Page 218 - (DK) Ocean - The Definitive Visual Guide

216 INTRODUCTION TO OCEAN LIFE

Bottom-living

ANIMALS LIVING ON THE OCEAN FLOOR or within its sand
and mud, either moving over it or firmly attached, are called
benthic animals. On land, plants provide a structural habitat
within which animals live. In the ocean, this is rarely the case,
except in shallow, sunlit areas dominated by kelp, seaweeds,
or seagrasses. Instead, wherever areas of hard sea bed provide
a stable foundation, a growth of benthic animals develops,
fixed to the sea bed and often resembling plants. A sea bed
of shifting sediments is no place for fixed animals.
Here, a community of burrowers develops instead.
BENEATH THE SEAWEED
Below the seaweed-dominated
Fixed Animals zone around northern European
coasts, on sea beds too deep
Many benthic animals such as sponges, sea squirts, corals, and hydroids and dark for photosynthesis, dead
spend their entire adult lives fixed to the sea bed, unable to move man’s fingers, sponges, and tube
around. On land, animals must move around in search of food, whether worms typically grow attached to
subtidal rocks.
they are grazers, predators, or scavengers. In the ocean, water currents
carry an abundant supply of food in the form of plankton and floating
dead organic matter. Fixed animals can
take advantage of this by simply catching,
trapping, or filtering their food directly from
SEABED IN THE SUN
the water, without having to move from
Seaweeds anchor in the tidal zone of rocky shores
place to place. When it is time to reproduce, and on rocky reefs, such as this one in the Canary
they simply shed eggs and sperm into the Islands. On sunlit, temperate sea beds,
water, where the eggs are fertilized and grow it is seaweeds that provide the
community structure.
into planktonic larvae. Sometimes, they
retain their larvae or eggs, and release them
REEF-FORMING TUBE WORM
In some Scottish sea lochs, the only when the young are well developed.
chalky cases of tube worms Water currents distribute the offspring to
form substantial reefs. new areas, where they can settle and grow.
Mobile Animals

Dense growths of seaweeds or fixed animals provide shelter and
food for many mobile animals. Grazers, such as sea urchins,
crawl through the undergrowth, eating both seaweeds and
fixed animals. Meanwhile, crabs, lobsters, and starfish
scramble and swim around, hunting and scavenging
for food. Sea slugs are specialist predators, each
species feeding on one, or a few, types of
bryozoans, hydroids, or sponges. Sea slugs
therefore live in close association with
their prey and rarely stray far. Kelp
holdfasts provide a safe haven for
small, mobile animals such as worms.

OCEAN LIFE FISH IN DISGUISE

Scorpionfish live on the seabed among the
seaweeds and fixed animals. Their intricate
skin-flaps blend in with this habitat.