Ocean diseases are spreading, and scientists aren’t sure if these are simply isolated occurrences or a sign of a larger problem. Disease is increasing among most kinds of marine organisms, according to a long term study by Cornell University and the National Center for Ecological Analysis and Synthesis (Ward and Lafferty. 2004). The study implicates a host of factors, including global warming, habitat destruction, and human overfishing, could be contributing to the increasing sickness among the world’s marine life. Only sea grasses and sharks display no apparent increases in disease levels.
There are many ocean-borne diseases that can affect ocean life. In the 1960’s, oyster harvesters off the shores of Maryland typically caught between two and three million bushels a year. But then a parasite, Perkinsus marinus, made its way up the coast from southern waters. That parasite causes a disease called dermo. Since the 1980s the annual oyster catch off the Maryland coast has averaged only 150,000 bushels a year. MSX, a disease caused by another parasite, is infecting some of the same populations. Scientists are studying the spread of both diseases, and trying to figure out whether or not their spread is related to shifts in ocean surface temperature.
In the 1980’s, a water-borne pathogen wiped out a type of sea urchin, causing dramatic shifts in parts of reef ecosystems. Now there appears to be an increase in diseases affecting coral. One fungal disease has been reported to cause lesions and tumors that can destroy entire reefs.
Marine life may be more vulnerable to diseases if they are contaminated. Marine mammal species are more likely to be infected by viruses if the mammals contain high levels of PCBs or other persistent organic pollutants.
Human diseases involving marine biotoxins, viruses, and bacteria appear to be increasing in the Northwestern Atlantic, Caribbean, and Gulf of Mexico, with seafood safety becoming a significant public health issue. In addition, since the early 1970s, the same region has seen a succession of acute and chronic diseases afflicting multiple plant and animal species groups. Diseases can serve as indicators of declining ecological integrity in coastal marine systems.
Algal biotoxins can cause paralytic shellfish poisoning (PSP), amnesic shellfish poisoning (ASP), and neurotoxic shellfish poisoning (NSP) in people eating contaminated shellfish and can adversely affect shorebirds, marine mammals, fish, shellfish, invertebrates, coral reefs, and seagrass beds. There have been increasing reports of mass mortalities of marine mammals and sea birds, including bottlenose dolphins off the United States east coast and Gulf of Mexico, and manatee off Florida. Scientists have reported the spread of fibropapillomas in sea turtles and die-offs afflicting fish, shellfish, and other invertebrates.
Many disease outbreaks peak during El Niño events, suggesting a significant climatic influence on the interactions among hosts, pathogens, and the environment. Anomalous (unusually warm or cold) sea surface temperatures can displace food sources, reduce host defenses, and alter the growth of disease pathogens. Intense rains and flooding (extreme weather events) can provide pulses of nutrients, chemical pollutants, and pathogens, all of which can promote disease outbreaks.
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