Biomass accumulation across trophic levels: analysis of landings for the Mediterranean Sea

The need to implement Ecosystem-Based-Management (EBM) in marine ecosystems and the recent adoption of European Union directives, such as the Marine Strategy Framework Directive (MSFD), make indicators that are able to describe ecosystem state particularly relevant. The trophodynamic context is promising in that it can define integrative ecosystem indicators from modelling and field data. Here we analyze energy accumulation across trophic levels (TLs), i. e. the accumulation of energy in various biomass components of an ecosystem. The analysis of biomass accumulation across TLs, previously applied to surveys and model output data, was applied to a time series (1970 to 2010) of landings in the Mediterranean Sea and its 8 sub-areas. The standardized cumulative biomass versus TL curves for each year were fit to a logistic function, revealing that the accumulation pattern was detectable using landings data and confirming prior patterns. Parameters describing the curve shape, i. e. basal biomass, inflection point and steepness, were considered as possible indicators for assessing changes of ecosystem state through time. These parameters were able to detect systems modification in terms of both space and time and exhibited differential sensitivity to external drivers. The inflection point was mainly fishery-driven, whereas steepness seems to respond to environmental features, indicating an ability to discriminate across major ecosystem drivers. The application of Monte Carlo un certainty analysis showed that all of the parameters are sufficiently robust to possible sampling errors in the TL assignment to the different taxa. Collectively, these results confirm the robustness of patterns for cumulative biomass across TL curves seen in a growing number of marine eco systems. These emergent features suggest that this approach could produce useful ecosystem indicators for the implementation of EBM and the MSFD.