Do microbes facilitate the range expansion of tropical fishes into temperate ecosystems?

Ocean warming is leading to poleward shifts in the distribution of tropical species. As ocean temperatures continue to rise, we expect that tropical fishes will become increasingly abundant in temperate waters; however, little is known about how these fish may adapt to a novel environment.

For example, tropical herbivorous fishes that settle in Sydney are faced with an unfamiliar algal diet, which they must adapt to for survival. How can fish cope with this new diet? We think that microbes are the answer.

Microbes make up a vast proportion of diversity and biomass in the oceans, and emerging evidence from many systems shows that macro organisms (like fish, marine plants and even humans), rely on these microbes for survival. For example, we have tiny bacteria in our gut that aid in immune defences and digestion. This is the case for most, if not all, animals. Scientific advances show that these microbes may also play a key role in determining the survival of some species in warmer climatic conditions.

Here at the Sydney institute of Marine Science, Shannen Smith from UNSW Sydney is doing feeding experiments with tropical convict tangs that are expanding their distribution into Sydney because of climate change. The research will test how these tangs cope with novel temperate diets when they arrive to our shorelines. Do tangs acquire new gut microbes when they get to Sydney or do they depend on microbes acquired in tropical waters?

How does this affect their survival? Potential changes in gut microbial communities may be indicative of an evolutionary adaptation to the Sydney ecosystem for tropical marine herbivores expanding to cooler climates.