Effect of nutrient enrichment on naturally occurring macroalgal species in six cave pools in Bermuda
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abstract
Bermuda has one of the highest concentrations of cave systems of any country in the world. As the island's resident human population and tourism expand, its unique subterranean habitats are becoming increasingly threatened by development and eutrophication. The response to nutrient enrichment of six macroalgal species found in Bermuda's anchialine cave pools (landlocked body with a subterranean connection to the ocean) was examined during summer of 2007. We used a combination of nutrient bioassays, productivity measurements, and water quality analysis. Ulva sp. (Chlorophyta) responded similarly across all nutrient treatments (+N as 30 Mnitrate, +P as 2 Mphosphate, and +NP as 30 M nitrate + 2 M phosphate) at Calabash, which had dissolved inorganic N (DIN):soluble reactive P (SRP) ratios of 13-16, whereas at Harbour Pool, Ulva sp. responded best to the +N addition alone. The latter was consistent with very low DIN:SRP (5.8) ratios indicative of potential N limitation in this pool. P limitation was only detected in nutrient assays conducted with Caulerpa mexicana (Chlorophyta) collected from Cliff Pool, which had DIN:SRP ratios of 110. Halymenia floresia (Rhodophyta) was found to be light rather than nutrient limited in the Emerald cave pool. In some combinations of cave pools (e.g. Grenadier and Deep Blue) and for some macroalgae [e.g. Caulerpa racemosa (Chlorophyta), Caulerpia sertularioides (Chlorophyta), and Cryptonemia sp. (Rhodophyta)], findings were not easily characterized with measured parameters. Our findings illustrate the importance of evaluating individual cave pools as well as individual macroalgal species in each cave pool. Of the six macroalgae examined, Ulva sp. and H. floresia showed the greatest potential as bioindicators for groundwater quality in Bermudian caves.
