Influence of puffer predation on vertical distribution of mangrove littorinids in the Gulf of Nicoya, Costa Rica

The eastern Pacific puffer fish Sphoeroides rosenblatti (family Tetraodontidae) preys on the mangrove periwinkles Littoraria fasciata and L. varia up to 13 cm above the water surface. Puffers capture snails by jumping partially out of the water and removing them by mouth from Rhizophora spp. prop roots. Field predation trials suggested puffer predation is intense, averaging 40.6% h(-1) on L. fasciata tethered at the water surface. L. fasciata < similar to 8 mm in shell length and L. varia <similar to 12 mm remained near or below the water surface and were easily crushed by puffers; gut content analyses showed that these snails were commonly eaten by puffers. L. fasciata > similar to 8 mm and L. varia similar to 12-16 mm were also crushed by puffers, but were generally located above their reach; these snails were much less abundant in puffer guts. L. varia >similar to 16 mm were abundant and some were submerged at high tide, however, none were found in puffer guts presumably because puffers encounter difficulty crushing these snails. S. rosenblatti is an important predator of L. fasciata and L. varia and appears to affect their vertical distributions.