandreae, it was evident that changes in the associated fauna were influenced by the feeding type of the bioturbating organism responsible. It was also shown that different elements of the associated community responded differently to biotic disturbance. The results indicate that the variability in density and distribution of such bioturbators are important factors in structuring infaunal communities, and in setting and maintaining levels of diversity in apparently homogeneous areas.