Conceptual Ecological Modelling of Shallow Sublittoral Mixed Sediment Habitats to Inform Indicator Selection.

Abstract

The purpose of this study is to produce a series of conceptual ecological models (CEMs) which represent shallow sublittoral mixed sediment habitats in the UK. CEMs are diagrammatic representations of the influences and processes which occur within an ecosystem. They can be used to identify critical aspects of an ecosystem which may be taken forward for further study, or serve as the basis for the selection of indicators for environmental monitoring purposes. The models produced by this project are control diagrams, representing the unimpacted state of the environment free from anthropogenic pressures. The project scope included the Marine Strategy Framework Directive (MSFD) predominant habitat type ‘shallow sublittoral mixed sediment’. This definition includes those habitats which fall into the EUNIS Level 4 classifications A5.43 Infralittoral Mixed Sediments and A5.44 Circalittoral Mixed Sediments, along with their constituent Level 5 biotopes which are relevant to UK waters. A species list of characterising fauna to be included within the scope of the models was identified using an iterative process to refine the full list of species found within the relevant Level 5 biotopes. A literature review was conducted to gather evidence regarding species traits and information to inform the models. All information gathered during the literature review was entered into a data logging pro forma spreadsheet which accompanies this report. Wherever possible, attempts were made to collect information from UK-specific peer-reviewed studies, although other sources were used where necessary. All data gathered was subject to a detailed confidence assessment. Expert judgement by the project team was utilised to provide information for aspects of the models for which references could not be sourced within the project timeframe. A model hierarchy was developed based on groups of fauna with similar species traits which aligned with previous sensitivity studies of ecological groups. A general model was produced to indicate the high level drivers, inputs, biological assemblages, ecosystem processes and outputs which occur in shallow sublittoral mixed sediment habitats. In addition to this, five detailed sub-models were produced. Each focussed on a particular functional group of fauna within the habitat: ‘temporary or permanently attached epifauna’, ‘mobile epifauna, scavengers and predators’, ‘suspension and deposit feeding fauna’, ‘temporary or permanently attached surface dwelling or shallowly buried larger bivalves’ and ‘small mobile epifauna and tube dwelling crustaceans’. Each sub-model is accompanied by an associated confidence model which presents confidence in the links between each model component. The models are split into seven levels and take spatial and temporal scale into account through their design, as well as magnitude and direction of influence. The seven levels include regional to global drivers, water column processes, local inputs/processes at the seabed, habitat and biological assemblage, output processes, local ecosystem functions, and regional to global ecosystem functions. The models indicate that whilst the high level drivers which affect each functional group are largely similar, the output processes performed by the biota and the resulting ecosystem functions vary both in number and importance between groups. Confidence within the models as a whole is generally high, reflecting the level of information gathered during the literature review. Important drivers which influence the ecosystem include factors such as wave exposure, depth, water currents, climate and propagule supply. These factors, in combination with seabed and water column processes such as primary production, seabed mobility, suspended sediments, water chemistry and temperature and recruitment define and Conceptual Ecological Modelling of Shallow Sublittoral Mixed Sediment Habitats influence the biological assemblages. In addition, the habitat sediment type plays an important factor in shaping the biology of the habitat. Output processes are variable between functional faunal groups depending on the fauna present. Important processes include secondary production, biodeposition, bioturbation, bioengineering and the supply of propagules. These influence ecosystem functions at the local scale such as nutrient and biogeochemical cycling, supply of food resources, sediment stability, habitat provision and in some cases microbial activity. The export of biodiversity and organic matter, biodiversity enhancement and biotope stability are the resulting ecosystem functions which occur at the regional to global scale. Features within the models which are most useful for monitoring habitat status and change due to natural variation have been identified using the information gathered during the literature review, through interpretation of the models and through the application of expert judgement. Features within the models which may be useful for monitoring to identify anthropogenic causes of change within the ecosystem have also been identified. Physical and biological features of the ecosystem have mostly been identified as potential indicators to monitor natural variation, whilst physical features and output processes have predominantly been identified as most likely to indicate change due to anthropogenic pressures.