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Understanding Global Warming: Case Study

This case study explores the work of Ceridwen Fraser and her team and their research into Bull Kelp populations in the Southern Hemisphere and how they can inform on past climate change events.

A Scientific Investigation


Ceridwen Fraser is part of a team of scientists who have been using genetics to investigate Southern Hemisphere Bull Kelp populations, looking at how closely the populations are related to each other. The team consisted of Ceridwen, Jon Waters, Hamish Spencer and Raisa Nikula of the Department of Zoology at the University of Otago. They set out to understand how these populations may be genetically connected as a result of the kelp’s ability to float long distances. Excitingly, they also discovered new evidence about climate change processes.

Profile of a Scientist

Ceridwen grew up in Canberra, Australia and, early in high school, decided she wanted to become a marine biologist. Many tried to discourage her, saying there were few jobs in marine science, so Ceridwen did a university degree in art conservation - but she eventually had to admit that biology was still her dream, jobs or no jobs. She started a degree in Marine Science at James Cook University in tropical northern Australia, finished it off at Macquarie University in Sydney, worked for a year in the marine invertebrate research group at the Australian Museum and then began a PhD in the Department of Zoology at the University of Otago, New Zealand, which she completed in 2009. She is now a postdoctoral researcher with the Allan Wilson Centre for Molecular Biology and Evolution. Since starting her degree in marine biology, she has never looked back, and instead looks forward to an exciting career filled with discovery and adventurous fieldwork.


Research Aim and Method


The specific questions that Ceridwen wanted to answer through her part of the project were: 

  • Does Southern Bull Kelp (Durvillaea antarctica) disperse via rafting? 
  • Was kelp wiped out by ice in the subantarctic during last ice age?   


By finding the answers to these questions, Ceridwen has contributed to what we understand about the effects of past climate change periods. This information can help predict the effect of future climate change.




The process of finding out starts with extensive planning and background research. Once an appropriate research plan had been formulated, Ceridwen began collecting her samples from sites around New Zealand, the subantarctic islands, Chile and the Falkland Islands. Ceridwen travelled to these places over a period of two years, with the help of other scientists that had been contacted during the planning process. This work enabled her to make observations and collect samples of kelp, as well as invertebrates found living in the kelp, to bring back to the lab.   


Of course, most people can’t bring samples of seaweeds into New Zealand because of biosecurity regulations, so Ceridwen needed special permits from the Ministry of Agriculture and Forestry. Ever since, these samples have been carefully stored in isolation within a specially regulated laboratory. 


Back in the lab Ceridwen and the team used modern molecular biotechnologies to find out how closely related the different species were. These analyses allowed Ceridwen to infer what had happened to this species during the last glacial period.  


The techniques used were: 

  • Extraction of DNA 
  • Polymerase Chain Reaction to amplify specific DNA targets   
  • DNA sequencing 
  • Analysis of variation in genes   
  • Phylogenetic analyses to reveal relatedness


By using these techniques Ceridwen and the team were able to build up a picture of the genetic relatedness of the different populations of kelp. 


Distribution of Buoyant and Non-Buoyant Bull Kelp Species

The genus Durvillaea contains a number of species in the Southern Ocean area in addition to D. antarctica. Bull Kelp species can be split into two groups ‐ one of buoyant species that can float, and one of non‐buoyant species. Fig 7 shows that the non‐buoyant species are restricted to the coasts of New Zealand and southern Australia. In contrast, the buoyant species D. antarctica (Southern Bull Kelp) is found throughout the region that was studied. This pattern suggests that the ability of D.antarctica to float allows it to occupy a larger geographical range. 

Computing and Mathematical Power

With screeds of raw data, Ceridwen and the team harnessed the power of computers and mathematics to make sense of it all. This raw data shows the DNA sequences that were identified from the target genes. Ceridwen needed to be able to identify patterns of similarity and difference in these sequences so that she could find out how closely related the different species of Bull Kelp were. To do this without the power of a computer would take years! Thanks to computing technology that has been developed by scientists around the world to cope with this type of data, Ceridwen was able to analyse the data over a period of many months to create the evolutionary tree that you can see below.


Interpreting an Evolutionary Tree


The evolutionary or phylogenetic tree that Ceridwen has drawn shows the relationship between the different genetic variants (called haplotypes) of Bull Kelp, Durvillaea antarctica, that she sampled.   


The colours in the diagram below, representing the different haplotypes, match those in the phylogenetic tree above. Each pie shows the proportions of different haplotypes at each location on the map. This diagram shows that one haplotype (the red one) dominates the subantarctic. This almost‐complete uniformity indicates that all these populations must have arisen from a common source population and that this event must have occurred relatively recently, suggesting that these islands were previously unoccupied by Bull Kelp.



Why would these habitats have been available? This diagram on the left shows the estimated extent of winter sea ice (WSI) in the Southern Ocean at the peak of the last ice age, the so‐called Last Glacial Maximum (LGM). These estimates were made using geological data compiled from sea‐floor sediment cores containing fossil diatoms. Diatoms are single‐celled algae, which occur in many habitats, and some species are most commonly found in sea ice. Geologists infer whether a core comes from an area that was under sea ice at the Last Glacial Maximum by looking at which diatom species are in the core. The blue dots on the diagram show the location of cores that indicate sea ice was present; the green‐and‐black dots show where the edge of the sea ice is thought to have been, and yellow dots represent cores that showed no evidence of sea ice.


Studies previously published by other scientists (researched by Ceridwen in her planning) show that Bull Kelp cannot survive where sea ice occurs. Could sea ice explain the genetic patterns found in Bull Kelp? Subantarctic populations could have been destroyed by sea ice during the last ice age. When the climate warmed and the ice receded, the kelp could have recolonised the newly‐freed islands by floating across the oceans from somewhere beyond the reach of the sea ice. This scenario could certainly explain the near‐complete genetic uniformity of the kelp populations throughout much of the subantarctic, versus the higher genetic diversity in places further north (such as in New Zealand and Chile) that remained free of ice.


The problem with this hypothesis was that sea ice at the Last Glacial Maximum was not thought to extend as far north as many of the supposedly recolonised islands (see Figure 10, above). The islands labelled in red are those that seem to have been recently recolonised by Bull Kelp, but some – such as Marion and Macquarie Islands – lie beyond the estimated range of Last Glacial Maximum sea ice. These islands, however, are in areas that have little geological data supporting the estimated limit of the sea‐ice. You can see from the diagram that, although geologists have taken numerous cores, data is still lacking in many places. Sea ice might, therefore, have been more extensive at the Last Glacial Maximum than previous studies have suggested.


This exciting research not only shows how organisms can be affected by climate change, but also how biological studies can give us great insights into past environmental conditions. Understanding ancient climate change and its evolutionary impacts is a crucial part of making good predictions about the effects of future climate change – whether natural or human‐induced.


Recent Research

Researchers at the University of Otago recently discovered evidence of an ancient earthquake believed to have hit New Zealand approximately 1000 years ago. The earthquake occured near Dunedin before humans had arrived in New Zealand. The genetic footprint of this earthquake was found by analysing modern kelp samples along the affected coastline. Read this article to learn more about this research.