Ocean Stories: Data from the Twilight Zone
July 12, 2018
By Mae Dorricott
With my face glued to the car window, mouth agape, making “ooos” and “aahhhs”, I kept my colleagues Vaughn and Kayem well amused as they drove myself and Sonia through the stunning scenery of Pohnpei to Nihco Marine Park. This place was to be our base and home for Sonia’s annual expedition to explore the twilight zone of Pohnpei and sister atoll’s reefs.
I was invited along on the expedition by Dr. Sonia Rowley, one out of three people to win the David Attenborough Award for field work. She is well deserving of this award as her research in the twilight zone takes her to depths of 140 m, the area of the reef where light begins to dwindle away.
With the use of rebreather technology, she is able to go to these depths which few would fathom of going to let alone be able to collect data from. It is a cross section of the ocean that is poorly studied – too shallow for remotely operated vehicles (ROVs) and submersibles and way too deep for normal scuba diving.
It is the gorgonian (sea fans) that lure her down to these incredible depths. They are her muse, and as the topography of the reef and life parameters begin to shift descending the reef wall, the gorgonians begin to dominate. Their branching skeleton reaches out from the rocky walls and into the water column to benefit from the passing currents sweeping nutrients their way. Not only do these organisms provide the perfect excuse for Sonia to push her own limits, but they highlight the unknowns. How can such an animal be so successful in such dynamic environment over geological time? Even the sole fact that these beautiful ornamental creatures have evolved deeply fascinates Sonia, and what better way to understand them, than in their home? To dive to such depths takes six hours, however, her dedication was rewarded by surfacing from most of her dives holding a new species.
It’s quite impossible to try to define the work that Sonia does as it manages to cover every aspect of marine biology from evolution, ecology, molecular and behaviour. It was truly inspirational to see this woman in action. She looked like a space rover with countless tools clipped onto her for the multiple experiments and data collection she would conduct. So, myself and another visiting scientist on the trip decided to make an acronym for SONIA (Sub Observing Nearly Into the Abyss). And every time she descended into that enticing deep blue we would shout “Deploy the SONIA”.
As a newbie to rebreather diving I was limited to 30 meters. Even at this depth, peering over the reef wall, I could already start to see the habitat shift from hard stony corals to the delicate branching organisms, such as gorgonians and sponges.
As we prepared for a dive at one of the atolls, a two hour boat ride out from Ponhpei, Sonia showed me footage of the site she took from the previous year. It looked stunning; a pristine atoll reef, almost like coral castles in a fairy tale land with schools of reef fish gliding through this wonderland. I couldn’t wait to jump in! But I didn’t even have to put my face underneath the water before my heart began to sink.
The waters of Pohnpei were so clear you could see the reef at 20 meters. But, there was no colour. No fish. As we dived down and got closer we saw a mummified coral reef. Just after Sonia had left the year before, this area had suffered from the highest increase in water temperature in the Pacific. The coral had bleached, displacing their algae counterpart, losing their colour and a primary source of energy production. And because it was so hot so fast, the crustose coralline algae, which normally cements the reef together had grown over everything. You could see the polyp structure of the corals beneath this thin embalmment that the coral could not be resurrected from.
When speaking to the coral researchers who joined the expedition from James Cook University, they told me that the crustose algae is the perfect substrate for baby corals to colonise, and so there is hope that in a few years time, the reefs on the atolls will be back. IF, nothing else happens.
However, the “IF” is large. Reefs are tenacious, but they can only deflect so many stressors.
If the reefs avoid being totally munched by the high number of crown of thorns we saw about on the reefs, then they still have to contend with the fact that there is a huge lack of fish on the reef due to overfishing. As we drove out of the lagoon to the dive sites, we would pass the ominous threat of international fishing vessels with their huge nets, who were fishing in the Micronesian waters for tuna and other commercially targeted fish species. What made this sight worse was the fact that none of the fish caught on these boats would make it back to the people of Pohnpei. Instead they would be transported all the way back to China, Japan, and Korea in tin cans.
With a big hole in the food chain created by commercially targeted species, who would normally graze away at the algae, being removed, the algae has nothing to hold it back. So, areas of reef that had not been hit by the bleaching were instead slowly being overgrown by algae, smothering them.
It was heartbreaking to see somewhere so remote become another victim of human hands. However, the effects of ocean warming, and overfishing was all in the shallow portions of the reef. Past the influence of coral bleaching, past the reaches of the fishing fleets, the deep still continues to be a haven for marine life. In a mysterious environment which few, but including Sonia could see, a magical underwater world still remains, with swirling schools of fish, sharks, stingrays and fields and fields of gorgonians.