Variations in the dietary compositions of morphologically diverse syngnathid fishes
Faculty of Computing, Health and Science
School of Natural Sciences
We examined the diets of 12 morphologically diverse syngnathid species in shallow seagrass-dominated marine waters of south-western Australia to determine whether they differed among species that varied in body form, size and snout morphology, and in particular whether species with long snouts ingested more mobile prey. Although all species consume mainly small crustaceans, the dietary compositions of these species often vary markedly. We suggest that these differences are related to factors that influence both their foraging capabilities and/or locations. Those species with long snouts (e.g. the common seadragon Phyllopteryx taeniolatus and long-snouted pipefish Vanacampus poecilolaemus) consume far more relatively mobile prey than species with short snouts. Species with short snouts (e.g. the pug-nosed pipefish Pugnaso curtirostris and Macleay’s crested pipefish Histiogamphelus cristatus) mainly consume slow moving prey. Spotted pipefish, Stigmatopora argus, and wide-bodied pipefish, Stigmatopora nigra, restrict their diets to planktonic copepods, probably because their small gape size limits their ability to feed on alternative larger prey. Both the short-snouted seahorse, Hippocampus breviceps, and West Australian seahorse, Hippocampus subelongatus, ingest mainly slow-moving prey, even though the latter species possesses a moderately long snout. This may reflect the fact that seahorses are weak swimmers that anchor themselves to vegetation or the substrate with a strongly prehensile tail and rarely venture into open water to pursue mobile prey. In contrast, the relatively large P. taeniolatus, which resides above, rather than within, the macrophyte canopy, consumes mysids, which aggregate in open water above the seabed. Those pipefishes with characters that imply relatively enhanced mobility, such as well developed caudal fins and non-prehensile tails, are trophically diverse, suggesting that they are able to feed either on the sediment or phytal surfaces or in the water column.