The importance of seahorses and pipefishes in the diet of marine animals

A review of 135 accounts of predation on seahorses and pipefishes identified 82 predator species, with nine species of seahorses and 25 of pipefishes recorded as prey. These cryptic fishes were generally depredated in low numbers. Where syngnathids formed a high proportion of predator diets, predation occurred on (1) a single abundant species during a population boom or large die-off, (2) concentrations of individuals utilising floating marine vegetation, or (3) juveniles when abundant during the breeding season. Predation coinciding with high syngnathid densities suggests their predators are foraging opportunistically rather than targeting syngnathids as prey. Invertebrates, fishes, sea turtles, waterbirds and marine mammals were all syngnathid predators: these included taxa that do not frequent the demersal habitat generally occupied by seahorses and pipefishes. Thus, seahorses and pipefishes may be moving in the open ocean more than suspected, perhaps using floating mats of marine vegetation. If so, this behaviour could act as a hitherto unknown vector for syngnathid movement and dispersal. Information on syngnathid abundance in predator diet (measured as percent number, volume, or mass) was available in 45 reviewed accounts; in 27% (n = 12) of these studies seahorses or pipefishes comprised ≥20% of predator diet (range 0.005–100%). Frequency of occurrence (percent stomachs, seabird bill-loads, or regurgitations in which a prey item occurred) was provided in 39 accounts, with 15% (n = 6) of these recording a frequency of ≥20% (range 0.003–65%).