0:00:02 > 0:00:04This ferry makes 23,000 crossings
0:00:04 > 0:00:07between Strangford and Portaferry every year.
0:00:07 > 0:00:11Hundreds of thousands of people make the trip across the narrows,
0:00:11 > 0:00:16but none of the passengers gets to see what's down there, right under our noses.
0:00:18 > 0:00:20This is Waterworld,
0:00:20 > 0:00:26and this is Strangford Lough, the jewel in the crown of our coastline.
0:00:58 > 0:01:01The scenery is beguiling, and for most of us,
0:01:01 > 0:01:05the beauty of Strangford Lough is only skin deep.
0:01:06 > 0:01:10But the Waterworld expedition will reveal the astonishing life
0:01:10 > 0:01:11under this famous shore.
0:01:12 > 0:01:17Joe Breen is a scientist with the Environment And Heritage Service.
0:01:17 > 0:01:20He is leading our expedition in search of horse mussels,
0:01:20 > 0:01:24also known by their scientific name, modiolas.
0:01:24 > 0:01:26You've got to see mounds surrounded by mud,
0:01:26 > 0:01:29and these mounds are actually mounds of horse mussels,
0:01:29 > 0:01:32not very interesting in themselves, but the fact is they make
0:01:32 > 0:01:35an artificial reef called a biogenic reef, and a hard substrate
0:01:35 > 0:01:39onto which other animals can attach, and also come and live within.
0:01:39 > 0:01:42So you're going to see the brittle stars, feather stars,
0:01:42 > 0:01:45sea cucumbers, anemones.
0:01:45 > 0:01:48We've located a site which is about 20 metres, and we're going to go to that.
0:01:48 > 0:01:50Now, in this big vessel we're sitting in now,
0:01:50 > 0:01:51we can't go anywhere near these beds,
0:01:51 > 0:01:54because if we put an anchor down, we're going to do a lot of damage.
0:01:54 > 0:01:56So, we're going into the smaller boat.
0:01:56 > 0:01:58We'll go over, there'll be a light shot put down.
0:01:58 > 0:02:00That boat won't anchor out of.
0:02:00 > 0:02:03We'll just roll out over the side, down the shot, and do the dive.
0:02:03 > 0:02:05And hopefully, we'll be on mussel bed.
0:02:05 > 0:02:08Possibility we may not. That's the problem, you know.
0:02:08 > 0:02:11Only 20 years ago, 15 years ago,
0:02:11 > 0:02:14these mussel banks were all over the entire lough,
0:02:14 > 0:02:17but unfortunately due to circumstances,
0:02:17 > 0:02:18I don't know, there's 5% left, possibly.
0:02:18 > 0:02:21- What happened to them, Joe? - Unfortunately, trawling.
0:02:21 > 0:02:24People just weren't aware. It's only now, with the advent of diving,
0:02:24 > 0:02:26people can get down and see this damage.
0:02:26 > 0:02:28Trawling has been stopped in the lough.
0:02:28 > 0:02:32The important thing now is to make sure we protect what we have left.
0:02:32 > 0:02:35What's the plan here? Who's going in first? Who's going in second?
0:02:35 > 0:02:40- These two go in first.- Yeah. - Then the three of us will go in.
0:02:40 > 0:02:42I'm ready for a challenging dive.
0:02:42 > 0:02:46Strangford is a dark lough, and with such a limited amount of reef left,
0:02:46 > 0:02:49it'll be tough to find the horse mussels.
0:02:57 > 0:03:01More than 20 metres down, day fades to night,
0:03:01 > 0:03:06and we discover a weird and wonderful world.
0:03:15 > 0:03:17This is just such an amazing sight.
0:03:17 > 0:03:21The bed of the sea is carpeted in brittle stars.
0:03:21 > 0:03:25And in among all of them is this,
0:03:25 > 0:03:30a fabulous creature called a sun star.
0:03:30 > 0:03:35And it's eating its own kin. It's dining on brittle stars.
0:03:35 > 0:03:37It's wonderful.
0:03:41 > 0:03:47So many starfish, so few horse mussels, and so little time.
0:03:51 > 0:03:54Unfortunately, we haven't found the horse mussel beds,
0:03:54 > 0:03:58and I'm nearly out of air, so we've got to pop to the surface.
0:04:02 > 0:04:06Surface to dive team, I understand that you are on your way up.
0:04:06 > 0:04:09If possible, could you confirm this? Over.
0:04:11 > 0:04:15The dive is almost finished, and suddenly, I'm in trouble.
0:04:15 > 0:04:19My ears are hurting quite badly.
0:04:19 > 0:04:23I couldn't relieve the pressure in my eardrums on the way up,
0:04:23 > 0:04:26a rare and painful condition known as a reverse block.
0:04:30 > 0:04:34My safety diver, Jim, was at my side the entire time,
0:04:34 > 0:04:36but he couldn't help.
0:04:36 > 0:04:37It's really shaken me.
0:04:37 > 0:04:40Two up behind the out burner.
0:04:40 > 0:04:41Ah!
0:04:42 > 0:04:43That was horrific.
0:04:45 > 0:04:47Oh!
0:04:47 > 0:04:50- Did that hurt, Darryl?- I was screaming on the way up.
0:04:50 > 0:04:52- I got a...- A reverse block?
0:04:52 > 0:04:56A reverse block, that's never happened to me before.
0:04:56 > 0:04:59The pressure as the water goes down, you clear,
0:04:59 > 0:05:01like being on an aeroplane.
0:05:01 > 0:05:03Swallow and relieve the pressure.
0:05:03 > 0:05:06On the way back up, it, er, it started to kick in,
0:05:06 > 0:05:09and I couldn't work out where I was in the water,
0:05:09 > 0:05:12and the more I went up, the more the pressure built, and built, and built.
0:05:12 > 0:05:16I was actually screaming, and I couldn't work out what to do.
0:05:16 > 0:05:18And I know, I know what the manual says.
0:05:18 > 0:05:22The manual says you stop, or descend, until it gets past, but I couldn't.
0:05:24 > 0:05:27- I don't want to repeat that again in a hurry.- Let's get you in, Darryl.
0:05:27 > 0:05:31The drama over, we can look on the bright side.
0:05:31 > 0:05:33But there are so many brittle stars down there,
0:05:33 > 0:05:37I couldn't see the shells for the brittle stars over the top of them.
0:05:37 > 0:05:39There were black ones, and the common ones,
0:05:39 > 0:05:41and they were all writhing, arms up in the current, feeding.
0:05:41 > 0:05:43Well, if you'd actually pushed them aside,
0:05:43 > 0:05:46you'd have seen the modiolus just in there.
0:05:46 > 0:05:49Nice site, but with the conditions, the current, the visibility,
0:05:49 > 0:05:51a bit difficult.
0:05:54 > 0:05:57We'll continue the search for horse mussels later.
0:05:57 > 0:06:01But first, we're off to meet marine conservationist Kate Reeves,
0:06:01 > 0:06:06who is convinced Strangford Lough must have more protection.
0:06:06 > 0:06:09Strangford is really unique across Europe and probably the world
0:06:09 > 0:06:13for the way that it's so special, with the way that the tide comes in.
0:06:13 > 0:06:16Very different communities, as that tide goes all the way up the lough,
0:06:16 > 0:06:18and different animals live in those different habitats.
0:06:18 > 0:06:20What we need in Strangford is areas that are set aside,
0:06:20 > 0:06:23where extractive human impacts cannot occur,
0:06:23 > 0:06:28and things such as excessive fishing, unsustainable fishing,
0:06:28 > 0:06:31and all the recreational activities that come in,
0:06:31 > 0:06:33waterskiing, jet skiing, sailing.
0:06:33 > 0:06:36It all has an impact on the birds, disturbs them, the seals,
0:06:36 > 0:06:38and so we just want to make sure that it is all being done
0:06:38 > 0:06:41appropriately within a very, very unique marine protected area.
0:06:41 > 0:06:44All right, in you go, Kate.
0:06:49 > 0:06:54We're making a very shallow dive, so my ears shouldn't be a problem.
0:06:58 > 0:07:02We're on the lookout for charismatic crustaceans
0:07:02 > 0:07:04with eyes like polished coals.
0:07:07 > 0:07:09Their fellow mud dwellers are a bizarre bunch.
0:07:12 > 0:07:15Down here, Neighbourhood Watch is always hungry...
0:07:16 > 0:07:20..endlessly searching the current for food.
0:07:20 > 0:07:24It's a case of eat or be eaten.
0:07:27 > 0:07:31Kate and I don't have long to wait for a close encounter
0:07:31 > 0:07:34of an unexpected kind, with a Dublin Bay prawn.
0:07:35 > 0:07:38What about that, Kate? It's come out to see us.
0:07:38 > 0:07:41It's fantastic, isn't it?
0:07:41 > 0:07:43They're a beautiful colour, aren't they?
0:07:43 > 0:07:45They are, bright orange,
0:07:45 > 0:07:46I can't believe it.
0:07:46 > 0:07:48Nobody would believe
0:07:48 > 0:07:52that they could see something that colourful under our seas.
0:07:52 > 0:07:55Look at those black eyes.
0:07:55 > 0:07:56My goodness!
0:07:56 > 0:07:59It's actually coming towards me right now.
0:07:59 > 0:08:01He seems very aggressive.
0:08:05 > 0:08:07Oh, no, he's coming for me!
0:08:07 > 0:08:08He's coming for me!
0:08:08 > 0:08:11I think he wants a fight.
0:08:14 > 0:08:16He's heading for home.
0:08:20 > 0:08:22They're not supposed to do that, you know.
0:08:22 > 0:08:25They're supposed to be tucked up in their holes until night-time.
0:08:25 > 0:08:28But that one is out for a stroll.
0:08:31 > 0:08:35With trawling banned here, fishermen now trap prawns in pots.
0:08:35 > 0:08:38But they're the most important commercial species
0:08:38 > 0:08:41to trawlermen in the Irish Sea.
0:08:41 > 0:08:45About eight million tons are landed here every year,
0:08:45 > 0:08:49with a total export value of up to £70 million.
0:08:49 > 0:08:51That's a lot of scampi.
0:08:53 > 0:08:56Look how powdery that mud sediment is.
0:08:58 > 0:09:03It's loaded with tiny creatures, crustaceans, worms, bacteria.
0:09:03 > 0:09:08It's where all of the Dublin Bay prawns get their food from.
0:09:08 > 0:09:14It's incredibly rich, and very, very, very full of life as well.
0:09:14 > 0:09:16You wouldn't believe it, just looking at it, but it is.
0:09:20 > 0:09:26On the move again, we spot the flimsy tentacles of a mud anemone.
0:09:26 > 0:09:28These guys have a trick up their sleeve.
0:09:28 > 0:09:32Their tentacles are waving very gracefully
0:09:32 > 0:09:35in the tide that's running here.
0:09:35 > 0:09:37I know, they are absolutely beautiful.
0:09:37 > 0:09:42You wouldn't believe they were related to jellyfish, would you?
0:09:42 > 0:09:46No. The rest of the body, I assume, is tucked away in the mud.
0:09:47 > 0:09:49Anchored there.
0:09:49 > 0:09:50It is. It's buried down there in the mud.
0:09:50 > 0:09:55You wouldn't believe that creature could move as quickly as that.
0:09:55 > 0:09:58I know, but if some predator is coming along to get you,
0:09:58 > 0:10:00you'd have to get out of the way quickly.
0:10:04 > 0:10:07We're on the move the next day to catch the tide
0:10:07 > 0:10:11and, hopefully, sight of a horse mussel reef teeming with wildlife.
0:10:13 > 0:10:15And our time on this dive is really quite limited
0:10:15 > 0:10:20because that sweep of current is going to just flush us off it.
0:10:20 > 0:10:24Comes in, floods in, and then it'll stop for about maybe half an hour,
0:10:24 > 0:10:27an hour max, and then, whoosh, move you away.
0:10:31 > 0:10:35We're in the right place and, happily, I'm feeling fine.
0:10:38 > 0:10:42There are enormous starfish down here.
0:10:42 > 0:10:46Yeah, unfortunately, these enormous starfish are chomping away on the mussels.
0:10:47 > 0:10:51You get all the mussels stuck together, and find a clump.
0:10:51 > 0:10:53The good thing is
0:10:53 > 0:10:56starfish can actually get into those mussels' hearts.
0:10:56 > 0:10:59I think we're looking for a few more than that.
0:10:59 > 0:11:01Yeah.
0:11:13 > 0:11:15This is quite an environment.
0:11:15 > 0:11:18It's absolutely crawling with life.
0:11:18 > 0:11:20Wonderful.
0:11:20 > 0:11:22I love these.
0:11:22 > 0:11:24Lightbulb sea squirts.
0:11:29 > 0:11:32That's a blue velvet swimming crab. Very, very striking red eyes.
0:11:32 > 0:11:34You can see him looking out.
0:11:34 > 0:11:36The thing about these guys, they're vicious.
0:11:36 > 0:11:38Most other crabs will shy away,
0:11:38 > 0:11:40but this boy will go for you. He will chase you.
0:11:40 > 0:11:43And even as a diver, he'll chase you up the line.
0:11:43 > 0:11:45I don't want to get nipped.
0:11:47 > 0:11:49And there they are, at last.
0:11:49 > 0:11:51The gaping shells of horse mussels
0:11:51 > 0:11:55are home to barnacles and a host of other animals.
0:11:55 > 0:11:56I'm reassured, you know,
0:11:56 > 0:11:59because I've been studying these mussel beds now for longer than
0:11:59 > 0:12:04I can remember, and that site is in the middle of a trawl area.
0:12:04 > 0:12:07And I'm happy to see that there are small clumps there now.
0:12:07 > 0:12:10There wasn't many individuals, maybe seven or ten individuals.
0:12:10 > 0:12:12In a proper clump, you'd have thousands.
0:12:14 > 0:12:16Studies have shown this recently,
0:12:16 > 0:12:18that the water moving from Strangford Lough,
0:12:18 > 0:12:22it's not just bound up within the lough, it feeds the whole Irish Sea.
0:12:22 > 0:12:25So if you could keep a good population of scallops and queenies here,
0:12:25 > 0:12:28they'll be releasing millions and millions of young,
0:12:28 > 0:12:30as little larvae, and they'll go out,
0:12:30 > 0:12:32and then they'll go into the commercial beds.
0:12:32 > 0:12:36If you destroy the nursery, you destroy the provider,
0:12:36 > 0:12:37you can destroy everything.
0:12:37 > 0:12:41So, it is very important. This area is a marine nature reserve,
0:12:41 > 0:12:45it's a special area of conservation because it has these special habitats.
0:12:45 > 0:12:50Among the mussels, a sea cucumber pulls food into its mouth.
0:12:50 > 0:12:54Its related to starfish and uses its arms to trap plankton.
0:12:57 > 0:13:00A juicy sea slug grazes peacefully on the reef.
0:13:02 > 0:13:08And a sponge-encrusted spider crab seeks anonymity among feather stars.
0:13:08 > 0:13:09It's magical.
0:13:09 > 0:13:16This has been an absolute delight, to come down and see something
0:13:16 > 0:13:19like this, which is just so rich,
0:13:19 > 0:13:22but you don't get long down here.
0:13:22 > 0:13:25I've got to go back up top. I'll see you later.
0:13:30 > 0:13:32Subtitles by Red Bee Media Ltd
0:13:32 > 0:13:34E-mail subtitling@bbc.co.uk