I thought I might do something a bit differently this week (23 Mar '98); instead of featuring a particular individual opisthobranch, this week I've decided to feature a unique association between a relatively well-known gymnodorid nudibranch (Gymnodoris nigricolor) and several species of gobiid perciform fishes (Ctenogobiops sp. and Amblyeleotris spp.). [See thumbnail / full images at the end of the page]
By way of introduction, certain species of gobies and snapping shrimps form a symbiotic relationship which is mutually beneficial for both individuals. The shrimp provide and maintain a burrow for the goby to dart into when a goby predator appears and the goby provides a tactile warning system for the poor-visioned shrimp. The goby rests at or very near the burrow entrance, waiting for the plankton it feeds upon to drift by, and as the shrimp excavates sand and rubble from the burrow it comes into close contact with the body of the shrimp, maintaining almost constant contact of the goby's body with its antennae; if the fish darts away to capture food the shrimp moves inside the burrow until the goby returns. In the event of a potential predator coming close to the burrow entrance, both the goby and shrimp rapidly disappear into the safety of the burrow.
The association of the goby and nudibranch was first reported by Williams & Williams (1986), and has been commented on by Mulliner (1991). More recently, Osumi and Yamasu (1994, 2000) report on the possible parasitic relationship of the relationship. To my knowledge, Okinawa (Ryukyu Archipelago) and nearby islands of the archipelago, are the only locations for this unusual association. I'd be very interested to learn of any other locations outside the archipelago where this association has been noted. I have collection and observational data from my initial witness (11 May, 1989) of these animals continuing to the present. It is perhaps noteworthy to mention that Baba (1993) described an association between an undescribed Gymnodoris and the chelipeds of the crab, Lybia hatagumoana.
During a typical year the association is first noted during January and seen until about the middle of June; reappearing about the middle of December. I have seen none at other times. The nudibranchs have been seen on all eight fins of the gobies: pectoral (L&R P-1), pelvic (L&R P-2), first dorsal (D-1), second dorsal (D-2), caudal, and anal. In some cases multiple nudibranchs have been seen on the same goby (in one case four, in several others, three). The attachment of the nudibranch to the fins would appear to be quite secure; it's quite remarkable to see the goby do an instantaneous turn about at the burrow entrance without dislodging the nudibranch. Depth range for the observed associations was from the intertidal to a maximum of 29m.
No goby-nudibranch associations were ever observed during the months of July, August, September, or October. The relationships have been observed during the following periods:
Click on either an image or the highlighted text to see a full sized image of the animals**.
Literature Cited:
