An innovative statistical approach to constructing a readily comprehensible food web for a demersal fish community

Many food webs are so complex that it is difficult to distinguish the relationships between predators and their prey. We have therefore developed an approach that produces a food web which clearly demonstrates the strengths of the relationships between the predator guilds of demersal fish and their prey guilds in a coastal ecosystem. Subjecting volumetric dietary data for 35 abundant predators along the lower western Australia coast to cluster analysis and the SIMPROF routine separated the various species x length class combinations into 14 discrete predator guilds. Following nMDS ordination, the sequence of points for these predator guilds represented a 'trophic' hierarchy. This demonstrated that, with increasing body size, several species progressed upwards through this hierarchy, reflecting a marked change in diet, whereas others remained within the same guild. A novel use of cluster analysis and SIMPROF then identified each group of prey that was ingested in a common pattern across the full suite of predator guilds. This produced 12 discrete groups of taxa (prey guilds) that each typically comprised similar ecological/functional prey, which were then also aligned in a hierarchy. The hierarchical arrangements of the predator and prey guilds were plotted against each other to show the percentage contribution of each prey guild to the diet of each predator guild. The resultant shade plot demonstrates quantitatively how food resources are spread among the fish species and revealed that two prey guilds, one containing cephalopods and teleosts and the other small benthic/epibenthic crustaceans and polychaetes, were consumed by all predator guilds.

A methodology for the assessment of local-scale changes in marine environmental benefits and its application

Local-scale planning decisions are required by the existing Environmental Impact Assessment process to take account of the implications of a development on a range of environmental and social factors, and could therefore be supported by an ecosystem services approach. However, empirical assessments at a local scale within the marine environment have focused on only a single or limited set of services. This paper tests the applicability of the ecosystem services approach to environmental impact appraisal by considering how the identification and quantification of a comprehensive suite of benefits provided at a local scale might proceed in practice. A methodology for conducting an Environmental Benefits Assessment (EBA) is proposed, the underlying framework for which follows the recent literature by placing the emphasis on ecosystem benefits, as opposed to services. The EBA methodology also proposes metrics that can be quantified at local scale, and is tested using a case study of a hypothetical tidal barrage development in the Taw Torridge estuary in North Devon, UK. By suggesting some practical steps for assessing environmental benefits, this study aims to stimulate discussion and so advance the development of methods for implementing ecosystem service approaches at a local scale.