File:American malacological bulletin (1988) (17968707448).jpg

Title: American malacological bulletin
Identifier: americanmal6719881990amer (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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Fig. 1. Map of Eleuthera Island, Bahamas, showing location of Sweetings Pond. Inset: map of Sweetings Pond, showing locations of Study Plots (numbered squares). R1 is the survey, collecting and experimental area. Dashed lines are dirt tracks. Adapted with per- mission from Bahamas Department of Lands and Surveys maps. 3 Algal Mat formations, this zone was termed the "patch zone." The main concentration of Octopus briareus occurred in cavities in and under some types of patch zone formations. Other octopuses were found under limestone rocks at shore. The patch zone thinned at its deep end, being composed mostly of flat orange sponges at a depth of 7.5 m. From the end of the patch zone to the center of the lake, the bottom consisted mainly of bare sediment, with scattered clumps of algae. Notable in the patch zone was the high density of ophiuroids, particularly the epifaunal suspension-feeder Ophiothrix oerstedi Lu'tken, which occurred at densities up to 434 ind./m2 (Aronson and Harms, 1985). Other conspicuous mobile invertebrates were the large spider crab Mithrax spinosissimus (Lamarck), the starfish Echinaster sentus (Say), the sea urchin Echinometra viridis Agassiz, the polychaete Eunice rubra Grube and the gastropod Fasciolaria tulipa (Linnaeus). In 1982 and 1983, much of Sweetings Pond did not follow the generalized profile of figure 2. Considerable areas were overgrown by Cladophora mats, and these mats expand- ed and regressed during 17 months of study. The cove that contains the Dock Entry (Fig. 1) was entirely patch zone in 1980. In February, 1983, almost the whole cove was covered by Cladophora, but the mats were dying back by June, 1983. Off the Cove Entry, a major portion of patch zone was covered by algal mat in 1982 to 1983. The algae destroyed all patch zone formations, leaving bleached coral skeletons and empty shells of Chione cancellata (Linnaeus) (the most common in- faunal bivalve) and Area imbricata Brugiere after it regressed. In this way much Octopus habitat was destroyed, including Study Plot 1 (Fig. 1). The cause of these dramatic changes in algal cover is unclear, but nutrient input via runoff from the cultivated fields surrounding Sweetings Pond could be responsible. The fish fauna of Sweetings Pond was remarkably depauperate: 17 species from 15 families were recorded (Aron- son and Harms, 1985). By contrast, 126 species from 50 families were recorded in shallow water (< 6 m depth) off the west coast of Eleuthera in the vicinity of Sweetings Pond. The only potential predators of Octopus sighted in hundreds of hours of diving in the lake were five schoolmasters, Lutjanus apodus (Walbaum), one Nassau grouper, Epinephelus striatus (Bloch), and one moray eel, Gymnothorax funebris Ranzani (see Randall, 1967). E Q Q 12- 15
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Bare Sediment Scattered Algal Mat 50 m Fig. 2. Benthic profile from the Cove Entry to the center of Sweetings Pond in July, 1980.

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