Seasonal Upwelling Research Articles

Evidence for resource partitioning in weakfishes from a coastal upwelling ecosystem

Resource partitioning plays an important role in supporting species coexistence. In a coastal upwelling ecosystem two weakfish species, Cynoscion guatucupa and C. jamaicensis co-occur and are key commercial species. The present study aimed to provide a comprehensive assessment of the feeding ecology of both species, including to; (i) quantitatively assess diet, (ii) evaluate ontogenetic and seasonal diet variations, and (iii) estimate dietary overlap in the context of competition or resource partitioning, using an integrated approach combining stomach content (SCA) and stable isotope analyses (SIA). Our results revealed that both C. guatucupa and C. jamaicensis prey mainly on pelagic fish and shrimp with ontogenetic and seasonal changes in diet detected. Weakfishes consume a large proportion of similar prey throughout the year and high isotopic niche overlap confirmed the SCA results. Despite the similar use of food resources by both species, the availability and abundance of prey promoted by seasonal upwellings and the possible spatial segregation between C. guatucupa and C. jamaicensis may promote their co-occurrence in an upwelling ecosystem. Due to their commercial value and fisheries importance in the southwestern Atlantic, these results contribute insights to support sustainable fisheries management.

Early Investigation of Tropical Cyclones Blake-Claudia’s Effect on Seasonal Downwelling in Southern Indonesia Waters

Abstract Indonesia southern waters area is one of the places where tropical storms form and develop into tropical cyclones. Apart from cyclones, southern Indonesia waters also experienced other oceanographic phenomena, the seasonal upwelling and downwelling. This study aims to investigate the physical conditions in southern Indonesia waters during the TC Blake-Claudia which occurred during seasonal downwelling period. Historical data shows that tropical cyclones in southern Indonesia generally occur in DFJ and almost never occur in JJA. Meanwhile, the downwelling period occurs during the DJF season. The results show TC Blake-Claudia has weaken or disrupted seasonal downwelling by decreasing SSHA and increasing chlorophyll concentration. This change in oceanographic parameter expected to be occur not only as the result of cyclonic activity which creates a void of water on the coast, but also supported by the initial conditions of the study area which tend to remain unstable just after upwelling event ends.

Study on the Typical Environmental Factors in the Middle Part of Zhoushan Fishery Based on HY-1C/D and Other Multi-Source Data

This study utilizes satellite data, including HY-1C/D, along with reanalysis data, to unveil the typical environmental characteristics of the sea surface in the middle of Zhoushan fishery. The article addresses three main issues. The first one is the development of an ocean primary productivity (OPP) inversion algorithm model. The second one is the study of chlorophyll-α (Chl-α) concentration and OPP distribution characteristics in Zhoushan fishery using China’s domestically produced ocean satellite HY-1C/D CZI data. The last one is the revelation of the characteristics of typical environmental factors on the sea surface at Zhoushan fishery by combining HY-1C/D with multi-source data. The results show the following: (1) The middle part of Zhoushan fishery exhibits significant seasonal and regional variations in Chl-α concentration and OPP. Chl-α concentration ranges mainly between 0.2 and 2.9 µg/L, with higher concentrations in spring and summer and lower Chl-α concentrations in autumn and winter. Spatially, Chl-α concentration gradually decreases from west to east. The OPP in the study area ranges from 100 mg·m−2d−1 to 1000 mg·m−2d−1, with high OPP values distributed on the western side, ranging from 400 mg·m−2d−1 to 1000 mg·m−2d−1, and gradually decreasing seaward. The highest OPP occurs in summer and the lowest in winter. (2) The correlation analysis between Chl-α concentration and OPP revealed a strong positive relationship. Consequently, this study developed an empirical model for estimating OPP based on Chl-α concentration and validated its feasibility. The model applies to areas with Chl-α concentrations ranging from 0.2 to 4 µg/L. (3) The convergence of freshwater injection, multiple ocean currents, and seasonal upwelling in the study area brings about a rich supply of nutrients. Additionally, the region is characterized by suitable conditions, including optimal Chl-α concentrations, OPP, SST, salinity, currents, and geological water depths. The synergistic effect of these factors together contributed to the formation of Zhoushan fishery.

Genetic Variability and Genetic Differentiation of Populations in the Grooved Carpet Shell Clam (Ruditapes decussatus) Based on Intron Polymorphisms

Genetic Variability and Genetic Differentiation of Populations in the Grooved Carpet Shell Clam (Ruditapes decussatus) Based on Intron Polymorphisms

Coastal and Marine Ecosystems of the Arafura and Timor Seas – Characterization, Key Features and Ecological Significance

The tropical Arafura and Timor Seas (ATS) region lies on the edge of the Coral Triangle, located at the intersection of two major Large Marine Ecosystems, the Northern Australian Shelf and the Indonesian Sea. Under the influence of the Indonesian Through Flow current and Pacific-Indian Ocean exchange, the ATS also lies at a major ‘cross-road’ of global ocean circulation and climate regulation. The ‘semi-enclosed’ ATS is characterized by diverse seascapes, pronounced ecological connectivity (marine biodiversity, shared fisheries, land-sea interactions), extensive coastal wetlands and shallow-water ecosystems, and globally-significant marine biodiversity (particularly corals reefs, mangroves, seagrasses, and populations of marine megafauna). Complex oceanography, bathymetry and large-scale, tidal and monsoon-driven circulation, and localized, seasonal upwellings are major features across the region, driving patterns of ocean productivity, reef biodiversity and sustaining rich pelagic ecosystems. With some of the most extensive, productive and near-pristine tropical coastal ecosystems in the world, the waters of the ATS are a global marine biodiversity ‘hotspot’ and play a crucial role in maintaining regional/global tropical marine biodiversity. Including providing major migration corridors, critical habitats and a regional/global refuge for some of the world’s most threatened marine megafauna and wildlife populations (particularly sea turtles, sharks/rays, sawfish/river sharks, whales, dolphins and dugongs). Coastal habitats in the ATS also provide a range of ecosystem services of fundamental importance to human well-being, including climate change; with climate-resilient coral reefs and some of the largest and intact, tropical wetlands (mangroves, saltmarshes, seagrasses) in the world, the ATS region is a recognized global blue carbon hotspot. The characterization and assessment of key ecosystems and processes in the ATS in this study provide the basis for protecting these resources through the Arafura and Timor Seas Ecosystem Action Program.

Biogeochemical Response of the Water Column of Concepción Bay, Chile, to a New Regime of Atmospheric and Oceanographic Variability

Concepción Bay is a socio-economic and ecologically important embayment whose hydrographic variability has been historically regulated by wind-modulated seasonal upwelling events during spring–summer and by freshwater from precipitation and river discharges during fall–winter. This system is subject to several anthropogenic and environmental strains due to the intense port activity and the increasing occurrence of extreme natural events. This study determines a new hydrographic regime and characterizes and analyzes the biogeochemical response of the water column to changes in rainfall and upwelling patterns. Despite the intrusion of nitrate-rich upwelled waters that enhance biological productivity remains more intense during spring–summer, the system remains fertilized year-long due to the occurrence of persistent upwelling pulses during fall–winter. The hydrographic structure presented a two-layer water column that was stratified thermally in spring–summer and primarily by freshwater inputs in fall–winter. Nevertheless, the regular pattern of the rainfall has changed (a decrease in precipitation and an increased frequency of extreme rainfall events), together with recurrent upwelling-favorable wind pulses during the non-upwelling season. This new regime has altered the seasonality of the physicochemical conditions and the structure of the microplanktonic communities, with productive and sanitary implications affecting the biogeochemical status of CB.

Pacific nurse sharks Ginglymostoma unami exhibit yearly patterns of site fidelity to a tropical embayment subjected to seasonal upwelling

Pacific nurse sharks Ginglymostoma unami exhibit yearly patterns of site fidelity to a tropical embayment subjected to seasonal upwelling

A New Species of the Shrimp Genus Salmoneus Holthuis, 1955 (Malacostraca: Decapoda: Alpheidae) from the Exposed Shores of Eastern and Southern Oman

Salmoneus sultanus sp. nov. is described based on several specimens collected on the exposed shores of Masirah Island and Dhofar, Oman, a region characterised by seasonal upwellings cooling water temperature to less than 23 °C. The new species is compared with the morphologically most similar congeners present in the north-western Indian Ocean, e.g., S. latirostris (Coutière, 1897), S. cristatus (Coutière, 1897), S. serratidigitus (Coutière, 1897), and S. chadwickae Ďuriš and Horká, 2016; the latter species is recorded for the first time from Oman. The conspicuous colour pattern of S. sultanus sp. nov. appears to be diagnostic, differing greatly from that of S. latirostris, S. cristatus, S. serratidigitus, and S. chadwickae.

Reproductive phenology of coralline algae Porolithon antillarum and Lithophyllum sp. under seasonal upwelling conditions, Colombian Caribbean

Crustose coralline algae are a group of calcified algae that has an important ecological role in coral reefs, such as cementation and stabilization of the reef framework, as well as providing habitat and food for different marine associates. Among the common genera, Lithophyllum and Porolithon (Corallinales) are conspicuous components of the Santa Marta reef communities in the Colombian Caribbean. From December to April, this area is influenced by seasonal trade winds, a phenomenon that is related to the upwelling of subsurface waters that causes a decrease in temperature from ∼29 °C to ∼22 °C and pH from ∼ 8.5 to ∼8.0. The aim of this study was to evaluate the effect of upwelling and non-upwelling (2017, 2018, and 2021) on the reproductive phenology of Lithophyllum sp. and Porolithon antillarum based on counts of superficial conceptacles per cm2 and a determination of the reproductive stages of the algae collected in Tayrona National Natural Park and Punta Venado, Santa Marta. The algae presented the highest number of mature conceptacles during the upwelling period for P. antillarum and Lithophyllum sp. (46 and 27 conceptacles cm2, respectively). Moreover, the tetrasporangial stage was the most frequent in all the thalli, thus indicating the predominance of this phase in the reproductive cycle of the algae studied. These results are important as they indicate the influence of seasonality on the reproductive stages of CCA and bring the need to do more research into the influence of the environment on the physiological mechanisms that determine the changes in the life cycle of these algae.

Variability of total alkalinity in coastal surface waters determined using an in-situ analyzer in conjunction with the application of a neural network-based prediction model

Total alkalinity (TA) is an important variable of the ocean carbonate system. In coastal oceans, carbonate system dynamics are controlled by a range of processes including photosynthesis and respiration, calcification, mixing of water masses, continental inputs, temperature changes, and seasonal upwelling. Assessments of diel, seasonal and interannual variations in TA are required to understand the carbon cycle in coastal oceans. However, our understanding of these variations remains underdeveloped due to limitations in observational techniques. Autonomous TA measurements are therefore required. In this study, an in situ TA analyzer (ISA-TA) based on a single-point titration with spectrophotometric pH detection was deployed in Tong'an Bay, Xiamen, China, over a five-month period in 2021 to determine diel and seasonal TA variations. The TA observations were combined with an artificial neural network (ANN) model to construct TA prediction models for this area. This provided a simple method to investigate TA variations in this region and was applied to predict surface water TA between March and April 2021. The in situ TA observations showed that TA values in Tong'an Bay varied within a range from 1931 to 2294 μmol kg−1 over the study period, with low TA in late winter, early summer and late summer, and high TA in early winter. The TA variations in late summer and early winter were mainly controlled by mixing of water bodies. The diel variations of TA were greatly determined by tides, with a diel amplitude of 9 to 247 μmol kg−1. The ANN model used temperature, salinity, chlorophyll, and dissolved oxygen to estimate TA, with a root-mean-square error (RMSE) of ∼14 μmol kg−1, with salinity as the input variable with the greatest weight. The approach of combining ISA-TA observations with an ANN model can be extended to study the carbonate system in other coastal regions.

Factors influencing nearshore hypoxia in the southeastern Arabian Sea: A sensor-based study

Seasonal upwelling and the associated incursion of hypoxic waters into the coastal zone is a widely studied topic over different upwelling zones. However, its persistence or variations over short time scales are poorly addressed. The present study, therefore, brings out a first report on hourly variations in the temperature, salinity and dissolved oxygen recorded by an environmental data buoy equipped with sensors, deployed in the nearshore waters of Alappuzha (southeastern Arabian Sea) from April to August 2022. The characteristic feature of the Alappuzha coast is the development of mud banks during the southwest monsoon, providing a tranquil environment suitable for continuous sensor-based measurements when the sea remains turbulent elsewhere. The results showed that despite an advance in the upwelling intensity, there is a significant variation in the oxygen concentration in the study domain on a diurnal scale. In general, the nearshore region was under hypoxia during the first half of the day (00:00 to 12:00 h), which increased steadily to reach normoxic and supersaturated levels during the rest of the day (12:00 to 24:00 h). Statistical analysis showed that winds significantly correlate to the coastal environment's subsurface oxygen concentration. During the morning hours, the wind was weak, and the water column remained stratified over the subsurface hypoxic water layer. The situation changed in the afternoon (12:00 h onwards), as there was a steady increase in the local wind speed (>5 m/s), which was sustained during the rest of the day. A local wind speed >5 m/s can disturb the stratification and enhance the mixing process from 12:00 to 24:00 h. The total kinetic energy of 11.5 J/m3 is the threshold for this oxygen supersaturation. These findings emphasize the role of wind-induced mixing in alleviating coastal hypoxia, highlighting the need for further biogeochemical and ecological investigations into the impacts of alternating oxic-hypoxic conditions in nearshore waters.

Seasonal upwelling influence on trophic indices of mesozooplankton in a coastal food web estimated from δ15N in amino acids

Mesozooplankton communities in upwelling ecosystems are known to be influenced by seasonal upwelling enhancing primary productivity. However, the extent to which changes in trophic dynamics of mesozooplankton are driven by variations in the baseline of nitrogen or in the trophic position (TP) is poorly understood. We used nitrogen stable isotopes (δ15N) in bulk and in specific amino acids (CSIA-AA), as well as the taxonomic composition of mesozooplankton samples collected monthly during two full years, to investigate whether the upwelling intensity affects the isotopic N baseline and other trophic indices at the community level in the coastal system off NW Iberian Peninsula. We hypothesized that enhanced phytoplankton productivity during upwelling events would lead to a shorter and more efficient food web. Upwelling induced mesozooplankton herbivory (by increasing the abundance and biomass of omnivorous-herbivorous copepods and other taxa), resulting in a linear decrease of TPGlx (estimated using Glx = glutamic acid + glutamine, which mainly involves metazoan links) from downwelling to upwelling situations. In contrast, TPAla (estimated using alanine, which also reflects microbial trophic pathways) was highest in low-moderate upwelling and decreased with upwelling strength. Thus, an optimal coupling between metazoan and microbial food webs was reached at low-moderate upwelling intensities when the microbial contribution was ca. 25 %, while this contribution decreased (<15 %) either during downwelling or during strong upwelling. However, the significance of differences in mean values of TP and zooplankton composition was small due to the rapid succession of upwelling and downwelling events. Our results illustrate how a combination of CSIA-AA and community data can provide valuable information on rapid changes in mesozooplankton food web structure in highly dynamic upwelling systems.

What happens in the shadows - Influence of seasonal and non-seasonal dynamics on domoic acid monitoring in the Monterey Bay upwelling shadow

Domoic acid produced by toxigenic Pseudo-nitzschia species is the main toxin threat from harmful algal blooms in Monterey Bay and the larger California Current region on the West Coast of the United States. Toxin monitoring in Monterey Bay includes a long-running time series of weekly measurements of domoic acid from water samples, sentinel mussels, and solid phase adsorption toxin tracking (SPATT) at the Santa Cruz Municipal Wharf (SCW). The SCW sampling site is unusual because of its position in the Monterey Bay upwelling shadow in the north bay. The upwelling shadow circulation pattern has been previously characterized as a bloom incubator for dinoflagellates, but it has not yet been analyzed in the context of long-term monitoring methods. In data collected from the SCW from 2012 - 2020, domoic acid from water samples and sentinel mussels had a different temporal distribution than domoic acid from SPATT. Here we explore the discrepancy through a seasonal and non-seasonal analysis including physical oceanography of the region. Results show that domoic acid from water samples and sentinel mussels are related to seasonal upwelling and Pseudo-nitzschia blooms. Domoic acid monitored by SPATT, on the other hand, is correlated to anomalous upwelling and warmer than usual temperatures during the relaxation season. This work builds on previous analyses of the SCW time series and contributes to understanding of the circulation of dissolved toxin in the environment. Results lend rationale for the continuation of rigorous domoic acid monitoring in Monterey Bay and encourage stakeholders to consider local physical dynamics when interpreting toxin monitoring data.

Reproduction of Carijoa riisei (Cnidaria: Octocorallia) in the Panamanian tropical eastern Pacific

Octocorals are the main component of rocky walls in the Panamanian tropical eastern Pacific (TEP), providing shelter and substrate for diverse marine invertebrates and demersal fishes. Despite their ecological importance, many essential biological traits of these corals remain undescribed. Like some cnidarians, octocorals may be related to bioinvasion. One emerging risk is the rise of the Indo-Pacific invasive octocoral Carijoa riisei, which overgrows other soft corals, competing for food and space and promoting the emergence of diseases. Considering the potential risk to native octocorals, we investigated the reproductive seasonality of C. riisei at 15 m depth every month for one year in the Gulf of Panama (Las Perlas Archipelago), an octocoral diversity hotspot with seasonal upwelling. Carijoa riisei showed an average fecundity (percentage of polyps with eggs sampled throughout the year from only female colonies) of 53% (SE 0.03%) with no seasonality. Carijoa riisei produced eggs continuously with overlapping generations, with an average of 23 (1–107; SE 0.75) eggs per fertile polyp and an average egg diameter of 0.12 (0.10–0.64; SE 0.0008) mm. The number of eggs inside the gastrovascular cavity was higher during the upwelling. However, the size and proportion of large eggs were greater towards the end of the upwelling season, with a drastic decrease from 30% to 2% at its end. Our results over a one-year sampling period show that in the Panamanian TEP, C. riisei reproduces continuously, seemingly energized by higher nutrient levels present during upwelling. This, along with its rapid growth rate, makes this species a formidable competitor for native species. Thus, we encourage future monitoring of these populations.

Seasonal upwelling conditions promote growth and calcification in reef-building coralline algae.

Crustose coralline algae (CCA) are important components of reef ecology contributing to reef framework construction. However, little is known about how seasonal upwelling systems influence growth and calcification of tropical CCA. We assessed marginal and vertical growth and net calcification rates of two dominant but morphologically different reef-building CCA, Porolithon antillarum and Lithophyllum cf. kaiseri, in a shallow coral reef of the Colombian Caribbean during upwelling and non-upwelling seasons. Growth and calcification rates varied seasonally with higher values during the upwelling compared to the non-upwelling (rainy) season. Annual vertical growth showed rates of 4.48 ± 1.58 and 4.31 ± 2.17 mm · y-1 , net calcification using crust growth estimates of 0.75 ± 0.30 g and 0.68 ± 0.60 g CaCO3 · cm-2 · y-1 and net calcification using the buoyant weight method of 1.49 ± 0.57 and 0.52 ± 0.11 g CaCO3 · cm-2 · y-1 in P. antillarum and L. kaiseri, respectively. Seawater temperature was inversely related with growth and calcification; however, complex oceanographic interactions between temperature and resource availability (e.g., light, nutrients, and CO2 ) are proposed to modulate CCA vital rates. Although CCA calcification rates are comparable to hard corals, CCA vertical accretion is much lower, suggesting that the main contribution of CCA to reef construction is via cementation processes. These results provide baseline data on CCA in the region and generate useful information for monitoring the impacts of environmental changes on tropical upwelling environments.

High primary productivity in an Ediacaran shallow marine basin influenced by strong seasonal to perennial upwelling

AbstractA significant area of late Neoproterozoic–early Cambrian seafloor hosted a ferruginous to euxinic condition as a result of expanded primary productivity-driven pumping of organic matter into subsurface water column and weak water column mixing in the concomitant sea. However, the cause and extent of increased marine primary productivity during this time interval remain unknown. To estimate the primary productivity in a late Neoproterozoic sea, this study investigated the Sirbu Shale, Vindhyan Supergroup, for trace elements, organic carbon isotopes and total organic carbon (TOC). Among the trace elements, cadmium (Cd), known for extremely low concentration in crustal rocks but higher abundance in biogenic organic matter, was the key parameter in the palaeoproductivity estimation. The Cd enrichment in the Sirbu Shale samples is comparable to that in modern marine sediments of the oxygen minimum zones in Chilean margins, Arabian Sea and Gulf of California characterized by high primary productivity and seasonal upwelling. In terms of Cd enrichment, the lower section of the Sirbu Shale was deposited under suboxic conditions, while the upper section was deposited under a relatively less reducing condition. Cd/Mo ratios &gt; 0.36 in the shale sample indicate that the palaeoproductivity was strongly influenced by the nutrient supply through sea-shelf upwelling. Using non-detrital enrichment of Cd in Sirbu Shale samples, we calculated that the TOC exported to the floor of Sirbu Shale palaeodepositional setting through primary productivity ranged from 0.71 to 10.16%.

Simulated upwelling and marine heatwave events promote similar growth rates but differential domoic acid toxicity in Pseudo-nitzschia australis

Along the west coast of the United States, highly toxic Pseudo-nitzschia blooms have been associated with two contrasting regional phenomena: seasonal upwelling and marine heatwaves. While upwelling delivers cool water rich in pCO2 and an abundance of macronutrients to the upper water column, marine heatwaves instead lead to warmer surface waters, low pCO2, and reduced nutrient availability. Understanding Pseudo-nitzschia dynamics under these two conditions is important for bloom forecasting and coastal management, yet the mechanisms driving toxic bloom formation during contrasting upwelling vs. heatwave conditions remain poorly understood. To gain a better understanding of what drives Pseudo-nitzschia australis growth and toxicity during these events, multiple-driver scenario or ‘cluster’ experiments were conducted using temperature, pCO2, and nutrient levels reflecting conditions during upwelling (13 °C, 900 ppm pCO2, replete nutrients) and two intensities of marine heatwaves (19 °C or 20.5 °C, 250 ppm pCO2, reduced macronutrients). While P. australis grew equally well under both heatwave and upwelling conditions, similar to what has been observed in the natural environment, cells were only toxic in the upwelling treatment. We also conducted single-driver experiments to gain a mechanistic understanding of which drivers most impact P. australis growth and toxicity. These experiments indicated that nitrogen concentration and N:P ratio were likely the drivers that most influenced domoic acid production, while the impacts of temperature or pCO2 concentration were less pronounced. Together, these experiments may help to provide both mechanistic and holistic perspectives on toxic P. australis blooms in the dynamic and changing coastal ocean, where cells interact simultaneously with multiple altered environmental variables.

Citizen science approach for monitoring fish and megafauna assemblages in a remote Marine Protected Area

Marine Protected Areas (MPA) safeguard threatened marine ecosystems by protecting fish populations, limiting anthropogenic stressors, and providing additional livelihood for local populations. However, many MPAs do not function effectively due to lack of funding and manpower, engendering the need to find long-lasting, sustainable solutions to monitor and maintain MPA performance. In this study, we utilized citizen science involvement to survey select fish families (Lutjanidae, Serranidae, Carangidae, Scombridae, Sphyraenidae, Lethrinidae, and Scaridae), key fish species (large and vulnerable piscivores), and megafauna in Nusa Penida MPA, Indonesia using the roving survey method. We found that despite a short training period and fast turnover rate, our participants were able to identify all target taxa, as well as detect spatial and temporal trends in fish and megafauna assemblages. An increase in fish density during austral winter was correlated with seasonal upwelling phenomena induced by the southeast monsoon, while site variations were influenced by local topography and type of current. We conclude that citizen science participation contributed immensely to the monitoring of Nusa Penida MPA, and subsequent self-sustained, long-term monitoring will be invaluable for future policy and decision making in MPA management and enforcement.

Shifting responses of phytoplankton to atmospheric and oceanic forcing in a prolonged marine heatwave

AbstractMarine heatwaves are becoming a severe challenge for marine ecosystems. However, current understanding of their impacts on phytoplankton, especially biomass and community structure, is still deficient or fragmentary. Here, we focus on the response of phytoplankton to a prolonged (372 d) marine heatwave in the southeastern tropical Indian Ocean in 2015–2016. Despite a similar surface warming throughout the marine heatwave, we found two distinctively different changes in chlorophyll a (Chl a) concentration, based on which the marine heatwave was divided into two phases of nearly equal duration. During Phase 1, the Chl a concentration and phytoplankton biomass increased slightly, while during Phase 2 they decreased dramatically, with a marked shift in phytoplankton community toward smaller‐size species. This difference mainly resulted from the change in dominant drivers of the marine heatwave, which shifted from atmospheric forcing (enhanced net air–sea heat flux) in Phase 1 to oceanic process (downwelling Kelvin waves) in Phase 2. The intensified near‐surface stratification and upwelling Kelvin waves led to a slight surface nutrient increase in Phase 1, while the downwelling Kelvin waves suppressed the seasonal upwelling in Phase 2, resulting in a substantial decrease in nutrient supply from the subsurface ocean, and hence dramatic decreases in Chl a concentration and biomass. Our results demonstrate the complex responses of phytoplankton to marine heatwaves and highlight the importance of distinguishing the driving mechanisms of marine heatwaves when evaluating their ecological impacts.

Growth and diet of a larval myctophid across distinct upwelling regimes in the California Current

Abstract Eastern boundary systems support major fisheries of species whose early stages depend on upwelling production. However, upwelling can be highly variable at the regional scale, leading to complex patterns of feeding, growth, and survival for taxa that are broadly distributed in space and time. The northern California Current (NCC) is characterized by latitudinal variability in the seasonality and intensity of coastal upwelling. We examined the diet and larval growth of a dominant myctophid (Stenobrachius leucopsarus) in the context of their prey and predators in distinct NCC upwelling regimes. Larvae exhibited significant differences in diet and growth, with greater seasonal than latitudinal variability. In winter, during reduced upwelling, growth was substantially slower, guts less full, and diets dominated by copepod nauplii. During summer upwelling, faster-growing larvae had guts that were more full from feeding on calanoid copepods and relying less heavily on lower trophic level prey. Yet, our findings revealed a dome-shaped relationship with the fastest growth occurring at moderate upwelling intensity. High zooplanktivorous predation pressure led to above average growth, which may indicate the selective loss of slower-growing larvae. Our results suggest that species whose spatio-temporal distributions encompass multiple regional upwelling regimes experience unique feeding and predation environments throughout their range with implications for larval survivorship.