M. Schratzberger

The structure and taxonomic composition of sublittoral meiofauna assemblages as an indicator of the status of marine environments

A study was conducted between 1997 and 1999 to investigate meiofauna assemblages from selected inshore and offshore locations around the UK coast. The main objective was to relate the differences in meiofauna distribution patterns to a number of measured environmental variables and to establish more clearly the sensitivity of meiofauna communities to anthropogenic disturbance. Results from univariate and multivariate data analyses show that distinct spatial differences in species distribution patterns exist and that these correlate with the natural physical characteristics and concentrations of trace metals in the sediment. Abundance and diversity of meiofauna assemblages were generally higher offshore than inshore and this difference can be attributed to both natural processes and anthropogenic impacts. The inclusion of meiofauna in applied monitoring programmes offers the potential for improving the resolution of the spatial extent of anthropogenic impacts over that achievable from macrofauna investigations alone.

Rapid bacterial colonization of low-density polyethylene microplastics in coastal sediment microcosms

BackgroundSynthetic microplastics (≤5-mm fragments) are emerging environmental contaminants that have been found to accumulate within coastal marine sediments worldwide. The ecological impacts and fate of microplastic debris are only beginning to be revealed, with previous research into these topics having primarily focused on higher organisms and/or pelagic environments. Despite recent research into plastic-associated microorganisms in seawater, the microbial colonization of microplastics in benthic habitats has not been studied. Therefore, we employed a 14-day microcosm experiment to investigate bacterial colonization of low-density polyethylene (LDPE) microplastics within three types of coastal marine sediment from Spurn Point, Humber Estuary, U.K.ResultsBacterial attachment onto LDPE within sediments was demonstrated by scanning electron microscopy and catalyzed reporter deposition fluorescence in situ hybridisation (CARD-FISH). Log-fold increases in the abundance of 16S rRNA genes from LDPE-associated bacteria occurred within 7 days with 16S rRNA gene numbers on LDPE surfaces differing significantly across sediment types, as shown by quantitative PCR. Terminal-restriction fragment length polymorphism (T-RFLP) analysis demonstrated rapid selection of LDPE-associated bacterial assemblages whose structure and composition differed significantly from those in surrounding sediments. Additionally, T-RFLP analysis revealed successional convergence of the LDPE-associated communities from the different sediments over the 14-day experiment. Sequencing of cloned 16S rRNA genes demonstrated that these communities were dominated after 14 days by the genera Arcobacter and Colwellia (totalling 84-93% of sequences). Attachment by Colwellia spp. onto LDPE within sediments was confirmed by CARD-FISH.ConclusionsThese results demonstrate that bacteria within coastal marine sediments can rapidly colonize LDPE microplastics, with evidence for the successional formation of plastisphere-specific bacterial assemblages. Although the taxonomic compositions of these assemblages are likely to differ between marine sediments and the water column, both Arcobacter and Colwellia spp. have previously been affiliated with the degradation of hydrocarbon contaminants within low-temperature marine environments. Since hydrocarbon-degrading bacteria have also been discovered on plastic fragments in seawater, our data suggest that recruitment of hydrocarbonoclastic bacteria on microplastics is likely to represent a shared feature between both benthic and pelagic marine habitats.

Interactions between microorganisms and marine microplastics: A call for research

Synthetic thermoplastics constitute the majority by percentage of anthropogenic debris entering the Earths oceans. Microplastics (=5-mm fragments) are rapidly emerging pollutants in marine ecosystems that may transport potentially toxic chemicals into macrobial food webs. This commentary evaluates our knowledge concerning the interactions between marine organisms and microplastics and identifies the lack of microbial research into microplastic contamination as a significant knowledge gap. Microorganisms (bacteria, archaea, and picoeukaryotes) in coastal sediments represent a key category of life with reference to understanding and mitigating the potential adverse effects of microplastics due to their role as drivers of the global functioning of the marine biosphere and as putative mediators of the biodegradation of plastic-associated additives, contaminants, or even the plastics themselves. As such, research into the formation, structure, and activities of microplastic-associated microbial biofilms is essential in order to underpin management decisions aimed at safeguarding the ecological integrity of our seas and oceans.

Impact of predation and sediment disturbance by Carcinus maenas (L.) on free-living nematode community structure

A microcosm experiment was conducted to investigate the effects of continuous and episodic biological disturbance by Carcinus maenas on estuarine nematode assemblages from sand and mud for a period of 57 days. Univariate methods of data evaluation failed to reveal major changes in community structure. Distributional techniques (dominance curves) were more sensitive in detecting changes in diversity patterns in the sand assemblage. Results of multivariate analyses indicated that nematode assemblages had changed characteristically due to biological disturbance. The observed changes in nematode community structure were the result of confounded effects of predation and modification of the sediment due to crab activity. Nematode assemblages from the organic-poor sand were mainly affected by crab predation, those from the organic-rich mud were mainly affected by changes to the sediment due to crab feeding activity. Effects of biological disturbance on both nematode assemblages were dependent on the frequency of disturbance events.

Effects of paint-derived tributyltin on structure of estuarine nematode assemblages in experimental microcosms

A microcosm experiment was designed to evaluate the effects of different levels of paint-derived tributyltin (TBT), and different modes of exposure, on the diversity, feeding mode and assemblage structure of estuarine nematodes. Estuarine meiofauna were exposed to two types of treatments (mixture and deposit), containing uncontaminated sediment and sediment spiked with paint-derived TBT at 1 and 10 mg kg−1 for a duration of 4 and 8 weeks. In the mixture treatments, meiofauna assemblages were incubated in clean and contaminated sediments. In the deposit treatments meiofauna assemblages were exposed to the deposition of clean and contaminated sediments simulating the disposal of TBT-contaminated dredged material at sea. Effects of TBT on nematode species are likely to occur by (a) the uptake of leached TBT from the sediment pore water through their permeable cuticle, resulting in decreased diversity and increased changes in assemblage structure with increasing levels of TBT contamination, and (b) direct ingestion of paint-particles with food, resulting in a significant decline of nonselective deposit feeders in contaminated sediments. The numbers of many species differed greatly between mixture and deposit treatments. Results from multivariate analyses showed an immediate and dominant effect of burial on most nematode species in the deposit treatments compared to the longer-term effect of TBT contamination. The survival rates of nematode species in the top layer of these sediments depended on their ability to withstand TBT contamination as well as their potential to migrate, survive and reproduce in the deposit. This study unambiguously showed that the response of nematode species depended not only on the level of TBT contamination but also on the duration and mode of exposure to contaminated sediment, which should be taken into account when assessing the effects of TBT on aquatic communities.

Response of estuarine meio- and macrofauna to in situ bioremediation of oil-contaminated sediment

Numerous studies have demonstrated the efficacy of bioremediation for enhancing oil removal but the ecological effect on shoreline biota is unclear. Therefore, a field experiment was designed at an intertidal sandflat in SW England to assess the effects of nutrient addition to oiled sediments on meio- and macrofauna for a period of up to 45 weeks. Natural assemblages were exposed to different types of experimental treatments (no oil, oil alone, oil treated with slow-release fertiliser or liquid fertiliser). Bioremediation stimulated the microbial population and increased oil biodegradation. This, however, did not result in faster recolonisation rates of fertilised versus non-fertilised oiled sediments. Mild effects of oil and bioremediation treatments on benthic fauna were observed, including short-term shifts in dominance patterns. Decreased abundance of dominant species in the oiled compared to unoiled sediments resulted in significantly higher evenness of benthic assemblages within the first 11 weeks of the experiment.

Nematode community dynamics over an annual production cycle in the central North Sea

Nematode species composition, trophic structure and body size distributions were followed over an annual production cycle in the central North Sea; to test responses to temporally changing food quality and quantity in the sediment. Changes in the phytoplankton concentration in the water column were quantitatively reflected in the concentration of chlorophyll a and breakdown products in the sediment, with higher concentrations in spring and autumn following blooms, and lower concentrations in summer and winter. The taxonomic and trophic structure of nematode communities differed significantly among stations over relatively short distances, potentially masking some of the temporal dynamics. Spatio-temporal differences in nematode species composition were linked to changes in the quality and quantity of organic material reaching the seabed, reflecting a species-specific response to the nutritional quality of sedimenting organic material and the biochemical changes in the sediment associated with its decomposition. The size distributions of selected nematode species indicated that most species bred continuously throughout the sampling period, although one species, the epigrowth feeder Spilophorella paradoxa, had periods of increased growth following the deposition of the spring phytoplankton bloom. There was no consistent temporal relationship between the trophic composition of nematode communities and spring chlorophyll a or carbon sedimentation, most likely a result of the trophic plasticity of most feeding types and the capacity of the community to use both freshly sedimented material as well as the subsequent breakdown products and refractory organic matter. Community metrics implied that there were small responses to the seasonal production cycle, but these belied strong responses of a few species with life histories that allowed them to track the availability of suitable food resources.

Sampling strategies to evaluate the status of offshore soft sediment assemblages

Reliable descriptions of the status of offshore seabed habitats usually require substantial investment in field data collection and sample analysis. While assessment of, for example, biogenic reef habitat can often include simple physical parameters (e.g. spatial extent), comparative measures for soft sediment habitats generally rely on the distribution and relative abundance of species, with a description of the associated sedimentary environment. To investigate the power of surveys to detect significant trends in assemblage structure, samples of meiofauna, macroinfauna and megafauna (i.e. representing ecological components from nematodes to demersal fish), were collected from four offshore mud and sand habitat sites in western UK shelf seas during July 2004 and 2005. Spatial arrays of samples within these sites, up to 23 km apart, were designed to optimise descriptions of assemblage structure and the patterns of spatial distribution at a local scale. Analyses of species abundance, biomass and taxonomic relatedness of the species complement at each site suggested that most assemblages represented relatively unimpacted regional conditions. The power of the sampling programme to detect a significant change in univariate community attributes was assessed. The variability in many of the community attributes indicated that intensive replicate sampling would be required to detect ecologically important changes. Improving the power of such benthic surveys to detect trends would therefore require substantial additional time and effort to be invested in sample collection and analysis. Resource analysis showed that the time from gear deployment to complete sample identification was gear-dependent, lowest per sample for meiofauna (10h) and megafauna (6-12h), and highest for macroinfauna (12-22 h). These results have implications for the development of meaningful indicators of habitat status for offshore soft sediment habitats, and the resources required for effective monitoring of change.

Practical implementation of ecosystem monitoring for the ecosystem approach to management

Summary The implementation of the ecosystem approach means there is a need to monitor an increased range of environmental conditions and ecological components in the marine environment. Many existing monitoring surveys have successfully added tasks or components to an existing monitoring programme while maintaining consistency of time series. This approach is not practical when the immediate data need for a wide range of ecosystem components requires substantial changes to the programme or when collections of different ecological components have conflicting requirements. We propose a more integrated approach aimed at not only assessing change, but simultaneously delivering evidence of the underlying reasons for observed changes. Using principles developed from observational and modelling efforts in the Barents Sea and the wider literature, we distil the essential characteristics an integrated monitoring programme must exhibit. We demonstrate how such an integrated programme can offer substantial operational efficiencies compared to a coordinated approach. Integrated monitoring based on ecosystem processes has significant advantages over the coordinated approach that uses ecosystem states independently and focuses on maximizing precision of each indicator. While integration is needed to address current policy requirements, changes to monitoring risk time-series consistency. However, we explain how such risks can be minimized while at the same time establishing a framework that allows the incorporation of important information from other less flexible data sources to be used in the assessment. Policy implications. Process-based integrated monitoring is essential for the ecosystem approach. The focus on ecosystem processes provides the essential elements for future proof efficient management: (i) It provides both unbiased status estimates for reporting requirements and describes the causes of state change. (ii) It minimizes risks to historic time series while coping with changing ecological conditions. (iii) It quantifies ecosystem processes and provides the means to test hypotheses on how different processes interact. (iv) It uses all available information efficiently when used in conjunction with integrated assessments. (v) It is effective due to its adaptability to meet future policy demands and ecosystem requirements while using data in the most efficient manner given these demands.

On the relevance of meiobenthic research for policy-makers

The need for scientific advice to manage the aquatic environment in an ecosystem context has never been greater. Many assessments of ecosystem state and change use inadequate data on non-conspicuous, non-target organisms. These include meiofauna, a diverse group of small-sized organisms (<1 mm) that live in a range of terrestrial and aquatic environments. Meiobenthic research published between 2007 and 2011 has failed to underpin ecosystem management and conservation practices. This is partly because of the belief amongst decision-makers and the public that microscopic organisms beyond our normal range of perception are ecologically unimportant. Methodological limitations related to the taxonomic identification of small-sized organisms and the narrow scope of many contemporary meiofauna studies are also to blame. This article explores ways in which meiobenthologists can improve the impact and uptake of their research.