Underwater Seeps in the Sangihe Islands

Image: Carbon dioxide bubbles seeping out from crevices in the rock



Seascape of an underwater seep


The Catlin shallow reef team has been cruising through the Selebes Sea off North Sulawesi, Indonesia, after finishing up surveys in Bunaken National Park.  On our way to the terminal island of Sangihe, we made a special stop at Mahangetang Island to photograph the ‘underwater volcano’, also known as a seep, just offshore.  Sitting on the Ring of Fire, the Indonesian Islands were largely formed by volcanoes and these tall, steep, verdant mountains jut from the ocean skyward.  The same can be found underwater.  Beneath the undulating waves, there is a bluer seascape of mountains and valleys of rocks, algae, and corals.  Occasionally, as with the one we visited off Mahangetang, these pinnacles are geo-thermally active with bubbles streaming from the holes and crevices in the rock.  There are even vents where hot spring-worthy water courses out and mixes with the surrounding cooler water.



Carbon dioxide and the ocean


The seep itself is coated in a rusty, fuzzy algae that tinges the rocks red-orange.  There is little coral on the top, likely because of increased acidity from the CO2 bubbles which makes calcification of corals more difficult.  This could be a snapshot of the future of coral reefs as carbon is pumped into the atmosphere through the burning of fossil fuels.  The increased concentration of CO2 in the atmosphere slowly enters the oceans, gradually acidifying them. 




What we can learn


Even if the burning of fossil fuels ceased tomorrow, the oceans would continue to acidify slowly with the amount of CO2 already present in the atmosphere.  With this committed acidification, it is important to understand the effects on calcifying marine organisms such as corals.  Professor Sophie Dove from the University of Queensland has been running experiments on Heron Island Research Station testing out different climate scenarios including acidified waters on mini-reefs in large aquaria.  She is also beginning a project at a seep in Papua New Guinea studying the corals in the naturally acidified waters.  These seeps are unique and potentially provide a glimpse into the future of coral reefs.  Corals are still around, so let us keep it that way.