Questions from the Spotlight Webinar - Kelp Farming in Aotearoa New Zealand
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Hi folks,
We had a great webinar with Greenwave Aotearoa last month. If you missed it, you can watch the recording here.
Our presenters from Greenwave Aotearoa, Premium Seas, and University of Waikato got A LOT of questions during the live session--more than we were able to answer at the time. The presenters took the time to respond to some of the outstanding questions -- so we're moving that exchange into the Community for all to enjoy.
I'm sharing some of the top questions about species and location below, along with answers from presenters Rebecca Lawton (RL) and Ryan Marchington (RM). I've also added a couple of reflections (KB). Stay tuned on this thread over the coming days for more Q&A about environmental conditions, farm design, restoration and ecosystem services.
Have more questions? Submit a reply and ask them below! Tag @rebecca_barclay @rebecca_lawton @lucas_evans @ryan_marchington1903 @liam_hansard6513 or other experts in the Community!Species and Seed Availability
Do we know whether Ecklonia or Gigartina can be harvested multiple years as a perennial or will it need to be replanted every year?
RM: We are still trialling our sea trials for both Ecklonia and Gigartina, so its difficult to determine the time we can farm the same crops over multiple years and harvest using a coppicing method. Even if kelps persist over multiple years on a longline system, other factors–such as desired market/end use, water temperature, and the presence of grazing or biofouling organisms–may influence the timing of outplanting and harvest. Based upon McNeill et al 2003 - preliminary trials showed G. atropurpurea could be ‘harvested’ up to three times during the growth period (August–December) by pruning.
When I looked into this (Macrocystis pyrifera) there was not commercial spat and seed line available - leaving aside the difficult resource consent process. Is there now a commercial seed line available?
RL: Commercial seed line for any seaweed species is not currently available in New Zealand. But this is something the Greenwave Aotearoa are working towards providing in the future.
Are Lessonia species being considered for culture and or commercialisation in New Zealand?
RL: Yes, Lessonia is being considered for culture by Greenwave Aotearoa and trials with Lessonia are also currently underway through the Cawthron Institute in Tasman Bay, in collaboration with our team at the University of Waikato. Initial results from at-sea trials for Lessonia are very promising and so far it seems to grow well in the hatchery too.Location
Do you have thoughts on why Ecklonia grew better at Wilson's Bay?
RL: I think it may be a combination of factors. Water flow/current is higher at both Wilsons Bay and Ponui compared to Esk. We also suspect that there might be more nutrients in the water at Wilsons Bay compared to the other two sites (Ponui in particular). So it could be that growth is better overall at Wilsons Bay due to the high flow and high nutrients. We haven’t finished this site comparison study yet and still have another round of monitoring to complete and all the data on the physical characteristics of the sites to analyse, so hopefully this will shed some more light on what is driving the differences in performance between sites.
Is biofouling risk lower in an open ocean environment?
RL: biofouling is highly stochastic and even within the same site the type of fouling, seasonality of occurrence and prevalence can vary considerably over time. However, in general, water quality is higher in open ocean environments and biofouling is lower compared to nearshore coastal waters.
Does the seaweed have to be grown in the ocean? Can there be land-based farms? Or is it too hard to mimic the ocean? Is the ocean preferable because it also creates a good environment for other species eg fish and contributes to ocean health?
KB: Some seaweeds are well-suited to tank-based cultivation, particularly those that propagate vegetatively and/or those that are prevalent in intertidal environments. Other species, particularly those that are from the low-subtidal area or have high nutrient demands may not work well or may be inefficient to grow in land- or tank-based culture. Ocean farms have the advantage of passively absorbing nutrients in the marine environment and, in the process, providing other ecological benefits. Site selection is extremely important.
Relevant Publications:
RL: These are the articles that we have published so far from work related to the Greenwave Aotearoa project:
https://www.tandfonline.com/doi/full/10.1080/00288330.2023.2256685
https://link.springer.com/article/10.1007/s10811-023-02969-2
https://link.springer.com/article/10.1007/s10811-022-02894-w
https://link.springer.com/article/10.1007/s10811-022-02806-y
https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.749154/full
https://www.sciencedirect.com/science/article/pii/S2211926424003898
Environmental conditions and farm design
Is the spectrum of available light important?
RL: The spectrum of available light is important to consider when assessing site suitability. This is impacted by water clarity (e.g. the amount of suspended solids in the water) and water depth (te light intensity decreases and the spectrum changes as depth increases). Optimal light conditions will depend on the particular seaweed species being grown. Some species grow well under higher light intensity, others prefer lower light intensity, and different seaweed species use different parts of the light spectrum to photosynthesize.
Was the benefit of vertical cultivation lines due to lower temperatures? If so, would more deeply submerged horizontal lines achieve the same but allow better water utilisation?
RL: It is unlikely that the vertical lines were better than the horizontal lines due to temperature differences. There were only very small decreases in temperature with depth during this study (~0.2 °C). In addition, we tested horizontal lines at 2 depths and performance was poor on all horizontal lines, regardless of depth. We think that vertical lines may have performed better due to differences in the hydrodynamic forces experienced by the seaweed on the different line types, but we haven’t been able to test this hypothesis. If you’re interested in more detail about this study then you can read a full write up of what we did and what we found here: https://www.tandfonline.com/doi/full/10.1080/00288330.2023.2256685
How does sedimentation from the land affect seaweed farming growth?
RL: this is really dependent on the specific species that you are growing. Some species are largely unaffected by sediment, while others do not grow well in water with high sediment loads. In some cases sediment can actually be beneficial so long as there’s not too much of it as it can increase nutrient concentrations in the water which the seaweed needs to grow.
Did you look into the effects of the marine heatwave on the kelp in the laboratory, sporulation, germination, fertilisation etc and then post heatwave growth? Is this available in a published paper?
RL: Unfortunately, this was all outside the scope of the current Greenwave Aotearoa project. However, I have just received funding for a 5 year study which will look into some of these effects and whether we can develop methods to improve heat tolerance in kelp. Some of these questions have also been investigated in other species of seaweed, with varying results (published papers on this topic should be fairly easy to find).
Have you looked at direct seeding with glue/gum onto grow ropes at sea?
RM: Direct seeding is something we are considering to scale our farming operations and reduce the production costs. Before we trial direct seeding - when we can prove a site is suitable with twine cultivation, we will explore direct seeding cultivation trials. Direct seeding has been trialed with Ecklonia radiata on very small scales in the Hauraki Gulf.
Are there examples of in-situ-only trials? Are there methods to encourage kelp (or other species) to grow with less intervention ('gardening')? A potential option for small-scale production?
KB: I’m not sure what is meant by in-situ-only trials in this context, but here are some examples of projects outside of the Greenwave Aotearoa pilot that may be of interest:
Could moveable lines help mean more production and mitigation of fouling i.e. fast initial growth to take up the space on the lines and move the lines down when established?
RL: yes, this is something that could be considered to help manage light intensity. For example, lines could be kept shallower in the winter when light intensity is lower, and then depth could be increased in spring when light intensity increases so that the light the seaweed receives isn’t too high. Changing the depth of lines wouldn’t affect the fouling – we see an even spread of fouling on our lines from 0 – 20 m depth.
Would seeded tiles work and cause less fouling or potentially higher wave action/cooler temps influence fouling?
RL: you can seed seaweed spores onto a wide range of different substrates including tiles and this is already done for restoration and ecological studies. However, tiles would be impractical and a hugely inefficient way to farm seaweed – they would take up too much space in the hatchery, and would be difficult to deploy and harvest.
Restoration, ecosystem services, and carbon credits
Has there been much work or trials of effective methods of reattaching adult kelp and Algae in Barron marine environments?
RL: Yes, there has been some work done on this from a restoration perspective. Cayne Layton at UTAS has published some methods for transplanting adult kelp. There is also lots of information out there about using an approach called “green gravel” for restoration. In this approach, kelp spores are seeded on small rocks/gravel in a lab/hatchery. Once the seedlings reach a certain size the gravel is then transferred to the restoration site and the kelp gradually overgrow the gravel and attach themselves to the reef that the gravel is sitting on.
Is there potential for blue carbon credits as a revenue source to strengthen the investment ROI? And help the environment! And, similar question: Have we been able to measure the carbon sequestration potential of Ecklonia or Macrocystis?
KB: Kelp farming can provide a range of ecosystem benefits, and it's the whole package that should be considered -- such as nitrogen remediation in eutrophied waters, providing habitat and structure for reef assimilated species, and taking up carbon. Kelp takes up carbon quickly, but the pathways for sequestration are complex and methods for monitoring and verification of those pathways have not been fully validated. The science is still a ways off. Dr. Catriona Hurd from University of Tasmania gave a great presentation recently on the potential for carbon sequestration for seaweeds. Dr. Hurd breaks down the state of the science, potential pathways, and challenges. Find that presentation here: https://vod.video.cornell.edu/media/The+Potential+of+Seaweeds+for+Carbon+Dioxide+Removal+and+Sequestration%3A+Challenges+in+Monitoring%2C+Reporting%2C+and+Verification/1_9spkbajz