Postsettlement movement patterns and homing in a coral-associated fish

Coral-associated gobies are highly specialized reef fishes with high host-coral fidelity. Flexibility in habitat choice, however, is important to compensate for potential habitat alteration or loss, but detailed information about the postsettlement movement behavior of such gobies is lacking. We examined movement patterns in Gobiodon histrio, both under natural conditions and during subsequent field experiments, involving breeding pair or partner removal from 3 of the 4 investigation plots. Additionally, we investigated homing behavior, and 2 aquaria experiments were designed to assess home coral and partner recognition of adult fish taken from breeding pairs. Under natural conditions, the movement rate was high for single adults, whereas breeding pairs showed high home-coral fidelity. Manipulations revealed little change of natural patterns except in single adults, which slightly decreased their movement rate in the breeding pair removal plot. In the homing experiment, 17% of tested fish returned to their home coral even after displacement of 4 m, and homing success was much higher at shorter distances (100% at 0.5 m, 53% at 2.25 m). In the aquarium, G. histrio exhibited higher recognition of its home-coral colony (75%) than of its breeding pair partner (60%). Our study shows that G. histrio frequently moves between corals, although this depends on the social status (juvenile, single adult, breeding pair) of the individuals. The high proportion and movement rate of single adults indicate low sensitivity to habitat alteration but also limited high-quality habitats in which breeding pairs could be established. Hence, vulnerability to habitat loss increases when individuals breed.