Effects of sediment on the energy budgets of four scleractinian (Bourne 1900) and five alcyonacean (Lamouroux 1816) corals

The physiological reactions to sediment of four scleractinia and five alcyonacea from South Mrica were observed in the laboratory. Species tested were Faviafavus Forskal, Favites pentagona Esper, Platygyra daedalea Ellis & Solander, Gyrosmilia interrupta Ehrenberg, Lobophytum depressum Tixier-Durivault, Lobophytum venustum Tixier-Durivault, Sinularia dura (Pratt), Sinularia leptoclados (Ehrenberg) and Sarcophyton glaucum (Quoy & Gaimard). Natural sedimentation levels and light conditions were simulated. Photosynthetic carbon production and respiration were measured by respirometry. Loss of fixed carbon through mucus production was measured directly by filtration. The results were used to model daily energy budgets for these species. One set of models allowed for 50 % PARs (photosynthetically active radiation at the surface), another set of models allowed for 25 % PARs. The models showed severely diminished productivity and decreased respiration under sedimented conditions. Production/respiration (P/R) ratios of all species were above 1 in the absence of sediment and dropped below unity when the corals were subjected to sedimentation. Although overall respiration dropped, its demand upon the also diminished amount of photosynthetically produced carbon rose dramatically. Without sediment, mucus output averaged 35% of daily respiration; this rose to 65% when sediment was applied. Sediment affects coral metabolism by decreasing photosynthetic production, increasing relative respiration and increasing carbon-loss through greater mucus output.