Continuing in our efforts to bring attention to the plight of the Goliath grouper (Epinephelus itajara), we are sharing the story of Chris Malinowski, a PhD student at Florida State University, who is searching for answers that can protect this giant fish and those who want to see it on their dinner plates.
Here’s what he has to say:
Coastal fish populations are facing burgeoning and unprecedented threats to their health and sustainability, and many have undergone substantial declines in recent decades. One of the most notable declines is that of the Atlantic Goliath Grouper (Epinephelus itajara). Don DeMaria described in a previous blog post (2014, Nov.25) how this species has undergone extensive overfishing, to the point of a near population collapse. Along with overfishing, habitat destruction and elevated levels of industrial contaminants are at the epicenter of this issue. Of particular concern is mercury (Hg) because of its neurotoxic effects, its ability to bioaccumulate in some forms, and because we have roughly tripled mercury levels in the upper ocean since the beginning of the Industrial Revolution. Mercury has been used as an indicator of environmental contamination and methylmercury (MeHg) is generally considered the most toxic form.
For large, long-lived fishes, like the Goliath Grouper, high mercury concentration may result in severe tissue damage, neurological impairment, reduced growth and development, starvation, disrupted blood chemistry (e.g., immune system function), reduced reproductive success, and even death. Humans that consume fish high in mercury can suffer from a variety of neurological impairments, diseases, and developmental issues. My research focuses on the dynamics of heavy metal bioaccumulation and the effects of heavy metals (with an emphasis on mercury) on Goliath Grouper. Specifically, I use non-lethal sampling techniques (Fig.1) and various analytical methods to answer questions about: (1) how high mercury levels are in various tissues (liver, muscle (fillet), gonads, and blood); (2) what adverse health and reproductive effects result; (3) how/where they are getting mercury (i.e. diet, residential locations); (4) the effects of other trace/heavy metals (e.g. selenium, aluminum); and (5) how these factors are effecting the overall sustainability and recovery of this population.
To answer these questions, I work with my advisors, Dr. Chris Koenig and Dr. Felicia Coleman (Florida State University Coastal and Marine Laboratory (FSUCML)), and colleagues to understand Goliath Grouper ecology. I use what we have learned about the ecology of this species from previous and ongoing research to understand how they are being effected by mercury and other heavy metals. I am at the beginning stages of this research, but preliminary liver and muscle results of mature adults show extraordinarily high concentrations of mercury, which are likely the highest reported for any grouper or any species in their family in the Gulf of Mexico or Atlantic Ocean (total mercury (Hg) wet weight: mean liver = 7.6 ug/g, mean WM = 1.9 ug/g, max liver = 34.3 ug/g, max WM= 3.6 ug/g) (Fig.2).
Muscle mercury concentration (primarily methyl-) is alarming due to the health risks that consumption of this fish would pose, which is a real threat with the ongoing consideration of lifting the harvest ban on Goliath Grouper. All muscle samples tested were above safe human consumption limits (0.5 ug/g wet weight, NRDC) (Fig.2a). Liver mercury concentration (primarily inorganic) is also alarming due to the health risks imposed on Goliath Grouper (Fig. 2b). Liver often has the highest mercury load of any organ due to its role in detoxification, and long-term exposure to such high mercury levels can impose damaging and even lethal effects.
I am in the process of analyzing additional liver and muscle samples in order to elucidate any correlations that may exist between mercury and size, age, sex, reproductive state, and location. Preliminary results indicate no correlation between size and mercury concentration, but sex may be a significant factor, with males having the highest levels of mercury. This pattern may be the result of maternal offloading via periodic egg release, but more analyses will be necessary to determine this possibility. I will analyze gametes (eggs and sperm) and blood for the presence and concentration of mercury. Gamete levels of mercury will indicate whether or not there is maternal or paternal offloading through the release of eggs or sperm, respectively. Blood has a shorter turnover time than muscle or liver, so mercury results will be more indicative of current mercury exposure from the sampling location. I am also in the process of determining whether Goliath Grouper liver tissue is damaged or compromised (on a microscopic scale), and if so, whether this correlates with levels of mercury exposure.
The next phase of this research will be to answer questions 2, 3, 4, and 5 stated above. Thus far, results indicate that Goliath Grouper are both unfit for human consumption and at high risk due to sublethal and lethal effects of mercury exposure. It is critical to continue this work so that we have a more complete understanding of the consequences of mercury and other heavy metal exposure, of how/where they are being exposed, its pathways, and to understand the fate of Goliath Grouper. Stay tuned for further updates on my research as I post updates here on Teens4Oceans.[Note: ppm = ug/g, mercury = Hg, total mercury = THg, methylmercury = MeHg]
Chris will be hosting a Live Chat on explore.org on Jan. 30th at 2 pm EST – hear more from him there!