Succession of invertebrates in vacant tests of Tetraclita stafactifera panamensis

The colonization of vacant Tetraclita stalactifera panamensis tests over a period of 15 months by a varied fauna of invertebrates is described. Vancant spaces are used first by the crab Pachygrapsus transversus. Within 1 month, a group of 6 species of mollusks and polychaetes and species of Balanus appear in the collections. Eventually 50 different species of invertebrates are found associated with T. stalactifera panamensis. The colonization curve typically shows a higher rate of species incorporation in the initial stages and a more or less stable plateau after a few months. New species colonizing the tests reach a maximum of 12 after 5 months and soon decrease to 3 or 4/month. Diversity (H) increases gradually for 8 months and then fluctuates around 0.77 to 1.21. Animals colonizing barnacle tests settle on external or internal surfaces or in parietal canals. Polychaetes are more diverse in parietal canals, mollusks on the internal surface and species other than mollusks or polychaetes, on the external surface. Over a period of 15 months (March 12, 1971 to June 13, 1972) as many as 62% of the T. stalactifera panamensis tests present in the study area disappeared through causes other than collection. Settlements of new T. stalactifera panamensis in the study area occurred throughout the observation period, and many of the young barnacles matured and produced cypris larvae when they reached a size about one fifth that of the old vacant tests where they had settled. After 6 months of colonization, the community of invertebrates associated with the barnacles reached a composition, diversity, biomass and spatial arrangement comparable to communities found on barnacles of adjacent areas in the midlittoral zone of Paitilla Beach (Panama). Within 1 year of the initiation of colonization some signs of aging emerge in the community, mainly through the appearance of some burrowing organisms, particularly the bivalve Lithophaga aristata, which weaken the structure of the barnacles leaving them prone to removal by wave shock.