OFF to the tropics for your holidays? You might have trouble finding the
beach, and pollution from increased tourism could be to blame. Researchers in
Florida have found evidence that effluent is preventing marine algae from
replenishing sand at Negril, one of Jamaica鈥檚 main resorts. They believe that
other beaches, including some in Barbados, could be disappearing for the same
reason.
Halimeda, a thick, crusty alga, produces 80 per cent of the sand on
Negril鈥檚 beaches. Like corals, the algae build a skeleton of calcium carbonate.
Eventually this skeleton disintegrates to form sand. Halimeda and
related algae supply varying amounts of sand to tropical beaches around the
world.
But during the past decade, Halimeda has run into trouble in the
shallow waters off Negril. Several species of seaweed that are normally only
present in small amounts have overrun corals and the sand-forming algae. At the
same time, the area began experiencing massive beach erosion, with some sections
receding by up to 20 metres.
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鈥淚t鈥檚 only been during the past five years that the erosion problem has
become a panic situation,鈥� says Katy Thacker, executive director of the Negril
Coral Reef Preservation Society. To combat the erosion, the town has been
trucking in sand from a nearby river and piling up sandbags along the beaches.
Prior to that 鈥渢here was a point where people actually had their lawn chairs in
the water鈥�, Thacker says.
Brian Lapointe of the Harbor Branch Oceanographic Institution in Fort Pierce,
Florida, and his colleagues have previously shown in experiments that the
quick-growing seaweeds flourish in high levels of nitrogen and phosphorus, as
found in polluted waters. This could allow the seaweeds to dominate the
widespread but slow-growing calcifying algae, which are adapted to the
low-nutrient conditions typical of tropical reefs.
Lapointe and his team decided to investigate whether this phenomenon is
causing the erosion at Negril, where a growth in tourism and agriculture has led
to increasing levels of pollution. They found that nitrogen isotope levels in
most seaweed matched those in fertilisers used on nearby sugar cane fields.
Seaweed from one site contained nitrogen levels that matched those in sewage,
and in peat removed through land clearing.
Lapointe believes this shows that pollution from runoff and groundwater
seepage has caused the growth of the seaweed. This, in turn, has pushed out
Halimeda, and prevented it from replenishing beaches eroded by storms. 鈥淚
think this is an entirely reasonable conclusion,鈥� says Robert Ginsburg, a marine
geologist at the University of Miami in Florida.
Previously, scientists had thought that overfishing caused the erosion, by
reducing the numbers of fish eating and controlling the seaweed. But without the
high nutrient levels in the pollution, Lapointe says, the seaweed could never
have taken over. He also believes that recent hurricanes and increasing numbers
of sea urchins are making the problem worse by damaging the reefs so they form
less of a barrier to wave erosion.
Lapointe says that pollution could be having similar effects in other areas
with nearshore reefs, and may be the cause of the beach erosion occurring now in
parts of Barbados. 鈥淚t鈥檚 really a global issue,鈥� he says. Ginsburg agrees that
researchers need to explore the possibility that the problem extends beyond
Jamaica