Abstract

Abstract. The effects of nutrients and pCO2 on zooxanthellate and azooxanthellate colonies of the temperate scleractinian coral Astrangia poculata (Ellis and Solander, 1786) were investigated at two different temperatures (16 °C and 24 °C). Corals exposed to elevated pCO2 tended to have lower relative calcification rates, as estimated from changes in buoyant weights. Experimental nutrient enrichments had no significant effect nor did there appear to be any interaction between pCO2 and nutrients. Elevated pCO2 appeared to have a similar effect on coral calcification whether zooxanthellae were present or absent at 16 °C. However, at 24 °C, the interpretation of the results is complicated by a significant interaction between gender and pCO2 for spawning corals. At 16 °C, gamete release was not observed, and no gender differences in calcification rates were observed – female and male corals showed similar reductions in calcification rates in response to elevated CO2 (15% and 19% respectively). Corals grown at 24 °C spawned repeatedly and male and female corals exhibited two different growth rate patterns – female corals grown at 24 °C and exposed to CO2 had calcification rates 39% lower than females grown at ambient CO2, while males showed a non-significant decline of 5% under elevated CO2. The increased sensitivity of females to elevated pCO2 may reflect a greater investment of energy in reproduction (egg production) relative to males (sperm production). These results suggest that both gender and spawning are important factors in determining the sensitivity of corals to ocean acidification, and considering these factors in future research may be critical to predicting how the population structures of marine calcifiers will change in response to ocean acidification.

Highlights

  • Rising levels of CO2 in the atmosphere are lowering the pH and carbonate ion concentration of the oceans, a process called “ocean acidification”

  • The increased sensitivity of females to elevated pCO2 may reflect a greater investment of energy in reproduction relative to males. These results suggest that both gender and spawning are important factors in determining the sensitivity of corals to ocean acidification, and considering these factors in future research may be critical to predicting how the population structures of marine calcifiers will change in response to ocean acidification

  • Syringes were capped and placed in a constant temperature bath prior to injection into the flow cell. pH on the total scale (pHT) calculations followed DOE (1994), code used for processing spectra and calculations is available online. pHT values measured with thymol blue (TB) and mCP usually agreed within measurement error, www.biogeosciences.net/9/29/2012/

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Summary

Introduction

Rising levels of CO2 in the atmosphere are lowering the pH and carbonate ion concentration of the oceans, a process called “ocean acidification” These changes have fueled concern for the survival of many forms of marine life, in particular, marine calcifiers which incorporate carbonate ions into their skeletons Many experimental investigations of the potential impacts of ocean acidification have focused on short-term calcification responses to decreased seawater pH and saturation state Experimental investigations have established that calcification by many marine organisms declines with decreasing seawater saturation state ( ) associated with elevated pCO2 (Gattuso et al, 1998; Langdon and Atkinson, 2005; Orr et al, 2005; Albright et al, 2008; Ries et al, 2009; Cohen et al, 2009). Previously unrecognized variables – gender and spawning – which were not taken into account in the experimental design, proved to be important factors which significantly affected the calcification response to ocean acidification and will likely need to be considered in future studies

Coral collection
Aquarium set up
Water supply
Aquaria
Temperature
Lighting
Feeding
Nutrients
Chemistry
Total alkalinity
Initial
Salinity
Buoyant weights
Gender identification
Statistics
Aquarium conditions
Coral growth
Discussion
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