ENVIRONMENTAL RELATIONS OF MODIFICATION COMPOSITIONS OF CERTAIN CARBONATE SECRETING MARINE INVERTEBRATES

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Abstract
Modification compositions of the Serpulidae were detd. on powdered smear slide prepns. using a Phillips X-ray spectrometer with attached Brown recorder. Where both calcite and aragonite were present, their relative amts. were detd. using a calibration curve derived from synthetic mixtures. Composites of Serpulidae worm tubes were used because of their small size and the survey was based on recently collected specimen series from widely distant locations ranging from high to low latitudes, with some check on micro-environmental deviations. Modification composition of Serpulidae worm tubes varied from one geographic location to another and also within local populations. Analysis of overall variability showed that entirely calcitic tubes were confined to high latitudes (subarctic) whereas mixtures with more than 85% aragonite were derivatives from subtropics and tropics. When modification compositional ranges for samples of each locality were plotted against yearly mean temps. of inhabiting waters, at least partial temp.-controlled modification synthesis was involved. Bermuda sample series was most suitable for further exploring temp. relationship, since yearly range in water temp. was from 16 to 30[degree]C and salinity was almost constant throughout year. When one sample was grown in a tank at the Biological Station, temp. during intermolt period ranging from 16 to 22.9CC, aragonite content of worm tubes was second lowest analyzed. For rest of samples there was a trend toward increasing aragonite content with increasing collection date temps., and influence of temp. extended down to the local population level. 3 sets of samples from Gloucester, Va. were correlated to a lesser degree than Bermuda samples, possibly because of partial growth cover of submergence period of the stake. A single sample from Norway and Bermuda samples from Mangrove Lake had aragonite percentages above upper limits of gross trend relationships which might be related to low salinity content. A temp. effect was also observed in Spirorbidae, several genera of pelecypods and gastropods. In Mollusca mineralogic comp. and temp. responses varied between genera and between spp. Specimens of Mytilus edulis were submerged over a 30-day period, during which temp. increased from 17.1 to 23.2[degree]C. Analyses of 7 individuals representative of entire size range showed a range in aragonite content from 35 to 69%. When weights of individual shells were plotted against aragonite percentages, there was a decrease in aragonite content with increasing weight. An explanation is that larger cells involve longer growth periods and include more of colder initial temps., which effect a lower aragonite-calcite ratio. A sp. effect on comparative secretion behavior in modification synthesis products was observed in Mytilidae, which may reflect a difference between the temp. niche of shell deposition and temp. tolerance of a given sp. In the case of 2 gastropod spp. from La Jolla, Cal., Littorina planaxis analyzed 100% aragonite and L. scutulata 21 to 45% aragonite, indicating extreme differentiation in 2 spp. from same environment. Major trace element, strontium, was found to increase with increasing aragonite percentages, suggesting possible evolutionary changes in skeletal carbonate modifications and ecologic responses.