The occurrence of active water transport (net transport against a free energy gradient) in photosynthetic organisms has been debated for several decades. Here, active water transport is considered in terms of its roles, where it is found, and the mechanisms by which it could occur. First there is a brief consideration of the possibility of active water transport into plant xylem in the generation of root pressure and the refilling of embolized xylem elements, and from an unsaturated atmosphere into terrestrial organisms living in habitats with limited availability of liquid water. There is then a more detailed consideration of volume and osmotic regulation in wall-less freshwater unicells, and the possiblity of generation of buoyancy in marine phytoplankton such as large-celled diatoms. Calculations show that active water transport is a plausible mechanism to assist cells in upwards vertical movements, requires less energy than synthesis of low-density organic solutes, and potentially on a par with excluding certain ions from the vacuole.
Bacteria from the genus Vibrio are a common and environmentally important group of bacteria within coastal environments and include species pathogenic to aquaculture organisms. Their distribution and abundance are linked to specific environmental parameters, including temperature, salinity and nutrient enrichment. Accurate and efficient detection of Vibrios in environmental samples provides a potential important indicator of overall ecosystem health while also allowing rapid management responses for species pathogenic to humans or species implicated in disease of economically important aquacultured fish and invertebrates. In this study, we developed a surface immuno-functionalisation protocol, based on an avidin-biotin type covalent binding strategy, allowing specific sandwich-type detection of bacteria from the Vibrio genus. The assay was optimized on 12 diverse Vibrio strains, including species that have implications for aquaculture industries, reaching detection limits between 7×103 to 3×104 cells mL-1. Current techniques for the detection of total Vibrios rely on laborious or inefficient analyses resulting in delayed management decisions. This work represents a novel approach for a rapid, accurate, sensitive and robust tool for quantifying Vibrios directly in industrial systems and in the environment, thereby facilitating rapid management responses.
The trace element selenium (Se) is required for the biosynthesis of selenocysteine (Sec), the 21st amino acid in the genetic code, but its role in the ecology of harmful algal blooms (HABs) is unknown. Here, we examined the role of Se in the biology and ecology of the harmful pelagophyte, Aureococcus anophagefferens, through cell culture, genomic analyses, and ecosystem studies. This organism has the largest and the most diverse selenoproteome identified to date that consists of at least 59 selenoproteins, including known eukaryotic selenoproteins, selenoproteins previously only detected in bacteria, and novel selenoproteins. The A. anophagefferens selenoproteome was dominated by the thioredoxin fold proteins and oxidoreductase functions were assigned to the majority of detected selenoproteins. Insertion of Sec in these proteins was supported by a unique Sec insertion sequence. Se was required for the growth of A. anophagefferens as cultures grew maximally at nanomolar Se concentrations. In a coastal ecosystem, dissolved Se concentrations were elevated before and after A. anophagefferens blooms, but were reduced by >95% during the peak of blooms to 0.05?nM. Consistent with this pattern, enrichment of seawater with selenite before and after a bloom did not affect the growth of A. anophagefferens, but enrichment during the peak of the bloom significantly increased population growth rates. These findings demonstrate that Se inventories, which can be anthropogenically enriched, can support proliferation of HABs, such as A. anophagefferens through its synthesis of a large arsenal of Se-dependent oxidoreductases that fine-tune cellular redox homeostasis.
Diatoms are the primary source of nutrition and energy for the Southern Ocean ecosystem. Microalgae, including diatoms, synthesise biological macromolecules such as lipids, proteins and carbohydrates for growth, reproduction and acclimation to prevailing environmental conditions. Here we show that three key species of Southern Ocean diatom (Fragilariopsis cylindrus, Chaetoceros simplex and Pseudo-nitzschia subcurvata) exhibited phenotypic plasticity in response to salinity and temperature regimes experienced during the seasonal formation and decay of sea ice. The degree of phenotypic plasticity, in terms of changes in macromolecular composition, was highly species-specific and consistent with each species known distribution and abundance throughout sea ice, meltwater and pelagic habitats, suggesting that phenotypic plasticity may have been selected for by the extreme variability of the polar marine environment. We argue that changes in diatom macromolecular composition and shifts in species dominance in response to a changing climate have the potential to alter nutrient and energy fluxes throughout the Southern Ocean ecosystem.
Ecological communities are increasingly exposed to multiple chemical and physical stressors, but distinguishing anthropogenic impacts from other environmental drivers remains challenging. Rarely are multiple stressors investigated in replicated studies over large spatial scales (>1000 kms) or supported with manipulations that are necessary to interpret ecological patterns. We measured the composition of sediment infaunal communities in relation to anthropogenic and natural stressors at multiple sites within seven estuaries. We observed increases in the richness and abundance of polychaete worms in heavily modified estuaries with severe metal contamination, but no changes in the diversity or abundance of other taxa. Estuaries in which toxic contaminants were elevated also showed evidence of organic enrichment. We hypothesised that the observed response of polychaetes was not a positive response to toxic contamination or a reduction in biotic competition, but due to high levels of nutrients in heavily modified estuaries driving productivity in the water column and enriching the sediment over large spatial scales. We deployed defaunated field-collected sediments from the surveyed estuaries in a small scale experiment, but observed no effects of sediment characteristics (toxic or enriching). Furthermore, invertebrate recruitment instead reflected the low diversity and abundance observed during field surveys of this relatively pristine estuary. This suggests that differences observed in the survey are not a direct consequence of sediment characteristics (even severe metal contamination) but are related to parameters that covary with estuary modification such as enhanced productivity from nutrient inputs and the diversity of the local species pool. This has implications for the interpretation of diversity measures in large-scale monitoring studies in which the observed patterns may be strongly influenced by many factors that covary with anthropogenic modification.
Fluorometers are widely used in ecosystem observing to monitor fluorescence signals from organic compounds, as well as to infer geophysical parameters such as chlorophyll or CDOM concentration, but measurements are susceptible to variation caused by biofouling, instrument design, sensor drift, operating environment, and calibration rigor. To collect high quality data, such sensors need frequent checking and regular calibration. In this study, a wide variety of both liquid and solid fluorescent materials were trialed to assess their suitability as reference standards for performance assessment of in situ fluorometers. Criteria used to evaluate the standards included the spectral excitation/emission responses of the materials relative to fluorescence sensors and to targeted ocean properties, the linearity of the fluorometers optical response with increasing concentration, stability and consistency, availability and ease of use, as well as cost. Findings are summarized as a series of recommended reference standards for sensors deployed on stationary and mobile platforms, to suit a variety of in situ coastal to ocean sensor configurations. Repeated determinations of chlorophyll scale factor using the recommended liquid standard, Fluorescein, achieved an accuracy of 2.5%. Repeated measurements with the recommended solid standard, Plexiglas Satinice® plum 4H01 DC (polymethylmethacrylate), over an 18 day period varied from the mean value by 1.0% for chlorophyll sensors and 3.3% for CDOM sensors.
Despite well-documented negative impacts of invasive species on native biota, evidence for the facilitation of native organisms, particularly by habitat-forming invasive species, is increasing. However, most of these studies are conducted at the population or community level, and we know little about the individual fitness consequences of recruitment to habitat-forming invasive species and, consequently, whether recruitment to these habitats is adaptive. We determined the consequences of recruitment to the invasive green alga Caulerpa taxifolia on the native soft-sediment bivalve Anadara trapezia and nearby unvegetated sediment. Initially, we documented the growth and survivorship of A. trapezia following a natural recruitment event, to which recruitment to C. taxifolia was very high. After 12 months, few clams remained in either habitat, and those that remained showed little growth. Experimental manipulations of recruits demonstrated that all performance measures (survivorship, growth and condition) were significantly reduced in C. taxifolia sediments compared to unvegetated sediments. Exploration of potential mechanisms responsible for the reduced performance in C. taxifolia sediments showed that water flow and water column dissolved oxygen (DO) were significantly reduced under the canopy of C. taxifolia and that sediment anoxia was significantly higher and sediment sulphides greater in C. taxifolia sediments. However, phytoplankton abundance (an indicator of food supply) was significantly higher in C. taxifolia sediments than in unvegetated ones. Our results demonstrate that recruitment of native species to habitat-forming invasive species can reduce growth, condition and survivorship and that studies conducted at the community level may lead to erroneous conclusions about the impacts of invaders and should include studies on life-history traits, particularly juveniles.
Different oceanographic provinces host discrete microbial assemblages that are adapted to local physicochemical conditions. We sequenced and compared the metagenomes of two microbial communities inhabiting adjacent water masses in the Tasman Sea, where the recent strengthening of the East Australian Current (EAC) has altered the ecology of coastal environments. Despite the comparable latitude of the samples, significant phylogenetic differences were apparent, including shifts in the relative frequency of matches to Cyanobacteria, Crenarchaeota and Euryarchaeota. Fine-scale variability in the structure of SAR11, Prochlorococcus and Synechococcus populations, with more matches to warm-water ecotypes observed in the EAC, indicates the EAC may drive an intrusion of tropical microbes into temperate regions of the Tasman Sea. Furthermore, significant shifts in the relative importance of 17 metabolic categories indicate that the EAC prokaryotic community has different physiological properties than surrounding waters.
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