The role of macroalgal species as bio-indicators of water quality in bermudian karstic cave pools



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Bermuda has one of the highest concentrations of cave systems of any country in the world, but as the resident human population and tourism expand, this unique habitat is becoming increasingly threatened by development and water pollution. A water quality assessment was performed in six of Bermuda?s anchialine cave pools during summer 2007. Vertical water profiles were collected at each site to determine temperature, salinity, dissolved oxygen, and pH levels throughout the water column. Each cave pool had its own unique hydrological patterns. Additionally, water samples were collected at the surface and at the maximum depth to determine the concentration of nitrate, nitrite, ammonium, phosphate, and urea in the water. Further samples were collected to establish the fecal bacteria content in the surface waters. High nitrate levels were measured in two of the cave pools, while unsafe bacterial levels were measured in three pools. In situ nutrient addition experiments were used to examine effects of nutrient enrichment on algae naturally occurring in the six cave pool. Initial assessments of the pools determined distribution of foliose species. Six algal species (Ulva sp., Caulerpa mexicana, C. racemosa, C. sertularioides, Halymenia floresii, and Cryptonemia sp.) inhabited multiple sites, but not all species occurred at all sites. Changes in the biomass of individual plants were recorded for 6 to 12 days in response to N (nitrate), P (phosphate), and NP additions. The effect of nutrient addition on increase in biomass was significant over a 6 day period for Ulva sp. and H. floresii. Intermediate to no growth was seen in C. mexicana and Cryptonemia sp. C. mexicana exhibited both increases and in biomass depending on the site. Cryptonemia sp. had low but positive growth. A significant decrease in biomass occurred with C. racemosa and C. sertularioides. Primary productivity was measured using the traditional light dark bottle method. Differences in net productivity and respiration may explain why some plants responded positively and other negatively to nutrient additions. Ulva sp. and H. floresii showed potential as bioindicators for groundwater quality.