94. Effects of ocean warming and acidification on the growth of juveniles of two Antarctic Heart Urchins, Abatus ingens and A. shackletoni

Melanie A. Ho (1), Jessica A. Ericson (2,4), Ashley Miskelly (1), Catherine K. King (3), Patti Virtue (2,4), Maria Byrne (1,5)

1 School of Medical Sciences, University of Sydney, Sydney, NSW Australia

2 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia

3 Australian Antarctic Division, Kingston, TAS, Australia

4 Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, TAS, Australia

5 Schools of Medical and Biological Sciences, University of Sydney, Sydney, NSW, Australia

Background
The heart urchins Abatus ingens and A. shackletoni are ecologically important bioturbators that dominate shallow subtidal areas around Antarctica. To date, there are no published empirical studies on how these echinoids may respond to global change, and polar waters are undergoing carbonate under-saturation earlier than temperate and tropical regions. Studies on Antarctic marine invertebrates are important as they help us predict species response to these changing conditions. In this study, spine growth in juvenile A. ingens and A. shackletoni was investigated in urchins incubated under experimental pCO2 and temperature scenarios predicted by the year 2100.

Methods
Adult A. ingens and A. shackletoni were collected from Heidemann Bay (68° 35’S, 77° 58’E) near Davis Station, East Antarctica, in the 2011 austral summer season (January-February). Juveniles were removed from the parental brood pouch of females and reared for four weeks in a flow-through aquarium system. Temperature controlled seawater (ambient -1°C and 1°C) was injected with CO2 enriched air to create the target pH levels (ambient pH 8.0, pH 7.8, pH 7.6), for a total of six temperature x pH combinations. Spine length in each individual was measured at the start of experiments, and after four weeks exposure.

Findings
Juvenile Abatus reared at pH 7.6 had significantly smaller spines than those in pH 7.8 and ambient control conditions. Spine growth was slower in juveniles of both species exposed to the most extreme treatment combination (1°C/pH 7.6) compared to other treatments. There were no signs of spine dissolution in any treatment.

Conclusions
Slow spine growth in juveniles in pH 7.6 treatments may be due to diversion of energy away from growth to maintain acid-base balance. However, adaptation to the low pH environment within the brood pouch and benthic sediments may explain why juveniles were able to maintain some spine growth in seawater pH levels predicted for 2100.