Trophic guild concept: factors affecting within‑guild consistency for tropical estuarine fish

Abstract

The trophic guild concept has proved useful in distilling the diverse feeding inter-actions displayed by fish in temperate estuaries into a standardised subset that simplifies the application of trophic information to management. However, the high species richness displayed by tropical flora and fauna introduces the potential for feeding diversity within presumed guilds, potentially reducing the value of the standard guild concept. We evaluated within-guild consistency for a group of tropical estuarine fish species comprising a presumably coherent trophic zoobenthivore feeding guild (i.e. fish that feed primarily on zoobenthic prey) within 10 estuarine systems in tropical northeastern Australia. The zoobenthivore assemblage did not form a single coherent trophic group, rather the different components of the zoobenthivore guild responded to the broad spectrum of available prey in distinctly different ways. Some species displayed quite general diets while others fed principally on particular types of zoobenthic prey. The distinct prey specialisations often lead to different members of the presumed guild participating in different food chain pathways within the estuarine food web. As a result, substantial and important trophic differences would be masked if these disparate components were aggregated into a single trophic guild. While simplifications can be valuable, and often necessary, in data-poor situations, the complexity uncovered in this study emphasises that caution is required in applying a broad simplified scheme such as the guild concept to specific situations. Caution must be used when applying a guild approach that imports interpretation from other species and/or locations and should be explicitly recognised as an interim position until more specific data can be acquired.