Zebra mussels originated in the Caspian sea, but began to spread throughout Europe after the creation of canals in the 1700s and 1800s. In 1985, they were brought to the United States after a ship from Europe released its ballast, and within one year, it had colonized the entirety of Lake Erie, and then went on to colonize all the great lakes. By 1992, it could be found as far south a St. Louis. Zebra mussles cause great damage wherever they are introduced because of their filter feeding and colonization on native species (8)

  Each mussels filters a quart of water every day, and an entire colony could filter an entire lake or river each day (9). Everything it filters is removed, which means that vast amounts of plankton and algae are removed. Other small fish depend on these plankton, which causes their populations to whither, which in turn hurts the populations of larger fish (8). Zebra mussels also have a habit of colonizing on top of other creatures, including native mussels, clams, crayfish, and turtles. This keeps these creatures from being able to eat, breathe, reproduce, or move (9). Wherever they colonize, water clarity is greatly improved (8).

  Sea otters are members of the weasel family. They float on their backs in groups in kelp forests, spending most of their time cleaning their precious, insulating fur (3). The fact that sea otters are keystone species was found out primarily because of this fur (4). In the 1700s and 1800s, Europeans hunted the otters for their fur (4), bringing their population down to only 1,000 (3). One of the main meals of a sea otter is sea urchins. The sea otter keeps the population of the urchins under control. When their population decreased, the sea urchin population boomed. The sea urchins feed on the kelp beds in which the sea otter and many other fish call their habitat, causing those forests to be ruined. The fish population then also started receding (4).

  Unfortunately, it was not until fishermen began to not be able to catch fish in those regions when humans realized that the sea otter was essential for that ecosystem, and an international treaty was designed to keep sea otters from being hunted to extinction (4). Today, their populations have increased dramatically to 150,000 otters, which has allowed the kelp forests, and the fish that inhabit them, to return. Although there are not nearly as many as pre-human interference times, the sea otters are no longer endangered.

  Archer fish live in mangrove swamps and eat insects and other small fish. There are several ways for them to get their prey; by jumping into the air and catching an insect in their mouths, by swimming after it underwater, or by shooting a stream of water at it to know it off an overhanging branch or the like, and then eating it in the water. Their bodies are flat, so above animals can only see a narrow profile of them as they approach, and their markings of black and white camouflage them. This allows them to sneak up on their prey (5).

  Their most amazing adaptation is their ability to shoot insects off of branches and leaves with a stream of water.  To form this water stream, they press their tongues into a groove in their mouth, which forms a tube, and then they quickly snap their gills shut, which forces the water out. This stream can travel up to 3 meters, but archer fish usually only shoot from about 1-1.5 meters away. Their tongue directs the flow of water to their prey, and their eyes are near their mouths for binocular vision. Their eyes do not automatically correct the refraction of light caused by the surface of the water, so archer fish must learn how to account for this. The fish can spit once they reach about 2 cm, although not as far as full-grown archer fish (5).

The bombardier beetle is a carnivorous beetle that hunts on the ground and in trees, and which are found in floodplains and riverbanks of most continents. The beetles, however, have some predators, which they protect themselves from by ejecting boiling, corrosive liquid from their abdomens on them. The beetle has two chambers within its abdomen, one which contains hydrogen peroxide and hydroquinone and the other which contains catalase and peroxidase. These chemicals react to form water, p-quinone, and oxygen. The heat from the reaction boils the solution, and builds up pressure so that it can be discharged from the body (6), which it does with a large bang. At their abdominal tip, the beetles have tiny deflectors which direct the spray; females have two and males have one (7).

  Bombardier beetles need this adaptation because they are unable to take to the air and fly away when threatened. They have covers over their wings, and what this explosion does, is it gives them time to unfurl those wings and get away. It is unknown how they can withstand the blast of their own defense, because the beetles are able to shoot the spray at themselves without harm (7).