Headline-grabbing die-offs of sea life could be just the tip of the iceberg as global warming and pollution allow old diseases to find new hosts, 13 biologists predict in this week's issue (Sept. 3, 1999) of the journal Science.

Dying seals infected with distemper from sled dogs, sardines with herpes virus imported in aquaculture feed and corals killed by a soil-borne fungus are among 34 organisms cited in a report that says many "less apparent" species may be disappearing without notice. Some diseases are introduced from other habitats, the biologists note, while others are familiar ones that overstressed marine life may be losing its natural ability to fight.

"The combined effects of rising temperatures, human activity and pollution are producing a a volatile mix that may threaten tropical corals and temperate species alike," said C. Drew Harvell, a Cornell University associate professor of ecology and evolutionary biology and lead author of the Science report, "Diseases in the Ocean: Emerging Pathogens, Climate Links and Anthropogenic Factors."

The authors of the Science report have expertise in microbiology, ecology, evolutionary biology, invertebrate immunology and biology, marine mammalogy, oceanography and epidemiology. Their survey covers cases, such as morbillivirus infection in dolphins and porpoises, Pfiesteria in Atlantic coast fish and the connection between cholera and plankton blooms, from 1931 to 1997.

The report makes three key points:

• Reports of diseases in the ocean are on the rise, and actual incidents probably are, too.
• Most "new" diseases occur by host shifts — from dogs to seals, for example — and not by the emergence of new microorganisms.
• Emergence of new diseases is aided by a long-term warming trend, extreme El ni–o-type events and human activities — such as aquaculture or land-based farming and development — that modify marine communities.

In addition to Harvell, other authors of the Science report are: Kiho Kim, Cornell University; J.M. Burkholder, North Carolina State University; R.R. Colwell, University of Maryland; P.R. Epstein, Harvard Medical School; E.E. Hoffmann, Old Dominion University; J. Grimes, University of Southern Mississippi; A.D.M.E. Osterhaus, Erasmus University, the Netherlands; R. Overstreet, University of Southern Mississippi; J.W. Porter, University of Georgia; University of South Carolina; G.W. Smith, University of South Carolina; and G. Vasta, Center of Marine Biotechnology, Baltimore.

Noting that some marine diseases are transmissible or toxic to humans — apart from their effect on biodiversity of the sea — Harvell said there is an "urgent need" for interdisciplinary studies of ocean epidemics.

"The molecular and computational tools we need to trace these diseases are beginning to come on line, and we are just starting to understand the mechanisms of disease resistance in marine organisms," she said. "We have identified some indicator species of heightened disease load, such as corals. The puzzle to solve is whether corals are unusually vulnerable to disease — due perhaps to ocean warming — or whether increased diseases in other less apparent species, like crabs and snails, are going undetected."