[5] Halimeda is responsible for distinctive circular deposits in various parts of the Great Barrier Reef on the north-east coast of Queensland, Australia.

The genus is one of the best studied examples of cryptic species pairs due to morphological convergence within the marine macroalgae.

[8] [9] [10] Some species grow so vigorously in tropical lagoons that the sediment is composed solely of the remains of their tissues, forming a calcareous "Halimeda sand".

In fact some tropical reef systems, such as atolls, consist largely of Halimeda sand accumulated over the aeons.

The medullary filaments branch out trichotomously to form peripheral utricles which stick to each other to enclose the intersiphonal spaces of each segment.

In the "rock-grower" type, the matted holdfast is composed of branched filaments which secure the thallus to a rock surface.

[14] Species of Halimeda with sand-grower type holdfasts grow on sandy or muddy substrates, and are thus common in lagoons and backreefs.

[24] Hard coral cover can actually play a key role in maintaining Halimeda biomass on reefs, as one study found that thalli growing under the canopy of Acropora colonies were larger than those in open areas exposed to herbivory.

These will mature overnight and release gametes in the morning of the next day, after which the thallus is left white and dies in a process known as holocarpy.

Methanol and dimethyformamide extracts of Halimeda opuntia have been observed to have antibacterial properties against some species of microorganisms, including Saccharomyces cerevisiae, Escherichia coli, Bacillus subtilis, and most significantly, Staphylococcus aureus.

[29] Halimeda opuntia ethanol extract exhibited activity against hepatitis C virus (HCV) due to polymerase inhibitory (HCV-796) binding sites based on molecular docking simulation.

[32] An experiment on rats showed that free phenolic acids of Halimeda monile have antioxidant properties which could aid in protecting against liver problems.