Macroalgal Communities Research Articles

Биосорбция техногенных радионуклидов баренцевоморской литоральной водорослью Fucus vesiculosus L.

The authors have conducted laboratory experiments to study the ability of the Barents Sea brown alga Fucus vesiculosus L. to adsorb technogenic radionuclides from seawater of various salinity (8, 18 and 35 psu). They have obtained new data on the role of macroalgae communities in the geodynamics of radionuclides in the coastal zone of the seas. Fucuses are able to adsorb 40—80% of the radionuclide activity from water. The maximum intensity of adsorption is observed during the first day of exposure. The alga most effectively absorbs 152Eu, 241Am, 65Zn, 54Mn from water. The possibility of using the alga as a sorbent in biobarriers in incidents with emergency discharges of radioactivity into the sea is shown.

Community gross primary production and respiration in epilithic macroalgae and Posidonia oceanica macrophytodetritus accumulation in the Bay of Revellata (Corsica)

We report estimates of community gross primary production (GPP), community respiration (CR), and net community production (NCP) based on the change of dissolved O2 during incubations over epilithic turf-forming macroalgae (Halopteris scoparia, Padina pavonica, and Dictyota dichotoma) on 7 occasions and in accumulations of Posidonia oceanica macrophytodetritus (i.e. litter) on 8 occasions in the Bay of Revellata (Corsica) from March 2009 to May 2011. In the epilithic macroalgae community, GPP ranged between 7.8 and 82.2 mmol O2 m−2 d−1, CR ranged between −108.5 and −13.6 mmol O2 m−2 d−1, and NCP ranged between −53.2 and −5.7 mmol O2 m−2 d−1. In the P. oceanica macrophytodetritus accumulation, GPP ranged between 5.7 and 91.6 mmol O2 m−2 d−1, CR ranged between −112.8 and −27.2 mmol O2 m−2 d−1, and NCP ranged between −46.8 and −9.9 mmol O2 m−2 d−1. GPP in both the epilithic macroalgae community and the P. oceanica macrophytodetritus accumulation peaked in summer and was lowest in fall, following the seasonal variation of incoming light. GPP correlated to macroalgal biomass but was unrelated to the biomass of living macroscopic plant material in the P. oceanica macrophytodetritus accumulation. The annual average of GPP was equivalent in the epilithic macroalgae and P. oceanica macrophytodetritus accumulation communities (17.6 and 19.4mol O2 m−2 yr−1). Both the epilithic macroalgae community and the P. oceanica macrophytodetritus accumulation were net heterotrophic with an annual average NCP of −6.1 and −8.8mol O2 m−2 yr−1, respectively. The NCP of the adjacent P. oceanica meadow at 10 m depth based on simultaneous measurements based on the open water O2 mass balance from moored O2 probes (optodes) was 28.9mol O2 m−2 yr−1. The potential export of dissolved organic carbon from the P. oceanica meadow could quantitatively meet the carbon demand to sustain the net heterotrophy of the adjacent epilithic macroalgae community in the Bay of Revellata. We also show the limitation and possibly over-estimation of extrapolating decay rates based on litter bag experiments with small quantities of material to “real” macrophytodetritus biomass densities.

Perbandingan Komposisi dan Struktur Komunitas Makroalga antara Pulau Semak Daun dan Pulau Pramuka di Taman Nasional Kepulauan Seribu, DKI Jakarta

Kepulauan Seribu have diverse biodiversity, one of which is macroalgae located in the Tourism Utilization Zone and the residential zone. Environmental factors, such as substrate, water quality and the presence of human activities, are very different on each island. The purpose of this study was to determine the differences in the composition and structure of macroalgae communities on islands in the Tourism Utilization Zone, Semak Daun Island and islands in the Settlement Zone, Pramuka Island. Settlement Zone, Pramuka Island. The method used is a quadrat transect. 16 types of macroalgae were found on Semak Daun Island and 26 types of macroalgae on Pramuka Island. The diversity value on Semak Daun Island is categorized as moderate with a value of 1.84 and on Pramuka Island is categorized as moderate with a value of 2.64. The highest INP value on Semak Daun Island is Sargassum binderi and the highest INP on Pramuka Island is Halimeda macroloba.

Nursery provision of red-algal habitats in temperate Algoa Bay, South Africa

This study examines the importance of both macroalgal heterogeneity and specific macroalgal species or morphotypes to nursery provision for juvenile sparids (Diplodus capensis and Sarpa salpa) in a shallow (< 2 m), sheltered rocky cove in warm-temperate Algoa Bay, South Africa. The rocky cove is comprised of a mosaic of two main benthic habitats; canopy-forming Plocamium corallorhiza beds on rocky outcrops and flat reef dominated by low growing red algae morphotypes. We assessed macroalgal communities and the trophic ecology (stomach contents and isotopes), abundance and size structure of D. capensis and S. salpa in the two different benthic habitats and the resources/food associated with the dominant macroalgae species/morphotypes. We found high densities of S. salpa and D. capensis, in both high profile reef (rocky outcrops) and low profile (flat) reef. Within this habitat mosaic resources (epiphytes and macroinvertebrates) were more abundant in the non-canopy forming low growing macroalgae (Laurencia spp. and coralline turf algae) and these algae were also assimilated in the diets of both sparids. The high abundance of both juvenile S. salpa and D. capensis in high profile and low profile reef, suggests that within this mosaic of habitats these species may be using canopy-forming algae in the high profile reef for shelter and non-canopy forming algae in both the high and low profile reef for food. This shows that macroalgal habitats comprising several morphotypes have the potential to support higher juvenile diversity and abundance through both food provision and shelter.

Evaluation of the ecological quality of the macroalgal communities along the Algerian coast (Algeria, Mediterranean Sea)

The assessment and preservation of the marine environment, particularly coastal ecosystems, has emerged as a global priority. In this study, the rocky bottom quality (CFR) index, which is based on macroalgae composition and abundance, was used to assess the ecological quality of coastal waters at six sites along the Algerian coast that represent a wide range of anthropogenic pressures. The sensitivity of the CFR index to the anthropogenic pressure index (MALUSI) was also assessed. Multivariate analyses (DCA, nMDS, cluster, SIMPER, and PCA) were used to assess the variability of macroalgal community structure. The CFR index calculated for this study was compared to the EEI-c and CARLIT indices. The CFR index classified the study sites based on ecological quality: good to high quality in the western sites (Ténès, Kouali1, and Kouali2) and moderate quality in the central sites (Fontaine, Fort de l’eau, and Surcouf). The findings indicate that the CFR and MALUSI indices are highly correlated. The abundance and composition of macroalgal communities are useful indicators of rocky shore quality, as demonstrated by structural analyses of characteristic macroalgae and opportunistic species. The competitive characteristic macroalgae of the Cystoseira sensu lato species were found to be associated with sites of good and high ecological quality. Stress-tolerant characteristic macroalgae (Pachymeniopsis lanceolata, Ellisolandia elongata, and Halopteris scoparia) and opportunistic ruderal species (Ulva rigida, Ulva lactuca, and Ulva linza) were found in sites with moderate ecological quality. The CFR index was compared with the EEI-c and CARLIT indices, and it can be noted that the three indices use different spatial scales, biological levels and species classifications. Therefore, CFR, EEI-c, and CARLIT indices are useful tools for assessing the quality of coastal waters.

Habitat characteristics shaping zoantharians’ distribution at intertidal habitats of the Canary Islands

Ocean warming is facilitating the proliferation of zoantharians worldwide due to their thermophilic affinities. However, other anthropogenic factors, such as declining water quality, have been appointed to favour the occurrence of zoantharians dominated areas and barrens. Subtropical and tropical intertidal habitats are especially vulnerable to zoantharians outbreaks due to the progressive increase in ocean temperature and because it is where most human pressure is concentrated. The aim of this study was to evaluate the abundance of intertidal zoantharians populations, related to habitat characteristics (rugosity and submerged substrate) and the presence of other benthic organisms, such as sessile invertebrates and macroalgae. Number and coverage of zoantharian colonies were recorded in transects (20 × 4 m) along 25 intertidal rocky platforms of the Canarian Archipelago, and photographic techniques in quadrats were used to examine the relationships between the percentage of substrate cover of zoantharians, macroalgae and sessile invertebrates by means of correlations analyses. Results indicated that high levels of rugosity favour the abundance and coverage of Palythoa aff. clavata and Zoanthus pulchellus, and the proportion of submerged substrate was also important in determining Zoanthus coverages. The presence of extensive macroalgae communities was seen to reduce zoantharian coverages, being the only sessile organisms that were able to outcompete them for space in the Canary Islands. Thus, this study provided valuable information about patterns of abundances and coverages of intertidal zoantharians useful for future monitoring of intertidal populations of zoantharians in Canary Islands and their interaction with surrounding marine organisms.

Contrasted trends of intertidal macroalgal communities and sharp decline of canopy-forming species across two decades

Macroalgal communities are essential to coastal ecosystems, yet increasing effects of global change and anthropogenic pressures are leading to their global decline. Investigating the long-term dynamics of these communities across different localities appears crucial to better understand their responses to such pressures, as our knowledge of spatial heterogeneities in macroalgal trajectories remains elusive. To fill this gap, the community trajectory analysis framework provides a set of innovative multivariate metrics to characterize and quantitatively compare the temporal dynamics of different communities. Using long-term monitoring data (2004-2022), this method was applied to intertidal macroalgal communities across 10 locations distributed over more than 500 km of coastline in Brittany, France. Three distinct temporal dynamics were identified. High-shore communities exhibited minimal changes over time, while low-shore communities were characterized by a fluctuating understorey species composition but a general stability pattern. In contrast, the mid-shore community dominated by Ascophyllum nodosum underwent conspicuous changes in composition and structure. Further analysis of the latter community unveiled clear spatial patterns, with a significant deterioration of the structural state attributed to canopy loss in eastern Brittany, negatively impacting understorey species. This decline may ultimately lead to massive changes in coastal ecosystem functioning and services. This study emphasizes the importance of maintaining long-term ecological monitoring as well as the pertinence of temporal trajectories methods to identify and understand community changes at various spatial scales.

Size‐specific reduction in kelp consumption by New Zealand urchins exposed to chemical cues from the red rock lobster

AbstractSea urchins can strongly reduce their mobility, exposure to predation, and feeding rates upon detection of chemical cues produced by predators, driving behavioral effects on grazing activity that may contribute to macroalgal community dynamics. However, the extent of chemically induced antipredator behaviors in urchins can vary by predator–prey species pair and ecological context and is therefore important to characterize in novel settings. Additionally, the effect of predator and prey size on urchin reactions to predator cues has rarely been considered, with the few existing examples yielding mixed conclusions. Here, we used a replicated split‐plot experiment to measure the effects of red rock lobsters (Jasus edwardsii) on consumption of macroalgae by the New Zealand sea urchin (Evechinus chloroticus) across a range of predator and prey body sizes. Overall, per‐capita consumption rates of kelp by urchins declined by 30% in the presence of lobsters, though feeding activity varied widely among individuals. Based on mass‐specific measurements of feeding rates, responses to predator cues appeared similar across all urchin sizes but only yielded distinguishable differences in the amount of kelp consumed in trials with larger urchins due to their considerably higher feeding capacity. Conversely, consumption rates of kelp by urchins had no apparent relationship with lobster size, likely due to chemical cue saturation in our experimental setting or a risk gradient that was insufficient to elicit a graded behavioral response. Our findings provide new evidence for a nonconsumptive effect of lobsters on feeding rates of an important grazer that can potentially reinforce the ecological role of this key predator in New Zealand kelp beds.

Effects of material type and surface roughness of settlement tiles on macroalgal colonisation and early coral recruitment success

Sexual propagation of corals is a promising strategy for coral restoration, but one of the main challenges is the high mortality of coral spat due to competitive interactions with macroalgae during the early life history stages. Optimising the properties of settlement substrates such as material types and surface roughness has the potential to improve the survival of spat by limiting the recruitment and growth of macroalgae. In this study, we assessed the effects of modifying surface roughness across three different tile materials (alumina-based ceramic, calcium carbonate (CaCO3), and concrete) on the settlement success and post-settlement survivorship of Acropora kenti coral larvae in six mesocosm tanks, each with different established macroalgal communities. The macroalgal community compositions on the tiles were significantly different among material types, but not surface roughness, although the type and abundance of macroalgal species were heavily influenced by the established tank communities. Increasing surface roughness did not affect larval settlement success or spat survivorship. Substantially higher larval settlement density was found on concrete tiles (1.92 ± 0.10 larvae cm−2), but spat survival was the highest on CaCO3 tiles (73.4 ± 4.2% survived). Very strong competitive interactions were observed between spat and macroalgae, with overgrowth by the crustose coralline alga Crustaphytum sp. and the brown alga Lobophora sp. being the primary cause of spat mortality. Overall, when taking into account both settlement and survival rates, concrete was the best performing among the tile types tested here.

Kelp forest community structure and demography in Kongsfjorden (Svalbard) across 25 years of Arctic warming.

The Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience a continuous increase in seawater temperature and glacial melt while sea-ice cover declines. In 1996/1998, 2012-2014, and 2021 macroalgal biomass and species diversity were quantified at the study site Hansneset, Kongsfjorden (W-Spitsbergen) in order to identify potential changes over time. In 2021, we repeated the earlier studies by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0, 2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m-2 at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the depth transect in 2021 was not significantly different compared to 2012/2013, the digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed into an Alaria esculenta-dominated kelp forest. Consequently, a pronounced shift in kelp forest structure occurred over time as we demonstrate that biomass allocation to thallus parts is kelp species-specific. Over the past decade, kelp demography changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth limits of all dominant brown algae declined noticeably over the last 25 years while the red algal flora abundance remained unchanged at depth. We propose that the major factor driving the observed changes in the macroalgal community are alterations in underwater light climate, as insitu data showed increasing turbidity and decreasing irradiance since 2012 and 2017, respectively. As a consequence, the interplay between kelp forest retreat to lower depth levels caused by coastal darkening and potential macroalgal biomass gain with increasing temperatures will possibly intensify in the future with unforeseen consequences for melting Arctic coasts and fjord ecosystem services.

From micro to mesoscale: Understanding the influence of macroalgal communities on Ostreopsis Schmidt blooms

Harmful Algal Blooms (HABs) are increasing in temperate areas, and the growth rates of benthic harmful dinoflagellates may be favoured in the context of global climate change. Benthic dinoflagellates, including species belonging to the Ostreopsis Schmidt genus, are known to develop on the surface of macroalgae and different macroalgal morphotypes and communities could host higher or lower cell abundances. The physical structure of the macroalgal substrate at the small scale (cm, microhabitat scale) and the structural complexity of the macroalgal community at the medium scale (few m, mesohabitat scale) could play a relevant role in bloom facilitation: the hypothesis that Ostreopsis species could be associated with macroalgal turfs and shrubs, structurally less complex communities than canopy-forming macroalgae, is especially under discussion and, if confirmed, could link bloom occurrence to regime shifts in temperate ecosystems. The present study, performed in two locations of the Ligurian Sea (Rochambeau, France and Vernazzola, Italy) aimed at understanding marine vegetation's role at the micro and mesohabitat scales in controlling the distribution and abundance of Ostreopsis. The abundance of the microalgal cells was quantified at different spatial scales, from cm to a few m, on different macroalgal species and communities, including artificial substrates, to tease apart the micro and mesohabitat effects. The results obtained show a high spatio-temporal variability, potentially hiding habitat-related patterns. The substrate's preferences diminish when cell abundances are very high, as in the case of Rochambeau, while in presence of moderate cell abundances as in Vernazzola or the first phases of blooms, it is possible to appreciate differences in abundances among substrates (in our study, Dictyota fasciola (Roth) Lamouroux supporting higher abundances). Our results open new research topics such as the study of blooms at a larger scale (macrohabitat) and testing different sampling methods to standardise the cells' abundances independently on the substrate.

Productivity of mixed kelp communities in an Arctic fjord exhibit tolerance to a future climate

Arctic fjords are considered to be one of the ecosystems changing most rapidly in response to climate change. In the Svalbard archipelago, fjords are experiencing a shift in environmental conditions due to the Atlantification of Arctic waters and the retreat of sea-terminating glaciers. These environmental changes are predicted to facilitate expansion of large, brown macroalgae, into new ice-free regions. The potential resilience of macroalgal benthic communities in these fjord systems will depend on their response to combined pressures from freshening due to glacial melt, exposure to warmer waters, and increased turbidity from meltwater runoff which reduces light penetration. Current predictions, however, have a limited ability to elucidate the future impacts of multiple-drivers on macroalgal communities with respect to ecosystem function and biogeochemical cycling in Arctic fjords. To assess the impact of these combined future environmental changes on benthic productivity and resilience, we conducted a two-month mesocosm experiment exposing mixed kelp communities to three future conditions comprising increased temperature (+ 3.3 and + 5.3°C), seawater freshening by ∼ 3.0 and ∼ 5.0 units (i.e., salinity of 30 and 28, respectively), and decreased photosynthetically active radiation (PAR, - 25 and - 40 %). Exposure to these combined treatments resulted in non-significant differences in short-term productivity, and a tolerance of the photosynthetic capacity across the treatment conditions. We present the first robust estimates of mixed kelp community production in Kongsfjorden and place a median compensation irradiance of ∼12.5 mmol photons m−2 h−1 as the threshold for positive net community productivity. These results are discussed in the context of ecosystem productivity and biological tolerance of kelp communities in future Arctic fjord systems.

First catalogue of benthic marine macroalgae from glacier-influenced environments of the Beagle Channel, deposited in the new Sub-Antarctic Cryptogamic Herbarium (SCH) of the University of Magallanes

The environmental characteristics and geomorphological landscape in the sub-Antarctic Magellanic ecoregion underpin a biological diversity that evolved adapting to the microhabitats produced by these heterogeneous ecological conditions. The high level of endemism found in these biological communities is nowadays protected thanks to the creation of the Cape Horn Biosphere Reserve (CHBR), a natural laboratory at the southern end of the sub-Antarctic Magellanic ecoregion. Studies produced in this region offer a valuable knowledge of its biological, ecological and cultural facets in a state still scarcely impacted by anthropogenic activities. The retreat of glaciers present along the channels and fjords of the CHBR due to global climate change impacts the marine benthic and macroalgae communities hosted in these water bodies. European expeditions in the 18th and 19th centuries pioneered the works which provided our current knowledge about this subantarctic marine flora. Nevertheless, there is still a gap of taxonomic information of macroalgae diversity in the CHBR. To solve this gap, with support of the Cape Horn Internationional Center (CHIC), we created the Sub-Antarctic Cryptogamic Herbarium (SCH) hosted at the Antarctic and Sub-Antarctic Marine Ecosystems Laboratory (LEMAS), University of Magallanes. In 2020, the New York Botanical Garden indexed the SCH in its Index Herbariorum. This indexation granted by this world-renowned institution places the SCH's biological collection as the world's southernmost cryptogamic repository. As such, the SCH's botanical collection is currently the only gateway to the subantarctic ecosystem's biological legacy. The catalogue below provides information about the ecological and morphological characteristics of macroalgae deposited in the SCH, with particular focus on those species present in the CHBR. We identified 54 species. Among them 23 belong to the Rhodophyta division (43%), 19 species to the Chlorophyta division (35%), and 12 species to the Ochrophyta division (22%). In the context of rapid global change, involving increasingly threatened taxa due to human impact, baseline studies and records deposited at the SCH will provide an essential tool for assessing patterns of change and defining conservation practices to protect the rich biodiversity of these sub-Antarctic ecosystems.

Spatio-temporal patterns in the biomass, species composition and nitrogen content of drift macroalgae in an urbanised coastal embayment

Understanding spatio-temporal variability in the production of drift macroalgae is useful for monitoring and assessing the influence of local anthropogenic nutrient sources on coastal ecosystems. In this study we: (1) assessed how the drift macroalgal community composition and biomass have changed over a 22-year period in Port Phillip Bay (a large coastal embayment in Victoria, Australia); and (2) measured the amount of accumulated nitrogen in drift macroalgae and the contribution of anthropogenic nitrogen sources through isotopic analysis. The surveys revealed little overlap in species composition (<13%) and a significant decrease in standing stock biomass (from 631 to 49 g m-2) between surveys (1995/1996 and 2017/2018). This was associated with a high degree of turnover (β-diversity) at the genus level between surveys (mean – 0.53), resulting in distinct communities at all sites, particularly among red algal genera. In addition, the occurrence of ephemeral macroalgal blooms and a semi-perennial mat of the red macroalga Botryocladia sonderi at 10-15 m depth at locations close to nutrient sources indicate drift macroalgae are important nutrient accumulators in the bay. Isotopic analysis revealed a high contribution of anthropogenic-derived nitrogen (δ15N > 17‰ and ~ 3% N content) at depths and locations close to nutrient sources, particularly at times of the year when large wastewater discharges occur. Harvesting of drift macroalgae could be a cost-effective solution for offsetting nitrogen inputs from anthropogenic sources, but it will be important to first investigate whether harvesting results in negative impacts to associated fauna or nutrient cycling.

Changes in maerl-associated macroalgal community dynamics as evidence of anthropogenic pressure.

Maerl-associated communities have received considerable attention due to their uniqueness, biodiversity and functional importance. Although the impacts of human activities are well documented for maerl-associated macrofauna, the spatio-temporal variations of macroalgae have comparatively been neglected, and the drivers that influence their dynamics are poorly known. We investigate the links between maerl-associated macroalgal communities, anthropogenic pressures and environmental conditions, and hypothesize that sites under human pressure would exhibit different dynamics when compared to reference sites. To better understand community variation through space and time, four subtidal maerl beds under different pressures were consistently monitored over one year in the bay of Brest, Brittany, France. Both macroalgae community monitoring and environmental data were acquired through field sampling and available models. Higher macroalgal biomass was observed within eutrophic sites, especially in summer (more than ten times higher than in the Unimpacted site), caused by free-living forms of opportunistic red macroalgae. The Dredged site also exhibited distinct macroalgal communities during summer from the Unimpacted site. Nutrient concentrations and seasonality proved to be key factors affecting the macroalgal community composition, although dredging and its effects on granulometry also had a strong influence. Over the long term, fewer than half of the species identified during historical surveys were found, indicating major temporal changes. Human pressures have strong impacts on maerl-associated macroalgal communities. Nutrient concentrations and dredging pressure appear as the main anthropogenic factors shaping maerl-associated macroalgal communities. Additionally, our results suggest historical changes in maerl-associated macroalgal communities over 25 years in response to changes in local human pressure management. This study suggests that maerl-associated macroalgal communities could be used as indicators of anthropogenically driven changes in this habitat.

Functioning of a canopy-dominated intertidal community during emersion: highly productive but heterotrophic at the annual scale

In order to address lack of data regarding coastal carbon budgets, we estimated the annual metabolic carbon budget of an intertidal rocky reef macroalgal community during emersion. This budget is based on direct in situ measurements during emersion and establishes the seasonal variations of the photosynthetic parameters of such a community. CO2 fluxes were measured hourly to study the response of community gross primary productivity (GPP) to irradiance and the variation of GPP and community respiration (CR) over the emersion period at different times of the year. These were combined together with existing monthly measures of GPP and CR hourly rates to model the variations of these fluxes as a function of irradiance and the tidal cycle throughout an entire calendar year. Daily, monthly and annual values of GPP, CR and net primary productivity (NPP) were calculated with a relatively low sensitivity to any of the parameters used. While GPP fluxes show comparable orders of magnitude to those measured in other systems, higher CR fluxes lead to a heterotrophic system during emersion, both under measured (NPP = −299 gC m−2 year−1) and theoretical irradiances (NPP = −119 gC m−2 year−1). This heterotrophy is directly linked to the light availability, varying according to combined daily, tidal and seasonal cycles, and to temperature at the seasonal scale. Measurements performed in situ at the community scale integrated interactions that are otherwise absent at the individual scale. This gives access to aspects of the functioning that cannot be otherwise identified.

Testing effects of bottom-up factors, grazing, and competition on New Zealand rocky intertidal algal communities.

Top-down and bottom-up factors and their interaction highlight the interdependence of resources and consumer impacts on food webs and ecosystems. Variation in the strength of upwelling-mediated ecological controls (i.e., light availability and herbivory) between early and late succession stages is less well understood from the standpoint of influencing algal functional group composition. We experimentally tested the effect of light, grazing, and disturbance on rocky intertidal turf-forming algal communities. Studies were conducted on the South Island of New Zealand at Raramai on the east coast (a persistent downwelling region) and Twelve Mile Beach on the west coast (an intermittent upwelling region). Herbivory, light availability, and algal cover were manipulated and percent cover of major macroalgal functional groups and sessile invertebrates were measured monthly from October 2017 to March 2018. By distinguishing between algal functional groups and including different starting conditions in our design, we found that the mosaic-like pattern of bare rock intermingled with diverse turf-forming algae at Twelve Mile Beach was driven by a complex array of species interactions, including grazing, predation, preemptive competition and interference competition, colonization rates, and these interactions were modulated by light availability and other environmental conditions. Raramai results contrasted with those at Twelve Mile Beach in showing stronger effects of grazing and relatively weak effects of other interactions, low colonization rates of invertebrates, and light effects limited to crustose algae. Our study highlights the potential importance of an upwelling-mediated 3-way interaction among herbivory, light availability, and preemption in structuring contrasting low rocky intertidal macroalgal communities.

The thermal journey of macroalgae: Four decades of temperature-induced changes in the southeastern Bay of Biscay

Global warming is triggering significant shifts in temperate macroalgal communities worldwide, favoring small, warm-affinity species over large canopy-forming, cold-affinity species. The Cantabrian Sea, a region acutely impacted by climate change, is also witnessing this shift. This study delved into the impacts of increasing sea surface temperature on the subtidal macroalgal communities in the southeastern Bay of Biscay over the last four decades, by using data from the years 1982, 2007, 2014, and 2020. We found that temperature has shaped the community structure, with warm-affinity species steadily displacing their cold-affinity counterparts. Notably, new communities exhibited a profusion of smaller algal species, explaining the observed increased biodiversity within the area. In the last period investigated (2014–2020), we observed a partial recovery of the communities, coinciding with cooler sea surface temperatures. Shallow algal communities were more reactive to temperature variations than deeper communities, possibly associated with higher exposure to increased temperatures. Our study offered insights into the intricate relationship between the changes in ocean temperature and algal species in the southeastern Bay of Biscay, shedding light on the ongoing ecological shifts in this region.

Distribution Pattern of Black Sea Cucumber (Holothuria atra Jaeger, 1833) at the Intertidal Ecosystem of Bilik Coastal, Baluran National Park

Baluran National Park (BNP) is a natural resource conservation area known for its diverse land and water ecosystems. The intertidal ecosystem of Bilik Coast is home to sea cucumbers (Holothuria atra), which have both ecological and economic value. It is important to note that H. atra is a protected species in the BNP conservation area. Therefore, studying the distribution pattern of H. atra in the intertidal ecosystem of Pesisir Bilik is crucial. This study aims to determine the type of distribution pattern of H. atra and describe its spatial distribution. Purposive sampling was conducted at maximum low tide, and biotic data were collected using the Global Positioning System (GPS) to obtain coordinates. Biotic data were measured at 9 points as a representative area. The type of distribution pattern of H. atra was analyzed using the Nearest Neighbor Index using ArcGIS 10.7 which shows the type of distribution pattern and describes its spatial distribution. The research results showed that the distribution pattern of H. atra was categorized as clustered based on the result of R (ratio) &lt; 1 (0.458). H. atra species were distributed in seagrass communities, macroalgae communities, open areas, and coral reef communities.

Floristic classification of opportunistic green macroalgae communities of the European myxomesohaline seas

Shallow-water communities of opportunistic green marine macroalgae in eutrophicated areas are currently gaining an advantage over communities dominated by other groups of macrophytes. Therefore, their classification, study of composition and observation of structural changes are of particular importance. One class (Ulvae intestinalis–Ulvetea linzae), one order (Ulvae intestinalis–Ulvetalia linzae), three alliances (Ulvae intestinalis–Ulvion linzae, Ulvae intestinalis– Ceramion virgati, Ulvae rigidae–Gelidion spinosi) and three new associations of macroalgal communities of meso- and polysaprobic sublittoral vegetation within the shelf of the Black, Azov and Baltic Seas are described for the first time, using the Braun-Blanquet approach. Principal components analysis revealed two main factors influencing the floristic composition of the investigated communities: salinity and nutrient enrichment with associated turbidity. The proposed classification of opportunistic communities of green algae should be used in assessing the dynamics of the state of vegetation during eutrophication of the aquatic environment.