Seasonal Community Structure Research Articles

Exposure to closed-loop scrubber washwater alters biodiversity, reproduction, and grazing of marine zooplankton

Shipping is a large industry responsible for atmospheric emissions of hazardous substances including SOX, NOX, and particulate matter. Many ships have installed exhaust gas cleaning systems (scrubbers) to remove primarily SOX from the exhaust, but the hazardous substances are instead transferred to the water used in the scrubbing process. Ships with closed-loop scrubbers recirculate the water but can still discharge around 126-150 m3 directly to the surrounding marine environment every day. The discharged water contains metals and organic substances, such as polycyclic aromatic hydrocarbons, that are known to be toxic to marine zooplankton. Here we show that closed-loop scrubber washwater is toxic to communities of marine mesozooplankton at our lowest tested dilution, 1.5% (v/v), and affects survival, reproduction, diversity, and ability to predate on microzooplankton. The cumulative toxic unit of the undiluted closed-loop scrubber washwater was estimated to 17, which indicates that the water could be toxic at levels below what was tested in this study. Among all detected substances, vanadium, copper, benzo[ghi]perylene, nickel, and zinc were identified as toxicity-driving substances in the order listed. Closed-loop scrubber washwater has been shown to affect development and survival in single species of copepods, but here we find evidence of toxicity at the community level, irrespective of seasonal community structure, and that the exposure has potential to disrupt the interactions between trophic levels in the pelagic food web. We show that the closed-loop scrubber washwater cause both lethal and sublethal effects in marine zooplankton, due to contaminants, some of which are persistent in the marine environment.

Seasonal variation in reef fish assemblages in the environmentally extreme southern Persian/Arabian Gulf

The southern Persian/Arabian Gulf experiences extreme seasonal temperature variation (> 20 °C) making it among the most hostile reef environments on Earth. Previous anecdotal evidence has suggested that seasonal temperature changes may influence regional reef fish assemblages, but to date research has been limited. To examine the influence of temperature on reef fish abundance and composition, we performed visual surveys in summer and in winter over three years at three reefs in the southern Gulf (Dhabiya, Saadiyat and Ras Ghanada). Overall abundance of fishes was 40% higher in summer than in winter, and multivariate analyses showed strong and significant differences in overall seasonal community structure, consistent at all sites and across all years. Seasonal differences were largely driven by nine of the 30 observed species, which together accounted for 70% of the divergence in community structure between summer and winter. Of these nine species, Lutjanus ehrenbergii, Lutjanus fulviflamma, Plectorhinchus sordidus and Abudefduf vaigiensis were significantly more abundant in summer, Parupeneus margaritatus and Acanthopagrus bifasciatus, were significantly more common on reefs in winter. We discuss these changes in terms of seasonal physiological and ecological constraints, and explore the implications of these changes on the functional ecology of reef fishes in this thermally variable and extreme environment.

Two-years of investigation revealed the inconsistency of seasonal dynamics of an ectomycorrhizal fungal community in Japanese cool-temperate forest across years.

Ectomycorrhizal (ECM) fungal communities show temporal dynamics. Such dynamics have been mainly assessed with 1 year of investigations and have been related to the seasonal changes in environment. Recent study in sub-tropical region has revealed that stochastic temporal-based process can affect ECM fungal community, making the community of the same season different between years. The different community structures across years have also been observed in the Arctic region with a grass host. Nevertheless, in temperate zones, the effect of temporal-based processes and the consistency of seasonal dynamics have never been investigated. We conducted a 2-year root sampling in a cool temperate Fagus crenata forest to test whether the temporal variation of ECM fungal community composition could be explained by season. The explanation powers of temporal distance and environmental factors for the temporal dynamics of ECM fungal community were simultaneously evaluated. The variation in community structure was significantly explained by year but not by season, indicating that seasonal community structure differed between years. This difference in the community structure across years was partly explained by temporal factors. Our study implies that the temporal dynamics of ECM fungal communities in temperate forests are affected by temporal-based factors and can vary across years.

Fitting methods and seasonality effects on the assessment of pelagic fish communities in Daya Bay, China

Abstract The general relationship indicating that biomass decreases with individual body size is referred to as size spectra. This is consistent with the power law that characterizes size frequency distributions. While many previous studies have used the estimated exponent in size spectra as a metric to assess external perturbations, limited empirical studies have focused on the fitting methods. Here, we compared the effects caused by fitting methods and distribution models based on one-year pelagic fish data from Daya Bay, China. Our empirical results showed that maximum likelihood estimation (MLE) is more suitable than traditional normalized biomass spectra (NBS), and that a power law is not always the best model when using MLE. Moreover, we found significant size structure variation in different seasons. Principal component analysis (PCA) and linear mixed effects model (LMM) results showed that temperature was the major factor in seasonal environmental variation, and fish migration might be the essential response strategy causing size structure changes. The estimated exponents and nonlinear structure indicated that the Daya Bay is under intensive human impact. Our results suggest that MLE methods are recommended in future size-based studies, and that environmental variation and migration patterns are crucial in understanding seasonal community structure changes.

Regional synchrony in full-scale activated sludge bioreactors due to deterministic microbial community assembly.

Seasonal community structure and regionally synchronous population dynamics have been observed in natural microbial ecosystems, but have not been well documented in wastewater treatment bioreactors. Few studies of community dynamics in full-scale activated sludge systems facing similar meteorological conditions have been done to compare the importance of deterministic and neutral community assembly mechanisms. We subjected weekly activated sludge samples from six regional full-scale bioreactors at four wastewater treatment plants obtained over 1 year to Illumina sequencing of 16S ribosomal RNA genes, resulting in a library of over 17 million sequences. All samples derived from reactors treating primarily municipal wastewater. Despite variation in operational characteristics and location, communities displayed temporal synchrony at the individual operational taxonomic unit (OTU), broad phylogenetic affiliation and community-wide scale. Bioreactor communities were dominated by 134 abundant and highly regionally synchronized OTU populations that accounted for over 50% of the total reads. Non-core OTUs displayed abundance-dependent population synchrony. Alpha diversity varied by reactor, but showed a highly reproducible and synchronous seasonal fluctuation. Community similarity was dominated by seasonal changes, but individual reactors maintained minor stable differences after 1 year. Finally, the impacts of mass migration driven by direct biomass transfers between reactors was investigated, but had no significant effect on community similarity or diversity in the sink community. Our results show that population dynamics in activated sludge bioreactors are consistent with niche-driven assembly guided by seasonal temperature fluctuations.

Seasonal community structure of mesozooplankton in the Daya Bay, South China Sea

Mesozooplankton are key components of coastal ecosystems, linking the microbial food web to the classic food chain. In this study, species composition and abundance of mesozooplankton is studied for the Daya Bay in April (spring) and October (fall), 2006. A total of 27 species of mesozooplankton were identified in spring and 58 species in fall. Dominant species were Oithona tenuis, Flaccisagitta enflata, Penilia avirostris and Centropages tenuiremis in spring, shifting to Microsetella norvegica, Oithona tenuis and Parvocalanus crassirostris in fall. Higher mesozooplankton abundance was found at Aotou Cove and Dapeng'ao Cove compared to other stations, indicating the influence of eutrophication on mesozooplankton community in the Daya Bay. The outbreak of Noctiluca scintillans bloom in spring reduced the species diversity and abundance of mesozooplankton.

The Influence of Freshwater on Nekton Community Structure in Hydrologically Distinct Basins in Northeastern Florida Bay, FL, USA

Natural patterns of freshwater delivery to the Florida Bay estuary have been disrupted by flood-control and water-supply projects. Restoration efforts are likely to alter salinity regimes and patterns of nekton distribution and abundance. Spatial and seasonal community structure differences were analyzed for small-bodied and large-bodied nekton collected by fisheries-independent monitoring from 2006 through 2009 in the northeastern basins of Florida Bay. The small-bodied nekton community was dominated by resident fish that may be indicators of ecosystem health because they spend their lives within the bay and are not directly influenced by human harvest; the large-bodied nekton community was dominated by transient and, in some cases, economically important species. Differences in community structure revealed a gradient in similarity that was associated with freshwater influence, as determined by salinity variability over the study period. These observed changes associated with salinity regimes within and between basins underscore the importance of monitoring communities before and after alterations in freshwater inflow.

Co-tolerance of phytoplankton communities to photosynthesis II inhibitors

Natural variability in sensitivity and pollution induced community tolerance (PICT) to atrazine, isoproturon and diuron and a mixture of these three herbicides to natural algal assemblages in mesocosms was determined. The specificity of PICT was examined by evaluating co-tolerance pattern for these photosystem-II (PSII) inhibitors. Phytoplankton communities were constantly exposed to equipotent concentrations of atrazine, isoproturon, diuron namely the 30% hazard concentration (HC 30) obtained from species sensitivity distributions and an equitoxic mixture (Σ3 × 1/3 × HC 30 of each herbicide) for five weeks in outdoor mesocosms. Induction of tolerance to the various herbicides was investigated by photosynthetic efficiency measurements of the algal assemblages in short-term laboratory tests. The composition of the algal communities in the various treatments was determined and ordination techniques such as the principal component analysis (PCA) were applied to log-transformed data to compare the seasonal community structure development. Temporal variation in sensitivity of the control algal assemblage to atrazine and isoproturon, but less to diuron was observed. The results further demonstrated that the control communities were in general more sensitive than the treated ones over the whole period tested indicating an enhanced tolerance of pre-exposed phytoplankton in the mesocosms. Co-tolerance was also observed for atrazine pre-exposed algal community to isoproturon, however, not vise versa. A pre-exposure to diuron induced similar tolerance to all three herbicides. A pre-exposure to the mixture treatment also lead to tolerance to isoproturon and diuron, less to atrazine. Overall, the observed co-tolerance pattern indicates that co-tolerance was not comparable between the herbicides with strong similarity in their biochemical mode of action.

FLORAÇÕES DE CIANOBACTÉRIAS TÓXICAS EM UMA LAGOA COSTEIRA HIPEREUTRÓFICA DO RIO DE JANEIRO/RJ (BRASIL) E SUAS CONSEQUÊNCIAS PARA SAÚDE HUMANA

revista vol 13 no 2.indd Normal 0 21 false false false MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:Tabela normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} The Jacarepagua Basin, Rio de Janeiro, Brazil has over the last four decades undergone a disordered process of urban and industrial growth with direct consequences on water quality and incidence of cyanobacterial blooms in the Jacarepagua Lagoon Complex (JLC). The present study combines data aiming to evaluate water quality in Jacarepagua Lagoon (JL) from monitoring of physical variables (pH, water transparency, temperature), chemical variables (salinity, dissolved oxygen, chlorophyll), the planktonic community, and the concentration of microcystins in fish from the region. The data herein presented were divided into three periods according to seasonal cycles: PI (aug/96 to sep/97), PII (jan/99 to nov/99), and PIII (feb/07 to jan/08). Dominance by cyanobacteria characterized most of the study period, interspersed with sudden peaks (e.g. during PII and PIII) of high diversity of phytoplankton. Phytoplanktonic peaks were represented by Chlorophyta, diatoms, Prasinophyta and Criptophyta. Interestingly, the events observed in 1999 repeated almost 10 years later, suggesting roughly seasonal community structure dynamism in the JLC. Disappearance of the bloom coincided with the lowest recorded water temperatures, suggesting that temperature is an important factor in the observed dynamics. The JL had a high abundance of zooplankton, yet species diversity was relatively low. Concentrations of microcystins found in muscles of fish from JL often contained values above the levels recommended by OMS for human consumption.

Seasonal community structure of the molluscan macrofauna at the marine‐lagoonal environmental transition at Kalloni solar saltworks (Lesvos Island, NE Aegean Sea, Greece)

Solar saltworks are extremely heterogeneous coastal aquatic ecosystems whose benthic biodiversity patterns have not been comprehensively investigated yet. The present study focuses on the seasonal community structure of the macrobenthic molluscs at the marine‐lagoonal environmental transition that takes place at Kalloni solar saltworks (Lesvos Island, NE Aegean Sea, Greece). The molluscan community was studied by means of four seasonal collections carried out in 2004 at four sites in the study area. The molluscan community was found to be considerably species‐rich and forming a coenocline, as marine species were gradually replaced by lagoonal species with increasing distance from the sea. The major variable in the implied environmental gradient structuring the molluscan community appeared to be confinement rather than salinity, although zonation of the molluscan community structure was rather broad. The pattern of spatial organization of the molluscan fauna did not appear to change seasonally, although seasonal shifts of the zones did occur in the study area.

Seasonal community structure of macromycetes in Veracruz, Mexico

A study of phenological patterns in macromycete communities in Veracruz, Mexico was carried out in order to understand changes in community structure across regions of different vegetation types. Previous studies suggest that similarities in community composition occur when there are similarities in certain geographical and climatological characteristics, however they do not address functional groups or seasonal changes across regions. Macromycete communities in Veracruz showed similar species distribution patterns, but individual assemblages changed structure seasonally, changes that were strongly correlated with rainfall. Interestingly, the number of functional groups (species performing similar ecological functions) was not determined by rainfall, but the distribution of species within functional groups was determined by rainfall. Temperature did not appear to play a role in structuring community diversity at this regional scale. However, temperature and other environmental factors such as pH or light may be the mechanism triggering phenological patterns, and influencing the species pool at localized scales. This work brings new light to fungal community diversity patterns in a largely unknown group of species.

IMPORTANCE OF PHYSICAL VARIABLES ON THE SEASONAL DYNAMICS OF EPILITHIC ALGAE IN A HIGHLY SHADED CANYON STREAM1

ABSTRACTThe seasonal abundance of epilithic algae was correlated with major physico‐chemical parameters in a first‐order, heavily shaded stream in northern Arizona. Diatoms made up over 85%, by numerical abundance, of the epilithon community Light energy, water temperature, and stream discharge were most highly correlated with seasonal abundance of epilithic diatom taxa when analyzed with stepwise multiple regression. None of the chemical variables measured in the study (NO3‐N, O‐PO4, SiO2, including PH) was found to be significantly correlated with the seasonal community structure of epilithic diatoms. Total diatom cell densities showed a significant negative correlation to stream bed light energy. Likewise, total diatom cell densities along a transect in the stream bed showed a negative correlation to current velocity during those months when base flow was low and stable, and current velocity was ≤25 cm·sec‐1. Most diatom taxa had highest cell densities at temperatures < 16°C and at daily mean stream bed light levels < 400 μE·m−2·s−1. Highest cell densities of green algae occurred at temperatures between 6–16°C and at daily mean stream bed light levels of > 400 μE·m−2·s−1. Blue‐green algae (cyanobacteria) grew best at the highest recorded water temperatures and daily mean stream bed light energy (16–20°C and 900–1200 μE·m−2·s−1). Abrupt increases in NO3‐N coincided with a brief pulse of Nostoc pruniforme colonies during June, and leaf drop from Alnus oblongifolia during October.

The seasonal community structure and drift of microcrustaceans in Valley Creek, Minnesota

Microcrustaceans represent a poorly known component of stream systems. This study examined the seasonal abundance of copepods and cladocerans found in Valley Creek, Washington County, Minnesota. Both benthic densities as well as drift rates were quantified. A total of 16 species was collected in quantitative benthic samples and two additional species occurred in drift samples. The Valley Creek microcrustaceans could be classified into two general groups, those residing in depositional stream habitats similar to a lake or pond littoral and favoring an epibenthic lifestyle, and those found in more erosional habitats where a hyporheic lifestyle is more likely. The microcrustacean community also demonstrated a distinct seasonality with peak abundance in the spring and early summer. Sediment size compositon also demonstrated a seasonal change but detrital composition did not. Microcrustacean drift generally paralleled changes in benthic density but in several cases it tended to lag behind the changes in the benthos. This lag could be due to a seasonal siltation of the sediments, which would compress the habitat volume available to interstitial meiofaunal elements.