Rheophilic/Oligotrophic Lagoonal Communities: Through the Eyes of Slugs (Mollusca: Opisthobranchia)
Rheophily (= love of current) constitutes one dimension of community structure in lagoonal ecosystems, and is indirectly associated with oligotrophy, in that organisms found in flowing systems show some decrease in tolerance to siltation and fouling that accompany anthropogenic eutrophication. This is demonstrated by evidence of a substantial decline in most Indian River Lagoon opisthobranch molluscs; of 61 species collected in the early 1970's, about 70% have declined in population density since 1980. Seventeen species (30%) showed a pattern of contraction of range within the lagoon to areas of highest current and lowest nutrients and siltation, termed here “rheophilic retreat.” Analysis of extant rheophilic communities offshore, or in western Florida, may provide clues for post facto evaluation of lagoonal community structure prior to anthropogenic disturbance. Opisthobranch molluscs show several anatomical and physiological traits (respiratory and reproductive specialization, stenotrophy) which confer high sensitivity to anthropogenic disturbance. Present strategy for management of mosquito impoundments (reconnection to the lagoon, allowing export of accumulated organic matter) may effect the loss of rheophilic/oligotrophic biodiversity components by decreasing levels of benthic boundary-layer oxygen and increasing growth of drift algae. This has apparently contributed to the local (possibly global) extinction of the emerald sea hare, Phyllaplysia smaragda, whose only known habitat was the northern basins of the Indian River Lagoon system. Effects of such productivity restoration should be critically evaluated to determine whether the potential increase in productivity justifies impacts on rheophilic/oligotrophic components of biodiversity, as these components have potentially important interactions with other components via control of planktonic mortality.
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Document Type: Research Article
Publication date: 1995-07-01
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