News
Fish On Acid Lose Fear Of Predators
Coral reef fishes exposed to acid oceans lose their sense of smell – and their sense of caution – and are more likely to fall prey to natural enemies, according to new research in Nature Climate Change.
The finding is based on observations of the behaviour of four species at a reef off the coasts of Papua New Guinea where natural carbon dioxide seeps out of the rock, and confirms a series of other such studies in the last year.
A cool volcanic discharge in the reef has served as a natural laboratory for years: water in the region reaches an average pH of 7.8. This standard measure of acidity is co-incidentally the level predicted for all the world’s oceans by 2100, as atmospheric carbon dioxide levels continue to rise, according to the Intergovernmental Panel on Climate Change.
Australian and US scientists observed the fishy behaviour from a boat moored above the reef, and also tested the fish on board the vessel. What they observed was that, away from the volcanic bubbles of carbon dioxide, in conditions of more normal ocean chemistry, damsel fish and cardinal fish seemed able to smell predators and stayed in sheltered places in the reef to avoid becoming prey.
Fish from the waters richer in carbonic acid seemed not to sense the presence of predators, and were more likely to venture into dangerous waters.
After a sudden scare that sent all the fish racing for cover, the fish from the bubble reef ventured forth much sooner. In normal circumstances, such fish spend 80% of their time under cover.
The bubble reef fish spent at most only 12% of their time in hiding. Mortality accordingly was five times higher.
“Their sense of smell was acutely affected in CO2-rich waters in ways that gravely threaten their survival,” said Alistair Cheal of the Australian Institute of Marine Science.
“We were able to test long-term realistic effects in this environment,” said another author, Danielle Dixson of the Georgia Institute of Technology in the US. “One problem with ocean acidification research is that it’s all laboratory-based, or you’re testing something that’s going to happen in 100 years’ time with fish that are from the present day, which is not actually accurate.”
The reasoning is that the change in pH levels disrupts a neuroreceptor in the fishes’ brains and affects faculties or alters behaviour. Similar experiments with Californian rockfish have demonstrated much the same effect.
But increased acidification of the oceans is also likely to affect shellfish and corals in other ways, and research in the Great Barrier Reef region of Australia has documented a dramatic behaviour change in a jumping snail that suggested impaired decision-making capability as pH levels alter.
Sea water is already 30% more acidic that it was at the start of the Industrial Revolution 200 years ago. The rate of change is at least 100 times faster than at any time in the last 650,000 years.
The bubbling waters of the reef under test are not unique – such localized carbonic acid seeps occur in many places all over the world – and the fact that predators might find easy pickings in such places makes no real difference to population levels in the vastness of the rest of the ocean. But such experiments raise the question: can ecosystems adapt to changing water chemistry?
“Continuous exposure does not reduce the effect of high CO2 on behaviour in natural reef habitat and this could be a serious problem for fish communities in the future when ocean acidification becomes widespread as a result of continued uptake of anthropogenic CO2 emissions,” the authors conclude.
Source: www.truthdig.com
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Jake Davies boards Ghazala Explorer for an unforgettable Red Sea diving experience…
Overnight, the wind picked up, making the planned morning dive a bit bumpy on the Zodiacs to the drop point on Thomas Reef. There, we would dive along the reef before descending through the canyon and then passing under the arch before ascending the wall with a gentle drift. The site provided great encounters with more pelagic species, including shoals of large barracuda, tuna, and bigeye trevally.
Once back on the boat, it was time to get everything tied down again as we would head back south. This time, with the wind behind us, heading to Ras Mohammed to dive Jackfish Alley for another great gentle drift wall dive before then heading up the coast towards the Gulf of Suez to moor up at the wreck of the Thistlegorm. This being the highlight wreck dive of the trip and for many onboard, including myself, it was the first time diving this iconic wreck. I had heard so much about the wreck from friends, and globally, this is a must on any diver’s list. Fortunately for us, there was only one other boat at the site, which was a rarity. A great briefing was delivered by Ahmed, who provided a detailed background about the wreck’s history along with all the required safety information as the currents and visibility at the site can be variable.
Kitting up, there was a lot of excitement on deck before entering the water and heading down the shoreline. Descending to the wreck, there was a light northerly current which reduced the visibility, making it feel more like the conditions that can be found off the Welsh coast. At 10m from the bottom, the outline of the wreck appeared as we reached the area of the wreck which had been bombed, as our mooring line was attached to part of the propeller shaft. Arriving on deck, instantly everywhere you looked there were many of the supplies which the ship was carrying, including Bren Carrier tanks and projectiles that instantly stood out.
We headed around the exterior, taking a look at the large propeller and guns mounted on deck before entering the wreck on the port side to take a look in the holds. It was incredible to see all the trucks, Norton 16H, and BSA motorcycles still perfectly stacked within, providing a real snapshot in time.
Overall, we had four dives on the Thistlegorm, where for all of the dives we were the only group in the water, and at times, there were just three of us on the whole wreck, which made it even more special, especially knowing that most days the wreck has hundreds of divers. Along with the history of the wreck, there was plenty of marine life on the wreck and around, from big green turtles to batfish, along with shoals of mackerel being hunted by trevally. Some unforgettable dives.
The final leg of the trip saw us cross back over the Suez Canal to the Gobal Islands where we planned to stay the night and do three dives at the Dolphin House for the potential of sharing the dive with dolphins. The site, which included a channel that was teeming with reef fish, especially large numbers of goatfish that swam in large shoals along the edge of the reef. These were nice relaxing dives to end the week. Unfortunately, the dolphins didn’t show up, which was okay as like all marine life they are difficult to predict and you can’t guarantee what’s going to be seen. With the last dive complete, we headed back to port for the final night where it was time to clean all the kit and pack before the departure flight the next day.
The whole week from start to finish on Ghazala Explorer was amazing; the boat had all the facilities you need for a comfortable week aboard. The crew were always there to help throughout the day and the chefs providing top quality food which was required after every dive. The itinerary providing some of the best diving with a nice mixture of wreck and reef dives. I would recommend the trip to anyone, whether it’s your first Red Sea liveaboard in the Red Sea or you’re revisiting. Hopefully, it’s not too long before I head back to explore more of the Red Sea onboard Ghazala Explorer.
To find out more about the Northern Red Sea reef and wrecks itineraries aboard Ghazala Explorer, or to book, contact Scuba Travel now:
Email: dive@scubatravel.com
Tel: +44 (0)1483 411590
Photos: Jake Davies / Avalon.Red
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