Abundance of oceanic sea skaters, Halobates in the tropical Indian Ocean with respect to surface chlorophyll and oxygen concentrations

This study aims to clarify the relationship between environmental factors and the abundance of oceanic sea skaters, Halobates mostly H. micans. Samplings were performed in the tropical Indian Ocean at 15 stations along a straight line from 04°09′S, 094°26′E to 16°39′S, 065°15′E in October-November, 2010 with a Neuston net with CTD casting. A significant positive correlation was seen between chlorophyll concentration and number of Halobates individuals (mostly H. micans) collected, while a significant negative correlation was seen between oxygen concentration and number of individuals. More food such as zooplankton available to sea skaters in high-chlorophyll and low-oxygen areas may lead to higher population densities. Neuston net samplings were also taken around a fixed station, 8°S, 80°30′E in September-October 2011. The larval density of H. micans tended to be higher in spots where the air temperature was between 27.5 °C and 28.0 °C than in spots where it was between 25 °C and 27 °C. Reproductive and growth activities of H. micans may be affected by even a relatively small variation in air temperature in the spots they inhabit even at the fixed point 8°S, 80°30E in the Indian Ocean.