Production Of Macroalgae Research Articles

Current Status of the Algae Production Industry in Europe: An Emerging Sector of the Blue Bioeconomy

The EU Bioeconomy Strategy aims to support the sustainable growth and development of the EU bio-based sectors while creating jobs, innovation and services. Despite the recognized potential of the algae biomass value chain, significant knowledge gaps still exist regarding the dimension, capability, organization and structure of the algae production in Europe. This study presents and analyses the results of a comprehensive mapping and detailed characterization of the algae production at the European scale, encompassing macroalgae, microalgae, and the cyanobacteria Spirulina. This work mapped 447 algae and Spirulina production units spread between 23 countries, which represents an important addition to the reported number of algae producing countries. More than 50% of these companies produce microalgae and/or Spirulina. Macroalgae production is still depending on harvesting from wild stocks (68% of the macroalgae producing units) but macroalgae aquaculture (land-based and at sea) is developing in several countries in Europe currently representing 32% of the macroalgae production units. France, Ireland, and Spain are the top 3 countries in number of macroalgae production units while Germany, Spain, and Italy stand for the top 3 for microalgae. Spirulina producers are predominantly located in France, Italy, Germany, and Spain. Algae and Spirulina biomass is directed primarily for food and food-related applications including the extraction of high-value products for food supplements and nutraceuticals. Algae production in Europe remains limited by a series of technological, regulatory and market-related barriers. Yet, the results of this study emphasize that the European algae sector has a considerable potential for sustainable development as long as the acknowledged economic, social and environmental challenges are addressed.

Effect of harvesting month and proximity to fish farm sea cages on the lipid profile of cultivated Saccharina latissima

Macroalgae aquaculture is thriving, and kelps such as Saccharina latissima, are now farmed over different production sites across Europe. Macroalgae production in integrated multi-trophic aquaculture setups is gaining relevance due to increased biomass yield and bioremediation potential. Nevertheless, there is a substantiated need to understand how this type of production shapes biomass composition. The present study evaluated the influence of time of harvesting and proximity to nutrient source (fish farm sea cages) on the elemental and biochemical composition of S. latissima, with special emphasis on its lipid content. Overall, the differences recorded for elemental, biochemical and lipid composition of S. latissima occurred consistently with harvesting period rather than with the distance to fish farm sea cages, evidencing that farming kelp in integrated multi-trophic aquaculture setups does not compromise nutritional quality while promoting increased biomass yield. Elemental and biochemical composition differed between kelp biomass harvested in April and those harvested in May and June, with lower C, H and carbohydrates, and higher ash contents in the later. Fatty acid profile analysis revealed an increase in monounsaturated fatty acids along the harvesting period, as well as a decrease in n-3 fatty acids with a concomitant increase of the n-6/n-3 ratio from April to May. Statistical analysis of the polar lipidome identified by liquid chromatography-mass spectrometry revealed differences in specific lipid signatures, displaying a perfect discrimination between harvesting periods. The discrimination between samples from reference and integrated multi-trophic aquaculture sites was only observed for kelp biomass harvested in June. Contributing particularly to these differences are betaine lipids, more abundant in the two later time points, and some lysolipid species, especially abundant in June. These findings will allow a more integrated look at macroalgae production under integrated multi-trophic aquaculture framework, thus promoting the systematization of farming practices that may enhance yield with biochemical quality to match the increasing demands by the food industry and sustainable biorefinary pipeline.

Examining the capacity for cultivating marine macroalgae using process liquids from biogas digestate as nutrient source and cultivation medium

The land-based and seawater-independent production of macroalgae as a source of renewable biomass with a multitude of potential applications increasingly attracts the attention of science and industry. However, the availability of a feasible nutrient source acceptable for supplying a large-scale cultivation facility on land remains a persisting obstacle that has not yet been overcome. Hence, this study aimed to test an uncomplicated technological approach to sufficiently reduce the nutrient load of the biogas digestate and to identify an optimal ratio of pretreated digestate to volume of cultivation medium. Based on an initial solid-liquid separation of biogas digestate, the liquid phase was treated with flocculation agent and fine separation (liquid A), followed by filtration through an organic sorption filter (liquid B) and finally through a high-performance soil filter (liquid C). The results showed notable differences regarding the nutritional value of the different process liquids. The mixtures of process liquids A to C with artificial seawater (ASW) optimal for biomass increase were 1:50, 1:10 and 1:1, respectively. Maximum biomass increase was achieved by using a mixture of process liquid A and ASW with the ratio 1:50, which resulted in a growth rate of 7.02% FW d−1 in comparison to a growth rate of 5.71% FW d−1 of the untreated control group that used f/2-standard nutrient supply. Regarding the attempt of using a maximum amount of digestate and of reducing the necessity of diluting the process liquid with ASW, process liquid C with a mixing ratio of 1:1 appeared promising for a large-scale land-based cultivation of marine macroalgae. However, the transfer of the data to other agricultural biogas plants needs to be adapted to the respective case as changing feeding strategies of the biogas fermenters with different biogas substrates might lead to a large variation of nutrients in the biogas digestate resulting in changing quality and quantity of nutrients in the produced process liquids.

Estimating the biomass density of macroalgae in land-based cultivation systems using spectral reflectance imagery

Sub-sampling large-scale, land-based macroalgal cultures to estimate stocking densities is time-consuming, labour-intensive, and inaccurate. Therefore, the development of innovative methods to monitor stocking densities are required to maximise macroalgal productivity. In this study the spectral reflectance of a range of biomass densities (0.5–12.0 g L−1) of Ulva ohnoi was measured using a spectroradiometer (ASD) and a multispectral camera (REMX). A two-band normalised difference vegetation index (NDVI), which was standardised by depth of the culture system, was quantified from both sets of data, and used to establish biomass density sensing models. The models developed using the ASD and REMX data had strong piecewise linear relationships between the standardised NDVI and biomass density (R2 > 0.85, residual mean standard error < 1.31, and mean standard error < 0.99), but differed in breakpoint and slope of the regression lines. Subsequently, both models were validated using data collected in 4000 L high-rate algal ponds, representing practical conditions of the commercial land-based production of macroalgae. Notably, the REMX model had a better fit with the validation data, and the mean difference in the actual versus predicted densities was ≤0.76 g L−1, with a maximum difference of 1.73 g L−1. Therefore, the REMX biomass density model is a useful management tool for differentiating between low (<2 g L−1), medium (2–4 g L−1), and high densities (>4 g L−1) using the standardised NDVI. This study has demonstrated that there is a predictive relationship between spectral reflectance and the biomass density of U. ohnoi. Notably, the REMX model will inform decision making around the frequency of harvest, as well as the quantity of biomass to be harvested, to maintain an optimal stocking density and, therefore, high productivities at a commercial scale.

Ocean warming combined with nutrient enrichment increases the risk of herbivory during cultivation of the marine macroalga Undaria Pinnatifida

Abstract Recent declines of macroalgal forests due to climate change imply that the aquaculture production of macroalgae may also be negatively affected by ocean warming. It has previously been shown that nutrient enrichment can offset the negative impact of warming on the survival and growth of the cultivated macroalga Undaria pinnatifida, although it can also increase the risk of herbivory by unrecognized mesograzers. Observations of several hundreds or thousands of the isopod Cymodocea japonica around U. pinnatifida cultivation ropes in autumn, prompted the analysis of their size-frequency distribution, relationship between body size and consumption rate, and combined effects of elevated temperature and nutrient enrichment on the consumption rate of the algae by the isopod in the current study. Although the body size of the isopods collected in autumn was smaller than those collected in winter and spring, the consumption rate of 600 small isopods was similar to the rate of a large individual. Additionally, the consumption rate doubled in response to an increase in temperature from 15 to 18°C and nutrient enrichment, and tripled with their combination. These results suggest that ocean warming combined with nutrient enrichment increase the risk of herbivory during U. pinnatifida cultivation, especially during isopod outbreak periods.

Response of the red algae Pyropia yezoensis grown at different light intensities to CO2-induced seawater acidification at different life cycle stages

Increasing CO2 levels in the surface water of oceans are expected to decrease oceanic pH and lead to seawater acidification. The responses of macroalgaea to this acidification of coastal waters have been studied in detail; however, most reports have focused on the adult stage only, while ignoring other life cycle stages. In this study, the economically important seaweed species Pyropia yezoensis was cultured under two CO2 concentrations (ambient CO2: 400 μatm; elevated CO2: 1000 μatm) and two light intensities (low light intensity: 80 μmol photons m−2 s−1; and high light intensity: 240 μmol photons m−2 s−1). The effects on the growth and photosynthetic performance of P. yezoensis were explored at different life cycle stages. Relative growth rates were significantly elevated at the conchocelis stage under high light intensity and elevated CO2 concentration. Moreover, the Pmax of P. yezoensis was also increased under high light intensity. However, this positive effect inversed at the thallus stage. The relative growth rate, relative electron transport rate (rETR), and net photosynthetic rate decreased at the thallus stage in response to high CO2 concentration. Under low light intensity, elevated CO2 concentration significantly increased the relative growth rates of conchocelis and thallus stages. These were 269% and 45% higher at elevated CO2 concentration compared with ambient CO2 concentrations, respectively. The Chl a and phycoerythrin levels were also higher under elevated CO2 level at the conchocelis stage. However, the rETR for the thallus stage was elevated under low light. This suggests that seawater acidification could positively affect algae at low light conditions (especially at the conchocelis stage). Different growth stages of P. yezoensis may respond differently to seawater acidification and changes of light intensity. Thalli growth stage, stocking density, and seawater depth should be considered in different areas to optimize the primary production of macroalgae.

Aeration and nitrogen modulated growth rate and chemical composition of green macroalgae Ulva sp. cultured in a photobioreactor

Bottom aeration is a common technology used in macroalgae cultivation. Productivity and chemical composition of macroalgae depend on the air flow rate injected to the cultivating systems through mechanical stimulation, the addition of CO2, or mass transfer of nutrients. However, detailed information about the different effects and aspects of aeration, which are critical for maximizing the growth of the algae and optimizing its quality, is still lacking. We quantified the effects of aeration rate on the biomass growth rate, protein, starch, and ash contents of Ulva sp., using different combinations of air flow rates and nitrogen concentration in an outdoor photobioreactor. Increasing the air flow from 0.5 L min−1 to 2 L min−1, increased by up to 36% the daily growth rate and the starch content up to 75%, of the Ulva sp. biomass, depending on the fertilization concentration. Protein and ash content were not significantly affected by aeration rates in the tested ranges of aeration for both fertilization with 58 μM and 430 μM of nitrate per week. Protein content increased, and starch decreased with increasing fertilization concentrations. Following the empirical evidence of the combined effect of nitrogen concentration and hydrodynamics we can expect that for increased starch production a cultivation method comprised of two phases could be beneficial: a nitrogen-rich initial phase that leads to higher biomass growth rates, followed by a nitrogen-limited phase with increased aeration for the carbohydrate/starch accumulation.

Cultivating the Macroalgal Holobiont: Effects of Integrated Multi-Trophic Aquaculture on the Microbiome of Ulva rigida (Chlorophyta)

Ulva is a ubiquitous macroalgal genus of commercial interest. Integrated Multi Trophic Aquaculture (IMTA) systems promise large-scale production of macroalgae due to their high productivity and environmental sustainability. Complex host-microbiome interactions play a decisive role in macroalgal development, especially in Ulva spp. due to algal growth- and morphogenesis-promoting factors released by associated bacteria. However, our current understanding of the microbial community assembly and structure in cultivated macroalgae is scant. We aimed to determine (i) to what extent IMTA settings influence the microbiome associated with U. rigida and its rearing water, (ii) to explore the dynamics of beneficial microbes to algal growth and development under IMTA and (iii) to improve current knowledge of host-microbiome interactions. We examined the diversity and taxonomic composition of the prokaryotic communities associated with wild versus IMTA-grown Ulva rigida and surrounding seawater by 16S rRNA gene amplicons. With 3141 Amplicon Sequence Variants (ASVs), the prokaryotic richness was higher in water than in association with U. rigida. Bacterial ASVs were more abundant in aquaculture water samples than water collected from the lagoon. The beta diversity analysis revealed distinct prokaryotic communities associated with Ulva collected in both aquacultures and coastal waters. Aquaculture samples (water and algae) shared 22% of ASVs, whereas natural, coastal lagoon samples only 9%. While cultivated Ulva selected 239 (8%) host-specific ASVs, wild specimens possessed more than twice host-specific ASVs (17%). Cultivated U. rigida specimens enriched the phyla Cyanobacteria, Planctomycetes, Verrucomicrobia, and Proteobacteria. Within the Gammaproteobacteria, while Glaciecola mostly dominated the microbiome in cultivated algae, the genus Granulosicoccus characterized both Ulva microbiomes. In both wild and IMTA settings, the phylum Bacteroidetes was more abundant in the bacterioplankton than in association with U. rigida. However, we observed that the Saprospiraceae family within this phylum was barely present in lagoon water but very abundant in aquaculture water. Aquacultures promoted the presence of known morphogenesis-inducing bacteria in water samples. Our study suggests that IMTA significantly shaped the structure and composition of the microbial community of the rearing water and cultivated U. rigida. Detailed analysis revealed the presence of previously undetected taxa associated with Ulva, possessing potentially unknown functional traits.

Ecological Vulnerability of Coral Reef Ecosystem in Wakatobi National Park During Indian Ocean Dipole Event

This research examines coral reefs vulnerability which threatening its existences and functions by climate change. The ecological vulnerability in Wakatobi (Wangi-wangi, Kaledupa, Tomia, and Binongko) was assessed during Indian Ocean Dipole (IOD) event in 2016. Climate exposure was determined using sea surface temperature, chlorophyll-a concentration, and wind speed magnitude; sensitivity was determined using coral susceptibility, fish susceptibility, and macroalgae primary productivity rate; then adaptive capacity was developed by hard coral cover, coral size distribution, coral richness, fish biomass, herbivore diversity, and herbivore grazing relative to algal production. The values of Exposure, Sensitivity, and Adaptive capacity in Wakatobi were 0.93±0.02, 0.42±0.18, and 0.44±0.10, respectively. Site specific vulnerability scores ranged from 0.52 to 1.60 (mean 0.92±0.26). Binongko was the least vulnerable than other islands. Tomia was observed as the least adaptive capacity and Wangi-wangi was the most bleaching incidents. These results could help coral reefs monitoring priority during the event and then when the event is gone by focusing on the marked islands and sites. Sites that were observed as more vulnerable is urgently need a management strategy to overcome the vulnerability status in the future, such as increasing site adaptability.

Plant-mediated community structure of spring-fed, coastal rivers.

Quantifying ecosystem-level processes that drive community structure and function is key to the development of effective environmental restoration and management programs. To assess the effects of large-scale aquatic vegetation loss on fish and invertebrate communities in Florida estuaries, we quantified and compared the food webs of two adjacent spring-fed rivers that flow into the Gulf of Mexico. We constructed a food web model using field-based estimates of community absolute biomass and trophic interactions of a highly productive vegetated river, and modeled long-term simulations of vascular plant decline coupled with seasonal production of filamentous macroalgae. We then compared ecosystem model predictions to observed community structure of the second river that has undergone extensive vegetative habitat loss, including extirpation of several vascular plant species. Alternative models incorporating bottom-up regulation (decreased primary production resulting from plant loss) versus coupled top-down effects (compensatory predator search efficiency) were ranked by total absolute error of model predictions compared to the empirical community observations. Our best model for predicting community responses to vascular plant loss incorporated coupled effects of decreased primary production (bottom-up), increased prey search efficiency of large-bodied fishes at low vascular plant density (top-down), and decreased prey search efficiency of small-bodied fishes with increased biomass of filamentous macroalgae (bottom-up). The results of this study indicate that the loss of vascular plants from the coastal river ecosystem may alter the food web structure and result in a net decline in the biomass of fishes. These results are highly relevant to ongoing landscape-level restoration programs intended to improve aesthetics and ecosystem function of coastal spring-fed rivers by highlighting how the structure of these communities can be regulated both by resource availability and consumption. Restoration programs will need to acknowledge and incorporate both to be successful.

Bioremediation potential of macroalgae Gracilaria edulis and Gracilaria changii co-cultured with shrimp wastewater in an outdoor water recirculation system

Abstract Effluent from the aquaculture industry discharged into water bodies and it impacts the environment severely. The shrimp industry is one of the developing aquacultures that releases a high amount of organic matters in the form of wastewater. As an effort to reduce the environmental impact, an integrated system with shrimp and macroalgae researched abundantly as the macroalgae are naturally capable of removing nutrient from wastewater. As a bioremediation potential, this study investigates the nutrient uptake and macroalgal growth performance in short term (21 days) using an outdoor recirculating water system stocked with two local macroalgae species Gracilaria edulis and Gracilaria changii as biofilter. The stocking density of 3 kg/m 2 with the flow rate of the water system set to 200 L/hr during the operation. The temperature, pH, dissolved oxygen (DO) and salinity was measured daily throughout the experimental period. Water temperature in all tanks were almost constant and ranged between 28.5 °C to 29.1 °C. The higher mean of pH of around 8.26 ± 0.15 and 8.28 ± 0.05 was observed in tanks with G. edulis and G. changii respectively. In the control tanks, mean pH was 7.87 ± 0.09. The mean concentrations of dissolved oxygen in G. edulis, G. changii and control tanks were 6.89 ± 0.05 mg/L, 6.84 ± 0.06 mg/L, and 6.10 ± 0.03 mg/L respectively. The mean growth rates of Gracilaria edulis and Gracilaria changii were found to be 4.3% day − 1 , 4.1% day−1 with carbon to nitrogen (C:N) ratio of 8.3 to 8.5 respectively. The removal rate of ammonium and nitrate by the two species were found to be 72.5%, 71.0%, and 58.8%, 56.8% respectively. The macroalgal biofilter is found to be an ecologically sustainable that has improved the shrimp water quality to an acceptable level that in turn ultimately enhanced shrimp and macroalgae productivity.

Removal of an established invader can change gross primary production of native macroalgae and alter carbon flow in intertidal rock pools.

The impact of invasive species on recipient communities can vary with environmental context and across levels of biological complexity. We investigated how an established invasive seaweed species affected the biomass, eco-physiology, carbon and nitrogen storage capacity of native seaweeds at sites with a different environmental setting due to a persistent upwelling in northern Spain. We removed the invasive Japanese wireweed Sargassum muticum from intertidal rock pools once every month during a one-year period and used an in-situ stable isotope pulse-chase labeling to estimate gross primary production (GPP), nitrogen uptake rate, 13C-carbon and 15N-nitrogen storage capacities. Following the addition of 13C-enriched bicarbonate and 15N-enriched nitrate to the seawater in the rock pools during the period of the low tide, we sampled macroalgal thalli at incoming tide to determine label uptake rate. After four days, we sampled macroalgal assemblages to determine both label storage capacity and biomass. After one year of removal there was no change in the macroalgal assemblage. However, both the GPP and 13C-carbon storage capacity were higher in the turf-forming Corallina spp. and, sometimes, in the canopy-forming Bifurcaria bifurcata. Nitrogen uptake rate followed similar, but more variable results. Although S. muticum inhibited carbon storage capacity of native species, the assemblage-level 13C-carbon storage was similar in the S. muticum—removed and control rock pools because the presence of the invasive species compensated for the functional loss of native species, particularly at sites where it was most abundant. No obvious effects were observed in relation to the environmental setting. Overall, the effect of the invasive S. muticum on carbon flow appeared to be mediated both by the effects on resource-use efficiency of native species and by its own biomass. Integrating physiological and assemblage-level responses can provide a broad understanding of how invasive species affect recipient communities and ecosystem functioning.

Development of a suitability assessment model for the cultivation of intertidal macroalgae in the United States

The focus of this novel study was to determine the comparative suitability of intertidal macroalgae production along the coast of the contiguous United States and determine the optimal locations to consider commercial cultivation using geographic information systems (GIS) software. Intertidal macroalgae cultivation represents an immense opportunity in the United States. The market demand for macroalgae has been growing and is expected to continue with the discovery of new uses. Currently, the coastal waters of the United States are extremely underutilized, particularly for macroalgae production. This study considered economic and environmental factors at a national scale, finally assessing the viability in a representative body of water with in-situ water sampling. The results of this study suggest that intertidal macroalgae cultivation is most ideally suited for the southeastern United States, primarily due to lower costs of production and more hospitable coastlines. Based on a limited water quality samples, it is feasible for macroalgae cultivation. However, due to the informational deficits, as acknowledged in this study, more work is required to refine and enhance the assessment model. This paper identifies these gaps and lists recommendations to overcome these knowledge gaps.

Phyconomy: the extensive cultivation of seaweeds, their sustainability and economic value, with particular reference to important lessons to be learned and transferred from the practice of eucheumatoid farming

ABSTRACTKappaphycus and Eucheuma, known collectively as ‘eucheumatoids’, are two related genera of red seaweeds which currently lead the rankings for volume of global production of farmed macroalgae. Since 2009, the combined cultivated volume of these carrageenophytes overtook that of the brown seaweeds Laminaria (Saccharina) and Undaria for global production tonnages, according to statistics of the Food and Agriculture Organization of the United Nations (FAO). The Southeast Asian region, particularly Indonesia, the Philippines, Malaysia, Tanzania, and East Africa are the major producers of eucheumatoid biomass. Despite several success stories of red seaweed cultivation and the economic and socioeconomic value of their ecosystem services, there remain a number of salutary lessons to be learned from ‘agronomic’ practices applicable to their extensive cultivation. These case studies should be further developed, analysed, and adopted as best-practice recommendations for future socioeconomic prosperity, as well as both economic and environmental sustainability. In this review, we propose the use of the term ‘phyconomy’ (i.e. large-scale production of marine macroalgae for economic and industrial purposes) as an alternative to the term agronomy (i.e. terrestrial plant production).

Assessment of blooming Ulva macroalgae production potential in the Yellow Sea, China

ABSTRACTSince 2007, large-scale blooms have periodically broken out in the Yellow Sea, leading to serious economic and ecological problems in the surrounding coastal environments. Previous studies reported that the blooms originated in the Rudong oceanic area of the southern Yellow Sea and drifted almost 400 km into the Qingdao oceanic area of the northern Yellow Sea. In this study, chlorophyll concentrations, chlorophyll fluorescence, growth rates, and reproductive characteristics of floating Ulva prolifera collected along the Yellow Sea coast were assessed. The results revealed that these four physiological parameters in the Rudong area at the bloom source were considerably higher (2.02 mg/g, 0.68, 28.49% d−1, and 4 × 107, respectively) than in the Qingdao area (0.34 mg/g, 0.31, 5.23% d−1, and 0.67 × 107, respectively). However, the abundance of microscopic propagules of Ulva in the Qingdao area (3980 ind/l) was significantly higher than that in the Rudong area (667 ind/l). These findings help increase our understanding of the formation of the world’s largest Ulva macroalgal blooms.

Interaction between salinity and phosphorus availability can influence seed production of Ulva ohnoi (Chlorophyta, Ulvales)

Although the global macroalgae production has increased in the last decades, the contribution of green macroalgae to this scenario is little motivated, mainly, by technical limitations in obtaining a reliable and constant source of germlings. Ulva ohnoi (Chrolophyta) is a widely distributed species that exhibit rapid growth and high rates of nitrogen and phosphorus absorption, making it a good candidate for biomass production. Therefore, the present study aimed to evaluate the interactive effects of salinity and phosphorus content in the water on U. ohnoi reproductive induction, reproductive cell release, as well as germination and growth of the germlings. The reproductive area in the thallus presented a maximum value of 94.17 ± 1.89% on day 4 with 1.0 μmol L−1 of phosphorus and SA 25. In the same condition, highest intensity of gamete release occurred with 284,000 ± 33,000 gametes L−1 on day 6. After release, 87.5 ± 3.5% of the zygotes germinated when kept at the concentration of 0.50 μmol L−1 phosphorus and SA 25. The growth rate of germlings was positive in all treatments tested with maximum values for incubated at SA 15, 25 and 35 (24.12 ± 2.11, 27.54 ± 0.86 and 24.21 ± 0.89% day−1, respectively) at the concentration of 1.0 μmol L−1 of phosphorus. In general, the results show a high potential of U. ohnoi biomass production using artificial seeding methods for large-scale commercial aquaculture.

Bottom-Up Effects on Coastal Marine Ecosystems Due to Nitrogen Input from Seabird Feces

Breeding seabirds, often nest at high densities and supply large amounts of marine-derived nutrients, such as nitrogen, in their feces into the ecosystems surrounding their breeding colonies. It has been well demonstrated that the nitrogen supplied by seabirds (seabird-N) into terrestrial ecosystems has a strong bottom-up effect on both producers and consumers. The seabird-N can reach into the surrounding marine ecosystems near the colony through multiple pathways including the surface run-off of rainwater or leaching by ground water. However, in marine ecosystems the bottom-up effects of seabird-N have been rarely documented. A few studies using stable isotope analyses have reported that seabird-N enhances the productivity of both phytoplankton and macro algae. There have been more limited studies documenting similar positive effects of seabird-N on marine consumers. Very little is known about spatio-temporal variations in the effects of the seabird-N on marine ecosystems. To understand the ecosystem functions of seabirds in marine nutrient cycling and the bottom-up effects of seabird-N in marine ecosystems, further research is necessary.

Capacity of Caulerpa lentillifera in the Removal of Fish Culture Effluent in a Recirculating Aquaculture System

Aquaculture is one of the fastest growing food producing industries in the world. Aquaculture effluent contains high concentrations of inorganic nutrients. Reduction of these inorganic nutrients in aquaculture effluent is crucial for fulfilling the effluent standards or reuse of aquaculture effluent. This study investigated the effective use of green macroalga Caulerpa lentillifera as a bioremediatory species for nutrient removal from aquaculture effluent by conducting an on-station experiment and measurements. The effluent of a fish culture unit was circulated through a macroalgal culture unit every four days for a total of 60 days, allowing 15 circulations. Concentrations of inorganic nutrients (NO2−-N, NO3−-N, NH3-N, and PO43−) were measured in the integrated system consisting of a fish unit, settling unit, macroalgal unit and extra tank for water circulation in triplicates. Multiple linear regression analysis revealed that the application of the bioremediation system led to a significant reduction in nutrient concentrations within one day, and slightly further in the following two days. On average over the 15 circulations, the first one day of application decreased the concentrations of NO2−-N, NO3−-N, NH3-N, and PO43− by 0.247 mg/L, 81.6 mg/L, 0.682 mg/L, and 0.352 mg/L, respectively. Furthermore, the C:N ratio of macroalgae decreased during the 60-day application period, providing evidence of the nutrient uptake by macroalgae. Based on the European Union (EU) standard and quality criteria of France and the Joint FAO/WHO Expert Committee (JFWEC), the macroalgae grown in the integrated system were at the safe level for human consumption in terms of contents of Cd, Pb, and As. The results of our study imply that recirculating aquaculture systems utilizing C. lentillifera for biofiltration have the potential for effective treatment of aquaculture effluent integrating fish and macroalgae production.

Whole community estimates of macroalgal pigment concentration within two southern New Zealand kelp forests1.

Light availability is a fundamental factor that controls the productivity and distribution of macroalgae and is highly variable, both spatially and temporally, in subtidal coastal systems. Our comprehension of how macroalgae respond to such variability is a significant knowledge gap that limits our understanding of how light influences the structure and productivity of these environments. Here, we examined the pigment characteristics of individual species, and for the first time the whole community, within one low-light, and one high-light kelp-forest system in southern New Zealand. The aim was to quantify the range of pigmentation seen within the two kelp-forests which differed in irradiance regime. Light availability was 33% and 64% greater at the high-light compared to the low-light site at 2 and 10m depth, respectively. Results suggested Phaeophyceae species at deeper depths in the low-light site may be living at the edge of their photosynthetic ability and pigment synthesis appeared significantly restricted. Even with greater investment in the pigment fucoxanthin, biomass of Phaeophyceae species was significantly lower in the low-light site. Highly pigmented Rhodophyceae species made a greater proportional contribution to community biomass within the low-light site where they likely possessed a photosynthetic advantage. This work helps explain discrepancies in community structure between the two study sites and explores the complex relationship between irradiance and photoacclimation. The comparison of community pigment concentration holds potential as a tool for assessing the relative degree of photoacclimation occurring between sites and provides a proxy of photosynthetic cost under a specific light regime.

Culture of the seaweed Ulva ohnoi integrated in a Solea senegalensis recirculating system: influence of light and biomass stocking density on macroalgae productivity

A growth model was developed to optimize the management of multi-trophic aquaculture systems by analyzing the influence of light and biomass stocking density (SD) in the productivity of Ulva ohnoi fed with the effluents from Solea senegalensis culture tanks. Growth rates and productivity were determined in three flat bottom algae tanks with different incident photon irradiances (E0) (163, 280, and 886 μmol photons m−2 s−1), photoperiod 12:12 h, and with stocking densities ranging from 82 to 340 gdw m−2. The distribution of photon irradiance in the algae tanks was estimated as a function of the E0 and SD. The results obtained showed that the algae exposed to the highest E0 (886 μmol photons m−2 s−1) and SD below 170 gdw m−2 showed a strong decrease in their growth rate, together with morphological changes. The model proposed to estimate the specific growth rate (μNET), on the basis of E0 and SD, assumed that photosynthetic activity is dependent on the local photon flux density and, therefore, spatially distributed in the tank. Non-linear regression used to estimate the growth kinetic parameters showed a standard deviation of the distance between measured and fitted μNET data values equal to 0.011 day−1. In terms of biomass productivity per unit area (BPA), the model shows, for each E0 level, a trend to increase with SD, achieving a maximum BPA, where SD can be considered optimal, and decreasing for higher SD values. The optimal SD and the maximum BPA achievable can be also determined as a function of E0.