GROWTH RATES OF PENICILLUS OVER A THIRTY-YEAR PERIOD: A POTENTIAL WAY TO MEASURE OCEAN ACIDIFICATION?

Calcareous green algae (Halimeda, Penicllus, Udotea and Rhipocephalus) are major producers of carbonate sediments in both the fine and coarse-grained fractions in tropical lagoons; Halimeda, in the coarse (>2mm) size fraction, and Udotea, Rhipocephalus and Penicillus, in the fine (<0.063mm) size fraction, precipitate CaCO₃ in the form of aragonite needles. For this study we collected specimens of Penicillus from Graham’s Harbour, San Salvador, Bahamas in 2000, 2010 and 2011. These data were compared to Wefer’s (1980) study of Penicillus capitatus in Harrington Sound, Bermuda. The purpose here is to quantify the changes in growth rates produced by these algae, especially Penicillus.

The Penicillus thalli were stained in situ with Alazarin-Red S and their subsequent growth rate determined by measuring the overall ‘brush’ growth over a period of between 10 to 14 days during July 2000, May 2010 and May 2011. Preliminary analysis shows Penicillus capitatus having a growth rate of 0.9mm/day, P. pyriformis 0.74mm/day, while P. dumetosus is 0.59mm/day. On the other hand, Wefer’s (1980) study calculated a daily growth rate of 1.04mm/day for Penicillus capitatus in a subtropical region (Bermuda) where the yearly turn-over rate is less than the Bahamas. This noticeable change in growth over the last 30 years could potentially reflect a reduction in inorganic carbon mass (CaCO₃), which could reflect the effects of ocean acidification. On-going studies with these algae and particularly SEMs could show whether or not carbonate productivity in the form of the aragonite crystal bundles have changed; specifically in the species Penicillus.