Interannual changes in δ¹⁵N values in Fucus vesiculosus L

Influence of Gender and Age of Brown Seaweed (Fucus vesiculosus) on Biochemical Activities of Its Aqueous Extracts

Fucus vesiculosus L. is a common coastal brown seaweed associated with various benefits to human health due to its phenolic content and nutrients and is used as food through different methods of consumption. This study aims to evaluate the influence of the seaweed’s gender and growth stage on different types of biological activities as well as its chemical constitution and elements present. Akin to food preparation, aqueous extracts of the seaweed were prepared at 25 °C (salad) and 100 °C (soup). Biological activities were determined by measuring total phenol content (TPC), antioxidant activity and inhibition of acetylcholinesterase (AChE). Liquid Chromatography High Resolution Mass Spectrometry (LC-HRMS/MS) was used for compound identification, and elemental analysis was carried out by using Total Reflection X-ray Fluorescence Spectrometry (TXRF). Older females and males had higher TPC compared to the new ones at 100 °C. Antioxidant activity depended on the extraction temperature but was higher for the youngest male at 100 °C. AChE inhibitory activity was higher for older males at 25 °C, but at 100 °C it was higher for older females. Primary metabolites and various phloroglucinol were the main compounds identified. Additionally, since this seaweed is often harvested in estuarine systems with high anthropogenic impacts, its safety was evaluated through the evaluation of the sample’s metal content. The heavy metals detected are within the limits established by various regulating entities, pointing to a safe food source.

Analysis of intra-thallus and temporal variability of trace elements and nitrogen in Fucus vesiculosus: Sampling protocol optimization for biomonitoring

To advance the methodological standardization of the biomonitoring technique using macroalgae, we comprehensively characterized the intra-thallus and temporal patterns of variation in concentrations of a wide set of elements (Al, As, Cd, Co, Cr, Cu, Fe, Hg, Ni, Pb, Zn, N) and δ15N signal in 6 consecutive Fucus vesiculosus apical dichotomous sections collected monthly over a four-year period (2015-2019) at 3 sites on the NW coast of Spain. The concentrations of Al, Co, Fe, Ni, Pb and Zn increased significantly from the youngest to the oldest dichotomies regardless of the sampling time and collection site; As, Cd, N and δ15N showed the opposite trend. Time series analysis revealed a significant and consistent seasonal variation of As, Cd, Co, Cu, Fe, Hg, Ni, Zn, N and δ15N concentrations, with maximum values in winter and minimum values in summer. We discussed the possible mechanisms driving these two sources of variation, and proposed an efficient and effective sampling strategy to minimize their impact in the results of biomonitoring studies, in which the part of the algal thallus selected for chemical analysis and the sampling frequency were carefully considered. This protocol will improve the conclusions and comparability of biomonitoring data from coastal environments.

Bladder wrack (Fucus vesiculosus) as a multi-isotope bio-monitor in an urbanized fjord of the western Baltic Sea

The spatial variations in the elemental and stable carbon, nitrogen, and sulphur isotope composition of bladder wrack (Fucus vesiculosus) growing along the shore line of the semi-enclosed urbanized Kiel Fjord (western Baltic Sea) was investigated at more than 60 sites. The analyses of the carbon-nitrogen-sulphur (CNS) stoichiometry and C and N stable isotope signature of F. vesiculosus displayed substantial differences between the north-western and the south-eastern parts of the Kiel Fjord. Different size classes displayed in part differences in C:N and C:S ratios, and the carbon isotope composition, reflecting the impact of the boundary conditions during growth. Whereas the sulphur isotope composition was controlled by the assimilation of seawater sulphate, the carbon isotope composition reflected the difference in the composition of surface waters. The δ15N values of the organic tissue tend to be an integrated monitor of anthropogenic impacts on the fjord. Results are compared to the composition of surface waters.

Translocation of isotopically distinct macroalgae: A route to low-cost biomonitoring?

Nitrogen stable isotope ratios (δ15N) in macroalgae are often used to identify sources of nitrogenous pollution in fluvial and estuarine settings. This approach assumes that the macroalgal δ15N is representative of the sources of the pollution averaged over a timespan in the order of days to weeks. The preferential uptake of a particular nitrogen compound or potential for fractionation in the water column or during uptake and assimilation by the macroalgae could make this assumption invalid. Laboratory studies were therefore performed to investigate the uptake and assimilation of both nitrate and ammonium at a variety of concentrations using the vegetative (non-fertile) tips of the brown macroalgae, Fucus vesiculosus. Nitrate appeared to fractionate at high concentrations, and was found to be taken up more rapidly than ammonia; within 13 days, the macroalgae tips were in isotopic equilibrium with the nitrate solution at 500 μM. These experiments were complemented by an investigation involving the translocation of macroalgae collected from a site enriched in 15N relative to natural levels (Staithes, UK), to the River Tees, Middlesbrough (UK), a site depleted in 15N relative to natural levels. The nitrogen isotope signature shifted by ∼50% within 7 days, with samples deployed nearer the surface subject to greater change. These findings suggest that the translocation of macroalgae with isotopically distinct signatures can be used as a rapid, cost-efficient method for nitrogen biomonitoring in estuarine environments.

Dynamics of δ(15)N isotopic signatures of different intertidal macroalgal species: Assessment of bioindicators of N sources in coastal areas

δ(15)N of annual (Ulva sp., Porphyra sp.) and perennial intertidal seaweed species (Chondrus crispus, Fucus sp.) collected on 17 sampling points along the French coast of the English Channel in 2012 and 2013 were assessed on their suitability as bioindicators of N pollution in coastal areas. A sine function applied for δ(15)N time series data showed for all the species the same seasonal trend with lowest δ(15)N values in April and highest in summer but with no significant interspecific differences of amplitude (α) and phase angle (ϕ). This model provides a useful tool for monitoring the inter-annual changes of N pollution. An interspecific variability of δ(15)N values was observed, probably due to their tolerance to emersion. An in vitro study for comparing the kinetic acquisition of the isotopic signal and N uptake mechanisms of each species underlined the influence of algal physiology on the δ(15)N interspecific variability.

Identifying nitrogen sources to thermal tide pools in Kapoho, Hawai'i, U.S.A, using a multi-stable isotope approach

Nitrogen (N) enrichment often results in coastal eutrophication, even in remote areas like Hawai'i. Therefore, determining N sources to coastal waters is important for their management. This study identified N sources to tide pools in Kapoho, Hawai'i, and determined their relative importance using three stable isotopes (δ(15)N, δ(18)O, δ(11)B). Surface waters and macroalgal tissues were collected along 100-m onshore-offshore transects in areas of high groundwater input for three months at low tide. Water samples from possible N sources were also collected. Mixing model output, along with macroalgal δ(15)N values, indicated that agriculture soil (34%) was the largest anthropogenic N source followed by sewage (27%). These findings suggest that more effective fertilizer application techniques and upgrading sewage treatment systems can minimize N leaching into groundwater. Overall, our multi-stable isotope approach for identifying N sources was successful and may be useful in other coastal waters.

Selection of effective macroalgal species and tracing nitrogen sources on the different part of Yantai coast, China indicated by macroalgal δ(15)N values

To determine the dominant nitrogen sources and select effective macroalgal species for monitoring eutrophication along the Yantai coast, the total carbon (TOC), total nitrogen (TN) and nitrogen stable isotope ratio (δ(15)N) in macroalgal tissue were analyzed in conjunction with environmental variables in seawater along the Yantai coastline. The ranges of macroalgal tissue δ(15)N values together with dissolved inorganic nitrogen (DIN) composition indicated that except for the atmospheric deposition, there were three dominant types of nitrogen sources along the Yantai coast, with the agricultural fertilizer usage and factorial wastewater input at the S1 (Zhifu Island coast), the sewage discharge at S2 (the Moon Bay coast), the sewage discharge together with aquaculture impacts at S3 (Fisherman Wharf coast) and S4 (the Horse Island coast). Macroalgal growth were not limited by DIN but limited by P at S2, S3 and S4. Macroalgal species suitable or not for DIN source tracing along the Yantai coast were discussed. For sites with low DIN concentration, many species of three phyla could be used for DIN sources tracing with Laurencia okamurai, Gloiopeltis furcata and Ulva pertusa being ideal species. For site with high DIN concentration, however, species of Rhodophyta were not suitable and only Scytosiphon lomentaria and Monostroma nitidium were chosen.

Impact of seaweed beachings on dynamics of δ(15)N isotopic signatures in marine macroalgae

A fine-scale survey of δ(15)N, δ(13)C, tissue-N in seaweeds was conducted using samples from 17 sampling points at two sites (Grandcamp-Maisy (GM), Courseulles/Mer (COU)) along the French coast of the English Channel in 2012 and 2013. Partial triadic analysis was performed on the parameter data sets and revealed the functioning of three areas: one estuary (EstA) and two rocky areas (GM(∗), COU(∗)). In contrast to oceanic and anthropogenic reference points similar temporal dynamics characterized δ(15)N signatures and N contents at GM(∗) and COU(∗). Nutrient dynamics were similar: the N-concentrations in seawater originated from the River Seine and local coastal rivers while P-concentrations mainly from these local rivers. δ(15)N at GM(∗) were linked to turbidity suggesting inputs of autochthonous organic matter from large-scale summer seaweed beachings made up of a mixture of Rhodophyta, Phaeophyta and Chlorophyta species. This study highlights the coupling between seaweed beachings and nitrogen sources of intertidal macroalgae.

Variability in δ¹⁵N of intertidal brown algae along a salinity gradient: differential impact of nitrogen sources

While it is generally agreed that δ(15)N of brown macroalgae can discriminate between anthropogenic and natural sources of nitrogen, this study provides new insights on net fractionation processes occurring in some of these species. The contribution of continental and marine sources of nitrogen to benthic macroalgae in the estuary-ria system of A Coruña (NW Spain) was investigated by analyzing the temporal (at a monthly and annual basis) and spatial (up to 10 km) variability of δ(15)N in the macroalgae Ascophyllum nodosum and three species of the genus Fucus (F. serratus, F. spiralis and F. vesiculosus). Total nitrate and ammonium concentrations and δ(15)N-DIN, along with salinity and temperature in seawater were also studied to address the sources of such variability. Macroalgal δ(15)N and nutrient concentrations decreased from estuarine to marine waters, suggesting larger dominance of anthropogenic nitrogen sources in the estuary. However, δ(15)N values of macroalgae were generally higher than those of ambient nitrogen at all temporal and spatial scales considered. This suggests that the isotopic composition of these macroalgae is strongly affected by fractionation during uptake, assimilation or release of nitrogen. The absence of correlation between macroalgal and water samples suggests that the δ(15)N of the species considered cannot be used for monitoring short-term changes. But their long lifespan and slow turnover rates make them suitable to determine the impact of the different nitrogen sources integrated over long-time periods.