Development of Macrocystis pyrifera and Undaria pinnatifida Meiospores under Ocean Warming, ocean acidification and Copper Pollution

Chair: Heidi Pethybridge

Pablo P. Leal (1)*, Catriona L. Hurd (2), Sylvia G. Sander (3,4), Evelyn Armstrong (3), Pamela A. Fernández (1) & Michael Y. Roleda (1,5)

1 Department of Botany, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand.
2 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia.
3 Marine and Freshwater Chemistry, Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand.
4 National Institute for Water and Atmospheric (NIWA) Research Centre for Chemical and Physical Oceanography, Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand.
5 Bioforsk Norwegian Institute for Agricultural and Environmental Research, Kudalsveien 4, 8049 Bodø, Norway (Present address).

Background
Macroalgae dominate temperate coastal environments and play a key role as structural engineers, providing food and habitat for a variety of marine organisms. Ocean warming and ocean acidification may have negative effects on macroalgal physiology, thereby affecting their abundance and distribution. A decline in native macroalgal populations might favour the establishment of invasive macroalgae, affecting the local ecosystem diversity and functioning. The effects of ocean warming and ocean acidification have been mainly studied on the macroscopic adult phase, despite their microscopic life stages being more vulnerable to abiotic stress. Additionally, the interactive effects of climate change factors and local abiotic stress (e.g., copper pollution) have rarely tested on macroalgae. Therefore, our objective was to evaluate the interactive effects of seawater temperature, pH and copper concentration on the meiospore development of the native Macrocystis pyrifera and the invasive Undaria pinnatifida.

Methods
Meiospores of both kelps were separately cultured for 18 days under two temperature treatments (12°C, ambient temperature and 16°C, projected temperature for 2100), in two seawater pH treatments (pHT 7.65, OA predicted for 2100 and pHT 8.16, ambient pH), and two copper concentrations (species-specific germination EC50).

Findings
Meiospore germination for both species decreased by 10–15% in the presence of copper compared to the controls, irrespective of pH and temperature. Germling growth rate under copper exposure was 50% lower than that in controls for both species under all pH and temperature treatments. Gametophyte development for both species was inhibited by copper in all pH and temperature treatments.

Conclusions
Meiospore germination, germling growth and gametophyte differentiation are tolerant to the pH-temperature interaction but copper negatively affects these processes. This suggests that a local stressor (e.g., copper) is more important to early life history phases of M. pyrifera and U. pinnatifida than global climate change factors.