Page 245 - (DK) Ocean - The Definitive Visual Guide

PLANT LIFE 243

Above High Water

Above the reach of the highest tides, the environment
is essentially terrestrial, but its proximity to the sea
makes life hard for all but a few specialized flowering
plants and lichens. In places, the coast is covered with
dunes of sand blown from the seashore. Dunes are
often alkaline, being rich in calcium carbonate
from marine shells and maerl (see p.245). With few
nutrients, dunes only support hardy colonizers tolerant
of infertile and salty soil. Acidic dunes made from
sand with little shell support many lichens and mosses
such as golden dune moss. Marram, a grass with a
fast-growing root and rhizome network stabilizes
dunes and takes the first steps toward soil formation.
Plants that can fix nitrogen in root nodules, such
as the casuarina tree, have an advantage here.
PLANTS OF SHIFTING SHORES
Sea mayweed, with daisylike white On rocky cliffs plants are safe from grazing animals
flowers, and oyster plants, with but must withstand salty spray, drying winds and
their dark blue-green leaves, scanty soil. Plants such as sea campion have very long
are salt-tolerant flowering
plants that grow on roots that reach deep into rock crevices for water
semi-sheltered draining from the land. Plants with succulent leaves
shores of shingle. and waxy cuticles can store the water they find.

ABOVE AND BELOW
THE TIDE LINE
Marine plants range from
coastal trees growing
above the high tide mark,
such as the Coconut Palm,
to seagrasses, the only
wholly aquatic marine
flowering plants, below it.

Between the Tides
Plants between the tides have to live both in and out of
water in variable conditions sometimes hot, dry, and salty,
and at other times drenched with cold, fresh rainwater.
Intertidal zones support green and red seaweeds, seagrasses,
and mangroves. Many green seaweeds are tolerant of
brackish water and grow down the upper shore in strips
following freshwater seeps and streams. Lower down, delicate
red seaweeds thrive in pools or in the damp beneath tough
brown seaweeds. Many are ephemeral, growing quickly
in fair conditions and dispersing many spores. They may SUBMERGED SALT MARSH
quickly cover tropical coasts where monsoons bring humid conditions, The salt-tolerant sea pink
but then dry up and blow away when the sun returns. Seagrasses grow grows in salt marshes, which
on lower intertidal flats; here the sediments retain moisture until the tide develop on sheltered coasts
returns. In the tropics, mangroves colonize intertidal sediments, but only in temperate regions. Like
other salt-marsh plants, the
their roots are regularly submerged, while the rest of the plant remains in sea pink is submerged only
the air. In colder climates, salt-marsh vegetation develops on mudflats. in the highest tides.

Aquatic Plants
Only microalgae, seaweeds, and seagrasses live
permanently submerged in seawater. All seaweeds
can absorb nutrients and gases over their whole body
surface, so they do not need the transport systems of
land plants, and their holdfast simply attaches them to
the seabed. Seagrasses have a land-plant anatomy, so
they need extra structures such as air spaces (lacunae)
to aid gas exchange. Plants living in seawater can only
thrive in the top few yards,
because enough light for
SEAWEED BED
Green seaweeds in the photosynthesis cannot
English Channel include penetrate beyond this.
Codium (in the foreground) Many marine plants are OCEAN LIFE
and sea lettuce (lower right).
They are growing here with tough to deter grazing
an unrelated brown seaweed animals or produce toxic
called serrated wrack. or distasteful chemicals.