Marine Conservation. Peter Shaw (with thanks to Claire Ozanne and Martin Speight). Issues to cover: Marine biodiversity – hotspots and global significance Fisheries – Zuckerman’s paradox Coastal land use changes Pollution Solutions?. Marine biodiversity.
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(with thanks to Claire Ozanne and Martin Speight)
Marine biodiversity – hotspots and global significance
Fisheries – Zuckerman’s paradox
Coastal land use changes
We know of c 300,000 species in the sea, including all known phyla (except velvet worms Onychophora) – guesstimates are quoted at 500,000 species in total, rather fewer species than on land (lacking the hyperdiversity of insects or orchids). Endemism is more difficult in the sea as it is interconnected (consider lakes, mountain ranges by way of comparison), but endemics do occur, especially in delimited zones such as the Red sea..
To the best of our current knowledge, the highest species richness of any marine habitat is found in tropical coral reefs, systems built on the calcareous skeletons of colonial anthozoa.
These occur within 20 degree of the equator in seas between 20 and 28C. Given this and their need for clear shallow water (<25m, exceptionally <100m) they cover about 1% of the earths surface (compare 14% for primeval rain forests).
Despite this estimate are around 25% of all marine species and 75% of all fish species. One fish expert (Gerard Allen, Perth museum) broke his own record for species in one scuba dive twice in one spot off Irian Jawa: 281 and 283 species respectively!!
There are under-studied communities inside the coral rubble, where divers cannot go, that appear to be very species-rich. Like rainforests these are inherently infertile systems, and many species are forced to live symbiotically – including the corals, 90% of whose energy comes from algae living within their tissues called zooxanthellae.Coral reefs
Coral reefs shown in yellow
These algae prove to be the Achilles heel of the reef, since they impose limits on the corals. They need light, hence the need for clear water. Anything which decreases light penetration hurts the corals, hence ultimately the whole reef community. Soil erosion is a common and serious nuisance here, as the agricultural runoff (it’s usually agricultural runoff) not only makes turbidity but is fertiliser-enriched, leading to explosive algal blooms that smother the corals.
If the sea temperature exceeds 28C the corals undergo a process called bleaching in which they eject their symbiotic zooxanthellae (algae who live symbiotically in the polyps), an act which usually (not always) proves suicidal. As the greenhouse effect bites, reefs all over the planet can be predicted to bleach. A second, potentially more serious issue ocurs at 1500ppm CO2, when calcium carbonate will cease to precipitate out of solution.
Bleaching was first recorded in the 1980s, but is now a widespread threat.
Fishing sensu latu clearly impacts on reef ecology, by removal of selected target species. We will cover the economics of fisheries soon.
Not just fish: The giant triton (Charonia tritonis) has a handsome shell for which it is harvested. It is also a major predator on crown-of-thorns starfish, which in turn damage coral reefs badly.
Sea cucumbers (holothurids) aka trepangs aka beches de mer are stripped by fishermen, collecting for the Asian market ($2 each). An invasion of trepang fishermen into the Galapagos islands, and the subsequent enforcement of fishing regulations, led to street riots that threatened to burn down the Charles Darwin research centre in the Galapagos in 1997. Nine giant tortoises has their throats cut.
We will look at the Galapagos spiny lobster fishery soon, which also led to serious violence .
Other influences on a reef system:
If you’re lazy and careless you throw in cyanide (which kills everything) or dynamite (which destroys most animals and the structure of the coral). These can only be condemned – are nowhere legal but prosecutions are uncommon.
How about divers? Divers are always taught not to touch, not to disturb, not to interfere (usually not even feeding fish). But divers come in great numbers – on some busy red sea reefs (Hurghada, Sharm el Sheik) divers come and go in an endless stream.
Some dive practices are certainly bad: anchoring to the living coral causes serious mechanical damage. Responsible diver operators set up fixed anchorages. In the Red sea in 1992 the operators dropped anchors on live reef, hating having to do it, since any permanent fixtures (even underwater ones) were stolen :=(
Recent studies in the Red Sea show that coral damage by tourist boats and divers could be considerable, although minimised by responsible briefings (Medio et al., 1997; Jameson et al., 1999). Damage is usually caused by careless accidental scraping of fins across living coral, although sometimes branches are snapped off.
Diver touching coral – note the snapped edges
Boat-damaged coral, Australia
Divers generate plastic litter – esp mineral water bottles. Future archaeologists will call us something involving plastic and detritus…
Of all the examples of human failure, our inability to regulate fisheries into sustainability must rank with our inability to predict earthquakes as a long-running tragedy that science seems unable to help with.
As a good approximation, if it’s worth money and lives in the sea it must be assumed to be potentially endangered!
Zuckerman S (1992). Between Stockholm & Rio. Nature 358, 273-276.
At the time the Limits to Growth report came out, there was a huge, healthy cod fishery on the Grand banks off Newfoundland. This had been discovered hundreds of years ago, was among the largest fisheries on the planet, and could be harvested sustainably for ever.
N0 = Catch per unit effort /(return per unit harvest * catchability)
What N0 does depends the economic value of the species. If value is high, it is worth harvesting to very low population levels. The problem is that economic value can change – a rare species may become worth more as consumers pay a premium for scarcity.
Idealised graph of a fishery collapse
Nth Pacific sardines
More trouble from the Galapagos, following the trepang riots of 1997.
In 1999 there were 500 fishers of Spiny lobsters with a 54 ton quota. These made money, and in 2000 there were 949 fishermen, who hit their quota in 2 months. When denied permission to continue fishing they rioted, and destroyed all the contents and records of the Charles Darwin research centre. The Ecuadorian government sent in its special forces to rescue the staff at the centre. Sometimes I’m ashamed to be human.
In the end the government set an 84 ton quota, against the conservationists advice – a partial sell out.
Cod Gadus morhua, staple of your corner chippy, eaten in this country for at least 2000 years, is so over-fished that the north sea cod fishery should really be shut down. Of course, fishermen object because that’s their livelihoods gone. AndCod!
as cod decline to uncatchability, I heard a food marketing person explaining how we should grow to like eating other fish, such as Orange Ruffy from deep waters around New Zealand.
And the population dynamics of this deep-water fish? It takes 25 years to reach maturity, lives to 100 years. It’ll be wiped in a decade of serious fishing. (Similarly for the Patagonian toothfish, 3500m deep in the southern oceans, with 100,000 tpa taken illegally each year (as of 2003).
As a consequence of what I have just told you, I am unable to avoid predicting that any high-value marine species in danger from over-fishing. Bluefin tuna is regulated by CITES due to its value in Japan ($24,000 for a single top-class fish, taking 60% of world tuna catch). Squids are harvested with industrial efficiency by ships using light traps. As a by-catch, albatrosses are regularly caught on the kilometer-long multi-hooked fishing lines, to the extent that extinction of species is a real possibility.
The best hope is the observation that the sea is a very big place, and it is much harder to find and kill the last few members of a species that on land. The time-honoured pattern is for species to decline to near-extinction then hang on at low levels (great whales being a classic example).
There aren’t as many of these in the sea as on land – as I said, the sea is a big place. But there area few. No fish have been exterminated in the sea yet AFAIK (plenty in isolated lakes – Rift valley cichlids providing many examples). But mammals and birds can’t make that claim.
How about Stella’s sea cow Hydrodamalis gigas, confined to the seaweed beds of Katchatka / northern Japan? It was the largest sirenian ever known, toothless, mashing algae between keratinous plates. It was also slow moving fat and fearless of humans. Discovered 1741, extinct 1768. (The other 4 sireneans are also all endangered)
The last population of Great Auks lived off Iceland. Up to 1800s they nested on an inaccessible volcanic island Geirfuglaske, but this was the centre of an eruption in 1830, and the birds moved to the relatively more accessible island of Eldey.
Eldey – on a calm day
More than on land, marine systems often have one highly productive keystone species which feeds the rest of the food chain. In the north sea this is the sand eel, in the northern atlantic it is the capelin, in the southern oceans it is krill.
What happens when you deplete this keystone species? Its predators must reduce in numbers.
There is concern for krill – recent work from the BAS shows krill numbers on the Antarctic peninsula to have declined in last decade; these crustaceans feed on algae on underside of icebergs. They feed penguins and whales.
We have a real conservation disaster this year, probably beyond the control of any conservation bodies, or even governments. It concerns our northern seabird cliffs, ecosystems relying on sandeels. These fish are the subject of an “industrial” fishery, harvesting their bodies for oils (fuel) and cheap meat for fishfood etc.
A combination of overfishing and warming has led to cold water fish all but disappearing from the north sea: Cod and Sand Eel being especially significant. (Haddock are doing better – so far).
Worse, far worse, is the impact of sandeel shortages on breeding seabirds. “This year the cliffs of these Northern Isles fell eerily silent and 10s of 1000s of seabirds failed to rear any young” (RSPB, Atumn04)
Marine conservation? Land use changes? Is this the correct lecture? Actually yes. I have already mentioned the deleterious impact of agricultural runoff on coral reefs. There is another one, linked to mangrove swamps.
Mangroves are among the few angiosperms which flourish in salt water, and form dense species-rich inter-tidal forests (mangrove swamps), valuable in themselves and as nurseries for young reef fish.
These are cut for BBQ charcoal, and replaced by aquaculture.
Shrimp farm cut into mangroves
These mangrove swamps are being depleted by conversion to commercial shrimp farms. Not only does this remove a valuable habitat but the shrimp farm requires major inputs of fish food, which eutrophies the water body and endangers offshore corals. Mangrove swamp used to shelter coastal communities from the full force of hurricanes – one reason that hurricane deaths have been so severe in India and Africa recently is the replacement of coastal mangroves by shrimp farming.
Greenpeace have a report (Hagler 1997) called Shrimp, the devastating delicacy, about the environmental damage caused by the expansion and intensification of shrimp farms.
THE BRUTAL SUPER-CYCLONE OF ORISSA
Super-cyclone with winds 260-300 km/hour (hurricane category 5) hit the 90 mile coast of Orissa with a
storm surge that created the Bay-of-Bengal water level 30 feet higher than normal, causing thousands of deaths.
Not very much really, but there a few small tips:
Express a consumer preference for farmed fish over wild-caught fish. (I know that these cause local pollution, but local pollution is better than global population collapse. I also know that fish-farmers tend to feed their stock on wild fishmeal, sadly. …).
Best avoid Tiger Shrimps – and make sure your BBQ charcoal is locally produced.
Don’t buy animal souvenirs on holiday.
And don’t buy shark fin soup, and tell your friends not to. Sharks are especially sensitive to harvesting pressure, and the method used is to hook the shark, chop its fins off and throw it back to starve.
On a bigger scale, there are useful (if unpopular) actions to take. The best appears to be the creation of marine reserves, areas where fishing is simply not permitted. This is usually deeply unpopular with local fishermen, but recent work in the Catribbean by Callum Roberts (York) has shown that the creation of large marine reservces does not in fact reduce fishermen’s overall long term catchm, and that the proportion of large (trophy) animals increases. They grow up safe in the reserve, then some spill out of the boundary into the fished waters beyond.
Roberts CM et al (2001) – effects of marine reserves on adjacent fisheries. Science 294, 1920-1923.