Variations in the dietary compositions of morphologically diverse syngnathid fishes

Abstract

SynopsisWe 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.

Native pipefish Entelurus aequoreus are promoted by the introduced seaweed Sargassum muticum in the northern Wadden Sea, North Sea

“…The importance of harpacticoid copepods as a food source for pipefish is also described for other species of syngnathids (Tripton & Bell 1988). However, prey composition varies among syngnatid species due to morphological differences such as snout length and species mobility (Kendrick & Hyndes 2005). Since data on the diet of Entelurus aequoreus are limited to fish taken from the S. muticum bed, results are biased and are not suggested to cover the entire spectrum of potential prey.…”

Habitat Preference and Population Structure of Two Data Deficient Seahorse (Syngnathidae) Species

“…They inhabit a variety of habitats such as coral reefs, seagrass meadows, mangroves, estuaries and open bottom habitats, although their distribution can be patchy and sparse (Perante, 2002;Foster & Vincen, 2004;Rosa et al, 2007). Seahorses are weak swimmers and tend to anchor themselves to vegetation or the substrate using a strong prehensile tail (Kendrick & Hyndes, 2005), and rely on prey coming within close range instead of actively pursuing them Lourie et al, 2004;Felício et al, 2006). As a result, they are highly localized with small home ranges, and life history characteristics such as low fecundity, lengthy parental care, and mate fidelity make them particularly vulnerable to overexploitation .…”

An adaptive explanation for the horse-like shape of seahorses

“…S eahorses are carnivorous fish that hide in strategic places along the edges of reefs or seagrass beds waiting for prey to come within striking reach 1 . Seahorses capture highly evasive prey such as small shrimp or larval fishes 1,2 .…”

“…Seahorses capture highly evasive prey such as small shrimp or larval fishes 1,2 . To do so, they make use of a two-phase prey-capture mechanism that is commonly referred to as pivot feeding 3,4 : a rapid upward rotation of the head is followed by suction to draw the prey into the seahorse's snout.…”