Page 248 - (DK) Ocean - The Definitive Visual Guide

246 PLANT LIFE

Green Seaweeds frond

GREEN ALGAE LARGE ENOUGH to be seen with the naked eye are
DOMAIN Eucarya
known as green seaweeds. They are classified with the microscopic
KINGDOM Plantae
green algae, or microalgae (see p.248). True plants of the sea, they have
DIVISION Chlorophyta
pigments and other features in common with higher plants. They can large, fibrous
holdfast
CLASSES About 8 be abundant in tropical lagoons, and proliferate seasonally on many
SPECIES 5,426 temperate seashores. Ulva (sea lettuce) is grown for food. SEAWEED BODY PARTS
Green seaweeds have a simple structure, with an
erect frond and a disk-shaped or fibrous holdfast.
Habitats Anatomy This tropical Udotea species has calcified fronds
with many branched siphons.
Green seaweeds often attach to rocks on rocky The body structure of green seaweeds lacks stems and
coasts, particularly in temperate and cold waters, roots. Green seaweed shapes range from threadlike
and are ephemeral colonizers in seasonally (filamentous) to tubes, flat sheets, and more complex FRAGILE FRONDS
This delicate Bryopsis
disturbed tidal and shallow subtidal habitats. forms. Their bright green color is due to the fact that plumosa has coenocytic
Ulva species, such as sea lettuce, dominate in their chlorophyll is not masked by additional pigments, fronds, meaning its
high-level rock pools, or where fresh water unlike red and brown seaweeds. Many of the features fronds do not have the
crosswalls common in
seeps over the shore, since they can withstand of green algae, including their types of chlorophyll, are other green seaweeds.
changes in saltiness and temperature. The more shared by higher plants (mosses, liverworts, and vascular
delicate Cladophora and Bryopsis species live in plants), so green seaweeds appear to be more closely
rock pools or among red and brown seaweeds related to higher plants than to red and brown seaweeds.
in the shallow subtidal zone. Green seaweeds
also thrive in shallow, tropical lagoons, where
species of Caulerpa, Udotea, and Halimeda are
often abundant. Caulerpa species have runners
(stolons), which creep through sand or cling to
rock, while the bases of Udotea and Halimeda are
a bulbous mass of fibers that anchor in sand.
Halimeda (cactus seaweed) is heavily encrusted
with calcium carbonate, which breaks up when
the plant dies, contributing to the lagoon sand.

CODIUM FOREST
FLEXIBLE SEAWEED This mini-forest of Codium fragile is
Able to handle fluctuations in salinity growing on shallow rocks in a sheltered
and temperature, Ulva species thrive bay in Scotland. The fronds are buoyant,
in this freshwater stream as it flows holding the plants up to the light.
across the seashore.

attached to its rock by a single cell
CLASS ULVOPHYCEAE CLASS ULVOPHYCEAE
called a basal cell, which may be
Flaccid Green given additional anchorage by Sea Lettuce
Seaweed outgrowths called rhizoids. This Ulva lactuca
seaweed reproduces by releasing
up to a hundred gametes, each with SIZE Up to 40 in (100 cm)
Ulothrix flacca
two flagellae, from some of the cells.
SIZE Up to 4 in (10 cm) In another phase of its life cycle HABITAT Intertidal and
shallow subtidal
HABITAT Intertidal on it is a single globular cell. WATER TEMPERATURE
various shore types
32–86˚F (0–30˚C)
HABITAT 32–68˚F
(0–20˚C)
DISTRIBUTION Coastal waters worldwide sheets over a yard long in sheltered,
shallow bays, especially where extra
OCEAN LIFE This seaweed is made up of many areas, growing in a wide range of by releasing gametes from some cells,
DISTRIBUTION Northern Atlantic, Mediterranean,
Sea lettuce is common worldwide
nutrients are available in polluted
waters off South Africa, Pacific
on seashores and in shallow subtidal
harbors. Sea lettuce reproduces
conditions and habitats. Its frond is
and it can also spread vegetatively by
unbranched green filaments, which
a bright green, flat sheet, which is
regeneration of small fragments. Large
fronds lying on the seabed may be full
often split or divided, and has a wavy
themselves consist of strings of cells.
edge. The plant is very variable in
of holes made by grazing animals. It is
The filaments form soft, woolly masses
a also popular food for humans
shape and size, ranging from short,
or flat green layers that stick to
in many parts of the world.
intertidal rocks. Each filament is
tufted plants on exposed shores to