Pollutants are known for their effects on development and growth of living organisms. I became curious as to what effects they have on different marine arthropods and how they affected development, and that was how I stumbled upon a chapter by Mark L. Botton and Tomio Itow. The book covers horseshoe crab biology and conservation, but the chapter that I read focused on how pollutants affected the development of horseshoe crab embryos and larvae.
The chapter addresses how horseshoe crab populations across the world are declining, and one of the reasons could be pollution. The chapter looks at multiple different studies that were done on different horseshoe crab species and how their development was affected by certain pollutants, and the results were shocking to me. Horseshoe crab are pretty resilient to pollutants all around. Most pollutants had little effect on horseshoe crabs which didn't make much sense to me. Of course, they found that as exposure to pollutants increased, survival decreases, but the level that the pollutants had be at to affect survival was high.
One of the main pollutants discussed in the chapter is heavy metals which is known to affect marine arthropods' survival especially during early development. However, horseshoe crabs, especially their larvae, were found to be able to survive at extremely high levels of certain heavy metals. Embryo development was effected by these metals, though, and many embryos had abnormalities after exposure. If a female horseshoe crab has been exposed to heavy metals, she can pass those pollutants to her eggs. These eggs have a very low survival rate, and they developed slowly with multiple abnormalities.
The chapter also looked at the affects of oil pollution which had even stranger results. Oil could have detrimental affects on horseshoe crabs which is what is expected, but if the oil is at a certain concentration, there is a higher hatching success.
Horseshoe crabs are also able to survive in a wide range of temperature and salinity conditions. The best temperature for development of horseshoe crabs is 25 to 33C, but when exposed to higher temperatures for short periods of time, it had no affect on their survival rate. Horseshoe crabs also develop the best when salinity concentrations are between 20-40%. When salinity was increased or decreased, there was also no change in survival rates, but instead, development took longer.
I found it fascinating how these organisms were able to tolerate such high levels of pollutants, and some pollutants had very little affect on their development depending on what stage of development they are at. It is amazing how horseshoe crabs can also survive in such a wide range of environmental conditions. The chapter contributes the horseshoe crab ability to survive in different environments to the production of stress protein, but it also mentions how more research needs to be done to totally understand horseshoe crab pollutant tolerance. However, seeing how high of tolerance that horseshoe crabs have against pollutants, it is believed that pollutants may not be the reason for declines in their populations.
Source:
Botton M.L., Itow T. (2009). The Effect of Water Quality on Horseshoe Crab Embryos and Larvae. In: Tanacredi J., Botton M., Smith D. (Eds.), Biology and Conservation of Horseshoe Crabs (439-454). Springer, Boston, MA. https://doi.org/10.1007/978-0-387-89959-6_27
Jenny, I have always enjoyed readings on arthropods, especially those integral to shorebird species. You highlighting the resilience that horseshoe crabs show raises an interesting idea. With these organisms showing resilience to these pollutants and their species persists despite high pollution levels, what happens to shorebirds that rely on their eggs?
ReplyDeleteWhen it comes to persistent bio-pollutants, typically the mother can pass these bio-affecters to their offspring. With these eggs possibly containing remanence from the mother's own bioaccumulation, I can only hypothesis how that might persist to the trophic levels that rely on theses eggs as food. Thank you for the thought provoking article!