Abundance Of Major Groups Research Articles

Zooplankton Abundance Reflects Oxygen Concentration and Dissolved Organic Matter in a Seasonally Hypoxic Estuary

Ocean deoxygenation, warming, and acidification resulting from global change and increasing nutrient inputs are major threats to marine ecosystems. Despite this, spatial and temporal patterns of oxygen availability and their impacts on marine life are understudied compared to warming and acidification, particularly in coastal tropical ecosystems. We measured the abundance of major groups of zooplankton in the context of five covarying environmental parameters [temperature, salinity, dissolved oxygen (DO), dissolved organic matter (DOM), and chlorophyll concentration] in a tropical estuary for one year. Partial least squares demonstrated that environmental conditions explained 20% of the variation in the community and found that temperature, salinity, DO, and DOM were most important (Variable Importance in Projection [VIP] > 0.8). A generalized linear model identified depth, DO, salinity, and chlorophyll as significant main effects, and temperature and DOM were also significant via two-way interactions (p < 0.05). When examined separately, the abundance of each zooplankton group was explained by a slightly different combination of environmental factors, but in all cases DO had large, significant effects, and in most cases DOM or its interactions were also significant. These results demonstrate that the seasonal cycle of hypoxia in this system significantly impacts the abundance of major zooplankton groups and likely also recruitment of benthic fauna through impacts on meroplankton and benthic-pelagic food webs.

Dynamics of the zooplankton assemblage of Ojirami Reservoir, Edo State, Nigeria

Zooplankton form an important trophic link between phytoplankton and fish in the aquatic food chain. Investigation was carried out on the zooplankton community of Ojirami, Reservoir, Nigeria, to document the composition, abundance and distribution and their interactions with the physico-chemical conditions. Surface water and zooplankton samples were collected from six sampling stations (A, B, C, D, E, and F) monthly from January 2009 to December 2010 and analyzed following standard methods. Twelve out of the 17 physico-chemical conditions showed higher wet season mean levels. The zooplankton community comprised 28 species of Rotifera, 12 Cyclopoida, 17 Cladocera, 6 Calanoida, 5 Diptera (larvae), 1 Ephemeroptera and 2 Arachnida. Rotifera was the most dominant group and Arachnida the least. No species was dominant; Brachionus falcatus, Asplanchna brightwelli and Tropodiaptomus species were subdominant. Rotifera was also the most abundant group in all stations, followed by Calanoida and Cladocera. Abundance of major groups was higher in wet than dry season, but not significant (P>0.05), except for Diptera that was higher in dry season (P<0.05). Overall community structure exhibited high species diversity and high taxa richness. Total zooplankton, Cyclopoida, Cladocera and Calanoida were negatively correlated with water temperature and water level; and positive with alkalinity, free CO2 andphosphate. The study revealed low pollution indicator species in the reservoir suggestive of moderate water quality.Keywords: Brachionus, Correlation, physico-chemical conditions, Ojirami Reservoir

Microbial Diversity in High Arsenic Groundwater in Hetao Basin of Inner Mongolia, China

The microbial diversity and community structure in twenty-one groundwater samples from high arsenic shallow aquifers of Hetao Basin, Inner Mongolia, China was investigated with an integrated approach including polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene phylogenetic analyses. A total of 25 bacterial and 32 archaeal DGGE bands were exercised for sequencing. Phylogenetic analyses showed that the bacterial DGGE bands were dominated by Proteobacteria, and the archaeal bands were dominated by Thaumarchaeota and Euryarchaeota. Based on arsenic concentrations, three samples (corresponding to low, medium, and high level of arsenic, respectively) were selected for construction of 16S rRNA gene clone libraries. A total of 912 (468 and 444 for bacteria and archaea, respectively) 16S rRNA gene clone sequences were obtained and subjected to phylogenetic analyses. The results showed that bacterial communities of these samples were dominated by Acinetobacter, Pseudomonas, Massilia, Dietzia, Planococcus, Brevundimonas, Aquabacterium and Geobacter, and archaeal communities by Nitrosophaera, Thermoprotei and Methanosaeta. The relative abundance of major groups varied as a function of changes in groundwater geochemistry. Acinetobacter, Brevundimonas, Geobacter, Thermoprotei and Methanosaeta dominated in high arsenic samples with high concentrations of methane and Fe(II), and low concentrations of SO2− 4 and NO− 3, while Pseudomonas and Nitrosophaera were abundant in low arsenic groundwater. These results imply that microbes play an important role in arsenic mobilization in the shallow aquifers of Hetao Basin, Inner Mongolia.

Macroinvertebrate community structure and its seasonal variation in the Upper Mississippi River, USA: a case study

We surveyed benthic macroinvertebrates in the Upper Mississippi River near Minneapolis and St. Paul, Minnesota, USA (1350–1380 river km) using Hester-Dendy multiplate samplers as artificial substrates. Two study sites were sampled in multiple seasons at two depths over two years during the period from 2007 to 2009. We examined the patterns of seven community metrics summarizing richness levels and/or relative abundances of major community subsets. Richness metrics were driven by rare (occurring in less than 10% of the samples) taxa but overall densities and relative abundances of major groups reflected the presence of a few dominant taxa. Using analysis of variance, community metrics differed between study years or sampling depths only sporadically, but consistently differed among survey periods. Non-metric multidimensional scaling analysis indicated samples primarily clustered by survey period (within years) and sampling depth at one of our sites and by study year and survey period at the other site. A relatively small number of taxa were consistently abundant in our study, many of which have been reported as community dominants in other large river studies. Annual variability in assemblage composition generally reflected atypically high numbers of one or more of these persistent dominants, and was likely related to differences in hydrological conditions between years. Seasonal variability, however, was relatively consistent between years at both study sites.

Distribution of meiobenthos at bathyal depths in the Mediterranean Sea. A comparison between sites of contrasting productivity

In order to study the distribution of meiobenthos (Metazoa and Foraminifera) at bathyal depths along a west-east productivity gradient in the Mediterranean Sea, stations along the continental slopes of the Balearic Sea, west Ionian and east Ionian Seas were sampled during the DESEAS Trans-Mediterranean Cruise in June-July 2001. Standing stock of total meiobenthos differed considerably among the sampling stations, with marked differences occurring between sampling depths and sites. At 600 m depth, meiobenthic abundances were slightly higher over the Balearic continental slope, whereas at the deeper stations (800 m and 1500-1700 m), abundances were significantly higher in the west Ionian Sea. Significant relationships were found between the abundances of major groups and the chloroplastic pigments, indicating that food availability is a major factor controlling the distribution of meiobenthos. Apart from the overall differences in productivity between the western and eastern Mediterranean Sea, local hydrographic features and topographic differences greatly influence the spatial variability of the environmental parameters within each sub-basin and thus the distribution of meiobenthos in the bathyal zone.

Metal stress on the plankton communities of Sado River (Portugal)

The effects of heavy metals on the structure of phytoplankton and zooplankton communities were determined in Sado River, Portugal, during the period of highest production (summer). Two tributaries, receiving wastes from pyrite mines, enter the river and gave rise, in the middle reaches, to dissolved metal concentrations up to 88 μg l −1 Cu, 2.6 μg l −1 Cd and 1800 μg l −1 Zn. At the most polluted sites phytoplankton responded mainly by a shift towards metal resistant species: dominant species such as Rhodomonas minuta, Synedra ulna, Crucigenia tetrapedia and Stephanodiscus hantzschii were replaced by Gomphonema parvulum, Scenedesmus armatus and Nitzschia frustulum, while the total algal standing crop was not significantly affected. In contrast, zooplankton displayed a strong reduction in the abundance of major groups (40–100%), species richness (59%) and diversity (58–75%), and only a few taxa, namely Acanthocyclops robustus, Arcella vulgaris, Philodina sp., seemed to tolerate high metal concentrations. At the lower river reaches, where metal contamination decreased substantially, a recovery in species composition and abundance was observed for both plankton communities.