Introduction to ecosystems
Introduction to ecosystems

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Introduction to ecosystems

5.4 Conserving a rare species

The fen-raft spider (Dolomedes plantarius) was only discovered in the UK in 1956. It is very rare and its distribution prior to 1956 is not known. This throws up some interesting questions about a re-introduction programme, since the habitats into which spiders are released may – or may not – have originally had the spider in.

Think about the implications, before watching the next video and learning more about the re-introduction programme.

Habitat restoration and managed re-introduction are two techniques that are key to conserving individual species. The fen-raft spider is an endangered species, as Dr Helen Smith and Chris Sperring explain in the video.

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Conserving a fen species

INTERVIEWER
Well, what a glorious autumn day here in the county of Suffolk. I'm actually on the open marshland of the Suffolk Wildlife Trust nature reserve of Carlton Marshes. And I'm actually here for a spider. And the person that's going to introduce me to these spiders is Helen Smith. Helen, what is it you're actually doing?
HELEN SMITH
Well, today, we are putting out some tiny fen raft spiders on the ditches on this reserve to start to set up a new population. This is one of Britain's rarest, biggest, most beautiful spiders. It occurs in only three places in the wild in the UK. And we're just starting work on Natural England's programme of introducing it to new sites to try and secure its population in this country for the future.
INTERVIEWER
So did this area, Helen, did it ever have fen raft spiders in big numbers?
HELEN SMITH
Well, we don't know the answer to that. We're never going to know the answer to that. They weren't discovered in the UK until 1956. I think we just have to make some sensible assumptions based on the current distribution, which is here in Suffolk, down in Sussex, and across in Wales; and a species that relies on clean, lowland wetlands. And we know what's happened to the majority of our clean, lowland wetlands. So I think it's almost inevitable that we've lost the species from large areas of Britain.
INTERVIEWER
Why choose this particular site, not any other site around? What's particularly good about this site for them?
HELEN SMITH
This site is part of the Suffolk Trust's move to try and connect back together a lot of its wetland nature reserves along the lower Waveney, creating huge areas for wildlife. And so introducing spiders here, and we're also introducing them to another site a bit upstream, is a first step, stepping stones if you like, to start to create a much bigger joined-up population and utilise that big network that the Trust are creating. But we've been working towards the translocation programme, really, for the last five years, very much starting to look at what sites would be suitable and actually how to achieve it in practice.
INTERVIEWER
Have you actually released before? Is this the first of the releases?
HELEN SMITH
No, we started last year. We released at a site just upstream from here. And just in the last few months, we've been starting to see the spiderlings looking fabulous out there on the water soldier over there, stripes gleaming in the sun.
INTERVIEWER
So a real success?
HELEN SMITH
Yeah, very--
INTERVIEWER
A real success--
HELEN SMITH
--every time we see one there.
INTERVIEWER
--especially after the winter we had.
HELEN SMITH
Yeah, no, it's just so exciting every time see one, particularly when we find a new ditch with one on. They look so at home.
INTERVIEWER
Well, Helen, you've just got out of the tub a full adult live raft spider. What a beautiful specimen.
HELEN SMITH
Yeah, she's fabulous.
INTERVIEWER
She's very dominantly, kind of, like a muddy brown, isn't she? Sort of like an estuary brown--
HELEN SMITH
Yes.
INTERVIEWER
--with these two very distinctive bands going around either side of the abdomen?
HELEN SMITH
--and the thorax.
INTERVIEWER
--and the thorax.
HELEN SMITH
Yeah, sort of like "go faster" stripes, really. They're sort of goldie-colored now. But often, in the younger spiders, they're brilliant white on a black background.
INTERVIEWER
What's the difference between the male and the female?
HELEN SMITH
Well, nothing really until they're sort of penultimate moult when they become sub-adult. And then suddenly, the male starts to acquire clubbed ends to his palps, which become the insemination organ in the adult.
INTERVIEWER
Is it true they go underwater as well?
HELEN SMITH
Yeah, absolutely. They spend quite a bit of time underwater. So sometimes it's an escape response from predators. So while I'm monitoring them on Redgrave and Lopham Fen, I get in the water and work with them there. And some spiders will go straight underwater as soon as I get in. But you can often see them there because the hairs on their body trap air, and so they look glistening silver underwater. But they also hunt underwater. So they'll catch sticklebacks and water boatmen underwater.
INTERVIEWER
So this is the adult. Now, what about the young ones?
HELEN SMITH
The young ones look exactly the same, just brighter and miniature.
INTERVIEWER
Now, we can hear you rattling around there. What you're actually carrying, what looks like, well, it's a plastic tray. And inside that plastic tray, it looks like hundreds of test tubes.
HELEN SMITH
Well, it is hundreds of test tubes. We've got about 600 tiny spiders to put out here today. These are basically the babies of spiders taken from Redgrave and Lopham Fen in June, with the egg sacs. So they hatch their egg sacs. We potted up the spiderlings into individual tubes to stop them cannibalising each other. And they're being fed in those tubes, so we can get very, very high survival rates that way. So we've bred something like 2,500 baby spiders this year. So that's me working with lovely collaboration with several UK zoos. And the other really big contributors are volunteers who make a huge difference to this project, some that's really carried me through some dark days of this project.
INTERVIEWER
So how do you actually rear a spiderling?
HELEN SMITH
Well, it's quite easy really. I mean, once they're about a week old, which is the stage where they'd normally leave their nursery, they go into the test tube with damp cotton wool in the bottom. And we have to get fruit flies in there for them on a very regular basis.
INTERVIEWER
So they really do spend their early life in these tubes.
HELEN SMITH
Yeah, they do.
INTERVIEWER
They're not just being transported today?
HELEN SMITH
Yes
INTERVIEWER
So Helen's got a group of test tubes in her hand there. And she's checking them over very thoroughly, I must add. Helen, why are you checking them out thoroughly?
HELEN SMITH
Well, I want to be quite sure that nobody's in the process of changing their skin because they usually attach themselves to the lid. And just before, during, and just after skin changing, they are very vulnerable because they're so soft. And things can go wrong if you disturb them at that stage. But this lot look fine. And you can just see the little shed skins in there from the last time they did it. You can actually see the white stripes on the shed skins.
INTERVIEWER
Yeah.
HELEN SMITH
So the tubes are strung together with lines of masking tape. And I do it that way so that they're well-spaced out as they leave the tubes, rather than ending up in the heap where--
INTERVIEWER
So Helen's undoing the top of the test tubes. I'm looking inside one of these tubes at the moment. And they really are tiny spiders. You can actually see a brown back on one of those, almost like a rusty brown back.
HELEN SMITH
Off you go.
INTERVIEWER
One's come out, lowering itself down on the thread into the vegetation. And it's off into its new world.
HELEN SMITH
It's quite nerve-wracking, the whole process, I find, you know, introducing something to a site where it probably hasn't been for a very long time. And however carefully you follow the guidelines for translocation, and we certainly do, there's always that bit of unknown out there.
INTERVIEWER
But that's good, isn't it?
HELEN SMITH
We can never be quite sure.
INTERVIEWER
You care. You don't just care, I can really hear you're passionate about these spiders.
HELEN SMITH
Well, they've lived with me for a long time. You get to like that about them. I am passionate about seeing their population restored in the wild.
INTERVIEWER
So these spiderlings now, we can see that they're making their way out quite slowly, and then lowering themselves from the tubes down into vegetation by their threads. How do they actually live on the water? How do they do it?
HELEN SMITH
At this stage, they actually spend very little time on the water. But by the spring, they will be out sitting along the water's edge. They're usually seen sitting where stems emerge from the water, often with their back legs on vegetation and their front legs on the meniscus. And they have specialised hairs in their legs and their feet. And they can detect tiny vibrations in the water surface which tell them where their prey are and where their predators are. So they're very tuned in with this sort of vibratory sensory system to living on water. And they use that system for courtship as well. So the courtship is very much based around creating vibrations on the water surface.
INTERVIEWER
Now, why do you release at this time of the year?
HELEN SMITH
Well, two reasons really. You can see these very, very tiny animals, lots of things will predate them at this stage; although as adults, they become very fierce predators themselves. But this stage, they're very vulnerable. And we know from the size of our wild populations, we can get over 90% survival rearing in this way. So we are skipping an enormous amount of the mortality that would happen in the wild.
INTERVIEWER
So they're being released now, what happens next?
HELEN SMITH
Well, the ones that don't get eaten will hibernate during the winter. And I have to say we know remarkably little about what they do in the winter. It's like looking for needles in haystacks. They're almost certainly in air spaces in hollow plant stems. Some of them could be in air spaces underwater. If you look at the Pevensey marshes in early spring, before the water soldiers come up, you see very few fen raft spiders. And a month later, they're absolutely everywhere. So once these ones, which hatched this summer, will spend next summer growing, they'll become sub-adult. Their penultimate skin change next autumn. And then the following spring, they'll mature into adults and breed during that summer and die at the end of it.
INTERVIEWER
So we're not just talking about the release of these. There's some quite intricate monitoring going on as well, isn't there?
HELEN SMITH
Yes, very much so. So we're monitoring both the populations of the new spiders, and something very much that volunteers are helping with increasingly, which is very valuable. And we're also doing genetic monitoring of the new population. So we're looking at what's going out and, genetically, what of that we retain over time.
INTERVIEWER
Presumably when you're doing that work as well, you're finding out that you haven't got a subspecies.
HELEN SMITH
Yes, no evidence at all of any barriers to breeding. We looked at breeding. And we looked at mating behaviour, courtship behaviour. We looked at survival of the young. We looked at the number of offspring produced. And actually next year, we're going to look at the F2, the next generation as well, just to be doubly sure.
INTERVIEWER
Is there a problem releasing another predator, another spider predator within an environment like this?
HELEN SMITH
It's very difficult to give you a very definitive answer to that. But I think the best answer is that the places where these spiders occur in the wild now are three of our richest wetlands - very, very high diversity. And these spiders clearly fit into that ecosystem. They have a place there. They would have been there in the past.
INTERVIEWER
This area here looks very similar to the area I come from, which is the Somerset Levels. What's the chances, Helen, of me having a few spiderlings to take back?
HELEN SMITH
One thing that we're going to be doing in the next few years is looking for additional sites for reintroductions. The action plan for this species suggests 12 sites in the UK by 2020. We're currently looking at six sites now. We're certainly going to start to look at some of the inland fens because of concerns that these broadland sites are going to be gradually salinised as sea levels rise.
INTERVIEWER
How long the monitoring go on for?
HELEN SMITH
I think monitoring needs to go on almost indefinitely for species as rare as this. These are animals which are so rare, they should be being monitored on a very regular basis. The action plan for this species has a 2020 target. If we're going to achieve that target, I think the programme will have to go on probably until 2020, but the monitoring very much longer. And the habitat here has been through bad patches in the post-war years. A lot of these fields have agriculturally improved. The ditches became eutrophic. And now, as you can see, they're being beautifully restored by the Trust. And so to have one of the species that have been lost back here, I think it's just very appropriate.
INTERVIEWER
: So we're not only talking about - earlier, we were talking about joined-up habitats, the fact that there's more habitats going to be created that are like this, we're also talking about joined-up spiders.
HELEN SMITH
Yes, joined-up spiders. And I think that it adds enormous point to the translocation. I think if we were introducing to a few more tiny isolated sites, I would see that as having much less future and being much less worthwhile than being able to bring them somewhere like this, where we know that if they do well, they can move out through these ditch networks over a huge area of the Norfolk Broads eventually.
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Figure 2 The fen raft spider (Dolomedes plantarius)
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