Distribution, abundance, and interspecific agonistic behavior of two mudflat stomatopods

Two species of stomatopod (Fam: Squillidae) were sampled on an intertidal mudflat at Ang Sila on the Gulf of Thailand. In 25 transects each of 23 m² we collected 219 Cloridopsis scorpio and 49 Oratosquilla inornata. In interspecific agonistic interactions, both in an open arena and with one animal defending a burrow, C. scorpio dominated O. inornata; in the burrow defense study, C. scorpio drove O. inornata out of a burrow on 8 of 11 occasions while O. inornata failed to drive C. scorpio out of burrows. In the field both species increased in numbers simultaneously on a per transect basis and both were also more numerous closer to shore indicating a degree of microhabitat overlap. Gut analyses indicated some dietary similarity. C. scorpio digs a longer and more complex burrow. Differences in abundance increased as numbers of C. scorpio increased suggesting that C. scorpio, where it is abundant, tends to exclude O. inornata; in areas where O. inornata was most numerous, individuals of this species were large and therefore presumably more successful in agonistic interactions. The evidence suggests that C. scorpio is the more abundant on the Ang Sila mudflat because it competes more successfully via agonistic behavior; sufficient resource overlap seems to exist for competition to occur thus conferring an advantage on the more aggressive species.