Page 145 - (DK) Ocean - The Definitive Visual Guide

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Vertical Rock

Underwater cliffs are often more heavily
colonized with invertebrates than gently sloping
rocks. In shallow water exposed to strong waves,
various mobile seabed animals, particularly
grazing sea urchins and predatory starfish, find
it harder to cling to vertical and overhanging
surfaces, and are knocked off by waves in rough
weather. Vertical walls receive less sunlight, and
are harder places for seaweed spores to settle, so
there is less competition from seaweeds here
than on horizontal rock. At sheltered sites,
upward-facing rock is often covered with silt, and
has few animals, but vertical and overhanging
rock, by contrast, is silt-free and may have JEWEL ANEMONES
Multicolored jewel anemones carpet vertical,
abundant life. Ledges and crevices in underwater wave-exposed rocks, with tentacles
cliffs provide safe refuges for fish and crustaceans. outstretched to catch food from the currents.

Crevices and Caves

Irregularities in underwater rock features can provide additional habitats for
marine life. Crevices and small caves provide shelter for nocturnal fish that
hide during the day and are active at night. Elongated fish are well shaped to
live in crevices, while fish that are active by day need holes to hide in at
night and when predators approach. Deep, dead-ended caves contain a range
of habitats, from sunlit, wave-exposed entrances to dark, still inner waters
and sheltered sediments. Shrimp and squat lobsters occupy cave ledges, while
animals that actively pump water
to feed live in the quiet water
inside the cave and coat the walls.
Flashlight fish hiding in caves
during the day signal to each
other with light produced by
bacteria in organs beneath their
eyes. Small crevices are important
because they form a refuge for
small animals from sea urchins.

TAKING REFUGE
The flattened body of this spiny squat lobster
enables it to retreat far into narrow crevices
if threatened, and the spines help to wedge
it in small spaces.

Storms and Scour
Shallow rocky reefs take the full force of waves
during storms, but rock-living animals and
seaweeds on open, exposed coasts are firmly
attached and are generally well-adapted to cope
with pounding waves. Larger seaweeds and
animals will be torn from shallower rocks,
KEELWORMS
making space for new life to settle, while many Keelworms have a hard,
seaweeds and colonial animals can regrow from calcareous shell that protects
holdfasts or basal parts. However, few animals or their bodies from sand scour.
plants survive on rolling boulders or on bedrock
scoured by nearby sand and pebbles. Where rock meets sand, there is
often a band of bare, sandblasted rock. Just above, tough-shelled animals
such as keelworms survive, together with patches of hard encrusting
calcareous red seaweeds. Above
this, fast-growing colonial
animals such as sponges and OCEAN ENVIRONMENTS
barnacles can colonize in the
intervals between storms.

CORALLINE ALGAE
Like a coating of hard pink paint, encrusting
coralline algae can withstand considerable
scouring from nearby sand and pebbles.