MOLUSCOS DE LA REGION DE LA CIENAGA GRANDE DE SANTA MARTA (COSTA DEL CARIBE DE COLOMBIA)

Abstract

This paper deals with the moDusk species known from the Ciénaga Grande de Santa Marta and from the littoral zone and the upper continental shelf of the coastal strip between lala de Salamanca and the balneario El Rodadero (Caribbean coast of Colombia, South America). 468 species and subspecies ofmarine, brackish-water and freshwater mollusks are reponed comprising 211 bivalves. 6 scaphopods and 251 gastropods. 101 species and 1 subspecies have been found in the Ciénaga Grande (most of them also in the sea), a further 9 marine species have been recorded only as old shells in the estuarine part of the Ciénaga Grande, the rest have been collected exclusively in the marine part of the investigated area. 268 species (120 bivalves, 3 scaphopods and 145 gastropods) have been live-collected, the remainder only as empty shells. 165 species and 9 subspecies (90 + 1 bivalves and 75 + 2 gastropods) are monographed and discussed in detail, among them 98 species and 1 subspecies (48 bivalves and 50 + 1 gastropods) from the Ciénaga Grande or its estuarine región, and 67 species and 2 subspecies only from the sea. Of the 98 species from the Ciénaga Grande, 64 have been live-collected, tlte oth*er 34 as empty shells only. The Ciénaga Grande de Santa Marta is the largest coastal lagoon of the Caribbean coast of Colombia, occupying an area of 450 km'. According to the season, drastic changes in salinity of between 0 and S0*/oo may be observed. Depth varies between 1 and 2.5 m, and the shore mostly consists of mangrove swamps. The bottom is muddy, some more or less extended areas having oyster reefs or shell concentrates. There are small areas in the northern part with sandy bottoms. Most mollusk species enter the lagoon and spread out within it as planktonic larvae by means of the currents, if conditions are favourable. Only very rarely are adult snails able to enter {he Ciénaga Grande actively. The propagation of the planktonic larvae within the lagoon depends on the nearest natural occurrence of the species, the duration of the pelagic phase, settlement depends on the presence of suitable substrate (besides the other ecological conditions needed). On account of finding older empty shells in a relative uniform state of preservation throughout the whole basin of the Ciénaga Grande, and of species not having been encountered there live, it can be assumed that there had previously existed an extremely long period of high salinity in the lagoon, with lower amplitudes than nowadays. According to C dates this period can be located ¿00-360 years ago, and its duration is estimated at at lea»t 3.5 years. The reason for this was most probably the greater interchange of sea and lagoonal water through several no longer existing, but still traceable, inlets. The zoogeographic division of those species treated in detail (except the freshwater species) is as follows: western Atlantic species. 68; Caribbean species. 48: southern Caibbean species, partly also from Brasil, 39. Í2 species are amphi-atlantic and 5 amphi-american. Six species known from Suriname, Venezuela or Brasil are recorded for the first time from Colombia and the southwestern Caribbean. 69 species have a win species (cognate species) existing in the Eastern Pacific (Panamic zoogeographic province). The portion of species with Pacific twin species found in the studied area is very high in comparison with other regions of the Caribbean, especially among the bivalves. This is due most probably to the similarity of the biotopes on large parts of the Colombian Caribbean coast and the tropical Eastern Pacific coast, preferred by these species.