Atlantic Ocean Research Articles

Influence of large-scale atmospheric circulation and Mediterranean sea surface temperature to extreme land precipitation: the case of storm Alex

Abstract Extreme (greater than 500 mm) amount of rain fell in southeastern France and northern Italy on 2nd and 3rd October 2020 during a "Mediterranean episode" triggered by the powerful extratropical cyclone Alex. Here we use a dynamical adjustment methodology based on constructed analogues to assess the contributions of different drivers to the magnitude of this extreme precipitation event. We first show that the mean effect of the observed atmospheric circulation pattern, an intense low-pressure system centered over the coasts of Western Europe associated with a cold pool and a secondary low-pressure system, can explain about 80 percent of the precipitation event magnitude. By contrasting the effect of Alex atmospheric circulation with an anomalously warm Mediterranean sea and eastern Atlantic ocean versus neutral sea surface temperature conditions, we show that the influence of September 2020 positive sea surface temperature anomalies can explain a large fraction of the 20 percent residual precipitation over southeastern France and northern Italy. Finally, based on a storyline approach, we find that the dynamic component, the atmospheric circulation contribution to the extreme precipitation event, was more extreme than it would have been, had it occurred during the mid-20th century. The increase in the magnitude of the dynamic component since 1950 follows a Clausius-Clapeyron scaling, in agreement with previous studies about the intensity changes of Mediterranean extreme precipitation episodes. (limit =300 words)

From physics to fish: 50 Years of research at Great Meteor Seamount, NE Atlantic

Seamounts are among the most common physiographic systems in the global deep ocean, defining habitat for a hugely diverse biome. Great Meteor Seamount is located in the subtropical Northeast Atlantic and is considered one of the largest seamounts worldwide. Despite its remoteness, it remains one of the few seamounts globally with a long research history dating back more than 50 years. In this study, we aim to review the recent history of scientific research at Great Meteor Seamount, integrating multidisciplinary datasets of the entire seamount ecosystem, including data on plankton, benthos, fishes, and physical oceanography. The interaction of the seamount topography with background low-frequency and tidal currents creates a unique dynamical response due to its location at the critical latitude for seamount trapped diurnal waves, and the high amplitudes of semidiurnal tides. Biological observations show elevated patchiness on horizontal scales smaller than the seamount, which compares well to other seamounts with shallow summits. Regardless of ecosystem pressures associated with geographic isolation and the nutrient and organic matter deprivation inside the North Atlantic Subtropical Gyre, Great Meteor Seamount hosts a diverse species composition including megafaunal taxa such as sponges and corals, as well as species rich fish populations and meiofaunal groups of copepods and nematodes. Due to the ecological vulnerability of seamount habitats to unsustainable exploitation and their important role as open ocean hotspots of marine life, the Portuguese government plans to designate Great Meteor Seamount as a Marine Protected Area (MPA) under the European Marine Strategy Framework Directive. Here, we summarize and recount important results from the long history of research at Great Meteor Seamount in the context of present-day challenges and the initiatives to protect vulnerable ecosystems.

Description of Colobomatus conodoni n. sp. (Cyclopoida: Philichthyidae), a New Parasitic Copepod from the Barred Grunt Conodon nobilis (Linnaeus, 1758) (Actinopterygii: Haemulidae) Off the Brazilian Coast.

Copepods of the genus Colobomatus Hesse, 1873 are parasites associated with subcutaneous spaces of marine fish. To date, around 76 species of the genus have been described in marine ecosystems, but few species have been recorded in the South Atlantic Ocean. One hundred and eight specimens of Co. nobilis were purchased along the littoral of Brazil. The copepods were collected from the skull bones associated to the nasal cavities, fixed and preserved in 80% ethanol and for microscopical observation, specimens were cleared in 85% lactic acid. Drawings were made with the aid of an Olympus BX51 microscope equipped with a drawing tube. Colobomatus conodoni n. sp. can be distinguished from all congeners by the combination of the following characters: (i) two cephalic processes that are longer than the cephalosome, (ii) third abdominal somite with a pair of processes, (iii) caudal rami forked at the tip. This is the first representative of the family Philichthyidae Vogt, 1877 described parasitizing a species of the teleost genus Conodon Cuvier. Together with the new species, the number of philichthyid species in the South Atlantic Ocean increases to 12 and extends the list of Colobomatus spp. to 77.

The effects of warming on loggerhead turtle nesting counts.

Global trends in marine turtle nesting numbers vary by region, influenced by environmental or anthropogenic factors. Our study investigates the potential role of past temperature fluctuations on these trends, particularly whether warmer beaches are linked to increased nesting due to higher female production (since sea turtles have temperature-dependent sex determination). We selected the loggerhead turtle (Caretta caretta) due to its wide distribution, strong philopatry and vulnerability to environmental changes. We compiled nest counts per year on 35 globally significant rookeries, analysing trends at regional and individual beach levels. We compiled air (CHELSA) and land surface (MODIS) temperature data sets spanning the last four decades (1979-2023) for each location. To analyse temporal trends in nest counts and temperatures, we used generalised additive models and Mann-Kendall trend tests. Additionally, we correlated nest counts with lagged air temperature variables. We found significant warming at 33 nesting locations, 23 of which also showed significant increases in nest counts. Our results suggest that rising temperatures may be boosting nest numbers in regions of the Caribbean, Atlantic Ocean and Mediterranean (sites in Cayman, Mexico, Brazil, Cyprus and Turkey). Furthermore, while some regions temporarily benefit, continued warming could precipitate long-term population declines. This regional variability helps predict species responses to climate change, with the general global increase in nest counts already indicating short-term warming effects. Nesting count trends might reflect a combination of natural ecological phenomena, conservation efforts, and warming effects. Long-term studies are needed to assess global trends in the sex ratio of hatchlings and the extent to which feminisation is driving nest numbers.

Improved GODAS reanalysis with MOM5 and impact of altimeter assimilation

The National Centers for Environmental Prediction (NCEP) produces operational reanalysis products based on the Global Ocean Data Assimilation System (GODAS) with the Modular Ocean Model (MOM3/MOM4p0d) as a physical model and 3D-Var as the data assimilation method. The Indian National Center for Ocean Information Services (INCOIS) also produces operational ocean analysis with the same GODAS with MOM4p0d. In this study, GODAS is upgraded with MOM5. The improved reanalysis is compared with respect to the EN4 and Ocean ReAnalysis System 5 (ORAS5) for the subsurface temperature and salinity. The microwave-based satellite-derived sea surface temperature (SST) is employed for the independent evaluation of the reanalysis SST products. We have assimilated observed temperature and salinity profiles from all in situ platforms over the global ocean and also assimilated along-track sea level anomaly from altimeter (Jason1 and Jason2) to produce the improved reanalysis. There is a significant improvement in the SST with biases of temperatures reduced from 1.5 to ~ 0.2 °C as compared to without assimilation. Moreover, a significant improvement is found in the subsurface temperature and salinity fields over the northwest Atlantic and Pacific Ocean, Nino 3.4, and Indian Ocean thermocline ridge regions. The biases in this new, improved reanalysis are even lower than ORAS5 when compared with EN4 analysis. Thermocline depth also shows improvement in terms of better representation and capturing seasonal variability. Altimeter assimilation further reduces Root Mean Square Deviation (RMSD) in SST over the global ocean. We also show the improvement in the new reanalysis with respect to the reanalysis based on MOM4p0d.

Redistribution of dissolved inorganic nitrogen loading and transport in global rivers via surface water regulation.

Surface water (SW) regulation, including reservoir regulation and surface water use, alters the soil-river hydrological processes and then influences the dissolved inorganic nitrogen (DIN) transport from rivers to oceans. However, global response of the DIN transfer to such human activity has not been well investigated. Therefore, in this study, we have taken advantage of a recently-developed land surface model to show the effects of SW regulation on DIN loading and transport in global major rivers. Three simulations were conducted at the global scale over the period of 1991-2000. Results show that, acceleration on riverine N loading caused by the SW regulation was more noticeable. With the reservoir regulation only, removal rates of DIN in most rivers were reduced by 5%, up to 20%, while the increase of removal rate in some reaches occurred when the DIN was transferred back to soil through SW withdrawal and use. Influenced by the SW regulation, DIN flow has decreased obviously by 100-1000tNyr-1. Mean DIN flow was most significantly reduced in the Yellow River basin. Yangtze River, Mississippi River, and Nelson River suffered from the strong effect of such water regulation. The DIN exported to oceans was reduced as well. Mean reduction of 40-50% occurred for those exported to the Pacific Ocean, the Atlantic Ocean and the Indian Ocean, while slight effect for the estuaries into the Arctic Ocean. The impact on the DIN exported to the Atlantic Ocean was lasting decreasing from 50% to 40%, while the trend of the impact on that exported to the Pacific Ocean was opposite. There was no evident temporal change in the impacts on the DIN transferred to the Arctic Ocean and the Indian Ocean. The findings of this study could provide new insights for the researches on nitrogen change in rivers under the impacts of human water use.

Systematic revision of the genus Prionitis (Halymeniales, Rhodophyta) from Taiwan including P. foliagissima sp. nov. and P. imbricata comb. nov

ABSTRACT Grateloupia imbricata is widely distributed in the northwestern Pacific and northeastern Atlantic Oceans. Recent studies have revealed its close relationship to Prionitis, specifically P. taiwani-borealis from northern Taiwan. In this study, we identified a new species, P. foliagissima sp. nov. based on new G. imbricata-like collections from Taiwan. The female reproductive structures of both G. imbricata (= Prionitis imbricata comb. nov.) and P. foliagissima were examined. We demonstrated that the development of carpogonial branch and auxiliary cell ampullae before and after diploidization were similar to those of P. taiwani-borealis. Namely, in P. foliagissima and P. imbricata, the cells of ampullar filaments after diploidization branched a few times and elongated, together with secondarily produced medullary filaments, forming a cellular cluster surrounding the developing carposporophytes. Prionitis foliagissima can be distinguished from the other species of Prionitis found in Taiwan by its smaller thallus size, strongly twisted branches, as well as densely bullate surface. It was noted that the branched ampullar filaments of the two Prionitis species were weakly developed, which differed from those found in species of Phyllymenia (P. taiwanensis and P. huangiae) from Taiwan, where the cells of auxiliary cell ampullar filaments branched several times to form a dense cellular cluster, and in which most cells remained distinct through maturation of gonimoblasts. Further investigation of the female reproductive structures and postfertilization stages of other lesser-known species of Grateloupia, Prionitis, and Phyllymenia is necessary to understand the generic delineation in the Grateloupia/Prionitis/Phyllymenia complex.

Removal of dissolved organic carbon in the West Pacific hadal zones

The deep oceans are environments of complex carbon dynamics that have the potential to significantly impact the global carbon cycle. However, the role of hadal zones, particularly hadal trenches (water depth > 6 km), in the oceanic dissolved organic carbon (DOC) cycle is not thoroughly investigated. Here we report distinct DOC signatures in the Japan Trench bottom water. We find that up to 34% ± 7% of the DOC in the trench bottom is removed during the northeastward transport of dissolved carbon along the trench axis. This DOC removal increases the overall DOC recalcitrance of the deep Pacific DOC pool, and is potentially enhanced by the earthquake-triggered physical and biogeochemical processes in the hadal trenches. Radiocarbon analysis on representative oceanic transects further reveals that the Pacific deep-water DOC undergoes distinct removal compared to those in the Atlantic and Indian Oceans along the thermohaline transport. Our findings highlight hadal trenches as previously unrecognized DOC sinks in the deep ocean system, with varying dynamics that warrant further investigation.

The acoustic detection of the Franciscana dolphin (Pontoporia blainvillei), in open sea off the coast of Argentina

ABSTRACT The Franciscana dolphin (Pontoporia blainvillei) is facing significant threats in the Southwestern Atlantic Ocean, largely due to entanglement in artisanal fishing nets, which makes it the most threatened dolphin species in the region Its conservation calls for a standardised methodology that enables the detection and monitoring of dolphin populations on a longer temporal scale. This study represents the first acoustic monitoring of wild Franciscana dolphins in Argentina, focusing on understanding their diel patterns of activity and their relationship with environmental variables. Our findings show that Franciscana dolphin acoustic presence in summer in Chapadmalal (Argentina) is more frequent in January than in February and March and is influenced by the interaction between tide and wind direction. Specifically, at higher tide levels, wind direction has a reduced impact on dolphin detections. This interaction varies seasonally, with shifts observed in February and March. This research advances standardised methodologies for detecting and monitoring Franciscana dolphin populations, supporting efforts to improve their conservation.

Corrigendum: Distribution of cetaceans in the Canary Islands (Northeast Atlantic Ocean): implications for the Natura 2000 Network and future conservation measures

Corrigendum: Distribution of cetaceans in the Canary Islands (Northeast Atlantic Ocean): implications for the Natura 2000 Network and future conservation measures

Analysis of the spatio-temporal variability of spawning mackerel in the Northeast Atlantic

The northeast Atlantic (NEA) mackerel (Scomber scombrus) is a commercially significant species, with expansive spawning migrations occurring along the continental shelf of northwestern Europe. To identify the main variables influencing the spatial distribution of mackerel eggs, this study analyzed data from egg surveys conducted by the Working Group on Mackerel and Horse Mackerel Egg Surveys (WGMEGS) of the International Council for the Exploration of the Sea (ICES). To achieve this objective, a Random Forest model was used to predict the presence of mackerel eggs based on temporal, geographical, and environmental variables. Applying the Random Forest model to the survey data revealed that the main variables affecting mackerel spawning were the bottom depth, latitude, temperature, and salinity. Subsequently, Quotient Analysis was used to determine the optimal ranges of the key variables identified as influencing mackerel spawning. The results demonstrated a clear preference for spawning at depths between 100 m and 200 m, as well as a consistent preference for the area between 43° and 44° North, corresponding to the Cantabrian Sea. Furthermore, the results indicated that mackerel exhibited a considerable range of temperature tolerance throughout the spawning process, with a preference for cooler waters in the Western area in recent years. Salinity seems to have an effect on spawning at salinities between 35.0 ppm to 35.5 ppm, but results were imprecise. These results contribute to our understanding of how environmental and geographical variables influence the spawning behavior of NEA mackerel.

Petrology of the Eocene alkaline volcanism from the western Rio Grande Rise, South Atlantic Ocean

The origin and evolution of the Rio Grande Rise is deeply related to the opening of the South Atlantic Ocean. The geology of the plateau records the transition from divergent plate margins at the Mid-Atlantic Ridge to an intraplate tectonic setting. Despite the potential to bring insights into the complex tectono-magmatic processes involved in the development of the Rio Grande Rise, there is an overall lack of integrated petrological studies regarding its intraplate Eocene alkaline magmatism. We have investigated trachytes, trachyandesites, alkali basalts, a trachybasalt and a basanite dredged from the western Rio Grande Rise to characterize its magmatic system. Integrated petrography, mineral chemistry and whole-rock geochemistry suggests that these rocks have evolved in a complex transcrustal polybaric magmatic system, where crystals were remobilized by host liquids with different composition at distinct depths. Disequilibrium between crystals and host magmas is evidenced by abundant clinopyroxene macrocrysts with resorbed or corroded cores and rims with contrasting composition, as well as by resorbed feldspar macrocrysts. Clinopyroxene crystals also record cyclic compositional variations in magmatic chambers submitted to multiple magma recharge episodes and a strong control by fractional crystallization. U-Pb dating of zircons from a trachyte yielded an age of 46.9 ± 0.3 Ma, which reinforces the importance of the Eocene volcanism from the western Rio Grande Rise. Moreover, results from Pb, Sr and Nd isotope analysis reveal that Eocene alkaline volcanic rocks from the Western Rio Grande Rise have EMI-flavored Tristan-type signatures. This suggests that the mantle sources from the western Rio Grande Rise and from the Walvis Ridge and Guyot Province magmatism still shared common characteristics long after its separation from the Walvis Ridge.

Spatio-Temporal Characteristics of Climate Extremes in Sub-Saharan Africa and Potential Impact of Oceanic Teleconnections

Sub-Saharan Africa (SSA) is a region vulnerable to extreme weather events due to its low level of adaptive capacity. In recent decades, SSA has been punctuated by more intense climatic phenomena that severely affect its population. Therefore, this study evaluates the performance of the ERA5 and CHIRPS datasets, and the spatio-temporal evolution of extreme weather indices and their potential relationship/response to climate variability modes in the Pacific, Indian, and Atlantic oceans, namely, the El Niño−Southern Oscillation, Indian Ocean Dipole, and Tropical Atlantic Variability (ENSO, IOD, and TAV). The CHIRPS dataset showed strong positive correlations with CPC in spatial patterns and similarity in simulating interannual variability and in almost all seasons. Based on daily CHIRPS and CPC data, nine extreme indices were evaluated focusing on regional trends and change detection, and the maximum lag correlation method was applied to investigate fluctuations caused by climate variability modes. The results revealed a significant decrease in total precipitation (PRCPTOT) in north−central SSA, accompanied by a reduction in Consecutive Wet Days (CWDs) and maximum 5-day precipitation indices (RX5DAYS). At the same time, there was an increase in Consecutive Dry Days (CDDs) and maximum rainfall in 1 day (RX1DAY). With regard to temperatures, absolute minimums and maximums (TNn and TXn) showed a tendency to increase in the center−north and decrease in the south of the SSA, while daily maximums and minimums (TXx and TNx) showed the opposite pattern. The IOD, TAV, and ENSO modes of climate variability influence temperature and precipitation variations in the SSA, with distinct regional responses and lags between the basins.

Ecological role of pelagic appendicularians in sub-Antarctic coastal and oceanic waters of the Southwest Atlantic Ocean

Ecological role of pelagic appendicularians in sub-Antarctic coastal and oceanic waters of the Southwest Atlantic Ocean

Unraveling the Bryocladia scopulorum complex from the Southwestern Atlantic Ocean with the description of three new species of Bryocladia (Rhodomelaceae, Rhodophyta).

The filamentous red algal genus Bryocladia was recently deeply revised based on molecular and morphological data. However, data from the Southwestern Atlantic Ocean are scarce. Here, we provide a phylogenetic study of Bryocladia representatives from the Brazilian coast with new additions to the genus. Our samples were collected from the north to southeastern Brazilian coast in marine and estuarine areas. We carried out a morphological and molecular study based on COI-5P and rbcL gene sequences. Our phylogenetic analyses confirmed the presence of seven species on the Brazilian coast, four of which were previously known: B. cuspidata, B. subtilissima, B. thyrsigera, and B. villum. Three new species are described here, B. itaipensis sp. nov., B. oceanica sp. nov., and B. mucuripensis sp. nov., all morphologically included in the B. scopulorum complex. Bryocladia subtilissima was observed only in Brazilian estuarine areas. However, it was split into two subclades, which require further investigation. The three new species expand the known diversity of the B. scopulorum complex from 12 to 15 species. Bryocladia itaipensis is closely related to B. canariensis and B. caespitosa, whereas B. oceanica and B. mucuripensis formed distinct lineages with unsolved relationships. All new species are restricted to their type localities in Brazilian waters, reinforcing the need for further study of tiny species, especially from the tribes Polysiphonieae and Streblocladieae.

Assessing changing baleen whale distributions and reported incidents relative to vessel activity in the Northwest Atlantic.

Baleen whales are among the largest marine megafauna, and while mostly well-protected from direct exploitation, they are increasingly affected by vessel traffic, interactions with fisheries, and climate change. Adverse interactions, notably vessel strikes and fishing gear entanglement, often result in distress, injury, or death for these animals. In Atlantic Canadian waters, such negative interactions or 'incidents' are consistently reported to marine animal response organizations but have not yet been analyzed relative to the spatial distribution of whales and vessels. Using a database of 483,003 whale sightings, 1,110 incident reports, and 82 million hours of maritime vessel activity, we conducted a spatiotemporal vulnerability analysis for all six baleen whale species occurring in the Northwest Atlantic Ocean by developing an ensemble of habitat-suitability models. The relative spatial risk of vessel-induced incidents was assessed for present (1985-2015) and projected near-future (2035-2055) distributions of baleen whales. Areas of high habitat suitability for multiple baleen whale species were intrinsically linked to sea surface temperature and salinity, with multispecies hotspots identified in the Bay of Fundy, Scotian Shelf, Laurentian Channel, Flemish Cap, and Gulf of St. Lawrence. Present-day model projections were independently evaluated using a separate database of acoustic detections and found to align well. Regions of high relative incident risk were projected close to densely inhabited regions, principal maritime routes, and major fishing grounds, in general coinciding with reported incident hotspots. While some high-risk regions already benefit from mitigation strategies aimed at protecting North Atlantic Right Whales, our analysis highlights the importance of considering risks to multiple species, both in the present day and under continued environmental change.

Meta-Analysis of Larval Bivalve Growth in Response to Ocean Acidification and its Application to Sea Scallop Larval Dispersal in the Mid-Atlantic Bight

Ocean acidification, caused by increasing atmospheric carbon dioxide and coastal physical, biological, and chemical processes, is an ongoing threat to carbonate-utilizing organisms living in productive coastal shelves. Bivalves exposed to acidification have shown reduced growth, reproduction, and metabolic processes, with larval stages exhibiting the greatest susceptibility. Here, we compile results from published studies on larval bivalve growth responses to acidification to estimate a relationship between larval growth and seawater aragonite saturation state. We then apply this relationship to a larval dispersal individual-based model for Atlantic sea scallops (Placopecten magellanicus), an economically vital species in the Mid-Atlantic Bight that is historically under-studied in acidification research. To date, there have been no published studies on sea scallop larval response to ocean acidification. Model simulations allowed the identification of potential impacts of acidification on scallop success in the region. Results show that larval sea scallops that are sensitive to ocean acidification had a 17% lower settlement success rate and over 50% reduction in larval passage between major Mid Atlantic Bight fisheries habitats than those that are not sensitive to acidification. Additionally, temperature and ocean acidification interact as drivers of larval success, with aragonite saturation states > 3.0 compensating for temperature-induced mortality (> 19 ˚C) in some cases. This balance between drivers influences larval settlement success across spatial and interannual scales in the Mid Atlantic Bight.

Deep-sea anemones (Cnidaria, Actiniaria) from off the northeastern coast of Brazil: new records and description of Stephanauge prima sp. nov.

Deep-sea anemones (order Actiniaria) are a diverse group of cnidarians found in basically all marine habitats, from soft sediments to hydrothermal vents and cold seeps. From the waters of Brazil, in the Southern Atlantic Ocean, the deep actinian fauna has been described to encompass 14 sea anemones species, belonging to three families: Hormathiidae, Amphianthidae and Actinoscyphiidae. Here we analyze material trawled from the Potiguar Basin, off the northeast coast of Brazil. We provide new occurrence records for Chondrophellia coronata (Verrill, 1883), Actinoscyphia saginata (Verrill, 1882), Amphianthus bathybium Hertwig, 1882, and Amphianthus michaelsarsi Carlgren, 1934. We also describe a new Amphianthidae species, Stephanauge prima sp. nov. This increases the total number of deep actinians found in Brazil to 17 and provides context for discussing the representativeness of these families and the potential richness of Actiniaria in deep Brazilian waters.

Invading and range-expanding pink salmon inform management actions for marine species on the move

Abstract Species redistributions, whether resulting from invasions or range expansions, pose similar challenges for conservation and management. Redistribution impacts on host ecosystems and species combine with those from climate change, which are already acute at northern latitudes. Using pink salmon Oncorhynchus gorbuscha, which are native to the Pacific Ocean, we employ knowledge exchange to inform decision-making in non-native marine areas: they are expanding their range to the Arctic Ocean and are invasive in the Atlantic Ocean. The predicted future marine distribution of pink salmon focuses effort on where and when pink salmon are present and informs on potential interactions with native species. Management actions taken in the Atlantic Ocean to reduce invasive pink salmon are resource-intensive, but removed salmon could be a food resource. Addressing identified gaps regarding the invasion potential of pink salmon, interactions among pink salmon and other species, and current mitigation efforts would support forward-thinking management decisions given predictions of continued environmental change. We also highlight steps that can be taken immediately to coordinate actions and better inform responses. Managed for production in the Pacific and as an invasion in the Atlantic, pink salmon provide a tangible approach to informed decision-making through collaboration for marine species on the move.

A population dynamics approach to understand the invasiveness of the seaweed Rugulopteryx okamurae (Ochrophyta, Dictyotales)

The success of invasive species can be measured by invasiveness, which depicts intrinsic characteristics that enable them to thrive in new environments. In invasive seaweeds, for example, the persistence of multiple overlapping cohorts throughout the year plays a key role in increasing plant cover and exerting unrelenting pressure on invaded areas. The marine brown macroalgae Rugulopteryx okamurae has recently established abundant populations in the Mediterranean Sea and Atlantic Ocean, negatively affecting both biodiversity and socioeconomic factors by unprecedently aggressive invasive behaviour. The objective of the study is to understand the invasiveness of R. okamurae through its popu lation dynamics. For this, a year-round study was conducted in a protected habitat of Posidonia oceanica in southern Spain, revealing that R. okamurae uses alternating mechanisms for population maintenance. It achieves high density of young individuals in late summer and autumn, peaking at 3285 individuals per square metre. In spring and early summer, the population shifts towards fewer – but larger – individuals, with densities dropping to 888 individuals per square metre and biomass reaching a peak of 170 g dry weight (DW) per square metre. Six overlapping cohorts were identified by Gaussian curves. They persisted throughout the year, but they were not related to environmental factors, which indicates adaptive physiological mechanisms that sustain dense monospecific populations. Additionally, the association between cohorts and different morphotypes suggests that R. okamurae phenotypic plasticity enables its persistence in introduced areas. These findings provide valuable insights into the biological traits underpinning its invasiveness in P. oceanica meadows, revealing temporal windows of invasiveness driven by different mechanisms. This knowledge is crucial for developing effective conservation and management strategies aimed at mitigating the impact of this invasive species.