EARLY POLYCHAETE COLONIZATION AT TODOS SANTOS BAY, BAJA CALIFORNIA, MEXICO
Diaz-Castañeda, V.
CICESE. Km 107 Highway Tij.-Ensenada Apdo. Postal 2732. Ensenada, B.C. Mexico
This work examined the process of polychaete colonization in Todos Santos Bay. In situ community development was followed using 100 cm² terra cotta plates, located at 8 m depth in the southern section of the bay. 36 plates were sequentially recovered and examined; the longest immersion period was 288 days. A total of 2,111 polychaetes were collected, representing 10 families (29 species): Spionidae, Phyllodocidae, Serpulidae, Amphinomidae, Polynoidae, Nereididae, Terebellidae, Opheliidae, Capitellidae and Chaetopteridae. Numerically dominant species were: Hydroides pacificus (53.7%), Polyophthalmus pictus (14.8%), Spiophanes missionensis (7.1%), Nereis sp (2.7%) and Paraprionospio pinnata (2.6%). Preceding polychaete colonization there was a "lag period" of 30 days during which macroalgae settled (Polysiphonia, Ceramium, Enteromorpha and Callithamion); the first macrofauna colonizers in this period were amphipods (Caprellidae, Corophiidae, Gammaridae) and barnacles (Balanus amphitrite). First polychaetes to settle were Nereis sp and Hydroides pacificus. Polychaete colonization was by larval settlement as well as adult migrations (e.g. Polynoidae). The Shannon diversity index varied during the first 4 months (April to August 1997) between 0 and 1.4 bits/ind., whereas during the last 5 months it oscillated between 1.25 and 1.85 bits/ind. Number of individuals, species richness and Shannon index increased progressively: the last replicates recovered (9.5 months of immersion) attained 17-19 species, 245-267 individuals and 1.50-1.85 bits/ind. Multivariate analysis helped elucidate the structure of the polychaete community and indicated changes in faunal composition. The first 3 axes extracted 76.5% of the total inertia.