Coastal habitats are the biosphere’s most imperiled ecosystems

At the event, leading international experts presented the findings of their latest research into the scale, causes and consequences of global loss of coastal habitats. The disappearance of these ecosystems, which include coral reefs, mangrove forests, wetlands and seagrass meadows, has serious consequences like loss of biodiversity, depletion of exploitable living resources, impaired capacity of the oceans to sequester CO2 and loss of the leisure value of the coastal zone. Not only that, the coastline becomes more vulnerable to the increased erosion associated with rising sea levels.

Carlos Duarte, researcher at the Spanish Council for Scientific Research (CSIC) and coordinator of the debate, informed the public that “coastal habitats are disappearing at a rate of between 1.2% and 9% a year and are now the biosphere’s most imperiled systems, with rates of loss 4 to 10 ten times faster than those of the tropical rainforest”.

The causes of these losses are many and include “the rapidly growing population of coastal zones, currently home to 60% of the planet’s inhabitants, along with the urban development, infrastructure works and ecosystem destruction this growth entails”. Also, increased discharges of nitrogen, phosphorus and organic matter have caused the deterioration of waters and sediments in many of the world’s coastal zones.

Duarte added that climate change is aggravating the impact of human activity on coastal habitats: “Global warming and the resulting rise in sea level are driving the loss and degradation of coastal habitats, reducing the effectiveness of conservation programs and causing an environmental problem of global dimensions which will also have a large economic impact on coastal societies”.

LACK OF OXYGEN IS CAUSING CATASTROPHIC MORTALITY AMONG MARINE ORGANISMS

Increased loadings of nitrogen and phosphorus due to coastal urbanization and the use of agricultural fertilizers are eroding the environmental quality of all coastal ecosystems, with tropical systems especially affected.

Scott Nixon (University of Rhode Island, USA) explained that this process, known as eutrophication, is not a recent phenomenon, but one that first appeared with the spread of urban sewage networks in the second half of the nineteenth century and has been accelerating sharply since 1970. According to Nixon, “we are seeing a clear global increase in the incidence of hypoxia in coastal ecosystems”, a phenomenon whereby the oxygen concentration in water drops so far that it causes catastrophic mortality among marine organisms. Prof. Nixon went on to add that “there is a relationship between the health damage done by the excessive consumption of meat in developed societies and the health damage done to coastal ecosystems by the massive nitrogen emissions associated with meat production”.

MEDITERRANEAN WARMING: A THREAT TO POSIDONIA MEADOWS

Núria Marbà, a researcher at the Mediterranean Institute for Advanced Studies (Imedea) talked about the results of the Praderas project, funded by the BBVA Foundation, which show that most Mediterranean meadows of Posidonia oceanica – extremely valuable ecosystems for the functions and services they provide – have experienced severe shrinkage in the last 40 years. “We have observed a rise in mortality among some marine angiosperm species in the aftermath of heat waves, suggesting that meadow decline will accelerate as the seawaters continue to warm”.

Studies carried out as part of this project, she explained, show that the seagrass meadows along the Spanish coast are losing about 5% of their extension each year, and even more in years like 2003 when the sea temperature rises higher than normal.

Bill Dennison, of the University of Maryland Center for Environmental Science (USA), clarified that “seagrass meadows are vital habitats which grow along the coasts at tropical and temperate latitudes and supply ecological services that make them among the most valuable ecosystems in the biosphere”. It is estimated that 54% of meadows have lost part of their coverage.

Dennison contends that seagrass meadows reflect changes in ecosystem quality and act as global biological barometers for man-made pollution; the meadows are like “coal mine canaries” for the health of coastal ecosystems and their decline is an unequivocal sign of coastal environmental stress.

According to Dennison, “reports on changes in seagrass meadow extension have documented losses since 1980 of an area equivalent to two football fields with each hour that passes. Most worrying of all is that these calculations are very much on the conservative side, since only 9% of seagrass meadows have been studied. So the total area lost probably equates to 10 football fields per hour.”

One of the factors favoring this loss is that seagrass meadows are not in the public eye, despite their ecological importance: “In the case of coral reefs, around 130 news items appear in the mass media for every scientific article published, compared to just 13 items appearing for every scientific article on seagrass meadows. It is vital that we bridge this gap between science and social awareness” added Dennison, before concluding his intervention with a call for “a global conservation effort to halt the loss of seagrass meadows”.

FISH CONTRIBUTE TO THE RECOVERY OF CORAL REEFS

“The combined effects of overfishing, pollution and global change have caused serious harm to coral reefs, which are increasingly being taken over by algae”, alerts Terry Hughes, director of the Australian Research Council Center for Coral Reef Studies.

Recent data suggest that 44% of the planet’s coral reefs have been destroyed or are about to disappear. In Hughes’ view, it is already too late to stop global warming causing more and more episodes of coral bleaching, but we can still combat global warming through strict international regulations on greenhouse gas emissions, while doing everything possible to limit the damage to corals and facilitate their recovery. He also pointed out that once the corals affected by global warming have been replaced by algae, it is extraordinarily difficult to undo the damage.

A spectacular experiment conducted by Hughes in Australia’s Great Barrier Reef has shown that a healthy fish population is the best way to help corals recover from a bleaching episode or a violent storm. “We monitored the recovery of corals that had undergone severe bleaching. What we did was cage fish into certain areas to compare the progress of recovery with and without their presence”, he explained. The results provided clear evidence of the importance of fish populations in maintaining coral health. Specifically, the corals grew rapidly in the areas with fish and were overgrown by algae in their absence. “Maintaining the response capacity of coastal habitats is crucial for their conservation” he concluded.

LOSSES TO DATE SUM 50% OF COASTAL WETLANDS AND 35% OF MANGROVE FORESTS

Coastal wetlands and mangrove forests have been wiped off the map of many world coasts. Ivan Valiela, professor at the Ecosystems Center of Woods Hole Marine Biological Laboratory (USA), warned that “the increase in the human population living by the sea has triggered the destruction of wetlands and mangrove forests, which have lost 50% and 35% of their extension respectively since 1980”.

Valiela affirmed that the rise in sea levels associated with man-made climate change is the biggest threat yet to wetlands and mangrove forests, “which increasingly find themselves trapped between faster rising sea levels and the proliferation of dykes and other defenses constructed to stop coastal erosion”.

Recent events have shown that the loss of these ecosystems also increases human mortality and multiplies the damages caused by storms and other severe weather. In Prof. Valiela’s words, “the loss of wetlands in the Mississippi Delta worsened Hurricane Katrina’s impact on New Orleans, while the felling of mangrove forests in SE Asia pushed up the number of victims of the tsunami disaster of December 26, 2004”.