The behavioral ecology of Alpheus clypeatus Coutiere (Decapoda, Alpheidae)

Abstract

The behavioral-and ecological adaptations associated with the construction and inhabitance of algal tubes by Alpheus clypeatus are examined.. Shelter procurement of this type differs from that of most other alpheid shrimps which utilize shelter, such as crevices in coral or the canals within sponges, that requires little or no modification. Field collections were carried out regularly over a 15 month period. Data from the field collections reveal that (1) A. clypeatus breeds throughout the year, (2) the greatest number of juvenile shrimps settle on the coral heads in the summer months, (3) the population consists of three size classes and each size class occupies a specific portion of the coral head, and (4) fishes capable of preying on alpheid shrimps occur in the coral heads. Observations on the positions of algal tubes of A. clypeatus within coral heads show that tubes are located in an area not occupied by other species of alpheid shrimps. The ability to utilize a portion of the habitat with reduced levels of interspecific competition is discussed. with respect to the adaptive significance of tube construction. Laboratory observations on A. clypeatus show that tube construction, a continuous process accomplished by the chelate second pereiopods, plays a significant role in pair formation and spacing of the species within the habitat. Intraspecific agonistic behavioral patterns which contain both ritualized and non-ritualized components are described. '!he influence of algae on agonistic behavior is shown for a number of different combinations of shrimps. The number of snaps produced by all combinations of shrimps, with the exception of single females, is significantly reduced for a 72 hour period by the presence of algae. Similar experiments of 25 days duration reveal that the presence of algae increases survival between members of heterosexual pairs of shrimps but not between two shrimps of the same sex or groups of three shrimps which consist of two shrimps of the same sex plus one shrimp of the opposite sex. In the latter two situations, the presence or absence of algae makes no difference, because in these longer duration experiments one of the two shrimps of the same sex ultimately is killed. The adaptive significance of algal tube construction and the associated behavioral patterns is that it permits A. clypeatus to utilize the dead coral head habitat to the greatest advantage. The algal tubes increase the exploitable surface area of the coral head, provide the basis for a territorial social system which allows a higher specific population density, and in addition, three species of algae that are present in the tubes are used as food.