Shark-cano

Sharks can be found in every single ocean in the world; from amongst the icecaps in the Arctic circle, to glistening, tropical reefs; from shallow coastal regions, to the abyssal deep, dark seas; in salt water, freshwater and brackish estuaries. Recently scientists have even discovered that sharks can be found in an especially unlikely place - in an extreme habitat around an underwater volcano. With continuous eruptions, great heat and harsh acidity, how do sharks live here? Which sharks are able to tolerate these challenging conditions? And what does this mean for sharks of the future?

Scientists have captured footage of hammerhead sharks living in the harsh environment around an undersea volcano (Image Source: Phillips et al, 2016)

Blowing Off Some Steam

Nestled amongst the Solomon Island Group in the south Pacific Ocean, the Kavachi Submarine Volcano is located at the boundary of three immensely powerful tectonic plates. Complex and dynamic subduction zones and crustal uplift make this one of the most active underwater volcanoes in the world and by far the most active in this region; continuously spewing plumes of searing hot steam, ash and gases (Phillips et al, 2016).

Kavachi as a submarine volcano within the Solomon Island group of the south Pacific (Image Source: Phillips et al, 2016)

Thanks to all this constant activity, the Kavachi summit is perpetually eroding and re-forming. Plunging down to more than 1000 metres under the water, violent eruptions regularly cause islands to emerge and then disappear, so the geography of the region is in a continuous state of flux (Phillips et al, 2016).

Under the surface of the ocean, around the mouth of the volcano itself is a very extreme environment. As magma bubbles to the surface, there are explosive interactions with surrounding sea water and temperatures are cranked to 13°C higher than neighbouring regions. The belching of noxious gases (carbon dioxide and sulphur, for example) turns the ocean acidic, and caustic bubbles can irritate and burn unexposed skin (Phillips et al, 2016).

I Will Survive!

Thanks to it's secluded location and violent nature, we still have a lot to learn about this fascinating habitat, but as our technology is developing, we are now able to start to get a glimpse right inside the belly of the beast... And scientists have now taken samples and recorded footage around and within this active crater (Phillips et al, 2016).

The Kavachi submarine volcano continuously spews steam, magma and caustic gases into the surrounding water (Image Source: Phillips et al, 2016)

We have now learned that there is actually a very complex community of life surviving and thriving in this extreme habitat, thanks to "chemosynthetic" bacteria at the bottom of the food chain, that are able to create energy from sulphur or carbon dioxide. These "extremophile" micro-organisms can withstand the extreme heat and acidic conditions, and form dense orange and white mats around the bubbling vents (Phillips et al, 2016).

These communities support higher "trophic levels" in the food chain; nourishing scavengers and filter feeders, which are, in turn, eaten by higher predators. So amazingly, this incredibly harsh place is actually home to a myriad of "zooplankton", "tunicate" worms, and many small fishes, like bluefin trevally (Caranx melampygus) and snapper (Lutjanus species) (Phillips et al, 2016).

Scientists have spotted silky sharks around the Kavachi underwater volcano (Image Source: Phillips et al, 2016)

And, yes, believe it or not, scientists have found that even some sharks are able to live in this hostile place! Video footage has revealed two species: silky sharks (Carcharhinus falciformis) and scalloped hammerheads (Sphyrna lewini) can be found swimming around the crater.

Scientists can't be sure how these sharks can withstand these conditions or how long they would be able to survive in such a harsh place, but it does give us a hint about how tough they really are (Phillips et al, 2016).

Sea Change

If these sharks are able to withstand such turbid water, high temperatures and extreme acidity, this gives us a glimmer of hope that at least some species may be able to withstand the conditions that are expected to arise because of climate change (Phillips et al, 2016; Zemah-Shamir et al, 2022).

Being able to withstand the acidity and heat around a volcano gives scientists hope that some sharks may be able to cope with the harsher conditions associated with climate change (Image Source: Phillips et al, 2016)

Scientists anticipate that by 2100 our oceans will have warmed by +4°C, and additionally, increased atmospheric carbon dioxide dissolving into the water will make our oceans increasingly acidic and "hypoxic" (low in oxygen). Experts project expanding "dead zones" a global drop of some −0.4 pH into acidity by 2100. To learn more about this problem check out How Low Can You O?

We already know of innumerable impacts that climate change will have (and is already having!) on shark behaviour and ecology (see Gut Punch, Climate Week and Pickled Eggs for more information). However, if sharks are, to some degree, able to tolerate conditions far harsher than these inside the Kavachi volcanic crater, there can maybe be some small hope that they may be able to withstand the rapid changes in our oceans as a result of climate change. Only time will tell, but I'll take good news wherever I can get it! (Phillips et al, 2016; Zemah-Shamir et al, 2022).

References

Phillips B, Dunbabin M, Henning B, Howell C, DeCiccio A, Flinders A, Kelley K, Scott, J, Albert S, Carey S, Tsadok R & Grinham A (2016). Exploring the Sharkcano": Biogeochemical Observations of the Kavachi Submarine Volcano (Solomon Islands). Oceanography, 29:4. Access online.

Zemah-Shamir Z, Zemah-Shamir S, Scheinin A, Tchernov D, Lazebnik T & Gal G (2022). A Systematic Review of the Behavioural Changes and Physiological Adjustments of Elasmobranchs and Teleost’s to Ocean Acidification with a Focus on Sharks. Fishes, 7:2, 56. Access online.

By Sophie A Maycock for SharkSpeak