Interview: Dr. John Incardona on Oil’s Heartbreaking Impact on Fish and What it Means for Gulf Restoration

(This blog is part of a series of interviews with scientists who are championing marine research in the Gulf of Mexico.)

Dr. John Incardona is an ecotoxicologist and researcher at the National Oceanic and Atmospheric Administration’s (NOAA) Northwest Fisheries Science Center who spent much of his childhood in the Gulf of Mexico. Trained as a physician, he did his postdoctoral research into human birth defects, which eventually led him to study how chemicals affect fish embryos. He found that specific chemicals in crude oil are toxic to the hearts of developing zebrafish – a major finding with implications for assessing the health of wild fish before and after large-scale disasters. Ocean Conservancy talked with Dr. Incardona about his work and the new research tools that could be put to use in the Gulf and elsewhere.

Ocean Conservancy: What is ecotoxicology?

Dr. Incardona: Ecotoxicology seeks to understand how chemicals impact ecosystems, from individual molecules at the biochemical level up to the level of cells, individual animals and entire populations. We often need to know how chemical contaminants impact individuals before we can understand the effects on a population or ecosystem.

OC: Could you elaborate?

Dr. I.: Consider the Pacific herring population in Prince William Sound after the Exxon Valdez oil spill. At the time, it was the biggest commercial fishery there. The population collapsed four years after the spill. No one could explain why, or draw clear connections to the oiling of herring spawning habitat. The state of the science in 1989 wasn’t far enough along that the natural resource community understood how exposures to very low levels of crude oil could have subtle but important effects on developing herring embryos — or that these effects could subsequently reduce individual survival later in life.

OC: How broadly studied is this field today? Is it still being developed?

Dr. I.: Ecotoxicology is a relatively young field. The term was coined in the late 1960s, and integrates ecology and toxicology, disciplines with much older roots. For comparison, modern medical toxicology has its roots in the early 1800s.

Ecotoxicology is still very much under development today. The field is moving away from the older “kill ‘em and count ‘em” approach emphasizing simple mortality assays, towards much more sophisticated assessments of organismal health, or so-called sublethal effects. In parallel to human health research, ecotoxicology is benefiting from recent, major advances in molecular and computational biology.

OC: What’s the major challenge?

Dr. I.: The big challenge is taking all this new and complex information about an individual animal’s physiology and connecting to the ecology of large coastal and open ocean habitats. That’s really the cutting edge right now – putting the “eco” in ecotoxicology.

In the U.S. Pacific Northwest, an example is coho salmon populations that have been driven locally extinct in urban watersheds. A small urban stream looks very different from a rural stream, largely due to the multiple stressors put on it. That changes everything, from the insects that live in the stream, to the fish that spawn there and the health of juveniles that survive. The challenge is to find out which stressors are key to limiting population recovery.

OC: How long have you been studying fossil fuel toxicity?

Dr. I.: Since the week I started [at the Northwest Fisheries Science Center], more than 10 years now. Crude oil and its products are extremely complicated chemically. There are a lot of compounds that have biological activity, many of which we haven’t even characterized yet. And the effects can change across different life stages of fish. Early developing embryos and larvae, juveniles and adults – they all have different physiologies, and this affects how they respond to chemicals in the environment.

We focused on a general syndrome in embryos comparable to a birth defect in humans. We wanted to identify the precise cause. We’ve learned that the syndrome results from heart failure. It’s caused by malformation of the developing fish heart by a specific, small set of chemicals among the thousands in crude oil.

Photos of zebrafish embryos. The arrow points to fluid accumulation around the heart. The scale bar (black line) in the top photo is 1 mm.

OC: That seems significant.

Dr. I.: It’s proven to be quite significant. It has also generated a new line of research that is helping us develop novel tools. The goal is to improve our ability to assess the health of a wide range of fish species in habitats affected by fossil fuels throughout the country and the world.

OC: What does your research in the Pacific Northwest tell us about the Gulf of Mexico and where to begin looking for the harm caused by the Deepwater Horizon disaster? And what do we want to know before restoration can begin?

Dr. I.: The take-home message from our work in the Northwest, Alaska and California is that developing fish embryos are very sensitive to oil toxicity – more so than nearly all life forms that have been studied to date.

The key question for the Gulf of Mexico spill is whether fish were spawning in proximity to oil, and, if so, whether environmental levels were high enough to cause losses of embryos and larvae, or cause adverse effects that might be delayed in time. Answers to these questions will eventually help NOAA and others estimate impacts to fish species under their management.

OC: Can you talk about work being done with “indicator species,” or species that give us a snapshot of the relative health of an ecosystem?

Dr. I.: Like a canary in a coal mine, fish have always been very good indicators of habitat quality, as a basis for ecosystem health. In fact, NOAA has been monitoring indicator or sentinel species throughout the U.S. for decades. How we choose a sentinel species depends on a number of different factors – distribution, sensitivity to pollution, economic and ecological significance, ease of sampling, and so forth. Indicator species can reveal long-term trends, identify pollution hotspots and serve as a warning for newly emerging contaminants.

For our work on fossil fuels in particular, we are trying to develop tools that will help those involved in surveillance and restoration. In most cases, you are not likely to have healthy fish embryos in unhealthy habitats.

OC: So these are all areas of research that can contribute to establishing a baseline for restoration efforts?

Dr. I.: That’s the idea. As restoration goes forward, the progress should be evident in the health of the species that are supposed to benefit from the cleanup efforts. In the Pacific Northwest, we’ve seen this from the long-term monitoring of fish at Superfund sites, before and after restoration.

OC: How do you do your research? What’s involved?

Dr. I.: We do research the same way it’s done at major academic medical centers. Medical scientists use models for humans, such as mice, rats, cell lines and molecular assays. We use the small, tropical freshwater zebrafish as a model for wild fish. This way we can rapidly answer basic questions about the physiological effects of chemical pollutants like crude oil.

Some wild marine species are really difficult to cultivate and work with in a laboratory, but we benefit from some very good partnerships with academic and other government labs. When we transfer studies from our laboratory model zebrafish to a marine species, it’s almost always a big team effort.

The recent advances in molecular and computational biology are a big help for our studies on marine species that are tough to obtain in large numbers, such as bluefin tuna.

OC: Can you share more about the research involving fish exposed to sublethal levels of oil?

Dr. I.: Studies of pink salmon after Exxon Valdez led to the discovery of what we call “oil exposure syndrome,” which resulted in malformed embryos. Embryos exposed to lower crude oil levels looked normal on the outside. But when released as juveniles, those fish died prematurely. That was a big black box and we really had no idea what the mechanisms were.

Zebrafish embryos are transparent. You can get a lot of information by simply looking at them under the microscope, which is how we were able to tell the hearts of exposed fish were being impacted by crude oil.

We could see that hearts in oil-exposed embryos functioned so poorly that fluid backed up behind them, leading to malformation. The fluid backup is a sign of reduced cardiac output, just like fluid accumulates in a person with heart failure.

In embryos that survived lower level exposure and looked normal – no fluid accumulation – we still found that these animals had subtle heart malformations later as adults. Later in life the speed with which a fish can swim depends on its cardiac output, and adults exposed to crude oil as embryos swam slower than their siblings grown in clean water. Swimming speed obviously is important for survival, for species that are either predators or prey.

OC: Any thoughts you wish to leave with us? Perhaps on what restoration standards might look like?

Dr. I.: (Laughing.) Pay attention to the fish! They will tell you if restoration is working as intended. You just have to ask them the right questions.

View bluefin tuna maps and hazardous materials spill maps from the Gulf of Mexico by clicking the thumbnail images below.

Hazardous materials spills.

Bluefin tuna

More from This Blog Series:

Browse Topics
Our work is focused on solving some of the greatest threats facing our ocean today. We bring people, science and policy together to champion innovative solutions and fight for a sustainable ocean.
Read more
View Current Posts
Back to Top Up Arrow