Kelp Farming Research Articles

Development and Diversity of Epibiont Assemblages on Cultivated Sugar Kelp (Saccharina latissima) in Relation to Farming Schedules and Harvesting Techniques.

Seaweed farming in Europe is growing and may provide environmental benefits, including habitat provisioning, coastal protection, and bioremediation. Habitat provisioning by seaweed farms remains largely unquantified, with previous research focused primarily on the detrimental effects of epibionts, rather than their roles in ecological functioning and ecosystem service provision. We monitored the development and diversity of epibiont assemblages on cultivated sugar kelp (Saccharina latissima) at a farm in Cornwall, southwest UK, and compared the effects of different harvesting techniques on epibiont assemblage structure. Increases in epibiont abundance (PERMANOVA, F4,25 = 100.56, p < 0.001) and diversity (PERMANOVA, F4,25 = 27.25, p < 0.001) were found on cultivated kelps over and beyond the growing season, reaching an average abundance of >6000 individuals per kelp plant with a taxonomic richness of ~9 phyla per kelp by late summer (August). Assemblages were dominated by crustaceans (mainly amphipods), molluscs (principally bivalves) and bryozoans, which provide important ecological roles, despite reducing crop quality. Partial harvesting techniques maintained, or increased, epibiont abundance and diversity beyond the farming season; however, these kelp plants were significantly fouled and would not be commercially viable in most markets. This paper improves understanding of epibiont assemblage development at European kelp farms, which can inform sustainable, ecosystem-based approaches to aquaculture.

Analysis of the Current Situation and Countermeasures for the Development of Shandong Rongcheng Kelp Industry Cluster

Rongcheng is a natural kelp production base due to its unique geographical environment and climatic advantages. Since the 1930s, the Rongcheng kelp industry has played an important role in the development of the Chinese kelp industry. Rongcheng's kelp output ranked first in China for more than ten years, from 2010 to 2021. Its kelp production accounts for nearly half of total Chinese kelp production. This paper analyzes the current development of the Rongcheng kelp industry cluster from six perspectives: natural environment and resources of kelp farming, supporting infrastructure of kelp farming and processing enterprises, main bodies in Rongcheng kelp industry cluster, relevant assistance of Rongcheng municipal government to kelp industry, development of relevant supporting industries in kelp industry. Then it concludes that there are four problems in the current development stage of Rongcheng kelp industry cluster and the development of Rongcheng kelp industry cluster's domestic and foreign markets. It then concludes that there are four issues in the current development stage of the Rongcheng kelp industry cluster. Based on the analysis of the problems and countermeasures, it is concluded that the current development stage of the Rongcheng kelp industry cluster has four problems: low cluster efficiency, an imperfect market system, a lack of technological innovation, and a weak influence of regional brands. It assists the Rongcheng kelp industry cluster in achieving high-quality development based on an analysis of the problems and countermeasures.

A deep dive into the epibiotic communities on aquacultured sugar kelp Saccharina latissima in Southern New England

Sugar kelp cultivation at the southern end of its range on the east coast of North America is being pursued commercially for human consumption, which demands a high-quality product. Blade quality can be compromised by attached organisms – epibionts. Biweekly examination of epibionts on sugar kelp was conducted April–May 2018, on a kelp farm in eastern Long Island Sound, CT, USA. Culturable Vibrio spp. were not present on kelp blades until May and were limited to only old sections. No Vibrio colonies were human pathogens V. parahaemolyticus or V. vulnificus, based upon ToxR-specific multiplex PCR assays. Neither epibenthic cyanobacteria Lyngbya spp. nor the dinoflagellate Prorocentrum lima, microbes of concern because of toxigenicity, were detected on kelp by microscopy or metabarcoding of partial rRNA genes. The lacy bryozoan was the only epibiotic animal observed that could cause damage to kelp, but its abundance was low.Summarizing most-common sequence reads, Gammaproteobacteria was the most abundant bacterial group on kelp blades (49%) and Alphaproteobacteria were the most abundant in seawater (39%). Bacillariophyta were the most abundant eukaryotes on kelp blades (36%) and Dinoflagellata were the most abundant eukaryotes in seawater (43%). Molecular operational taxonomic unit matrices were used for non-metric multidimensional scaling; the most prominent structure for both prokaryotic and eukaryotic communities was the separation between blade and seawater samples. This spatial separation explained 81% and 76% of the variation among prokaryotic and eukaryotic samples, respectively. Indicator Species Analysis identified Gammaproteobacteria (55%) and Bacillariophyta (56%) to be the most important blade indicator prokaryotes and eukaryotes, respectively. A closer examination of indicator species temporal patterns and their ecophysiology suggested that Aquimarina, Parcubacteria, and Peronosporomycetes are potential pathogens to sugar kelp. Ciliates may be the most important grazers that keep epiphytes (Bacillariophyta, Rhodophyta, and Phaeophyta) and Peronosporomycetes on kelp in check.

Carrying capacity of Saccharina latissima cultivation in a Dutch coastal bay: a modelling assessment

Abstract Kelp cultivation receives increasing interest for its high-value products and ecological services, especially in Europe and North America. Before industrial kelp farming in marine ecosystems continue to scale up, evaluation of the site-wide production relative to ecological carrying capacity (CC) of the identified system is essential. For this purpose, a mechanistic kelp model was developed and applied for hypothetical numerical experiments of expanding the farming area in a Dutch coastal bay (the Eastern Scheldt), where cultivation of Saccharina latissima (sugar kelp) is emerging. The kelp model was implemented within a three-dimensional hydrodynamic–biogeochemical model to account for the environmental interactions. The model captured the seasonal growth dynamics of S. latissima, as well as its carbon and nitrogen contents measured at the Eastern Scheldt pilot sites. The model results suggest that expanding the kelp farming area to ∼1–30% of the bay (representing ∼3.4–75 kt harvest dry weight in the 350-km2 bay) had the potential to weaken the spring bloom, and thereby affected the coexisting shellfish culture in the bay. Competition between S. latissima and phytoplankton mostly occurred in late spring for nutrients (dissolved inorganic nitrogen). The ecological CC should be weighed according to these negative impacts. However, the production CC was not reached even when farming ∼30% of the Eastern Scheldt, i.e. harvesting totally 75 kt dry mass, given that the simulated overall S. latissima production kept increasing with the farming activity. Our modelling approach can be applied to other systems for S. latissima cultivation and assist in assessing CC and environmental impacts.

Engineering A Low-Cost Kelp Aquaculture System for Community-Scale Seaweed Farming at Nearshore Exposed Sites via User-Focused Design Process

For over 50 years, government fishery agencies have recognized the need to transition excess fishing capacity in coastal waters to aquaculture. For the most part, investment strategies to move wild capture and harvest efforts into aquaculture have failed since the technology and capital expense for entry, such as large fish pens, was not conducive for acceptance. In contrast, low trophic level aquaculture of shellfish and seaweeds is suitable as an addition to the livelihoods of seasonal fishing communities and to those displaced by fishery closures, especially if vessels and gear can be designed around existing fishing infrastructures, thus allowing fishers to maintain engagement with their primary fishery, while augmenting income via aquaculture. In this study, an inexpensive, lightweight, and highly mobile gear for kelp seaweed farming was developed and tested over a 3-year period in southern Maine, USA. The system was different from existing kelp farming operations used in nearshore waters that use low-scope mooring lines, and heavy, deadweight anchors. Instead, a highly mobile, easy to deploy system using lightweight gear was designed for exposed conditions. The entire system fit into fish tote boxes and was loadable onto a standard pickup truck. The seaweed system had small but efficient horizontal drag embedment anchors connected to a chain catenary and pretensioned with simple subsurface flotation. The system was able to be deployed and removed in less than 4 h by a crew of three using a 10 m vessel and produced a harvest of 12.7 kg/m over an 8-month fall-winter growth period. The target group for this seaweed research and development effort were coastal fishing communities who move seasonally into non-fishing occupations in service industries, such as construction, retail, etc. An economic assessment suggests farmers would realize an 8% return on investment after3 years and $13.50/h greater income as compared to a non-farming off season job at minimum wage. This low-cost seaweed farming system for fall-winter operations fits well into a “livelihood” strategy for fishing families who must work multiple jobs in the offseason when their main fishery is unavailable.

Dispersal and Deposition of Detritus From Kelp Cultivation

A high resolution coastal and ocean hydrodynamic model system was used to investigate the transport and deposition patterns of Particulate Organic Matter (POM) from kelp farmed at three locations of different properties: a sheltered location, an exposed location, and an offshore location. Published values on the sinking speeds of organic particles from kelp were used, spanning several orders of magnitude. Recent work on quantifying the release of particulate organic matter from farmed kelp was used to link the release of carbon to possible cultivation volumes and scenarios, and finally to link this to the potential for carbon loading on the ocean floor. The results are presented in terms of loading and distribution per unit harvested kelp, and the loading estimates are compared with estimates of natural (background) primary production. According to the simulation results, organic matter may be transported anything from a few (hundred) meters up to a hundred km away from the release site, depending on the sinking rates, time of release, and the location. The depth at which the matter settles on the sea floor likewise depends on the properties of the matter and the sites. The time until settlement varied from minutes to several hundred hours. The results underscore the importance of constraining the dispersal and deposition of detritus from kelp cultivation in order to better understand and quantify associated environmental risks posed by organic loading, and the potential for seafloor carbon sequestration by kelp farming as a nature based climate solution.

부산, 울산 지역의 다시마 및 미역 양식업 경제성 분석

This study was aimed to analyze the economic feasibility of seaweed aquaculture production performance in Busan and Ulsan on the southeast coast of Korea. For the analysis, 10 seaweed aquaculture farms were surveyed. The 10 seaweed farms were classified as kelp farm, sea mustard farm, and mixed farm (kelp+sea mustard). In the study, various analyses including cost structure analysis, profitability and economic feasibility analysis were conducted for the 10 seaweed aquaculture farms. Based on the survey results, the study carried out profitability and economic analyses of seaweed farming for the kelp farm, sea mustard farm, and mixed farm. It was found that the average NPV was the highest for the sea mustard farm with 3.27 billion won. The kelp farm produced the lowest NPV of –0.18 billion won indicating a negative economic feasibility.

Erosion Dynamics of Cultivated Kelp, Saccharina latissima, and Implications for Environmental Management and Carbon Sequestration

A growing trend of interest for the cultivation of kelp is driven by predictions for high global demands of important commodities, which require the development of alternative supplies of natural resources. In this study the dynamics of loss of biomass from cultivated Saccharina latissima were studied from February to August 2018 at two kelp farms in Northern (69°45.26′N/019°02.18′E) and in Mid-Norway (63°42.28′N/08°52.23′E). Kelp fronds at each farm were individually followed throughout the growing season. Sectional regression was applied for conversion of measured frond lengths to estimated dry weights. The study shows that between 40 and 100% of all individuals in the studied kelp population constantly eroded slightly from their distal ends. However, until June the accumulated loss was only 8% of produced dry weight. Due to dislodgement of whole sporophytes this picture changed in July and August to heavy losses in Mid-Norway. Thus, the overall losses of kelp in terms of accumulated dry weight were only 8–13% of the gross growth until harvest in June in Mid-Norway and August in Northern Norway. Losses increased significantly in Mid-Norway during July and reached 49.4% of the annual production in August. The rates of losses were separated into specific erosion and dislodgement rates. Erosion rates over the whole experimental period for the two sites were not significantly different, while differences in dislodgement rates between farm sites proved to be highly significant. The exported annual amount of carbon was estimated on the basis of lost and measured carbon content in the tissue. From these data a scenario was built for a commercial Norwegian kelp farm growing S. latissima showing a carbon export of 63–88 g C m–2y–1. This is eight times less than has been reported from scenarios for kelp farms in China. This study confirms that optimal timing of harvest is the most important management tool for avoidance of heavy losses from kelp farms. In conclusion, an industry with early harvest will likely have a low carbon export, while a late-harvested bulk production could export four to six times as much carbon with an increased potential for carbon sequestration.

Wave attenuation by suspended canopies with cultivated kelp (Saccharina latissima)

Many kelp aquaculture farms consist of moored arrays of long horizontal lines that grow kelp near the water surface. Most kelp farms are deployed in the same direction of wave propagation. However, with numerous longlines of densely grown kelp, these farms may have the potential to attenuate waves if installed perpendicular to the direction of wave propagation. In this application, the kelp farm may serve as a form of nature-based coastal protection. To assess this potential, a set of 1:10 scale physical model experiments were conducted to measure the wave attenuation of a suspended kelp model. The model was scaled based on the morphological and mechanical properties of the cultivated Saccharina latissima (sugar kelp) from Saco Bay, Maine, USA. Experimental results demonstrated that suspended blades have asymmetric oscillatory motions with more bending in the opposite direction of wave propagation. Due to severe asymmetric blade motion in large waves, the suspended blade could roll over the attached line following the wave orbital motion. The results also showed that suspended kelp farms in the designed configuration with 20 longlines of 1-m-long blades and 100 blades/m have the potential attenuating wave energy by up to 33.7% under the experimental wave conditions. Based on the experimental data, empirical formulas were developed for the bulk drag coefficient (CDB) and effective blade length (le) of suspended kelp canopies for wave attenuation. To predict wave attenuation under a wider range of conditions and to identify the key parameters affecting wave attenuation, a numerical model was developed that could resolve blade motion. The benefits of resolving blade motion were to improve the model accuracy and reduce the number of experiments needed for obtaining CDB or le, which is required in the conventional wave attenuation models based on the rigid blade assumption. The results indicate that (i) the wave energy dissipation ratio (EDR defined as the ratio of the dissipated wave energy to the incident wave energy) of suspended kelp farms decreases with increased water depth, (ii) EDR is not sensitive to wave height, (iii) EDR first increases and then decreases with wavelength, and (iv) EDR increases with blade size, kelp vertical position, plant density, and the number of longlines. Therefore, the technique to improve the wave attenuation capacity of suspended kelp farms for nature-based coastal defense is to install the kelp farms in shallower water, expand the farm size by adding more longlines, locate the kelp in a higher position of the water column, grow the kelp more densely, and choose the kelp species with more rigid, wider, and longer blades/biomass.

The effect of distal‐end trimming onSaccharina latissimamorphology, composition, and productivity

AbstractAs kelp cultivation increases around the world, so does the need for farm management strategies that produce specific crop characteristics, optimize yield, widen harvesting windows, and prevent biomass loss. Distal‐end trimming of macroalgae has been recommended as a farm management method addressing these needs. In this study, we trimmed cultivatedSaccharina latissimasporophytes grown in the Western Gulf of Maine (WGoM) to 60 cm above the stipe–blade interface. We characterized the effect of trimming on the morphology, tissue nutrient content, stable isotope ratio, and nitrate reductase activity of the kelp. We also evaluated the economic trade‐offs of trimming using a simple production model. The results suggest that trimming the blade to 60 cm may have minimal biological consequences. Additionally, the trimming appears to benefit “short” kelp blades in proximity to the trimmed blades. Daily yield (% increase in weight day−1) after trimming was initially lower than the control, but late‐season daily yields and crop‐retention following storms were markedly improved. Ultimately, we conclude that growers could use trimming to acquire kelp biomass earlier in the season, retain late‐season biomass, and potentially increase the total revenue gained from kelp farming if price premiums can be exacted for this biomass.

Comparative analysis of morphometric traits of farmed sugar kelp and skinny kelp, Saccharina spp., strains from the Northwest Atlantic

AbstractOur team has initiated a selective breeding program for regional strains of sugar kelp, Saccharina latissima, to improve the competitiveness of kelp farming in the United States. Within our breeding program, we also include an endemic putative species, Saccharina angustissima, locally referred to as skinny kelp. We crossed uniclonal gametophyte cultures derived from 37 wild‐collected blades representing five sugar kelp strains and one skinny kelp strain to produce 104 unique crosses. Each cross was outplanted on a near‐shore research farm located in the Gulf of Maine (GOM). After the first farming season, our results indicated that sugar kelp and skinny kelp were interfertile, and produced mature and reproductively viable sporophytes. Morphological traits of individual blades varied depending on the parental contribution (sugar vs. skinny), with significant differences found in progeny blade length, width, thickness, and in stipe length and diameter. Despite these differences, wet weight and blade density per plot showed no statistical differences regardless of the cross. Given their published genetic similarity and their interfertility shown here, S. angustissima and S. latissima may not be different species, and may each contribute genetic diversity to breeding programs aimed at meeting ocean farming and market needs.

Mariculture research of Macrocystis pyrifera and Saccharina latissima in Southeast Alaska

AbstractThere has been increasing interest in Alaska regarding the commercial mariculture of kelp. Kelp farming can be an economic engine for coastal communities of Alaska. Other benefits include ecosystem services, including carbon sequestration and mitigation of eutrophication. In support of this interest, several kelp species have been examined for commercial potential. In the 1980s–1990s, experiments were performed on the giant kelp Macrocystis pyrifera. Female gametophytes were exposed to varying levels of chelated iron. Relatively low levels of chelated iron (1–5 μM) stimulated the onset of oogenesis. In contrast, higher iron concentrations inhibited egg production. Outplant experiments with Macrocystis in Sitka, AK showed growth in the winter and spring, slowing down to zero growth by the end of summer. Fertilizing outplants in August allowed plants to survive and grow during the ensuing winter. Mariculture experiments with Saccharina latissima carried out near Juneau, Alaska showed exponential growth for seeded lines set out from September to March. Optimal growth occurred for outplants in October–November, with growth rates of up to 5% per day. The best growth occurred when lines were 2–3 m below the surface. Growth rates declined in May–June corresponding to a decrease in inorganic nitrogen in the water. Slower growth also resulted in severe fouling.

Modelling effects of seaweed aquaculture on phytoplankton and mussel production. Application to Strangford Lough (Northern Ireland)

Coupled macroalgal-phytoplankton and shellfish models were used to investigate the effect of macroalgae cultivation on phytoplankton and mussel growth in Strangford Lough, Northern Ireland. The study focused on the kelp species Saccharina latissima for which observational data were available from rope deployments at an experimental seaweed farm. The calibrated model gave good agreement with observed nutrient and chlorophyll concentrations as well as matching observation of kelp growth rates and frond area. Timing of spring phytoplankton growth and subsequent nutrient drawdown in the model was found to have a large effect (~50% change) on predicted kelp frond area in summer. The model was used to investigate the effect of light shading and nutrient competition between farmed S. latissima and phytoplankton (a key food source for shellfish) for a range of farm sizes. Simulations showed that kelp farming had minor impacts in general but that very intensive farming over an extensive area could lead to significant decreases in phytoplankton and mussel biomass. Simple criteria were developed for estimating the size and density of macroalgal farming that would lead to significant nutrient competition with phytoplankton. Modelling in the strong nutrient competition regime with a hypothetical very high intensity farm occupying 22% of the Lough surface, gave decreases in spring/summer phytoplankton chlorophyll concentrations of 11% (nutrient competition only) and 23% (nutrient competition and light shading). The impact on harvested dry weight of mussels is similar but smaller, with decreases of 4% (nutrient competition) and 10% (light and nutrient competition). It should be noted these are based on model compartment averages and localised changes, not resolved by the model, may be higher.

Research on integrated specialized ship for kelp harvesting, classifying and grading

In this study, an integrated specialized ship for kelp harvesting, classifying, and grading is developed in order to (1) solve issues in mechanization of traditional raft-frame-based kelp farming, (2) reduce labor intensity and labor input in the kelp harvesting process, and (3) accelerate the industry by upgrading and transforming the current system of kelp farming. In addition, the influence of sea conditions on operation of this ship is evaluated and analyzed using three-dimensional modeling and simulation. The ship is designed according to the state-of-the-art raft-frame structure. Based on man-machine coordination, a duplicated raft-frame structure is adopted, such that the processes of harvesting, classifying, grading and packing can be integrated. This shortens the process flow, improves on efficiency, and addresses the non-standard and irregularity issues of traditional rafts that are trussed by hand. In the meantime, the impacts of sea waves and turbulence on the mechanized kelp harvesting are also minimized. Furthermore, the combination of theoretical calculation and experimental verification is implemented successfully. Through the research and development of this integrated specialized ship for kelp harvesting and grading, the "bottleneck" can be overcome, which is mainly caused by the inefficiency of the current kelp industry and the contradictions in labor force structure.

Effect of large-scale kelp and bivalve farming on seawater carbonate system variations in the semi-enclosed Sanggou Bay

Although cultured algae and shellfish can be the dominant species in some localized coastal waters, research on the effect of large-scale mariculture on the carbonate system variations in these local waters is still lacking. We conducted five cruises from May to September and studied spatiotemporal variations in the seawater carbonate system in the semi-closed Sanggou Bay, which is famous for its large-scale mariculture. Our results showed that both kelp and bivalve farming induced significant spatiotemporal variations in the carbonate system within the bay. When cultured kelp reached its highest biomass in May, the maximum ΔDIC, ΔpCO2 and ΔpHT between the seawater from the kelp farming area and the non-farming outer bay area was −156 μmol kg−1, −102 μatm and 0.15 pH units, respectively. However, no significant effect of kelp farming on seawater total alkalinity (TA) was observed. Kelp farming also caused the carbonate system variations of seawater from the bivalve farming area. Assuming no kelp was farmed in May, the average pH and pCO2 would reduce by 0.12 pH units and increase by 179 μatm, respectively, in the bivalve farming area. Bivalve farming significantly reduced seawater TA, indicating that fast deposition of calcium carbonate occurred in the bivalve farming area. Although bivalve respiration released CO2 into seawater and elevated seawater pCO2 level and reduced seawater pHT, surprisingly, seawater dissolved inorganic carbon (DIC) reduced significantly in the bivalve farming area. These results indicated that bivalves fixed a larger amount of inorganic carbon by calcification than that released into seawater by respiration. Overall, large-scale kelp and bivalve farming are important biological drivers of variations in the carbonate system within the semi-enclosed Sanggou Bay. Altered carbonate systems by kelp farming may favour calcification of farmed bivalves and provide an essential refuge for these species during the future ocean acidification.

Technical challenges for offshore cultivation of kelp species: lessons learned and future directions

Abstract Traditional kelp farming methods require a high amount of labor and are limited in geographic distribution – occurring mainly in nearshore, sheltered sites. To address growing global demand for sustainable biomass, the continued expansion of kelp cultivation will most likely have to move further offshore. Although many offshore cultivation trials have been done over the last 50 years, few were sufficiently robust to be viable in exposed and deep-water areas. In the North Atlantic Ocean, a Faroese company developed and tested a structural farm design that has survived in open-ocean conditions since 2010. The durable structure has withstood harsh weather events common in the Faroe Islands and thereby presents a potential strategy and method for moving kelp farming further offshore. This paper describes the primary challenges of offshore kelp farming and provides an overview of work previously done. Ultimately, the improved productivity, system survivability and scalability the MacroAlgal Cultivation Rig (Faroe Islands) and the BioArchitecture Lab cultivation grid (Chile) represent state-of-the-art and powerfully transformative strategies to pursue large-scale offshore farming to support mass production of kelp in the near future.

Growth and biofouling in kelp aquaculture (Saccharina latissima): the effect of location and wave exposure

Seaweed aquaculture is receiving increasing attention for food and non-food applications in Europe, where it is still an emerging industry. The cultivation of seaweeds in the sea is attractive as it does not compete with agricultural crops for land and freshwater, whilst generating high yearly biomass yield. The selection of suitable cultivation sites in coastal waters is essential for the sustainable establishment and further development of seaweed aquaculture in Europe. Here, we investigate the effects of wave exposure and geographic location on growth and biofouling of kelp (Saccharina latissima), using a transplantation experiment along the Swedish west coast. Biofouling of kelp decreased with increased wave exposure, from 10 and 6% coverage at sheltered and moderately exposed locations, respectively, to 3% at exposed locations. Growth, measured as blade surface area, generally increased with decreased wave exposure, with approximately 40% less growth at exposed locations compared to sheltered or moderately exposed location. We identified that there is large spatial variation in growth and fouling of the seaweed biomass at the selected farm sites, with significant differences from the km-scale to the m-scale. In addition, exposure level affected the tissue composition, with a high carbon, but low nitrogen and water content at exposed locations compared to moderate and sheltered sites. Isotope signatures (i.e. δ13C and δ15N) also differed between exposure levels. Together, these results indicate that wave exposure is an important factor to consider in site selection for both yield as well as quality of the seaweed biomass for future kelp farms.

Kelp cultivation effectively improves water quality and regulates phytoplankton community in a turbid, highly eutrophic bay

Coastal eutrophication and its associated harmful algal blooms have emerged as one of the most severe environmental problems worldwide. Seaweed cultivation has been widely encouraged to control eutrophication and algal blooms. Among them, cultivated kelp (Saccharina japonica) dominates primarily by production and area. However, the responses of water quality and phytoplankton community to kelp farming remain unclear. Here, thirteen cruises were conducted in the kelp farms and control areas in the turbid, highly eutrophic Xiangshan Bay of the East China Sea from 2008 to 2015. Results indicated that kelp cultivation slightly increased dissolved oxygen and pH, but reduced dissolved inorganic nitrogen and phosphorus. We estimated that kelp harvesting would remove 297 t of nitrogen and 42 t of phosphorus from this bay annually. Because of decreased flow velocity, turbulence, and sediment resuspension, kelp farming greatly reduced suspended solids and increased transparency, resulting in increases in phytoplankton chlorophyll a and abundance. Additionally, kelp farming appreciably increased phytoplankton species number, Marglef richness, and Shannon–Wiener diversity indices by 51.6%, 40.1%, and 13.1%, respectively. Analysis of similarity and similarity percentages demonstrated that phytoplankton community composition differed significantly between the farm and control area, which was mostly attributed to long-chained diatoms and single-celled dinoflagellates. However, after the kelp harvesting, all measurements of water quality and phytoplankton biomass, diversity, and community composition exhibited no significant difference. Our study highlights that kelp cultivation alleviates eutrophication and acidification and enhances phytoplankton diversity, thus providing guidance for macroalgal aquaculture and remediation in eutrophic waters.

Evaluation of the genetic relationship between the farmed populations on a typical kelp farm and the adjacent subtidal spontaneous population of Undaria pinnatifida (Phaeophyceae, Laminariales) in China

In our previous study, asymmetric gene flow was revealed between sympatric farmed populations of Undaria pinnatifida and spontaneous ones on the cultivation rafts on a kelp farm in Dalian, China. However, the spontaneous population in the adjacent subtidal zone, which is assumed to be closely related to the spontaneous and farmed populations on the cultivation rafts, was not included in that study, making the whole scenario incomplete. Here, specimens of U. pinnatifida, including the spontaneous populations occurring on the cultivation rafts of U. pinnatifida (UWT-18) and Saccharina japonica (KWT-18), and the farmed population (F1–18) on the same farm and the adjacent subtidal spontaneous population (SW-18), were collected in 2018 and analyzed with the same set of microsatellites. The genetic diversity was highest in UWT-18 and lowest in F1–18 in terms of number of alleles and expected heterozygosity. Analyses of the genetic structure were conducted based on the combined genotypic data from the previous and the present studies. Neighbor-joining cluster analysis based on genetic distance, Bayesian model-based structure analysis, and discriminant analysis of principal components revealed most significant genetic divergence between the farmed populations and the subtidal spontaneous one. SW-18 contained nearly no membership from the farmed populations and vice versa, suggesting that the reciprocal gene flow between them was scarce. The population UWT-18 contained mixed membership from both the farmed populations and SW-18. The population KWT-18 contained almost only membership from SW-18, which was likely due to the close distance between them. Combination of the two studies depicts an intact picture about reciprocal impacts between sympatric spontaneous and farmed populations of U. pinnatifida.

Assessment of the Genetic Connectivity Between Farmed Populations on a Typical Kelp Farm and Adjacent Spontaneous Populations of Saccharina japonica (Phaeophyceae, Laminariales) in China

The commercially important brown alga Saccharina japonica in China has been believed to be accidentally introduced from Japan in 1920s. Meanwhile, spontaneous populations in the wild are assumed to be derived from the locally farmed populations. Spontaneous populations are often observed in the subtidal zones and on the cultivation infrastructure near farmed populations in the north of China. However, the genetic connectivity between these sympatric spontaneous and farmed populations remains unclear. Here, three commonly farmed cultivars (farmed populations) and three spontaneous populations (two from subtidal zones and one from cultivation rafts) were sampled from a typical kelp farm in Dalian, China, and analyzed with ten polymorphic microsatellite markers. Genetic diversity of farmed populations was found to be higher than that of the subtidal spontaneous populations. Neighbor joining cluster analysis based on genetic distance, Bayesian model-based structure analysis, and discriminant analysis of principal components revealed significant genetic divergence between the farmed populations and the subtidal spontaneous ones. Gene flow out of farmed populations to the subtidal spontaneous populations was revealed to be very limited, but gene flow in the contrary direction was more prominent. The spontaneous sporophytes on the structural rafts contained pedigree from both farmed and subtidal spontaneous populations. Results of this study may help us to understand reciprocal impacts between sympatric spontaneous and farmed populations of S. japonica