Catching up with the Sea Empress Oil spill
On February 15th, 1996 at 8 PM, the Sea Empress oil tanker ran aground just off the coast of Pembrokeshire in Southwest Wales. In the week that followed, 70,000 tons of North Sea light crude oil spilled out and it affected 120 miles of shoreline and some of the UK's most important and biodiverse coastal habitats. The oil killed tens of thousands of sea birds and affected 26 protected areas known as Sites of Special Scientific Interest or SSSIs. I went to West Angle Bay, one of the worst hit beaches to meet local ecologist, Robin Crump, to find out more about how the coastline is getting on, 14 years after spill...
Robin - Well, if you look on the underside of this stone, you'll see that there are two starfish here. One is the big green one which is Asterina gibbosa, the common one and it's commonly found on the shore. And then there's a little tiny one here. Can you see? It's dark green with a chocolate brown substar on the back. This is a very rare species called Asterina phylactica and a colleague and I described it as a new species in 1978. You can imagine how I felt when I came down here the morning after the spill and found these rock pools completely covered in 10 centimetres of North Sea crude oil. All the pools were affected. The upper shore pools were almost pure oil. The ones with the starfish in had a surface layer of oil which completely covered them and I really thought they'd all be killed. In fact, something strange happened. Only the small Asterina phylactica, the rare one, turned out to be very susceptible to oil and all but five died. By June, we could only find 5 animals left. Whereas, only the baby Asterina gibbosa died and the adults of Asterina gibbosa, the common one, then laid eggs and it was a huge population explosion. So one benefited from the oil and the other one was almost wiped out. Now this Asterina phylactica is very rare and at that time there were only 6 sites for it in Britain. We were very concerned to try and ensure that it survived and so I carried on monitoring the pools every month. In June after the spill, I took one animal which was sitting on eggs, it already laid its eggs and was brooding them, took it on its stone into the lab. It hatched out 50 babies. I put them back and it's never looked back. The species now is more common than it was before the spill, just with a little help from its friend. Asterina gibbosa interestingly, as the numbers of Asterina phylactica grew to nearly a thousand, gibbosa became less and less common and there is intense competition between these two species for space on the shore. But at least the species have survived at this site. And because it became quite famous over the oil spill, people have looked for it elsewhere and there are now 20 or 30 sites for it in Britain.
Helen - So Robin, you know these shores probably better than anyone else. You've been here, studying these shores for decades but you were also here to study the changes after the oil spill, and quite an interesting story unfolded and an essential character were these chaps, the limpets. Can you tell us more about that?
Robin - Well that's right. We often called a limpet 'the rabbit of the shore' because limpets graze across the surface of the rocks. You can actually see their feeding marks here on the rock, the zigzag trail of scratches where they're scraping off the algae. Now, they're also very susceptible to oil. They're not generally killed by it but it sends them to sleep. So they relax their hold, fall of the rocks, and then either the gulls come down and eat them - oyster catchers had a field day! - or they get washed away by the waves and die that way. There was a huge mortality of limpets here at West Angle Bay. It was the most important effect of the spill from an ecological point of view because once you remove the limpets it gives free reign for the seaweeds to grow. This shore you're looking at here, if you look along, you'll see it's grey-white now with limpets and barnacles. But six months after the spill, it was completely covered in green algae which had come in and there were just not enough limpets left to eat it off. The next year, in came the brown algae and you had a lovely thing called Fucus versiculosis variety linearis, the bladderless bladder wrack, which covered the whole shore, all the way through the middle shore and that of course then acted as a habitat for other animals. So you've got flat periwinkles, and other things which never normally grow on these exposed outer shores in Pembrokeshire, suddenly coming in and invading this new ecosystem. So by removing one keystone species, the limpet, you actually affect the whole ecosystem.
Helen - But the limpets came back?
Robin - Oh yes! Well limpets have planktonic larvae and so, the next year, once the oil had been washed up more or less by the waves, then you got a resettlement of young limpets coming in. But another interesting thing was that the few limpets that had survived grew to enormous size because they had a huge amount of food each. Normally, they're kept small because they're half starved but because there was so few of them, they got to - well some of the biggest limpets in Britain - 7 centimetres long! But then you had a lot of young limpets coming in, settling in amongst the base of the seaweed. After about 4 years, the seaweed dies anyway of old age and is smashed off the rocks by the waves and then the limpets begin to grow and grow, and now, we're back to a situation where most of the limpets here you'll see are quite small, perhaps only 2 centimetres long.
Helen - So with your expert eyes, can you look at the shore and see a fingerprint of the oil spill or does it really look much as it did 14 years ago before this all happened?
Robin - It's quite incredible to me, the way the shore has recovered. I'll be honest, when I stood here 14 years ago, I thought it was the end of my teaching career here because we use this all the time. Not a bit of it. In fact in some ways, the shore is almost richer now than it was, for some species, than it was before the spill. Generally speaking, looking around you, the shore looks very much as it did before the spill happened. Having said that of course, we don't know about genetic effects on organisms or possibly tiny trace elements of poisons which may still be in the system, but to the naked eye, and to an amateur biologist like me, it looks just as good as it's ever done.
Helen - Well it was really good to see how thriving the coastline is after such a potentially dreadful disaster. And actually, a lot of people are saying it was really lucky that things weren't an awful lot worse. That was Robin Crump, former Head of the Orielton Field Research Centre in Pembrokeshire, introducing me to some of the survivors of the Sea Empress Oil Spill.
Find out more
Robin Crump et al (2003).
West Angle Bay: a case study. The fate of limpets. Field Studies. (PDF)British Marine Life Study Society information about the Sea Empress oil spill