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

摘要

Bermuda has one of the highest concentrations of cave systems of any country inthe world, but as the resident human population and tourism expand, this unique habitatis becoming increasingly threatened by development and water pollution. A waterquality assessment was performed in six of Bermuda?s anchialine cave pools duringsummer 2007. Vertical water profiles were collected at each site to determinetemperature, salinity, dissolved oxygen, and pH levels throughout the water column.Each cave pool had its own unique hydrological patterns. Additionally, water sampleswere collected at the surface and at the maximum depth to determine the concentrationof nitrate, nitrite, ammonium, phosphate, and urea in the water. Further samples werecollected to establish the fecal bacteria content in the surface waters. High nitrate levelswere measured in two of the cave pools, while unsafe bacterial levels were measured inthree pools.In situ nutrient addition experiments were used to examine effects of nutrientenrichment on algae naturally occurring in the six cave pool. Initial assessments of thepools determined distribution of foliose species. Six algal species (Ulva sp., Caulerpamexicana, C. racemosa, C. sertularioides, Halymenia floresii, and Cryptonemia sp.)inhabited multiple sites, but not all species occurred at all sites. Changes in the biomassof 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 biomasswas 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 bothincreases and in biomass depending on the site. Cryptonemia sp. had low but positivegrowth. A significant decrease in biomass occurred with C. racemosa and C.sertularioides. Primary productivity was measured using the traditional light dark bottlemethod. Differences in net productivity and respiration may explain why some plantsresponded positively and other negatively to nutrient additions. Ulva sp. and H. floresiishowed potential as bioindicators for groundwater quality.