Inlet mouth phase influences density, variability and standing stocks of planktonic
Introduction
Likewise, the closed phase can fluctuate from days to years, mainly associated with river floods, which usually trigger a renewed open phase (Perissinotto et al., 2010). Several authors have reported significant biological changes between the open and closed phase in these systems (Whitfield et al., 2008).
Material and Methods
The resulting data set contained one data point for each sampling date in a given estuary and included one to more data points for each estuary's open and closed phases. A volume estimate for the open and closed phases was used to estimate standing stocks, along with mean phytoplankton chlorophyll-a concentrations, zooplankton density, and biomass values during each phase.
Results
- Nutrients
- Chlorophyll-a
- Zooplankton density and biomass
- Temporal dynamics of dissolved inorganic nutrients and planktonic communities
- Plankton standing stocks per estuary
In the Mhlanga Estuary, standing phytoplankton stocks during the closed phase were 242 times higher than in the open phase (Fig. 1.4a). Standing stocks of zooplankton were up to 18 times higher during the closed phase than in the open phase.
Discussion
The matrix transformation (S) accounts for the intermediate transfers between partitions, this transformed matrix is called the total dependency matrix (D). Also shown are the results of the original networks for the Mlalazi (d & i) and Mpenjati (e & j) estuaries.
Variability and temporal stability of communities in estuaries (Mlalazi and Mpenjati,
Introduction
Finally, other mechanisms such as species traits (Flöder and Hillebrand, 2012), food chain length, and omnivory (Long et al., 2011) may also determine the stability of community traits. This marked seasonal change in environmental conditions causes spatio-temporal changes in estuarine planktonic and macrobenthic invertebrate communities in this region (Perissinotto et al., 2010 and references therein).
Materials and Methods
- Study sites
- Environmental variability
- Biological variability
- Data analysis
To determine whether community-level trait variability changed significantly over time in both estuaries (Aim 2), the coefficient of variation (CV), defined as the ratio of the standard deviation to its mean (CV=δ/µ), was used. . To determine the temporal stability of the analyzed traits at the community level and its stabilization mechanisms (objective 3), temporal stability (S) was used as a measure of stability.
Results
- Spatio-temporal changes in abiotic factors
- Spatio-temporal changes in biological communities
- Variability of the community-level properties
- Stability of community-level properties
At the Mlalazi estuary, mean DIN concentrations were highest during May 2010 (dry season) and lowest during February 2011 (end of wet season). At the Mpenjati estuary, mean DIN concentrations were highest during September 2010 (dry season) and lowest during February 2011 (end of wet season). PERMANOVA analysis found a significant season × station interaction effect at the Mlalazi and Mpenjati estuaries (Table 2.2, 2.3).
Average inter-station variability of the analyzed community-level properties at the Mlalazi (left) and Mpenjati (right) estuaries. Differences in community characteristics at the Mlalazi (left) and Mpenjati (right) estuaries, a) temporal stability b) species synchrony, c) species dominance and d) species richness. Pearson correlation between temporal stability and community properties at the Mlalazi and Mpenjati estuaries.
Discussion
Two-way ANOVA results for %C, %N and C:N ratio of suspended to sediment litter in Mlalazi and Mpenjati estuaries. In the eastern Kleinemonde estuary, the fish community contributed the most to the system's energy needs in all seasons. In the Mlalazi and Mpenjati estuaries, macrobenthic compartments contributed most to the carbon demand of these systems (Table 4.4).
Carbon and nitrogen sequestration: herbivore ratios were also higher during the wet season in the East Kleinemonde and Mpenjati estuaries. The FCI of carbon and nitrogen networks was highest in the East Kleinemonde estuary and lowest at the Mlalazi estuary. Reproduction as one of the main causes of temporal variation in the elemental composition of zooplankton.
Temporal patterns in planktonic and benthic elemental composition and stoichiometry
Introduction
Consumer-driven nutrient recycling can thus determine the overall regime of nutrient limitation experienced in a system (Elser et al., 1988; Elser and Urabe, 1999). The theory of ecological stoichiometry has been used to quantify ecosystem-level changes by analyzing the quality and quantity of nutrients and food resources (e.g. Glibert et al., 2011; Sterner and Elser, 2002). For example, terrestrial and freshwater herbivores facing severe nutrient limitations exhibited reduced gross growth efficiency (DeMott et al., 1998; Elser et al., 2000).
Empirical support for ecological stoichiometry theory is mainly derived from studies on zooplankton species, with less research focused on benthic taxa (Frost et al., 2003). Estuaries are nevertheless among the most affected of all marine-related ecosystems (Lotze et al., 2006). Seasonal variability in precipitation and river inflow has been found to cause significant spatiotemporal changes in the estuarine communities of this region (chapters 1 and 2, Perissinotto et al., 2010 and references therein).
Materials and Methods
- Study sites
- Sampling procedure
- Biomass determinations
- Elemental analysis
- Data analysis
Map of the study areas (Mlalazi and Mpenjati estuaries) on the east coast of South Africa. The stations were located so that representative spatial samples were collected in the upper, middle and lower part of the respective estuaries. For the rest of the study, macrobenthos samples were collected with a van Veen grab (sampling area 0.025 m2, 10 cm depth).
Dry weight was determined for the most representative zooplankton species (accounting for 99% of the abundance) after 48 h of oven drying at 60°C. All zooplankton and macrobenthos samples were ground and homogenized with a glass rod in the centrifuge tubes to avoid loss of the reduced material available for some samples. Information on %C and %N was available for most zooplankton and macrobenthic species for each sampling event.
Results
- Carbon and nitrogen mass of abiotic and biotic components
- Spatio-temporal variations in elemental content of suspended and sediment detritus
- Seasonal variations in elemental content of planktonic and benthic species
- Significant differences in elemental content among species
- Carbon and nitrogen signatures of abiotic and biotic components
Higher carbon and nitrogen biomass for planktonic and benthic communities was recorded during the dry season (closed phase) in the Mpenjati estuary. In terms of spatial differences, the highest nutrient content was recorded in the upper middle region of the Mlalazi estuary (Fig. 3.2). The %N and C:N ratio of sediment debris were lowest and highest in the upper reaches of the Mpenjati estuary, respectively.
Overall, the highest nutrient content of suspended and sediment detritus was recorded in the upper reaches of both estuaries. δ13C of zooplankton species in the Mlalazi estuary were usually more depleted than those in the Mpenjati estuary. However, slightly more enriched δ15N signatures were recorded by the zooplankton species in the Mlalazi Estuary compared to those in the Mpenjati Estuary (Fig. 3.6).
Discussion
Map of study areas (East Kleinemonde, Mlalazi and Mpenjati estuaries) on the east coast of South Africa. The above set of indices were calculated for carbon and nitrogen networks in the East Kleinemonde, Mlalazi and Mpenjati estuaries. During the closed phase of the East Kleinemonde estuary, phytoplankton, microphytobenthos and macrobenthos had the highest flow.
Higher nitrogen FCI values were recorded during the closed phase of East Kleinemonde and Mpenjati. System indices of carbon and nitrogen (right) aggregate networks in the East Kleinemonde, Mlalazi and Mpenjati estuaries. However, this pattern was not recorded in three of the nine subsystems analyzed in the same bay (Baird et al., 2011), East Kleinemonde and the Mpenjati Estuary.
Comparative analysis of carbon and nitrogen dynamics of three estuaries on the east
Introduction
The duration of the closed and open phases varies between systems and biogeographical regions, with the open phase lasting from days to weeks or months, while the closed phase can last from weeks to years (Perissinotto et al., 2010). Most TOCEs are located in the subtropical (93) and warm temperate biogeographical regions (84), with only five TOCEs in the cool temperate region (Perissinotto et al., 2010). Freshwater inflow to estuaries is a crucial factor controlling the species composition, abundance and biomass of estuarine communities in South Africa (e.g. Adams et al., 1999;
For example, higher phytoplankton and microphytobenthic biomass have been recorded during the closed phase of TOCEs in South Africa (Perissinotto et al., 2002; Skinner et al., 2006; . Walker et al., 2001). Similarly, increases in zooplankton abundance and biomass during the closed phase of TOCEs have been reported (Deale et al., 2013; Froneman, 2002b; Kibirige and Perissinotto, 2003b). Ecological network analysis indices have been widely used to evaluate the impact of different environmental conditions in estuaries and other marine systems (as summarized by Christian et al., 2005).
Materials and Methods
- Study areas
- Data sources and model construction
- Nitrogen networks
- Balancing of networks
- Ecological network analysis
Biomass for the planktonic and benthic compartments of the Mlalazi and Mpenjati networks were obtained from quarterly sampling in both systems from August 2010 to May 2011 (Chapter 2-3). Imports and exports from all boundaries of the system were included in the networks of the three estuaries. Conversely, the sum of the rows of coefficients in the dependency matrix represents the dependencies of all other partitions in the system on a particular partition.
The sum of the rows of contribution coefficients determines the total contribution of each department to all other departments in the system. Total system throughput (T.) is a measure of system size and activity (Ulanowicz and Kay, 1991). The ratio of accretion to developmental capacity or relative accretion (A/DC) is a measure of the degree of order of a system, with lower A/DC values indicative of low-order systems (Ulanowicz, 2012).
Results
- Total flows, contributions and dependencies
- Trophic structure
- Cycling structure and distribution
- Ecosystem status
The amount of detritivores and the detritivore:herbivore ratio did not differ between stocked and original nets in the Mlalazi and Mpenjati estuaries. In terms of nitrogen, the second TL had the highest trophic efficiency in the East Kleinemonde and Mpenjati estuaries during all seasons (Fig. 4.4f, h). APL and FCI values did not differ between pooled and original nets in the Mlalazi and Mpenjati estuaries.
The relative increase (A/DC) for carbon and nitrogen networks was highest in the Mpenjati estuary and lowest in the East Kleinemonde estuary (Table 4.6). Relative redundancy (R/DC) for carbon and nitrogen networks was highest in East Kleinemonde Estuary, lowest for carbon networks in Mlalazi Estuary, while R/DC was similar for nitrogen networks in Mlalazi and Mpenjati estuaries (Table 4.6). R/DC was higher than A/DC between seasons in East Kleinemonde, but not in the Mlalazi and Mpenjati estuaries.
Discussion
Studies on the chemical composition of the major zooplankton groups in the Sargasso Sea off Bermuda. In situ feeding rate and grazing impacts of the mysid Mesopodopsis africana O Tattersall in the St. Response of the plankton to three different hydrological phases of the temporarily open/closed Kasouga Estuary, South Africa.
Stable carbon isotopes and the C:N ratio in the estuaries of the Pamlico and Neuse Rivers, North Carolina. A comparison of the macrobenthic faunas of permanently open and temporarily open/closed South African estuaries. A quantitative study of the trophic relationships within the fish community of the Mhlanga Estuary, South Africa.
