The role of benthic algae in the shallow reef of Curaçao (Netherlands antilles). I: Primary productivity in the coral reef

Abstract

In order to make an accurate estimate of the primary productivity of the shallow reef (0.5–3 m deep, c. 25 m wide) along the south-west coast of Curaçao, oxygen production and consumption of the non-endosymbiotic algae and the abundance of the various community components (including corals) were measured. Oxygen production and consumption were measured using the light-and-dark-bottle technique. Expressed per substrate surface area, midday gross productivity of the investigated crustose coralline algae ( Porolithon pachydermum (Fosl.) Fosl., Lithophyllum sp. 3, Lithophyllum intermedium Fosl., Lithophyllum sp. 4 and Neogoniolithon solubile (Fosl. et Howe) Setch. & Mason) ranges from 0.023–0.043 mg O 2/cm 2/h, and midday net productivity from 0.015–0.034 mg O 2/cm 2/h. Productivity of a “sparse vegetation” of fleshly and filamentous algae ( Calothrix crustacea (Thur.) Born. et Flah., Lyngbya majuscula [(Dillw.) Harv.] Gom., Trichosolen sp., Giffordia duchassaingiana (Grün.) Taylor) growing in and on limestone was within the range of the crustose coralline productivity, but productivity of a “dense vegetation” ( Sphacelaria tribuloides Menegh., Herposiphonia tenella (C. Ag.) Ambr., Polysiphonia subtilissima Mont., Pterocladia americana Taylor, Taenioma nanum Kütz., Wurdemannia miniata (Drap.) Feldm. & Hamel) was about twice as high. Net productivity of the “dense vegetation” (0.064 mg O 2/cm 2/h) was about as high as that of corals. As a result of production measurements made at different light intensities and various times during 24 h, it was concluded that 24-h gross production is about 9.8 times the hourly midday gross production, and 24-h oxygen consumption is about 19.6 times the hourly midday oxygen consumption. About 5.5 m 2 of substrate surface was present under an average horizontal square metre in the shallow reef zone; of this 5.5 m 2, coral tissue occupied about 2.1 m 2 of substrate surface, crustose corallines also 2.1 m 2 and the fleshly and filamentous algae in and on limestone occupied 0.8 m 2 of substrate surface. Gross productivity of the algae present under an average horizontal square metre was estimated at 5650 g C/year. Net productivity amounted to 2330 g C/horizontal m 2/year; about one third was produced by crustose corallines and fleshy and filamentous algae, and this is available to herbivores. It was concluded that substrate surface enlargement is a key factor for the high primary productivity of the coral reef. The total dry weight of the primary producers of the shallow reef was estimated to be about 1400–2800 g/horizontal m 2.