Critical-zone reactions involve inorganic and biogenic colloids in a cation-rich environment. The present research defines the rates and structure of purified Mg-montmorillonite aggregates formed in the presence of monovalent (K+) and divalent (Ca2+, Mg 2+) cations using light-extinction measurements. Time evolution of turbidity was employed to determine early-stage aggregation rates. Turbidity spectra were used to measure the fractal dimension at later stages. The power law dependence of the stability ratios on cation concentration was found to vary with the reciprocal of the valence rather than the predicted reciprocal of valence-squared, indicating that the platelet structure may be a factor influencing aggregation rates. The critical coagulation concentrations (CCC) (3 mM for CaCl2, 4 mM for MgCl2, and 70 mM for KCl) were obtained from the stability ratios. At a later time and above a minimal cation concentration, turbidity reached a quasi-stable state, indicating the formation of large aggregates. Under this condition, an approximate turbidity forward-scattering correction factor was applied and the fractal dimension was determined from the extinction spectra. For the divalent cations, the fractal dimensions were 1.65 ± 0.3 for Ca2+ and 1.75 ± 0.3 for Mg2+ and independent of cation concentrations above the CCC. For the monovalent cation, the fractal dimension increased with K+ concentration from 1.35 to 1.95, indicating a transition to a face-to-face geometry from either an edge-to-edge or edge-to-face orientation.

The variability in sediment concentration and spatial distribution of meltwater discharges from tidewater glaciers can be used to elucidate climatic evolution and glacier behaviour due to the association between sediment yield and glacier retreat (e.g. Domack & McClennen 1996). In an accelerated deglaciation environment, higher sediment concentrations in the water column can change the glacimarine costal dynamics and affect productivity and sea floor ecosystems (e.g. Marín et al. 2013). In the Antarctic Peninsula Region, meltwater or turbid plumes were previously believed to be rare or without an important role in the sedimentary glacimarine environment (e.g. Griffith & Anderson 1989), but recent studies have shown that this is a common phenomenon in subpolar and transition polar climates (Yoo et al. 2015, Rodrigo et al. 2016). In the current climate change scenario, accelerated glacier retreats and mass losses can produce an increasing input of glacial meltwater into the fjord regions, a situation that is not yet well evaluated in the Antarctic Peninsula. In this short note, after in situ observation of an unusual waterfall from the southern side of the main western tidewater glacier (Shoesmith Glacier) of Horseshoe Island (Lystad Bay), Marguerite Bay (Fig. 1), we report high turbidity values associated with plumes from the glacier, whose values were higher than reported data from subpolar/transition polar Antarctic climates.

Macroalgal fouling communities are potentially useful as bioindicators in environmental monitoring as they are considered to be sensitive to changes in environmental conditions and the use of artificial substrata facilitates the implementation of standardized sampling strategies. The response of macroalgal fouling communities on buoys to changes in water quality was investigated with a view to the possible utilization of these assemblages in environmental monitoring programmes. Seven study sites were selected based on previously collected environmental data and Principal Components Analysis (PCA) was used to order sites according to beam attenuation coefficient (BAC) and concentration of dissolved nitrates and phosphates, relative to a minimally impacted reference site. At each site, all fouling macroalgae were collected from 10 buoys of standard shape and size, and were identified to the lowest possible taxonomic level. Species composition and species dominance were highly variable among impacted sites, indicating that qualitative aspects of community structure may not be useful as indicators of changes in water quality. However, higher levels of nutrient enrichment and turbidity were associated with lower macroalgal species richness, lower overall abundances, and decreased diversities, and therefore these quantitative aspects of community structure are potentially useful as indicators of environmental change. Intermediate levels of turbidity and nutrient enrichment were associated with lower evenness, but did not influence species richness, suggesting that macroalgal abundances respond to changes in environmental conditions before species replacement occurs.

Recent rapid retreat of glacial front lines and the loss of land ice along the Antarctic margins may play an important role in exporting suspended particulate matter (SPM) potentially rich in bioavailable (defined as ascorbate leachable) iron (FeA) to coastal areas of the Southern Ocean. Sediment ablation is an additional source of iron for this high-nutrient low-chlorophyll region. In Potter Cove, King George Island, meltwater streams discharge up to 18 000 mg l-1 (average 283 mg l-1) of slightly weathered, finely ground bedrock particles into coastal waters during the summer. Approximately 15% of this SPM is exported within a low-salinity surface plume into Bransfield Strait. Based on our data, an estimated 12 mg m-2 yr-1 of FeA is exported from the South Shetland Island land surface (ice-free and subglacial areas) to the surrounding coastal waters. Extrapolated to an area of 2.5x104 km2, this FeA input is comparable to the contribution from icebergs and c. 240-fold higher than aeolian input via dust. An observed rise in local sediment accumulation rates suggests that glacial erosion has been increasing over recent decades and that (sub-)glacially derived SPM is becoming more important as a source of iron to the Southern Ocean.

Glacimarine sedimentary environments provide information about climate and oceanographic evolution in the Antarctic Peninsula. This study focuses on the generation of sediment plumes from glaciers. In February 2013 and 2014, two Chilean Antarctic Institute (INACH) Scientific Expeditions were carried out on board the Chilean Navy vessel Aquiles. Five relatively small bays were visited: Curtiss Bay, Recess Cove, Beaupre Cove, Paradise Harbour/Oscar Cove and Salvesen bay. Hydrography and turbidity profiling was carried out up to 100 m depth using an SBE19 Plus-V2 CTD-T. In general, the results showed sediment plumes at two levels: an upper plume from the surface up to 10 m deep and a deeper plume at 40–100 m. These plumes were identified by higher turbidity concentrations and their association with colder water tongues. The deeper plume tended to remain below the 1027.5 kg m-3 isopycnal and extended ~4 km from the glacier, maintaining its shape with a gradually decreasing particle concentration. This longitudinal extension was favoured by ebb tides. The characteristics of the sediment plumes may be influenced by the heat input from water masses. The contribution of the sediments from these small bay systems could play an important role in regional sedimentary processes.

The Ponto-Caspian hydroid Cordylophora caspia has been found for the first time in the Tagus estuary. There is only one previous citation for this invasive species in Portuguese waters. The colonies of C. caspia were branched and had healthy gastrozooids and gonophores. The specimens were collected from a saline boundary zone characterized by high fluctuations in salinity (maximum of 15.3 and minimum of 0.2) and high suspended solids loading. Cordylophora caspia is capable of colonizing man-made infrastructures such as industrial facilities and can inhabit both brackish and freshwater environments. These features of C. caspia, together with its resilience when in a dormant stage (menonts), indicate that the monitoring of this invasive species is advisable in the Tagus estuary.

The effect of copper(II) ions (Cu+2) on the structure of β-lactoglobulin (β-lg) was investigated spectroscopically using UV-visible, fluorescence and circular dichroism (CD) and calorimetrically using isothermal titration calorimetry (ITC), at different temperatures. Results of the UV-visible studies showed that adding Cu+2 to β-lg solution caused increasing turbidity, indicative of protein aggregation. It was noticeable that the rate of increasing turbidity was directly proportional to increasing temperature. The far-UV CD studies displayed that the Cu+2 cannot induce any significant changes in the secondary structures of β-lg at different temperatures. Also, the ITC data indicated that the binding process of Cu+2 to β-lg is mainly entropically driven. The results highlight that copper ions cause the tertiary structure of β-lg to change and induce a slightly open structure leading to the formation of supramolecular aggregates in β-lg which may result in the reduced allergenicity of β-lg and its increased use in industrial applications.

We investigated morphological differences in specimens of the arcid bivalve Scapharca kagoshimensis collected from two sites differing in turbidity in the inner part of Ariake Bay. First, we confirmed if the specimens collected from the two sites were the same species by comparing the sequences of their nuclear 18S ribosomal DNA (18S rDNA) and cytchrome c oxidase subunit I gene (COI) of mitochondrial DNA (mtDNA), since the closely related species S. inequivalvis could be distributed in one site. The results of DNA analyses showed that specimens from both sites belonged to the same species. Shell morphology, gill and posterior adductor muscle size did not differ between the two populations. However, the size of the labial palp was significantly larger in bivalves living in an area of high turbidity compared with those living in an area with low turbidity. This difference could not simply be attributed to differences in meat content because the total weight of the soft body parts did not differ between the two populations. The labial palp is an organ functioning in preingestive particle selection. Hence, the large palps would presumably be a response to high turbidity conditions in which the need for particle processes increases. To the best of our knowledge, this is the first study demonstrating palp size flexibility in arcid bivalves, and such flexibility could be a factor enabling S. kagoshimensis to successfully exploit a wide area of shallow water in the inner part of Ariake Bay.

The effect of increased levels of suspended sediment on fertilization success in the scleractinian coral Pectinia lactuca was investigated in a laboratory experiment following a mass coral spawning event on reefs off Singapore. Egg–sperm bundles were collected from tank-spawned coral colonies collected from the field several days prior to the anticipated mass spawning. Eggs and sperm from each colony were separated and distributed systematically across replicated treatments (N = 9) with three concentrations of fine suspended sediment. Spawning and embryo development in Pectinia lactuca followed a pattern similar to other scleractinian coral species. There was a significant effect of increased suspended sediment concentration on fertilization success (P < 0.05). Both high- (169 mg l−1) and medium- (43 mg l−1) suspended sediment treatments decreased fertilization success compared to controls. These results imply that increased turbidity levels (whether chronic, such as in the waters around Singapore, or short-term, caused by a dredging operation)—when coinciding with the coral spawning season—may affect the reproductive success of corals and compromise coral recruitment and recovery of degraded reefs.

The proliferation of the voluntarily-introduced cupped oyster, Crassostrea gigas, has attained the proportions of species invasion in many intertidal habitats in Europe, presumably resulting from successful reproduction of farmed individuals. It is thus imperative to better understand the reproductive characteristics of farmed oysters, since they are directly under human control. We quantified the dry tissue mass (DTM), gametosomatic index (GSI), and reproductive cycle of farmed oysters at two sites in Bourgneuf Bay, France, in relation to environmental parameters using continuously-recording probes in 2005 and 2006. The GSI was developed for this study, based on the actual area occupied by gametes, rather than the area of the gonad previously used for quantitative histological estimation of reproductive effort. The two sites, intermediate – (IT) and high-turbidity (HT), differed markedly in the amount and quality of particulate suspended matter, and also in fine-scale temperature variations. Oysters at both sites presented two spawning periods in both 2005 and 2006; Bourgneuf Bay is thus near the northernmost European limit for a 2-spawning cycle in Crassostrea gigas. Gonad maturation was initiated when spring water temperature reached 8–10 °C, and gamete atresia occurred when water temperatures transiently dipped to 15–18 °C. Spawns, which occurred above 18 °C, were timed by fine-scale water temperature variations. Particulate organic matter quality peaks, coinciding with gonad maturation, were related to DTM variations before spawning periods, for the IT oysters in both years, and for the HT oysters in 2006. The reproductive effort (GSI) of oysters was similar at both sites; however, the fates of the gametes differed according to site. At the first spawning, the IT oyster gamete emissions were +1 month delayed, as were peak water temperatures greater than 18 °C, and more pronounced, compared to the HT site. Although the second spawning showed high proportions of atretic oocytes at both sites in both years, the IT oysters evacuated twice as many gametes as the HT oysters in 2005. The IT conditions therefore appear more suited to Crassostrea gigas gamete evacuation than the HT conditions.

The clarity of 39 meltwater ponds on the McMurdo Ice Shelf was determined as the horizontal viewing range of a black disc. Visual ranges varied widely from pond to pond from 0.14–5 m; so did the concentrations of optically-active constituents, including the suspended particulates, phytoplankton (10-fold variation) and inorganic suspensoids (> 100-fold), and dissolved yellow substance (10-fold). In six of the ponds the ratio of beam attenuation coefficient to total suspended solids concentration was low (< 0.6 m2 g−1) compared to that in the others (0.7–2.0 m2 g−1, suggesting that generally larger particles were present suspended in the water in these ponds. In both groups, relationships between beam attenuation and constituent concentrations indicated that much of the attenuation was due to inorganic suspensoids. Organic detritus also appeared to be important in many ponds, while phytoplankton and dissolved yellow substance were generally less important. Even though the clarity of many of the ponds was poor, their relative shallowness meant levels of underwater light were probably generally adequate for benthic plant growth.

Un modèle écophysiologique déterministe de la croissance, de la reproduction et des interactions entre le bivalve et son environnement estuarien a été élaboré pour l'huître japonaise Crassostrea gigas. Pour fonctionner, le modèle a besoin de la température de l'eau, des concentrations en matière en suspension, matière organique particulaire, matière minérale particulaire, chlorophylle-a, phéopigments, protéines, lipides et glucides particulaires. Les fonctions de filtration, consommation, ingestion, absorption et respiration ainsi que les efficacités de rétention, sélection et absorption sont modélisées à l'aide de variables endogènes (poids sec de l'animal, allocation d'énergie entre la croissance et la reproduction) et exogènes (température, quantité et qualité de la nourriture). Le modèle simule l'évolution temporelle de deux compartiments : somatique et réserves-gonades. L'énergie provenant de la nourriture absorbée est allouée au compartiment somatique jusqu'à un maximum de croissance somatique. Ce maximum décroît avec l'âge du bivalve et ne dépasse jamais 0,02 g.j−1.individu−1. L'énergie en excès est alors attribuée au compartiment réserves-gonades. Cette représentation permet d'identifier les périodes de stockage de réserves et de gamétogénèse ainsi qu'une bonne simulation de l'intensité des pontes.Le modèle tient compte d'une efficacité de sélection plus importante pour les microphytes que pour les particules détritiques. L'efficacité d'absorption a été représentée en fonction du pourcentage de matière organique dans la fraction ingérée afin de tenir compte de la dilution de la nourriture par les particules minérales. L'efficacité d'absorption des microalgues varie de 20 à 60 %, tandis que pour les particules organiques détritiques, le modèle simule des valeurs négatives pour tenir compte des pertes fécales métaboliques. Ces formulations permettent de suivre l'évolution temporelle des quantités de microphytes et de matières détritiques rejetées sous la forme de pseudofèces et de fèces.