The glacial fjords of Southeast Alaska are deep watery valleys inhabited by a vast array of marine life. Sharks, whales, salmon and teeming schools of herring swim in these waters. Crabs, octopus and shrimp live on the sea floor, a murky realm inhabited by rockfish, cod, skates and halibut, which can grow to weigh hundreds of pounds. But the most important and abundant life-forms in the sea are plankton, tiny, free-floating plants and animals that form the basis of the food web for virtually all life in the ocean.
Phytoplankton are plants, algae that make food from sunlight. Zooplankton are tiny animals; some are single-celled and others are larval forms of crabs, sea stars and fish that eventually transform into free swimming or seafloor-dwelling creatures. Zooplankton feed on each other, bacteria, phytoplankton, fish waste and dead animals. Some plankton are phosphorescent and can make the water glow at night, especially when agitated by a boat wake or wave action.
Plankton feed copepods, tiny, incredibly abundant crustaceans, which in turn feed euphausiids, shrimp-like crustaceans often called krill. They also feed small fish such as herring, smelt, sticklebacks and sand lance. Juvenile salmon, cod, hake, and pollock feed on the herring and krill; giant humpback whales filter the tiny creatures from the water by the ton.
Much of the life in the sea makes daily (and seasonal) migrations up and down through the water column. Zooplankton tend to be deeper by day than at night. Some animals, like sleeper sharks, hunt and swim in an oscillating pattern, ranging between the sea floor and the surface. Schools of herring form balls, large masses of thousands of fish. Salmon and marine mammals pursue these balls of herring.
The sea floor can be rocky, sandy or muddy. Corals, sponges, shellfish, sea pens and other life grow on the bottom. Many sea floor dwellers feed on the rain of detritus (sinking plankton, dead animals and waste) that falls from above.
Different conditions affect the fertility of the Inside Passage: the salinity, depth and temperature of the water, the season of the year, and the proximity to the open ocean, rivers, glaciers and wetlands. Currents and upwelling mix water and create places that are especially productive - and these can be hot spots for fishermen and wildlife watchers.