Biotic Characteristics of the Anchialine Ponds of Bermuda
Abstract:The anchialine ponds of Bermuda over 0.5 ha in area are all fringed with mangroves, the root structures of which provide most of the hard substrate colonized by organisms within the ponds. The biota are quite different from anchialine ponds of this type described from elsewhere and extremely variable from pond to pond within Bermuda. Although both red and black mangroves are present in various ponds, most ponds have only one or the other species while species associated with the mangroves are also very variable from pond to pond. The attached aquatic biota is rich in species, particularly red and green algae and filter-feeding sponges, bryozoans and ascidians; however the majority of species occur in only a single pond and extremely few species occur in all five. The reasons for the very high interpond variability are discussed and it is concluded that no one factor is responsible, opportunity for colonization, ability to survive in the ponds, pond size or volume and the physical stability of ponds all playing a part. Diverse shell remains in the sediments showing species not present today suggest either cyclical or changing conditions with time. The mangrove roots show vertical zonation that varies among the ponds; the intertidal zone is characterized by Oscillatoria lutea or Bostrychia montagnei, a topmost subtidal zone characterized by spirorbids and/or Oscillatoria lutea and/or Caulerpa sertularioides, a large mid root zone in deeper ponds either dominated by Caulerpa verticillata or supporting a very diverse community of sponges, anemones, sabellids, tunicates, bryozoans and algae, and a root-tip zone characterized by various sponges and ascidians. There is considerable biotic variation among the roots but this does not correlate with their position within the mangrove or their location within the ponds. The rock walls of Walsingham Pond show only two zones, an intertidal (not studied here) and a subtidal. The subtidal rock wall community is strongly dominated by a dense assemblage of algae containing the same species as found on the roots but here covering 2/3 of the substrate. Intermixed with the algae is a species-rich community of fauna comprising the same taxa as on the roots but showing considerably more diversity. Temporal changes over the 8-year study period have been minimal on both the roots and rock walls. Both the root and rock wall faunas comprise mainly filter feeders and have a high biomass.
The submerged caves of Walsingham Pond showed an entrance zone dominated by pink crustose coralline algae, gradually changing to a sponge-bryozoan-tunicate-sabellid zone with diminishing irradiance. Several species occur only in the caves.
Document Type: Research Article
Publication date: January 1, 1992
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