Publication Abstract

Efficiency of trophic interactions as an indicator of food web structure

G.M. Daskalov

The effects of predation and fishing on structure, functioning and trophic control in exploited marine ecosystems are analysed. The efficiency of trophic interactions (also called consumption or ecotrophic efficiency), defined as a ratio of predator's consumption to prey's production, is proposed as an indicator of food web structure. The fisheries catch is, by analogy, considered as a removal by a predator, that allows comparison between effects of fishing and those of marine predators. The efficiency indicators can be regarded as an extension of the consumption or mortality matrices. They enable to detect both energetically and functionally important interactions in the food web. The trophic interaction efficiency is related to various important ecosystem characteristics like coupling between trophic groups, top-down and bottom-up control and trophic cascades, interaction strength and key-stone species, r- and K-selection, and energy transfer across trophic levels. Biomass or catch ratios can be used as simple surrogates of the trophic efficiency. The system trophic efficiency is an indicator of ecosystem health, related to important ecosystem services like fisheries, water quality control, and energy conservation. A simple aggregated model of the Black Sea ecosystem is used to illustrate the application of the efficiency indicators. In this system, major changes in structure, biomass and fisheries took place between the 1960s and 1980s and some of the changes were hypothesised to be due to overfishing of marine predators and subsequent trophic cascade down to phytoplankton and nutrients. The mechanism and effects of the changes are interpreted using trophic interaction efficiencies and other trophic indicators.

Reference:

G.M. Daskalov. Efficiency of trophic interactions as an indicator of food web structure. ICES ASR Vigo, Spain, 2004. CM 2004/FF 41