Filter Feeders

Of all the activities that animals go through on a day-to-day basis perhaps the most important one for staying alive is the gathering of food. Food represents the fuel that organisms use to carry out their day-to-day activities, such as respiration, movement growth and reproduction. There are a wide range of strategies and techniques that animals use to get food, some of the most intricate happen just below the surface of the ocean. While some animals actively hunt for their prey, there is a group of organisms that are much more passive in nature. They are known as the filter feeders or suspension feeders. This group of animals feed by straining suspended food particles from water typically by passing the water over a specialized filtering structure. The strategy of filtering small particulate matter out of the water is hardly new. In fact, it dates back over 400 million years when suspension feeding was quite common in what is know as the Paleozoic era. There is an extremely wide array of animals that use filter feeding as a means of acquiring food. This group includes animals from several different phyla Some of these included are: Fish, Crustaceans, Bivalves, Sponges, Jelly Fish, Worms, and Tunicates. This group also represents a huge variety in species size ranging from the microscopic to the largest animals on earth, the whales. Although filtration seems like a rather simple and straightforward method for capturing food, the details and mechanics on how the animals do it are quite varied and elegant. Some animals create currents with their swimming legs which direct the water through appendages covered with hairs which tend to filter out the food particles. Others, like bivalves such as clams, scallops or mussels have modified body parts into siphons which direct water over sophisticated gills gills to use a combination of mucus and physical filtration to capture particles. Other animals such as polychaete worms and sea cucumbers have feeding appendages that are held up in the current flows flows to capture particles that are drifting by. Filter feeders have evolved within communities of other filter feeders to effectively share the wealth of food available. They do this by specializing on certain size ranges of particles that are often proportional to their own size. The types of food that filter feeders extract from the water column, range from seston – the small particles of living and nonliving matter found in the ocean, to zooplankton to small fish. For this reason small worms and crustaceans would eat much smaller food particles than those of the blue whale. and since filter feeders are dependent on food produced within the ecosystem, they are also subject to natural variations in its supply. If they are sessile or physically attached to the bottom, then they simply run out of food when the concentrations in the water drop out. Filter feeders play a major role in the cycling of energy in marine ecosystems. Because of their ability to clear particles from the water, they form one of the major links in coupling production in the pelagic realm with that in the benthic realm. They are so efficient in their filtering abilities that removal of filter feeders through man’s activities such as fishing or pollution can change the dynamics of entire areas. With a single blue mussel able to filter up to 3 litres of water per hour their positive environmental impact is huge. An example of this impact was witnessed on the east coast of America, when the over-fishing of oysters in Chesapeake Bay resulted in a critical increase in phytoplankton populations in the bay – stripping the water of its oxygen. With a lack of Oysters to filter this phytoplankton and remove the particles from the water the end result was a loss of many of the animals that originally lived in the bay. The Chesapeake Bay program and the National Marine Fisheries service recorded a massive 96% decrease in oyster populations in just over 100 years. Filter feeding is one of the oldest and most varied methods of acquiring food by animals in the ocean. Its use is so widespread in marine ecosystems that many systems would cease to function without it. Filter feeders are key organisms that remove particles from the water column and convert it into body tissue and energy that then become available to other organisms on the ocean floor. The myriad of ways that organisms have evolved to capture these particles over millions of years are sophisticated and elegant. They are customized to allow that particular animal to successfully exploit its own little niche in nature.

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