Impaired growth and survival of tropical macroalgae (Sargassum spp.) at elevated temperatures

Graba-Landry, Alexia C., Loffler, Zoe, McClure, Eva C., Pratchett, Morgan S., and Hoey, Andrew S. (2020) Impaired growth and survival of tropical macroalgae (Sargassum spp.) at elevated temperatures. Coral Reefs, 339. pp. 475-486.

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Increasing ocean temperatures associated with ongoing climate change have resulted in regional reductions in the cover of live coral and increasing concerns that coral reefs will be overgrown by macroalgae. The likelihood of macroalgal overgrowth will, however, depend on the thermal sensitivities of the macroalgae themselves. We exposed recently settled propagules of the common canopy-forming macroalga Sargassum swartzii and adult thalli of three species of Sargassum (S. swatzii, S. cristaefolium, S. polycystum) to three experimental temperatures: ambient, + 2 degrees C, and + 3.5 degrees C, reflective of summer minimum, mean, and maximum temperatures for the region. Growth and survival of Sargassum swartzii propagules were assessed over 48 days, and the growth, physical toughness, elemental composition, and susceptibility to herbivory of adult thalli were assessed after short-term exposure (2-weeks) to experimental temperatures. Growth and survival of S. swartzii propagules were reduced by 43% and 84%, respectively, when cultured at the elevated (+ 3.5 degrees C) temperature compared to ambient temperature. Similarly, elevated temperature resulted in a 17-49% decline in the growth of adult Sargassum thalli relative to controls. Susceptability of S. swartzii and S. cristaefolium to herbivory (i.e. mass removed by herbivores) was 50% less for thalli cultured at elevated (+ 3.5 degrees C) compared to ambient temperature, but this pattern was not related to changes in the physical or chemical properties of the thalli as a result of elevated temperature. The negative effects of elevated temperatures on the growth and survival of both Sargassum propagules and adult thalli will likely restrict the capacity of Sargassum, and potentially other macroalgae, to establish in new areas, and may also threaten the persistence of existing macroalgal meadows under future ocean temperatures. The thermal sensitivities of tropical Sargassum, together with those of corals, suggest ongoing ocean warming may lead to novel reef ecosystems that are low in both coral cover and macroalgal cover.

Item ID: 62633
Item Type: Article (Research - C1)
ISSN: 1432-0975
Keywords: Ocean warming, Plant-herbivore interactions, Physical toughness, Consumption, Propagules, Coral reefs, Climate change, Herbivory
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Copyright Information: © Springer-Verlag GmbH Germany, part of Springer Nature 2020.
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A version of this publication was included as Chapter 4 of the following PhD thesis: Graba-Landry, Alexia (2020) The effect of increasing temperature on algae-fish interactions on coral reefs. PhD thesis, James Cook University, which is available Open Access in ResearchOnline@JCU. Please see the Related URLs for access.

Funders: Australian Research Council (ARC), Lizard Island Reef Research Foundation (LIRRF), Holsworth Wildlife Research Endowment (HWRE), Great Barrier Reef Marine Park Authority (GBRMPA), Sigma Xi-Grants-In-Aid of Research Award (SXGIARA)
Projects and Grants: ARC DP10104668, LIRRF Doctoral Fellowship JCU23037, HWRE JCU22709, GBRMPA Reef Guardian's Grant JCU24819, SXGIARA G201603151990802
Date Deposited: 25 Mar 2020 07:42
FoR Codes: 31 BIOLOGICAL SCIENCES > 3103 Ecology > 310305 Marine and estuarine ecology (incl. marine ichthyology) @ 50%
41 ENVIRONMENTAL SCIENCES > 4101 Climate change impacts and adaptation > 410102 Ecological impacts of climate change and ecological adaptation @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
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