Is our marine life in hot water?
OURS SEAS ARE GETTING WARMER. OK, don’t get the shortie wetsuit out just yet but, largely as a result of human activities, scientists expect sea temperatures around the UK to increase between 1.5 and 4°C over the next century.
This might mean only the difference between donning your thick gloves or your thin ones, but is it likely to have a significant impact on our marine wildlife
How species are affected depends on their life-style. Sedentary coldwater species such as corals and anemones may not be able to adapt quickly enough and may die out in southern areas if water temperatures exceed their comfort range.
Mobile species such as crabs and fish (or those with a mobile larval stage, such as sea squirts and sponges) are likely to take the opportunity to relocate further north.
UK and Irish waters are an ideal living laboratory to study these changes, as our marine life contains examples of both northern “Arctic-boreal” species at the southernmost extent of their range on our north and east coasts (think of those sea loch specialities such as the straggly white seafan Swiftia pallida and the chunky deeplet sea anemone Bolocera tuediae) and southern “Lusitanean” species on our south-west coasts (for example the sunset cup-coral Leptopsammia pruvoti and pink seafan Eunicella verrucosa).
While simple shifts in distribution may not sounds too serious, these can have a knock-on effect on other species in the food chain.
For example, studies of plankton have shown how one copepod (planktonic crustacean) species in the Atlantic has been replaced by a warmer-water one that peaks in numbers later in the summer.
Cod juveniles preyed on the colder-water species but the other one does not grow in time for when they need food.
The result Hungry, less-successful cod, which in turn impacts on species that feed on them higher up the food chain (including fish–and-chip-munching humans!).
The whole appearance of our seabed could potentially change, because the humble kelp
is extremely sensitive to small increases in water temperature.
There are no studies indicating that kelp is currently being affected in the UK, but scientists in Tasmania have observed dramatic declines in their kelp forests, and in some areas only 5% of the original amount remains.
While the thought of swimming around our shores unhindered by a jungle of clinging kelp fronds is initially appealing, anyone who has paused during their battle (try it on your next dive) will see the diversity of life that kelp forests support, from sponges creeping around the holdfast to curious wrasse frolicking in the canopy.
Any loss in important structural species such as kelp would have a dramatic effect on our marine environment.
CHANGES CAUSED BY INCREASES in our sea temperature have already been observed in marine organisms including plankton, algae and intertidal species.
Fish have responded particularly quickly, with the southern species red mullet, anchovy and pilchard newly reported in the North Sea, and the Marine Biological Association’s Marine Biodiversity & Climate Change (MarClim) programme has found that shore species are creeping northwards and eastwards along British coasts.
There are fewer studies on the marine life we encounter as divers, because large data-sets are harder and more expensive to collect.
However, in my day job as marine biologist at National Museums Northern Ireland we’ve just completed a study, with Northern Ireland Environment Agency, comparing data collected on our recent dive surveys with the baseline survey for Northern Ireland, which was conducted in the 1980s.
Over just 20 years (in fact the working lifetime of Curator of Marine Invertebrates Bernard Picton, who participated in both the 1982-86 and 2006-2009 diving surveys) we found significant changes.
Species at the edge of their bio-geographic ranges in their study area were the groups primarily affected. There were increases in the frequency and areas in which 19 extreme southern species were recorded and three species, the sponge Hexadella racovitzai, the nudibranch Caloria elegans and the crab Maja brachydactyla, appear to have recently colonised Northern Ireland.
Changes in northern species were less pronounced but there were declines in, for example, the brittlestar Ophilopholis aculeate, which Bernard remembers being very abundant on some sites. It was not recorded in recent surveys of any the three study areas, even at sites where it was formerly common.
These changes are similar to those predicted by Keith Hiscock of the Marine Biological Association. “Divers should not expect to see major changes in native seabed marine life as a result of warming for many years,” he says.
“Species in British waters tolerate wide temperature variations, are often long-lived, and are slow to extend their range, as many
have very short-lived larvae that do not go far from their parents. Nevertheless, there are species to look out for as ‘no longer seen’ or ‘new kids on the block’.”
This provides a great excuse to go critter-spotting. In recent years several exotic southern beauties have appeared around our coasts, and other northern rarities have retreated.
While some species are expected to gradually change distribution, others that repopulate less well may jump rapidly into new locations.
As divers, we all know our local patch and are best placed to spot, snap and report any unusual sightings. Several schemes welcome records of climate-change winners and losers from divers. These go into national databases and help scientists studying climate-change effects around our coasts.
This section contains our handy guide to some of these species – happy spotting!
1 BLACK-FACED BLENNY (Tripterygion delaisi)
The male has a jet-black head and bright yellow body. It was first recorded in the UK in 1977 at Portland Harbour, Dorset. Seasearch has been recording its spread along the south coast of England. Now present along the south coast of England from the Lizard to Brighton and recorded in 2010 in the Llyn peninsula, North Wales.
2 RED OR PORTUGUESE BLENNY (Parablennius rubber)
Early records of this species from the UK and Ireland were mistaken for the tompot blenny Parablennius gattorugine (even by fish experts). It can be distinguished by its red colouration and the two white stripes extending from its eye to its mouth. The first confirmed record is from the west coast of Ireland in 1982 but it has now been recorded along the entire west coast of the British Isles from the Scilly Isles to St Kilda. Likely to spread up the English Channel and Irish Sea.
3 ANEMONE PRAWN (Periclimenes sagittifer)
This tiny prawn lives in the tentacles of snakelocks anemones and requires some careful spotting. It has distinctive blue stripes on its legs. First recorded in the UK at Swanage Pier in Dorset in 2007, it has so far been recorded mainly in that vicinity. The westernmost record is from Devon’s Babbacombe Bay and this year it was recorded in Selsey in Sussex, the most easterly record yet, so it may be spreading.
4 GOLDEN KELP (Laminaria ochroleuca)
This kelp can be distinguished from our normal forest kelp Laminaria hyperborea as it has a distinctive yellow area at the junction of the stipe (or stem) and blade. Unlike forest kelp its stipe is not covered in overgrowing plants and animals. Currently mainly found in south-west England including Lundy, the Isles of Scilly, and south Devon and Cornwall, though there is one record from the Shetland Isles.
5 SPINY SPIDER CRAB (Maja brachydactyla)
This large spider crab’s body can measure up to 20cm across. As the name suggests, it has distinctive spines. Researchers have recently changed the taxonomy of our UK species and in most ID guides it will still be listed as Maja squinado. Found on west and south-west coasts including Scotland, this is one of the species we found had recently moved into Northern Ireland.
6 YELLOW STAGHORN SPONGE (Axinella dissimilis)
This yellow branching sponge has a velvety texture. It is common in the south-west and Wales and there are scattered records from Northern Ireland and the west coast of Scotland.
7 AMBERJACK (Seriola spp)
Before 1990 only two of these warmwater jack had been recorded in Britain. Now around 50 Almaco jack (Seriola rivoliana) or greater amberjack (Seriola dumerili) have been seen. They can grow to more than 1.6m, but none seen in our waters has been bigger than 60cm. Amazingly, between July and September 2007 divers photographed these rare fish off Lundy, in Pembrokeshire, and County Kerry, Ireland.
8 GILTHEAD BREAM (Sparus aurata)
This large sea bream was first seen in Cornwall in 1846, but was very rare until the 1970s. However, it is increasingly common in the south-west, south Wales and Ireland and turning up in commercial catches, with large numbers of young occurring in suitable estuaries. Those increasingly found in British fishmongers and supermarkets are farmed in Greece or Turkey.
9 COUCH’S SEA BREAM (Pagrus pagrus)
Like a rosy version of a gilthead, these bream are greatly prized by anglers. Before 1997 only four had been caught, yet now twice this number can be caught in a day. There seem to be at least three breeding areas around Devon and Cornwall. Our local ones have striking white tips to the tail. American and Caribbean fish of the same species, known as red porgies, lack these.
10 GREY TRIGGERFISH (Balistes capriscus)
With its oval flattened body and beak-like mouth, the form of this brown-green-to-grey fish, reaching up to 60cm long, will be familiar to anyone who has dived in warmer waters, where the family is common. Breeding in warmer Atlantic waters and the Mediterranean, this once-rare visitor is now spotted increasingly frequently on our coasts, mainly between August and November, and can be seen in large numbers at hotspots such as Pembrokeshire. As spawning occurs in waters above 21°C, however, it is likely to remain a visitor until our seas get considerably warmer – perhaps just as well, given their aggression to potential predators (including divers) while nest-guarding.
Species disappearing from southern parts of their range
1 NORTHERN SEAFAN (Swiftia pallida)
This white or greyish seafan forms straggly colonies with little branching. It can reach up to 20cm tall. Found on the west coast of Scotland and in the Kenmare River, Ireland. Can usually be distinguished from the pink seafan by colour (though beware white pink seafans on Ireland’s west coast!).
2 DEEPLET SEA ANEMONE (Bolocera tuediae)
This pale pink to orange sea anemone can reach a massive size – up to 30cm across its tentacles. It has been recorded on all coasts of Britain but is rare in the south and found north to the Arctic Circle. Most commonly spotted by divers in Scottish sea lochs.
3 PURPLE SUNSTAR (Solaster endeca)
This large purple starfish usually has 9-10 arms. Unlike the common sunstar Crossaster papposus it has no bands of white. Found from southern Ireland to the North Sea, but far more common in Scotland.
4 ATLANTIC WOLF-FISH (Anarhichas lupus)
This ferocious-looking fanged fish is unlikely to be mistaken for anything else by any diver lucky enough to encounter it. With its long single dorsal fin it is rather like a giant blenny, reaching up to a metre in length. While it is found all around Britain and Ireland in depths of 60-300m, it ventures into shallower waters where divers are likely to encounter it only in the north of the British Isles. As our waters warm
it is likely to retreat back into deeper water or
5 NORTHERN STONE CRAB (Lithodes maia)
This brown or orange crab has a pear-shaped body up to 11cm long. Both body and legs are covered in distinctive conical spines and its rostrum (long projection) splits into two at the end. Most frequently spotted in the British Isles in mainland Scotland and the Orkneys and Shetlands, its wider range is as far north as Svalbard and Greenland.
Seasearch is a project in which volunteer divers can get involved in recording marine species and habitats, www.seasearch.org.uk
Marine Biological Association has a recording scheme and can help with identification if you have pictures, www.mba.ac.uk/recording
Porcupine Marine Natural History Society runs a sightings scheme, pmnhs.co.uk/found-something-unusual
UK Marine Fish Recording Scheme – email records to douglas.herdson@
BSAC’s new app Sealife Tracker involves divers in recording climate-change indicators and invasive species, www.bsac.com
Seasearch publishes a variety of ID guides for UK and Irish divers, www.mcsuk.org/acatalog
Facebook group Seasearch Identifications can help with ID from photos
Encyclopaedia of Marine Life of Britain & Ireland, www.habitas.org.uk/