File:American malacological bulletin (1987) (18130153156).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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270 AMER. MALAC. BULL. 5(2) (1987) 1 0 10* - 03 DC c/) C/5 03 E o - 10 00 10
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oStiligeridae a Elysiidae a Conchoidea • Other 10' 2 0' 3 0 Latitude 4 0c Fig. 19. Relationship of latitude and biomass ratio (dry weight of slugs: dry weight of algae) of north Atlantic ascoglossan populations: Log™ (biomass ratio) = 0.0744 (latitude) - 4.449, with r = .535; the relationship is highly significant (p<.01) with 28 degrees of freedom. Peak densities and algal ash level correlated strongly and inversely (Fig. 20), with nearly a 1000-fold range in den- sity. Densities were generally highest in mangrove habitats and lowest in reef areas (Table 2). A similar effect was ob- served for biomass ratio and algal ash level (Fig. 21), but a narrower range of values suggests that differences in animal size (smaller animals on low-ash algae) can affect biomass ratios. DISCUSSION Ascoglossans' life histories are strongly entrained upon those of their algal foods (Clark, 1975). Consequently, their populations occur as a spatial and temporal subset of the occurrences of their algal foods, which are themselves often quite habitat-specific. This generates a highly "clumped" distribution for many species, in which relatively small populations occur, scattered within a very small percen- tage of the area of a potential habitat. These patterns of oc- currence make quantitative sampling difficult, because the principle of fully-randomized population sampling is difficult to apply in the analysis of strongly disjunct, low-density populations. Consequently, the probability of collecting even a few slugs by standard marine sampling protocols is very small. Ascoglossans rarely appear in general community analysis tabulations, and when they do, occur as minor com-

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