A review of ecological studies on seagrass—fish communities, with particular reference to recent studies in Australia

Abstract

This paper reviews studies on various aspects of the ecology of fishes inhabiting seagrass (particularly Zostera, Posidonia, Thalassia and Halodule) habitats in different geographical areas throughout the world, with special emphasis on studies carried out during the past decade in Australia and other areas of the Indo-Pacific region. The main aspects dealt with include community structure, autecology, trophic relationships, shelter requirements and temporal changes in these various seagrass—fish assemblages. Examination of the literature revealed a number of common patterns in relation to these factors in many of the studies. Classification and ordination analyses of 30 fish assemblages occurring in a wide variety of seagrass habitats in the Mediterranean, north-western Atlantic, Gulf of Mexico, Caribbean, north-western Pacific, Indian Ocean, Southern Ocean and south-western Pacific areas, and based on proportional representation of faunal elements at the family level, were carried out in order to examine the relationships of these assemblages to each other. In general, these relationships were found to be determined primarily by zoogeographical factors rather than seagrass habitat type (though the latter, i.e., presence of dominant seagrass genera, is to a large extent itself determined by latitudinal gradients within any one geographical region). However, the cool to warm temperate Australian seagrass (mainly Posidonia and Zostera) fish fauna, although distinct from, was found to have strong affinities with that of Mediterranean Posidonia habitats as well as the faunas of other Indo-Pacific sites. The single tropical Atlantic (Panama) Thalassia site studied also showed strong affinities with the single tropical Indo-Pacific (Madagascar) Thalassia site. In general, a common suite of seagrass fish families (particularly Syngnathidae, Gobiidae, Monacanthidae, Sparidae, Labridae, Gerreidae, Scorpaenidae, Sciaenidae, Tetraodontidae and Blenniidae) was found to be dominant throughout a wide range of seagrass habitats in many geographical areas. Of these the Syngnathidae, Monacanthidae, Gobiidae, Scorpaenidae, Sparidae, Tetraodontidae, together with the Teraponidae, Apogonidae, Ambassidae and Kyphosidae, were found to be dominant in the Australian region. The significance of seagrass habitats in many parts of the world as nursery areas for the juvenile and sub-adult stages of fishes important to commercial and recreational fisheries is stressed. The utilization of such seagrass habitat as “fish nurseries” appears to be based on their provision of both adequate shelter for small fishes from predators and an abundant food source, particularly in the form of small epibenthic crustaceans which in turn depend on the seagrass detritus cycle as the basis for their food resources.