Bathyal gastropods of Bimini Chain, Bahamas Author(s): Anton E. Oleinik, Edward J. Petuch, and William C. Aley IV Source: Proceedings of the Biological Society of Washington, 125(1):19-53. 2012. Published By: Biological Society of Washington DOI: http://dx.doi.org/10.2988/11-26.1 URL: http://www.bioone.org/doi/full/10.2988/11-26.1 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/ terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 125(1):19–53. 2012. Bathyal gastropods of Bimini Chain, Bahamas Anton E. Oleinik*, Edward J. Petuch, and William C. Aley, IV (AEO, EJP) Department of Geosciences, Florida Atlantic University, 777 Glades Road, Boca Raton, Florida 33631, U.S.A., e-mail: [email protected]; [email protected]; (WCA) 835 8th Avenue North, Jacksonville Beach, FL 32250 Abstract.—This paper summarizes the taxonomic findings of the three cruises on board of Florida Institute of Oceanography research vessels Bellows and Suncoaster conducted between 2000 and 2005 as well as to discuss the unique regional oceanographic settings that were found to be essential in supporting the diverse and unique bathyal molluscan fauna encountered in the depths of the eastern Straits of Florida. Approximately 30 stations were sampled, from South Cat Cay (25u42.0859N) through Victory Cay (25u28.3559N), at depths ranging from 120–600 meters and averaging 400 m depth. A total of 74 molluscan taxa belonging to 34 families were identified from over 400 individual mollusk specimens. The gastropods Architectonica sunderlandi Petuch 1987, Bursa finlayi McGinty 1962, and Exilia meekiana (Dall, 1889a) were collected from the eastern side of the Straits of Florida for the first time. The Ranellid Pisanianura grimaldii (Dautzenberg, 1889) is reported from the western Atlantic Ocean for the first time. Two new taxa are described, including a new species of eratoid, Hespererato pallida, new species, and a new species of volute, Scaphella (Scaphella) biminiensis, new species. Additionally, a number of rare or otherwise poorly known molluscan taxa are illustrated, described, and discussed in context of the oceanographic settings from which they were collected. The presence of a diverse and unique deep-water molluscan community is attributed to the distinctive current structure and temperature asymmetry that has been observed between the western and eastern slopes of the Straits of Florida. Keywords: Bahamas, bathyal zone, Bimini Chain, Gastropoda, mollusks The molluscan communities of the the Blake expeditions (Dall 1881, 1889a, Straits of Florida have been extensively, 1927). The Blake expeditions extensively but sporadically, sampled since as early as surveyed the Gulf of Mexico and the the 1870s when Louis Franc¸ois Pourtale`s Caribbean Sea, including the Straits of and Alexander Agassiz first reported on Florida. The next intensive Caribbean the deep-sea dredging work done by the molluscan faunal survey was carried out United States Coast Survey’s Steamer by the University of Miami (UM) between Bibb (Agassiz 1888). The pioneering work 1962 and 1972 aboard R/V John Elliott of Pourtale`s and Agassiz was continued Pillsbury and R/V Gerda and was reported into the twentieth century by William H. on by Dr. Fredrick M. Bayer. Bayer Dall, who reported on the collections (1971) was the first of only three brief amassed between 1877 and 1880 during studies, to date, to have been focused particularly on the deep-water gastropods * Corresponding author. of the western Bahamas. More recently, 20 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON two works by Petuch (1987, 2002) de- 4.0 fms/nm (57.3 m/nm), and the bottom scribed a number of new deep-water taxa topography becomes more irregular from the western Bahamas and clearly (Hurley et al. 1962) as it plunges into its indicated the richness and endemism of maximum depths to the south and the the regional malacofauna. west (Fig. 2). The Straits of Florida is the The strikingly steep and sometimes even longest of the several submarine channels concave banks of the eastern (Bahamas) or valleys of the Bahamas region. The side of the Straits of Florida have been trough of the Straits of Florida separates noted for at least half of a century, since Florida from the Bahamas and Cuba and the earliest geologic reconnaissance sur- is of particular interest for several rea- veys of the Straits of Florida and the sons, including the presence of the Flor- Great Bahama Bank (Newell & Rigby ida Current. The Florida Current trans- 1957, Siegler 1959, Hurley et al. 1962) but ports immense amounts of water (36 3 have only recently begun to be systemat- 106 m3 s21) (Richardson & Schmitz 1965) ically investigated by detailed depth through the Straits at velocities as high as soundings and biological surveys. A great 4.0 knots or more (Hurley et al. 1962) deal of the research done has been focused combining with the Antilles Current from on the Miami and Pourtale`s Terraces on the east to form the Gulf Stream. the western (Florida) side of the Straits of The area of the Straits of Florida Florida (Hurley et al. 1962, Kofoed & between Miami, Florida, and Bimini, Malloy 1965, Rona & Clay 1966, Uchupi Bahamas is the narrowest portion of the 1966, 1969; Malloy & Hurley 1970, Straits being only approximately 45 nau- Ballard & Uchupi 1971) and more recent- tical miles wide (Malloy & Hurley 1970) ly, detailed research has been conducted (Fig. 2). Here, powerful ocean currents on the deep-water coral reefs which are are funneled between Miami, Florida, located throughout the Straits (Reed 1980, and Bimini, Bahamas, providing a large 2002a, 2002b, 2004; Reed & Mikkelsen amount of warm productive water flow 1987, Messing et al. 1990, Land & Paull through the area. It is also here where the 2000, Brooke & Young 2003, Grasmueck Florida and Antilles Currents merge and et al. 2006, 2007). become deflected toward the north by the The Straits of Florida is an articulate constriction of the Straits of Florida trough 700 km long and 90–145 km wide between the western margin of the Great that is located to the east and south of the Bahama Bank and the eastern margin of Florida Plateau (Fig. 1). Depths along the Florida’s continental shelf. As a result of axis of the Straits of Florida range from this constriction, northern deflection, and 2200 m, south of Dry Tortugas, to 740 m merging of currents, warm, surface de- west of Little Bahama Bank (Uchupi rived waters also are forced downward 1966). The floor of the northern Straits along the slopes of the western Bahama of Florida is a smoothly graded valley, Bank but not along the eastern slopes of with a general slope of 0.6 fathoms/ Florida’s continental shelf. This flow nautical mile (51.1 m/nm), which runs bathes the Bimini shelf ecosystems in as far south as about 25u309N where the warm, surface derived waters (16.5uCat valley empties into an elevated ‘abyssal’ 400 m), while at comparable depths plain at the not quite abyssal depth of across the Straits of Florida the shelf 845 meters, west of Cat Cay, Bahamas. faunas are exposed to cooler (7.5uCat This deeper plain remains nearly flat for 400 m) bottom derived waters (Sverdrup about 60 miles to the south until it nears et al. 1942). Unique and diverse benthic Cay Sal Bank. Here the valley begins to invertebrate assemblages, including mol- narrow, the grade increases to about lusks, in this area suggest that these VOLUME 125, NUMBER 1 21 Fig. 1. Location of the study area within the Straits of Florida. currents carry a plentiful supply of north of the Great Bahama Bank, are nutrients and plankton that allow these steep, at times concave and typically have deep-water communities to flourish. piles of various sized talus at their base. The eastern and the western slopes of Recent studies showing that the compli- the Straits of Florida are very different cated bathymetry, which has been report- biologically and geologically. The western ed to exist extensively beyond the base of slope has a conspicuous step-like appear- the eastern slopes of the Straits of Florida, ance, resulting from a prominent ridge at is often attributed to the wide spread around 366 meters, and a number of presence of deep-water ahermatypic coral terrace, ledge, and scarp features (the mounds such as those initially reported by Miami Terrace) that are not found on Neumann et al. (1977), and most recently the Bahamian side. All the slopes of the systematically investigated by Grasmueck eastern or Bahamian side of the Straits, et al. (2006, 2007). While the distinctive including Cay Sal Bank but with the slope morphology of the eastern Straits of exception of the broad nose extending Florida has been recognized for at least 22 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig. 2. Bathymetric map of the northern Straits of Florida. Modified after Malloy & Hurley (1970). half of a century, contemporary mapping shallower upslope areas.