Abstract
British Phycological APPLIED PHYCOLOGY Society 2023, VOL. 4, NO. 01, 44–53 Understanding and using algae https://doi.org/10.1080/26388081.2023.2174903 Nursery optimization for kelp aquaculture in the Southern Hemisphere: the interactive effects of temperature and light on growth and contaminants Wouter Visch , H. Lush, J. Schwoerbel and C. L. Hurd Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia ABSTRACT ARTICLE HISTORY Received 7 July 2022 Kelp aquaculture is typically a two-stage process, with an indoor nursery phase and a grow-out Accepted 21 January 2023 phase at sea. For the successful development and implementation of commercial kelp aquaculture, production of viable seeded lines in the nursery is essential. This study investigated optimal KEYWORDS nursery conditions of three kelp species native to Tasmania, Australia: Ecklonia radiata, Lessonia Algal cultivation; biofouling; corrugata, and Macrocystis pyrifera. The interactive effects of temperature (12°C, 15°C, and 18°C) Ecklonia radiata; −1 −2 −1 −2 and light level (~30 µmol photons s m , and ~ 60 µmol photons s m ) on sporophyte length, gametophytes; giant kelp; sporophyte density, and contamination of spools were examined over a 34-day period. The hatchery; Laminariales; −2 −1 Lessonia corrugata; optimal temperature and light levels were 15°C and 30 µmol photons m s for E. radiata, 12°C −2 −1 −2 −1 Macrocystis pyrifera; and 60 µmol photons m s for L. corrugata, and 12°C and 30 or 60 µmol photons m s for mariculture M. pyrifera. Under these optimal conditions, the mean ± SEM sporophyte lengths after 34 days were 0.60 ± 0.02 mm, 1.04 ± 0.04 mm, and 0.60 ± 0.01 mm for E. radiata, L. corrugata, and M. pyrifera, respectively. The mean ± SEM sporophyte densities for each of these three species were 15.5 ± 6.2 −1 −1 −1 sporophytes cm of line, 10.8 ± 5.9 sporophytes cm of line, and 19.3 ± 8.1 sporophytes cm of line, respectively. Contamination increased with increasing temperature and was not significantly affected by light level. This work highlights the need for a species- and ecotype-specific approach in the nursery phase to ensure successful seaweed aquaculture outcomes in new regions of cultivation. Introduction Sánchez, 2019; Su, Pang, Shan, & Li, 2017). Culture Laminarian kelps (Phaeophyceae, Laminariales) have conditions for gametophytes and early sporophytes of substantial global economic and ecological importance commercial kelp species non-native to Australia such as (Bennett et al., 2015; Chopin & Tacon, 2021; Steneck Saccharina japonica, S. latissima, and Undaria pinnati- et al., 2002). Kelp aquaculture has developed signifi- fida are well known, and optimal temperature, photon- cantly in recent years, with a wide array of products flux density, light spectrum, photoperiod, and nutrient already on the market, and new kelp-based products requirements have been elucidated (Camus & constantly in development (Gutierrez et al., 2006; Buschmann, 2017; Nielsen, Kumar, Soler-Vila, Holdt & Kraan, 2011). Whilst kelp aquaculture has Johnson, & Bruhn, 2016; Ratcliff, Soler-Vila, Hanniffy, historically been focused in Asia, it is gaining worldwide Johnson, & Edwards, 2017; Su, Pang, Shan, & Li, 2017; interest (Naylor et al., 2021). There are many benefits of Wang et al., 2010). As a result, several technical manuals seaweed farming when compared to terrestrial crop have been produced to help people establish effective production, i.e., seaweeds do not need fertilizer, pesti- nursery culture (Edwards, O’Mahony, Connellan, cides, or freshwater irrigation, and as such kelp aqua- Dring, & Werner, 2011; Flavin, Flavin, & Flahive, culture is now emerging in “non-traditional” regions of 2013; Forbord, Steinhovden, Rød, Handå, & Skjermo, production, including Australia (Kelly, 2020). 2018; Redmond, Green, Yarish, Kim, & Neefus, 2014; Kelp mariculture is a two-stage process, with an Rolin, Inkster, Laing, Hedges, & McEvoy, 2016). In indoor nursery (hatchery) phase, and an at sea grow- Australia, to date, the research focus on kelps has been out phase. Optimizing the production of seeded lines largely of an ecological nature (Layton & Johnson, 2021; bearing juvenile sporophytes in the nursery is essential Novaczek, 1984; Suebsanguan, Strain, Morris, & for successful commercial kelp aquaculture (Camus & Swearer, 2021; Tatsumi et al., 2022; Tom Dieck, 1993), Buschmann, 2017; Hu et al., 2021; Peteiro, Bidegain, & which provides a starting point but can be challenging CONTACT Wouter Visch wouter.visch@utas.edu.au Supplemental data for this article can be accessed online at https://doi.org/10.1080/26388081.2023.2174903 © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. APPLIED PHYCOLOGY 45 to translate to aquaculture. Therefore, to support the Neefus, 2014). However, despite these treatments, con- development of the Australian kelp aquaculture indus- tamination often remains a challenge and is sometimes try, optimal conditions for gametophyte and early spor- unavoidable, especially when scaling up to larger nur- ophyte development need to be determined. sery volumes (e.g., Mooney-McAuley, Edwards, There are three laminarian kelp species native to Champenois, & Gorman, 2016; Su, Pang, Shan, & Li, Tasmania, Ecklonia radiata (C.Agardh) J.Agardh, 2017). How the environmental conditions in nursery Lessonia corrugata A.H.S.Lucas, and Macrocystis pyri- culture might affect levels of contaminants has not fera (L.) C.Agardh (Scott, 2017), and all are gaining been tested systematically and is absent for Australian commercial interest (Kelly, 2020). With respect to bio- kelp species, but this information is needed to improve geographical genetic variation in southern Australia, the effectiveness of kelp nurseries. E. radiata and M. pyrifera have relatively low genetic The purpose of this study was to optimize nursery diversity compared to L. corrugata (Durrant, Barrett, conditions of three kelp species (E. radiata, L. corrugata, Edgar, Coleman, & Burridge, 2015). E. radiata is sub- and M. pyrifera). We examined the interactive effects of tidal and found in New Zealand, Madagascar, South temperature (12°C, 15°C, and 18°C) and light (~30 µmol −1 −2 −1 −2 Africa, and in southern Australia where it is the domi- photons s m , and ~60 µmol photons s m ) on nant habitat-forming kelp of the “Great Southern Reef” sporophyte length and density of spools inoculated with (Bennett et al., 2015; Wernberg et al., 2019). This rela- gametophytes. We simultaneously evaluated the effect tively large geographical range suggests a broad toler- of nursery conditions on contamination of the spools. ance of gametophytic and juvenile sporophytic life- The results provide information that will help optimize stages to environmental conditions, including tempera- nursery conditions and assist in the development of ture and light level (Mabin, Gribben, Fischer, & Wright, a kelp aquaculture industry in southern Australia. 2013; Tom Dieck, 1993; Wernberg et al., 2019). M. pyrifera is more globally distributed and can be found from the low intertidal zone to a depth of 30 m Materials and methods in all cold-temperate waters in the Southern Gametophyte culture establishment and spool Hemisphere and along the west coast of North preparation America (Schiel & Foster, 2015). Its distribution is lar- gely determined by temperature, and its upper thermal Fertile sorus tissue from five individuals of E. radiata and tolerance for gametophytes is higher than that of spor- L. corrugata was collected by divers from Apex Point ophytes (Mabin, Johnson, & Wright, 2019; Schiel & (43.1033°S, 147.7077°E), with similar samples taken Foster, 2015; Tom Dieck, 1993). L. corrugata is endemic from M. pyrifera from Blackmans Bay (43.0122°S, to Tasmania and appears to have a relatively narrow 147.3312°E), Tasmania, Australia. Zoospores were temperature and irradiance range for optimal gameto- released following the methods described in Forbord, phyte growth (Paine et al., 2021; Tom Dieck, 1993). Steinhovden, Rød, Handå, & Skjermo (2018). In short, In addition to establishing optimal culture condi- mature sorus tissue was dissected out of the main thallus tions, management of contaminants is recognized as with individuals treated separately. Sori were thoroughly one of the major limitations to seaweed aquaculture wiped clean with a paper towel to remove any debris or development (Kim, Yarish, Hwang, Park, & Kim, epiphytes, then washed three times for 10 s in an iodine −1 2017). Contamination and/or fouling by unwanted (Betadine®) solution (5 ml l ) with successive rinsing organisms, such as pathogens, diatoms and other using sterile seawater, before being kept overnight at algae, nematodes, and ciliates, that negatively impact 12°C in damp paper towel in the dark. Subsequently, growth in the nursery phase should be avoided or kept zoospores were released in autoclaved seawater with F/ to a minimum (Bartsch, 2018; Forbord, Steinhovden, 2-medium (Guillard & Ryther, 1962) and kept in aerated Rød, Handå, & Skjermo, 2018; Redmond, Green, Yarish, (0.2 µm PTFE syringe filters) 3 l glass flasks at 12°C under −2 −1 Kim, & Neefus, 2014). Measures to deal with contam- red light conditions (~15 µmol photons m s ) and ination depend on the type and source of contaminants, long-day photoperiod (16 h light:8 h dark) provided by and the nursery production method typically entails LEDs (Fluval aquasky®). The zoospores were sterilizing glassware and culture media, disinfecting allowed to develop into gametophytes that were the sori prior to zoospore release, and using germanium grown vegetatively for >3 months under these dioxide or antibiotics to control diatom- and bacterial- culture conditions, with the culture medium growth, respectively (Bartsch, 2018; Forbord, being changed biweekly (Bartsch, 2018). Steinhovden, Rød, Handå, & Skjermo, 2018; Kerrison, Ten days before the start of the experiment, the Le, & Hughes, 2016; Redmond, Green, Yarish, Kim, & gametophyte cultures from five individuals were mixed 46 W. VISCH ET AL. in equal densities, and the light spectrum changed to ITC-308; see Supplementary fig. S1). Light was −2 −1 white light (~80 µmol photons m s ) to induce game- provided by LEDs (Clipsal©, 5000k, togenesis (Lüning & Dring, 1975). Gametogenesis was TPWPLED2) overhead and light level was con- induced to reduce the time in the nursery and minimize trolled by wrapping half of the jars in white mesh potential differences in the transition rate of gameto- to achieve the lowest light treatment (30 µmol −2 −1 phytes to sporophytes between experimental treatments. photons m s ), the remaining jars were uncov- The developing gametophyte solution was concentrated ered and received the highest light-level treat- −2 −1 to 25 filaments per µl using a cell counting chamber ment (60 µmol photons m s ). Light levels (Sedgewick Rafter S50) with a 10-cm filter. This game- were measured using a LI-COR Light Meter tophyte culture was then evenly sprayed using (LI-250A) with a spherical quantum sensor a sterilized 1.25 l handheld pressure sprayer (Hozelock attached. Media and culture jars were changed Ltd. Viton®) onto 10-cm PVC pipes (75 mm diameter) twice per week, after which the jars were ran- around which 10 m of polypropylene twine (~1 mm domly placed back into the corresponding tub. diameter) was wound, hereafter called “spools”. The All jars, lids, and culture media were UV steri- spools were sterilized prior to spraying, by soaking in lized in a laminar flow unit for 60 minutes prior to a 10% bleach solution overnight, after which they were each media change. thoroughly rinsed, dried in a laminar flow cabinet, and treated with UV light for 20 min. Sporophyte length, density, and contamination measurements Experimental design At the end of the experiment, the length of each spor- The experiment sought to determine the interactive ophyte (measured from holdfast to distal end of the −2 −1 effects of light (30 and 60 µmol photons m s ) and thallus) and density of the sporophytes on the twine temperature (12°C, 15°C, 18°C) on sporophyte develop- was measured using the ImageJ software. This was ment for E. radiata, L. corrugata, and M. pyrifera, with n done by analysing images taken with the aid of = 3 replicates for each treatment. Both light and tempera- a stereo microscope (Leica, M165 C) fitted with ture treatments were chosen based on temperatures the a camera, of a 10 cm section of twine carefully removed species typically experience in nature in Tasmanian from the middle section of each spool. To assess con- coastal waters and that have previously yielded relatively tamination, each spool was randomly divided into good results for M. pyrifera (Biancacci, Sanderson et al., thirds around its circumference, a photo from top to 2022, Biancacci, Visch et al., 2022). In total, we examined bottom was taken of each third, and a 1 cm column in 54 spools (3 species × 3 temperatures × 2 light × 3 the centre of each image given a contamination score replicates). Each seeded spool was treated as an indepen- (0–5; where zero is no contamination and five is 100% dent replicate and carefully placed individually in 2 l covered). This gave three scores per spool, which were transparent plastic jars filled with 1.5 l UV treated filtered averaged to represent the contamination score of the seawater (0.22 µm) with F/2-medium and GeO (0.02 whole spool. A more detailed illustration of the sam- −1 µmol l ). To allow the gametophytes and microscopic pling design can be found in Supplementary fig. S2. juvenile sporophytes to adhere, there was no aeration in the jars for the first 3 days after spraying, after which the aeration was slowly increased until the jars were gently Statistical analysis aerated. Each jar was supplied with air filtered with 0.2 µm syringe filters (25 mm diameter, PTFE). All analyses were conducted using R software (R Core Based on previous experience, the duration of the Team, 2018). The individual and interactive effect of experiment was 34 days and carried out in temperature (fixed factor, three levels) and light level a temperature-controlled room set at 11°C (Biancacci, (fixed factor, two levels) on sporophyte length and den- Visch et al., 2022). The seawater temperature in the jars sity, and level of contamination were statistically ana- was controlled by randomly placing six (3 species × 2 lysed for each of the three species. Sporophyte length light × 1 replicate) of the 2 l plastic jars into a tub (36 l; and density were analysed with two-factor analysis of dimensions 34 cm wide, 47 cm long, 25 cm high) par- variance (ANOVA) using the lm function. When sig- tially filled with freshwater that was thermally con- nificant, multiple comparisons were performed with trolled to obtain the three temperature treatments a Student–Newman–Keuls (SNK) post hoc test (α = (12°C, 15°C, and 18°C) using aquarium heaters (Aqua 0.05), using the SNK.test function of the agricolae pack- One®) regulated by a thermostat (Inkbird Tech Inc, age (version 1.2–8) (Mendiburu de Fy, 2020). Data were APPLIED PHYCOLOGY 47 checked for violations of ANOVA assumptions (nor- 12°C independent of light level and 15°C at 30 µmol −2 −1 mality and homoscedasticity), and the best suited nor- photons m s , compared to 15°C at 60 µmol −2 −1 malizing transformation was estimated using the photons m s and 18°C independent of light level. bestNormalize package (Peterson, 2017), data was trans- The maximum sporophyte length obtained after 34 days formed where necessary. Contamination level was ana- in the nursery was (mean ± SE, average n = 308) 0.60 ± lysed with a non-parametric two-way ANOVA 0.02 mm, 1.04 ± 0.04 mm, 0.60 ± 0.01 mm for E. radiata, Scheirer–Ray–Hare test, using the scheirerRayHare L. corrugata, and M. pyrifera, respectively function of the rcompanion package (version 2.4.15) (Supplementary table S1). (Mangiafico, 2022). When significant, pairwise compar- isons were performed with a Dunn’s post-hoc test (α = Sporophyte density 0.05), using the dunnTest function of the FSA package (version 0.9.3) (Ogle, Wheeler, & Dinno, 2022) with Sporophyte density in the twine of both L. corrugata and p value adjustment using the Bonferroni correction. M. pyrifera was significantly affected by temperature, with a negative relationship between sporophyte length and increasing temperature (Table 2, Fig 1b). Light level had no significant effect on the sporophyte density of Results L. corrugata and M. pyrifera. The sporophyte density of Sporophyte length E. radiata was not significantly affected by temperature and light level. The maximum sporophyte density The length of the sporophytes of L. corrugata was sig- per cm of line after 34 days in the nursery (mean ± SE, nificantly affected by temperature, with a negative rela- n = 3) was 16.8 ± 6.2, 11.8 ± 4.1, and 19.3 ± 8.1 for tionship between sporophyte length and increasing E. radiata, L. corrugata, and M. pyrifera, respectively temperature (Table 1, Fig 1a), and there was no effect (Supplementary table S1). of light level. Both E. radiata and M. pyrifera were interactively affected by temperature and light level. E. radiata sporophytes grew longer at 15°C and 18°C, Contamination score compared to 12°C. The culture condition that resulted in the largest E. radiata sporophytes was 15°C and 30 There was a significant positive relationship between −2 −1 µmol photons m s . At 12°C, the 30 µmol contamination score on the spools and temperature −2 −1 photons m s treatment resulted in longer for all three species (Table 3, Fig 2, Supplementary −2 −1 E. radiata sporophytes compared to 60 µmol m s . table S1). Pairwise comparisons using Dunn’s test indi- M. pyrifera sporophytes were significantly longer at cated that the contamination scores at 12°C were Table 1. Sporophyte length per species. Summary of two-way ANOVA of the mean sporophyte length (mm) exposed to three −2 −1 temperatures (12°C, 15°C, and 18°C) and two light levels (30 and 60 μmol photons m s ), followed by a Student–Newman–Keuls (SNK) post-hoc test. Ecklonia radiata Lessonia corrugata Macrocystis pyrifera Source of variation df MS F p SNK MS F p SNK MS F p SNK Temperature 2 7.68 41.31 <0.001 39.94 79.43 <0.001 §2 11.11 50.20 <0.001 Light 1 2.18 11.71 <0.001 0.01 0.02 0.88 19.85 89.71 <0.001 Temperature x Light 2 2.74 14.74 <0.001 §1 0.89 1.77 0.17 3.42 15.46 <0.001 §3 Residual 12 0.19 0.50 0.22 −2 −1 −2 −1 −2 −1 −2 −1 −2 −1 −2 −1 §1: 12°C 60 μmol m s < 12°C 30 μmol m s = 18°C 30 μmol m s = 15°C 60 μmol m s ≤ 18°C 60 μmol m s ≤ 15°C 30 μmol m s §2: 18°C < 15°C < 12°C. −2 −1 −2 −1 −2 −1 −2 −1 −2 −1 −2 −1 §3: 18°C 60 μmol m s = 15°C 60 μmol m s = 18°C 30 μmol m s < 12°C 60 μmol m s = 15°C 30 μmol m s = 12°C 30 μmol m s Table 2. Sporophyte density per species. Summary of two-way ANOVA for the main and interactive effect of the mean number of sporophytes per cm of line, followed by a Student–Newman–Keuls (SNK) post-hoc test. Ecklonia radiata Lessonia corrugata Macrocystis pyrifera Source of variation df MS F p SNK MS F p SNK MS F p SNK Temperature 2 136.01 2.56 0.12 154.19 5.58 0.02 §1 413.06 5.18 0.02 §2 Light 1 0.47 0.01 0.93 1.33 0.05 0.83 0.53 0.01 0.94 Temperature x Light 2 40.24 0.76 0.49 0.69 0.02 0.98 1.98 0.02 0.98 Residual 12 53.25 27.65 79.75 §1: 18°C < 15°C = 12°C. §2: 18°C < 15°C = 12°C. 48 W. VISCH ET AL. Figure 1. Bar plots of (a) sporophyte length and (b) sporophyte density on the seeded twine. Letters above the bars indicate significant differences based on the SNK-test (p < 0.05). Error bars show SEM, with n = 3. Table 3. Contamination score per species. Scheirer–Ray–Hare test results for the main and interactive effects of a two-way non- parametric ANOVA. Temperature Light level Interaction Species df H p df H p df H p Ecklonia radiata 2 11.45 0.003 1 1.61 0.205 2 0.41 0.813 Lessonia corrugata 2 12.72 0.002 1 0.08 0.782 2 0.15 0.926 Macrocystis pyrifera 2 9.90 0.007 1 1.36 0.244 2 1.16 0.560 significantly lower from those at 18°C for E. radiata and light levels separately and interactively affect the growth L. corrugata, but no other differences were statistically and density of juvenile sporophytes, but contamination significant (Suplementary table S2). For M. pyrifera, we that accumulated over the 34-day culture period mark- found significantly lower contamination scores at 12°C edly affected the culture outcomes. For all three study compared to 15°C and 18°C, and no significant differ- species, temperature was a stronger driver for maximiz- ence between 15°C and 18°C. We were unable to pro- ing success in the nursery than light level. Growth vide a detailed taxonomic description of the maxima were at lower temperatures and light levels contaminants, but cyanobacteria and Ectocarpus spp. than previously reported for all three study species appeared to be the most dominant. (Camus & Buschmann, 2017; Paine et al., 2021; tom Dieck, 1993; Wernberg et al., 2019). However, this lower temperature optima could be confounded by an Discussion increased level of contamination at higher temperatures, Our findings suggest that understanding the effects of where more contamination leads to reduced growth, temperature and light levels are key to optimizing spor- rather than a higher temperature per se. ophyte growth of Australian kelp species (E. radiata, For E. radiata, nursery conditions of 15°C and 30 −2 −1 L. corrugata, and M. pyrifera). However, contaminants µmol m s resulted in the longest sporophytes, rela- also need to be taken into account to ensure the best tively high sporophyte density in the twine, and outcomes for nursery production. Temperature and a relatively low level of contamination. Our results APPLIED PHYCOLOGY 49 Figure 2. Boxplots of contamination score (between 0–5) for three kelp species. One asterisk (*) indicates a p value smaller than 0.05. Two asterisks (**) indicate a p value smaller than 0.01 as per Dunn’s post-hoc test. suggest a thermal growth optimal for juvenile E. radiata that L. corrugata gametophytes cultured from zoos- sporophytes from Tasmanian of around 15°C, although pores that were sampled in late autumn, grew maxi- −2 −1 a thermal response curve is needed to confirm this. In mally around 70 µmol photons m s which is southern New Zealand (45°S) growth and productivity broadly consistent with the highest experimental light −2 −1 of mature E. radiata sporophytes was maximum in late treatment (60 µmol photons m s ) used in the pre- winter/spring and correlated strongly with seawater sent study. L. corrugata has a relatively high genetic temperature which is typically between 12°C and 14°C diversity compared to the other two species in the (Goodwin & Cornelisen, 2012; Miller, Hurd, & Wing, study region (Durrant, Barrett, Edgar, Coleman, & 2011). This contrasts with E. radiata sporophytes from Burridge, 2015), which provides opportunities to lower latitudes (28°S–35°S), which have a higher opti- further explore the effect of high performing mal temperature (~24°C) for photosynthesis (Wernberg Tasmanian ecotypes with potentially improved growth et al., 2019; Wernberg, de Bettignies, Joy, & Finnegan, at higher temperatures and irradiance. 2016) that is a few degree Celsius higher than the ther- M. pyrifera had a maximum sporophyte growth and mal optimum for growth in most seaweeds (Hurd, density, and minimal contamination at 12°C and 30 or −2 −1 Harrison, Bischof, & Lobban, 2014). Overall, tempera- 60 µmol photons m s . Our findings largely corrobo- ture was found to be a stronger driver for maximizing rate Camus & Buschmann (2017) who found that the the success of the nursery production for E. radiata optimal nursery conditions for Chilian M. pyrifera were −2 −1 compared to light level. 12°C and 12 μmol photons m s and a long-day The optimal nursery condition for Lessonia corru- photoperiod (16 h light : 8 h dark). The lower optimal −2 −1 gata was 12°C and 60 µmol m s , with maximal light level might be because gametophyte development growth and sporophyte density, and least contami- can occur in a relatively low light environment (~5 μmol −2 −1 nants in the spools. Similar to E. radiata, the optimal photons m s ), and a temperature between 11°C and temperature was colder than expected based on the 19°C (Deysher & Dean, 1984, 1986). Interestingly, even previously observed growth optimum between 15.7°C though Camus & Buschmann (2017) seeded the spools and 17.9°C (Paine et al., 2021) or other Lessonia species with zoospores, they found 0.4 to 0.5 cm long sporo- (Nelson, 2005; Oppliger et al., 2012; Tom Dieck, 1993). phytes within 45 days. We found that the longest It is, however, within the range of its natural conditions M. pyrifera sporophytes reached an average length of in Tasmania. Furthermore, Paine et al. (2021) found only 0.06 cm after 34 days, which suggests that 50 W. VISCH ET AL. contamination, different genotypes, or other potential (Lüning & Dring, 1975), nutrients (Fernández et al., differences in culture condition may have negatively 2020; Gao, Endo, Nagaki, & Agatsuma, 2016), hydro- affected sporophyte growth. dynamics (Camus & Buschmann, 2017; Peteiro, After 34 days in culture, contamination was observed Bidegain, & Sánchez, 2019), interactive effects of in all experimental treatments, despite having under- environmental variables (Camus & Buschmann, taken significant preventive measures against epiphytic 2017; Gao, Endo, Nagaki, & Agatsuma, 2017; Mabin, and epizoic contaminants, including cleaning the sorus Johnson, & Wright, 2019), and varying culture condi- tissue prior to zoospore release (Alsuwaiyan et al., tions following optimal culture conditions of each life- 2019), filtering and UV-treatment of culture media stage (i.e., zoospore, gametophyte, or juvenile sporo- necessary to support growth, filtering the air used in phyte) throughout the nursery phase (Gerard, 1997; mixing of the culture medium, sterilizing the culture- Su, Pang, Shan, & Li, 2017). Given the gametophyte ware, and working in a sterile laminar-flow cabinet for stock-cultures of all the species used in the present production and culture of both the free-floating game- study have been kept at ~12°C under laboratory con- tophytes throughout the experiment. The source of the ditions for >6 months, an additional concern may be epiphytic and epizoic contamination was not identified, the potential for drifting sex-ratios to negatively affect but we observed a trend of a lower contamination at the reproductive success (Ebbing et al., 2021) and a more −2 −1 lowest light level (30 μmol photons m s ) compared narrow temperature optimum compared to in nature with the high light-level treatment (60 μmol (Hurd, Harrison, Bischof, & Lobban, 2014). The −2 −1 photons m s ). This partially corroborates with Su, potential beneficial effects of an acclimation period Pang, Shan, & Li (2017) who noted reduced contamina- to the environmental conditions at-sea prior to tion when the light level was limited to below 20–25 deployment when using vegetatively propagated −2 −1 μmol photons m s . This could, however, be con- gametophytes in seaweed nurseries needs further founded by the relatively low level of nutrients used in examination (Fernández et al., 2020; Gauci, Bartsch, −1 −1 their study (8–11.8 μmol l NO and 0.7–1.5 μmol l Martins, & Liesner, 2022). Finally, our study high- PO ) compared to nutrient levels in the present study lights the importance of optimized culture conditions −1 −1 (F/2-medium: 882 μmol l NO and 36.2 μmol l PO ). in the nursery phase for a more efficient seaweed 3 4 In this study, we did not take any reactive measures to aquaculture production process. reduce or manage contaminants throughout the course of the experiment. Both proactive and reactive deconta- Acknowledgements mination methods may be improved using a combination of treatments; mechanical removal of We appreciate the support of the partners within the “Seaweed solutions for sustainable aquaculture CRC Project” epiphytic contaminants (Alsuwaiyan et al., 2019; Su, (CRCPSIX000144), in particular Catriona Macleod and Alecia Pang, Shan, & Li, 2017) may be used alongside chemical Bellgrove for their comments on the manuscript. treatment (Guillard, 2005; Rød, 2012) and/or an adjust- ment of culture conditions (e.g., temperature, light level, or water motion) (Su, Pang, Shan, & Li, 2017) to dis- Disclosure statement criminate against the contaminant and favour juveniles The authors declare the following financial interests/personal of the target kelp species. relationships which may be considered as potential competing interests: Cost for sampling and analyses reports financial support was provided by Australian Government Fisheries Research and Development Corp. The corresponding author Conclusions W. Visch is currently employed as a post-doctoral researcher Our results highlight the importance of species- in the Seaweed Solutions for Sustainable Aquaculture CRC-P project, in partnership with Tassal Group Ltd. and Spring Bay specific culture conditions in the nursery phase of Seafood Pty Ltd. kelp aquaculture production systems. The results could furthermore be used to reduce contamination in juvenile sporophyte cultures and provide Funding a framework to find growth optima for seaweeds in This research was funded by the “Seaweed solutions for sus- non-traditional regions of cultivation, such as the tainable aquaculture CRC Project” [CRCPSIX000144] funded Tasmanian kelp species examined in this study. 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Journal
Applied Phycology
– Taylor & Francis
Published: Dec 31, 2023
Keywords: Algal cultivation; biofouling; Ecklonia radiata; gametophytes; giant kelp; hatchery; Laminariales; Lessonia corrugata; Macrocystis pyrifera; mariculture
