Physiological basis of the species abundance-salinity relationship in molluscs: A speculation

✍ Scribed by L. F. Gainey; M. J. Greenberg

• Publisher: Springer-Verlag
• Year: 1977
• Tongue: English
• Weight: 815 KB
• Volume: 40
• Category: Article
• ISSN: 0025-3162
• DOI: 10.1007/bf00390626

✦ Synopsis

The relationship between the osmotic pressures of the blood and the ambient medium was determined for 4 species of bivalve molluscs whose habitats represent distinct salinity regimes within the range from fresh to full seawater. These organisms included 3 corbiculids: Corbicula manilensis (freshwater); Polymesoda caroliniana (brackishwater); Pseudocyrena floridana (marine) and I unionid: Elliptic lanceolata. On the basis of the data and similar measurements from the literature, we have placed the molluscs into 5 categories: marine stenohaline, marine euryhaline, oligohaline, freshwater euryhaline and freshwater stenohaline. Marine stenohaline and euryhaline species are osmoconformers. They differ only in the size of the free amino acid pool available for intracellular volume regulation, and thus in the range of salinities that they tolerate. Oligohaline species tolerate salinities from seawater down to freshwater; they not only possess a large capacity for volume regulation, but can also osmoregulate below 3~ S. Freshwater species also osmoregulate below 3~ S, but they are usually limited to salinities below 2~. Presumably, in evolving from the marine to the freshwater habit, they have lost the ability to volumeregulate in response to hyperosmotic stress. We propose that the varying physiological characteristics underlie the well-known relationship that species abundance declines from both freshwater and full seawater to a minimum between 3 and 5~ S. We have related this species minimum to physical-chemical discontinuities in the ionic composition of seawater which are, again, reflected in the physiological mechanisms of the molluscs.