It’s pretty in pink and it doesn’t stink!


NIWA scientists are in the pink! They’re studying the deep candy pink or purple coralline algae, abundant around the New Zealand shoreline and throughout the world, which play a vital role in marine ecosystems.

To the untrained eye, some of these species look identical to others. A splash or crust of pink along the NZ coastline, they can be found in almost all marine habitats where there is sunlight and something to attach to.  Their habitat ranges from high intertidal pools through to subtidal waters. In fact, there are more than 30 known species that occur in New Zealand, and NIWA scientists estimate that there are at least a dozen more species they can recognise, which are either new to science, or new to New Zealand.

Initially it was thought that these red algae, which have calcium carbonate in their cell walls, were animals. “When you look at them and feel them, they are hard and you don’t think algae, because they’re more like a shell or a coral. That’s why they are called coralline algae; algae that are like coral,” says NIWA biodiversity scientist, Tracy Farr.  It wasn’t until the mid 1800s that their plant-like nature was established.

Coralline algae are either jointed (geniculate) or not jointed (non-geniculate). The jointed species have branches, and can be quite fine, and their joints give them flexibility. They’re often known as “coralline turf”, and can form a dense carpet in intertidal and deeper waters. Non-jointed species – often called “encrusting”, or “crustose” – are completely calcified. They may feel “warty” or “lumpy” to touch; some grow in complex and beautiful layered or folded forms, like a rose carved from chalk. But across all of these different growth forms, all of them are pink!

NIWA scientists begun studying them in 2002, armed with chisels and hammers, prising them off rocks. The scientists are currently focusing on one form of coralline algae, rhodoliths, literally “pink rocks,” which roll around on the sea floor. “These algae play key roles in the lives of invertebrates, fishes, and other algae. They provide a three-dimensional structure which is a habitat for organisms, a place where things can hide, a hard substrate where seaweeds can attach,” says Farr.

Some coralline algae produce chemicals which actively promote both settlement and early development of paua and other invertebrate larvae. Research overseas, and in New Zealand, indicates that some algae species are more attractive to paua than others. There is also some evidence that post-settlement survival may vary on different species or growth forms of corallines.

Crustose coralline algae are important to the construction and ecology of coral reefs, acting as the main cementing agent and providing strength for the reef. Research so far suggests that the calcium carbonate in the cell walls of the non-geniculate coralline algae species are a major store of carbon in the near-shore environment.

These coralline algae represent great biodiversity and the individual species are really important. “It’s difficult to tell some of them apart, but when you look at their DNA sequences, they are very different. There are very clear differences, and when you have the clue of the DNA you can look for other differences and find them,” says Farr.

The impact of ocean acidification on coralline algae is also the subject of current research. “We are measuring what happens when we grow coralline algae under more acidic conditions, to look at the impact on their growth rate, health and their structure,” says Farr.

Farr has been studying coralline algae since 2001. She is a scientist in marine biodiversity and biosecurity group at NIWA.

The Ministry of Fisheries recognises the importance of coralline algae to the ecosystem, and has funded three research projects since 2001.

Fact file 

Phylum: Rhodophyta (red algae)

Order: Corallinales

Other names: In Europe, rhodoliths are known as maerl, from an old Breton word.

Diet: Like all algae and higher plants, they photosynthesize, converting carbon dioxide and water into sugars using energy from sunlight, producing oxygen in the process.

Lifespan: They are considered to be very slow growing, with most species growing just 1 or 2 millimetres each year, so larger plants may easily be tens to a hundred or more years old.

Over the next two years, NIWA scientists will be measuring growth rates of New Zealand rhodolith species in the field and in culture tanks.

Size: They can be little tiny parasites, only just visible to the naked eye, that grow on another coralline algae, or single plants can be up to 20 centimetres across. Large areas can be covered by adjoining plants of the same or mixed species, so that whole rock walls or reefs can be covered, as far as the eye can see.

Habitat:  They are found all around New Zealand and all around the world, from the tropics to polar regions. They can grow in and around intertidal rock pools, where they are out of the water for long periods at low tide; and they have been found at depths of 150 metres or more, where light sufficient for photosynthesis penetrates.

Something strange:  They don’t smell!

What makes seaweeds smell bad is often the animals that are living on them or in them. With their hard, calcified structure, coralline algae don’t break down to rot or ferment when they die – they simply dry out, and bleach to a chalky white colour and texture if they’re exposed to light.

Reproduction: There are three “sexes” of coralline algae: females, males, and tetrasporophytes. All reproduction takes place inside small chambers on the algae surface, little lumps, like pimples up to 1 mm across at the largest. These chambers will hold either male sperm, female spores, or tetrasporangia (spores that will grow into female or male plants).

Non-geniculate coralline algae - Campbell Island (Department of Conservation, S.Cooper)