On safari for rare seaweeds in Northland
Science Centres: Aquatic Biodiversity and Biosecurity
Gelidium allanii growing on mussels on a low intertidal reef.
Gelidium longipes
Red seaweeds belonging to the genus Gelidium are well studied around the world because they contain the commercially valuable polysaccharide agar. Agar is essential for many pharmaceutical, microbiological, and biotechnology applications, and is also used widely in the food industry.
World supplies of agar are completely dependent on harvesting it from certain species of red algae, which make it naturally as part of their cell walls. Each seaweed species produces agar with slightly different properties, depending on the chemical structure of the molecule.
The New Zealand species of Gelidium have not been widely studied, so NIWA, through the National Centre for Aquatic Biodiversity & Biosecurity, is undertaking a research programme to understand more about the six species recorded here. We have made a number of trips throughout the country to collect specimens, from the Three Kings Islands to Stewart Island, and including the Chatham Islands.
We have focused our studies on the northern North Island where some rarely collected species have been recorded. When we began our work one species, Gelidium longipes, had not been collected for 50 years and another, G. allanii, had been recorded only from a single site since it was first discovered in 1942. Both species are very distinctive and can be easily distinguished from other New Zealand seaweeds. However, they are small, and could easily be overlooked by the untrained observer.
After searching suitable habitats across parts of Northland we found two very small populations of G. longipes about 200 m apart in the Bay of Islands. Extensive studies of comparable sites to the north and south of this region found no further populations of this species. We intensively searched 30 sites in Northland in our hunt for G. allanii and found it at 6 of them – but only in very small numbers. While looking for these species we found more undescribed species of Gelidium – also with apparently very restricted distributions.
Molecular sequence data is an important tool for hunting down these rare algae. Many species of Gelidium are small and sometimes difficult to tell apart, especially if the material is not fully reproductive (male and female structures are sometimes vital to identification). We also do not want to over-collect or damage small populations of these rare seaweeds. By using molecular sequence analysis we can work with very small samples, and the material does not have to be reproductive. The gene sequences allow us to definitively identify even tiny samples.
What are the implications of these discoveries?
- A number of these species have highly restricted distributions, which make the populations extremely vulnerable to coastal modifications or developments. This information may be important for making decisions about conservation and coastal management.
- New Zealand’s Gelidium species are more diverse than previously thought. Although the naturally occurring populations of the species found so far clearly could not sustain harvesting, this diversity may contain commercially useful variants of agar that could be the basis for the cultivation of species for unique new products.