An investigation of the calcification response of the scleractinian coral Astrangia poculata to elevated pCO_2 and the effects of nutrients, zooxanthellae and gender

摘要

The effects of nutrients and pCO_2 on zooxanthellateand azooxanthellate colonies of the temperate scleractiniancoral Astrangia poculata (Ellis and Solander, 1786)were investigated at two different temperatures (16 ℃ and24 ℃). Corals exposed to elevated pCO_2 tended to havelower relative calcification rates, as estimated from changesin buoyant weights. Experimental nutrient enrichments hadno significant effect nor did there appear to be any interactionbetween pCO_2 and nutrients. Elevated pCO_2 appearedto have a similar effect on coral calcification whether zooxanthellaewere present or absent at 16 ℃. However, at 24 ℃,the interpretation of the results is complicated by a significantinteraction between gender and pCO_2 for spawning corals.At 16 ℃, gamete release was not observed, and no genderdifferences in calcification rates were observed – female andmale corals showed similar reductions in calcification ratesin response to elevated CO_2 (15% and 19% respectively).Corals grown at 24 ℃ spawned repeatedly and male and femalecorals exhibited two different growth rate patterns – femalecorals grown at 24 ℃ and exposed to CO_2 had calcificationrates 39% lower than females grown at ambient CO_2,while males showed a non-significant decline of 5% underelevated CO_2. The increased sensitivity of females to elevatedpCO_2 may reflect a greater investment of energy in reproduction(egg production) relative to males (sperm production).These results suggest that both gender and spawningare important factors in determining the sensitivity of coralsto ocean acidification, and considering these factors in futureresearch may be critical to predicting how the populationstructures of marine calcifiers will change in response toocean acidification.