Effects of ocean acidification and water flow on calcification, photosynthesis, and respiration for different morphologies of coralline algae

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Ocean acidification (OA) is becoming a threat to many marine organisms, particularly calcifers such as coralline algae that play important roles in coral reef ecosystems. However, it is expected that the effects of OA on coralline algae will vary depending on certain environmental factors, such as water flow. In this study, five algal species were incubated in different treatments of pCO₂ and water flow. Algal species were selected to represent a broad range of coralline algal morphology: branching Amphiroa fragilissima, crustose Porolithon onkodes, and crustose species with varying degrees of protuberances including Hydrolithon reinboldii, Neogoniolithon frutescens, and Lithophyllum kotschyanum. Algal samples were placed in placed in different plastic mesh containers with varying opening sizes to create different water flow environments, and were maintained in flumes under ambient pCO₂ and high pCO₂ (1000 μatm). Following a two-week incubation period, rates of calcification, photosynthesis and respiration were measured for each sample and used to compare algal individuals maintained in different treatments. Results from this study are expected to enhance our understanding of how different species of coralline algae will respond to future OA conditions.