''Halimeda opuntia'', sometimes known as the watercress alga, is a species of

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

green

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of ''Rhodophyta'' (red), '' Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

in the order

Bryopsidales Bryopsidales is an order of green algae, in the class Ulvophyceae. It is a diverse group of mostly marine macroalgae. Characteristics The thallus is filamentous, highly branched, and may be packed into a mass. It is coenocytic, having multi-nu ...

. It is native to reefs in the Indo-Pacific region, the Atlantic Ocean and the Mediterranean Sea.

Description

''Halimeda opuntia'' forms thick, frequently-branched clumps of calcified, leaf-like segments up to high. The segments are flat and kidney- or fan-shaped, up to high and broad. They have a distinct central rib and a smooth, sinuous, or lobe-shaped, upper margin.

Rhizoid Rhizoids are protuberances that extend from the lower epidermal cells of bryophytes and algae. They are similar in structure and function to the root hairs of vascular land plants. Similar structures are formed by some fungi. Rhizoids may be un ...

s grow where the segments touch the substrate. The plants are often crammed closely together forming a dense mat of herbage in which the individual plants are not easily discernible.

Distribution and habitat

''Halimeda opuntia'' is found in the Indo-Pacific Ocean, the Atlantic Ocean, the Mediterranean Sea, and the Caribbean Sea and around the coasts of Florida and the Bahamas. It grows in grooves, depressions and cracks in rocks and between coral heads in moderately protected parts of the reef, at depths down to about .

Ecology

Where degraded coral reefs have abundant

macroalgae Seaweed, or macroalgae, refers to thousands of species of Macroscopic scale, macroscopic, Multicellular organism, multicellular, ocean, marine algae. The term includes some types of ''Rhodophyta'' (red), ''Brown algae, Phaeophyta'' (brown) and ...

, it has been shown experimentally that the coral larvae will settle in as great quantities on the seaweed as it will on the rubble substrate. Researchers found that the larvae of ''

Favia fragum ''Favia fragrum'' is a species of colonial stony coral in the family Mussidae. It is commonly known as the golfball coral and is found in tropical waters on either side of the Atlantic Ocean. Description The golfball coral is small and usually ...

'' readily settled on ''Halimeda opuntia'', however the alga was ephemeral and therefore unsuitable for long-term survival of the coral. This settlement practice may have significant consequences for the recruitment of corals on degraded reefs. The

secondary metabolite Secondary metabolites, also called ''specialised metabolites'', ''secondary products'', or ''natural products'', are organic compounds produced by any lifeform, e.g. bacteria, archaea, fungi, animals, or plants, which are not directly involved ...

s include growth regulators such as

auxin Auxins (plural of auxin ) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essent ...

gibberellin Gibberellins (GAs) are plant hormones that regulate various Biological process, developmental processes, including Plant stem, stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence. They are one of th ...

s and

cytokinin Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in Cell (biology), cell growth and cellular differentiation, differentiation, but also affect apical ...

s, and substances with antibacterial and antifungal properties, but these are not being harvested for commercial use.

References

{{Taxonbar, from= Q3125994, from2= Q105464775 Bryopsidales Plants described in 1816