Kelp forests create complex habitats that support a diverse and productive community of marine life. They also underpin coastal food-webs, fisheries, and a suite of other ecosystem services including nutrient and blue carbon cycling.
Across many regions of the world, kelp forests are in decline and under threat from stressors including urbanisation, overgrazing, and ocean warming and marine heatwaves due to climate change.
Australia’s giant kelp (Macrocystis pyrifera) forests are listed as a Threatened Ecological Community under the Environment Protection and Biodiversity Conservation Act 1999. Habitat restoration is a potential tool for the conservation and management of giant kelp ecosystems. Given the direct impacts of climate change and ocean warming, there is growing recognition of the need for habitat restoration to be ‘future proofed’.
Previous research supported by the NESP Marine Biodiversity Hub (a forerunner of the Marine and Coastal Hub) demonstrated the presence of warm-tolerant family-lines of giant kelp sourced from remnant kelp patches in eastern Tasmania. The research also pioneered techniques of giant kelp restoration, establishing two sites that together support more than 200 healthy and well developed warm-tolerant giant kelp.
While these warm-tolerant giant kelp strains have been identified to assist with future-proofing kelp restoration, the physiological mechanisms that provide the thermal tolerance are unclear. It is also unknown whether cross-breeding the identified warm-tolerant giant kelp strains will affect and potentially improve their thermal tolerance capacity.
This project explored the physiology of kelp thermal performance, specifically the mechanisms potentially responsible for the warm water tolerance identified in particular giant kelp strains. It confirmed the improved ability of the warm-tolerant strains to develop at stressful warm temperatures relative to normal giant kelp, and demonstrated for the first time that their improved thermal performance may extend to the development and fertilisation.
Approach and findings
The project team cultivated the warm-tolerant giant kelp strains, along with giant kelp strains of normal tolerance, at both cool (16°C) and warm temperatures (20°C). The juvenile kelp was harvested and examined for a suite of physiological traits that may be responsible for their differences in thermal tolerance, including nutrient usage (carbon and nitrogen content), cellular membrane processes (fatty acid contents), and photosynthesis (PAM fluorometry and photosynthetic pigments).
The cultivation trials again illustrated the improved ability of the warm-tolerant strains to develop at stressful warm temperatures relative to normal giant kelp. They also demonstrated for the first time that their improved thermal performance may extend to the development and fertilisation of the earlier kelp ‘gametophyte’ life-stage.
Despite the clear differences in growth between the two test groups, the physiological assessments illustrated a complex pattern of responses, some of which are contrary to expected based on prior knowledge of thermal performance in kelps. Nonetheless, our results indicate that the warm-tolerant strains of giant kelp have a greater capacity to alter the composition of their fatty acids and may be more efficient users of nitrogen (a key nutrient for growth and development).
This new information will help to guide ongoing kelp breeding and selection programs for future-proofing kelp restoration in Australia and globally. This improved understanding of the physiology of kelp thermal tolerance may also help with identifying individuals and populations of Macrocystis, and other kelps, that may be resilient to (or especially threatened by) ocean warming and climate change.
University of Tasmania