Article: Seaweed secrets reveal a biodiversity hotspot

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  Reddish-brown mats of ‘true’ Bangia cover rocks in the intertidal region. (Photo: Tracy Farr)
The biphasic life history of Bangia. (Graphic: Tracy Farr)
A comparison of the two new Bangiales species. (Graphic: Tracy Farr)
They may look nondescript, but the reddish-brown mats of Bangiales seaweed common to many New Zealand beaches have a hidden identity.

 PDF of this article (530 KB)


Reddish-brown mats of ‘true’ Bangia cover rocks in the intertidal region. (Photo: Tracy Farr)

The biphasic life history of Bangia. (Graphic: Tracy Farr)
A comparison of the two new Bangiales species. (Graphic: Tracy Farr)

They may look nondescript, but the reddish-brown mats of Bangiales seaweed common to many New Zealand beaches have a hidden identity. As Tracy Farr, Wendy Nelson, and Judy Broom have discovered, they’re not all as common as they might seem.

There’s a group of seaweeds growing on rocks in the upper intertidal zone of many New Zealand beaches that you could be forgiven for overlooking. And if you did notice them, you might not even realise they are seaweed. But these simple organisms hide extraordinary genetic diversity. NIWA scientists and colleagues from the University of Otago have recently described two new, distinct genera in this group. They are known only from New Zealand, and, genetically speaking, they’re incredibly different from other related seaweeds.

An unexpected discovery

Until recently, the order Bangiales contained just two genera of red algae. Filamentous algae were placed in the genus Bangia, and those with blades went into Porphyra. The commercially and culturally valuable genus Porphyra – more commonly known in New Zealand as karengo, and in Japan as nori – contains the better known members of the order. However, the simplicity of the form of these seaweeds masks the true diversity that exists within the Bangiales. For both Porphyra and Bangia, specimens that look essentially the same on the beach or under the microscope have been shown to be very different when analysed in more depth; this is known as cryptic diversity. Our research on Porphyra and Bangia has revealed New Zealand as a hotspot for Bangialean diversity.

Widespread globally, Bangia grows in a broad range of habitats, both marine and freshwater. While no freshwater collections of the genus have yet been made from New Zealand, Bangia is relatively common in our marine environment, particularly in the upper intertidal region where it’s exposed at each low tide. Until our group’s recent work, it was thought that only one species of Bangia occurred in New Zealand, and that it was uncommon. This underestimate of Bangia was partly a result of what we now know to be the seasonal, ephemeral growth typical of several species.

Bangia grows as very simple, unbranched filaments. Like Porphyra, it has a biphasic (two-part) life history in which a microscopic form (the conchocelis) alternates with the more obvious filaments. Also like Porphyra, Bangia has several strategies for reproduction – it can reproduce asexually, as well as sexually – giving it a flexibility and adaptability which help explain its wide range of habitat and distribution.

Simplicity of form masks genetic diversity

Since the late 1990s, we have collected Bangia from throughout New Zealand. We assess our Bangia collections by DNA sequencing. With the shortage of physical differences to distinguish between specimens, DNA has been the key to unlocking diversity in the order. Using sequencing, we’ve uncovered more than a dozen unique and distinct ‘DNA sequence entities’ from New Zealand collections. Each of these DNA entities is likely to be different enough at a genetic level to warrant description as a new and distinct species. And in two outstanding cases, we’ve described them as new genera.

These two newly described organisms, Minerva aenigmata and Dione arcuata, are very different genetically, both from each other and from any other Bangia or Porphyra from New Zealand or anywhere in the world. DNA analysis of Bangialean specimens from around the world shows that Minerva and Dione are the only known living representatives of groups which diverged from ‘true’ Porphyra and Bangia a very long time ago. Their common ancestor is in the distant past.

There’s a confounding factor in distinguishing organisms within the Bangiales. While Dione and Minerva have such distinctive DNA, both from each other and from any other Bangia, only Dione arcuata is noticeably different in terms of its growth and morphology, distribution, and habitat. Despite its startling difference at the genetic level, Minerva aenigmata looks and acts like any ‘true’ Bangia. The simplicity of the form of the organisms – the lack of clear, obvious, distinguishing anatomical features – masks the genetic diversity within.

Recognising biodiversity hotspots

These simple organisms have the potential to help us recognise local biodiversity hotspots. At one site near Kaikoura on the east coast of the South Island, we’ve identified as many as three different Bangia entities at a given time and, over the course of a year, we’ve collected five different Bangia entities, including Dione arcuata, from the site. At each collection date (in December, March, June, and September), we discovered a different combination of entities. This seasonality of entities means that a single sampling would certainly fail to give a true picture of the site’s biodiversity.

There was no obvious clue that this site was a local biodiversity hotspot. At a range of other sites along the same stretch of coastline, both north and south of Kaikoura, each with similar physical characteristics (exposed rocky shore, freshwater runoff), we found only one Bangia entity.

Research on Minerva, Dione, and the ‘true’ Bangia species has alerted us to the level of care required in surveying algal flora, and interpreting those surveys. Potential conservation issues arise: if the biodiversity at a site (such as the biodiverse Kaikoura site) can be so different from neighbouring, apparently equivalent sites, then what criteria must we use to assess the conservation values of habitats? And how does this relate to our assessment of individual sites?

The wider view

New Zealand’s unique Bangialean flora provides a rich source of knowledge about the relationships and possible origins of this globally important group of seaweeds. Our research on Minerva, Dione, Bangia, and Porphyra is continuing, and informs our understanding of diversity in macroalgae in particular and, in the wider context, of marine biodiversity in general.

DNA detecting

  • Widespread in New Zealand, the Bangiales order of red seaweed includes the genus Porphyra (also known as karengo or nori) and the genus Bangia.
  • Though they look just like Bangia, two new genera have been discovered through DNA analysis.
  • The Kaikoura beach where they were collected has turned out to be a hotspot for biodiversity.

Further reading

Nelson, W.A.; Farr, T.J.; Broom, J.E.S. (2006). Phylogenetic relationships and generic concepts in the red order Bangiales: challenges ahead. Phycologia 45(3): 249–259.

Nelson, W.A.; Farr, T.J.; Broom, J.E.S. (2005). Dione and Minerva, two new genera from New Zealand circumscribed for basal taxa in the Bangiales (Rhodophyta). Phycologia 44: 139–145.

Broom, J.E.S.; Farr, T.J.; Nelson, W.A. (2004). Phylogeny of the Bangia (Rhodophyta) flora of New Zealand suggests a southern origin for Porphyra and Bangia. Molecular Phylogenetics and Evolution 31: 1197–1207.

Tracy Farr and Dr Wendy Nelson are based at NIWA in Wellington, where they work on various aspects of marine macroalgal growth and taxonomy. Dr Judy Broom is based at the University of Otago, and works on molecular analysis of marine macroalgae.

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