Most marine parks fail to protect the world's tropical coral reefs from illegal fishing, mining and pollution, a Canadian-led research team says.

The reefs are home to species including clown fish and sharks, and the areas help protect coasts from erosion.

Scientists are casting doubts on the effectiveness of marine protected areas.
(Courtesy of Census of Marine Life)

On paper, marine protected areas cover nearly 19 per cent of tropical reef habitat.

"Less than two per cent are extended protection complete with regulations on extraction, poaching and other major threats," the study's authors wrote in a policy paper in Friday's issue of the journal Science.

Camilo Mora of Dalhousie University in Halifax and his colleagues studied how reefs are protected by marine protected areas (MPAs) from the Caribbean to the Indian Ocean.

"Unfortunately, the establishment of MPAs is rarely followed by good management and enforcement, which means that the numbers of MPAs and their coverage can be misleading indicators of effective conservation," the team said.

They call for global conservation strategies to be reassessed to expand the size of MPAs, as well as curb poaching and fishing on reefs.

Humans harm species: study

The same issue of the journal includes a report on human disturbance to coastal ecosystems in Europe, North America and Australia.

The study looks back to the impact of the ancient Romans on the Adriatric Sea, noting the damage has accelerated in the past 150 to 300 years as populations and demand for resources have grown.

Historically, estuaries and coastal seas offered habitat for commercial fish species, and a buffer for natural disasters, says Heike Lotze, a marine biologist at Dalhousie and the study's lead author.

Human exploitation is responsible for 96 per cent of species extinctions, often in combination with habitat destruction.

The two destructive effects should be a priority for restoration plans, the study's authors said.

Despite the degradation, some birds and seals are recovering, raising hopes for conservation efforts.