While the team, co – lead by Dr. Sandra Brooke (above) and Dr. Steve Ross, is out on the water, we will mark the six month anniversary of the BP Deepwater Horizon oil spill. Drs. Brooke and Ross are part of an independent team of scientists studying the impacts of the spill on deep sea corals.
This is Dr. Brooke’s blog:
Day 1 (15th October)
We set sail yesterday in the late evening in slightly choppy seas and headed out to our first dive site, Viosca Knoll 826, probably the best studied deep coral reef in the Gulf of Mexico. This is a good location for comparison of pre and post oil spill since we already have so much baseline data on the reef communities and the corals themselves.
The first task on station was to deploy our Benthic Lander; this is a metal frame with a heavy weight and an array of floats that we use as a platform for a variety of instruments and experiments. The instruments will collect data on temperature, oxygen, turbidity and current speed over a 12 month period, will tell us how the physical environment varies over time. There is also a revolving sediment trap that will collect particles falling through the water column every month for a year. This gives us some idea of the food flow to the animals on the reef.
Since this is the spawning period for the reef building coral Lophelia pertusa, we have specially treated plates hanging on the Lander to try and assess coral larval settlement. Finally there are three Plexiglas chambers, each holding three coral fragments that are stained pink. After a year, the new growth (which is white) will be visible and can be measured. We have pre-spill data on coral growth rates so this will be a post-spill comparison.
The Lander was deployed just before lunch (which was delicious!) and the Deepworker was launched in the early afternoon with the objective of finding the Lander, making sure it was properly positioned and that the corals were happy. Unfortunately we didn’t find it this dive, but we’ll try again tomorrow.
Day 2 (16th October)
Today was another sunny slightly choppy day, with a nice breeze. We launched the Deepworker in the morning and an hour later it found the Lander, safe and upright with the corals seemingly doing fine.
This was a relief since there is a lot of time and funding invested in these instruments and experiments. So far so good, but it will be even more of a relief to get it back next year!
The submersible continued surveying the reef nearby, which was a low lying series of hummocks capped with Lophelia colonies and dense carpets of small black corals. We had never seen anything quite like this site, but it appeared to be healthy and thriving.
As we watched the high definition video footage after the dive, we were surprised to see a small fish swim close by an anemone and disappear. There ensued a battle between the struggling fish and the anemone which seemed unwilling to relinquish its lunch. As we drifted on by, it seemed the poor fish was losing the fight.
A little further on we saw three squat lobsters, each gnawing on a mid-water salp. This certainly seems like a bad place to be for a small pelagic animal.
Day 3 (17th October)
The deepworker had some problems today and we could not do the deep dives we wanted, so we changed our plans and headed for a shallow site called Alabama Alps. This is a large rocky feature just 5 miles up slope from Viosca Knoll in approximately 100m.
This kind of depth is known as the ‘twilight’ or mesophotic zone, where light is dim but may support some photosynthesis.
The species of stony corals that live at these depths either have specialized zooxanthellae or can live without them. The visibility at this site was pretty miserable (less than 4 m for the most part) so we were fumbling around a little.
The Alabama Alps are aptly named; they are giant jagged boulders over 20m tall that pop up out of nowhere. They are covered in soft corals, black corals and some stony corals, we saw many different fish hiding in the crevices. Some of these were Caribbean species such as angel fish, and like red snapper and amberjack are common in the Gulf of Mexico.
This was a very lush and rugged habitat and would have been a spectacular dive if visibility had been better, but it was a little stressful creeping though the gloom waiting for the next wall of rock to pop up in front of the sub.
The good news is that nothing had apparently been impacted by the oil. There was no obvious impact to the dense sessile communities on the rocks and there were lots of different fish visible.
There was a lot of ‘marine snow’ in the water column, but it is hard to tell whether or not this is normal. The trouble with measuring subtle impacts on little studied systems is that we have limited understanding of baseline conditions.
These data should have been collected years ago, but it is not too late to start, especially with the recent harsh reminder of potential environmental disaster, and the specter of climate change snapping at our heels.
Day 4 (18th October)
We managed a good dive today on one of our Viosca Knoll sites; it is the shallowest of these deep coral sites, and is a little different from the others.
There are isolated colonies of Lophelia on large carbonate blocks, but they do not form the tangled thickets here that we see in many deeper places. This area has lots of large fish including schools of Barrelfish that cruise around the large blocks.
We traversed the areas that we have studied before the spill and nothing seems amiss, but we will continue to collect samples to analyze for sub-lethal effects.
Day 5 (19th October)
Today we were accompanied by a pod of dolphins as we were waiting for permission to descend. They did not follow us far into the depths, but we could hear their clicks and whistles for quite a while.
We reached the bottom, but the dive was shortened because the communication with the sub was not stable. We saw the base of the reef and were just reaching the really dense area at the top of the mound when we were ordered to the surface – like reaching the doors of Disneyworld and finding it was closed! Very unfair, but we’ll try again tomorrow.
Day 6 (20th October)
Today’s dive was fantastic. We saw a Manta Ray on the surface and it was so large, it was still quite visible at 400ft. This is the first time I have seen one in the wild, and they are quite impressive.
The coral mound we dove on was quite small but very lush with large Lophelia colonies and dense patches of fluffy-looking black corals. As in previous dives we saw no signs of damage from the oil spill.
The coral polyps were open and there was a fantastic abundance of life around the reef with all of the expected fauna present and apparently in good health. We saw squat lobsters feeding on animals that are usually in the water column, but obviously ventured too close to the reef. We even saw an anemone snatch a small fish that wandered too close. The reef is a dangerous place to be if you are small and tasty!
Todays dive was the last unfortunately; the sub team noticed a small crack in the plexiglass dome of the Deepworker so that was the end of operations. Although this is disappointing, its not worth risking two lives and a million dollar sub. We will pack up everything tonight in preparation for unloading tomorrow, say our goodbyes and head off home.
It’s always bittersweet at the end of a cruise; you get to know people pretty well in a short space of time and most of them you never see again. On the other hand, cruises are hard work and long days with no day off and it always nice to go home.