Marine Ecosystems
For some time now, the world’s oceans and the people who fish them have been a constant source of bad environmental news. Cod is effectively an endangered species now; every year, thousands of dolphins are drowned and fatally injured by Spanish sea-bass trawlers in the Channel; dredging for oysters and scallops is destroying vast areas of coral reef; huge tuna farms are wrecking the Mediterranean Sea.
And when environmentalists aren’t pointing fingers at the fishermen, they’re pointing them at globalisation and the supermarkets. Now marine biologists have warned that our seafood is in terminal decline. According to research published in Science last November, stocks of all of the fish, prawns, crabs and lobsters that we currently eat will collapse before 2050. Or at least, that’s how the media reported it.
However, the scientist who led the study has told Geographical that the main thrust of his research has been buried beneath the shrill headlines. While the danger to our seafood supply is real enough, says Boris Worm, assistant professor of marine conservation biology at Dalhousie University, Canada, there is a more serious point: that the way in which we manage the oceans is not only threatening the survival of individual species, it’s upsetting the delicate balance of marine communities and, in doing so, causing the collapse of entire ecosystems.
Indeed, the evidence is mounting: research published in October has shown that the number of ecosystems where all higher forms of life are extinct, so-called dead zones, has increased from 150 to 200 in the past two years. These include a zone in the Baltic Sea that now has an area of 120,000 square kilometres – about half the size of the UK.
The point that many reports failed to highlight, says Worm, is that we have to revolutionise the way our marine resources are managed, changing the focus from stocks and quotas to biodiversity and ecosystem protection. And in order to do that, we have to change the way the debate about our marine resources is conducted in the public domain and at policy level.
Human interference
Around 7,500 years ago, retreating glaciers and subsequent sea-level rise created what’s known today as the Wadden Sea, a 13,500-square-kilometre area of the North Sea off the coasts of Denmark, Germany and the Netherlands.
During the first 5,000 years or so of its existence, the sea’s waters teemed with life: cod, haddock, rays and herring as well as an array of cetaceans, including right whales, grey whales, harbour porpoises and bottlenose dolphins. On the seabed, rich expanses of oyster banks, sea moss stands, mussel beds, sand-coral reefs and seagrass meadows provided food and shelter to all manner of creatures, including pipefishes, sticklebacks, sponges, sea anemones, worms, whelks and sea urchins.
The freshwater rivers, brackish estuaries and coastal lagoons that fed the sea were also brimming with life, including vast numbers of salmon, sea trout and sturgeon. And the peatlands, bogs, salt marshes and mud flats on the coast supported millions of waterfowl, seabirds and shore birds, including such fantastic species as the Dalmatian pelican, white-tailed eagle and the greater flamingo.
This diversity thrived until around 2,000 years ago, when human pressure began to tell. According to research by Heike Lotze, professor of marine ecology at Dalhousie University, Canada, some of the larger whales and birds disappeared more than 500 years ago. And by the late 19th century, populations of most of the small whales, seals, birds, large fish and oysters were severely reduced, leading to the collapse of several traditional fisheries, including haddock, ray, salmon, sturgeon and shad.
The Wadden Sea is one of 12 coastal ecosystems whose histories were analysed in the Science paper. Although they stretched from the northern Adriatic to the Gulf of St Lawrence and from San Francisco Bay to Moreton Bay in Australia, in each case, the story was the same: human interference had led to a decline in the health and productivity of the ecosystem, increasingly so during the past 150 years.
What’s interesting is that overfishing wasn’t the primary cause of the declines, as we might have assumed. A combination of exploitation, habitat destruction and pollution has caused
a loss of biodiversity and, subsequently, the breakdown of critical ecosystem services.
Coastal development for residential, agricultural and industrial purposes, for example, destroys large areas of wetlands that provide food and shelter for young birds, fish and invertebrates. And practices such as raking
and dredging destroy reefs that provide a
similar function under the water.
At the same time, pollution has fuelled
a process known as eutrophication, which
kills seagrasses. Nutrients such as nitrogen
and phosphorus contained in raw sewage, agricultural run-off and industrial waste
promote the growth of phytoplankton, leading to blooms that starve the seagrass of sunlight. This over enrichment of the sea can ultimately lead to the collapse of the entire system
through oxygen starvation.
Most marine ecosystems have an in-built capacity to deal with a certain amount of nutrient pollution because suspension feeders such as oysters and mussels remove phytoplankton from the water column. But in many cases, these have been removed or their number dramatically reduced by fishermen, so the effects of any nutrient-rich pollutants entering the system is enhanced. In a healthy system, coastal wetlands also act as filters, so their destruction causes more pollution – particularly from agriculture – and, in turn, eutrophication.
These processes have been fairly well understood for a number of years. What the Science paper has been able to show, however, is that the decline in the health and productivity of ecosystems is more pronounced in areas of low biodiversity and is accelerated by the loss of biodiversity.
And it isn’t just in coastal areas. Worm
and his colleagues analysed data for fish and invertebrates caught in 64 large offshore ecosystems between 1950 and 2003. Their research revealed that those with higher biodiversity were more productive and more resistant to exploitation than those with lower levels of biodiversity.
The population of marbled rock cod around the South Atlantic island of South Georgia, for example, still hasn’t recovered after overfishing caused its collapse during the 1970s. By contrast, North Sea cod has withstood very heavy fishing for hundreds of years, says Worm, and although it has declined substantially, it hasn’t yet collapsed completely. “The point seems to be that the higher level of biodiversity in the North Sea means that the populations there are more able to withstand being severely depleted,” he says.
Although little research has identified exactly why this is, Worm believes that biodiversity
acts as a buffer against human-induced and environmental change. “To have a greater number of species makes an ecosystem more robust,” he says. “In areas of high biodiversity, you have more species performing a certain function. If one is lost, there will be others
that can fulfil the same role.”
His hunch is backed up by evidence from a series of experiments looking at how ecosystems react to change. “We found that where there are more species, the resources available are used more effectively and efficiently,” he says. “So
it’s like an economy that has lots of different companies serving society’s diverse needs. It
will be able to function more efficiently and be more productive than an economy that’s built on only a few companies.”
And some good news came from the study. Worm and his colleagues were able to show that it’s possible to reverse the damage caused by exploitation, pollution and habitat destruction as long as there are enough species. A survey of 44 protected areas and four large-scale fisheries closures revealed increases in diversity averaging 23 per cent and a four-fold increase in catches outside the reserves.
Worm says he’s disappointed that the media chose to focus exclusively on the decline of seafood, rather than the broader message of the relationship between biodiversity and ecosystem services. “The message we want to get across is that an ecosystem’s most important trait is its diversity, rather than the individual species within it,” he says. “And that with this in
mind, we should be focusing our attention
on protecting all of our marine resources at the ecosystem level, and managing levels of fishing, pollution and habitat disturbance to ensure that crucial services that maintain the health of the ecosystem continue to function.”
Limitless resource
To anyone who knows anything about ecology, it would appear that Worm is just stating the obvious. Indeed, natural resource management at the ecosystem level is nothing new; conservationists have understood its value
for more than 40 years. And on land, many protected areas are now managed in this way.
However, marine resources are a different matter. A historical tendency to view our
oceans as a limitless resource, combined with
a widespread failure to make an emotional connection with most marine wildlife, has meant that this concept has yet to find its way into the vast majority of marine ecosystem management plans.
True, we have created a number of marine protected areas. And, as Worm’s research
shows, these areas are proving to be most effective in maintaining and restoring biodiversity and ecosystem services. However, they cover only about one per cent of the
world’s oceans and are distributed unevenly.
“We seem to have understood the value of protecting ecosystems in those areas, such
as the Great Barrier Reef, that we consider to
be particularly beautiful or exotic,” says John Shepherd, professor of marine sciences at Southampton University. “But everywhere,
else our marine resources are managed as fisheries – in terms of stocks and quotas
of particular species.”
The bias in the distribution of marine protected areas is a reflection of the way in which we tend to perceive the natural world,
he continues. “Human nature will always draw us towards those species or habitats that are more aesthetically pleasing. That’s why there
will always be support for protecting pandas and very little for worms, even though nematodes play a vital role in maintaining
the health of an ecosystem.”
The same tendency is evident in marine conservation, says Kate Reeves, marine policy officer at WWF-UK, where whales, dolphins and tropical coral reefs receive the most support from the public. However, it’s felt more acutely than in terrestrial conservation. “There is a huge amount of biodiversity throughout the oceans that is equally important but most of us never get to see, so the support is never generated,” she says. Part of the fault lies with the conservation organisations, she feels, which haven’t done enough to highlight its significance.
However, the bias has been distorted by the fact that fishermen, like farmers, generate a lot
of sympathy among the general public because they provide us with food. “And by the fact that the fishing industry has tended to shout the loudest,” says Reeves.
Consequently, the only connection the
public, the media and the politicians have
with such places as the North Sea is through seafood, explains Reeves, so the debate about marine resource management tends to be
limited to a discussion about quotas of single species. “But what marine biologists have been saying for some time – and what the Science paper now confirms – is that we have to
manage at the ecosystem level in every marine environment, not just those areas that we consider particularly beautiful,” she says.
Now that the evidence is there for all to
see, says Shepherd, it’s time that the debate moved on. “The fact that fishermen provide
us with food and have historically had the
closest connection with our seas doesn’t
mean they should be allowed to dominate
the debate,” he says. “I’d like to see the
discussion broadened to acknowledge the
fact that there are a range of impacts on our oceans, all of which need to be considered in marine resource management plans.”
Worm agrees that the focus on the fishing industry and stocks of seafood has diverted attention away from the widespread destruction going on at the ecosystem level. “People see a piece of cod on the fish counter and they get
the impression that the situation isn’t that
bad,” he says “It may be a bit more expensive than it used to be, but it’s still there, so it must be okay.” The problem is, he continues, that even though the species itself may not be
extinct as a whole, there will have been local extinctions in many areas; all that’s happening
is that the fishermen are going farther and farther away to find the fish. “That’s alright
for consumers. But for the ecosystem that has lost its cod – and other species with it – there may be dramatic consequences.”
Worm believes that we should use a broader perspective to view our seafood. “It’s important to understand that the cod on our plates is
there because of a large number of other flora and fauna that together provide a clean, safe environment with enough food and habitat to support a viable population,” he says. “It’s now clear that we have to protect all of the species within an ecosystem in order to keep our oceans healthy and to maintain stocks of seafood.”
And when environmentalists aren’t pointing fingers at the fishermen, they’re pointing them at globalisation and the supermarkets. Now marine biologists have warned that our seafood is in terminal decline. According to research published in Science last November, stocks of all of the fish, prawns, crabs and lobsters that we currently eat will collapse before 2050. Or at least, that’s how the media reported it.
However, the scientist who led the study has told Geographical that the main thrust of his research has been buried beneath the shrill headlines. While the danger to our seafood supply is real enough, says Boris Worm, assistant professor of marine conservation biology at Dalhousie University, Canada, there is a more serious point: that the way in which we manage the oceans is not only threatening the survival of individual species, it’s upsetting the delicate balance of marine communities and, in doing so, causing the collapse of entire ecosystems.
Marine Ecosystems
Start the slideshow (9 pictures)
Indeed, the evidence is mounting: research published in October has shown that the number of ecosystems where all higher forms of life are extinct, so-called dead zones, has increased from 150 to 200 in the past two years. These include a zone in the Baltic Sea that now has an area of 120,000 square kilometres – about half the size of the UK.
The point that many reports failed to highlight, says Worm, is that we have to revolutionise the way our marine resources are managed, changing the focus from stocks and quotas to biodiversity and ecosystem protection. And in order to do that, we have to change the way the debate about our marine resources is conducted in the public domain and at policy level.
Human interference
Around 7,500 years ago, retreating glaciers and subsequent sea-level rise created what’s known today as the Wadden Sea, a 13,500-square-kilometre area of the North Sea off the coasts of Denmark, Germany and the Netherlands.
During the first 5,000 years or so of its existence, the sea’s waters teemed with life: cod, haddock, rays and herring as well as an array of cetaceans, including right whales, grey whales, harbour porpoises and bottlenose dolphins. On the seabed, rich expanses of oyster banks, sea moss stands, mussel beds, sand-coral reefs and seagrass meadows provided food and shelter to all manner of creatures, including pipefishes, sticklebacks, sponges, sea anemones, worms, whelks and sea urchins.
The freshwater rivers, brackish estuaries and coastal lagoons that fed the sea were also brimming with life, including vast numbers of salmon, sea trout and sturgeon. And the peatlands, bogs, salt marshes and mud flats on the coast supported millions of waterfowl, seabirds and shore birds, including such fantastic species as the Dalmatian pelican, white-tailed eagle and the greater flamingo.
This diversity thrived until around 2,000 years ago, when human pressure began to tell. According to research by Heike Lotze, professor of marine ecology at Dalhousie University, Canada, some of the larger whales and birds disappeared more than 500 years ago. And by the late 19th century, populations of most of the small whales, seals, birds, large fish and oysters were severely reduced, leading to the collapse of several traditional fisheries, including haddock, ray, salmon, sturgeon and shad.
The Wadden Sea is one of 12 coastal ecosystems whose histories were analysed in the Science paper. Although they stretched from the northern Adriatic to the Gulf of St Lawrence and from San Francisco Bay to Moreton Bay in Australia, in each case, the story was the same: human interference had led to a decline in the health and productivity of the ecosystem, increasingly so during the past 150 years.
What’s interesting is that overfishing wasn’t the primary cause of the declines, as we might have assumed. A combination of exploitation, habitat destruction and pollution has caused
a loss of biodiversity and, subsequently, the breakdown of critical ecosystem services.
Coastal development for residential, agricultural and industrial purposes, for example, destroys large areas of wetlands that provide food and shelter for young birds, fish and invertebrates. And practices such as raking
and dredging destroy reefs that provide a
similar function under the water.
At the same time, pollution has fuelled
a process known as eutrophication, which
kills seagrasses. Nutrients such as nitrogen
and phosphorus contained in raw sewage, agricultural run-off and industrial waste
promote the growth of phytoplankton, leading to blooms that starve the seagrass of sunlight. This over enrichment of the sea can ultimately lead to the collapse of the entire system
through oxygen starvation.
Most marine ecosystems have an in-built capacity to deal with a certain amount of nutrient pollution because suspension feeders such as oysters and mussels remove phytoplankton from the water column. But in many cases, these have been removed or their number dramatically reduced by fishermen, so the effects of any nutrient-rich pollutants entering the system is enhanced. In a healthy system, coastal wetlands also act as filters, so their destruction causes more pollution – particularly from agriculture – and, in turn, eutrophication.
These processes have been fairly well understood for a number of years. What the Science paper has been able to show, however, is that the decline in the health and productivity of ecosystems is more pronounced in areas of low biodiversity and is accelerated by the loss of biodiversity.
And it isn’t just in coastal areas. Worm
and his colleagues analysed data for fish and invertebrates caught in 64 large offshore ecosystems between 1950 and 2003. Their research revealed that those with higher biodiversity were more productive and more resistant to exploitation than those with lower levels of biodiversity.
The population of marbled rock cod around the South Atlantic island of South Georgia, for example, still hasn’t recovered after overfishing caused its collapse during the 1970s. By contrast, North Sea cod has withstood very heavy fishing for hundreds of years, says Worm, and although it has declined substantially, it hasn’t yet collapsed completely. “The point seems to be that the higher level of biodiversity in the North Sea means that the populations there are more able to withstand being severely depleted,” he says.
Although little research has identified exactly why this is, Worm believes that biodiversity
acts as a buffer against human-induced and environmental change. “To have a greater number of species makes an ecosystem more robust,” he says. “In areas of high biodiversity, you have more species performing a certain function. If one is lost, there will be others
that can fulfil the same role.”
His hunch is backed up by evidence from a series of experiments looking at how ecosystems react to change. “We found that where there are more species, the resources available are used more effectively and efficiently,” he says. “So
it’s like an economy that has lots of different companies serving society’s diverse needs. It
will be able to function more efficiently and be more productive than an economy that’s built on only a few companies.”
And some good news came from the study. Worm and his colleagues were able to show that it’s possible to reverse the damage caused by exploitation, pollution and habitat destruction as long as there are enough species. A survey of 44 protected areas and four large-scale fisheries closures revealed increases in diversity averaging 23 per cent and a four-fold increase in catches outside the reserves.
Worm says he’s disappointed that the media chose to focus exclusively on the decline of seafood, rather than the broader message of the relationship between biodiversity and ecosystem services. “The message we want to get across is that an ecosystem’s most important trait is its diversity, rather than the individual species within it,” he says. “And that with this in
mind, we should be focusing our attention
on protecting all of our marine resources at the ecosystem level, and managing levels of fishing, pollution and habitat disturbance to ensure that crucial services that maintain the health of the ecosystem continue to function.”
Limitless resource
To anyone who knows anything about ecology, it would appear that Worm is just stating the obvious. Indeed, natural resource management at the ecosystem level is nothing new; conservationists have understood its value
for more than 40 years. And on land, many protected areas are now managed in this way.
However, marine resources are a different matter. A historical tendency to view our
oceans as a limitless resource, combined with
a widespread failure to make an emotional connection with most marine wildlife, has meant that this concept has yet to find its way into the vast majority of marine ecosystem management plans.
True, we have created a number of marine protected areas. And, as Worm’s research
shows, these areas are proving to be most effective in maintaining and restoring biodiversity and ecosystem services. However, they cover only about one per cent of the
world’s oceans and are distributed unevenly.
“We seem to have understood the value of protecting ecosystems in those areas, such
as the Great Barrier Reef, that we consider to
be particularly beautiful or exotic,” says John Shepherd, professor of marine sciences at Southampton University. “But everywhere,
else our marine resources are managed as fisheries – in terms of stocks and quotas
of particular species.”
The bias in the distribution of marine protected areas is a reflection of the way in which we tend to perceive the natural world,
he continues. “Human nature will always draw us towards those species or habitats that are more aesthetically pleasing. That’s why there
will always be support for protecting pandas and very little for worms, even though nematodes play a vital role in maintaining
the health of an ecosystem.”
The same tendency is evident in marine conservation, says Kate Reeves, marine policy officer at WWF-UK, where whales, dolphins and tropical coral reefs receive the most support from the public. However, it’s felt more acutely than in terrestrial conservation. “There is a huge amount of biodiversity throughout the oceans that is equally important but most of us never get to see, so the support is never generated,” she says. Part of the fault lies with the conservation organisations, she feels, which haven’t done enough to highlight its significance.
However, the bias has been distorted by the fact that fishermen, like farmers, generate a lot
of sympathy among the general public because they provide us with food. “And by the fact that the fishing industry has tended to shout the loudest,” says Reeves.
Consequently, the only connection the
public, the media and the politicians have
with such places as the North Sea is through seafood, explains Reeves, so the debate about marine resource management tends to be
limited to a discussion about quotas of single species. “But what marine biologists have been saying for some time – and what the Science paper now confirms – is that we have to
manage at the ecosystem level in every marine environment, not just those areas that we consider particularly beautiful,” she says.
Now that the evidence is there for all to
see, says Shepherd, it’s time that the debate moved on. “The fact that fishermen provide
us with food and have historically had the
closest connection with our seas doesn’t
mean they should be allowed to dominate
the debate,” he says. “I’d like to see the
discussion broadened to acknowledge the
fact that there are a range of impacts on our oceans, all of which need to be considered in marine resource management plans.”
Worm agrees that the focus on the fishing industry and stocks of seafood has diverted attention away from the widespread destruction going on at the ecosystem level. “People see a piece of cod on the fish counter and they get
the impression that the situation isn’t that
bad,” he says “It may be a bit more expensive than it used to be, but it’s still there, so it must be okay.” The problem is, he continues, that even though the species itself may not be
extinct as a whole, there will have been local extinctions in many areas; all that’s happening
is that the fishermen are going farther and farther away to find the fish. “That’s alright
for consumers. But for the ecosystem that has lost its cod – and other species with it – there may be dramatic consequences.”
Worm believes that we should use a broader perspective to view our seafood. “It’s important to understand that the cod on our plates is
there because of a large number of other flora and fauna that together provide a clean, safe environment with enough food and habitat to support a viable population,” he says. “It’s now clear that we have to protect all of the species within an ecosystem in order to keep our oceans healthy and to maintain stocks of seafood.”
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