Marine Communities Divided By "Boundaries"

Ocean zones can be categorized in a variety of ways by the boundaries that separate them.

Thus the boundary between the pelagic zone (the water column) and the benthic zone, or sea floor is the level of water involved. And of course each zone is divided into furrther zones, with specific levels for each.

Then there is the boundary between light and dark - between those organisms that thrive in sunlight (th e photic zone) and those that thrive in darkness (the aphotic zone.)

Another boundary is that of chemistry. Warmer water, or water that is less salty, is less dense than colder, or saltier watter, and tends to stay on the surface. Between the warmer water and the cooler water is the "pycnocline", or "zone of rapidly changing densiry" and different organism live in each.

Currents are another set of boundaries. The water is full of plantonic organisms that are weak swimmers - travelling against or even crossing major currents is impossible for these organisms.

But there are yet more categories!

Ocean zones can also be categorized based on the dominant features of a particular community.

On land, there are forests of trees. In the oceans, there are kelp forests. Bull kelp, for example grows very quicklyy. A tiny spore can grow into a 200 foot long plant in only a few months.

On land, there are tall-grass prairies, in the oceans, there are sea-grass meadows.

Some communities, such as mangrove forests and salt marshes, , straddle the area between land and sea.

Then there's such communities as:
Coral reefs
Mussel reefs
Hydrothermal vents
Methane seeps

Each type of community is distinct, and has a unique set of opportunities and challkenges for the organisms that live there.

Bibliography
Ocean Science 101, Jennifer Hoffman