The Arrow Goby is a significant component of the diet of non-breeding Long-billed Curlews (Numenius americanus) around Humboldt Bay, California, U.S.A. (Leeman et al. 2001).
The Arrow Goby is often found inhabiting the burrows of several invertebrate species, including the ghost shrimp Neotrypaea californiensis (=Callianassa californiensis), the mud shrimp Upogebia pugettensis, and the fat innkeeper worm Urechis caupo (an echiuran worm). The goby uses the burrows as a refuge from predators and desiccation (drying out) at low tides. In a study in Coos Bay, Oregon, during the late spring and the summer Arrow Gobies were found in the field in shallow pools with less than 3 cm of water, as well as in occupied and unoccupied N. californiensis burrows. The gobies were found lower intertidally in the spring, were found higher intertidally in the summer, and were not found intertidally in the fall and winter. The presence of N. californiensis may inhibit the presence of Arrow Gobies in the burrow, since the ghost shrimp were often observed chasing the gobies out of the burrows. Field observations indicate that the Arrow Gobiess may be using the N. californiensis burrows as a refuge, but only during the spring and summer. There is some controversy in the literature over where Arrow Goby eggs are laid. Some authors have stated that the nonadhesive eggs are laid in large groups, presumably outside the burrows, with the eggs then sinking into the sediments. However, at least one author has suggested that this goby lays its eggs inside burrows, athough not necessarily in the burrows of N. californiensis. If the eggs survive in areas other than N. californiensis burrows, and the adult Arrow Gobies do not always coinhabit burrows with N. californiensis, then the two species may be facultative associates, as seems likely. However, if the eggs survive only in N. californiensis burrows, then this might be an obligate association. Neotrypaea californiensis clearly provides shelter for the Arrow Goby, but no data are available on whether N. californiensis benefits at all from its association with the goby in this relationship (it likely does not, given that the ghost shrimp often behave aggressively toward the gobies). However, there is also no evidence that the ghost shrimp suffers any harm as a result of its association with the Arrow Goby. Thus, this relationship is likely a commensal one (i.e., one partner--in this case, the goby--benefits and the other partner experiences no significant benefit or harm). (Hoffman 1981)