Relatively little is known about the wild diet preferences of seahorses, except that they are ambush predators. In this study, we investigated diet preferences of lined seahorses (Hippocampus erectus) from a unique, low predator diversity tidal pond system, by comparing their diets to available planktonic dietary components. Replicate 2-minute surface and benthic plankton tows were collected with a 150 µm 0.5 m net at each end of the 1600 m long lake just after dawn and before dusk across October 2015, February, and June 2016. In addition, 12-hour light traps collected benthic organisms at each sampling time point. A non-lethal gastric lavage technique was performed to assess seahorse diet breadth, anesthetizing animals and flushing food items through their continuous gut with fresh water. Animal size, reproductive condition, and gender were assessed at each sampling event.
Results/Conclusions
Overall, the plankton community of the pond was dominated by calanoid copepods, with calanoids, harpacticoids, and cyclopoids observed in all tows, and amphipods, annelids, metazoans, echinoderms and shrimp observed intermittently. Light traps were characterized by copepods and shrimp, with a significantly higher species diversity compared to plankton tows across the year. Seahorses across size and gender consumed predominantly copepods, with few differences observed except that larger animals preferred larger foods. However, ichthyofauna, echinoderms, and diatoms also played a substantial role in seahorse diets. Seahorse numbers globally are on the decline due to overfishing and habitat degradation, and thus, Sweetings Pond animals represent a unique opportunity to study a healthy, intact population to gain a deeper insight into seahorse food requirements on a larger scale.