Some algae are good for blue crabs but others are not. Algae are photosynthetic organisms that occur in most habitats, ranging from marine and freshwater to desert sands and from hot boiling springs to snow and ice. Algae vary from small, single-celled forms to complex multi-cellular forms, such as the giant kelps of the eastern Pacific that grow to more than 60 meters in length and form dense marine forests.
Algae are found in the fossil record dating back to approximately 3 billion years in the Precambrian. They exhibit a wide range of reproductive strategies, from simple, asexual cell division to complex forms of sexual reproduction. Algae are important as primary producers of organic matter at the base of the food chain. They also provide oxygen for other aquatic life. Algae may contribute to mass mortality of other organisms, in cases of algal blooms, but they also contribute to economic well- being in the form of food, medicine and other products.
Harmful Algal Blooms (HABs) derive their “harmful” stature because they produce extremely potent neuro-poisons or bio-toxins. Some of these compounds are the most toxic substances known. These toxins usually manifest themselves by causing illness and death in human populations that consume products from the sea.
In some very unusual circumstances, due to coastal wind and wave action, HAB bio-toxins can be transported by and through the air, causing severe eye, nose, and throat irritation. In other instances, obnoxious odors and smells can emanate from blooms, especially in confined tidewaters and bays. Marine algae are extremely important to life on earth–probably the most important living organisms on the planet. They impact crabs in at least three ways. First, they appear to be a significant factor in controlling atmospheric carbon dioxide (CO²), a green house gas, which in turn can influence heat retention in the Earth’s atmosphere.
Secondly, the phytoplankton and bacteria are the basis of my food web. Crabs convert inorganic nutrients like phosphate, nitrate, and carbon dioxide to larger more complex organic molecules necessary for life. In turn, these microscopic organisms provide the food for the higher trophic levels in the food web or larger organisms higher in the food web, such as fishes and mammals. For example bivalve shellfish (oysters, mussels, scallops, clams) almost exclusively consume phytoplankton for their food. And lastly, marine algae are important because they can produce a variety of highly toxic compounds–marine bio-toxins. These compounds, some of which can be released to the surrounding water while others are retained in the phytoplankton, can enter the food web and accumulate in fish and shellfish. In most cases we are not affected by these potent compounds, but organisms higher in the food web, such as marine mammals and humans, can be made ill or even die. It is this very lack of affect on the fish and shellfish that you consume that makes marine bio-toxins so dangerous, since there is no outward sign that can forewarn the consumer. In virtually all cases, the marine bio-toxins produced by these phytoplankton, can only be detected through laboratory analysis.
If conditions are right, phytoplankton can sometimes grow and reproduce at such a high rate that they create dense, highly colored patches in the water. When this happens, because the growth rate is so high, they deplete necessary nutrients from the water, particularly dissolved oxygen (O²). When this happens, fish and crabs can suffocate (picture right). This sudden depletion in a small area can be a serious problem in aquaculture since marine creatures are constrained and cannot escape into more oxygenated waters.