Benthic Water Research Articles

Comparison of fish detections, community diversity, and relative abundance using environmental DNA metabarcoding and traditional gears

AbstractBackgroundDetecting species at low abundance, including aquatic invasive species (AIS), is critical for making informed management decisions. Environmental DNA (eDNA) methods have become a powerful tool for rare or cryptic species detection; however, many eDNA assays offer limited utility for community‐level analyses due to their use of species‐specific (presence/absence) ‘barcodes’. Metabarcoding methods provide information on entire communities based on sequencing of all taxon‐specific barcodes within an eDNA sample.AimsEvaluate measures of fish species detections, community diversity, and estimates of relative abundance based on eDNA metabarcoding and traditional fisheries sampling approaches in the context of fish community characterization and AIS survellience.Materials and MethodsIn 2016, eight limnologically diverse lakes (surface area range: 13 – 1,728 ha) in Michigan, USA were sampled using a variety of traditional fisheries gears to characterize fish community composition. Environmental DNAs from surface (33 ± 6, mean ± 1 SD) and benthic (14 ± 2) water samples from each lake were isolated and amplified for two metabarcoding markers (mitochondrial 12S and 16S rDNA loci) using fish‐specific primers. Fish species detected within each lake were determined by comparing the sequencing data to a database of sequences from native Michigan fish species and 19 AIS on the Michigan's Watch List.ResultsAnalysis of species accumulation curves indicated multi‐locus eDNA metabarcoding assays can enhance species detection capacities and characterize 95% of a fish community in fewer sampling efforts than traditional gear (range: 2 – 62, median: 14). In addition, all AIS detected in traditional gear samples were also detected by eDNA, while some AIS detected by eDNA assays were absent from traditional gear samples.DiscussionResults reported here are, in part, driven by the lack of species‐selectivity during eDNA sampling events. Given the efficacy of eDNA assays, we suggest multi‐locus eDNA metabarcoding assays be implemented in early detection efforts.

The Burdwood Bank Circulation

AbstractA suite of high‐resolution numerical simulations characterizes the oceanic circulation in the Burdwood Bank, a shallow seamount located in the northeastern end of the Drake Passage. Model analysis shows energetic upwelling and mixing uplifting deep and benthic waters into the photic layer. Tides and the Antarctic Circumpolar Current are the primary drivers of the bank's circulation. Tidal forcing is the main driver for the entrainment of deep waters into the upper layers of the bank and local wind forcing for the detrainment of these waters into the deep ocean. Passive tracer diagnostics suggest that the dynamical processes triggered by the Burdwood Bank could have a significant impact on local ecosystems and the biogeochemical balance of the southwestern Atlantic region, which is one of the most fertile portions of the Southern Ocean. Model results are robust—they are reproduced in a wide array of model configurations—but there is insufficient observational evidence to corroborate them. Satellite color imagery does not show substantial chlorophyll blooms in this region but it shows strong phytoplankton plumes emanating from the bank. There are several potential explanations for the chlorophyll deficit, including lack of light due to persistent cloud cover, deep mixing layers, fast ocean currents, and the likelihood that blooms, while extant, might not develop on the surface. None of these possibilities can be confirmed at this stage.

Closing the oxygen mass balance in shallow coastal ecosystems

AbstractThe oxygen concentration in marine ecosystems is influenced by production and consumption in the water column and fluxes across both the atmosphere–water and benthic–water boundaries. Each of these fluxes has the potential to be significant in shallow ecosystems due to high fluxes and low water volumes. This study evaluated the contributions of these three fluxes to the oxygen budget in two contrasting ecosystems, a Zostera marina (eelgrass) meadow in Virginia, U.S.A., and a coral reef in Bermuda. Benthic oxygen fluxes were evaluated by eddy covariance. Water column oxygen production and consumption were measured using an automated water incubation system. Atmosphere–water oxygen fluxes were estimated by parameterizations based on wind speed or turbulent kinetic energy dissipation rates. We observed significant contributions of both benthic fluxes and water column processes to the oxygen mass balance, despite the often‐assumed dominance of the benthic communities. Water column rates accounted for 45% and 58% of the total oxygen rate, and benthic fluxes accounted for 23% and 39% of the total oxygen rate in the shallow (~ 1.5 m) eelgrass meadow and deeper (~ 7.5 m) reef site, respectively. Atmosphere–water fluxes were a minor component at the deeper reef site (3%) but a major component at the shallow eelgrass meadow (32%), driven by diel changes in the sign and strength of atmosphere–water gradient. When summed, the measured benthic, atmosphere–water, and water column rates predicted, with 85–90% confidence, the observed time rate of change of oxygen in the water column and provided an accurate, high temporal resolution closure of the oxygen mass balance.

Susane, a device for sampling chemical gradients in the benthic water column

AbstractIn aquatic environments, the benthic water column exhibits strong concentration gradients of various substances. They result from transfers and chemical reactions that may occur both within this layer, and at the sediment–water interface (SWI). Characterization of these gradients yields important information for the quantification of such processes and transfers. However, it is difficult to actually sample these gradients in the field, since turbulence decreases their vertical scale. This article describes a sampler designed to collect simultaneously 16 discrete water column samples at a centimeter‐scale vertical resolution. This small device (40 × 40 × 60 cm) is reliable, safe to handle, and easily deployed from a small boat using a cable or a Scuba diver. It is made of materials compatible with trace element and dissolved gases work, and simultaneously draws samples from various heights above the SWI into 60 mL syringes. The altitude of the sample inlets is field‐adjustable. Sampling artifacts are minimized by in situ flushing of tubing dead volumes, by rapid and simultaneous sample collection, and by sampling an undisturbed water‐column. Thus, this device can contribute to the characterization of vertical concentration gradients in benthic water‐columns. Such gradients of various compounds and metals from two coastal sites (Quiberon Bay and Berre Lagoon) are shown, illustrating the sampler's usefulness to describe and investigate processes in the benthic zone.

Microbiology and Nitrogen Cycle in the Benthic Sediments of a Glacial Oligotrophic Deep Andean Lake as Analog of Ancient Martian Lake-Beds.

Potential benthic habitats of early Mars lakes, probably oligotrophic, could range from hydrothermal to cold sediments. Dynamic processes in the water column (such as turbidity or UV penetration) as well as in the benthic bed (temperature gradients, turbation, or sedimentation rate) contribute to supply nutrients to a potential microbial ecosystem. High altitude, oligotrophic, and deep Andean lakes with active deglaciation processes and recent or past volcanic activity are natural models to assess the feasibility of life in other planetary lake/ocean environments and to develop technology for their exploration. We sampled the benthic sediments (down to 269 m depth) of the oligotrophic lake Laguna Negra (Central Andes, Chile) to investigate its ecosystem through geochemical, biomarker profiling, and molecular ecology studies. The chemistry of the benthic water was similar to the rest of the water column, except for variable amounts of ammonium (up to 2.8 ppm) and nitrate (up to 0.13 ppm). A life detector chip with a 300-antibody microarray revealed the presence of biomass in the form of exopolysaccharides and other microbial markers associated to several phylogenetic groups and potential microaerobic and anaerobic metabolisms such as nitrate reduction. DNA analyses showed that 27% of the Archaea sequences corresponded to a group of ammonia-oxidizing archaea (AOA) similar (97%) to Nitrosopumilus spp. and Nitrosoarchaeum spp. (Thaumarchaeota), and 4% of Bacteria sequences to nitrite-oxidizing bacteria from the Nitrospira genus, suggesting a coupling between ammonia and nitrite oxidation. Mesocosm experiments with the specific AOA inhibitor 2-Phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) demonstrated an AOA-associated ammonia oxidation activity with the simultaneous accumulation of nitrate and sulfate. The results showed a rich benthic microbial community dominated by microaerobic and anaerobic metabolisms thriving under aphotic, low temperature (4°C), and relatively high pressure, that might be a suitable terrestrial analog of other planetary settings.

Light quality determines primary production in nutrient-poor small lakes

The availability of nutrients for primary producers has long been thought to be the main limiting factor for primary productivity in nutrient-poor lake ecosystems. However, recent studies have indicated that the availability of light energy is also important. On the other hand, the amount of phototroph was reported to decrease in summer in Antarctic lakes, furthermore, the light environment underwater was shown containing high amount of ultraviolet energy in small Antarctic lakes. Here, we hypothesized that primary productivity is limited by not only nutrients and simple light quantity but also light quality in nutrient-poor lakes. Then, we investigate factors influencing primary production by benthic phototrophic communities in shallow nutrient-poor lakes. We examine the relationships between primary production in 17 Antarctic freshwater lakes and nutrient concentrations in lake and benthic water, temperature and light energy. Primary production is decreased by ultraviolet energy reaching the lake bed, showing that production is determined by light quality. We also correlate ultraviolet energy in lake water with the catchment area of each lake. Our results show that the underwater light environment has an important influence on primary production as a key limitation factor and is sensitive to materials in runoff from the surrounding environment for pristine lakes.

Rh protein is key for crab waste disposal

The seabed is far from pristine and can accumulate toxic ammonia in the debris and decaying remains that accumulate there, threatening other dwellers. ‘Ammonia is a major environmental limitation for crabs’, says Luqing Pan from the Ocean University of China. In addition, crabs and other marine species naturally produce and excrete the gas as waste and he details several mechanisms that allow the resourceful crustaceans to excrete it in polluted environments. However, it was not clear whether crabs also carry a specialised class of proteins, known as Rhesus-like glycoproteins (Rh proteins), which pump ammonia out of tissues in mammals, some insects and crustaceans. Intrigued by the possibility that the Japanese blue crab (Portunus trituberculatus) may depend on the protein to clear their bodies of ammonia, Pan and Lingjun Si began searching for one of the elusive Rh protein genes in the crab's DNA.Collecting gills from the crabs, the duo successfully identified a 1855 base pair gene that codes for a protein with all of the essential amino acid characteristics of a Rh protein. And when they searched for evidence of mRNA produced by the gene in a variety of tissues, they found it was mostly produced in the gills, which are the main site of ammonia excretion in many aquatic species. But the duo needed evidence that Rh protein was actually produced from the mRNA in the gill and was responsible for ammonia excretion.Injecting small fragments of RNA into the crustaceans to disrupt production of the protein, the team noticed that the crabs switched to producing other proteins that could contribute to ammonia excretion. And, when they measured how fast the animals were expelling ammonia from their bodies, the rate fell dramatically in the animals that had lost use of their Rh gene, while ammonia accumulated in their haemolymph.Having convinced themselves that the crabs produce the Rh protein, Si and Pan teamed up with Hongdan Wang and Xin Zhang to monitor the responses of several genes that are involved in ammonia excretion in real time to better understand the role of the Rh protein, in combination with other pump proteins, in ammonia waste disposal and they suspect that it is critical. ‘[It] may be the basis of the crab's ability to inhabit benthic water with high ammonia levels’, says Si.

Physical dynamics structures and oxygen budget of summer hypoxia in the Pearl River Estuary

AbstractA summertime hypoxia sporadically occurred in the lower Pearl River Estuary (PRE) for more than three decades. Although its mechanism has already been extensively studied, the topic on why seasonal hypoxia is persistent in patchy waters is still an open question. Here, we presented the investigation of physical dynamics structures and dissolved oxygen (DO) processes for controlling the spatial distribution and maintenance of coastal hypoxia. Field observations were conducted in the 2015 summer in the PRE and adjacent shelf sea. High river discharge forms intense haloclines in the river plume, while salinity intrusion of shelf benthic waters results in a notable pycnocline at the top of salt wedge. A mid‐depth transitional layer with the weakest mixing over water column functions as a barrier for DO vertical exchange between river plume and shelf salt wedge. A benthic hypoxia in the 2015 summer appears at the overlapping zone between river plume and shelf salt wedge. Based on physical and biological processes, a DO budget for the hypoxic system was established. The DO advection by gravitational circulation from shelf benthic waters is roughly balanced by bacterial respiration in water column. The DO diffusion from river plume to benthic hypoxia is completely inhibited by the barrier layer. The patchy distribution of benthic hypoxia for the 30‐yr period in the PRE can be satisfactorily predicted by the numerical simulations of the overlapping zones between river plume and shelf salt wedge. These findings will have an important implication for predicting and mitigating coastal hypoxia.Physical structures and processes of DO dynamics were investigated to understand the spatial distribution and maintenance of coastal hypoxia. Summertime hypoxia appear near the head of shelf salinity intrusion, where a mid‐depth barrier layer inhibits the vertical exchange between river plume and shelf salt wedge. DO advection by gravitational circulation from DO‐rich shelf benthic waters is roughly balanced by bacterial respiration in water column. The spatial distribution of coastal hypoxia can be well predicted by the overlapping zone between river plume and shelf salt wedge.

Sex-specific foraging strategies of Adélie penguins (Pygoscelis adeliae): Females forage further and on more krill than males in the Antarctic Peninsula

Sexual segregation characterises many animal communities, and in seabirds (including penguins), foraging strategies are known to vary with sex. The forging strategies of Adelie penguins (Pygoscelis adeliae) have been studied to some extent in some Antarctic locations; however, sex-based differences in foraging in this species have only been studied in depth in East Antarctica. Therefore, in this study, we aim to determine whether sexual segregation drives the foraging ecology [in terms of foraging habitat and diet based on analysis of stable carbon (δ13C) and nitrogen (δ15N) isotopes, respectively] of Adelie penguins in the Antarctic Peninsula (Hope Bay) during the breeding season. Our results showed strong sexual isotopic spatial segregation. Females forage for more krill than fish in more offshore, pelagic waters in contrast to males which feed equally on both items in more inshore, benthic waters. These results suggest a link between foraging habitat and diet that differs according to sex, similar to that found in East Antarctica. Given these similarities, we hypothesise that the foraging ecology of Adelie penguins varies with sex throughout the Antarctic continent. Nevertheless, further research in other locations such as in western Antarctica is needed to confirm this hypothesis.

Spring and Late Summer Phytoplankton Biomass Impact on the Coastal Sediment Microbial Community Structure

Two annual Baltic Sea phytoplankton blooms occur in spring and summer. The bloom intensity is determined by nutrient concentrations in the water, while the period depends on weather conditions. During the course of the bloom, dead cells sink to the sediment where their degradation consumes oxygen to create hypoxic zones (< 2 mg/L dissolved oxygen). These zones prevent the establishment of benthic communities and may result in fish mortality. The aim of the study was to determine how the spring and autumn sediment chemistry and microbial community composition changed due to degradation of diatom or cyanobacterial biomass, respectively. Results from incubation of sediment cores showed some typical anaerobic microbial processes after biomass addition such as a decrease in NO2− + NO3− in the sediment surface (0–1 cm) and iron in the underlying layer (1–2 cm). In addition, an increase in NO2− + NO3− was observed in the overlying benthic water in all amended and control incubations. The combination of NO2− + NO3− diffusion plus nitrification could not account for this increase. Based on 16S rRNA gene sequences, the addition of cyanobacterial biomass during autumn caused a large increase in ferrous iron-oxidizing archaea while diatom biomass amendment during spring caused minor changes in the microbial community. Considering that OTUs sharing lineages with acidophilic microorganisms had a high relative abundance during autumn, it was suggested that specific niches developed in sediment microenvironments. These findings highlight the importance of nitrogen cycling and early microbial community changes in the sediment due to sinking phytoplankton before potential hypoxia occurs.

Spatial distribution of sewage pollution on a Hawaiian coral reef

While sewage pollution is contributing to the global decline of coral reefs, its offshore extent and direct reef impacts from water column mixing and benthic seeps are poorly documented. We addressed this knowledge gap on a Hawaiian coral reef using sewage indicator and benthic cover measurements, macroalgal bioassays, and a pollution scoring tool. Fecal indicator bacteria (FIB) and nutrient concentrations were spatially variable in surface and benthic waters, with shoreline values being highest. Shoreline macroalgae δ15N and %N indicated high nitrogen loads containing sewage, while offshore surface and benthic values suggested lower nitrogen loads from environmental sources. Coral cover was negatively correlated with FIB, macroalgal δ15N, and nutrient concentrations. Benthic salinity and temperature measurements detected daily tidal groundwater pulses which may explain these associations. While pollution scores revealed that sewage was largely concentrated along the shoreline, results showed some reached the reef and may be contributing to its declining condition.

Alum efficacy 11 years following treatment: phosphorus and macroinvertebrates

ABSTRACTSteinman AD, Hassett MC, Oudsema M, Rediske R. 2018. Alum efficacy 11 years following treatment: phosphorus and macroinvertebrates. Lake Reserv Manage. 34:167—181.Internal phosphorus loading and benthic macroinvertebrate community structure were analyzed at 4 sites in Spring Lake, Michigan, ˜11 yr following an alum treatment. Phosphorus (P) release rates, benthic macroinvertebrate community structure, sediment chemistry, and water quality variables (total dissolved solids, pH, dissolved oxygen, water clarity) were compared to measurements taken previously (2003/2004: pre-alum application, 2006: 8 mo post-alum application, and 2010: 5 yr post-alum application) at the same sites and using comparable methods. Total phosphorus (TP) concentrations in surface water samples from 2016 (38—45 νg/L) were similar to those measured in 2006 and 2010 (20—80 νg/L) at all sites; however, 2016 TP concentrations in the near-bottom water at the 2 deeper sites were elevated (˜250 and 1,000 νg/L, respectively) compared to TP concentrations of <60 νg/L in 2006 and 2010, suggesting internal loading may be increasing, at least at these 2 sites. In contrast, maximum P release rates from the 2016 sediments were similar to or lower than 2010 rates, and an order of magnitude lower than before alum was applied. Phosphorus content in the sediment was fractionated; loosely sorbed sediment SRP concentrations were very low at all sites. Macroinvertebrate community was similar in density and composition to the 2010 results. These results are suggestive, but not conclusive, that internal P loading is increasing in parts of Spring Lake. Alum application can serve as an effective short-term solution to the longer-term problem of internal P loading, but its effectiveness is critically tied to concurrent reductions in external P loading.

Ecology of benthic crustaceans in the Tolten river (39°S, Araucania region, Chile)

The Cautin river is located in the Araucania region, Chile (38°S), and is characterized by alterations through human interference in its surrounding basin, by the presence of introduced salmonids, and by its mixed regime, which originates from melting snow in summer and rains in winter. The fauna of this river includes an invertebrate fauna composed of both endemic and widespread species, which has, however, been only poorly studied until now. The aim of the present study was to make a review of the ecological role of the benthic inland water crustaceans of the River Cautin, in order to understand their importance in the ecosystem of the river. The literature revealed the presence of abundant populations of amphipods and freshwater crabs as well as of aquatic insects along the river’s course. Many of these crustaceans are prey for both introduced salmonids and native fishes. Similar results have been reported for other southern Argentinean and Chilean Patagonian rivers.

Benthic Diversity of Sessile Organisms in Rocky Reef Habitats of Coastal Brazil: An Insight into the Implementation of Marine Protected Areas

Marine Protected Areas are increasingly becoming a tool of choice for conservation and management of marine resources and ecosystems. Data on biodiversity are necessary to assist in establishing protected areas for conservation objectives to be met. Toward that effect, we investigated reef biodiversity patterns in three large-scale coastal regions of Brazil. The study areas comprised of an upwelling region, an adjacent high impacted region, and a more distant marine park. We surveyed four reef sites in each study region. Species counts of sessile benthic organisms, substrate relief, and average monthly water temperatures were recorded during the surveys. Benthic organisms were identified to the lowest taxa possible using still photos. Biodiversity was estimated using Shannon’s index on richness of organism taxa. Diversity was highest at the upwelling and high-impacted areas. No substrate relief patterns were found. Temperature readings showed lower average values at the upwelling and high impacted regions. Our results favor the upwelling region for establishment of a Marine Protected Area. Moreover, the similar diversity between the upwelling and the high impacted regions showed evidence of spillover effects from the former into the latter region, further demonstrating the importance of the former region for conservation.

Identification of the role of Rh protein in ammonia excretion of the swimming crab Portunus trituberculatus.

In Portunus trituberculatus, a full-length cDNA of Rhesus-like glycoprotein (Rh protein), encoding the entire 478 amino acid protein, has been identified in gills, and plays an essential role in ammonia (NH3/NH4+) excretion. Phylogenetic analysis of Rh-like proteins from crabs was clustered, showing high conservation of the ammonium transporter domain and transmembrane segments essential to the function of Rh protein. Rh protein of P. trituberculatus (PtRh) was detected in all tested tissues, and showed the highest expression in the gills. To further characterize the role of PtRh in ammonia metabolism and excretion, double-stranded RNA-mediated RNA interference of PtRh was employed. Knockdown of PtRh upregulated mRNA expression of ammonia excretion-related genes encoding aquaporin (AQP), K+ channels and vesicle-associated membrane protein (VAMP), increased the activity of Na+/K+-ATPase (NKA) and V-type H+-ATPase (V-ATPase), and initially reduced then elevated the expression of the Na+/H+-exchanger (NHE). dsRNA-mediated reduction in PtRh significantly reduced ammonia excretion rate and increased ammonia and glutamine (Gln) levels in the hemolymph, together with an increase of glutamate dehydrogenase (GDH) and glutamine synthetase (GS) activity, indicating a central role for PtRh in ammonia excretion and detoxification mechanisms. Taken together, we conclude that Rh protein is a primary contributor to ammonia excretion of P. trituberculatus, which may be the basis of their ability to inhabit benthic water with high ammonia levels.

The elemental stoichiometry (C, Si, N, P) of the Hebrides Shelf and its role in carbon export

A detailed analysis of the internal stoichiometry of a temperate latitude shelf sea system is presented which reveals strong vertical and horizontal gradients in dissolved nutrient and particulate concentrations and in the elemental stoichiometry of those pools. Such gradients have implications for carbon and nutrient export from coastal waters to the open ocean. The mixed layer inorganic nutrient stoichiometry shifted from balanced N:P in winter, to elevated N:P in spring and to depleted N:P in summer, relative to the Redfield ratio. This pattern suggests increased likelihood of P limitation of fast growing phytoplankton species in spring and of N limitation of slower growing species in summer. However, as only silicate concentrations were below potentially limiting concentrations during summer and autumn the stoichiometric shifts in inorganic nutrient N:P are considered due to phytoplankton nutrient preference patterns rather than nutrient exhaustion. Elevated particulate stoichiometries corroborate non-Redfield optima underlying organic matter synthesis and nutrient uptake. Seasonal variation in the stoichiometry of the inorganic and organic nutrient pools has the potential to influence the efficiency of nutrient export. In summer, when organic nutrient concentrations were at their highest and inorganic nutrient concentrations were at their lowest, the organic nutrient pool was comparatively C poor whilst the inorganic nutrient pool was comparatively C rich. The cross-shelf export of these pools at this time would be associated with different efficiencies regardless of the total magnitude of exchange. In autumn the elemental stoichiometries increased with depth in all pools revealing widespread carbon enrichment of shelf bottom waters with P more intensely recycled than N, N more intensely recycled than C, and Si weakly remineralized relative to C. Offshelf carbon fluxes were most efficient via the inorganic nutrient pool, intermediate for the organic nutrient pool and least efficient for the particulate pool. N loss from the shelf however was most efficient via the dissolved organic nutrient pool. Mass balance calculations suggest that 28% of PO43−, 34% of NO3− and 73% of Si drawdown from the mixed layer fails to reappear in the benthic water column thereby indicating the proportion of the nutrient pools that must be resupplied from the ocean each year to maintain shelf wide productivity. Loss to the neighbouring ocean, the sediments, transference to the dissolved organic nutrient pool and higher trophic levels are considered the most likely fate for these missing nutrients.

Karyotype, sex determination and male meiosis in three benthic water bugs (Hemiptera: Nepomorpha: Aphelocheiridae)

ABSTRACTWe report here the first chromosome numbers for benthic water bugs (Nepomorpha: Aphelocheiridae). All three studied species, Aphelocheirus aestivalis (Fabricius, 1794), A. murcius Nieser and Millán, 1989 and Aphelocheirus sp. from Ebro River (northern Spain), have karyotype 2n = 22 + XX/X(0) and inverted sequence of the X chromosome divisions in male meiosis. The similarity and difference in cytogenetic traits between Aphelocheiridae and other families of Nepomorpha are shortly discussed.

Sexual and individual foraging segregation in Gentoo penguins Pygoscelis papua from the Southern Ocean during an abnormal winter.

Knowledge about sexual segregation and gender-specific, or indeed individual specialization, in marine organisms has improved considerably in the past decade. In this context, we tested the “Intersexual Competition Hypothesis” for penguins by investigating the feeding ecology of Gentoo penguins during their austral winter non-breeding season. We considered this during unusual environmental conditions (i.e. the year 2009 had observations of high sea surface and air temperatures) in comparison with the long term average at Bird Island, South Georgia. Through conventional (i.e. stomach contents) and stable isotopic values from red blood cells, plasma and feathers of both male and female Gentoo penguins, we showed that there were significant differences between sexes, with males feeding mainly on fish (54% by mass) followed by crustaceans (38%) whereas females fed mainly on crustaceans (89% by mass) followed by fish (4%). Themisto gaudichaudii was the most important crustacean prey for males (64% by mass; 82% by number; 53% by frequency of occurrence) and females (63% by mass; 77% by number; 89% by frequency of occurrence), contrasting with all previous studies that found Antarctic krill Euphausia superba were generally the main prey. Stable isotopic data showed that, in terms of habitat use (based on δ 13C), there were significant differences in short-term carbon signatures between males and females (based on plasma and red blood cells), suggesting that both sexes explored different habitats, with females exploring more offshore pelagic waters and males feeding more in coastal benthic waters. Based on δ 15N, males fed on significantly higher trophic level than females (based on plasma and red blood cells), in agreement with our diet results., Thus, Gentoo penguins behave in a similar manner to other non-breeding penguins species (e.g. king, macaroni and rockhopper penguins), albeit at a smaller spatial scale (as they do not disperse as these other penguins do), in that they have a wider habitat and trophic niche during the Antarctic Winter (in comparison to Summer). We also detected individual specialization in feeding/trophic levels for each gender, with certain males feeding mainly on fish and certain females mainly on crustaceans, which may be driven the prevailing environmental conditions that lead individuals to search for alternative prey, and cause sexual diet segregation. Our results provide further information to help improve understanding about sexual segregation and individual specialization of marine organisms, while contributing valuable information on the winter diet for Antarctic monitoring programs and for modelling Antarctic marine food webs.

Observations of distribution and flocculation of suspended particulate matter in the Minjiang River Estuary, China

In this study, we described the distribution pattern of suspended particulate matter (SPM) and its influencing factors in the waters around the Minjiang River Estuary. Further, we investigated the flocculation process of SPM and its underlying mechanism in the study area. The objectives were achieved using water temperature, salinity, turbidity, fluorescence and particle size distribution of SPM data measured in August 2009. As influenced by dilution from the Minjiang River water, the water column structure was significantly stratified in the estuary, with an obvious thermocline and halocline. The turbidity was relatively low in the surface water (SSC<5mg/l) but sufficient to form nepheloid layer in the near-benthic (SSC>15mg/l). Fluorescence was high (up to 10μl/l) in the surface water, which was markedly lower and more uniform in the lower water layer. The total volume concentration and particle size of the SPM in the upper water layer were significantly higher than those of the lower water layer. The in-situ particle size frequency distribution of SPM markedly changed in the different water layers, whereas the dispersed particles were fine, with little difference in frequency distribution. The mean effective density of SPM was generally <600kg/m3 in the surface and benthic water, and the values were slightly higher in the benthic water layer than in the surface water layer, with a significant increase in the middle water layer. The significant differences between the distribution trends of the total volume concentration and water turbidity were controlled by the size distribution of SPM. The concentration distribution of SPM was mainly influenced by source, re-suspension and thermocline, among other factors. Flocs widely occurred in the study area, and the flocculation mechanism of SPM varied in the different water layers. In the upper water layer, intense biological activity promoted the formation of stable macroflocs. In the benthic water layer, the biological activity was limited, the flocculation of sediment particles was mainly caused by physico-chemical attraction of inorganic particles, and the hydrodynamic conditions and high settling velocity were also unfavourable to the formation of macroflocs.

Pengelompokkan Foraminifera Bentik Di Perairan Teluk Balikpapan Berdasarkan Komposisi Pembentuk Cangkang

Balikpapan Bay is one of the bays in Indonesia. One of the organisms in these waters are benthic foraminifera. The objective of this research was to determine the type of benthic foraminifera based composition forming the shells in Balikpapan Bay, East Kalimantan. The sediment samples were taken at a depth of 0-20 meters, then do picking, collection, as well as the identification of the type and composition shells forming of the benthic foraminifera. The results showed the benthic foraminifera Balikpapan Bay waters with sediment samples at a depth of 0-20 meters consists of benthic foraminifera shell of sandy, benthic foraminifera shell of porcelain, and benthic foraminifera shell of hyalin.