Thecosome pteropod (gastropoda) assemblages of the mexican caribbean sea (1991)

The composition, distribution, and abundance of the thecosome pteropods collected off the Mexican coast of the Caribbean Sea were analyzed. Samples were collected during four months (February, March, May, and August) of 1991. Highest mean thecosome pteropod density was recorded in May (329 org./103m3), while lowest mean density occurred in March (71 organisms/103m3). Seventeen species and subspecific forms were identified. Creseis acicula acicula, Limacina trochiformis, L. inflata, Clio pyramidata pyramidata and Cavolinia longirostris longirostris were the more abundant species, accounting for 84% of the overall thecosome pteropod counts. The first two species represent the influence of Caribbean surface waters in the surveyed area. The local thecosome pteropod fauna also shows some affinity with that from the southern Gulf of Mexico. Cluster analysis of the stations revealed two types of assemblages of low and high densities, with distributions that showed month-to-month variations. Circadian variations were well defined for two of the more abundant species; the other two species were nearly equally abundant in day and night samples. The thecosome pteropod community along this oceanic area seems to be represented by a homogeneous complex dominated by neritic-oceanic species with a strong influence of C. acicula acicula even in fully oceanic areas. Intermixing of these assemblages and the co-occurrence of neritic and oceanic species near the coast could be attributed to the narrow width of the continental shelf and to local circulation patterns. eng