Biomass and Relative Coverage of Benthic Algae in the Fore-Reef of Curagao (Netherlands Antilles) in Relation to Production

Abstract

Biomass of benthic algae, expressed as chlorophyll a content (pg cm-') and as dry weight (mg cm-2) per substrate surface area in the coral reef of Curacao at 12 m and 25 m depth was measured from August 1978 to March 1979. To determine dry weights. substrates containing endolithic and epilithic algae were oxidized by means of wet combustion with hydrogen peroxide. Loss of weight caused by this process was regarded as algal dry weight. The crustose corallines Archaeolithothamnjon dimotum Fosl, et Howe (25 m), Hydrolithon boergesenii (Fosl.) Fosl. (12 m and 25 m) and Lithophyllum cf. interrnedium Fosl. (12 m), vegetations of endolithic algae dominated by Ostreobium quekettii Born. et Flah. (12 m and 25 m), and mixed turfs of epilithic filamentous algae and sometimes Lithophyllum cf. intermedium on substrates containing endolithic algae (12 m and 25 m) were examined. Chlorophyll a values ranged from 8.7 pg cm-' for H. boergesenii at 12 m to 20.5 pg cm-' for epilithic filamentous algae on substrates containing endolithic algae at 25 m. Dry weights varied from 12.7 mg for L. cf. intermedium at 12 m to 25.7 mg cm-2 for epilithic filamentous algae on substrates containing endolithic algae at 25 m. Both at 12 m and at 25 m, differences in chlorophyll a content and dry weights between substrates containing endolithic algae with and without epilithic filamentous algae were low. Biomass of endolithic algae is quantitatively more important than that of epilithic filamentous algae. It is concluded that, at 12 m, biomass of the algal vegetation as a whole is lowest while production is highest. This is attributed to maximum grazing pressure at this depth ('drop off' community), especially on epilithic filamentous algae.