Researchers have found ocean warming is impacting the nutritional quality of seaweed as a food source for Blacklip abalone off eastern Tasmania, which is adversely affecting the body condition of these molluscs during warmer years. This research offers insights into how ocean warming causes stress on the state’s abalone stock and habitat.
In a recent project, Βι¶ΉΣ³» researchers identified regional patterns in the nutritional quality of understory seaweeds that correlate with regional Blacklip abalone fishery productivity. They also determined that rising ocean temperatures and inorganic nutrient concentrations influenced the growth and photosynthesis – known as performance – and nutritional quality of key seaweeds in abalone habitat.
Seaweed quality and abalone fishery productivity
“We found that temperate rocky reefs in south and south east Tasmania have a higher biomass of nutritious red seaweeds, which have a greater availability of protein and essential fatty acids, than those in the north east,” Βι¶ΉΣ³» seaweed researcher and project leader, Dr Damon Britton said. “The higher the nutritional quality of seaweed assemblages in these areas correlates with higher annual catch rates of abalone.
“Researchers also identified seasonal variations in the nutritional quality of seaweed, which is an abalone’s primary food source. This included reduced essential fatty acids in seaweed during warmer seasons, correlating with the seasonal decline in abalone condition in these warmer months."
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| Red seaweed, Plocamium sp. (Photo: Βι¶ΉΣ³») | Red seaweed, Phacelocarpus peperocarpus. (Photo: Βι¶ΉΣ³») |
Impacts of rising ocean temperatures on seaweed
Dr Britton said the research showed that protein and essential fatty acid content in seaweeds will decline under elevated temperatures.
“Essential fatty acid contents in seaweeds in the field were lower during the warmer months and protein content declined at high temperatures during laboratory experiments. This suggests that continued strengthening of the East Australian Current due to climate change will reduce the nutritional quality of seaweeds in eastern Tasmania.”
“Furthermore, we highlighted that both crayweed and strapweed – key seaweeds in abalone habitat – will experience reductions in growth and photosynthetic rates under the elevated temperatures expected under climate change and marine heatwaves.
“This suggests that the growth, photosynthesis and nutritional quality of these vital habitat-forming seaweeds will decline under ocean warming and marine heatwave events along eastern Tasmania.
“Reduced growth and photosynthesis could lead to less seaweed biomass, resulting in reduced quality abalone habitat, while the lower nutritional quality of seaweed makes them a less nutritious food source to abalone. Together these changes are likely to exacerbate the direct effects of increased temperatures on abalone.”
Preparing for oceanic changes
“This data fills a knowledge gap on one aspect of how ocean warming affects the productivity of abalone stocks through changes in the supporting kelp community," Dr Britton said.
“While we can't mitigate climate change effects on abalone or kelp, we can be more precautionary with our expectations from the stock in years with warmer summers.”
Additional field sampling must investigate how the nutritional quality of seaweed is altered by the duration and intensity of marine heatwaves. This research, if conducted over multiple years, will identify direct links between marine heatwaves and seaweed quality.
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| Crayweed (Phyllospora comosa) (Photo: Matthew Doggett) | Strapweed (Lessonia corrugata) (Photo: Hunter Forbes) |
The Department of Natural Resources and Environment Tasmania provided funding through the Abalone Industry Reinvestment Fund, and the Sustainable Marine Research Collaboration Agreement between the Tasmanian Government and the University of Tasmania.
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Published 24 May 2024