15 – Macroalgae
149
Seasonality
The abundance, growth and reproduction of many
GBR macroalgae are highly variable in time. Large
seaweeds like Sargassum are strongly seasonal, with
peaks in biomass and reproduction generally during
the summer and lowest biomass during the winter.
Extensive blooms of fleshy brown macroalgae like
Chnoospora and Hydroclathrus are common on shallow
reef flats during winter. Due to these strong seasonal
changes, some authors argue that the seasonality of
the GBR flora may be as strong as that from temperate
zones.
Common genera and identification
Identification of coral reef macroalgae to the genus level
is relatively easy, but the identification at the species
level is more difficult and generally requires examination
under a compound microscope (see Box 15.2 for preservation methods). The reproductive structures, internal
tissues, cell organisation, and so on, are key features required for rigorous species identification.
Common red algae
L Amphiroa: heavily calcified, branches cylindrical to
flattened, composed of smooth segments linked by
very short non-calcareous joints. Pale pink to red,
also called geniculated Corallinaceae. Common
throughout the GBR (Fig. 15.1A).
L Asparagopsis taxiformis: plants soft, with creeping
stems and upright fluffy or feathery tufts. Bright
pink and common on inshore reefs (Fig. 15.1B).
L Corallophila: red filamentous alga with creeping axes
and erect branches with pointed tips, usually found
overgrowing corals (Fig. 15.1C).
BOX 15.1 INTER-REEF AREAS AND HALIMEDA BEDS
Seaweeds are abundant in the deep water, inter-reefal areas of the northern part of the
GBR. Large mounds formed from the green calcareous alga Halimeda are estimated to
cover up to 2000 km
2 in this region and may be up to 20 m high. These Halimeda meadows occur principally in the northern sections at depths between 20 m to 40 m, but there
are also some in the central and southern sections of the GBR, where they have been
found at depths down to 96 m. The GBR apparently contains the most extensive actively
calcifying Halimeda beds in the world, although the real extent of such meadows is unknown. Tidal jets and localised upwelling events in the northern section of the GBR
provide the nutrients needed to sustain extensive deep (30–45 m) meadows of
Halimeda.
BOX 15.2 PRESERVATION
Macroalgae used for taxonomic purposes should be collected with the anchoring systems and preferably with reproductive structures. Macroalgae can be preserved in a solution of 4% formalin or in ethanol 70% (although decolouration may occur). However,
dry herbarium specimens are easier to use and transport. White cardboard acid-free
sheets are used for mounting specimens. Each herbarium sheet should contain basic information on the locality of collecting, date, depth, habitat, colour, and the collector’s
name. Permits are required, see Chapter 12.
149
Seasonality
The abundance, growth and reproduction of many
GBR macroalgae are highly variable in time. Large
seaweeds like Sargassum are strongly seasonal, with
peaks in biomass and reproduction generally during
the summer and lowest biomass during the winter.
Extensive blooms of fleshy brown macroalgae like
Chnoospora and Hydroclathrus are common on shallow
reef flats during winter. Due to these strong seasonal
changes, some authors argue that the seasonality of
the GBR flora may be as strong as that from temperate
zones.
Common genera and identification
Identification of coral reef macroalgae to the genus level
is relatively easy, but the identification at the species
level is more difficult and generally requires examination
under a compound microscope (see Box 15.2 for preservation methods). The reproductive structures, internal
tissues, cell organisation, and so on, are key features required for rigorous species identification.
Common red algae
L Amphiroa: heavily calcified, branches cylindrical to
flattened, composed of smooth segments linked by
very short non-calcareous joints. Pale pink to red,
also called geniculated Corallinaceae. Common
throughout the GBR (Fig. 15.1A).
L Asparagopsis taxiformis: plants soft, with creeping
stems and upright fluffy or feathery tufts. Bright
pink and common on inshore reefs (Fig. 15.1B).
L Corallophila: red filamentous alga with creeping axes
and erect branches with pointed tips, usually found
overgrowing corals (Fig. 15.1C).
BOX 15.1 INTER-REEF AREAS AND HALIMEDA BEDS
Seaweeds are abundant in the deep water, inter-reefal areas of the northern part of the
GBR. Large mounds formed from the green calcareous alga Halimeda are estimated to
cover up to 2000 km
2 in this region and may be up to 20 m high. These Halimeda meadows occur principally in the northern sections at depths between 20 m to 40 m, but there
are also some in the central and southern sections of the GBR, where they have been
found at depths down to 96 m. The GBR apparently contains the most extensive actively
calcifying Halimeda beds in the world, although the real extent of such meadows is unknown. Tidal jets and localised upwelling events in the northern section of the GBR
provide the nutrients needed to sustain extensive deep (30–45 m) meadows of
Halimeda.
BOX 15.2 PRESERVATION
Macroalgae used for taxonomic purposes should be collected with the anchoring systems and preferably with reproductive structures. Macroalgae can be preserved in a solution of 4% formalin or in ethanol 70% (although decolouration may occur). However,
dry herbarium specimens are easier to use and transport. White cardboard acid-free
sheets are used for mounting specimens. Each herbarium sheet should contain basic information on the locality of collecting, date, depth, habitat, colour, and the collector’s
name. Permits are required, see Chapter 12.