Do studies of functional groups give more insight to amphipod biodiversity?

Abstract

Amphipod crustaceans are able to colonise different micro-habitats of coastal marine benthos due to a multiplicity of trophic and morpho-functional adaptations, and may be considered a key taxon in describing the structure of assemblages. Literature concerning amphipod feeding behaviour and way of life showed that studies on functional groups (FGs) started only in the 1980s. A short review about the state of the art of the knowledge is presented here. Aiming at investigating the functional role of amphipods and to ascertain to what extent their adaptations could be a response to different biotic and abiotic conditions, some examples of studies conducted in the Mediterranean Sea on various plant substrata (Posidonia oceanica, Cymodocea nodosa, Zostera marina, Caulerpa racemosa var. cylindracea), at different spatial and temporal scales, were given. Despite many doubts about some species, due to the lack of information and their opportunistic behaviour, the identified taxa were grouped in the main categories of suspension feeders, deposit feeders, carnivores, commensals, herbivores, plant detritus feeders, omnivores, and in the mixed categories of deposit-suspension feeders, deposit feeders-carnivores, herbivores-deposit feeders, according to the food ingested and their feeding strategies; and, according to their life-habits, in epifaunal free-living and domicolous, and infaunal free-burrowing and tube-building. FGs might be considered good descriptors of zonation patterns, mainly against gradients such as depth, where strong environmental factors play a role. FG composition was differentiated according to the structural complexity and the stability of the host plant. Changes observed on a long-term scale, due to regression phenomena in P. oceanica meadows or to the spread of the invasive species C. racemosa var. cylindracea, were well described by FGs. In the first case the trophic diversity was maintained and in the latter the lack of herbivorous forms pointed out the poor role as structuring plant of the seaweed. Although caution is suggested in studies on FGs, they can give further insight in comprehending structural and functional processes in amphipod ecology.