Growth And Calcification Response Of The Common Collector Urchin, Tripneustes Gratilla, To Projected Climate Change: Effects Of Warming And Acidification

Abstract

As climate change leads to alterations in ecosystem and organism functions, the need to explore the breadth of effects is paramount. Increased sea surface temperatures (SST) and ocean acidification (OA) are major contributors leading to alterations in body size and calcification in marine invertebrates, however the full effects are not fully understood. Ecologically important invertebrates, such as sea urchins, calcify in both larval and post-metamorphic life stages, requiring long-term studies that cover changes into adulthood. The goal of this research is to contribute to the understanding of potential climate change impacts on post-metamorphic calcifying marine invertebrates, specifically the common collector urchin native to Hawaiʻi, Tripneustes gratilla. In this experiment, individual T. gratilla from juvenile (~16 mm) to adult (~60 mm) were grown under projected environmental conditions of warming (+2C) and increased acidity (-0.3 pH units) and a combination of both. The objectives were to explore the sensitivity of T. gratilla to warming and OA through comparisons of 1) growth (% change from initial to final diameters) and 2) calcification (calculated ratios through Scanning Electron Microscopy (SEM) images of cross-sections) of the urchin spines. Additional proxies of growth (relative spine length calculated proportionally to body size) and calcification (number of dropped spines) were also measured. Results of this research reveal that warmer temperatures increased growth while acidification reduced calcification at the base of spines with no interactive effects of the two factors. Urchins in low pH treatments shed their spines more readily than those in ambient pH, regardless of temperature, indicating that calcification may be hindered in these acidic conditions. These results suggest that while survivorship and growth were normal, the energy required to keep up with calcification, regardless of temperature change, may be inhibitive for the long term.