Swimming in a Sea of Chemicals
We don’t often think of it as such, but we live in a chemical world; we always have and always will. When you take a walk along the shore and fish the surf, a multitude of processes are firing away in your body, breaking and creating chemical bonds to produce the energy to fire impulses to muscles that move you toward a breaking fish. Toss a lure into the air and it splats down into a sea of chemicals (H20, mostly) that allow every form of life (at least all those we know of) to eke out an existence on this chunk of rock we call Earth. Take in a giant breath of air and your lungs are flooded with oxygen and a suite of other chemicals. Scan the landscape and everything within the scope of your vision is nothing more than a complex array of chemicals bound together in myriad patterns and structures. Chemicals – we cannot get away from them, and yet the word almost immediately evokes a sense of danger and foreboding.
We have been hearing a lot lately in the news about chemicals – chemicals leaching out of plastics into the foods we eat and the liquids we drink; chemicals, in the form of gasoline, spiraling upward in cost and negatively impacting our way of life; chemicals seeping into groundwater and runoff and making their way to the sea, where they are possibly impacting the creatures that live there in a negative way. One chemical in particular that has been in the news of late is methoprene, a chemical used as a larvicide to control mosquito populations and reduce the risk of mosquito-borne diseases such as West Nile virus and EEE (eastern equine encephalitis).
Few, of course, would argue the benefit of reducing mosquito populations and the various diseases they transmit. In the case of methoprene, however, there is concern that because the chemical eventually finds its way into the sea, it negatively impacts marine crustaceans, particularly the lobster. With lobster being of such commercial importance, any threat to the health and well-being of the industry is to be taken seriously.
Methoprene is a chemical that affects the growth of mosquito larvae, but it does not cause outright death like more typical insecticides do. In essence, methoprene is a growth regulator that keeps the mosquito larvae in its juvenile phase, preventing it from metamorphosing into an adult insect. With its life cycle thus interrupted, the mosquito larvae dies and the population of adult mosquitoes – the ones responsible for the transmittal of disease – is curtailed, and disease prevalence is reduced. One perceived benefit of methoprene is that since the chemical is not directly toxic, it is presumably safer to use.
So how do we get from the happy place of reduced mosquito populations and disease prevalence to the nasty wasteland of lobster mortality? Methoprene, along with a suite of other chemicals that control insect populations by breaking the life cycle rather than by killing them outright through toxicity, works its magic by disrupting and/or blocking hormone production. More specifically, methoprene disrupts the production schedule of juvenile hormone, which must be absent for the mosquito larvae to change into its adult form. Although physiologically the mosquito larvae is no longer producing juvenile hormone and is ready to become an adult, when methoprene is in the water, the larvae “senses” juvenile hormone as being present and the change to the adult form doesn’t happen. These kinds of chemicals, which mess with hormone production, are technically referred to as endocrine disruptors.
So how does all this get us to a point in the story that leads to the ocean and possible impact to lobsters? Well, in order to reach the mosquito larvae, methoprene is placed in catch basins and other places where water pools, stagnates and creates conditions conducive to mosquito population growth. During rainstorms, some of the treated water can make its way from the catch basins into rivers, estuaries or directly into the sea. Once there, you’d assume that dilution and currents would prevent any kind of problem, right? Well, maybe not.
Ever hear of lobsters referred to as “bugs?” There is a reason for that: lobsters, along with their many relatives in the crustacean group, are very similar in form and function to terrestrial insects. You can think of crustaceans as the marine analog of insects, and as such, endocrine disruptors that work on insects can potentially have some impact on crustaceans. Juvenile hormone/endocrine disruptors have been found to affect lobsters, grass shrimp, mud crabs and a variety of other crustaceans much like they do mosquitoes, hindering their ability to molt from one larval phase to another. Other impacts have been suggested as well.
But the jury is not in on whether or not it is methoprene per se that is harming crustaceans – lobsters in particular – or if it is another similar endocrine disruptor, or perhaps something entirely different. Some researchers have suggested causal links between endocrine disruptors and lobster shell disease, which has erupted as a major problem in Long Island Sound and is of concern in regions both to the north and to the south.
Lobsters like this one, ravaged by epizootic shell disease, are becoming more common in southern New England waters. Could a mosquito-control chemical be responsible? (Photo courtesy of Barbara Somers, Rhode Island Sea Grant & the University of Rhode Island)
Dr. Hans Laufer at the University of Connecticut, for instance, thinks there is a connection between endocrine disruptors and lobster shell disease, and he is in the process of conducting research that will help shed light on the issue. While his research does yet not show the same type of impact as for mosquito larvae – the inability to molt to adulthood – he does see other impacts that can be related back to endocrine disruption. If nothing else, he sees a weakening of the shell of the lobster, which then makes the lobster vulnerable to disease, parasites and increased stress, which can eventually lead to death.
But there is still a long way to go in getting a grasp on things. Other researchers, as part of the New England Lobster Shell Disease Initiative, are conducting a suite of research projects that together will move our understanding of lobster shell disease forward by significant strides. Results of this research will begin to unfold about a year from now, and you can bet that you will hear lots more about this issue, so stay tuned.
That the introduction of chemicals to control one species might have impacts on other species should not come as a huge shock. We have witnessed this many times in the past with a variety of chemicals, DDT being a particularly nasty example. We tend to forget how closely related organisms are and how sensitive they can be to similar threats. DNA mapping has shown that humans and chimpanzees are 99 percent similar in genetic coding, and that we share 75 percent genetic similarity with a pumpkin! Who would have guessed?
Though it is unlikely that humans will grow on vines anytime soon, it is highly likely that the chemicals we devise to have specific impact on one type of organism will have further, unintended impacts on other organisms. The similarities across common ancestries make the odds increasingly high for such an event to occur, and we need to be vigilant and proceed with caution. The base of most marine food chains incorporates the very abundant zooplankter, the copepod, which is a crustacean.
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