Whether we live close to them or not, we rely on our oceans for so much more than fish. Oceans also filter toxins, absorb carbon dioxide, provide recreation for millions and yields important marine products, such as biofuels from algae.
These ocean services can be severely compromised by disease outbreaks among little-appreciated plants and animals like seagrasses, corals, sea stars, lobsters, abalones, oysters and fish. Just in the past year, we have witnessed thousands of strandings by sea lions from domoic acid toxicosis, thousands of beachings of dolphins from morbillivirus and widespread devastation of starfish due to sea star wasting disease. Over 20 species of sea stars — keystone species that were common three years ago — have virtually disappeared from many California, Oregon and Washington shores.
That's the bad news. The good is that even as the threat of high impact disease outbreaks is increasing in the ocean, so is our potential to manage these ecosystems for resilience to disease. We know a lot about how to manage better-studied diseases in aquaculture for consumer favorites, such as oysters and salmon, and we are rapidly increasing our understanding of disease management in wild species, as well.
Management of marine diseases has direct implications for human health. The incidence of human infections with pathogenic vibrios, such as V. parahaemolyticus and V. vulnificus, is increasing. Vibriosis can cause human gastrointestinal illness, septicemia, cellulitis and, in some cases, death.
A recent paper shows that marine fisheries and aquaculture can suffer severe economic impacts from marine diseases. The global pandemic of white spot viral syndrome in shrimp cost billions worldwide in economic losses in our world's most valuable fishery. At the height of the outbreak, this led to losses of over $6 billion in Southeast Asia and $1 billion in Ecuador. This is only one disease; more than 65 different marine diseases affect the economics and sustainability of our wild and farmed marine fisheries.
These outbreaks are out of sight and mind, under the ocean, and so the scale of the impacts are rarely appreciated. However, as the potential for outbreaks and their impacts grows, this will change.
Management of diseases in species moving across vast oceans may seem an impossible task. However, scientists and management agencies have demonstrated success with appropriate resources and organization.
When diseases are detected early, there are many routes for intervention. Management programs often target the host directly by reducing the pool of infectious or susceptible individuals. Marine mammals can be vaccinated against diseases, sick populations or individuals can be culled — as has occurred in abalone infested with sabellid worms — and animals like oysters can be bred for resistance to disease.
Our abilities to detect diseases before they are outbreaks is continuously evolving. For example, Canada's Department of Fisheries and Oceans is developing a bioassay that can simultaneously test for the presence of 46 fish pathogens that can lead to disease outbreaks. Other effective strategies for disease management involve manipulating environmental conditions. For example, seagrasses and mussels have been shown to remove waterborne pathogens through sediment retention and filter-feeding, respectively. Maintaining or enhancing these key organisms can create healthier ecosystems that are more resilient to disease.
As the too-slow response to the Ebola virus outbreak showed on land, we need to improve our capacity to respond to sudden disease outbreaks. The first step is to immediately identify the agent and assess its routes of transmission. In the case of Ebola, it was a human disaster that our response lagged behind the rate of disease transmission. In the case of marine diseases, prevention and early intervention is paramount since management of full-blown outbreaks is particularly challenging in the open waters of our ocean. But even if an outbreak starts, the capability to respond promptly will improve our chances of a good outcome.
Legislation currently being considered by Congress could make all the difference. The Marine Disease Emergency Act (H.R. 936) could enhance the funding and organizational framework to implement effective disease management in the ocean.
Let's tip back the balance to a healthy ocean.
Harvell is a professor of ecology and evolutionary biology at Cornell University and faculty fellow at Cornell's Atkinson Center for a Sustainable Future. Groner is a postdoctoral fellow in the Atlantic Veterinary College at the University of Prince Edward Island, part of the Canada Excellence Research Chair program in aquatic epidemiology.