File:American malacological bulletin (1987) (17534010584).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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260 AMER. MALAC. BULL. 5(2) (1987) tropical Caribbean province. MATERIALS AND METHODS Quantitative samples were collected from mangrove cays and the barrier reef near Carrie Bow Cay, Belize, C.A. and from several locations in Florida (Figs. 1, 2). Quantitative sampling generally involved a period of qualitative presamp- ling of potential habitats and algal foods (concentrating on Siphonales, Siphonocladales, and Cladophorales), using snorkel or SCUBA. In this phase we attempted to identify "op- timal" habitats as evidenced by high-density populations and the presence of mature animals. During this phase, poten- tial algal foods were detached from the substrata and vigorously shaken underwater. The approximate numbers and species of slugs detached were noted. Evidence of feeding (evacuated algal cells and thai I i) and presence of ascoglossan egg masses were typically used to locate poten- tial study populations, but we attempted to analyze all macrophytic algae belonging to the above groups in each of the habitats. To ensure comprehensive surveys of community composition, we spent a minimum of 30 hr presampling in each study area, with total field observation time in Belize of about 300 hr and about 150 hr in Bermuda, each made during two visits. Florida observations represent cumulative studies since 1968 at various sites, with most sites studied on a monthly basis for several years. Communities were compared on the basis of co- occurrence of species using Czekanowski's similarity coef- ficient (Clifford and Stephenson, 1975). Populations from the selected microhabitats were quantified by collecting all slugs detached by the above method, using individual suction collectors (Clark, 1971) for each sample. In the case of growths of filamentous algae (e.g. Cladophora) we detached masses of algae containing slugs and separated slugs and eggs in the laboratory. Water temperature was measured with a stem thermometer in situ. After each handful of algae was processed, it was stored in a mesh collecting bag. On return to the laboratory, each algal Mexico J \;Atlantic /' M Ocean Belize) \'j (. Florida '^T jatemala Caribbean Sea Honduras A Fig. 1. Locations of principal collection sites in this study. A. Beli- zean barrier reef system. B. Eastern Florida, from north to south: north Indian River; Sebastian Inlet; Fort Pierce Inlet; Key Largo; Long Key.
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Fig. 2. Vicinity of Carrie Bow Cay, Belize and Twin Cays (from Rutzler and Macintyre, 1982). sample was again examined for slugs possibly missed dur- ing the underwater sampling. Slugs were sorted by species, egg masses were removed if present, and slugs and eggs were counted, placed in pre-weighed foil cups, and dried. Algal samples were placed in aluminum foil pans and dried. Belizean samples were partially dried in air or a warm gas oven to prevent decomposition. All samples were dried at 80°C to constant weight before final weighing, following re- turn to our laboratory. Portions of "anchored" siphonales (Penicillus, Caulerpa spp., Udotea) that are not used as food by ascoglossans were removed to equalize comparisons with other algae (e.g. Cladophorales) in which the entire thallus is utilized as food (Fig. 3). In general, portions with excep- tionally tough cell walls (Caulerpa paspaloides (Bory) Greville basal stolon and lower stalk) or heavily calcified (white/yellow) portions were removed. In the less differentiated Caulerpa species (C. racemosa (Forsskal) J. Agardh, C. verticillata J. Agardh) the entire thallus' contents appear usable as food, and we used the entire plant in weight determinations. In many locations, slugs can be qualitatively collected but den- sities are below levels at which algae can be reasonably pro- cessed with our present technique (less than one animal per 100 g algal dry weight). To facilitate comparison of quantitative data based on algal displacement volume or net weight, we have converted other investigators' data to approximate equivalent dry weights using Floridan congeneric algae, rinsed briefly in fresh water and oven dried at 80°C to constant weight. Data for Limapontia capitata (Mueller) (Jensen, 1975) were con- verted from displacement volume to dry weight using

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