An Ecological Survey of the Marine Invertebrates of Bimini, Bahamas
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AN ECOLOGICAL SURVEY OF THE :MARINE INVERTEBRATES OF BIlVIINI, BAHAMAS, WITH A CONSIDERATION OF THEIR ZOOGEOGRAPHICAL RELATIONSHIPS! GILBERT L. AND NANCY A. VOSS The Marine Laboratory, University of Miami ABSTRACT The marine invertebrates of the shallow waters of Bimini, Bahamas, are listed, with descriptions of the habitats. Numbers and vertical distribution of the species occupying the intertidal zone and above are given, together with their plant and animal associates. The hydrographic conditions on the Great Bahama Bank are briefly discussed in relation to the distribution of the invertebrates. The fauna is compared with that of Soldier Key in the Florida Keys and the possible origins of the two faunas are discussed. INTRODUCTION In 1955, the authors published a paper on the invertebrate ecology of Soldier Key, the first of a proposed series on the ecology of various selected areas along the southeast Florida coast. While this study was in progress, the authors made a brief visit to the island of North Bimini in the Bahama Islands. The visit, extending from November 23 through November 28, 1953, presented the opportunity of studying in some detail an area similar to Soldier Key located on the opposite side of the Florida Straits. It was considered that such a survey might aid in solving some perplexing problems of zoogeography existing in this area. The original study has been supplemented by specimens and observations from other western Bahamian localities including the Cat Cays furnished by Marine Laboratory staff members. Among these should especially be noted Dr. C. Richard Robins who has also critically read the manuscript and Dr. Hilary B. Moore for his reading of the manuscript and his usual helpful suggestions. The study was greatly aided by the generous and wholehearted assistance of Miss Joan Feil and Mr. Edmund Clancey, then of The Marine Laboratory, who accompanied the authors and who were in the field or working up data from early morning until after midnight each day. The authors also wish to thank the authorities of the Lerner Marine lContribution No. 260 from The Marine Laboratory, University of Miami. This constitutes a technical report to the National Geographic Society. 1960J Voss & Voss: Bimini Invertebrates 97 Laboratory who placed the facilities of that institution at the disposal of the party, including collecting equipment, boats, lodging and lab- oratory space for the period of the visit. In particular they wish to thank Dr. Charles M. Breder, Jr., the director, for his kind interest in the work, his many helpful suggestions and the loan of tidal record- ings for the zonal studies. In addition, they wish to thank Mr. Bishop, at that time the resident biologist, and his wife, and their staff for their kind aid and assistance. Finally, the authors wish to thank the National Geographic Society for the financial assistance which made the study possible. All identifications are the responsibility of the authors except where otherwise stated. Most identifications were made in the field but all specimens not immediately and positively recognized were collected and taken back to the Lerner Laboratory for further study. All speci- mens were finally taken to The Marine Laboratory, University of Miami, and were deposited in the Marine Museum of that institution. HISTORICAL RESUME 1 The marine invertebrate life of the Bimini group is very poorly known and mention of invertebrates in the literature is very meager. Papers specifically dealing with the marine life of Bimini have appear- ed only since the founding of the Lerner Marine Laboratory in 1947. Apparently the first paper to deal with Bimini was that of de Lau- benfels (1949) on the sponges of the Western Bahamas. He listed 29 species and published a key to the 14 commonest ones. In 1950 Pearse studied the inhabitants of certain sponges at Bimini, listing the numbers of individuals and species, and compared them with those from similar studies carried out at the Dry Tortugas in the Florida Keys (Pearse, 1932). Again in 1951 he published a paper on the parasitic crustacea from fish and invertebrates of Bimini waters in which were recorded 26 copepods, 5 isopods and 3 cirri- pedia. In 1953 Andrew and Andrew published a paper on annelids and sipunculids and in 1956 Renaud reported upon collections of annelids collected both by her and by the authors during this study. Clarke (1955) published a description of a new species of mysid commensal upon actinians. A few observations on the mollusks were given by McGinty, 1948, and P. and L. McGinty, 1948. ---- ISince this paper was finished an important paper on the Bimini area by Norman. Imbrie, Purdy and Thurber (1959) has appeared. Much supporting evidence is found in this work and the genera] intertidal areas are enumerated, with a brief lis'! of the associated fauna and flora. 98 Bulletin of Marine Science of the Cuif and Caribbean IJO( 1) An important paper on the distribution and ecology of madre- porarian corals in Bimini waters was published in 195 ~ by Squires. While not agreeing entirely with the present findings, it is essential to an understanding of the ecology of Bimini and some of the factors at work. Under the direction of Dr. Norman D. Newell, a series of investigations are being carried out at Bimini on the bottom fauna, sedimentation and reef formation. Newell and Imbrie (1955) sum- marized some of these findings and gave diagrammatic profiles across the offshore slope of the island. Hydrographic information is scarce but Turekian (1957) reported upon salinity transects at Bimini and the formation of water masses in the area. Earlier, C. L. Smith (1940) carried out hydrographic studies on the shallow banks back of Andros and the Berry Islands, some of which are pertinent to the present area. In areas of calcium carbonate sediments, these sediments may play an important role in the ecology of the animals and plants. A paper of great importance is that by Ginsburg (1956) on the carbonate sediments of Florida Bay. This paper draws comparisons with the Bahama banks and summarizes effects and differences. The interstitial serval fauna was surveyed briefly by Renaud - Debyser (1955), De- boutteville (1955) and Chappuis and Deboutteville (1956). No papers dealing with the algae of the area have come to the attention of the authors except for that by Howe (1904). TOPOGRAPHY The Bimini Islands lie 60 miles due east of Miami on the eastern edge of the Straits of Florida. The group consists of three major islands, North, South and East Bimini, situated on the western edge of the Great Bahama Banks. These islands together form the some- what equilateral triangle which embraces a small bay in which are scattered small islands (Fig. I). With the exception of North Bimini, all are low and in the main covered with a growth of mangroves; red mangrove (Rhizophora mangle), black mangrove (Avicennia nitida), and further towards the land the white mangrove (Laguncularia racemosa) and the buttonwood (Conocarpus erect us). North Bimini. the only island that projects above the sea to any extent, is about 30 feet above mean sea level at one point on the western side. The land is formed from aeolian limestone, and along the western side of North Bimini this forms abrupt cliffs, some of fair hei1!ht, and in many places, especially at Paradise Point and the Bluffs, it forms thin sheets about 1 inch thick which often are separated and fallen away along 1960] Voss & Voss: Bimini Invertebrates 99 47' •. o• BAILEY'S LABORATORY /f t:i TOKAS CAY ALICE TOWN SOUND ENTRANCE POIN~ 43' ~~TH BIMINI 19' j~ \79017' 15' FIGURE I. Map of Bimini, Bahamas, showing localities discussed in the text. the exposed surface. On the western side of North Bimini the shoreline is composed almost entirely of the exposed limestone with areas of sandy beaches. Southward, especially at Entrance Point, the rocks dip slowly below the sea, permitting a considerable extent of wave-eroded rock to be bared at low tide, and the formation of numerous tidepools. Offshore, the bottom falls away rapidly at a distance of several hundred yards, forming the "drop-off" marking the eastern edge of the canyon of the Florida Straits. 100 Bulletin of Marine Science of the Gulf and Caribbean 110( 1) To the north, east and south the islands are surrounded by the shallow water of the Great Bahama Bank which terminates miles to the eastward at the Berry Islands. This bank is composed largely of calcium carbonate sediment and is covered by about 8 to 10 feet of water. Marine life is not plentiful on the bank and the bottom is sparsely covered by marine grasses, calcareous green algae, worm and crab mounds and sculptured by wave action. For a review of the bank and its formation see Newell and Imbrie (1955). Within the triangle formed by North, East and South Bimini is a large body of water containing scattered islands and having a mean depth of about 3 feet, but on certain tides (mean tidal range 2.4 feet) and winds much of the water may drain out of the bay leaving vast extents of turtle grass, Thalassia testudinum, exposed. The nature of the sediments, etc. of the area have recently been described by Newell and Imbrie. The outer portion of the area opening onto the bank is known as the Sound, while the inner portion surrounded by North Bimini and its adjacent islands is called the Lagoon. This again is divided into the Outer and Inner Lagoon (Figure 1). ECOLOGICAL SURVEY During the period of our visit seven areas were studied in some detail. Examination was made by wading, the use of glass bottom buckets and face plates.