Behavioral observation of a facultatively symbiotic goby at a shrimp burrow entrance

Abstract

Ecological studies of the facultatively symbiotic goby Acentrogobius sp. 2（sensu AKIHITO et al., 2013）are important because there is limited knowledge on the facultative relationship in goby-shrimp symbiosis in the Pacific. The present study surveyed the surface activity of Acentrogobius sp. 2 around the burrows of snapping shrimp（Alpheus brevicristatus）by quantitative observation on a tidal flat during high tides in southern Japan. Acentrogobius sp. 2 used the area in front of the burrow entrance for approximately 30% of the 10-min observation period only. Acentrogobius sp. 2 sometimes went farther than 10 cm from the burrow entrance, but most gobies returned to the burrow entrance. Surveys conducted at low tides confirmed that the goby showed surface activity in tidepools, but with a reduced time than that at high tides. The burrow-retreating bouts by the goby were triggered by approaching omnivorous and carnivorous fish and crab species. Future studies on shrimp burrow use by closely related Acentrogobius species may elucidate the evolutionary process of the facultative relationship of this genus.