Mixed Diatom Research Articles

β-N-methylamino-L-alanine production, photosynthesis and transcriptional expression in a possible mutation strain and a wild strain of Thalassiosira minima

The neurotoxin β-N-methylamino-L-alanine (BMAA) produced by marine diatoms has been implicated as an important environmental trigger of neurodegenerative diseases in humans. However, the biosynthesis mechanism of BMAA in marine diatoms is still unknown. In the present study, the strain of diatom Thalassiosira minima almost lost the biosynthesis ability for BMAA after a long-term subculture in our laboratory. The production of BMAA-containing proteins in the mutant strain of T. minima reduced to 18.2 % of that in the wild strain, meanwhile the cell size decreased but pigment content increased in the mutant strain. Take consideration of our previous transcriptional data on the mixed diatom and cyanobacterium cultures, the current transcriptome analysis showed four identical and highly correlated KEGG pathways associated with the accumulation of misfolded proteins in diatom, including ribosome, proteasome, SNARE interactions in vesicle transport, and protein processing in the endoplasmic reticulum. Analysis of amino acids and transcriptional information suggested that amino acid synthesis and degradation are associated with the biosynthesis of BMAA-containing proteins. In addition, a reduction in the precision of ubiquitination-mediated protein hydrolysis and vesicular transport by the COPII system will exacerbate the accumulation of BMAA-containing proteins in diatoms.

Phaeocystis globosa and diatom blooms promote distinct bacterial communities and associations in a coastal ecosystem.

Phytoplankton and bacteria form the foundation of marine food webs. While most studies on phytoplankton bloom influence on bacteria dynamics focus on diatom-dominated blooms due to their global ecological significance, it is unclear if similar patterns extend to other species that compete with diatoms like Phaeocystis spp. This study aimed to contribute to the understanding of associations between phytoplankton and bacteria in a temperate ecosystem. For this, we studied the dynamics of phytoplankton and bacteria, combining 16S metabarcoding, microscopy, and flow cytometry over 4 years (282 samples). Phytoplankton and bacterial communities were studied throughout the year, particularly during contrasting phytoplankton blooms dominated by the Haptophyte Phaeocystis globosa or diatoms. We applied extended local similarity analysis (eLSA) to construct networks during blooming and non-blooming periods. Overall, the importance of seasonal and species-specific interactions between phytoplankton and bacteria is highlighted. In winter, mixed diatom communities were interconnected with bacteria, indicating a synergistic degradation of diverse phytoplankton-derived substrates. In spring, despite the intensity variations of P. globosa blooms, the composition of bacterial communities remained consistent over several years, suggesting establishing a stable-state environment for bacterial communities. Specific associations between monospecific diatom blooms and bacteria were evidenced in summer.

Surface sediment diatoms in the northern and middle Okinawa Trough and their correlation with environmental variables

Determining the relationship between diatoms in surface sediments and the local sedimentary environment is important for paleoenvironmental reconstruction, including in marine settings. In this study, we used canonical correspondence analysis of 41 surface sediment samples from the northern and middle Okinawa Trough to analyze the relationship between diatom species and environmental variables. The principal results are as follows. (i) The diatom assemblages are closely correlated with the environmental variables, specifically, July sea surface salinity (SSS-Jul), February sea surface temperature (SST-Feb), and June sea surface temperature (SST-Jun). (ii) Three diatom assemblages are distinguished, representing environments with different hydrological characteristics. The high-temperature diatom assemblage may indicate a warm-water mass (the Kuroshio Current), and the polyhaline diatom assemblage can be used as an indicator of a high salinity water mass. The mixed diatom assemblage is associated with the warm-water masses of the Kuroshio Current, and shelf water masses with a low salinity and low temperature. (iii) The high-temperature and mixed diatom assemblages occur on the boundary of the continental shelf and Okinawa Trough, and are temperature sensitive; the high-temperature assemblage is located further upstream of the Kuroshio Current, indicating higher temperatures. Changes in the distribution of the polyhaline diatom assemblage within sediment cores can be regarded as an indicator of changes in water masses, and of possible salinity variations, in this area. These three assemblages are potentially important for future palaeoceanographic studies.

Geological record of 18th and 19th century tsunamis along the Japan Sea coast of Tsugaru Peninsula, northwestern Japan

Our stratigraphic and paleontological investigations revealed three sandy event deposits (E1, E2, and E3) within peaty clay at the Sotomeyachi site on the Japan Sea coast of Honshu (mainland of Japan), northwestern Japan. Visual examination and X-ray computed tomographic images of samples of the deposits provided evidence of strong currents characterized by rip-up mud clasts, load casts, and erosional lower stratigraphic contacts. Marine, brackish, and freshwater diatom species in the deposits indicate they were derived from various coastal sources. Radiocarbon dating constrained the ages of event deposit E2 to 1764–1902 CE and E3 to 1558–1845 CE, 1699–1918 CE, and 1704–1781 CE. According to historical records, the E2 deposits likely correspond to the tsunami generated by the 1833 Shonai-oki earthquake, and the E3 deposits correspond to a tsunami associated with either a submarine landslide associated with the 1741 Oshima-Oshima eruption or the 1793 Nishi-Tsugaru earthquake. Because our numerical simulation of the 1741 tsunami showed no significant inundation at the study site, it is more likely that the 1793 earthquake was responsible for tsunami deposit E3. The E1 deposit is discontinuous and showed different characteristics (absence of load structures, rip-up mud clasts and mixed diatom assemblages) to those of events E2 and E3, so it is unlikely to be a tsunami deposit.

Co-production of fucoxanthin and lipid from Indonesian diatom and green algae growing on palm oil mill effluent under mixotrophic condition

Recently, the mass scale production of fucoxanthin and fatty acid from microalgae has increased. However, a new and low cost cultivation strategy is needed to enhance the production. This work investigated the potency of mixed diatom and green algae isolated from Morosari Bay, Java Sea, Indonesia, to enhance the production of fucoxanthin and lipid by employing mixotrophic condition. A four stepwise experiment was done to study the environmental and nutritional factors, as well as to optimize the selected parameters by employing Box Behnken response surface methodology. The mixed algae was found to grow well on palm oil mill effluent (POME). Changing condition from autotrophic to mixotrophic decreased the pigment content. The highest fucoxanthin concentration (6 mg L−1) was found on the glycerol addition compared to other organic carbon sources. The optimal condition to produce 160 mg L−1 d−1 biomass and 60 mg L−1 d−1 lipid was found on 30% POME, supplemented with 3 g L−1 glycerol and 200 mg L−1 urea at 30 °C. Mono unsaturated fatty acid (MUFA) was the most dominant fatty acid class found in the mixed algae.

Seasonal and interannual variation in lower Columbia River phytoplankton (2005-2018): environmental variability and a decline in large bloom-forming diatoms

Understanding the influence of biotic and abiotic factors on riverine phytoplankton dynamics is challenging, particularly as anthropogenic stressors such as eutrophication, invasive species, and climate change alter these relationships. We examined a 14 yr (January 2005 to December 2018) dataset of phytoplankton and water quality variables, along with zooplankton and nutrient concentrations, from the Columbia River (the largest river in the US Pacific Northwest) to identify seasonal and interannual patterns of phytoplankton assemblage structure and their environmental associations. Non-metric multidimensional scaling, cluster, and indicator species analyses revealed: (1) a diatom/flagellate cluster in spring/summer, associated with chlorophylla, discharge, ciliates, and Sarcodina; (2) a cyanobacteria/chlorophyte cluster in late summer/early fall, associated with higher water temperatures, increased clarity, the invasive copepodPseudodiaptomus forbesi, and veligers of the invasive Asian clamCorbicula fluminea; and (3) a mixed-taxa winter cluster of minimal abundance and biomass. Nutrients were not strongly associated with the observed structural patterns. Phytoplankton bloom duration varied interannually, between years with short springtime blooms vs. years when blooms extended across multiple months. Springtime blooms of the diatomAsterionella formosadecreased in recent years, giving way to blooms of a mixed diatom assemblage. Further, high temperature, low discharge, and more invasive zooplankton were associated with cyanobacterial blooms, suggesting that increased temperature and reduced river flows predicted due to climate change in the Pacific Northwest may lead to further impacts on the late summer/early fall Columbia River plankton community.

Mixed diatom floras in sedimentary deposits from the 2016 Kaikōura Tsunami at Little Pigeon Bay, Aotearoa-New Zealand

Abstract This study records the diatom flora from sedimentary deposits found within a coastal cottage, following the November 2016 Kaikōura earthquake and tsunami at Little Pigeon Bay, Banks Peninsula, Aotearoa-New Zealand. Unlike previous studies of diatoms from modern tsunami deposits, the sediments in this study were isolated from any previous (and subsequent) reworking of sediments. The diatom flora (n = 117 taxa) are dominated by benthic and planktonic lifeforms with preferences for marine (28%), brackish-marine (25%), fresh-brackish (19%) and fresh-water (17%) conditions. The higher abundances of benthic marine and brackish-marine diatoms are attributed to direct in-washing and reworking of open ocean-water with sandy marine sediments from the sub-tidal and inter-tidal zones. Comparatively high percentage counts of benthic fresh-brackish and freshwater diatom taxa also indicate significant freshwater sources and sediments from the stream and land adjacent to the cottage. Fractured and damaged diatom frustules within the flora, including broken sponge spicules, emphasise dynamic processes of reworking, abrasion and erosion during incoming and outgoing tsunami waves. Likelihood-based ordination analysis of the diatom flora indicates statistical differences between the flora in the back area of the cottage and the centre and front areas which we attribute primarily to the influence of different waves that inundated the cottage from the seaward and landward directions. Such a record affirms a highly mixed diatom flora from multiple sources and habitats. It also offers a first modern analogue from Aotearoa-New Zealand to assist future assessments of multi-proxy-based records of past tsunami events preserved in the geological record.

Artificial breeding and culture of the crown-of-thorns starfish Acanthaster planci (Linnaeus, 1758) larvae in China

Though the breeding and the rearing of Acanthaster planci larvae had been reported before, the descriptions of them are not all-around, and there are no clear and detailed pictures indicating the whole process of embryonic and larval development. Besides, some methods described previously for culturing A. planci larvae are troublesome and even not available. In this study, adult A. planci were artificially induced to spawn and fertilized eggs were incubated and cultured indoor with disinfected seawater. A. planci developed from fertilized eggs to early bipinnaria by 50 h. Once a large number of late brachiolaria occurred, the diets were replaced by mixed benthic diatoms on settlement plates. Five-armed juveniles were reached after 23-day rearing when enough live Chaetoceros mueller and oceanic red yeast were supplied. It is critical to prevent infections by protozoa and pathogenic bacteria. The diets used here are universal in larval rearing and easily obtainable, which guarantees constant supply of diets and thus largely increases the successful rate of the rearing. Artificial breeding and culture of A. planci larvae not only enriched the knowledge on the spawning, larval culture, and developmental process of A. planci but also provided abundant materials to facilitate various studies.

The Influence of Storms on Water Quality and Phytoplankton Dynamics in the Tidal James River

Due to the unpredictable nature of intense storms and logistical constraints of sampling during storms, little is known about their immediate and long-term impacts on water quality in adjacent aquatic ecosystems. By combining targeted experiments with routine monitoring, we evaluated immediate impacts of two successive storm events on water quality and phytoplankton community response in the tidal James River and compared these findings to a non-storm year. The James River is a subestuary of the Chesapeake Bay and sampling was conducted before, during, and after Hurricane Irene and Tropical Storm (TS) Lee in 2011 and during the same time period (late summer/early fall) in 2012 when there were no storms. We collected and compiled data on nutrient and chlorophyll a concentrations, phytoplankton abundance, nitrogen uptake, primary productivity rates, and surface salinity, temperature, and turbidity in the meso- and polyhaline segments of the James River. Hurricane Irene introduced significant amounts of freshwater over the entire James River and Chesapeake Bay watersheds, while rainfall from TS Lee fell primarily on the tidal fresh region of the James River and headwaters of the Chesapeake Bay. Dinoflagellates dominated the algal community in the meso- and polyhaline segments prior to the storms in 2011, and a mixed diatom community emerged after the storms. In the mesohaline river segment, cyanobacteria abundance increased after TS Lee when salinities were depressed, likely due to washout from the oligohaline and tidal fresh regions of the river. In 2012, dinoflagellates dominated the community in both segments of the river during late summer but diatoms were also abundant and their biomass fluctuated throughout the summer and fall. Cyanobacteria were not present in either segment. Overall, we observed that the high-intensity rainfall from Hurricane Irene combined with high flushing in the headwaters as a result of TS Lee likely reduced primary productivity and altered community composition in the mesohaline segment but not the more estuarine-influenced polyhaline segment. Understanding the influence of high freshwater flow with a short residence time associated with storms is key to the planning and management of estuarine restoration as such disturbances are projected to increase as a result of climate change.

Beneficial effects of benthic diatoms on growth and physiological performance in juvenile sea cucumber Apostichopus japonicus (Selenka)

Benthic diatoms are considered a key dietary component, particularly for early juvenile sea cucumber. Physiological effects of benthic diatoms on growth of juvenile sea cucumber Apostichopus japonicus (2.55 g, average initial wet body weight) fed with a formulated diet (the control), Navicula sp., Nitzschia sp., and a mixture of both species (1:1 dry weight) were evaluated. Frozen-thawed diatom paste served as feed for juvenile sea cucumber. All animals exhibited active feeding behavior and diatom frustules occurred in their feces. Our results revealed that specific growth rates (SGRs) of juvenile sea cucumber fed on benthic diatoms were higher than those of the control. The highest SGR (1.41 ± 0.30 % day−1) was found in juvenile sea cucumber fed on Navicula sp. and the SGR of juveniles fed on Nitzschia sp. came second (0.73 ± 0.10 % day−1), showing no significant difference with that of mixed diatoms (0.72 ± 0.12 % day−1). Based on activity of intestine digestive enzyme and coelomic fluid immune enzyme, juveniles fed on Navicula sp. contained higher levels of amylase, protease, and lipase, as well as lysozyme, acid phosphatase, alkaline phosphatase, and superoxide dismutase in the late growth stage than those in the early growth stage, while their protease, amylase, alkaline phosphatase, and catalase activity was significantly higher than that of the control. These results indicated that the benthic diatom Navicula sp. had a positive effect on growth of juvenile sea cucumber probably by enhancing digestive and immune enzyme activities. This information could assist in the development of appropriate diets and feed ingredients for cultured holothurians.

Temperature-induced changes in fatty acid dynamics of the intertidal grazer Platychelipus littoralis (Crustacea, Copepoda, Harpacticoida): Insights from a short-term feeding experiment

Dietary lipids, and in particular the essential fatty acids (EFA), EPA (20:5ω3) and DHA (22:6ω3), guarantee the well-being of animals and are recognized for their potential bottom-up control on animal populations. They are introduced in marine ecosystems through primary producers and when grazed upon, they are consumed, incorporated or modified by first-level consumers. As the availability of EFA in the ecosystem is affected by ambient temperature, the predicted rise in ocean temperature might alter the availability of these EFA at the basis of marine food webs. Despite the FA bioconversion capacity of certain benthic copepod species, their lipid (FA) response to varying temperatures is understudied. Therefore, the temperate, intertidal copepod Platychelipus littoralis was offered a mono and mixed diatom diet at 4, 15 °C (normal range) and at 24 °C (elevated temperature) to investigate the combined effects of temperature and resource availability on its FA content and composition. P. littoralis showed a flexible thermal acclimation response. Cold exposure increased the degree of FA unsaturation and the EPA%, and induced a shift towards shorter chain FA in the copepod’s membranes. Furthermore, a mixed diet reduced the impact of heat stress on the copepod’s membrane FA composition. Temperature affected the trophic transfer of EPA and DHA differently. While dietary resources could fully compensate for the temperature effects on total lipid and EPA content in the copepods, no such counterweigh was observed for the DHA dynamics. Heat stress lowered the DHA concentration in copepods regardless of the resources available and this implies negative effects for higher trophic levels.

Differences between mono-generic and mixed diatom silicon isotope compositions trace present and past nutrient utilisation off Peru

In this study we combine for the first time silicon (Si) isotope compositions of small mixed diatom species (δ30SibSiO2) and of large handpicked mono-generic (i.e. genus=Coscinodiscus) diatom samples (δ30SiCoscino) with diatom assemblages extracted from marine sediments in the Peruvian upwelling region in order to constrain present and past silicate utilisation.The extension of a previous core-top data set from the Peruvian shelf demonstrates that δ30SiCoscino values record near-complete Si utilisation, as these are similar to the isotopic composition of the subsurface source waters feeding the upwelling. In contrast, the δ30SibSiO2 of small mixed diatom species increase southward along the shelf as well as towards the shore. We attribute highest δ30SibSiO2 values partly to transient iron limitation but primarily to the gradual increase of Si isotope fractionation within the seasonal diatom succession, which are mainly recorded by small diatom species during intense bloom events. In contrast, lower δ30SibSiO2 values are related to initial Si isotope utilisation during periods of weak upwelling, when low Si(OH)4 concentrations do not permit intense blooms and small diatom species record substantially lower δ30Si signatures. As such, we propose that the intensity of the upwelling can be deduced from the offset between δ30SibSiO2 and δ30SiCoscino (Δ30Sicoscino–bSiO2), which is low for strong upwelling conditions and high for prevailing weak upwelling.We apply the information extracted from surface sediments to generate a record of the present-day main upwelling region covering the past 17,700years and find that this location has also been characterized by a persistent offset (Δ30Sicoscino–bSiO2). By comparison with the diatom assemblages we show that the coastal upwelling system changed markedly between weak and strong upwelling conditions. In addition, our model calculations to quantify species-specific Si isotope fractionation effects based on the diatom assemblages indicate an overall minor influence that cannot explain the high amplitude in the measured δ30SibSiO2 record.

남극 엽층리 퇴적물로부터 규조 종을 이용한 고기후 변화 연구

This study investigated the paleoclimatic change using diatoms that were extracted from the high-resolution laminated layers of diatom ooze sediment cores GC08-EB01 in the eastern basin of the Bransfield Strait, Antarctica. The range of diatom valves per gram of dry sediment was from in quantitative diatom assemblage analysis. Laminations are classified using visually dominant diatom species and terrigenous content. Biogenic diatom ooze laminae characterised by bloom of Corethron crilophilum, Eucampia antarctica, Fragilariopsis curta, F. kerguelensis, Odontella weissflogii, Proboscia inermis, R. styliformis, Thalassiosira antarctica, and Chaetoceros resting spores. Terrigenous laminae characterised by mixed diatom assemblage. The ratio of (Fragilariopsis curta+F. cylindrus)/Thalassiosira antarctica increase in horizons, suggesting increased sea-ice cover in the study area during the late Holocene (cold events). As a result, five cold events are identified on the basis of frequency of the critical taxa throughout the section.

Single-taxon field measurements of bacterial gene regulation controlling DMSP fate.

The 'bacterial switch' is a proposed regulatory point in the global sulfur cycle that routes dimethylsulfoniopropionate (DMSP) to two fundamentally different fates in seawater through genes encoding either the cleavage or demethylation pathway, and affects the flux of volatile sulfur from ocean surface waters to the atmosphere. Yet which ecological or physiological factors might control the bacterial switch remains a topic of considerable debate. Here we report the first field observations of dynamic changes in expression of DMSP pathway genes by a single marine bacterial species in its natural environment. Detection of taxon-specific gene expression in Roseobacter species HTCC2255 during a month-long deployment of an autonomous ocean sensor in Monterey Bay, CA captured in situ regulation of the first gene in each DMSP pathway (dddP and dmdA) that corresponded with shifts in the taxonomy of the phytoplankton community. Expression of the demethylation pathway was relatively greater during a high-DMSP-producing dinoflagellate bloom, and expression of the cleavage pathway was greater in the presence of a mixed diatom and dinoflagellate community [corrected].These field data fit the prevailing hypothesis for bacterial DMSP gene regulation based on bacterial sulfur demand, but also suggest a modification involving oxidative stress response, evidenced as upregulation of catalase via katG, when DMSP is demethylated.

Preliminary comparison of quantification efficiency between DNA-derived dataset and cell-derived dataset of mixed diatom sample based on rDNA-ITS sequence analysis

Quantification of eukaryotes, such as diatom within a water community is extremely difficult due to the different copy number of the measured gene. ITS sequence was considered to be useful in defining intra-specific or population-level differences for their fast evolving. To assess the possibility of exploring rDNA-ITS region in quantification analysis of environment samples, the fragment of 5.8S + ITS-2 was amplified from extracted DNA and sedimental cell samples derived from the same natural-simulated water community, respectively. Two clone libraries were built from the above DNA-derived (DD) and cell-derived (CD) amplifications. The operational taxonomic units (OTUs) of the libraries were calculated. In most cases, number of OTUs for CD dataset was smaller than DD dataset. For the DD and CD datasets, 112 sequences yielded 6 OTUs-96 and 4 OTUs-97 and were assigned to six and four species, respectively. Intraspecific variations existed in these cultivations. The sequences percentage in datasets did not match with the cell portions in mixed sample, which revealed that 5.8S + ITS-2 copies varied between different diatom species, and it was not suitable for quantitative analysis of diatom community structures in mixed sample. More researches are necessary to seek for proper gene to quantify diatoms in the environmental samples.

Nitrogen uptake of phytoplankton assemblages under contrasting upwelling and downwelling conditions: The Ría de Vigo, NW Iberia

Regenerated production (including organic nitrogen) is shown here to be important in the Ría de Vigo (Galicia, NW Iberia) in supporting both harmful algal bloom communities during the downwelling season, but also (to a lesser extent) diatom communities during stratified periods of weak to moderate upwelling. The Galician Rías, situated in the Iberian upwelling system, are regularly affected by blooms of toxic dinoflagellates, which pose serious threats to the local mussel farming industry. These tend to occur towards the end of summer, during the transition from upwelling to downwelling favourable seasons, when cold bottom shelf waters in the rías are replaced by warm surface shelf waters. Nitrate, ammonium and urea uptake rates were measured in the Ría de Vigo during a downwelling event in September 2006 and during an upwelling event in June 2007. In September the ría was well mixed, with a downwelling front observed towards the middle of the ría and relatively high nutrient concentrations (1.0–2.6 μmol L−1 nitrate; 1.0–5.6 μmol L−1 ammonium; 0.1–0.8 μmol L−1 phosphate; 2.0–9.0 μmol L−1 silicic acid) were present throughout the water column. Ammonium represented more than 80% of the nitrogenous nutrients, and the phytoplankton assemblage was dominated by dinoflagellates and small flagellates. In June the water column was stratified, with nutrient-rich, upwelled water below the thermocline and warm, nutrient-depleted water in the surface. At this time, nitrate represented more than 80% of the nitrogenous nutrients, and a mixed diatom assemblage was present. Primary phytoplankton production during both events was mainly sustained by regenerated nitrogen, with ammonium uptake rates of 0.035–0.063 μmol N L−1 h−1 in September and 0.078–0.188 μmol N L−1 h−1 in June. Although f-ratios were generally low (<0.2) in both June and September, a maximum of 0.61 was reached in June due to higher nitrate uptake (0.225 μmol N L−1 h−1). Total nitrogen uptake was also higher during the upwelling event (0.153–0.366 in June and 0.053–0.096 μmol N L−1 h−1 in September). Nitrogen uptake kinetics demonstrated a strong preference for ammonium and urea over nitrate in June.

Larval Competency of Red Abalone (Haliotis rufescens): A New Timeframe for Larval Distribution.

ABSTRACT Settling cues in the form of coralline algae were presented to groups of hatchery-reared red abalone (Haliotis rufescens, Swainson 1822) larvae daily from day 4 to day 32 posthatch (temperature, 14°C). Survival of postlarval abalone after settlement was monitored for 30 days to quantify the effect of delayed metamorphosis on the subsequent survival of benthic juvenile abalone. After exposure to live coralline algae, an average of 85% of the larvae metamorphosed and settled the following day. The number of settled postlarvae increased gradually the longer the settling cue was withheld. Postsettlement juveniles were raised in individual containers on mixed diatoms for up to 34 days. Red abalone larvae remained competent to settle 32 days after fertilization. Larvae that metamorphosed from day 4 through day 19 had longer survival during the next 30 days (average, 19%) than those presented with a settling cue from day 20 to day 32 (average, 8%). Statistical analysis using a threshold cut point indica...

Assessing the micro-phytoplankton response to nitrate in Comau Fjord (42°S) in Patagonia (Chile), using a microcosms approach

Anthropogenic (aquaculture) changes in environment nutrient concentrations may affect phytoplankton (biomass and taxa composition) in marine coastal waters off the Chilean Patagonia. The effects of adding nitrate (NO₃(-)) to natural phytoplankton assemblages were evaluated considering biomass, cell abundance, and taxonomic composition. Microcosm experiments were performed in the spring, summer, and winter in the Comau Fjord located in Subantarctic Patagonia. At the end of the experiments, NO₃(-) decreased rapidly and was undetectable in treatments, indicating a strong NO₃(-) deficiency associated with an exponential increase in Chl-a concentrations, particulate organic nitrogen, and carbon in these treatments. Moreover, given the depleted nitrate concentrations of the spring and summer experiments, the micro-phytoplankton taxa structure shifted from mixed diatom and dinoflagellate assemblages (Ceratium spp., Dinophysis spp., Coscinodiscus sp., Rhizosolenia pungens) to assemblages dominated by blooms of the classic chain-forming diatoms found in temperate and cold waters such as Chaetoceros spp., Skeletonema spp., and Thalassiosira spp. Thus, nitrogen sources (i.e., nitrate, ammonia) may influence phytoplankton abundance and biomass accumulation dynamics in the northern section of Patagonia. It also emphasizes the importance of diatom taxa in regards to the short-term response of phytoplankton to changing environmental nutrient conditions due to natural (decreasing freshwater stream flow) and anthropogenic (aquaculture) events. This situation may be one of the future scenarios in the Patagonian fjords, thus stressing the needs for active environmental monitoring and impact assessment.

Phytoplankton photosynthetic response to solar ultraviolet irradiance in the Ross Sea Polynya: Development and evaluation of a time‐dependent model with limited repair

The relationship of photosynthesis (14C incorporation) to ultraviolet (UVR) and photosynthetically active radiation (PAR) was measured over the course of the late‐spring to early‐summer phytoplankton bloom in the Ross Sea Polynya (Southern Ocean). Experiments were conducted in November 2005 to determine PAR‐only photosynthesis–irradiance (P‐E) curves, biological weighting functions (BWFs) using a new version of the “photoinhibitron” laboratory spectral incubator, and variation in photosynthesis under high vs. low solar UVR treatments in on‐deck incubations. These observations were incorporated into a new spectral model of photosynthetic response to UVR + PAR with time‐dependent repair rates. The distinguishing feature of this model is that repair scales with inhibition up to a maximum absolute repair rate (rmax). Once repair is limited at the maximum rate, additional exposure has a more severe inhibitory effect on photosynthesis, consistent with measured exposure response curves. Parameters for the BWFRmax/P‐E model were determined for 10 sampling locations ranging from mixed diatom and Phaeocystis antarctica assemblages at the beginning of the bloom to assemblages dominated by P. antarctica at the peak of the bloom. The model explained 86–97% of the measured spectral variation with BWFs severalfold higher (more inhibitory) than those previously measured in the Weddell–Scotia Confluence and coastal waters near the Antarctic Peninsula. Predicted relative productivity (ratio of modeled photosynthesis under high vs. low UVR) was close to observed relative productivity, but absolute photosynthetic rates were higher in the on‐deck incubations than in the photoinhibitron.

Live Foods for Juveniles’ Production of Blue Swimming Crab, Portunus pelagicus (Linnaeus, 1766)

The study were aim to demonstrate the affects of live food type’s i.e., mixed diatom, Artemia nauplii and rotifer on survival rate and molt time of larvae stage till 1st day juvenile crabs (C1) of P. pelagicus. Three types of feeding regimes given to the crab larvae through out the study trials are with and without mixed diatom, with and without Artemia nauplii and with and without rotifer. The study shows that zoea fed with rotifer alone was not enough to sustain survival in the next zoea stages and to promote metamorphosis up to megalopa stage. Survival of zoea fed with Artemia nauplii alone shows that this type of food is not suitable for the very early zoea stages. The study also shows that the adding of mixed diatom to larvae rearing system where rotifer and Artemia nauplii is main food items did not produced high survival rate as compared to larvae rearing fed on rotifer and Artemia nauplii alone. The results of the study demonstrated that the food types not only effect survival rate but also the growth of crab larvae. The study generally ended that the combination diet of rotifer and Artemia nauplii alone is enough to produced C1