(East Coast Dolphin Strandings by State and Year. Image source: NOAA)
According to reports from NOAA, as of early October more than 550 dolphins had died and washed up along the US East Coast. The deaths, which NOAA has causally linked to morbillivirus infection, are occurring at a more rapid pace than the massive 1987 die-off which eventually resulted in more than 1100 East Coast dolphin deaths over the course of a 1 year period. By the time the first three months had passed in the 1987 die-off about 350 dolphins had perished. If the current event lasts as long as the 1987 die-off we could possibly see nearly 2000 deaths, setting up the current event as the worst in modern memory.
Morbillivirus — Cause, or Symptom of a More Ominous Problem?
In recent calls to NOAA and the various state institutes of marine science, I continue to receive confirmation that morbillivirus is listed as the primary cause of dolphin deaths. Most of the stranded dolphins have tested positive for morbillivirus and the disease has been implicated in dolphin deaths before. (For reference, morbillivirus is the same disease that causes measles in humans and is similarly virulent in dolphins. )
That said, numerous scientific sources, including The Scientific American and researchers at the NRDC, have questioned whether morbillivirus is the primary cause or just a symptom of a larger problem with ocean health. They point to research showing stranded dolphins with high levels of biotoxins in fatty tissue and individuals that are generally plagued by parasites and other infections. Many of these dolphins display compromised or weakened immune systems as a result of elevated toxicity levels. Meanwhile, a large enough segment of these animals are among the adult population to rule out age as a major secondary cause of mortality.
Algae Blooms as Source of Biotoxins
(Satellite Shot of Green and Brown Tinted Water Indicative of Algae Blooms off the Virginia Coast on Oct 18. Image Source: Lance-Modis)
Sitting on the top of the food chain as one of the oceans’ high-order predators, dolphins consume a large volume of fish. These fish, in turn, are fed by lower food chain sources. As food passes up the chain, any toxin within the food will reach higher levels of concentration, making top order predators, like dolphins, more vulnerable to poisoning.
The biotoxins found in recently deceased dolphins can be linked to harmful forms of algae that tend to develop in low oxygen ocean environments. Some of these toxins can cause various forms of food poisoning in mammals (including humans). Others, like hydrogen sulfide, can build up in adipose tissue to have a number of long-term effects resulting in stresses to major organ systems, neurological and psychological health, and strains on a body’s immunity to disease and infection.
Most of the dead dolphins discovered, thus far, are either males or nursing infants. Both are more vulnerable than females to toxicity due to the fact that males have no means of rapidly shedding biological toxins and infants receive higher doses of harmful substances from toxins concentrating in mother’s milk.
Fasting Dolphins Likely to be More Affected
As toxins build up in the dolphins’ fatty tissues, they come under increased risk of immuno compromise and infection during times when they tap the energy from these stores. Elevated toxicity can happen any time a dolphin may decide to fast rather than forage. As the fats are tapped by the body, the toxins are re-released into the dolphin’s blood stream where they can build up to harmful levels.
Morbillivirus Shouldn’t be So Lethal
Supporting the biotoxin/immuno compromise theory is the fact that morbillivirus shouldn’t carry such a high lethality rate. The virus normally only results in death among the most vulnerable individuals — primarily the very young, the very old, or the already weak or sick. The fact that morbillivirus, in this case, is carrying such a high lethality rate is a direct sign that the virus isn’t the only cause and that a higher portion of the dolphin population is far less healthy than is usual. High biotoxin levels in dead dolphins also point toward a combination of causes.
Dying Oceans and Dying Dolphins
A recent report on the health of the world’s oceans resulted in ominous findings that may also provide further hints as to why so many East Coast dolphins are dying this year. The IPSO 2013 State of the Oceans report found that oceans were experiencing anoxia (loss of oxygen) not just along coastal regions where human nutrient run-off was resulting in massive algae blooms and dead zones, but also in the deep ocean. There, in even the far off-shore waters, ocean oxygen levels were falling. Other high order predators, requiring high oxygen levels to sustain their high metabolisms — like the deep sea marlin — were found to have changed their migratory patterns to avoid deep ocean, oxygen-poor, dead zones forming and expanding throughout the world’s oceans.
The expanding anoxia is both an ocean killer and a direct signal of the changes resulting from human caused climate disruption. Warmer ocean waters hold less oxygen in solution and so they dump more into the atmosphere. In addition, increased fresh water run-off from melting glaciers and more intense rainfall events (due to increases in the world’s hydrological cycle directly caused by warming), result in less mixing of surface waters and deeper waters. Increased run-off also results in more algae blooms which further starve the oceans of oxygen.
These all contribute to increasingly anoxic waters. And once the ocean environment flips to anoxic states, it becomes a host to numerous toxin-producing bacteria. These toxins, in turn, end up in the food chain and directly impact the dolphins and a whole host of other animals.
In other words, a more anoxic ocean is an ocean that produces more harmful bacteria. An ocean full of harmful bacteria is one that increases the risk of dolphin mortality. And when we see spikes in dolphin deaths, as we have on the US east coast this year and on the US gulf coast for every year since 2010, we had better sit up and pay attention. As it’s a clear signal that the oceans, as a whole, are in trouble.
Implications for Both Ocean and Land Dwellers
Because the ocean and the atmosphere are interconnected and because humans greatly rely on the oceans for both foods and livelihoods, it is pure folly to ignore the ongoing plight of the world’s oceans. Toxic fish, mass deaths of ocean animals, and a thinning of the ocean biosphere could result in the loss of enough food to feed upwards of a billion people. Increasing instances of toxic algae blooms will also likely result in higher sickness and mortality rates for those who frequently come into contact with the seas. In the most extreme cases, blooms of hydrogen sulfide producing bacteria could poison the air near toxic algae blooms, resulting in severe hazards for those who live on land.
Transitioning to a stratified, anoxic and/or Canfield ocean state is an outcome of climate change that is all too often ignored. A risk that should be listed among the worst potential outcomes of human greenhouse gas emissions. A risk that has echoes in the great Permian Extinction event in our world’s deep past. It is a danger exists now and the growing risk of its emergence are becoming increasingly apparent.
The dolphins, our ‘sentinels of ocean health’ are dying. And in their deaths are a message that we should be hearing loud and clear. Will we listen?
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Hat Tip to Commenter Steve