Otters are an essential keystone species. A "keystone species" is a species that is critical to how an ecosystem functions because it has large-scale effects on the communities in which it lives. Along the Pacific coast, sea otters help control the sea urchin population. Fewer sea urchins in turn help prevent kelp forests from being overgrazed. In California, research has found that sea otters also enhance seagrass beds, and in Alaska's Glacier Bay National Park, sea otters' expansion into the area marked a gradual return of a more diverse ecosystem and an exciting moment in colonization efforts.

When hunting, dolphins produce bubbles to herd their prey to the surface. They sometimes also use a hunting technique called 'fish-whacking', where they use their tail to hit fish and so stun them - making them easier to catch.

Geoducks filter feed using their long siphons to bring seawater down to where they are buried. They remove excess nutrients, algae, and organic matter from the water before releasing it. That process actually improves water quality and once they're harvested, they remove those materials from the ecosystem completely.

There has been much confusion about the lifespan of the orange roughy species. When the fish first came to the market, it was believed that they only lived to about 30 years of age. Later in the '90s, it was discovered that the orange roughy lived a much longer life than that. The average lifespan of the fish is now estimated to be between 125-156 years! However, much older specimens have been discovered in many places. In 2015, an orange roughy of 230 years old was caught in New Zealand, while in Tasmania, the oldest fish ever caught had a record age of 250 years! In comparison, the bowhead whale lives up to 200 years.

Even though the pokémon Qwilfish takes its name from the quill fish it more closely resembles a puffer fish. Quill fish have an elongated and slender body. Its body appears like a quill because the dorsal and anal wings are long and tall. The dorsal fins are made up of 90 low spines that are isolated and these are followed by around 190 soft rays.

Honeybees collect honey to survive through the winter, but bumblebees don't need to prepare for the cold because they die in the fall. Only new queen bumblebees hibernate and make it until spring — their naturally depressed metabolism gives them a longer lifespan than the rest of the colony. While wild bumblebees do collect sugary nectar, they always consume it before they have a chance to convert it into honey.

Beavers have a tremendous impact on ecosystems. Dams alter the flow of rivers and can flood hundreds of acres. Dams prevent erosion and raise the water table, which helps purify the water as silt builds up and breaks down toxins, according to ADW. As sediment and debris build up, carbon increases and nitrogen decreases. The chemical changes alter the type of invertebrates, and the new water source attracts new species of birds, fish and amphibians. Flooded timber dies off and a forest becomes an open water ecosystem. Over time, abandoned dams decay, and meadows appear.

Snake-necked turtles are a group of side-necked turtles with necks that range from nearly as long as to slightly longer than the shell. They inhabit the waterways of Australia and southern New Guinea and possess the longest neck of any group of turtles in the world. The neck is so long that it cannot be retracted completely beneath the margin of the shell. They are carnivores and prey on fish. When hiding from predators or stalking prey, the neck is folded against the body. When prey is close, the neck and head lunge forward, and the animal opens its mouth and throat to create a vacuum. Water and prey are sucked into the mouth, which snaps shut. The mouth may then open slightly to allow water, but not the prey, to escape.

Blue whale calves are the biggest babies on Earth, easily, and at birth already rank among the largest full-grown animals. They pop out at around 8,800 pounds (4,000 kg) with a length of some 26 feet (8 meters). They gain 200 pounds (90 kg) a day! Their growth rate is likely one of the fastest in the animal world, with a several billion-fold increase in tissue in the 18 months from conception to weaning.

In the Mediterranean Sea the spawning season lasts from June through August. Female tunas are typically around eight years old when they lay their first hatch of eggs. Males and females swim together during spawning, which typically occurs at night when 10+ million eggs are released from each female. This may seem like a lot, but each individual egg has only a 1 in 40 million chance of surviving and maturing into a full grown adult tuna.