Heatwave grazing kelp microbes sequences

The range-expansion of tropical herbivores due to ocean warming can
profoundly alter temperate reef communities by overgrazing the seaweed
forests that underpin them. Such ecological interactions may be mediated
by changes to seaweed-associated microbiota in response to warming, but
empirical evidence demonstrating this is rare. We experimentally simulated
ocean warming and marine heatwaves (MHWs) to quantify effects on two
dominant temperate seaweed species and their microbiota, as well as
grazing by a tropical herbivore. The kelp Ecklonia radiata’s microbiotain
sustained warming and MHW treatments were enriched with microorganisms
associated with seaweed disease and tissue degradation. In contrast, the
fucoid Sargassum linearifolium’s microbiota was unaffected by temperature.
Consumption by the tropical sea-urchin Tripneustes gratilla was
greater on Ecklonia where the microbiota had been altered by higher
temperatures, while Sargassum’s consumption was unaffected. Elemental
traits (carbon, nitrogen), chemical defences (phenolics) and tissue
bleaching of both seaweeds were generally unaffected by temperature.
Effects of warming and MHWs on seaweed holobionts (host plus its
microbiota) are likely species-specific. The effect of increased
temperature on Ecklonia’s microbiota and subsequent increased consumption
suggest that changes to kelp microbiota may underpin kelp-herbivore
interactions, providing novel insights into potential mechanisms driving
change in species’ interactions in warming oceans.