Year-round high abundances of the world’s smallest marine vertebrate (Schindleria) in the Red Sea and worldwide associations with lunar phases

Abstract

Very little is known about the ecology and biology of the smallest marine vertebrates, fishes in the genus Schindleria. Even though over half of named Schindleria species have been described from the Red Sea, very few specimens have been identified. Here, we assessed abundance patterns of nearly two thousand Red Sea adults and found evidence for putative seasonal and spatial differences, likely related to differing habitat and environmental conditions. Within the Red Sea, the highest abundances were neither found during seasonal temperature extremes nor during peaks of coral reef fish recruitment. We also found evidence for global trends in abundances related to lunar cycles, for which data from a recently published large collection of specimens from the DANA Expedition (1928-1930) were included. The abundance of Schindleria in relation to lunar phases differed significantly, with most Schindleria being caught outside the full moon. Adult specimens in our Red Sea collections were most abundant during the new moon, while the 3rd quarter moon yielded the highest abundances in the DANA collection. We further suggest that the abundances of Schindleria at coral reefs may be related to reproductive cycles and that these cycles may be timed with the moon, since back-calculations of hatch dates from otoliths resulted significantly around the new moon. Schindleria may be the most numerous coral reef fish in the world, for which we encourage increased research.