2023 Recipient – Lisa Wolf
The sea anemone Handactis nutrix lives in close association with various species of native and endemic brown macroalgae such as species of Cystophora, Carpophyllum, Sargassum and Lessonia. This symbiotic association is found all throughout New Zealand, in particular around the south coast of Wellington. Within my master’s thesis, I am aiming to define the sea anemones abundance and host specificity, as well as nutritional interactions between the sea anemone and ladder weed (Cystophora scalaris), one of their most preferred host species found around Wellington’s south coast. With help of stable isotope analyses at NIWA, it was possible to trace nitrogen and carbon. First results show considerable transfer of nitrogen from the sea anemone to the seaweed. As nitrogen is generally known to be the most limiting nutrient for a seaweed’s growth, this study opens a new area of research relating to enhanced fitness, resilience, and the biogeographic distribution of NZ seaweeds and its episymbiotic sea anemones.
During my abundance surveys at Taputeranga Marine Reserve (TMR), I found more species of sea anemones that are living in similar associations, such as the unknown species (photo below) which is found on the stipes of Lessonia variegata.
With support of the Kevin Smith Memorial Scholarship, I was able to undertake extensive surveys around the south coast of Wellington, including TMR, during all seasons.
Left: Carpophyllum maschalocarpum with associated Handactis nutrix on Paua at TMR; Middle: stereomicroscopic images of the brooding anemone, Handactis nutrix, with developing brood in its pouch; Right: Handactis nutrix on Cystophora scalaris at Moa Point
Results from the field: Host specificity and specific assemblage patterns in the seaweed-sea anemone symbiosis
The results of my research have been very intriguing and support an intimate symbiotic relationship between the sea anemone and its seaweed hosts. Specifically, the results of my field surveys provide strong evidence for host specificity of H. nutrix towards species of Cystophora compared to Carpophyllum across various depths, locations, three levels of wave exposure, and seasons. H. nutrix was not found on any other surface besides the seaweed in this study, and specific assemblage patterns of the sea anemone were observed such as its position on the stipe vs. the blade of the thallus, a higher abundance of the sea anemone in correlation to increased structural complexity (volume, weight) of the seaweed and its preferred position 25-40 cm from the seabed. These may represent specific adaptations for life on the seaweed host, which can be very turbulent due to strong hydrodynamic forces around the south coast of Wellington. Hopefully, this information will also help you spot these beautiful creatures on your next snorkel or dive in Taputeranga Marine Reserve.
Results from the laboratory: Nutritional interactions in the seaweed-sea anemone symbiosis
Besides the findings of my field surveys, my lab experiments provided strong evidence for a nutritional symbiosis between the sea anemone, Handactis nutrix, and its seaweed host, Cystophora scalaris. Although no transfer of carbon could be detected between the partners, there is strong evidence for nitrogen transfer in form of ammonium, the waste product, from the sea anemone to the seaweed. Further the stable isotope ẟ15N natural abundance signature differed between seaweeds colonised with H. nutrix and those without further suggesting a mutually beneficial relationship in which the sea anemone provides significant amounts of nitrogen to the seaweed host. Given the importance of nitrogen for the seaweed’s photosynthesis and its frequent limitation in the natural environment, especially around Wellington’s south coast with particularly low levels in summer, this nutritional symbiosis likely has significant implications for the survival, growth, and overall health of both the sea anemone and its seaweed host.
Left and Middle: Handactis nutrix on Lessonia variegata at TMR; Right: Transect line in the shallows around Taputeranga Island.
Undescribed anemone species on Lessonia variegata around Taputeranga Island.
Future work: What are the implications of this symbiosis for partner nutrition, growth and survival?
In my PhD, I plan to explore these effects of the sea anemone’s nutritional benefit for the seaweed in detail. First, I will investigate the implications of this symbiosis for partner nutrition, growth, and survival in a long-term-controlled laboratory experiment over 2-3 months. During this experiment, the presence and abundance of the sea anemone will be manipulated in association with the seaweed. Growth, survival, and physiological parameters that indicate the health of the partners will be measured using novel technologies such as spectrophotometry, pulse-amplitude modulated fluorometry, and lipid and fatty acid analysis using Gas Chromatography-Mass Spectrometry. Finally, radioisotope labelling experiments will establish whether the nutrient status of the seaweed is directly linked to the feeding regime of the anemone by adapting the ammonium enhancement of dark carbon fixation method. Further, I aim to investigate the association between the seaweeds and the unknown anemone species that I came across in my first year of field studies, identify them and collaborate with the local iwi for the assignment of te reo Māori names.
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Photos Lisa Wolf