Читать книгу Oceans For Dummies - Joseph Kraynak - Страница 91

The photic zone is basically the same as the epipelagic zone — the topmost 200-meter (650-foot) layer of the ocean. Personally, we prefer the term photic over epipelagic, because it’s more descriptive (photic means related to light), easier to remember, and easier to pronounce. As with the epipelagic zone, the photic zone describes the layer of the ocean that has enough light for plants to grow.

Aphotic is the opposite of photic. It is the absence of light or, more precisely, insufficient light for plants to grow, which describes about 90 percent of ocean water from 200 meters deep to the seafloor. In the aphotic zone, animals can’t rely on plants to anchor the food web. If they want to eat, they have three options:

 Eat the table scraps that drop down from the photic zone.

 Eat their neighbors (prey tell!)

 Move to vent systems on the bottom (these are few and far between) where chemosynthetic bacteria (instead of plants) called chemoautotrophs anchor the food web. (Chemoautotrophs get their energy from oxidizing inorganic compounds instead of capturing energy from the sun through photosynthesis. Photoautotrophs capture energy from the sun through photosynthesis.)

Some deep-sea organisms establish symbiotic relationships with chemoautotrophs. For example, giant tube worms, which hang out near deep-sea hydrothermal vents, provide a place for the bacteria to live in exchange for organic matter (food). Without the bacteria, the worms couldn’t survive, and without the worms, the bacteria wouldn’t have the “comfortable home” they need to grow and prosper.