A weekend with Wendy: An introduction to the seaweeds of Aotea

BARRY SCOTT (Trustee and Editor of Environmental News)

BACKGROUND

With a strong interest in the exotic caulerpa incursion that has impacted Aotea I have asked myself many times why no one noticed it was so widespread in Okupe Bay before June 2021, when Jack Warden discovered it there. Given the extent of spread through the bay it is likely to have been there for two years or more before first detected. The conclusion I have reached is that as a community we are not as connected with our marine natural world as we are with the more accessible terrestrial natural world. Most New Zealanders walking through the bush can identify several native plants and generally distinguish between what are weeds and what is native. But those that do venture into the sea with mask and snorkel are on-the-whole focused on harvesting fish for kai and see the rest as just ‘seaweed’. For one I know my terrestrial native flora reasonably well but have a relatively poor grasp of our marine native flora. However, spending more time by the ocean at Awana Bay, scrambling along the rocks in the intertidal zone with grandkids, and kayaking around the Aotea coastline, has drawn me more and more into the marine natural world. In the spring of 2023 Christine and I started collecting a few seaweeds from beach cast at Awana and set to work to identify them using Wendy Nelson’s excellent revised edition of New Zealand Seaweeds(1). With an email or two for help on IDs, Wendy quickly got us on the right track. One of the things we learnt early on was what we, and others, were calling ‘sea rimu’ on Aotea, was in fact Caulerpa flexilis, whereas the true sea rimu is Caulerpa brownii, which is confined to the lower NI and most of the SI. I have also been inspired by the Ahu Moana initiative on Aotea, that has been led by Glenn Edney, where the goal is to get communities into the ocean and begin to understand the dynamics of these ecosystems(2). With this background the next obvious step was to purchase mask and snorkel and familiarize ourselves more with the flora and fauna of the reefs in Pohutukawa Bay at Awana.

Having made those first steps on improving our understanding of the marine flora I thought it would be great to have a workshop on seaweeds on Aotea where a wider community group could learn from an expert like Wendy Nelson. Given she had not been to Aotea before it was not too difficult to persuade her to come across for a weekend to run a workshop. Luckily for me we have ‘Ecology Vision’ on the island who were willing to pick this one up and run with it.

Within 48 hours of Isobel advertising the workshop, it was full with the maximum number of 20 that Wendy felt she could manage given the hands on nature of the workshop. We timed it for the weekend of 16/17th November to fit in with Wendy’s busy work schedule but importantly to match an afternoon low tide so workshop participants could easily access the inter-tidal zone.

Immediately after Wendy arrived on Saturday 16th November the three of us headed down to Medlands to check out Boatshed Rock as the site for the field work. While most of us would be gazing at the wonderful panoramic view around us, Wendy headed directly to the rock shelves on the southern side of the reef as it was a bit more sheltered from the wind and quickly began picking up and examining what seaweed species were present. Among her early finds was an ‘invasive’ species in the genus Hypnea, confirming for me straight away why we need more local knowledge of what is present in our bays and washing up on the beaches. Among the drift was the beautiful red alga, Sarcodia montagneana(1, p.312). Having confirmed Boatshed Rock was a perfect site for the field trip we headed back to the Schoolmaster’s House where Wendy unpacked from her very heavy suitcase, books, collection bags, cardboard for mounting herbarium specimens and much else. For many seaweeds microscopic examination of vegetative and reproductive structures is necessary to get an ID at the species level, so Isobel had borrowed a couple of microscopes from Mulberry School.

Saturday night was very wet and windy but first thing Sunday morning Wendy and I headed down to the Awana campground to see what had been washed up along the estuary from the high seas. It was a rather windy morning but a perfect time, immediately after a storm, to find lots of different seaweeds on the beach. Wendy set to work gathering up a great collection of different seaweeds to take to the workshop which started at noon. Among the ones I remember her collecting was the brown alga, Desmarestia ligulata(1, p.56), which breaks down very quickly, and becomes rather smelly because of the release of sulphuric acid from the intracellular vacuoles. Wendy frequently gets enquiries from people thinking they have found seaweed fossils but are just rock etchings from the released acid. She also picked up a second invasive species, Bonnemaisonia hamifera, among this cast. We then headed back to Claris to set up for the workshop. The workshop comprised three parts: first a lecture introducing us to the general taxonomy, life style and habitat of seaweeds followed by an overview of the many uses of seaweeds; then a trip to the northern side of Boatshed Rock where we explored what seaweeds were present on the rock shelves and pools in the different intertidal zones; and finally a return to the Schoolmaster’s House at Claris to identify what we had found and learn how to prepare herbarium specimens by mounting on herbarium paper/light cardboard.

Her depth of knowledge and understanding of seaweeds was apparent as soon as she started talking, with all 20 of us quickly becoming engaged. Each slide was a short story in itself. The seaweed flora of New Zealand is very rich with over 1200 different species, with many more to still discover and characterize. By way of background, algae are not a single taxonomic entity. Molecular phylogeny (based on gene sequences) combined with vegetative and reproductive morphology place them in four kingdoms: Plantae (chlorophytes and rhodophytes – green and red algae); Chromista (phaeophytes – brown algae, dinoflagellates and diatoms); Protozoa (euglena) and Bacteria (blue-green algae). However, our workshop was confined to the brown, green and red algae.

Among the many things we learnt was that:

• Seaweeds provide an important ecosystem services role as food and habitat for many other marine organisms

• Very few of the seaweeds are eaten directly by marine organisms but rather it is the secreted slimy mucilage on the surface of the algae and small pieces of tissue that are the foodstock for many bacteria and invertebrates that in turn are the food for other species higher up the food chain

• Some seaweeds like bull kelp grow from the tips whereas others like Undaria pinnatifida, an invasive that is now widespread in New Zealand, grow from the base of the blade where it joins the stipe

• Seaweeds are an important buffer for ocean acidification, which is increasingly becoming a problem as more and more CO2 is sequestered in the oceans

• Seaweeds are used for food, biofuel and as a source of various compounds in the food and pharmaceutical industries; but while there are over 11,000 different species world-wide very few species have been domesticated with around just six genera widely used

• Some of the red seaweeds in the genus Asparagopsis synthesize brominated compounds, which inhibit the growth of methanogens in the rumen of ruminants, so consequently there is considerable global interest, including from New Zealand (CH4 Global, based out of Ruakaka in Northland) to scale up production of these seaweeds for use as ruminant feedstock to reduce methane emissions.

One of the gems for me was hearing about the symbiosis between coralline algae and paua with the former sending out a chemical signal (GABA) that attracts the larvae to settle and grow on the algal substrate. If sediment covers the algae then photosynthesis is blocked as is the chemical signalling between these two organisms. I was also fascinated to hear about rhodoliths/maërls, which are colourful, free living crustose benthic marine red alga that resemble coral(3). The deposition of calcium carbonate within their cell walls gives rise to hard structures or nodules, which can roll along the seabed. Their growth rates are very slow so, like coral, it is very important to know where they are and protect them. Very little is known about where they are located around Aotea, one of the many knowledge gaps about the marine biodiversity at Aotea. Rhodoliths played a key role in recovery of the seabed in the Gulf of Mexico after the BP oil drilling rig, Deepwater Horizon, exploded and sank in 2010, resulting in the largest spill of oil in the history of marine oil drilling.

Among the many uses of seaweeds are their source of compounds for the food, medical and pharmaceutical industries. Some brown algae are used commercially as a source of alginates, but they are also used for fertilisers (a source of potash) and animal feed. Some of the red algae are a rich source of agars and other species of carrageenans, which are used in foods to thicken, gel, emulsify and stabilze. Some such as karengo (Porphyra spp. & Pyropia spp.), are a delicacy for Māori, and a rich source of protein and nutrients. Understanding the life cycles of these foliose red algae has been very important for their domestication and growth in aquaculture industries4. A good example is nori (Pyropia sp.), which is an edible seaweed used in Japanese cuisine. However, cultivation of blades of nori was only successful after the complex three stage life cycle was discovered. The much less conspicuous filamentous sporophyte stage grows separately in mollusc shells (conchocelis stage), a discovery made by British phycologist Kathleen Mary Drew-Baker working with Porphyra umbilicalis that grow in the seas around Wales(4). This discovery enabled the Japanese to seed and grow nori, thereby rescuing their industry. Kathleen Baker is hailed in Japan as the “Mother of the Sea” and a statue was erected in her memory in Sumiyoshi Park, Uto City, Kumamoto, Japan.

The second part of the workshop involved a field trip to the Northern side of Boatshed Rock to learn which species grew in the different inter-tidal zones, and to collect some for identification and pressing later on. In the upper tidal zone we found small tufts of Pyropia plicata(1, p.146-147) growing on the rocks;  Psilophycus alveatus(1, p.267), a moss like seaweed with very delicate tips when viewed close up and one of the first seaweeds to be named by Europeans, covering the rocks; the slimy extensive layers of Ulva sp.(1, p.48-51)  across the rock shelves; Clymene sp.(1, p.144) that are often bleached with male blades having a golden edge; Myriogloea intestinalis(1, p.74) comprised of long brown/olive-green strands to give a rope like appearance; Catenellopsis oligarthra(1, p.194) with the distinctive pear shaped bladders, growing in clumps; Perithalia capillaris(1, p.134), which has a horsehair like appearance and a coarse and firm texture; and Cladhymenia oblongifolia(1, p.223) characterized by the parallel sided blades with blunt tips with cystocarps on the edge of the blades.

In the mid-tidal zone we found the northern species of Scytothamnus (S. australis)(1, p.124) on exposed rocks; Caulacanthus ustulatus(1, p.256) forming a turf like growth across the rocks together with the slimy layers of Ulva sp.(1, p.50) covering the rock shelves; Chondria sp(1, p.220); the dichotomously branched Gigartina macrocarpa(1, p.265) with flattened axes; and two species of Microdictyon (M. mutabile and M. umbilicatum)(1, p.39) with blades of varying shapes forming networks with a very delicate, lace-like appearance; and in the rock pools the beautiful iridescent red seaweed, Champia laingii (1, p.315); the highly branched Plocamium(1, p.308) and the red to brown Gigartina atropurpurea(1, p.263) with its characteristic surface cystocarps.

A characteristic feature of the low tidal zone was the very distinct bands of seaweeds that change from one species to another, as you move into deeper waters, with Hormosira banksii(1, p.96) on the outer edge; then Xiphophora chondrophylla with highly forked branches(1, p.117); the very distinctive Carpophyllum maschalocarpum/flapjack(1, p.103) with its flat stems; and in the deeper waters Sargassum sinclairii(1, p.112) and Ecklonia radiata(1, p.122).  

After returning from the field trip Wendy showed us how to mount the seaweeds on acid free herbarium paper/light cardboard and then press for long term storage. She emphasized the importance of this material as a reference for samples collected and identified in different parts of New Zealand. Her routine practice is to record where and in what habitat the sample was growing and to remove a small bit of tissue for DNA sequencing, given some species can only be resolved using molecular phylogeny. The small sample of tissue is wrapped in chux cloth, placed in a small plastic bag, silica gel added to dry it out, and then sealed. She was very enthusiastic for the Aotea community to start their own seaweed herbarium as a visual resource and record of what is present on the island, but at the same time make a duplicate sample to deposit in the herbarium at the Auckland War Memorial Museum. As I watched participants tease out their samples for mounting, I realized there was a lot of artistic talent in the room, as some mounted different combinations of form and colour to generate beautiful pieces of art. One I later saw for sale at the Elephant Gallery.

On the Monday morning before Wendy left, we made a quick visit down to Awana beach. Again, she rapidly honed in on the seaweeds lying along the tidal zone, quickly identifying them and holding them for me to photograph. Her enthusiasm and knowledge was infectious and such a privilege to have her at ‘my’ beach. At low tide after she had left I returned to Awana beach to make a comprehensive photographic record of as many seaweed species as I could while everything was still fresh in my mind. Some species I was able to identify myself and the remainder were kindly identified by Wendy. Most of these I have now posted on iNaturalist so I have a pocket guide for when I next visit the beach.

CONCLUSION

Where to from now. For me it would be great if we had a place on Aotea where people could go to study, work and research the natural world of Aotea – something akin to the history house – but with some books, desks, and a couple of microscopes. I saw what I thought was the ideal at the Visitor Centre on Lord Howe Island, which I visited in 2023. It would be great to have such a place where community could mount and store specimens collected from around the island in a small herbarium that specialists and enthusiastic amateurs like ourselves could use as a reference source. Wendy knows from talking with colleagues at NIWA that there are still a number of uncharacterized seaweeds around the coast of Aotea. It would be great for these to be identified and samples sent to Auckland Museum as well as duplicates kept on the island.

Meanwhile, put on your mask, snorkel and flippers and start exploring the exquisite marine natural world around Aotea.

Wendy Nelson is New Zealand’s preeminent seaweed expert. She became a Fellow of the Royal Society Te Apārangi in 2010, won the Royal Society’s Hutton Medal in 2016, just the second women to do so (the other being Lucy Moore), and became a member of the New Zealand Order of Merit in 2000 (MNZM)(5). She began working under Nancy Adams at New Zealand’s National Museum in the 1970s and was appointed curator of botany when Adams retired in 1987. Over the next 15 years, she added more than 8,000 new specimens to the Te Papa seaweed collections. She then went on to work at the National Institute of Water & Atmospheric Research and was appointed a Professor at the University of Auckland. She is now back at the Auckland Museum. She has documented the diversity of New Zealand’s seaweeds from the Kermadecs to the Subantarctics, conducting research on taxonomy, evolution, algal ecology, alien seaweeds, seaweed aquaculture and commercial harvesting. She has shown how important New Zealand is in understanding the evolution of the world’s seaweeds; campaigned to remove aggressive weeds from our coastal waters; and worked to generate new knowledge on ocean acidification.

Acknowledgements

First Wendy Nelson for leading this wonderfully informative workshop; Isobel Edwards for organizing the workshop on behalf of Ecology Vision; and all the participants in the workshop who listened attentively, asked lots of questions and enthusiastically embraced this opportunity to learn more about our wonderful marine flora. They were: Isobel Edwards, Lorraine Merrick, Rex Dubbelman, Jackie Peers, Nell Williams, Kathy Sutherland, Anna Davis, Cynthia Macnee, Annamarie Clough, Linda Power, Bree Biederman, Rylie Arnell, Saskia Missar, Monique Stevenson, Hilda Hoven, Lynaire Abbott, Eunate Puy Azurmedni and Barry Scott.

References

1. Nelson, Wendy (2020). New Zealand Seaweeds. An illustrated guide. Te Papa Press, Wellington, 2020. ISBN 9780995113602. The superscript page references refer to this book.

2. Glenn Edney (2024). The Ahu Moana Vision. Environmental News, Issue 49, Summer 2024.

3. Nelson, W. A. (2012). Rhodolith beds in northern New Zealand: characterisation of associated biodiversity and vulnerability to environmental stressors. Wellington, NZ: Ministry for Primary Industries. ISBN 978-0-478-40077-9. OCLC 812180715.

4. Nelson, W. A. & Zuccarello GC (2024). Bangiales (Rhodophyta) in New Zealand: current state of knowledge and future directions. New Zealand Journal of Botany. https://doi.org/10.1080/0028825X.2024.2307871.

5. Nelson, Wendy. 1968 to the present time. Women contributing knowledge from 1968 to the present time. 150 years of Royal Society Te Apārangi. https://www.royalsociety.org.nz/150th-anniversary/150-women-in-150-words/1968-2017/wendy-nelson/