Microbial assemblages involved in tropical coastal bioerosion: An Atlantic-Pacific comparison

Bioerosion on tropical limestone coasts consists of interaction between microbial endoliths and invertebrat e grazers. Distribution of both is correlated with the frequency of wetting and water retention on the habitat. A steep gradient in water availability across the intertidal ranges causes a general zonal distribution of organisms, modified by bio-karstic microtopography. Several zones of characteristic color can be distinguished, as they are dominated by particular assemblages of organisms each with its own pigmentation. From the subtidal level upward, the zones are dominate d by: 1 - the chlorophyte Ostreobium quekettii; 2 - Conchocelis-stages of bangiacean rhodophytes; 3 - cyanobacteria Mastigocoleus testarum and Plectonema terebrans; 4 - cyanobacteria Herpyzonema intermedium, Scytonema endolithicum and Hormathonema luteobrunneum. The dominant grazers are sea urchins, followed by polyplacophores and gastropods. Maximum bioerosive effect is in the mid-intertidal ranges, where a combine d and interdependent microboring-grazing activity results in formation of a deep bioerosive coastal notch. Such notches occur on carbonate coasts of all warmer seas, however, their development is most accentuated in soft calcarenitic limestone in protected lagoonal waters. Good preservation potential of microbial endoliths permits assessment of coastal paleo-environments and determination of the position of ancient sea levels.