Benthic Macroalgae Research Articles

Kandungan Fenol dan Aktivitas Antioksidan Makroalga Bentik Caulerpa racemosa (Forsskal) dari Teluk Hurun, Lampung

Caulerpa racemosa is a green benthic macroalga that mainly grows in tropical regions which is expected to bask of strong ultraviolet radiation from sunlight. This circumstance can cause to increase levels of reactive radical species. To reduce and/or protect, organism like macroalga may change its metabolism and stimulate to produce some active compounds, therefore, tropical macroalgae are estimated possessing a large number of active compounds such as antioxidant. In this experiment, edible green benthic macroalga Caulerpa racemosa grown in different water condition were used. The content of total phenol and antioxidant activity of ethyl acetate extract were performed. Pearson correlation between waters condition and antioxidant activities i.e. total phenol and DPPH inhibition were also analyzed. Caulerpa racemosa grown in station 2, exposed in strong radiation from sunlight, had the highest content of total phenol and percentage of DPPH inhibition, with their values were 12.60% and 46.43% respectively. Sunlight intencity in waters had strong positive correlation to the total phenol content and reducing activity of DPPH, however, parameters of nitrate and ammonia had strong negative correlation.

Inventory and Historical Changes in the Marine Flora of Tomioka Peninsula (Amakusa Island), Japan

Intensive algal sampling was conducted from 2012 to 2017 in the Tomioka Peninsula, Amakusa-Shimoshima Island (the East China Sea, Japan), yielding a total of 293 benthic macroalgal taxa, of which 63% were red algae, 16% were brown algae, and 19% were green algae. The majority (69%) of species were previously recorded only for the tropics and/or subtropics, whereas 31% of species were recorded for temperate latitudes. Among all species of algae found from 2012 to 2017 in the Tomioka Peninsula, 163 species (56%) were newly identified species for Amakusa-Shimoshima Island, including six taxa, which were recorded in Japan for the first time. Comparison of the current data from the Amakusa-Shimoshima Island with those of nearby tropical regions suggested that the recent marine flora of the Amakusa-Shimoshima Island was more closely affiliated with the flora of a warm-temperate region. Moreover, we found that the benthic flora of the Tomioka Peninsula was significantly changed between the 1950s (Segawa & Yoshida 1961) and 2012–2017. For example, the species diversity was increased by two times, mainly at the expense of red and green algae, and the biogeographic status of the benthic flora was changed from the flora of a cold-temperate region to the flora of a warm-temperate region, which could be attributed to an introduction of red algae from the tropics of South East Asia and widespread opportunistic green algae, as well as the disappearance of cold-water brown algae. Collectively, our data suggested that these changes were driven by the global warming effect on the ocean.

Algae Growth Distribution and Key Prevention and Control Positions for the Middle Route of the South-to-North Water Diversion Project

The Middle Route of the South-to-North Water Diversion Project (MRP) is an important water supply for 20 large cities and 100 counties in Northern China. However, since 2016, the growth of large filamentous algae clusters has threatened the safety of the main canal water supply and water quality. In this study, a field investigation, monitoring, and hydrodynamic simulation were performed to analyze the hydrodynamic habitat conditions in areas with vigorous algae growth and establish a relationship between the hydrodynamic habitat conditions of the main canal and the growth, distribution, and correlation of macrobenthic algae in the main canal. The results showed that: (1) algae zones in the main canal are more likely to appear along curves, and the largest algal zone was at the front of the large curved section; (2) the length of the algae growth zone is related to the flow rate; and (3) a lower flow velocity in the main canal facilitates faster growth of an algae zone. This study provides specific and effective suggestions for the key prevention and control positions, which has important guidance on improving the efficiency of algae control in the main canal.

Shipwrecks and underwater objects of the southern Baltic – Hard substrata islands in the brackish, soft bottom marine environment

Objects of anthropogenic origin submerged in the sea, such as shipwrecks, may induce significant environmental changes in their close proximity. There may be more than 100 000 shipwrecks in the Baltic Sea, however to date, their effects on biodiversity by the introduction of large hard substrates in this typically low-evenness, species-poor ecosystem have received little attention. This study compared separately macrobenthic assemblages found on three different objects (an old torpedo house, a former submarine and a minesweeper) lying at various depths (2–21 m) in Puck Bay (the Gulf of Gdańsk, Baltic Sea), and corresponding assemblages in soft sediments from their close (5 m away) and far vicinity (50 m away). A total of 26 taxa of macrobenthic algae, vascular plants and fauna were recorded. Nineteen species were found directly on the study objects. Nine species among them were only found on the submerged objects but none was substrate specific. At two locations clear differences in the assemblage structure between seabed in the close proximity of submerged objects and the seabed located farther apart were noted. Higher species richness, abundance and diversity (measured as Shannon-Wiener H′) was recorded only in the location of the deepest object. Its high similarity (both in terms of the assemblage structure and S, N, H’) with the closest neighbouring sediments may indicate a direct impact of the object on the surrounding seabed. The submerged objects generally supported a two - three times higher number of species and a ∼25 times higher number of individuals (but not diversity) than the soft bottom in the vicinity. The shallowest object lying within the euphotic zone hosted the most species rich (on avg. 10 species/144 cm2) and abundant (on avg. 379 ind./144 cm2) assemblages. Differences in the assemblage structure found between different objects are most likely associated with depth related environmental variables. The results of the study can serve as a baseline for future investigations and for evaluation of local ecological effects of the artificial reef concepts, breakwaters and offshore wind farms.

Massive Occurrence of the Harmful Benthic Dinoflagellate Ostreopsis cf. ovata in the Eastern Adriatic Sea.

In September 2015, a massive occurrence of the Ostreopsis species was recorded in central Adriatic Kaštela Bay. In order to taxonomically identify the Ostreopsis species responsible for this event and determine their toxin profile, cells collected in seawater and from benthic macroalgae were analyzed. Conservative taxonomic methods (light microscopy and SEM) and molecular methods (PCR-based assay) allowed the identification of the species Ostreopsis cf. ovata associated with Coolia monotis. The abundance of O. cf. ovata reached 2.9 × 104 cells L−1 in seawater, while on macroalgae, it was estimated to be up to 2.67 × 106 cells g−1 of macroalgae fresh weight and 14.4 × 106 cells g−1 of macroalgae dry weight. An indirect sandwich immunoenzymatic assay (ELISA) and liquid chromatography–high-resolution mass spectrometry (LC-HRMS) were used to determine the toxin profile. The ELISA assay revealed the presence of 5.6 pg palytoxin (PLTX) equivalents per O. cf. ovata cell. LC-HRMS was used for further characterization of the toxin profile, which showed that there were 6.3 pg of the sum of ovatoxins (OVTXs) and isobaric PLTX per O. cf. ovata cell, with a prevalence of OVTXs (6.2 pg cell−1), while the isobaric PLTX concentration was very low (0.1 pg cell−1). Among OVTXs, the highest concentration was recorded for OVTX-a (3.6 pg cell−1), followed by OVTX-b (1.3 pg cell−1), OVTX-d (1.1 pg cell−1), and OVTX-c (0.2 pg cell−1).

Hydrodynamic Controls on Primary Producer Communities in Spring‐Fed Rivers

AbstractIn many spring‐fed rivers, benthic macroalgae and periphytic algae are increasing and, in some cases, replacing rooted vascular plants, which are critical to ecosystem function. While most research has focused on the role of nutrients in driving this change, in‐channel hydrodynamics also control vascular plant and algal abundances and their interactions. Understanding relationships between hydrology and primary producers is essential for developing ecologically relevant flow regulations. We investigated the relationship between flow velocity and primary producer abundance in spring‐fed rivers using observational data from 16 springs to determine critical velocity thresholds for periphyton, macroalgae, and vascular plants. We also used flow suppression experiments to quantify periphyton growth rates and test for hysteretic behavior. Results suggest a critical velocity of 0.22 m/s (95% CI: 0.13–0.28 m/s) for periphyton but no specific thresholds for macroalgae or vascular plants. Experimental and theoretical results supported these findings and suggest periphyton establishment is not hysteretic.

Impact of wastewater treatment plant discharges on macroalgae and macrofauna assemblages of the intertidal rocky shore in the southeastern Bay of Biscay

Rocky intertidal habitats are particularly vulnerable to anthropogenic pressures especially in areas with high urban concentrations such as southeastern Bay of Biscay. This research aims to establish an assessment of the potential impact of sewage discharges on intertidal rocky benthic assemblages on macroalgae and on macrofauna as required by the European Directives (Water Framework Directive -WFD and Marine Strategy Framework Directive -MSFD). The assemblages were sampled at five locations according to a control-impact design. A moderate detectable effect of discharges was highlighted on the assemblage structure by means of multivariate analyses but this was less evident using other biological and ecological metrics. Results would also suggest that benthic macroalgae constitute for the study area the best relevant biotic component to assess the effect of this pressure on the intertidal rocky platform habitats. Changes in the relative abundance of Ceramium spp., Corallina spp. and Halopteris scoparia were mainly responsible of the dissimilarities found. Finally, a pseudo-ecological quality ratio, based on the current WFD metrics, was also calculated for each site within locations (i.e. each distance from the outfall) to assess its sensitivity to this type of pressure. Results were conformed with those of the WFD monitoring because the un- or less-impacted sites were ranked as “Good” contrary to the others ranked as “Moderate”. Thus, this work provides additional information for the MSFD and bridges deficiencies emphasized by Directives on the response of biological indicators to various pressures and the biocenosis of southeastern Bay of Biscay.

Density of benthic macroalgae in the intertidal zone varies with surf zone hydrodynamics

ABSTRACTSurf zone hydrodynamics influence subsidies (larval settlers and phytoplankton food) to the intertidal zone; subsidies have been observed to be much higher at more dissipative shores compared to reflective shores. Benthic macroalgal populations may be favoured at more reflective surf zones due to slower water exchange with the coastal ocean, facilitating retention of spores. In addition, larval invertebrate settlers are far less abundant at more reflective surf zones, and benthic macroalgae may experience lower competition from sessile invertebrates for space. We used surf zone width as an indictor of surf zone hydrodynamics; surf zones are wider at more dissipative surf zones compared to reflective surf zones. We tested the hypothesis that as surf zone width increases, macroalgal density would decrease. We used aerial near-infrared and visible light images to calculate the normalised difference vegetation index (NDVI) at eight intertidal sites along the Oregon coast and compared NDVI with algal biomass (dry and wet weight per square metre) at each specific location; linear regressions between NDVI and dry and wet algal biomass were significant (P < 0.01); NDVI was an accurate indicator of macroalgal density. Surf zone width was measured using Google Earth images. NDVI and dry and wet algal biomass were significantly lower at wider surf zones (P < 0.01). Although the mechanism underlying this relationship is unknown, the intertidal macroalgal community clearly varied with surf zone hydrodynamics as indicated by surf zone width.

Impacts of gastropods on epiphytic microalgae on the brown macroalga Himantothallus grandifolius

AbstractChemically defended benthic macroalgae that dominate shallow, hard bottom communities along the western Antarctic Peninsula support very high densities of mesograzers, particularly amphipods but also small gastropods. Previous studies have demonstrated that the macroalgae and amphipods form a mutualistic relationship. The chemically defended macroalgae provide the amphipods with a refuge from predation while the macroalgae benefit from the amphipods greatly reducing surface fouling by smaller algae. One of the three most important macroalgae in terms of overstory cover, Himantothallus grandifolius, forms huge blades that can carpet the benthos. Field observations suggest that gastropods may be higher in relative abundance in proportion to amphipods on H. grandifolius than on other overstory macroalgae. The present study documents the finding that natural abundances of gastropods on H. grandifolius maintained in mesocosms reduce fouling by microscopic algae, primarily diatoms. However, amphipods are probably also important in keeping the macroalga clean of diatoms in nature. In a smaller scale experiment, three gastropod species were differentially effective at reducing diatom coverage on H. grandifolius. The hypothesis that gastropods benefit from associating with H. grandifolius in potentially gaining a refuge from sea-star predation was also tested but not supported by the experimental results.

Green Tides: New Consequences of the Eutrophication of Natural Waters (Invited Review)

In recent decades, alongside the comparatively well-studied bloom caused by phytoplankton, a bloom of marine and fresh waters caused by littoral benthic macroalgae of three genera—Ulva, Cladophora, and Spirogyra—have become a global phenomenon. In the present review, an attempt is made to gain an understanding of why it is these taxa of green filamentous algae that start to grow rapidly in the spring in many water bodies and streams, including oligotrophic waters, and then float up from the bottom, forming floating mats (metaphyton); then their decaying masses are washed ashore and cause substantial ecological and economical losses. Peculiar and common ecological and physiological features of Ulva, Cladophora, and Spirogyra favorable for the formation of green tides are considered. Although eutrophication (the supply of nitrogen and phosphorus from agricultural lands, industrial and domestic wastewaters, and aquaculture) is the evident cause of the increase in algal biomass, it is suggested that the location of external fluxes of inorganic nutrients (surface runoff or groundwater discharge), as well as the biogenic redirection of internal fluxes of nitrogen and phosphorus from pelagial to littoral (benthification), play a key role in the formation of green tides. Measures for controlling green tides are discussed. The necessity for detailed studies of the metaphytonic form of vegetation of benthic macroalgae is emphasized. Obviously, a revision of the present concept of oligotrophic/eutrophic waters which considers only the pelagic compartments of aquatic ecosystems is required.

Water and sediment parameters at the algae culture area of Salimpur coast Chittagong

Macro-benthic algae Catenella nipae was cultured from November '06 to August '07 at the Salimpur planted mangrove area. Some physico-chemical parameters of the study area were recorded during the culture period and found as water temperature ranges from 24.0 to 31.5˚C, salinity from 6.0 to 21.0‰, dissolved oxygen (DO) from 3.8 to 5.8ml/l, water pH from 7.2 to 8.4, total dissolved solids (TDS) from 410 to 598mg/l, total suspended solids (TSS) from 50 to 118mg/l, Total alkalinity from 95 to118 ppm, NO2-N from 0.18 to 0.47mg/l, NO3-N from 0.56 to 0.69mg/l, PO4-P from 0.90 to1.10mg/l, HCO3 from 69.88 to 93.80mg/l. The soil texture of the study area was sandy clay loam. Soil organic carbon, soil organic matter, soil PO4-P, soil pH were ranges from 2.22-2.37%, 4.22-4.51%, 1.10-1.39mg/100g and 5.9-6.7 respectively. Physico-chemical parameters of both water and soil revealed that the coastal area of Salimpur could be a significant place for C. nipae cultivation.

Holding (not so) fast: surface chemistry constrains kelp bioadhesion

ABSTRACT Benthic macroalgae must attach firmly to the substrate to prevent being detached and washed away by water motion. The success of the bioadhesion system can be strongly influenced by surface chemistry and so this should be optimized for large-scale cultivation. This is especially important during the early stage of cultivation when the juveniles have little thigmotactic attachment, which is needed to interlock with surface rugosity. Juvenile sporophytes of Saccharina latissima (Phaeophyceae) were directly applied onto polymer films of varied surface composition to determine how the attachment force of the developing holdfast was influenced by surface chemistry. Eight polymer chemistries were examined: polyamide (PA), polyethylene (PE), polyester (PES), polypropylene (PP), polymethylacrylate (PMA), polyvinylalcohol (PVA), polyvinylchloride (PVC) and thermoplastic polyurethane (TPU). The PP and PE were also examined as three grades: commercial grade with additives, pure polymer, or pure polymer following a corona treatment. Additive inclusion and corona significantly reduced the water contact angle (p < 0.0001), indicating an increase in the surface free energy available for bioadhesion. After 6 weeks, the attachment force was greatest on PVA, PA and PVC (0.19–0.33 N), correlating strongly with the achieved biomass (R2 = 0.68). Additives and corona treatment improved holdfast attachment force, particularly corona treated PE (0.28 ± 0.08 N: 0 N without corona). Generally, attachment force appeared greatest on chemistries with a contact angle of 60–75°. These results confirm that the bioadhesion of the phaeophyte holdfast is strongly influenced by the surface free energy of the substrate chosen. Through alteration of the additive composition, attachment could be improved to create bespoke cultivation substrates. Corona treatment is highlighted as a very suitable method for improving holdfast attachment force during cultivation.

Controls on iron(II) fluxes into waterways impacted by acid mine drainage: A Damköhler analysis of groundwater seepage and iron kinetics

When acidic groundwater flows into an aquatic system the sediment water interface (SWI) acts as a transition zone between the groundwater and lake water, and often exhibits strong physical and biogeochemical gradients. The fate of groundwater-borne solutes, such as Fe(II), is determined by the balance between the exposure time during transport across the SWI and the reaction time within the SWI, however the relative role of groundwater seepage rates and iron kinetics on acidity generation in lakes is unknown. Porewater seepage velocities, porewater chemical profiles, and limnological data were collected across multiple field campaigns over the last two decades, in acid Mine Lake 77, in Lusatia, Germany. This rare data set was analyzed using a Damköhler approach that compares exposure and reactions timescales, to determine that Fe(II) would typically be transported with little reaction across the SWI, spatially separating it from sediment-processes that produce alkalinity and providing a source of acidity to the lake. This Damköhler analysis further showed that remediation should be focused on reducing groundwater seepage velocities and enhancing exposure times. Strategic planting of submerged benthic macroalgae would slow groundwater inflows, as well as oxygenating overlying waters and supplying organic matter to the sediments. A similar Damköhler analysis could be used to assess the fate of any groundwater-borne reactive chemicals (e.g. phosphorus) into lakes and streams.

The Critical Importance of Rhodoliths in the Life Cycle Completion of Both Macro- and Microalgae, and as Holobionts for the Establishment and Maintenance of Marine Biodiversity

Rhodoliths are the main hard substrata for the attachment of benthic macroalgae in the NW Gulf of Mexico rubble habitats that are associated with salt domes, unique deep bank habitats at ~50-90m depth on the continental shelf offshore Louisiana and Texas. With the advent of additional sequencing technologies, methodologies for biodiversity assessments are now rapidly shifting to DNA metabarcoding, i.e. High Throughput Sequencing (HTS) of environmental DNA mixtures with standardized molecular markers, such as 16S V4, for rapid, cost-effective biodiversity measurement. We newly tested 16S V4 metabarcoding on endolithic portions of mesophtic rhodoliths exhibiting low phototroph colonization that revealed a hidden, cryptic algal diversity targeting spores, propagules, and unsuspected life history stages. We explored cryo-SEM as a potentially more informative method than regular SEM to minimize artefacts of sample preparation in the study of endolithic cell inclusions which brought to light a suite of microalgal stages. We were able to differentiate floridean starch from cellular inclusions. We associated the effect of anatomical growth pattern on presence or absence of cellular inclusions in biogenic rhodoliths. Analyses of combined 16S V4 metabarcodes and 16S Sanger sequences of two red algal orders, the Halymeniales and Bonnemaisoniales, increased the established record of diversity in the region. We view rhodoliths as marine biodiversity hotspots that may function as seedbanks, temporary reservoirs for life history stages of ecologically important eukaryotic microalgae, or as refugia for ecosystem resilience following environmental stress.

Macroalgas submareales de los canales interiores del Parque Nacional Bernardo O&amp;#8217;Higgins (~49°- 51° S), región de Magallanes, Chile

The Bernardo O’Higgins National Park (BONP) covers a total area of 3,525,901 hectares, where a great diversity of terrestrial and marine habitats converges. Its coastal area is characterized by a complex system of Patagonian Channels and Fjords. This marine ecosystem does not have an ecological simile with other along the Souther Pacific coast, with a high biodiversity in its marine biota, specifically in its marine benthic algae. There are few or almost no scientific contributions regarding which species of macroalgae inhabit this conservation area between ~ 49° - 55° of South latitude. Therefore, the aim of this work was to be a first qualitative approximation of macroalgae flora in these coastal systems of BONP. In order to corried out the objetive of this work, qualitative subtidal samplings in mover delante de qualitative stations on the coast of the BONP, through SCUBA diving during the summer of 2010. A total of 64 taxa were of subtidal benthic macroalgae belong to 31 families. The most diverse taxa was the Delesseriaceae (8 species), followed by Ceramiaceae (7 species) and Ulvaceae (7 species). In addition, we observed that Macrocystis pyrifera is the dominant subtidal macroalgae species in the whole study area. This work contributed to the phycological knowledge of the Subantarctic ecoregion. However, it is necessary to continue developing research effort in the area, which without a doubt would provide more records to those already achieved.

Hydrocarbon potential and depositional environment of the Lower Cretaceous black mudstones and shales in the coastal Guangdong Province, China

Abstract The Mesozoic (especially the Cretaceous) sequences in the northern South China Sea (SCS) are important potential targets of oil and gas exploration; however, they are currently poorly understood. We use organic petrology and geochemistry to evaluate the hydrocarbon potential and study depositional environment of the Cretaceous black mudstones and shales from the Dayawan Section in the Guangdong Province, China. These mudstones and shales yield total organic carbon (TOC) contents of 0.63%–2.76% and most samples meet the requirement for higher TOC source rocks. Organic matters in the mudstones and shales were sourced mainly from higher plants as well as subordinate benthic macroalgae. Organic petrology and geochemical data suggested that the organic matters were dominated by Type-III and minor Type-II, and generally have low thermal maturity. Thus, we evaluated the black mudstones and shales have a potential for hydrocarbon generation (especially gas prone). Pr/Ph, trace elements, and mixture source of organic matter suggested that these black mudstones and shales formed in a coastal–lacustrine environment, characterized by weakly oxidizing−weakly reducing conditions and low-salinity. A marine transgression developing in the middle part of the section was recognized. Generally, the northern SCS, which exhibits the more marine influence, likely contains source rocks with higher TOC contents and better organic matter types. The Cretaceous source rocks with higher liquid hydrocarbon generation potential may occur locally in the Pearl River Mouth Basin.

Photosynthesis by marine algae produces sound, contributing to the daytime soundscape on coral reefs.

We have observed that marine macroalgae produce sound during photosynthesis. The resultant soundscapes correlate with benthic macroalgal cover across shallow Hawaiian coral reefs during the day, despite the presence of other biological noise. Likely ubiquitous but previously overlooked, this source of ambient biological noise in the coastal ocean is driven by local supersaturation of oxygen near the surface of macroalgal filaments, and the resultant formation and release of oxygen-containing bubbles into the water column. During release, relaxation of the bubble to a spherical shape creates a monopole sound source that ‘rings’ at the Minnaert frequency. Many such bubbles create a large, distributed sound source over the sea floor. Reef soundscapes contain vast quantities of biological information, making passive acoustic ecosystem evaluation a tantalizing prospect if the sources are known. Our observations introduce the possibility of a general, volumetrically integrative, noninvasive, rapid and remote technique for evaluating algal abundance and rates of primary productivity in littoral aquatic communities. Increased algal cover is one of the strongest indicators for coral reef ecosystem stress. Visually determining variations in algal abundance is a time-consuming and expensive process. This technique could therefore provide a valuable tool for ecosystem management but also for industrial monitoring of primary production, such as in algae-based biofuel synthesis.

Effects of green turtle grazing on seagrass and macroalgae diversity vary spatially among seagrass meadows

Seagrass meadows are often comprised of diverse assemblages of seagrasses and algae. Green turtles (Chelonia mydas) are a prominent megaherbivore in seagrass meadows—capable of consuming large amounts of aboveground seagrass biomass and driving shifts in seagrass species dominance. Previous green turtle grazing studies have focused on diversity and dynamics of seagrasses, but there has been little focus thus far on diversity of other primary producers within meadow communities. We investigated the effects of grazing on seagrasses and benthic macroalgae composition by surveying a series of seagrass meadows across two separate bays in Little Cayman, Cayman Islands, in which green turtles had established foraging areas. Effects of grazing on diversity were spatially variable among meadows. Diversity of the seagrass and macroalgae community (Simpson’s Index) was not significantly different between areas grazed by turtles compared to ungrazed areas in one surveyed bay but was significantly lower among grazed areas in the other bay. Lower diversity was the result of lower densities of all seagrass and macroalgae species other than Thalassia testudinum among grazed areas in one bay. Diversity was also positively correlated with densities of total seagrass and total macroalgae across all meadows. Density of the dominant seagrass, T. testudinum, did not differ between the two bays or between grazed and ungrazed areas. As green turtle abundance increases and more seagrass meadows return to a naturally grazed state, it is important to understand the effects grazing has in these ecosystems and how effects may vary among locations.

Marine environmental vulnerability and cumulative risk profiles to support ecosystem-based adaptive maritime spatial planning

Abstract Human use of marine and coastal areas is increasing worldwide, resulting in conflicts between different interests for marine space, overexploitation of marine resources, and environmental degradation. In this study we developed a methodology that combines assessments of marine environmental vulnerability and cumulative human pressures to support the processes of ecosystem-based adaptive maritime spatial planning. The methodology is built on the spatially explicit marine environmental vulnerability profile (EVP) that is an aggregated product of the distribution of essential nature values (habitat-forming benthic macroalgal and invertebrate species, benthic species richness, birds and seals as top marine predators) and their sensitivities to disturbances. The marine environmental cumulative risk profile (ERP) combines the EVP and the HELCOM Baltic Sea Pressure Index (BSPI), the latter representing the spatial distribution of intensities of cumulative anthropogenic pressures. The ERP identifies areas where environmental risks are the highest due to both long recoveries of the biota and high intensities of human pressures. This methodology can be used in any other sea areas by modifying the list of nature values, their sensitivity to disturbances, and the intensities of human pressure.

Mud-entrained macroalgae utilise porewater and overlying water column nutrients to grow in a eutrophic intertidal estuary

Sediment porewater nutrients often occur at concentrations that are orders of magnitude higher than nutrients in overlying waters, and accordingly may subsidise growth of benthic macroalgal mats in estuarine ecosystems. The relative contribution of porewater nutrients is expected to be particularly important for macroalgae entrained in intertidal mudflat sediments, where access to water column nutrients is tidally constrained. In this study, filamentous Gracilaria chilensis thalli were simultaneously exposed to sediment and overlying water nutrient sources, labelled using 15N tracers (15NH4+ or 15NO3−) during a 5-day experiment. Dissolved inorganic N (DIN) uptake from porewater and overlying water accounted for 33 and 52%, respectively, of the N estimated as necessary to support the growth of G. chilensis, despite the two-fold lower DIN concentration of the overlying water and its periodic availability (8 h day−1). Of the total N assimilated by the plants, ~ 15% could not be accounted for, supporting the acquisition of other N forms in order to meet demand. We also found that regardless of background NH4+:NO3− ratios (i.e. 1:3 in overlying water and 12:1 in porewater), plants accumulated 15NH4+ significantly more readily than 15NO3−, indicating a preference for NH4+. This ability to utilise multiple sources and species of N relatively rapidly may partly explain the competitive success of entrained macroalgae relative to non-entrained species and historically abundant seagrass beds in these environments. These results underscore the significance of both internal nutrient loading and external inputs as important in sustaining opportunistic macroalgal blooms in shallow estuaries.