Seasonal Upwelling Events Research Articles

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.

Swimming performance and physiological responses of juvenile Cojinoba Seriolella violacea in hypoxic conditions

Understanding environmental constraints and associated physiological adaptations of culture organisms is key for the implementation of off-shore grow-out facilities. In the southeast Pacific Ocean along the coasts of Chile and Peru, seasonal upwelling events lead to hypoxic conditions, which are projected to increase in both frequency and intensity with climate change. Aquaculture operations must take into account the physiological adaptability of a species for environmental conditions. For Cojinoba (Seriolella violacea), a native target species for aquaculture diversification in northern Chile, little is known in regard to physiological capacity for hypoxia. Therefore, hypoxia tolerance studies were conducted followed by measurement of resting and active metabolism and associated energy facilitation in response to hypoxia in juvenile Cojinoba. Hypoxia tolerance studies found they were resilient to dissolved oxygen levels of 1.0 mg O2 Lˉ1 for 8 h. Swimming metabolism studies exposed Cojinoba to normoxia (7.5 mg O2 Lˉ1) or hypoxia (1.0 mg O2 Lˉ1), and quantified minimum metabolic rate (MO2 min), active metabolic rate (MO₂ max), critical swimming speed (Ucrit) and associated energetic metabolites and hematological variables. In hypoxia, there was a decrease in MO₂ max (34%) leading to a large (82%) decrease in aerobic metabolic scope. MO2 min decreased as well by 12%, with lactate increasing presumably to temporarily maintain basic metabolic function. In addition, Ucrit decreased by 53% in hypoxia, although tail beat frequency was similar in normoxia and hypoxia up to a velocity of 40 cm s−1. Moreover, although erythrocyte concentration increased in hypoxia, hemolysis was observed in exercised fish in this condition. There was a notable increase (5-fold compared to normoxia) in lactate levels of exercised fish in the hypoxia group, which suggests a quick conversion to anaerobic metabolic pathways to maintain energy balance when swimming in hypoxic environments. Therefore, Cojinoba have adaptive responses that may facilitate survival during severe hypoxic events although overall physiological performance is diminished.

Using fisheries data to model the oceanic habitats of juvenile silky shark (Carcharhinus falciformis) in the tropical eastern Atlantic Ocean

Investigating the relationship between species and environmental conditions is key for the correct management of highly migratory large pelagic species like silky shark (Carcharhinus falciformis). This species is currently ranked as vulnerable by the International Union for Conservation of Nature and the population trend may be decreasing globally. Tuna fisheries annually catch around 5 million tons worldwide but may have effects on the ecosystem, including impacts on certain sensitive non-target species. We provide the first insights into the environmental preferences of silky shark in the Atlantic Ocean by modelling their presence from tropical tuna purse seine observer data (~ 7500 fishing sets between 2003 and 2015) with a set of biotic and abiotic oceanographic factors, spatial–temporal terms and fishing operation variables. Oceanographic data (sea surface temperature, sea surface temperature change, salinity, sea surface height, chlorophyll-a, chlorophyll-a change, oxygen, and current information such as speed, direction and eddy kinetic energy) were downloaded and processed from the EU Copernicus Marine Environment Monitoring Service. Results provide information on the hotspots dynamics of silky shark as well as its habitat preferences. Models detected a significant relationship between seasonal upwelling events, mesoscale features and silky shark presence and suggested strong interaction between productive systems and the spatial–temporal distribution of the species. The model also highlighted both persistent (i.e. Gabon) and temporary areas (i.e. Guinea and southern-central tropical Atlantic Ocean) for silky shark in the region. This information could be used to assist tuna regional fisheries management organizations in the conservation and management of this vulnerable non-target species.

On the use of optical remote sensing to assess phytoplankton biomass dynamics in the Pelagos Sanctuary (Ligurian-Provençal Sea)

If Marine Protected Areas (MPAs) are to aid in protecting and conserving marine ecosystems in the face of extensive and severe impacts of human activities, underpinning scientific knowledge and understanding of MPAs are imperative. This study aims to describe and evaluate phytoplankton dynamics in a pelagic Mediterranean MPA (The Pelagos International Marine Mammals Sanctuary) in the north-western Mediterranean Sea as a means to understand better the spatial and temporal distribution of basal ecosystem resources. Ocean colour data collected by orbital remote sensing (Sea-viewing Wide Field-of-view Sensor [SeaWiFS] data) were analysed to elucidate spatial and temporal variations in the concentration of chlorophyll-like pigments (chl). Mean chl images were generated for consecutive 10-day periods, to provide quasi-continuous coverage of the study area, combined with a Principal Component Analysis and analysis of a time series ​(1998–2004). The chl surface patterns traced seasonal upwelling events recurring annually, demonstrating the critical role of physical oceanography in sustaining the food web of the PelagosSanctuary. Phytoplankton blooms, however, differ in terms of peak timing, spatial distribution and chl concentration, due in part to the influence of broad-scale environmental factors that are beyond direct and regional control. Further research is needed to elucidate the relationship between the biomass of primary and secondary producers to understand better the implications of phytoplankton biomass distribution in space and time for charismatic and protected biota such as cetaceans.

Effects of structural factors on upwelling fouling community, Southeast Brazil

Abstract To assess the successional pattern of fouling organisms three hypotheses were tested: 1) a thermocline is caused by seasonal upwelling events, and therefore, depth influences the successional trajectory of the fouling community; 2) a reduction in the intensity of natural light of the substrate influences the fouling composition and the successional trajectory; 3) fish predation influences the community composition and its successional trajectory. During one year, up-facing and down-facing PVC panels on open, partially caged or fully caged, and placed at depths of 1.5 and 3.5 meters were monthly sampled by digital photograph to determine the community composition and by contact point to estimate the percent coverage of organisms. The upwelling impact provided different water masses, and light intensity was also a determining factor of the overall successional trajectory of the fouling community. After the installation of full and partial cages, differences were identified in the respective successional trajectories. The results of this study suggest that each physical factor or biological process can change the successional trajectory of the community, and the successional model (e.g., convergent, divergent, parallel, or cyclic) depends on the magnitudes of the determinants that act on the community at each stage of its trajectory.

Effects of simulated overfishing on the succession of benthic algae and invertebrates in an upwelling-influenced coral reef of Pacific Costa Rica

Overfishing and nutrient enrichment are among the major local stressors to coral reefs worldwide, as they can alter the benthic reef community by promoting fast growing algae and bioeroders. The Northern coast of Pacific Costa Rica is strongly influenced by seasonal upwelling events that naturally increase nutrient concentrations between December and March. This study therefore investigated the combined effects of simulated overfishing and naturally increased nutrients on benthic community composition and succession on settlement tiles over a period of 24weeks (October 2013 until March 2014) using exclusion cages deployed in a coral reef in the Gulf of Papagayo. Tile cover of functional groups and development of organic C and N on light-exposed and –shaded tile sites were assessed. Results revealed that the exclusion of fish significantly increased the development of organic C and N and decreased the C/N ratio on light-exposed tiles. Large filamentous algae (>2mm), fleshy macroalgae and the colonial ascidian Didemnum sp. (Savigny 1816) (up to 80% tile coverage) were dominant on both tile sites. A significant peak of filamentous algae growth and associated organic matter C/N ratio occurred on light-exposed tiles throughout all treatments in February when nutrient concentrations were elevated. These results suggest that both herbivore exclusion and natural eutrophication have a strong influence on the benthic reef community composition and its early succession patterns. The presence of Didemnum sp. and turf algae could represent good early warning bioindicators for local overfishing and eutrophication and may therefore be included in management and monitoring strategies.

Fish larvae retention linked to abrupt bathymetry at Mejillones Bay (northern Chile) during coastal upwelling events

The influence of oceanic circulation and bathymetry on the fish larvae retention inside Mejillones Bay, northern Chile, was examined. Fish larvae were collected during two coastal upwelling events in November 1999 and January 2000. An elevated fish larvae accumulation was found near an oceanic front and a zone of low-speed currents. Three groups of fish larvae were identified: the coastal species (Engraulis ringens and Sardinops sagax), associated with high chlorophyll-a levels; larvae from the families Phosichthyidae (Vinciguerria lucetia) and Myctophidae (Diogenichthys laternatus and Triphoturus oculeus), associated with the thermocline (12°C), and finally, larvae of the families Myctophidae (Diogenichthys atlanticus) and Bathylagidae (Bathylagus nigrigenys), associated with high values of temperature and salinity. The presence of a seamount and submarine canyon inside Mejillones Bay appears to play an important role in the circulation during seasonal upwelling events. We propose a conceptual model of circulation and particles retention into Mejillones Bay. The assumption is that during strong upwelling conditions the flows that move along the canyon emerge in the centre of Mejillones Bay, producing a fish larvae retention zone. Understanding the biophysical interactions responsible to trap and/or concentrate particles is essential to protect these fragile upwelling ecosystems.

Seasonal phenology of Sargassum liebmannii J. Agardh (Fucales, Heterokontophyta) in an upwelling area of the Eastern Tropical Pacific

Seasonal changes in growth, biomass, abundance and reproduction of brown algae have been reported from subtropical and temperate regions, but there are very few reports from tropical regions, and none from the Eastern Tropical Pacific (ETP). Sargassum liebmannii is a common brown alga in the ETP at Bahía Salinas, a seasonal upwelling area in the northern Pacific coast of Costa Rica. We measured the length of ∼50 individuals every two months from 2005 to 2007 and collected samples for reproductive analyses from 2008 to 2009. The growth rate of S. liebmannii peaked during the seasonal upwelling events (November to May), when minimum temperatures reached 15.5°C and nutrient concentrations were high. During upwelling events, S. liebmannii grew from a few millimeters to over 1m high, with a maximum mean growth rate of 0.68cmd−1 during the most intense upwelling period. Sexual reproduction occurred in the non-upwelling period. After attaining maximum size, S. liebmannii reproduces (June) and becomes detached from the substrate, floating in the bay and sometimes accumulating in nearby beaches. Sargassum liebmannii at this study site was absent in 2013 following a population outbreak of the black sea urchin, Diadema mexicanum.

The effect of long-term water table manipulations on dissolved organic carbon dynamics in a poor fen peatland

Dissolved organic carbon (DOC) production, consumption, and quality displayed differences after long-term (~55 years) hydrological alterations in a poor fen peatland in northern Michigan. The construction of an earthen levee resulted in areas of a raised and lowered water table (WT) relative to an unaltered intermediate WT site. The lowered WT site had greater peat aeration and larger seasonal vertical WT fluctuations that likely elevated peat decomposition and subsidence with subsequent increases in bulk density, vertical hydraulic gradient, decreased hydraulic conductivity (Ksat), and a greater pore water residence time relative to the unaltered site. The raised WT site displayed a decreased Ksat combined with seasonal upwelling events that contributed to a longer residence time in comparison to the unaltered site. These differences are potentially contributing to elevated DOC concentrations at the lowered and raised WT site relative to the unaltered site. Additionally, spectrophotometric indices and chemical constituent assays indicated that the lowered site DOC was more aromatic and contained elevated concentrations of phenolics compared to the intermediate site. The raised site DOC was less aromatic, less humified, and also had a greater phenolic content than the intermediate site. Furthermore, an incubation experiment showed that DOC in the raised site contained the greatest labile carbon source. Based on our results, long-term WT alterations will likely impose significant effects on DOC dynamics in these peatlands; however, WT position alone was not a good predictor of DOC concentrations, though impoundment appears to produce a more labile DOC whereas drainage increases DOC aromaticity.

Turritella declivis Adams & Reeve, in Reeve, 1849 (Mollusca: Gastropoda) – a South African not an Australian species, and a characteristic component of the Agulhas Bank benthos

The name Turritella declivis, as described by Adams and Reeve in the ‘The Zoology of the Voyage of HMS Samarang’ (Adams & Reeve 1848-1850), is currently used for two distinct species of turritellid gastropod, one inhabiting the Agulhas Bank off South Africa and the other occurring off the Australian coast. Examination of the type material clearly shows that the name is referable to the southern African species. The Australian species must henceforth be known as Turritella captiva Hedley, 1987, a name previously regarded as a junior synonym of T. declivis. The original type locality ‘China Seas’ is erroneous, as was often the case with material collected during the voyage of the Samarang. It is emended to be the Agulhas Bank, over much of which T. declivis is common and may, in places, be hugely abundant, forming Turritella-dominated benthic communities. Such communities have been recorded in other parts of the world and are frequently associated with seasonal upwelling events, but have not previously been documented off South Africa.

Turritella declivisAdams & Reeve, in Reeve, 1849 (Mollusca: Gastropoda) — a South African not an Australian Species, and a Characteristic Component of the Agulhas Bank benthos

The name Turritella declivis, as described by Adams and Reeve in the ‘The Zoology of the Voyage of HMS Samarang’ (Adams & Reeve 1848–1850), is currently used for two distinct species of turritellid gastropod, one inhabiting the Agulhas Bank off South Africa and the other occurring off the Australian coast. Examination of the type material clearly shows that the name is referable to the southern African species. The Australian species must henceforth be known as Turritella captiva Hedley, 1987, a name previously regarded as a junior synonym of T. declivis. The original type locality ‘China Seas’ is erroneous, as was often the case with material collected during the voyage of the Samarang. It is emended to be the Agulhas Bank, over much of which T. declivis is common and may, in places, be hugely abundant, forming Turritella-dominated benthic communities. Such communities have been recorded in other parts of the world and are frequently associated with seasonal upwelling events, but have not previously been documented off South Africa.

High-resolution measurements of atmospheric molecular hydrogen and its isotopic composition at the West African coast of Mauritania

Abstract. Oceans are a net source of molecular hydrogen (H2) to the atmosphere, where nitrogen (N2) fixation is assumed to be the main biological production pathway followed by photochemical production from organic material. The sources can be distinguished using isotope measurements because of clearly differing isotopic signatures of the produced hydrogen. Here we present the first ship-borne measurements of atmospheric molecular H2 mixing ratio and isotopic composition at the West African coast of Mauritania (16–25° W, 17–24° N). This area is one of the biologically most active regions of the world's oceans with seasonal upwelling events and characterized by strongly differing hydrographical/biological properties and phytoplankton community structures. The aim of this study was to identify areas of H2 production and distinguish H2 sources by isotopic signatures of atmospheric H2. For this more than 100 air samples were taken during two cruises in February 2007 and 2008. During both cruises a transect from the Cape Verde Islands towards the Mauritanian Coast was sampled to cover differing oceanic regions such as upwelling and oligotrophic regimes. In 2007, additionally, four days were sampled at high resolution of one sample per hour to investigate a possible diurnal cycle of atmospheric H2. Our results indicate the influence of local sources and suggest the Banc d'Arguin as a pool for precursors for photochemical H2 production, whereas oceanic N2 fixation could not be identified as a source for atmospheric H2 during these two cruises. The variability in diurnal cycles is probably influenced by released precursors for photochemical H2 production and also affected by a varying origin of air masses. This means for future investigations that only measuring the mixing ratio of H2 is insufficient to explain the variability of an atmospheric diurnal cycle and support is needed, e.g. by isotopic measurements. Nevertheless, measurements of atmospheric H2 mixing ratios, which are easy to conduct online during ship cruises, could be a useful indicator of production areas of biological precursors such as volatile organic compounds (VOCs) for further investigations.

Satellite Tracking of Manta Rays Highlights Challenges to Their Conservation

We describe the real-time movements of the last of the marine mega-vertebrate taxa to be satellite tracked – the giant manta ray (or devil fish, Manta birostris), the world's largest ray at over 6 m disc width. Almost nothing is known about manta ray movements and their environmental preferences, making them one of the least understood of the marine mega-vertebrates. Red listed by the International Union for the Conservation of Nature as ‘Vulnerable’ to extinction, manta rays are known to be subject to direct and incidental capture and some populations are declining. Satellite-tracked manta rays associated with seasonal upwelling events and thermal fronts off the Yucatan peninsula, Mexico, and made short-range shuttling movements, foraging along and between them. The majority of locations were received from waters shallower than 50 m deep, representing thermally dynamic and productive waters. Manta rays remained in the Mexican Exclusive Economic Zone for the duration of tracking but only 12% of tracking locations were received from within Marine Protected Areas (MPAs). Our results on the spatio-temporal distribution of these enigmatic rays highlight opportunities and challenges to management efforts.

Reef fish mass mortality event in an isolated island off Brazil, with notes on recent similar events at Ascension, St Helena and Maldives

Events of mass mortality of marine fish have been reported to occur world wide, mainly in coastal regions of continental shelves. Here we report an event at Trindade Island, located 1160 km from the Brazilian coast. Melichthys niger was the species most commonly seen affected. Twenty-four other species were found washed ashore. Victims were demersal (72% of species), pelagic (20%) and benthonic species (8%), comprising eight trophic categories. There is evidence that fish kills have occurred at Trindade since at least the 1990s. Mortality events mainly involving primarily Balistidae (Trindade, Maldives and Ascension), Chaetodontidae (St Helena) and Serranidae (Ascension) have been reported for other isolated oceanic localities with low human occupation. It is possible that blooms of toxic algae, under certain conditions cause cascading intoxication along the trophic web. A second hypothesis is that seasonal upwelling events of anoxic or hypoxic waters may be implicated.

Hydromedusa blooms and upwelling events in the Bay of Panama, Tropical East Pacific

Seasonal upwelling events dominate the coastal areas of some regions of the Tropical East Pacific. The effects of upwelling on gelatinous zooplankton are largely unknown and undocumented for this or any region, although upwelling is known to shape phytoplankton dynamics. Small hydromedusae, the most widespread and diverse representatives of gelatinous plankton, are often neglected in plankton ecology as they are inconspicuous and escape direct observation. Their occurrence is seasonal and standard plankton sampling techniques easily overlook their blooms. In order to investigate whether upwelling affects hydromedusae dynamics, we monitored their abundance and diversity in the Bay of Panama, a region on the Pacific Coast of Panama characterized by seasonal upwelling events. Our results show that, although the number of species is relatively constant throughout the year, hydromedusa abundance in the Bay of Panama can be up to two orders of magnitude higher during upwelling than non-upwelling conditions. The difference in the numbers of hydromedusae between the two seasons is mostly due to temporally short medusa blooms that occur only during the upwelling season. Our results point to a link between hydromedusa blooms and upwelling events, and the increased productivity associated with them. The results are consistent with a scenario in which upwelling events act on the benthic colonies thus inducing medusa production.

Domoic acid accumulation in the sardine Sardina pilchardus and its relationship to Pseudo-nitzschia diatom ingestion

Planktivorous fish are key potential vectors for the phycotoxin domoic acid (DA), pro- duced naturally by diatoms from the genus Pseudo-nitzschia. The diet of the Atlantic sardine Sardina pilchardus is largely dominated in number by microplanktonic species such as chain-forming diatoms, making the accumulation of this toxin and its transfer to the higher trophic levels likely. DA concentration in sardine tissues and Pseudo-nitzschia ingestion were monitored fortnightly during 2002 and 2003 off the NW coast of Portugal, where seasonal upwelling events are responsible for the occurrence of algal blooms. Sardine stomach content analysis showed that Pseudo-nitzschia prey reached concentrations as high as 7.8 × 10 6 cells g -1 ; in some cases this diatom genus represented more than 99% of the phytoplanktonic prey identified in the stomachs. Four different diatom species were distinguished using scanning electron microscopy (SEM): P. australis, P. pungens, P. pseudodel- icatissima and P. delicatissima. DA accumulation in sardines was linearly dependent on P. australis consumption. Toxin content per individual cell was estimated by comparing DA and P. australis con- centrations in the stomach contents. DA production by P. australis was significantly higher in the summer months than during the spring. In both years, DA in sardine guts was initially detected in May and peaked several times until late summer. Toxin distribution in the different tissues was also determined, with the highest DA levels detected in the intestine. The maximum toxin concentration observed in sardine guts was 128.5 µg DA g -1 . No DA was found in the sardine muscle; consequently implications for human health appear minimal.

Palaeoenvironmental Signals and Growth Rates of Rhodoliths — a Geochemical Approach

Electron microprobe and stable isotope studies were undertaken on Recent rhodolith specimens (coralline red algae) in order to accurately determine their growth rates and palaeotemperature signal. Results show a cyclic variation of the Mg/Ca ratio and an amplitude of the oxygen isotope curve that accurately reflects the sea-surface temperature. Geochemical signals extracted from coral growth bands are commonly used as long term highresolution palaeoenvironmental indicators for reconstructing temperature and salinity variations of surface water masses. The main constraint in using corals is their limited geographical range of distribution, which is confined to tropical and subtropical seas. In order to deduce high resolution geochemical sea surface water signals from nontropical seas, mollusks have been employed by various authors in recent years. This paper introduces rhodoliths as a new organism for palaeoenvironmental analysis of tropical and non-tropical seas. Rhodoliths, which live in the subtidal zone to water depths of 100 m, are defined as nodules and unattached branched growths with a nodular form composed principally of coralline red algae (Bosence, 1983). The High-Mg calcite skeleton can exhibit different growth morphologies which range from spherical to ellipsoidal and can be thickly or thinly branching, with individual branches reaching up to lcm in diameter. Rhodolith morphology is a result of frequent overturning due to water motion (during storms) or biogenic activity (bottom feeding fish, inand epifaunal organisms). Vertical growth rates of coralline red algae are poorly studied but have been reported by various authors to range from 200 gm to 5 ram/year (see Edyvean and Ford (1987) for a compilation of growth rates). We have selected rhodoliths for geochemical studies because (1) they show well developed growth bands, (2) their geographic range spans from tropical to Arctic seas and (3) they exhibit longevity (specimens with an age of several hundred years have been reported; Bosellini and Ginsburg, 1971). This latter will allow us to eventually acquire palaeoenvironmental records dating back further than those derived from molluscan shells. This will have special importance for assessing Arctic records, which, if they are derived from mollusks, do not date back more than a few dozen years. For the present study we collected live (or partially living) specimens of Lithothamnium sp. from the southern Gulf of California, Mexico, where rhodoliths are the second most important carbonate producers after corals. Lithothamnium sp. is most abundant in 2 5 m water depth and individuals with diameters of up to 10 cm have been reported (Foster et al., 1997). For this study we prepared polished thick sections of branches with widths of up to 0.8 cm and lengths of up to 3.5 cm. The COADS SST data set for this site shows an average sea surface temperature range from 19.9-30.8~ however, the geochemical signal could be complicated by nearby seasonal upwelling events. Rhodolith thick sections were element mapped with an electron microprobe for Ca and Mg and individual growth bands were microsampled for stable isotope analysis using a bandwidth of 40 microns and a dril l depth of 60 microns. Complicating factors during the microsampling were the high concavity and slight irregularity of the growth bands and the extremly small sample size (<10 I-tg) that was obtained by drilling along growth bands for a maximum length of 3 mm.