Continental Shelf Research最新文献

{"title":"Association between selenium levels and the distribution of mangrove forests in the brackish water exchange zone of the Pearl river estuary","authors":"Zhenyan Zhang,&nbsp;Dan Su,&nbsp;Shuwen Xue,&nbsp;Jiaxuan Zhang,&nbsp;Jie Wang","doi":"10.1016/j.csr.2025.105573","DOIUrl":"10.1016/j.csr.2025.105573","url":null,"abstract":"<div><div>Mangroves are vital coastal wetland system widely distributed in tropical and subtropical intertidal zones around 30° latitude. In most coastal ecosystems, plant growth is generally inhibited by salinity. However, mangroves thrive in brackish coastal areas. Previous studies have shown that mangrove distribution is strongly influenced by seawater, likely due to its chemical composition and role in global biogeochemical cycles. Seasonal variations in salinity and selenium (Se) levels in coastal regions exhibit similar patterns, and low doses of supplemental Se can protect plants against reactive oxygen species (ROS)-induced oxidative damage. This study focused on the Pearl River Estuary to examine the relationship among Se content, salinity, and mangrove distribution. Clear seasonal fluctuations in Se levels were observed in the estuary. Se concentrations in the estuary were significantly higher than the average level due to runoff. Dissolved inorganic selenium (DISe) decreased with increasing distance from the estuary. Results revealed a significant positive correlation between mangrove distribution and Se content (<em>p</em> &lt; 0.05), whereas no significant relationship with salinity was found. Furthermore, Se application enhanced mangrove tolerance to salt stress-induced oxidative damage by strengthening antioxidant defense systems. These findings provide valuable insights for the conservation and management of mangrove ecosystems.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105573"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145118582","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Plutonium radioisotopes as radiotracers of sedimentation processes in the Black Sea coastal areas","authors":"A.A. Paraskiv,&nbsp;N.N. Tereshchenko,&nbsp;V. Yu Proskurnin","doi":"10.1016/j.csr.2025.105579","DOIUrl":"10.1016/j.csr.2025.105579","url":null,"abstract":"<div><div>The vertical distribution of plutonium radioisotopes (²³⁸Pu and ^239+240Pu) in five bottom sediment cores from the coastal marine area of Sevastopol Bay (the Black Sea) was studied. Based on the analysis of the ²³⁸Pu, ^239+240Pu activity and ²³⁸Pu/^239+240Pu activity ratio profiles, geochronological dating of bottom sediments was carried out and the main parameters of sedimentation processes (SR – sedimentation rate and MAR – mass accumulation rate) were calculated. It was found that each of the studied areas of the Sevastopol Bay has individual sedimentation features, which are reflected in SR and MAR values. SR values ranged from 2.5 to 7.5 mm year⁻¹ while MAR – from 1679 to 4833 g m⁻²·year⁻¹. The obtained results indicate that the intensity of water self-purification via plutonium removal into the sediments varies within the studied areas. It is shown that under the conditions of the spatiotemporal regime of plutonium input into the Black Sea it is possible to determine the SR and MAR for two time periods: 1962–1986 and 1986–2019. It has been established that on a half-century scale the SR and MAR have changed in the Sevastopol Bay. Thus, in the post-Chernobyl period, in the bay mouth, the SR and MAR increased by 2.1 and 1.8 times, respectively, while in the bay headwaters they decreased by 2.0 and 2.3 times, respectively. These changes are apparently a consequence of the construction of hydraulic structures both in the Sevastopol Bay and in its drainage basin.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105579"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145266907","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shear instabilities in Internal Solitary Waves under high and low-wind regimes","authors":"Jorge M. Magalhaes ,&nbsp;Martin J. Coubard ,&nbsp;José C.B. da Silva ,&nbsp;Maarten C. Buijsman ,&nbsp;Ana Isabel Santos ,&nbsp;Ana Amorim ,&nbsp;Paulo B. Oliveira","doi":"10.1016/j.csr.2025.105561","DOIUrl":"10.1016/j.csr.2025.105561","url":null,"abstract":"<div><div>Wind and Internal Solitary Waves (ISWs) are well-known to mix the ocean's surface and inner stratification, but their combined effects appear to have not yet been investigated. A large ensemble of ISWs measured off the Portuguese Coast reveals that wind and ISWs may combine to increase turbulence and mixing beyond the linear combination of their individual contributions. It is found that low bulk Richardson numbers (<span><math><mrow><mi>R</mi><mi>i</mi><mo>&lt;</mo><mfrac><mn>1</mn><mn>4</mn></mfrac></mrow></math></span>) and temperature inversions increase respectively by nearly four-fold and an order of magnitude, when comparing ISWs propagating under high and low-wind regimes. Furthermore, depth ranges where <span><math><mrow><mi>R</mi><mi>i</mi><mo>&lt;</mo><mfrac><mn>1</mn><mn>4</mn></mfrac></mrow></math></span> associated with ISWs propagating with high winds are observed to extend at least between unperturbed thermocline and intermediate depths. Understanding how turbulence and mixing from ISWs and wind combine may have important implications ranging from parametrizations in ocean models to our understanding of biogeochemical processes modulated by diapycnal mixing.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105561"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145027203","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ecological role and productive potential of a ∼30 years artificial reef - Southeastern Brazil","authors":"Igor David da Costa ,&nbsp;Ana Cristina Teixeira Bonecker ,&nbsp;Leonardo Lopes Costa ,&nbsp;Juliano Silva Lima ,&nbsp;Ilana Rosental Zalmon","doi":"10.1016/j.csr.2025.105572","DOIUrl":"10.1016/j.csr.2025.105572","url":null,"abstract":"<div><div>Artificial Reefs (ARs) increase the heterogeneity of areas that previously had homogeneous unconsolidated substrate, favoring the survival of juvenile fish by providing more anti-predation refuges. The efficacy of ARs to increase the abundance of fish and decrease the impacts of fisheries depends on their functionality as either attractors or producers of fish biomass. The present study sought to elucidate on the potential production role of a reef complex installed on the northern coast of Rio de Janeiro in 1996 besides the well-known attraction potential. Specifically, we aimed to compare the structure and composition of the ichthyoplankton community along a distance gradient from the ARs (0–1000 m). A total of 1941 ichthyoplankton specimens were sampled on dry and rainy seasons, including 13 families, 8 genera, and 11 species. During the rainy season, higher abundance of fish larvae was collected near the ARs, while in the dry season, ichthyoplankton was concentrated at greater distances from the reef complex. In both periods, fish eggs were mostly collected &lt;100 m from the ARs. Newly hatched larvae predominated at 1000 m distance, mainly during the rainy season. The number of larvae in the pre-flexion stage was predominant at 0 m, mainly during the rainy season. The presence of eggs and the predominance of pre-flexion larvae in areas closer to the reef modules indicate that this reef is an important spawning site for various fish species. The results reinforce spatial distribution characteristics of fish larvae in the ARs area, also suggesting that these structures initially acted as fish attractors but are now functioning as biomass producers for some species, including commercial ones. The ARs, being no-fishing zones, can be an effective tool both for fisheries management and biodiversity conservation.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105572"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145059911","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shift in the phytoplankton composition associated with reversal in east India coastal currents in the Bay of Bengal","authors":"R. Sreevidhya,&nbsp;V.V.S.S. Sarma","doi":"10.1016/j.csr.2025.105566","DOIUrl":"10.1016/j.csr.2025.105566","url":null,"abstract":"<div><div>The alteration of phytoplankton composition due to variations in physical mixing, salinity, nutrient concentrations and their stoichiometric ratios would impact the overall ecosystem, affect the food web and influence the carbon cycle. The seasonal reversal in the East Indian Coastal Currents (EICC) significantly modifies stratification, physical mixing and nutrient levels in the coastal waters. To examine the impact of reversal in EICC on nutrient stoichiometry and phytoplankton composition, coastal waters were measured at a monthly time scale in the inshore and offshore regions of the Bay of Bengal for one year. The EICC flows northward between February and September, bringing saline waters along the coast, associated with winds from the south-west direction, promotes coastal upwelling. Elevated concentrations of nutrients (nitrate, phosphate and silicate) and phytoplankton biomass were observed associated with coastal upwelling dominated by fucoxanthin (Bacillariophyceae), and chlorophyll-b (Chl-b; green algae). CHEMTAX analysis suggests that diatoms contributed significantly (60–70 %) during the upwelling period, with up to 90 % of the contribution coming from microplankton in both coastal and offshore regions. The EICC reverses its flow towards the south between October and January, bringing low saline, nutrient-poor waters along the coast, resulting in a decrease in Chlorophyll-a (Chl-a). During this period, the coastal waters were dominated by zeaxanthin (cyanobacteria). Despite nutrients not being limiting, picoplankton dominance during this period is caused by the transport of cyanobacteria from the river to the coastal region due to their abundance in the river water. The CHEMTAX analysis suggested that diatoms, prochlorophytes, and cyanobacteria contributed significantly in the inshore region, whereas chlorophytes and cyanobacteria contributed to the offshore region. Picoplankton (&gt;50 %) contributed significantly, followed by micro (30 %) and nanoplankton (∼20 %). Fucoxanthin and Chl-b displayed a significant linear relationship with salinity, whereas zeaxanthin displayed an inverse relationship with salinity. The fraction of microplankton linearly correlated with salinity, whereas nano- and picoplankton inversely correlated. This study highlights the effect of temporal variabilities in salinity associated with reversing the EICC modified the phytoplankton composition, and it may have a significant impact on the coastal ecosystem. Understanding intra- and interannual variability in the EICC and associated salinity changes may allow for the prediction of phytoplankton composition in the coastal Bay of Bengal.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105566"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145158153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Interaction and variability of silicon and carbon associated with particulate matter in the Changjiang and Yellow Rivers","authors":"Xiangbin Ran ,&nbsp;Yingxiao Li ,&nbsp;Xiaosong Zhong ,&nbsp;Xiaotian Liu ,&nbsp;Hao Wang","doi":"10.1016/j.csr.2025.105574","DOIUrl":"10.1016/j.csr.2025.105574","url":null,"abstract":"<div><div>The interrelated biogeochemical cycles of silicon and carbon (Si-C) are essential for the effective functioning of aquatic ecosystems. However, there exists a notable gap in methodological research addressing the quantitative transport dynamics of Si-C within riverine systems. This study examines the spatiotemporal variations, sources, and export mechanisms of Si-C in the Changjiang and Yellow Rivers. Our results reveal that biogenic silica (BSi) concentrations are significantly affected by dam operations, while dissolved silicate (DSi) concentrations exhibit a modest downstream decline. Moreover, BSi associated with suspended particulate matter (SPM) shows an inverse relationship with SPM concentration. Particulate organic carbon (POC) in the Changjiang River predominantly originates from terrestrial C3 plants, whereas in the Yellow River, there is a greater contribution from C4 plants. Variations in the stoichiometric ratios of POC to nitrogen (C/N_bulk) and BSi suggest that carbon degradation during river transport is more pronounced than in estuarine environments. Additionally, the δ¹³C of bulk POC (δ¹³C_bulk) in the river exhibits greater sensitivity to environmental changes compared to the δ¹³C associated with BSi (δ¹³C_BSi). We propose a normalization-based methodology to assess the potential decay rates of POC and organic carbon associated with BSi within river systems. Carbon is more readily mineralized from particulate matter than from that associated with silicon, and the coupled Si-C dynamics can be employed to explore their differential behaviors and the role of silicon in carbon preservation. This study provides valuable insights into Si-C dynamics in river-estuary systems, particularly under the increasing influence of anthropogenic activities.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105574"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Genetic differentiation in populations of two snappers, Lutjanus malabaricus and Pristipomoides multidens, in the Makassar Strait and adjacent waters, Indonesia: Implications for management","authors":"Tri Ernawati ,&nbsp;Mennofatria Boer ,&nbsp;Mohammad Mukhlis Kamal ,&nbsp;Nurlisa Alias Butet ,&nbsp;Fayakun Satria ,&nbsp;Peter J. Mous","doi":"10.1016/j.csr.2025.105563","DOIUrl":"10.1016/j.csr.2025.105563","url":null,"abstract":"<div><div>The Makassar Strait and adjacent waters, which is crossed by the Wallace line, has variations in bathymetry and unique ocean currents. This condition allows for genetic differences in the Malabar blood snapper (<em>Lutjanus malabaricus</em>) and the Goldband snapper (<em>Pristipomoides multidens</em>) in the strait. Specimens were collected from some landing bases in Makassar Strait and adjacent waters as part of Indonesia's Fisheries Management Area (FMA) 713 and assessed using d-loop mtDNA. Both <em>L.malabaricus</em> and <em>P.multidens</em> obtained the same sequencing results of around 400 bp with 67 and 71 of number haplotypes, respectively. The results of the polymorphism of the two species showed high genetic diversity (<em>L.malabaricus</em>: <em>h</em> = 0.9284, <em>π</em> = 0.0434; <em>P.multidens</em>: <em>h</em> = 0.9766, <em>π</em> = 0.0532). Based on differences analysis to examine the population genetic structure showed different results. <em>L.malabaricus</em> was identified as having no population genetic structure. On the other hand, <em>P. multidens</em> has significant (<em>Φ</em>_<em>ST</em> = 0.07010, <em>p</em> &lt; 0.001) structural differences among sub-areas, the western part of the Makassar Strait, the eastern part of the Makassar Strait, and south of the Makassar Strait, Flores Sea. The different stock units need to be considered in the development of fisheries management and surveillance. Management of fish resources requires a flexible and adaptive approach, taking into account the fishery characteristics of each population and the broad ecosystems in which they occur.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105563"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144933128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Frontal features and mixing regimes along the shelf region of the Southern Benguela upwelling system","authors":"Jonathan Rogerson ,&nbsp;Jennifer Veitch ,&nbsp;Samantha Siedlecki ,&nbsp;Sarah Fawcett","doi":"10.1016/j.csr.2025.105560","DOIUrl":"10.1016/j.csr.2025.105560","url":null,"abstract":"<div><div>Mesoscale fronts are ubiquitous features in all Eastern Boundary Upwelling Systems and are the result of prominent sea surface temperature (SST) gradients and baroclinic jets. Their seasonal variability and presence can impact the horizontal mixing patterns of particles and nutrients. Here, we examine the role of alongshore fronts in shaping the seasonal patterns of cross-shore mixing, residence times, and surface particle transport along the shelf region of the Southern Benguela Upwelling System. Using a numerical ocean model together with a front-detection algorithm, Lagrangian particle tracking, and Finite Time Lyapunov Exponents, we investigate mesoscale frontal variability. In summer, fronts are typically long and continuous alongshore features that are defined by strong SST gradients and associated with prominent Lagrangian Coherent Structures (LCSs). These fronts can act as cohesive barriers that limit cross-shore mixing and offshore advection of particles. In winter, fronts are generally found further offshore and are more filamentous and numerous compared to summer. Furthermore, they are defined by weaker SST frontal gradients and shorter frontal lengths. Fronts in winter are not associated with any obvious LCSs, which implies that particles and material experience greater rates of dispersion and cross-shore mixing. Lagrangian float experiments confirm this and show surface particle trajectories in winter to be more variable and chaotic compared to the more uniform patterns observed in summer. Therefore, defined alongshore fronts in summer aid in the retention of particles on the shelf. The seasonal erosion of these defined frontal features allows for greater cross-shore mixing of particles, water masses and nutrients in the upper water column during winter.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105560"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096248","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaluating the hydrodynamic and transport responses to storm surge barriers in a partially mixed Estuary: A case study of the Hudson–Raritan estuary","authors":"Sajjad Feizabadi ,&nbsp;Sarah M. Brannum ,&nbsp;Masoud Ghodsian ,&nbsp;Mohammad Nabi Allahdadi ,&nbsp;Nazanin Chaichitehrani","doi":"10.1016/j.csr.2025.105567","DOIUrl":"10.1016/j.csr.2025.105567","url":null,"abstract":"<div><div>Storm surge barriers (SSB), as engineering measures within broader coastal risk mitigation strategies, have been implemented or proposed in estuaries around the world. During non-storm periods, some parts of barriers restrict cross-flow area which alters water exchange and estuarine hydrodynamics. This study investigates the effects of permanent barrier infrastructure on the hydrodynamics of the Hudson-Raritan Estuary (HRE), a partially mixed estuary characterized by a complex geometry that includes bays connected by tidal straits and multiple tidal inlets. Our research employs a three-dimensional hydrodynamic model (EFDC) to focus on five distinct scenarios developed by the United States Army Corps of Engineers (USACE), exploring aspects of these systems that have not been examined previously. The implementation of SSBs leads to increased salinity content, intrusion, and stratification in tributaries and a decrease on the landward side of the barrier, particularly when key pathways for water exchange are obstructed. Depending on the specific configurations of the SSBs, salinity variations in different regions range from an increase of 12 % to a decrease of 10 %. Results indicate a reduction in both semi-diurnal and diurnal tidal signals across the HRE, significantly affecting the energy partitioning. For instance, an SSB at the Lower Bay entrance reduces the semi-diurnal component of the total energy budget from 73 % in the base case to 46 %, while increasing the subtidal component's contribution from 23 % to 50 %. Additionally, SSBs alter the residual currents, induce eddy formations, and amplify currents across both surface and bottom layers. The response of residence times to SSB configurations varies spatially across the domain; on average, residence time in the HRE rises between 13 % and 67 % across the different SSB configuration scenarios compared to the base case, which has a spatially averaged residence time of approximately 15.9 days. The impact of SSBs on estuarine hydrodynamics strongly depends on their specific location and configuration. This study provides a framework for understanding the potential impacts of any proposed surge barrier systems and enhances our comprehension of their ecological and environmental effects.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105567"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145049679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Changes in free-living zooxanthellae abundance during summer in a temperate Japanese coastal sea (Takashima, Japan)","authors":"Hiroyuki Takasu ,&nbsp;Takanobu Yamaguchi ,&nbsp;Maiko Ito ,&nbsp;Kotaro Miyahara ,&nbsp;Rintaro Kiyama ,&nbsp;Manabu Fukumura ,&nbsp;Shuzo Komura","doi":"10.1016/j.csr.2025.105577","DOIUrl":"10.1016/j.csr.2025.105577","url":null,"abstract":"<div><div>Free-living or exogenous zooxanthellae play a crucial role in coral survival; however, their ecological dynamics remain largely unexplored. This study focused on tracking the abundance of free-living zooxanthellae (Clades A to F) in seawater around the temperate coastal sea (Takashima, Japan) from summer to early autumn using quantitative polymerase chain reaction (qPCR). In addition, we examined the influence of temperature, light conditions (photosynthetic photon flux density [PPFD]), dissolved inorganic nitrogen (DIN), and coral health on the abundance of zooxanthellae. Our findings revealed an increase in the abundance of free-living zooxanthellae from late summer to early autumn, irrespective of clade. A significant negative correlation was observed between the ribosomal RNA (rRNA) gene copy number, amplified using a universal primer, and coral health scores. Conversely, there was a positive correlation between the rRNA gene copy number and seawater temperature. The relationship between PPFD and DIN was not significantly correlated with rRNA gene copy number. Notably, the rRNA gene copy number, amplified using the Clade C primer, was the most abundant and exhibited a significant positive correlation with seawater temperature, whereas it was negatively correlated with coral health scores. The increase in the abundance of free-living zooxanthellae, particularly Clade C, in seawater was facilitated by rising seawater temperatures and the release of zooxanthellae cells from host corals, with the latter likely being the predominant factor. To our knowledge, this is the first study to monitor temporal changes in the abundance of free-living zooxanthellae in seawater.</div></div>","PeriodicalId":50618,"journal":{"name":"Continental Shelf Research","volume":"295 ","pages":"Article 105577"},"PeriodicalIF":2.2,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145220402","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}