John Booker

Program Director at SeaCamp /Newfound Harbor Marine Institute on Big Pine Key, FL.

In areas where sediments form stable but thin coverings over the hardbottom, mixed algal communities develop. The algae dominating this community are rhizophytic species, which attach in the sediments by forming rhizoidal "root balls" or holdfasts. The most common species are members of the green algae family Codiaceae. Important representatives include several species of shaving brush algae (Penicillus spp.), halimeda (Halimeda spp.), ripweed (Rhipocephalus phoenix) and mermaid’s fan (Udotea flabellum). Many other types of algae are found, including several species of feather algae (Caulerpa spp.). Algae and fauna common to the surrounding communities are also represented here.

Many of these algae are calcareous algae. As they grow, they extract calcium from seawater and form calcium carbonate (limestone), usually in the form of tiny sediments or grains of sand. Over time, these algae build tremendous amounts of sediment. Penicillus capitatus sediments account for one-third of the lime mud in Florida Bay. In other areas, Halimeda contributes a large component of sediment and beach sands. It has been reported that members of the family Codiaceae are composed of from 25-90 percent calcium carbonate. Studies have shown that certain species of Halimeda calcify 1.5 to 10 times faster than hermatypic (reef) corals and up to 20 times faster than ahermatypic (stony) corals. The species of Codiaceae deposit calcium carbonate in the form of aragonite while the coralline red algae deposit calcium carbonate in the form of calcite.