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Big
Bank Shoals of the Timor Sea
An
environmental resource atlas
| Biological
Environment |
Epi-benthic
communities of the Big Bank Shoals |
HALIMEDA
ECOSYSTEMS
The general
biology of Halimeda
| Halimeda is a genus of macroscopic, calcareous, green algae belonging to the
order Caulerpales (Chlorophyta). They are easily recognised by their
articulated, plate-like and calcified segments. These are joined together by
small, uncalcified nodes into branching chains, to produce a more or less bushy
plant. Thirty species of Halimeda have been identified in marine science
studies, and have been classified according to the shape, size and internal
structure of their segments. |
A Halimeda
plant (AIMS)
|
A Halimeda
plant surrounded by dead Halimeda segments (E.
Drew) |
Halimeda are among the most abundant seaweeds in tropical habitats and are of
global importance. They are substantial components of many reef ecosystems.
Halimeda has generally been considered as a plant of sand substrata, growing
most commonly in shallow, lagoonal environments. Some species do indeed grow in
sand, where they are fixed by a relatively large holdfast of 13 cm or more in
length. |
Figure 7: Halimeda
growth forms and holdfast systems (modified after Hills-Colinvaux, 1980)
However, a large proportion have very different habitats and growth
forms (Figure 7). Several species are attached by a single, small holdfast and
grow on rock surfaces or hang in large draperies from rocks. These may sometimes
appear as if they also grow in sand, as the rock itself may be buried in the
sediment. A third group of species sprawl across rock, sand or coarse algal and
coral debris.
A Halimeda
segment (AIMS) |
They attach by thread-like filaments produced at intervals along
the plant. Halimeda may grow in depths up to 100-150 metres, where light levels
are calculated to be only 0.05-0.08 percent of the surface intensity
(Hillis-Colinvaux, 1980). Since most other algae are restricted to only one of
the above substrata, and to relatively shallow waters, the ability of Halimeda
to grow in a very wide range of habitats is notable. |
This capability undoubtedly
contributes to the considerable success of the genus on tropical reefs.
|
