Diversity in Rock Pools - A Marine Mesocosm
Stuart - Here we are at a medium sized rock pool. It's about half a square meter in size, about 30 centimetres deep, and first of all, what we can see is that it's literally full of marine life.
Sue - Hold on. You say literally full of marine life. All I can see is seaweed and - would this be called seaweed as well?
Stuart - Yup!
Sue - This sort of more frond-like plant?
Stuart - Yes. Don't discount the seaweed! We've got probably about 30 species of seaweed in this rock pool.
Sue - Good grief!
Stuart - We've got this large, canopy forming algae called Fucus serratus, growing on the Fucus serratus are lots of brown, slimy Ectocarpus. We've got the brightly coloured green, so we have some Ulva lactuca, some Ulva linza, we have these beautiful red algae. This is a species of Ceramium. So, for these, all these limpets and grazing snails, the molluscs, for those guys, the seaweed forms a base of the food chain. Also, the seaweed acts like a mini-forest. So if you imagine you're an amphipod or a prawn, or a crab, you want somewhere to hide so living in amongst that seaweed, the whole diversity of marine life which relies on that for shelter, somewhere to hang out, and perhaps to act as an ambush predator.
Sue - You're interested in particular in the diversity of life that's in a rock pool. Why did you choose a rock pool when you've got, even behind us, we've got an enormous amount of water and then going into the seas and going into the oceans?
Stuart - Man is having a huge impact on our oceans and our coastal waters, and that impact can have a negative effect on our biodiversity. When we lose biodiversity, that's bad in itself, but we can ask the question: "If we lose species, what effect is that going to have on the functioning of our ecosystems?" Now as a marine ecologist, to try to answer that question, it's really hard working out in the open ocean. I like to do experiments and I like to manipulate biodiversity. A rock pool such as this provides an amazing mesocosm - a mini world. An isolated body of water when the tide goes out, then I can manipulate the diversity and look at how that affects various response variables that I measure. Things like productivity and the uptake of nutrients.
Sue - When you change the diversity of rock pools for seaweed species, what did you find?
Stuart - We found that in the pools with high functional diversity, with seaweed species which were very different from each other, we've got greater productivity, and what I mean by productivity is, the seaweed grew faster. If the seaweed grows faster, it provides a lot more food for all those animals that live in the pool, the snails, the shrimps, and the fish, so we get a much more diverse and healthy ecosystem.
Sue - Did you do this with sort of any larger life forms?
Stuart - As well as looking at seaweeds, we've also looked at some of the animals that live in these pools. We can see here a number of different grazing molluscs, so we can see the typical limpets that we're all familiar with. We can see things like the common periwinkle, Littorina littorea.
Sue - Which is a common periwinkle?
Stuart - Just this one, just here. But also, a whole range of other snails that look similar to that. The question is, all these snails, these grazing molluscs look very similar. Does that diversity actually matter? So what we did in rock pools was again, we performed an experiment and we manipulated the diversity of those grazing molluscs. Here, we looked simply at the ability of the rock pool to go from a very bare area. We cleared the rock pools first and then for all seaweeds, those diverse seaweeds to grow.
Sue - And what did you find?
Stuart - What we found with it, the actual number of species didn't matter. It was certain key species which had a much larger effect on the amount of food eaten and other species, in particular, the limpet that we can see just here. What that says in terms of our biodiversity research, is that it's important to understand what species do. The number of species is important, but actually the functioning is important. And that, to me, means that natural history is really, really important in understanding the ecology of this rock pool, or if we look out to sea, the ecology of the wider oceans, or any marine habitat.
Sarah - Fantastic! There was just so much diversity and science, looking in even the most modest rock pool. That was Bangor University's Stuart Jenkins, dipping into the biodiversity of the rock pool with Planet Earth podcast presenter, Sue Nelson.