Seasonal growth and calcification of three species of crustose coralline algae in Moorea, French Polynesia

Abstract

Crustose coralline algae (CCA) play a critical role in the ecology and resilience of coral reefs by contributing to reef carbonate production and facilitating coral recruitment. However, little is known about their rates of in situ growth and calcification, particularly at the species level. To investigate the spatial and seasonal dynamics of CCA growth and calcification, we deployed CCA fragments embedded within epoxy rings at 3 mo intervals over 15 mo across 2 reef habitats in Moorea (French Polynesia). We studied 3 species differing in their microhabitat preferences (exposed, subcryptic and cryptic). Annual net calcification rates were highest in the exposed species Porolithon cf. onkodes (0.51 g CaCO3 cm-2 yr-1), intermediate in the subcryptic species Neogoniolithon cf. megalocystum (0.16 g CaCO3 cm-2 yr-1) and lowest in the cryptic species Lithophyllum sp. (0.03 g CaCO3 cm-2 yr-1). Growth and/or calcification rates differed between time intervals for all species. However, no consistent seasonal pattern was observed. P. cf. onkodes and N. cf. megalocystum had higher marginal growth rates at the fore reef habitat relative to the back reef habitat. This difference coincided with a lower occurrence of epiphytes on their crusts in the fore reef, suggesting that species interaction may be an important spatial driver of CCA growth. Our results show that CCA growth and calcification is species-specific and spatially and temporally variable. They highlight the need to consider subcryptic and cryptic CCA in reef carbonate budgets and provide important baseline information to understand how CCA communities are responding to environmental changes.