Rhodoliths and Rhodolith Beds

Abstract

Rhodolith (maërl) beds, communities dominated by free living coralline algae, are
\na common feature of subtidal environments worldwide. Well preserved as fossils, they have long
\nbeen recognized as important carbonate producers and paleoenvironmental indicators. Coralline
\nalgae produce growth bands with a morphology and chemistry that record environmental variation.
\nRhodoliths are hard but often fragile, and growth rates are only on the order of mm/yr. The
\nhard, complex structure of living beds provides habitats for numerous associated species not found
\non otherwise entirely sedimentary bottoms. Beds are degraded locally by dredging and other anthropogenic
\ndisturbances, and recovery is slow. They will likely suffer severe impacts worldwide
\nfrom the increasing acidity of the ocean. Investigations of rhodolith beds with scuba have enabled
\nprecise stratified sampling that has shown the importance of individual rhodoliths as hot spots of
\ndiversity. Observations, collections, and experiments by divers have revolutionized taxonomic studies
\nby allowing comprehensive, detailed collection and by showing the large effects of the environment
\non rhodolith morphology. Facilitated by in situ collection and calibrations, corallines are now
\ncontributing to paleoclimatic reconstructions over a broad range of temporal and spatial scales.
\nBeds are particularly abundant in the mesophotic zone of the Brazilian shelf where technical diving
\nhas revealed new associations and species. This paper reviews selected past and present research on
\nrhodoliths and rhodolith beds that has been greatly facilitated by the use of scuba.