Adult Red-necked Grebe

I posted a blog a few days ago about a red-necked grebe's chick (go here). The above photo is a photo I took of the adult; males and females show no visible dimorphism and cannot be told apart in the field. If you click on the link you will get a new window and you can move back and forward between blogs to see how they are similar or different. As I said in that blog, I find it amazing to see how the feathers of a young bird change into that of a mature one.

The presence of grebes in a freshwater ecosystem is always heartening to see. Not just because I find them to be interesting, attractive birds, but also because it speaks of the relatively low levels of substances that bioaccumulate or biomagnify. Heavy metals such as mercury and lead and halogenated compounds like DDT and PCBs are persistent chemicals that build up in the tissues of organisms. Bioaccumulation refers to an increase in the concentrations of these materials over time while biomagnification involves an increase of these substances up the food chain.

Mercury by itself does not enter the body tissues with ease, but bacteria act on it to produce methyl-mercury which is easily absorbed. All these toxic compounds which build up over time and increase through trophic levels are fat-soluble. They are stored in fatty tissues in the body and are not readily removed. As the concentrations increase, body metabolism, or parts of the nervous system are adversely affected. Much of the brain, spinal chord, and peripheral nerves use fats to facilitate nerve conduction. DDT, which has been banned in North America since the early '70s, affects calcium metabolism; carnage up the food chain occurred when top predators such as the peregrine falcon could not successfully lay eggs without the shells breaking. Mercury and lead compounds cause nervous disorders, which is why paint and gasoline no longer use lead.

It all begins with pollutants entering the water and being absorbed by phytoplankton and bacteria. Protists consume the bacteria which are then consumed by zooplankton. Plankton of all types is consumed by larger planktonic forms. Aquatic insects and other invertebrates consume a myriad of food sources, each having greater and greater levels of these bio-hazardous contaminants depending on its trophic level (biomagnification) and age (bioaccumulation). Small fish eat the invertebrates which are, in turn, preyed on by larger fish. This is where the grebes come in. And not just the grebes, but otters, osprey, loons, eagles, and so forth. It's the same in marine environments where seals, whales, salmon, and tuna become impacted. When we eat fish from both fresh and saltwater sources, we too become biotic storage bins for these hazardous persistent chemicals.

The bright side of the whole thing is that we are learning about how we impact the environment and what that impact has on us, both directly and indirectly. It is only through careful management and education that we will keep our waterways clean and free from these life-altering contaminants. The next time you see a grebe fishing on a lake surface, remember the value of a clean ecosystem. It's important for everyone.

Thanks for reading.     Ericspix     Eric Svendsen