On relaxation of the influences of treated sewage effluent on an adjacent seaweed farm in a tidal strait

An Eulerian passive tracer model coupled with a quadruple-nested 3D circulation model was used to assess the coastal dispersal of treated wastewater effluent from a sewage treatment plant and the associated impacts on an adjacent seaweed farm using three different operational scenarios. When the discharged volume and source effluent fluxes were decreased by ~16.7%, the accumulated effluent in the farm was reduced by ~25.4%. A tracer flux budget analysis revealed the apparent predominance of the transient component that accounts for the nonlinear interactions primarily from tidal currents and eddies. The transient flux promoted the effluent influx to impede effluent accumulation in the farm, whereas the mean flux contributed to the outgoing flux. A source flux reduction caused a remarkable decrease in the transient flux and thus an even greater effluent accumulation reduction. In turn, a modified source density scenario without total effluent volume change did not work as expected.

Salinity mediates the effects of nitrogen enrichment on the growth, photosynthesis, and biochemical composition of Ulva prolifera

To study the combined effects of multiple nitrogen (N) sources and salinity on the growth and physiology on macroalgae, we cultured Ulva prolifera under three N levels (N₀, 0.1235 mg L^-1; N₁, 0.6 mg L^-1; and N₂, 4.4 mg L^-1; the ratios were 18:74:8 for NH₄-N, NO₃-N, and NO₂-N, respectively) and three salinity conditions (15, 25, and 35). Then, the growth, pigment content, photosynthetic performance, superoxide dismutase (SOD) activity, and contents of soluble protein and carbohydrates were measured. The results showed the following: (1) Compared to that grown at salinity 25, the growth of U. prolifera decreased under salinity 35, especially under the N₀ and N₂ levels, but there were no significant effects of salinity 15 under any of the N levels. (2) There were no significant effects of salinity on the chlorophyll a (Chla) content, but compared to the content at salinity 25, the chlorophyll b (Chlb) content was enhanced by salinity 15 and 35; lower ratio values between Chla and carotenoids (Car) occurred under the salinity 25 treatment. Under each salinity condition, the pigments were enhanced by a high N level. (3) A relatively higher salinity level decreased the photosynthetic oxygen evolution rate, while a higher N level increased this value. Compared to the rate at salinity 25, the dark respiration rate (R_d) significantly increased at salinity 15 under the N₀ condition. (4) SOD activity was enhanced by a high N level, but no significant effects of salinity were observed. (5) The carbohydrate content was enhanced at salinity 35 under the N₀ and N₁ levels, and under salinity 15, this value increased with increasing N levels. In conclusion, although the growth of U. prolifera decreased at high N levels under high salinity conditions, a high N level induced an increase in photosynthesis, while no significant decrease in growth occurred. These findings indicate that low salinity and high N levels may be nonnegligible reasons why this species thrives, and low salinity was the better choice when this species was used for wastewater treatment.

Uncertainty in the optical remote estimation of the biomass of Ulva prolifera macroalgae using MODIS imagery in the Yellow Sea

A laboratory experiment was conducted to obtain a floating algae index (FAI) of the floating macroalgae (Ulva prolifera), corresponding to various values of biomass per unit area (BPA). A piecewise empirical model was used to fit the statistical relationships between BPA and FAI, corresponding to FAI ≤ 0.2 (BPA ≤ 1.81kg/m²) and FAI ˃ 0.2 (BPA ˃ 1.81 kg/m²). Spectral mixing derived results show that a linear relationship between FAI and BPA is maintained when the BPA of endmembers is less than 1.81 kg/m². However, when the BPA of the endmembers exceeds 1.81 kg/m², there is substantial uncertainty in the optical remote estimation of biomass. Although the MODIS-derived FAI of Ulva prolifera is often less than 0.2, it is very difficult to determine whether the FAI results from low BPA (≤ 1.81kg/m²) of the endmembers, or from a low area ratio including high BPA (˃ 1.81 kg/m²), due to pixel mixing. If it is assumed that the unit biomass distribution of pure endmembers is a standard Gaussian distribution, then the uncertainty in the biomass estimation of Ulva prolifera from MODIS data can be expressed. This results in the uncertainty of ~36% in total biomass estimation, ~43% of which was contributed by a few pixels (10% of total pixels) with high FAI (˃ 0.05). The uncertainty in BPA caused by high FAI (˃ 0.05) pixels is about 7.2 times that for low FAI (≤ 0.05) pixels. In future research, the spatial distribution characteristics of the FAI of pure endmembers need to be considered in order to improve the accuracy of optical remote estimation of floating Ulva prolifera.

Seagrass restoration in Gulf of Mannar, Tamil Nadu, Southeast India: a viable management tool

Seagrass beds are important marine ecosystems that provide significant ecological services. The global decline of seagrass beds is becoming severe due to the increasing pressure of human-induced factors and changing climatic conditions. Restoration of seagrasses is an evolving science that started in 1939. In this study, we report a remarkably successful restoration activity carried out in the Gulf of Mannar (GoM), Southeast India. This is the first wide-scale effort in Indian waters. After the initial experimentation, manual transplantation of seagrass sprigs was carried out near Vaan and Koswari islands in GoM. Transplantation was performed with PVC quadrats and jute twines in areas of 800 m² in both the islands during February to May 2014. An increase from 16.4 ± 0.3 to 32.3 ± 0.6% in Vaan and from 15.1 ± 0.2 to 35.1 ± 0.9% in Koswari was observed in seagrass percentage cover during the period from June 2014 to May 2016. Area cover, shoot density, macrofaunal density and fish density increased at the restoration sites after the transplantation. Bottom trawling was found to be the most serious threat to the seagrass beds in these islands. This method of transplantation can be replicated in other areas of degraded seagrass in India to carry out wide-scale restoration of seagrasses.

Climate change induced range shifts in seaweeds distributions in Europe

There are evidences of how climate change is affecting seaweeds distribution and the ecosystems services they provide. Therefore, it is necessary to consider these impacts when managing marine areas. One of the most applied tools in recent years to deal with this are species distribution models, however there are still some challenges to solve, such as the inclusion of hydrodynamic predictors and the application of effective, transferable and user-oriented methodologies. Five species (Saccorhiza polyschides, Gelidium spinosum, Sargassum muticum, Pelvetia canaliculata and Cystoseira baccata) in Europe and 15 variables were considered. Nine of them were projected to the RCPs 4.5 and 8.5 for the mid-term (2040-2069) and the long term (2070-2099). Algorithms for each species were applied to generate models that were assessed by comparison of probabilities and observations (area under the curve, true skill statistics, Boyce index, sensitivity, correct classification rate), niches overlap (Schoener's D, Hellinger's I), geographical similarity (interquartile range) and ecological realism. Models built demonstrated very good predictive accuracy and sensitivity, without overfitting risk. A medium overlap in the historical and RCPs environmental conditions were obtained, therefore the models can be considered transferable and results accurate because only some isolated points were detected as outliers, corresponding to low probabilities. The areas of S. polyschides and G. spinosum have been identified to be dramatically reduced, meanwhile S. muticum and C. baccata were predicted to expand their range. P. canaliculata was expected to keep its sites of presence but with a decrease in its probability of occurrence. For all species it was remarkable the importance of hydrodynamic variables and parameters representing extreme conditions. Spatially predictions of the potential species and areas at risk are decisive for defining management strategies and resource allocation. The performance and usefulness of the approach applied in this study have been demonstrated for algae with different ecological requirements (from upper littoral to subtidal) and distributional patterns (native and invasive), therefore results can be used by marine planners with different goals: marine protected areas designation, monitoring efforts guiding, invasions risk assessment or aquaculture facilities zonation.

Life Cycle Assessment of Seaweed Cultivation Systems

Life cycle assessment (LCA) is a holistic methodology that identifies the impacts of a production system on the environment. The results of an LCA are used to identify which processes can be improved to minimize impacts and optimize production.LCA is composed of four phases: (1) goal and scope definition, (2) life cycle inventory analysis, (3) life cycle impact assessment, and (4) interpretation.The goal and scope define the purpose of the analysis; describe the system and its function, establish a functional unit to collect data and present results, set the system boundaries, and explain the assumptions made and data quality requirements. Life cycle inventory analysis is the collection, processing and organization of data. Life cycle impact assessment associates the results from the inventory phase to one or multiple impacts on environment or human health. The interpretation evaluates the outcome of each phase of the analysis. In this phase the practitioner decides whether it is necessary to amend other phases, e.g., collection of more data or adjustments of goal of the analysis. In the interpretation, the practitioner draws conclusions, exposes the limitations, and provides recommendations to the readers.The quality of LCA of seaweed production and conversion is based on data availability and detail level. Performing an LCA at the initial stage of seaweed production in Europe is an advantage: the recommended design improvements can be implemented without significant economic investments. The quality of LCA will keep improving with the increase of scientific publications, data sharing, and public reports.

Coral reef systems of the Mexican Caribbean: Status, recent trends and conservation

Over the last four decades the Mexican Caribbean has experienced intensive coastal development, and change on the reef system condition has already been observed. This paper describes the reef system characteristics, at local and seascape scales, and discusses the current status and trends, considering the main research efforts from academia and Non-Governmental Organizations. To date, the coral cover of most reefs in the region is between 15 and 20%, following a slight recovery on mean coral cover over the last decade. During this same period, fleshy macroalgae and herbivorous fish biomass appear to have increased. At seascape scales, an increase of macroalgae and the loss of seagrass habitat have been observed. Considering that anthropogenic and environmental disturbances will most likely increase, the establishment of newly protected areas in the Mexican Caribbean is appropriate, but sufficient accompanying funding is required.

Mechanical properties of the wave-swept kelp Egregia menziesii change with season, growth rate and herbivore wounds

The resistance of macroalgae to damage by hydrodynamic forces depends on the mechanical properties of their tissues. Although factors such as water-flow environment, algal growth rate and damage by herbivores have been shown to influence various material properties of macroalgal tissues, the interplay of these factors as they change seasonally and affect algal mechanical performance has not been worked out. We used the perennial kelp Egregia menziesii to study how the material properties of the rachis supporting a frond changed seasonally over a 2 year period, and how those changes correlated with seasonal patterns of the environment, growth rate and herbivore load. Rachis tissue became stiffer, stronger and less extensible with age (distance from the meristem). Thus, slowly growing rachises were stiffer, stronger and tougher than rapidly growing ones. Growth rates were highest in spring and summer when upwelling and long periods of daylight occurred. Therefore, rachis tissue was most resistant to damage in the winter, when waves were large as a result of seasonal storms. Herbivory was greatest during summer, when rachis growth rates were high. Unlike other macroalgae, E. menziesii did not respond to herbivore damage by increasing rachis tissue strength, but rather by growing in width so that the cross-sectional area of the wounded rachis was increased. The relative timing of environmental factors that affect growth rates (e.g. upwelling supply of nutrients, daylight duration) and of those that can damage macroalgae (e.g. winter storms, summer herbivore outbreaks) can influence the material properties and thus the mechanical performance of macroalgae.

A simple and effective method for monitoring floating green macroalgae blooms: a case study in the Yellow Sea

Several algorithms have been proposed to detect floating macroalgae blooms in the global ocean. However, some of them are difficult or even impossible to routinely apply by non-experts because of performing a sophisticated atmospheric correction scheme or due to the mismatch in spectral bands from one sensor to another. Here, a generic, simple and effective method, referred to as the Floating Green Tide Index (FGTI), was proposed to detect floating green macroalgae blooms (GMB). The FGTI was defined as the difference between greenness and wetness features extracted from digital number (DN) observation through Tasseled Cap Transformation analysis, providing the advantage of bypassing the atmospheric correction procedure. Through cross-index and cross-sensor comparisons, the FGTI showed similar performance to the existing VB-FAH (Virtual-Baseline Floating macroAlgae Height) and FAI (Floating Algae Index) algorithms but proved more robust than the traditional NDVI (Normalized Difference Vegetation Index) in terms of response to perturbations by environmental conditions, viewing geometry, sun glint, and thin cloud contamination. Given the requirement for spectral bands in the current and planned satellite sensors, the FGTI design can easily be extended to any satellite sensor, and therefore provide an excellent data resource for studying GMB in any part of the global ocean.

Macroalgae bloom decay decreases the sediment organic carbon sequestration potential in tropical seagrass meadows of the South China Sea

Seagrass meadows are experiencing worldwide declines mainly because of nutrient enrichment, which always result in macroalgae bloom and consequently periodic collapse and decomposition. However, effects of macroalgae decay on the sediment organic carbon (SOC) sequestration capacity remain unknown. Depending on the macroalgae biomass in eutrophic seagrass meadows of South China Sea, we carried out a laboratory chamber experiment to investigate the sediment labile organic carbon (OC) compositions and the influencing SOC transformation enzyme activity variations of seagrass meadows in response to common macroalgae bloom species (Cladophora spp.) decomposition. Although the dehydrogenase and β-glucosidase activities were not affected by macroalgae decomposition, the macroalgae decomposition significantly elevated the salt-extractable carbon (SEC) content, SEC/SOC, levels of invertase and polyphenol oxidase activities, and the CO₂ release. Overall, this study indicates that macroalgae decomposition stimulates the SOC transformation, and therefore, it is not benefit for SOC sequestration within seagrass meadows of the South China Sea.

Comparison of UVB effects on growth and induction of UVB screening compounds in isolates of metaphytic algae from temperate zone streams and ponds

Filaments in the surface layers of metaphytic mats are exposed to high photon flux densities of PAR and UVBR. We investigated the effect of UVBR exposure on growth of eight isolates of common metaphytic algae (Cladophora, Mougeotia, Oedogonium, Pithophora, Spirogyra, and Zygnema) acclimated to either high or low PAR levels prior to UVBR exposure. All isolates acclimated to low PAR exhibited significant reductions in growth rate caused by the UVBR exposure (P < 0.05). Acclimation to high PAR resulted in seven of the isolates being more tolerant of the UVB exposure. The two Zygnema isolates exhibited the most pronounced effect of high PAR acclimation with growth rates of UVB exposed treatments being equal to that of controls (P > 0.05). High PAR acclimation also protected chlorophyll a levels in the Zygnema isolates. Absorption of UVB by methanol extracts increased 322%-381% for the two Zygnema isolates when high PAR acclimated. The broad absorption peak at 270 nm suggests that phenolic compounds were responsible. Previous studies have shown that Zygnema isolates from extreme environments tolerate UVBR and contain UVB screening compounds, but our results extend these adaptions to Zygnema from typical temperate zone habitats. Although none of the other metaphytic algae produced UVB absorbing compounds, they all exhibited higher growth rates under UVBR exposure following high PAR acclimation. This suggests that the algae evaluated have inducible defenses against UVBR exposure that coupled with their mat structure would provide an adaption to the challenging light environment in shallow-water habitats.

Stable isotopic evidence of nitrogen sources and C4 metabolism driving the world's largest macroalgal green tides in the Yellow Sea

During recent years, rapid seasonal growth of macroalgae covered extensive areas within the Yellow Sea, developing the world's most spatially extensive "green tide". The remarkably fast accumulation of macroalgal biomass is the joint result of high nitrogen supplies in Yellow Sea waters, plus ability of the macroalgae to optionally use C4 photosynthetic pathways that facilitate rapid growth. Stable isotopic evidence shows that the high nitrogen supply is derived from anthropogenic sources, conveyed from watersheds via river discharges, and by direct atmospheric deposition. Wastewater and manures supply about half the nitrogen used by the macroalgae, fertiliser and atmospheric deposition each furnish about a quarter of the nitrogen in macroalgae. The massive green tides affecting the Yellow Sea are likely to increase, with significant current and future environmental and human consequences. Addressing these changing trajectories will demand concerted investment in new basic and applied research as the basis for developing management policies.

The impact of elevated atmospheric CO2 on cadmium toxicity in Pyropia haitanensis (Rhodophyta)

Cadmium is one of the major heavy metal pollutions in coastal waters, and it is well known that cadmium at trace concentration is toxic to macroalgae. Change in marine carbonate system and ocean acidification caused by elevated atmospheric CO₂ also alter physiological characteristics of macroalgae. However, less research is focused on the combined impacts of elevated CO₂ and cadmium pollution on the growth and physiology in macroalgae. In this study, the maricultivated macroalga Pyropia haitanensis (Rhodophyta) was cultured at three levels of Cd²⁺ (control, 4 and 12 mg L^-1) and two concentrations of CO₂, the ambient CO₂ (AC, 410 ppm) and elevated CO₂ (HC, 1100 ppm). The results showed that 12 mg L^-1 Cd²⁺ significantly suppressed the relative growth rate and superoxide dismutase activity in AC-grown P. haitanensis, while such inhibition extents by Cd²⁺ were alleviated in HC-grown algae. Cd²⁺ had no effects on efficiency of electron transport (α) and maximum electron transport rate (ETR_max), but α was increased by elevated CO₂. Cd²⁺ dramatically suppressed the maximum net photosynthesis oxygen evolution rate (NPR_m) and the minimum saturation irradiance (I_k) when the algal thalli were grown at AC, while such suppression of NPR_m by Cd²⁺ was much decreased when the thalli were grown at HC. Collectively, our results suggested that elevated CO₂ would alleviate Cd²⁺ toxicity on P. haitanensis.

A study of the environmental factors influencing the growth phases of Ulva prolifera in the southern Yellow Sea, China

Macroalgal blooms of U. prolifera in the southern Yellow Sea (SYS) have become an ecological disaster. In this study, we attempt to explore the influence of environmental factors and human activity on the annual development of U. prolifera during 2011-2016, combining geostationary ocean color imager images and monitored environmental factors. Blooms of U. prolifera were mainly distributed in the central SYS, drifting from the southern Yellow Sea Radial Sand Ridges. Three growth phases were defined (initial phase, outbreak phase and dissipation phase) to facilitate analysis of the relationship between the environmental factors and growth conditions of U. prolifera. Seaweed cultivation, sea surface temperature (SST) and available radiation influenced the algal biomass during the initial phase; the seawater transparency, precipitation and wind activity affected the algae during the outbreak phase; and SST, intense radiation and cleanup operations increased the rate of algal extinction in the dissipation phase.

Remote sensing of early-stage green tide in the Yellow Sea for floating-macroalgae collecting campaign

The world's largest green tide originated from the Jiangsu Shoal of the Yellow Sea was due to fast reproduction of floating green macroalgae (Ulva prolifera). It brought significant impacts on marine environment and ecosystem in the Yellow Sea. In this study, we examined the expansion of green tide from the Jiangsu Shoal during the period from 29 April to 25 June 2016. Using high-resolution satellite images, we revealed a declined growth rate during the northward drifting of early-stage green tide for the first time, i.e., the green tide had higher growth rate (up to 25% per day) in the turbid waters of the Jiangsu Shoal in May and a lower growth rate (low to 3% per day) in the relatively clear waters in the middle of the western Yellow Sea in June, which suggests that water clarity might not be the key factor controlling the growth rate of the floating macroalgae in the surface waters under natural conditions. The high growth rate led to shortened time windows for controlling the green tide by employing macroalgae collecting campaigns at the initial sites of the green tide, which was no more than 14 days in the 2016 case.

Investigation of broad scale implementation of integrated multitrophic aquaculture using a 3D model of an estuary

A 3D ecosystem model was used to quantify changes in water quality brought about by salmon aquaculture in the D'Entrecasteaux Channel and Huon Estuary in southeast Tasmania. Macroalgae-based integrated multitrophic aquaculture (IMTA) was simulated and showed that IMTA is capable of reducing the increased chlorophyll concentration attributable to fish farming by up to 10-15% in large areas of the region, during the season of highest production. Kelp farms (Macrocystis pyrifera) recovered between 6 and 11% of the dissolved inorganic nitrogen (DIN) input by salmon aquaculture over a nine month period, with DIN remediation increasing linearly with farm size. Under a ten-fold increase in aquaculture to very high loads, a much lower remediation effect was found for both chlorophyll and DIN. Model results indicate that IMTA could have an important impact on reducing negative effects of finfish aquaculture on water quality providing that stocking rates are not too high.

Vitamin D Content of Australian Native Food Plants and Australian-Grown Edible Seaweed

Vitamin D has previously been quantified in some plants and algae, particularly in leaves of the Solanaceae family. We measured the vitamin D content of Australian native food plants and Australian-grown edible seaweed. Using liquid chromatography with triple quadrupole mass spectrometry, 13 samples (including leaf, fruit, and seed) were analyzed in duplicate for vitamin D₂, vitamin D₃, 25-hydroxyvitamin D₂, and 25-hydroxyvitamin D₃. Five samples contained vitamin D₂: raw wattleseed (Acacia victoriae) (0.03 µg/100 g dry weight (DW)); fresh and dried lemon myrtle (Backhousia citriodora) leaves (0.03 and 0.24 µg/100 g DW, respectively); and dried leaves and berries of Tasmanian mountain pepper (Tasmannia lanceolata) (0.67 and 0.05 µg/100 g DW, respectively). Fresh kombu (Lessonia corrugata) contained vitamin D₃ (0.01 µg/100 g DW). Detected amounts were low; however, it is possible that exposure to ultraviolet radiation may increase the vitamin D content of plants and algae if vitamin D precursors are present.

Enhancement of Biochemical and Nutritional Contents of Some Cultivated Seaweeds Under Laboratory Conditions

Six species of macroalgae belonging to the Chlorophyta, Phaeophyta, and Rhodophyta divisions were cultivated in a closed system with Guillard's f/2, Walne's, Provasoli Enriched Seawater (PES) medium, and seawater (control) for 6 weeks. The growth rate and parameters of the tested seaweeds showed that all used media enhanced the growth rate and chemical content as compared with other seaweeds cultivated in seawater without addition of any nutrients. There are significant differences in the effect of the used media on the seaweed composition at p = .01; PES is more effective than the f/2 and Walne's media. The results indicate that the cultivation technique of some macroalgae was an efficient tool for increasing the seaweeds' biomass and increasing their chemical compounds, calories, and energy under laboratory conditions.

Effect of water motion and microhabitat preferences on spatio-temporal variation of epiphytic communities: a case study in an artificial rocky reef system, Laoshan Bay, China

Epiphytic fauna community structure is mainly determined by macro-scale environmental characteristics (e.g., water motion), whereas the influences of, and interaction with, micro-scale habitat-forming species are not well known. In order to explore the effects of water motion and functional macroalgal group on the community structure of epiphytic faunas, macroalgae and epiphytic faunas from four isolated artificial rocky reefs with different levels of hydrodynamic conditions were investigated in Laoshan Bay of China. A total of 32 macroalgal species and 22 faunal species were recorded on the surveys. The biomass and abundance of macroalgae and epiphytic faunas showed significant variations among stations and months. The biomass and abundance of epiphytic faunas were highest at outer Huangshankou station (H1) with medium hydrodynamic force. The lowest biomass of epiphytic faunas occurred at inner Huangshankou station (H3) with highest level of water motion, while the lowest abundance of epiphytic faunas occurred at Liepo station (L) with lowest level of water motion. Results showed that medium water motion level contributed to increasing biodiversity of epiphytic faunas. Epiphytic communities generally presented higher biomass and abundance in summer than in spring or autumn, which indicated temperature could be the ecological driver for temporal variation of epiphytic communities. The epiphytic faunas showed distinct preferences to structural morphology of macroalgae which forms suitable habitat for these organisms. This study suggests that artificial rocky reefs are of great significance to restore and maintain coastal biodiversity, and appropriate physical disturbance promote community reestablishment.

Transcriptomic study to understand thermal adaptation in a high temperature-tolerant strain of Pyropia haitanensis

Pyropia haitanensis, a high-yield commercial seaweed in China, is currently undergoing increasing levels of high-temperature stress due to gradual global warming. The mechanisms of plant responses to high temperature stress vary with not only plant type but also the degree and duration of high temperature. To understand the mechanism underlying thermal tolerance in P. haitanensis, gene expression and regulation in response to short- and long-term temperature stresses (SHS and LHS) was investigated by performing genome-wide high-throughput transcriptomic sequencing for a high temperature tolerant strain (HTT). A total of 14,164 differential expression genes were identified to be high temperature-responsive in at least one time point by high-temperature treatment, representing 41.10% of the total number of unigenes. The present data indicated a decrease in the photosynthetic and energy metabolic rates in HTT to reduce unnecessary energy consumption, which in turn facilitated in the rapid establishment of acclimatory homeostasis in its transcriptome during SHS. On the other hand, an increase in energy consumption and antioxidant substance activity was observed with LHS, which apparently facilitates in the development of resistance against severe oxidative stress. Meanwhile, ubiquitin-mediated proteolysis, brassinosteroids, and heat shock proteins also play a vital role in HTT. The effects of SHS and LHS on the mechanism of HTT to resist heat stress were relatively different. The findings may facilitate further studies on gene discovery and the molecular mechanisms underlying high-temperature tolerance in P. haitanensis, as well as allow improvement of breeding schemes for high temperature-tolerant macroalgae that can resist global warming.

Food selection of a generalist herbivore exposed to native and alien seaweeds

Understanding which factors influence the invasion of alien seaweed has become a central concern in ecology. Increasing evidence suggests that the feeding preferences of native herbivores influence the success of alien seaweeds in the new community. We investigated food selection of a generalist native grazer Paracentrotus lividus, in the presence of two alien seaweeds (Caulerpa cylindracea and Caulerpa taxifolia var. distichophylla) and two native seaweeds (Dictyopteris membranacea and Cystoseira compressa). Sea urchins were fed with six experimental food items: C. cylindracea, C. taxifolia var. distichophylla, a mixture of C. cylindracea and C. taxifolia var. distichophylla, D. membranacea, C. compressa and a mixture of D. membranacea and C. compressa. P. lividus ingested all the combinations of food offered, though it preferentially consumed the alien mixture, C. cylindracea and D. membranacea. The alien C. taxifolia var. distichophylla was consumed significantly less than the other food items and, interestingly, it was ingested in a greater amount when mixed with C. cylindracea than when on its own. This finding suggests that C. taxifolia var. distichophylla may become vulnerable to sea urchin grazing when it grows intermingled with C. cylindracea, which does not gain immediate protection from the presence of the very low palatable congeneric seaweed. The present study highlights the potential role of native grazers to indirectly affect the interspecific competition between the two alien seaweeds in the Mediterranean Sea.

Variations of dominant free-floating Ulva species in the source area for the world's largest macroalgal blooms, China: Differences of ecological tolerance

Species composition and seasonal variations of free-floating Ulva species were investigated in the source area of the world's largest macroalgal blooms during 2009-2015. Based on a combination of a morphological analysis and sequences of nuclear-encoded ITS and 5S rDNA spacer regions, the dominant species in the free-floating Ulva community at the early stage of green tides were Ulva compressa, Ulva flexuosa, and Ulva linza. The first appearance of Ulva prolifera on the sea surface was in mid-May and it dominated the floating Ulva community in June from 2009 to 2011. From 2012-2015, U. prolifera was not only the first species to appear on the sea surface but also the dominant species during the whole early stage of green tides. To explain the successional mechanism, the effects of environmental factors on the growth of four Ulva species were examined in the laboratory under different combinations of light intensity and temperature. It was found that the highest growth rate of U. prolifera was 44.9%/d, which was much higher than the other three Ulva species. The strong tolerance of U. prolifera to extreme conditions also helps it survive and bloom in the Yellow Sea.

ALEX index enables detection of alien macroalgae invasions across habitats within a marine protected area

A modified version of the ALien Biotic IndEX (ALEX) has been recently proposed to evaluate biological invasions in macroalgal assemblages. ALEX was applied in a Marine Protected Area where a recreational-fishing port is present testing the following hypotheses: ALEX increases with the distance from the port, it changes between the two directions off the port and it changes among three different habitats: Cystoseira beds, algal turf and dead matte of the seagrass Posidonia oceanica. A total of 78 native macroalgal taxa and 4 introduced species were found, the Chlorophyta Caulerpa cylindracea and the Rhodophyta Apoglossum gregarium, Acrothamnion preissii and Womersleyella setacea. All study sites were in high quality status highlighting that the assemblages investigated were at an early stage of NIS invasion. However, ALEX detected different values among conditions and habitats within the MPA, suggesting a local dynamics of NIS spread and different resistance to invasion of the investigated habitats.

Nutritional and bioactive compounds of commercialized algae powders used as food supplements

The main nutritional/bioactive compounds (protein; aminoacids, AA; fucose; minerals; vitamins B12 and C; and total phenolic content, TPC) of nine commercial algae powders, used as food supplements, were studied. Undaria pinnatifida showed the highest protein/aminoacid contents (51.6/54.4 g 100 g-1). Among brown macroalgae, Himanthalia elongata showed the highest fucose content (26.3 g kg-1) followed by Laminaria ochroleuca (22.5 g kg-1). Mineral contents of 15-24% were observed in the algae, being particularly excellent sources of iodine (69.0-472.0 mg kg-1). Porphyra spp. and Palmaria palmata showed the highest vitamin B12 contents (667-674 µg kg-1). Vitamin C ranged among 490.4-711.8 mg kg-1. H. elongata showed the highest total phenolic content (14.0 g kg-1). In conclusion, the studied algae are excellent sources of protein, AA, minerals, vitamin C and some of them presented particularly high vitamin B12 and fucose contents, which may have a potential use as food supplements.

Intertidal geothermal hot springs as a source of trace elements to the coastal zone: A case study from Bahía Concepción, Gulf of California

We investigated the influence of the intertidal geothermal hot spring (GHS) on the biogeochemistry of trace elements in Santispac Bight, Bahía Concepción (Gulf of California). The geothermal fluids were enriched in As and Hg mainly in ionic form. The suspended particulate matter of the GHS had elevated enrichment factor (EF) >1 of As, Bi, Cd, Co, Cu, Mn, Mo, Sb, Sn, Sr, Ti, U and Zn. The sediment core from GHS1 had high concentration of As, Hg, Corg, S, V, Mo, and U and the extremely high EF of these elements at 8cm of the core. The maximum bioaccumulation of As and Hg was in seaweeds Sargassum sinicola collected near the GHS2. The results confirm the input of trace elements to the coastal zone in Bahía Concepción from geothermal fluids and the evident modification of the chemical composition of the adjacent marine environment.