Surface Seawater Salinity Research Articles

Effects of Climate Events on Abundance and Distribution of Major Commercial Fishes in the Beibu Gulf, South China Sea

Improving prediction of ecological responses to climate variability requires understanding how local fish population dynamics are impacted by climate events. The present study was conducted in the Beibu Gulf of the northwestern South China Sea where the fisheries are characterized by high ecological and commercial value. We evaluated the relationship between major commercial fish population dynamics (abundance and distribution) and climate periods, using survey data from 2006–2020. The analysis using random forest and GAM models show that climate events are not the best predictors for the variations of fish abundance, because abundance of most fish stocks decreases significantly with the year, and the increasing fishing pressure over time can better explain the overall downward trend in fishery stocks. However, environmental variables that correlate significantly with interannual variation in ONI may impact fish abundance in short terms. Our research suggests that climate events leading to higher surface seawater salinity in winter favors pelagic fishes by improving habitat availability, and higher near-surface chlorophyll-α concentration during La Niña events provides better food condition for overwintering fish. In addition, there is no clear evidence that climatic events have a significant impact on gravity center of fish distribution, whereas climate change has caused most fishes to move to cooler coastal waters in the north.

Habitat suitability evaluation of Harpadon nehereus in nearshore of Zhejiang province, China

Coastal waters provide an important spawning and nursery ground for offshore marine organisms. To understand the suitable habitat and distribution of Harpadon nehereus, a key nearshore species, this study assessed the survey data of fishery resources and environment in Zhejiang’s nearshore fishery in Spring of 2017 to 2020. We used the generalized additive model (GAM) and random forests model (RF) to analyze the environmental factors affecting the selection of spawning habitats by H. nehereus and analyzed the suitable habitat characteristics of H. nehereus in nearshore fisheries. Our results indicate that H. nehereus is widely distributed in Zhejiang’s nearshore and that its density is higher in waters near islands and reefs. Among the relative importance scores of predictors calculated based on RF, seawater salinity is an important environmental factor affecting the distribution of H. nehereus in April (surface seawater salinity was 38.67% and bottom seawater salinity was 34.5%), followed by depth (34.19%), whereas the change in water temperature had no obvious effect on H. nehereus distribution. The suitable habitat characteristics of H. nehereus mainly include high salinity near a water depth of 40 m and a water area with sea bottom dissolved oxygen levels < 6 mg/L. The prediction results of the model indicate that the suitable habitat of H. nehereus is mainly located in the region near Zhoushan Islands in the north of the fishing grounds. Overall, these results may serve as a basis for determining the protection strategies of key nearshore species and enhancing fishery management units.

Ocean surface responses to super typhoon in coastal zone based on biogeochemical buoys data: A case study of “Lekima”

Situ observations were conducted by biogeochemical buoys (BGC buoys) to discover the physicochemical processes during super typhoon Lekima's passage in Zhejiang coastline, helping us gain deep insights into the responses of the sea surface on the coastal zones throughout the whole typhoon's lifetime, especially during typhoon's landing. The results show that precipitation and terrestrial inputs induced by Lekima led to the hyposalinity, demonstrated by the sharp reduction of surface seawater salinity in estuary. Phosphate concentration reached its highest point 2–4 days after the typhoon's passage, with the concentrations increasing two folds to values between 20 μg L−1 and 91 μgL−1. High chlorophyll a (Chl-a) value (4.9 μg L−1) appeared shortly after the Lekima's arrival, accompanied by algal bloom. Chl-a correlation with other physicochemical parameters showed significant variation in the typhoon's different stages of development, which have unique factors of influence. The lower N/P ratio in the coastal zones play roles in Chl-a concentration and phytoplankton bloom and the optimal N/P ratio for Prorocentrum donghaiense and Skeletonema costatum is 25 and 15 respectively.

Evaluation of oxygen isotopes and trace elements in planktonic foraminifera from the Mediterranean Sea as recorders of seawater oxygen isotopes and salinity

Abstract. The Mediterranean Sea is characterized by a relatively strong west to east salinity gradient, which makes it an area suitable for testing the effect of salinity on foraminiferal shell geochemistry. We collected living specimens of the planktonic foraminifer Globigerinoides ruber albus to analyse the relation between element ∕ Ca ratios, stable oxygen isotopes of their shells, and surface seawater salinity, isotopic composition and temperature. The oxygen isotopes of sea surface water also correlate with salinity in the Mediterranean during winter, which is when sampling for this study took place. Seawater oxygen and hydrogen isotopes are positively correlated in both the eastern and western Mediterranean Sea, although the relationship differs from previously reported values, especially in the eastern region. The slope between salinity and seawater oxygen isotopes is lower than previously published results. Still, despite the rather modest slope, seawater and foraminiferal carbonate oxygen isotopes are correlated in our dataset, albeit with large residuals and high residual variability. This scatter could be due to either biological variability in vital effects or environmental variability. Numerical models backtracking particles show that ocean-current-driven mixing of particles of different origins might dampen sensitivity and could result in an offset caused by horizontal transport. Results show that Na ∕ Ca is positively correlated with salinity and independent of temperature. As expected, foraminiferal Mg ∕ Ca increases with temperature, which is in line with earlier calibrations, and in the high salinity environment. By using living foraminifera during winter, the previously established Mg ∕ Ca–temperature calibration is extended to temperatures below 18 ∘C, which is a fundamental prerequisite of using single foraminifera for reconstructing past seasonality.

Precipitation‐Induced Reduction in Surface Ocean pCO2: Observations From the Eastern Tropical Pacific Ocean

AbstractDetermining air‐sea CO2 fluxes using pCO2 disequilibrium requires knowing the gas transfer velocity and air‐sea pCO2 difference. Most pCO2 measurements are made from ships, whose uncontaminated seawater intakes are located at >5‐m depth to prevent ingestion of air. However, there could be bias in determinations of CO2 fluxes if there is disagreement between pCO2 measurements at the surface and 5 m. Seawater measurements made at the near surface and 5 m in the eastern Equatorial Pacific Ocean show that precipitation can dilute surface seawater salinity and lower the pCO2 and dissolved inorganic carbon and raise pH of the same water, and that these changes in ocean chemistry are largely missed by measurements at 5 m. This finding implies that estimates of ocean CO2 uptake might be underestimated, since rain will lower surface ocean pCO2 in both source and sink regions and, hence, increase uptake in sink regions and decrease outgassing in source regions.

Planktonic and parasitic stages of sea lice (Lepeophtheirus salmonis and Caligus clemensi) at a commercial Atlantic salmon (Salmo salar) farm in British Columbia, Canada

Planktonic and parasitic sea lice (Lepeophtheirus salmonis and Caligus clemensi) were examined at a commercial Atlantic salmon (Salmo salar) farm near the Broughton Archipelago, British Columbia (BC) from December 2012 through March 2014. Parasitic sea lice were counted on a minimum of 20 fish in three pens per month. Surface seawater salinity ranged from 19 to 35PSU. Parasite abundance was highest in winter, peaking in January 2013 at 6.5 ind fish−1 (motiles were 14.3% L. salmonis, 85.7% C. clemensi) and February 2014 at 3.3 ind fish−1 (motiles were 96.5% L. salmonis, 3.5% C. clemensi). SLICE® (emamectin benzoate) administered in both winters rapidly reduced parasitic sea lice numbers. Monthly parasite abundance was significantly correlated with the density of sea lice larvae (nauplius and copepodid stages) (r2=0.65, p=0.01) suspended in the water column of the salmon pens. Larval density was calculated monthly via triplicate vertical plankton hauls within six pens, as well as at a reference site approximately 150m away. Larval density at the farm peaked in January 2013 (mean±SE: 1.3±0.6indm−3) and January 2014 (1.0±0.3indm−3). Sea lice nauplii were found in all samples at the reference site in densities similar to those observed within pens. Overall, the majority (87.8%) of sea lice in the plankton samples were nauplii, with copepodids comprising 5.2% and motile stages 1.8%. Surprisingly, the remaining 5.2% of planktonic sea lice were chalimus stages of C. clemensi, and were found both before and after SLICE® administration. For comparison, L. salmonis nauplius densities were estimated from established relationships between water temperature and salinity, the number of female lice present, and the approximate number of fish on site. These estimated densities were significantly (t=3.41, p=0.009) higher than actual nauplius densities observed at the farm, suggesting that sea lice larvae quickly dispersed from the farm after hatching. This study provides information on all sea lice stages present throughout an Atlantic salmon production cycle in BC (through two SLICE® treatments) and the first report of planktonic chalimus stages of C. clemensi, a commercially-relevant though relatively under-studied sea louse species.

Dinoflagelados bentónicos nocivos, asociados con el sedimento arenoso en dos playas de la isla de Margarita, Venezuela

Los dinoflagelados bentonicos nocivos (DBN) pueden generar intoxicaciones severas, de alli la importancia de su estudio. Objetivo: Se evaluaron la composicion y abundancia de DBN asociadas con el sustrato arenoso en dos playas de la isla de Margarita, Venezuela. Metodologia: Los microorganismos se recolectaron mensualmente entre enero y julio de 2015 en la zona infralitoral de cada playa. Se midio la salinidad y la temperatura superficial del agua de mar. Para cuantificarlos se uso el metodo de Utermohl y se examinaron en un microscopio invertido. Resultados: Se identificaron 22 especies, siendo el genero mas abundante Prorocentrum (35%). La abundancia total de DBN no vario entre ambas localidades (p>0,05). En playa Pampatar, la variacion mensual fue evidente, los mayores valores (48 Cel/cm2) se presentaron en mayo, al igual que por tamano de malla (30 μm=49 Cel/cm2). No se detecto relacion directa entre las variables ambientales y las especies de DBN. Por otra parte, en playa Barbasco se detectaron diferencias significativas entre las estaciones y con el tamano de poro, registrandose la mayor abundancia en la estacion S6 y la abertura de malla de 30 μm (41 Cel/cm2 y 36 Cel/cm2 respectivamente). Conclusiones: La mayoria de las especies reportadas en este estudio poseen un estatus nocivo considerable y pueden desencadenar floraciones algales nocivas (FAN) en areas donde se realiza la pesca artesanal de peces y moluscos de interes comercial en la isla de Margarita, Venezuela.

Revisiting reconstructed Indian monsoon rainfall variations during the last ∼25 ka from planktonic foraminiferal δ18O from the Eastern Arabian Sea

A careful reanalysis of recently published large body of surface seawater salinity and δ18O data indicates that the variations in the surface seawater δ18O of the Eastern Arabian Sea appear to be governed mainly by the influx of low salinity water through the Winter Monsoon Current from the relatively fresher Bay of Bengal, and transported northwards by the West India Coastal Current. Armed with this “calibration” for the present day, we revisit the south Asian summer monsoon variability during the past ∼25 ka by compiling high resolution fossil planktonic foraminiferal δ18O data from a large number of well dated sediment cores from the Eastern Arabian Sea. We clearly demonstrate that there is no evidence to believe that the south Asian summer monsoon steadily declined during the Holocene as reported in a few earlier papers from the Western Arabian Sea and speleothems from Oman. On the contrary, a majority of sediment core data corroborate the inference of a much earlier paper (Sarkar et al., 2000) of a steadily increasing monsoon rain during the Holocene. That the south Asian monsoons were driven solely by past insolation change appears invalid.

Autumn ichthyoplankton assemblage in the Yangtze Estuary shaped by environmental factors.

This study investigated the response of the ichthyoplankton community to environmental changes in the Yangtze Estuary using canonical correspondence analysis. Ichthyoplankton community and environmental data were recorded during the autumns of 1998, 2000, 2002, 2003, 2004, 2007 and 2009. Among the ichthyoplankton, the dominant larval and juvenile families were the Engraulidae, Gobiidae and Salangidae, and the most common eggs were from Trichiurus lepturus. The ichthyoplankton was identified via canonical correspondence analysis to three assemblages: an estuary assemblage dominated by Chaeturichthys stigmatias, a coastal assemblage dominated by Engraulis japonicus and Stolephorus commersonii, and an offshore assemblage dominated by Trichiurus lepturus. Regarding environmental factors in the Yangtze Estuary, suspended matter and surface seawater salinity were the main factors influencing the distributions of the different assemblages, while sediment from the Yangtze River during the rainy season and chlorophyll a were the principle drivers of the annual variances in the distribution of ichthyoplankton assemblages. Our aims in this study were to provide detailed characterizations of the ichthyoplankton assemblage in the autumns of seven years, examine the long-term dynamics of autumn ichthyoplankton assemblages, and evaluate the influence of environmental factors on the spatial distribution and inter-annual variations of ichthyoplankton assemblages associated with the Yangtze Estuary.

Seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in the southern South China Sea under the influence of the East Asian monsoon

Abstract. To examine seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in oligotrophic tropical waters under the influence of seasonal reversing monsoon, dilution experiments were conducted during the summer of 2009 (21 May to 9 June) and winter 2010 (9 to 18 November) in the southern South China Sea (SSCS). The results showed that environmental variables, phytoplankton biomass, phytoplankton growth rate (μ), microzooplankton grazing rate (m), and correlationship (coupling) between the μ and m, rather than the microzooplankton grazing impact on phytoplankton (m/μ) significantly varied between the two seasons. Higher relative preference index (RPI) for the larger-sized (> 3 μm) phytoplankton than pico-phytoplankton (< 3 μm), indicating significant size-selective grazing by microzooplankton on the larger-sized phytoplankton, were also observed. The μ and m were significantly correlated with seawater salinity and temperature, and phytoplankton biomass, which indicated that salient seasonal variations in the phytoplankton growth and microzooplankton grazing in the SSCS were closely related to the environmental variables under the influence of the East Asian monsoon. We propose that intermittent arrivals of the northeast winter monsoon could lead to the low μ and m, and the decoupling between the μ and m in the SSCS, through influencing nutrient supply to the surface water, and inducing surface seawater salinity decrease. The low m/μ (< 50 % on average) indicates low remineralization of organic matter mediated by microzooplankton and mismatch between the μ and m, and thus probably accounts for part of the high vertical biogenic particle fluxes in the prevailing periods of the monsoons in the SSCS. The size-selective grazing suggests that microzooplankton grazing partially contributes to the pico-phytoplankton dominance in the oligotrophic tropical waters such as that of the SSCS.

High resolution geochemical investigation of the bivalve shells (Glycymeris sp.) from shell mounds in Jeju Island, Korea: Late Holocene paleoclimatic implications related to East Asian Monsoon climate

Recent and shell mound bivalves (Glycymeris sp.) were collected from two sites (Sangmori and Udo, Jeju Island) to investigate paleoceanographic conditions using high resolution stable isotope and trace element data. The radiocarbon ages are about 3210 ± 50 and 4210 ± 60 BP for the Sangmori and Udo shell mounds, respectively. Both oxygen and carbon isotopic compositions of the shell mound bivalve shells show clear seasonal cycles with depleted values during summer and the coeval trend, which indicates that they were controlled by freshwater input. Similar ranges of both isotopes indicate that shallow seawater conditions near the Sangmori and Udo shell mounds are more or less similar. However, more negative oxygen and carbon isotope values of the shell mound bivalves than the recent counterpart suggest that surface seawater salinity near Jeju Island was lower due to the increase in Changjiang River Discharge. Mg contents of the recent bivalve reflect surface seawater temperature changes whereas Sr and Ba contents were controlled by nutrient concentrations directly influenced by Changjiang River Discharge. Geochemical data of the recent and shell mound bivalves may imply higher precipitation (more intense East Asian Summer Monsoon activity) at ∼3.2 and 4.2 ka under the influence of the terminal stage of Holocene climatic optimum in south China or may reflect smaller fluctuating peaks during its decline.

First high-resolution marinopalynological stratigraphy of Late Quaternary sediments from the central part of the Bulgarian Black Sea area

Spores, pollen and dinoflagellate cysts of Late Pleistocene and Holocene sediments were analyzed from Giant Gravity Core 18 from the Black Sea continental slope, recovered from a water depth of 971 m. The investigated length of the core is 203.5 cm. It includes 3 lithological units: light grey clay, sapropels and coccolith-bearing ooze. The core was sampled at 5–10 cm intervals. Sampling of the interval 141.5–126 cm was carried out at every cm. AMS radiocarbon dating of bulk organic carbon was performed on 18 selected sediment layers. This chronological data allowed the first high-resolution pollen stratigraphy of Late Quaternary sediments from the western Black Sea area to be presented. The percentage spore–pollen diagram is divided into 6 local pollen assemblage zones. The trends in the vegetation dynamics and climate changes and the early history of migration of the majority of the arboreal taxa that nowadays occur in the Eastern Balkan Range were traced out. The palynological record suggests that open oak forests were spread in the Eastern Balkan Range at the beginning of the Holocene and shows early migration of the major temperate arboreal species such as Quercus, Ulmus, Tilia and Carpinus betulus. This vegetation palaeosuccession continues with the spreading of mixed oak forests from 8950 until 2620 cal. BP (8650 ± 40 until 3120 ± 35 14C BP) followed by destructive changes due to human impact and climate deterioration. A cooling of Holocene climate that is well known in the North Atlantic region as the “8200 yrs cold event” is identified for the first time in marine records from the Bulgarian Black Sea area. The assemblages of dinoflagellate cysts and acritarchs were investigated to provide a reconstruction of surface seawater salinity and surface seawater temperature changes. Two main dinoflagellate cyst assemblages, one dominated by fresh- to brackish water species such as Spiniferites cruciformis and Pyxidinopsis psilata and a subsequent one, that is characterized by euryhaline marine Mediterranean species such as Lingulodinium machaerophorum, Spiniferites belerius, Spiniferites bentorii, Operculodinium centrocarpum and acritarchs Cymatiosphaera globulosa testified a change in SSS from low salinity (<7‰) to present day conditions after 7990 cal. BP. Substantial freshening of Black Sea surface waters at 2570 cal. BP is established and connected with the transition from a relatively dry and warm to relatively cold and wet climate.

Diurnal variation of phytoplankton community in a high frequency area of HABs: Daya Bay, China

Phytoplankton community was investigated in the cage culture area of Daya Bay during a diurnal cycle. Two rainfalls occurred during the course of the experiment and decreased the surface seawater salinity in the aquaculture area. A total of 38 species were identified, of which the dominant species included Pseudo-nitzschia spp. and Skeletonema costatum. Water stratification obstructed the vertical migration of dinoflagellates. Statistical analysis indicated that Synechococcus showed negative relationship with silicate and ammonia, which indicated that Synechococcus adapted to grow at oligotrophic environment. Phytoplankton community structure implied the risk of Pseudo-nitzschia spp. blooms in the aquaculture area of Daya Bay.

THE OCCURRENCE OF LEPEOPHTHEIRUS SALMONIS AND CALIGUS CLEMENSI (COPEPODA: CALIGIDAE) ON THREE-SPINE STICKLEBACK GASTEROSTEUS ACULEATUS IN COASTAL BRITISH COLUMBIA

Infections with sea lice species belonging to Lepeophtheirus and Caligus are reported from examinations of 1,309 three-spine sticklebacks collected in coastal British Columbia. Over 97% of the 19,960 Lepeophtheirus specimens and nearly 96% of the 2,340 Caligus specimens were in the copepodid and chalimus developmental stages. The parasites were identified as Lepeophtheirus salmonis and Caligus clemensi based on morphology of adult stages. Between 1,763 and 1,766 base pairs (bp) of 18S rDNA from adult specimens collected from sticklebacks and salmon differed from the GenBank L. salmonis reference sequence by a single bp and were distinct from those of 2 other Lepeophtheirus species. A 530-bp region of 18S rDNA from chalimus stages of Lepeophtheirus obtained from sticklebacks and salmon was identical to that of the L. salmonis reference sequence. The three-spine stickleback is a new host record for L. salmonis. The prevalence of L. salmonis was 83.6% and that of C. clemensi was 42.8%. The intensities of these infections were 18.3 and 4.2, respectively. There was no significant relationship between sea lice abundance and stickleback condition factor. Significant spatial and temporal variations both in abundance of sea lice and surface seawater salinities were measured. The abundance of both sea lice species was lowest in zones in which surface seawater salinity was also lowest. Sticklebacks appear to serve as temporary hosts, suggesting a role of this host in the epizootiology of L. salmonis. The stickleback may be a useful sentinel species with which to monitor spatial and temporal changes in the abundance of L. salmonis and C. clemensi.

Changes in equatorial CO&lt;sub&gt;2&lt;/sub&gt; flux and new production estimated from CO&lt;sub&gt;2&lt;/sub&gt; and nutrient levels in Pacific surface waters during the 1986/87 El Niño

The seasonal variabilities of the CO2 system and dissolved nutrients (nitrate, phosphate, and silicate) in surface seawater of the central tropical Pacific Ocean before and during the 1986/1987 El Nino/Southern Oscillation (ENSO) warm event were observed as part of a ship-of-opportunity program. Beginning in late 1986 and continuing through 1987, there was a gradual increase in sea surface temperature (SST) and slight decrease of surface seawater salinity around the central equatorial region. These changes were accompanied by decreasing levels of dissolved nutrients, ocean-surface pC02 , dissolved inorganic carbon (Σ CO2) and net CO2 evasion. In September 1987, equatorial SST was warmest while CO2 evasion, pCO2 , Σ: CO2 , and the dissolved nutrients reached their lowest levels. In September 1987, owing to the weakened equatorial upwelling, the supply of Σ: CO2 from deeper waters was reduced by about 97-194 mM m-2 d-1, while the low replenishment of nitrate represented a loss of about 17-34 mM Cm -2 d-1 in new production. The evasion of CO2 from the central equatorial Pacific between 5°S and 5°N [l0°S and l0°N] was estimated to be about 1.2 M CO2 m-2 yr-1 [0.9 M CO2 m-2 yr-1] prior to the 1987 El Nifio, but only 0.2 M CO2 m-2 yr-1 [0.2 M CO2 m-2 yr-1] during the El Niño.