The Role of Macroalgal Species as Bio-indicators of Water Quality

in Bermudian Karstic Cave Pools
 

Bridget Maloney
Department of Wildlife and Fisheries Sciences, Texas A&M University
                                          College Station, Texas USA

Bermuda consists of a series of mid-ocean islands located 1000 km (600 miles) off the eastern coast of the United States. Geologically, the islands are composed of highly cavernous limestone overlying a volcanic seamount. Due to this foundation, Bermuda has one of the highest concentrations of cave systems of any country in the world. The caves are characterized by  inland entrances, interior cave pools, underwater passages, and tidal spring outlets to the ocean. Contained within these ecosystems are many rare species of plants and animals as well as abundant speleothems (stalactites and stalagmites).

Bermuda is one of the most densely populated countries on earth, in addition to attracting hundreds of thousands of foreign tourists each year. The karst topography of the island provides a direct link between the human activities on the surface and the groundwater and cave systems below. As the resident human population and tourism expand, this unique habitat is becoming increasingly threatened by development and water pollution. These major threats include: construction projects and limestone quarrying, water pollution (particularly cesspits and wastewater injection boreholes), and dumping of trash and other wastes into sinkholes.  Seepage from these cesspits, boreholes, and unlined land fills allow sewage, detergents, pharmaceuticals, and other contaminants to enter the cave systems through underground passages and fissures and transport them for considerable distances with little to no filtration.

This study will determine if the various algal species present in inland pools at the entrance to many Bermuda caves can serve as bio-indicators for groundwater quality. Initially floral surveys of submerged and intertidal algae will be conducted at eleven different sites to determine the diversity present. More detailed experiments will be carried out on one to two species of algae at six of the sites. These experiments will measure productivity and respiration rates as well as determine the effects of nutrient enrichment on growth. Algae are autotrophic organisms at the bottom of the trophic food web. They rely directly on nutrients in their environment for growth and survival. Due to this relationship, they are very sensitive to pollution and nutrient enrichment and show rapid and quantifiable morphological changes.

Entrance cave pools with lower water quality and higher nutrient loading exhibit different algal distributions and show higher primary productivity and growth characteristics than cave pools with high water quality and less or no nutrient loading relative to background levels. By determining if there is a correlation between the presence and distribution of different algal species in the cave pools and the water quality, environmental health in the various inland cave pools and in the groundwater can be monitored.

This research will add to the knowledge of karst ecosystems and their interconnections. All acquired data will be provided to the Bermuda Biodiversity Project (BBP) of the Bermuda Aquarium, Museum, and Zoo. This research is intended for use in conservation efforts to preserve and protect the cave systems and the flora and fauna that inhabit this unique environment.