THE EFFECT OF THE INTRODUCED REEF-BUILDING POLYCHAETE FICOPOMATUS ENIGMATICUS ON THE BENTHIC SPECIES OF A SW ATLANTIC COASTAL LAGOON
Schwindt, E. & Iribarne, O.
Departamento de Biología, FCEyN, Universidad Nacional de Mar del Plata,
CC573 Correo Central (7600) Mar del Plata. Argentina.
Ficopomatus enigmaticus is a cosmopolitan reef-building polychaete (up to 4 m diameter, 0.5 m high) that was introduced to the SW Atlantic Mar Chiquita coastal lagoon (Argentina, 37º 32' to 37º 45' S, and 57º 19' to 57º 26' W; a MAB site) in the early seventies. Today a large portion (80%) of the lagoon is covered by reefs, possibly affecting its dynamics and ecology. In this work we investigate larval substrate selection, the effect of reefs on distribution and abundance of benthic organisms and the formation of new reefs. Samples and field experiments showed that settlement was preferentially on shells of the gastropod Adelomelon brasiliana and secondarily Mactra isabelleana, Tagelus plebeius and PVC pipe. The presence of reefs did not affect the recruitment of conspecifics; however, given that the distribution of reefs is homogeneous we believe that some interaction may occur. Indeed the diameter of reefs that were in fusion was not statistically different suggesting that they settle at similar time. The most dense inhabitant between the reef tubes were the amphipod Melita palmata (x= 0.137 ind cm-3, SD= 0.123, n= 9) and the gastropod Littoridina parchappi (x= 0.083 ind cm-3, SD= 0.055, n= 9). Five polychaetes species were also found: Polydora ligni, Laeonereis acuta, Heteromastus similis, Nephtys fluviatilis and Neanthes succinea, together with alga, bryozoans, ostracods, nematodes and copepods. The most common polychaete species that inhabit the lagoon benthos H. similis, L. acuta and N. fluviatilis showed statistically significant variation in density as the result of distance (0.1 m, 2 m and 6 m) to the reefs. H. similis and L. acuta decrease in density with distance while N. fluviatilis increases. Meiofauna (organisms <0.5 mm) showed no significant reef effect in density. The abundance of adult crabs underneath the reefs was higher (x= 92 ind m-2, SD= 47, n= 23) than outside (0.21 ind m-2, SD= 0.41, n= 64) and increased as a function of reef size. Our evidence suggests that reefs of F. enigmaticus increase the available habitat for benthic organisms by providing shelter, an important environmental alteration.