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Marine Ecology Progress Series

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MEPS 299:89-99 (2005)  -  doi:10.3354/meps299089

Why is bacterioplankton growth in coral reef framework cavities enhanced?

S. R. Scheffers1, 2, 3,4,*, R. P. M. Bak1,3, F. C. van Duyl1

1Royal Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands
2CARMABI Foundation, PO Box 2090, Willemstad, Curaçao, Netherlands Antilles
3University of Amsterdam, IBED, PO Box 94766, 1090 GT Amsterdam, The Netherlands
4Present address: University of Essen, Faculty of Biology and Geography, Universitätsstraße 5, 45141 Essen, Germany

ABSTRACT: Abundance, growth rates and nutrient limitation of the heterotrophic bacteria present in the reef water column and reef cavity water were measured on a fringing reef at Curaçao (Netherlands Antilles). Bacterial in situ growth rates were measured using dialysis bags. Nutrient limitation was measured using bioassays with different amendments of inorganic nutrients (nitrate, ammonium, phosphate) and dissolved organic carbon (glucose). Cell sizes were measured in the reef water column and over an intra-cavity gradient inside reef cavities, from the cavity center to the wall of the cavity. Bacterial abundance was lower in cavities, while growth rates were on average 3.6 times higher than in open reef water. The bacterial community in open reef water was limited in its growth by all nutrients, in contrast to cavity water, in which bacteria were limited by phosphate. Cell volumes decreased significantly from open reef water towards the cavity wall. Results suggest that conditions in cavities have a positive effect on bacterial growth. Growth limitation by N is alleviated through enhanced mineralization in cavities. Through rapid exchange with the ambient water, cavities enrich the overlying reef water with inorganic N.

KEY WORDS: DOC · DIP · DIN · Nutrient limitation · Growth rates · Heterotrophic bacteria ·Cavities · Coral reef

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