Coral Reef Project—Papers in Memory of Dr. Thomas F. Goreau. 15.
West Indian Molluscan Communities in the Rocky Intertidal Zone: A Morphological Approach
Abstract:Morphological and biogeographic analyses were carried out on the intertidal rocky-shore gastropod molluscs at five localities in Jamaica, Curaçao, and Guadeloupe, West Indies. Gastropods living on open surfaces at low shore levels in wave-exposed areas have rather uniformly high expansion rates, W; large apical half-angles, A/2; large posterior gravitational stability angles, GT; and large lateral gravitational stability angles, GW; apertures tend to be ovate to round. They may vary greatly in size, but many species tend to be relatively large. Open-surface species in more sheltered low-shore habitats may take on lower A/2, W, GT and GW values than their more wave-exposed counterparts, and the aperture may become elongate. Littoral-fringe species on open surfaces may also have A/2, W, GT and GW values somewhat lower than those of wave-exposed lower-shore species, but the aperture is uniformly ovate to round. Species in this category range somewhat less widely in size than at lower shore levels. High-shore splashpools contain a limited fauna of small species with ovate to round apertures and widely ranging A/2, W, GT, and GW values. Among lower-shore species living cryptically in crevices or beneath stones, there is a great diversity in all parameters except size, which tends to be small. Thus, where size diversity is greatest, morphological diversity appears to be least, and and vice versa. The relative morphological uniformity on low-shore wave-exposed open surfaces may reflect morphological restrictions imposed by the requirement of adapting to water turbulence. Rigors of temperature and desiccation impose certain restrictions on form in open-surface species of the littoral fringe.
Unique features of West Indian intertidal molluscan communities as compared to those in other parts of the tropics include a highly diverse littoral-fringe fauna, particularly of littorinids; a rather high diversity of open-surface keyhole limpets (genus Fissurella); the absence or near absence of such typical intertidal groups as cowries (genus Cypraea), pulmonate limpets (genus Siphonaria), conids, cerithiids, and open-surface mitrids; and a lack of substratum specialization among upper-shore neritids and limpets. The most substantial differences between physically similar intertidal communities in different parts of the tropics occur among open-surface assemblages at low shore levels and particularly in the littoral fringe. The geographic distribution of species in these habitats is significantly smaller than in more sheltered open-surface and cryptic habitats.
Document Type: Research Article
Publication date: June 1, 1973
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