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Nutrient Dynamics of Estuarine Invertebrates Are Shaped by Feeding Guild Rather than Seasonal River Flow.

Ortega-Cisneros K, Scharler UM - PLoS ONE (2015)

Bottom Line: The nutrient content and ratios of the analyzed invertebrates did not significantly vary among seasons with the exception of the copepod Pseudodiaptomus spp. (C:N) and the tanaid Apseudes digitalis (%N, C:N).These changes did not track the seasonal variations of the suspended or sediment particulate matter.As climate change scenarios for the east coast of South Africa predict increased rainfall as a higher number of rainy days and days with higher rainfall, our results suggest that future changes in rainfall and river inflow will have measurable effects on the nutrient content and stoichiometry of food sources and possibly also in estuarine consumers.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, Westville Campus, University of KwaZulu-Natal, Durban, South Africa.

ABSTRACT
This study aimed to determine the variability of carbon and nitrogen elemental content, stoichiometry and diet proportions of invertebrates in two sub-tropical estuaries in South Africa experiencing seasonal changes in rainfall and river inflow. The elemental ratios and stable isotopes of abiotic sources, zooplankton and macrozoobenthos taxa were analyzed over a dry/wet seasonal cycle. Nutrient content (C, N) and stoichiometry of suspended particulate matter exhibited significant spatio-temporal variations in both estuaries, which were explained by the variability in river inflow. Sediment particulate matter (%C, %N and C:N) was also influenced by the variability in river flow but to a lesser extent. The nutrient content and ratios of the analyzed invertebrates did not significantly vary among seasons with the exception of the copepod Pseudodiaptomus spp. (C:N) and the tanaid Apseudes digitalis (%N, C:N). These changes did not track the seasonal variations of the suspended or sediment particulate matter. Our results suggest that invertebrates managed to maintain their stoichiometry independent of the seasonality in river flow. A significant variability in nitrogen content among estuarine invertebrates was recorded, with highest % N recorded from predators and lowest %N from detritivores. Due to the otherwise general lack of seasonal differences in elemental content and stoichiometry, feeding guild was a major factor shaping the nutrient dynamics of the estuarine invertebrates. The nutrient richer suspended particulate matter was the preferred food source over sediment particulate matter for most invertebrate consumers in many, but not all seasons. The most distinct preference for suspended POM as a food source was apparent from the temporarily open/closed system after the estuary had breached, highlighting the importance of river flow as a driver of invertebrate nutrient dynamics under extreme events conditions. Moreover, our data showed that estuarine invertebrates concentrated C and N between 10-100 fold from trophic level I (POM) to trophic level II (detritivores/deposit feeders) and thus highlighted their importance not only as links to higher trophic level organisms in the food web, but also as providers of a stoichiometrically homeostatic food source for such consumers. As climate change scenarios for the east coast of South Africa predict increased rainfall as a higher number of rainy days and days with higher rainfall, our results suggest that future changes in rainfall and river inflow will have measurable effects on the nutrient content and stoichiometry of food sources and possibly also in estuarine consumers.

No MeSH data available.


Related in: MedlinePlus

Mean (± SD) δ13C and δ15N of zooplankton species in the Mlalazi (right) and Mpenjati (left) estuaries.Color and shape indicate group or taxa (grey rhombus = susPOM, grey square = sedPOM, black circle = Acartia spp (a) and Acartia natalensis (b), black square = Pseudodiaptomus spp. (a) and Pseudodipatomus hessei (b), black triangle = M. africana (a) and R. terranatalis (b)).
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pone.0137417.g002: Mean (± SD) δ13C and δ15N of zooplankton species in the Mlalazi (right) and Mpenjati (left) estuaries.Color and shape indicate group or taxa (grey rhombus = susPOM, grey square = sedPOM, black circle = Acartia spp (a) and Acartia natalensis (b), black square = Pseudodiaptomus spp. (a) and Pseudodipatomus hessei (b), black triangle = M. africana (a) and R. terranatalis (b)).

Mentions: Little variation was recorded for the mean susPOM δ13C and δ15N values between the Mlalazi (δ13C = -24.02 ± 2.02 ‰ SD and δ15N = 7.75 ± 1.22 ‰ SD) and Mpenjati estuaries (δ13C = -21.51 ± 3.41 ‰ SD and δ15N = 6.02 ± 0.77 ‰ SD) (Figs 2 and 3). Mean sedPOM δ13C (Mlalazi = -21.40 ± 1.02 ‰ SD; Mpenjati = -22.73 ± 1.38 ‰ SD) and δ15N (Mlalazi = 3.34 ± 1.35 ‰ SD; Mpenjati = 3.12 ± 1.34 ‰ SD) were also similar in both estuaries. Whereas susPOM had similar δ13C signatures to sedPOM, the δ15N of susPOM was considerably higher than that of sedPOM in both estuaries (Figs 2 and 3). Significant spatio-temporal differences were found for δ13C and δ15N in both susPOM and sedPOM in the Mlalazi Estuary (Table 2), however no clear seasonal trend was observed with high and low values recorded during both dry and wet seasons. In the Mpenjati Estuary, significant spatio-temporal differences were recorded for δ13C and δ15N of susPOM, but not for sedPOM (Table 2). More enriched δ13C and δ15N of SusPOM were recorded during the dry season month September 2010, with the opposite pattern during the wet season month February 2011.


Nutrient Dynamics of Estuarine Invertebrates Are Shaped by Feeding Guild Rather than Seasonal River Flow.

Ortega-Cisneros K, Scharler UM - PLoS ONE (2015)

Mean (± SD) δ13C and δ15N of zooplankton species in the Mlalazi (right) and Mpenjati (left) estuaries.Color and shape indicate group or taxa (grey rhombus = susPOM, grey square = sedPOM, black circle = Acartia spp (a) and Acartia natalensis (b), black square = Pseudodiaptomus spp. (a) and Pseudodipatomus hessei (b), black triangle = M. africana (a) and R. terranatalis (b)).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4564196&req=5

pone.0137417.g002: Mean (± SD) δ13C and δ15N of zooplankton species in the Mlalazi (right) and Mpenjati (left) estuaries.Color and shape indicate group or taxa (grey rhombus = susPOM, grey square = sedPOM, black circle = Acartia spp (a) and Acartia natalensis (b), black square = Pseudodiaptomus spp. (a) and Pseudodipatomus hessei (b), black triangle = M. africana (a) and R. terranatalis (b)).
Mentions: Little variation was recorded for the mean susPOM δ13C and δ15N values between the Mlalazi (δ13C = -24.02 ± 2.02 ‰ SD and δ15N = 7.75 ± 1.22 ‰ SD) and Mpenjati estuaries (δ13C = -21.51 ± 3.41 ‰ SD and δ15N = 6.02 ± 0.77 ‰ SD) (Figs 2 and 3). Mean sedPOM δ13C (Mlalazi = -21.40 ± 1.02 ‰ SD; Mpenjati = -22.73 ± 1.38 ‰ SD) and δ15N (Mlalazi = 3.34 ± 1.35 ‰ SD; Mpenjati = 3.12 ± 1.34 ‰ SD) were also similar in both estuaries. Whereas susPOM had similar δ13C signatures to sedPOM, the δ15N of susPOM was considerably higher than that of sedPOM in both estuaries (Figs 2 and 3). Significant spatio-temporal differences were found for δ13C and δ15N in both susPOM and sedPOM in the Mlalazi Estuary (Table 2), however no clear seasonal trend was observed with high and low values recorded during both dry and wet seasons. In the Mpenjati Estuary, significant spatio-temporal differences were recorded for δ13C and δ15N of susPOM, but not for sedPOM (Table 2). More enriched δ13C and δ15N of SusPOM were recorded during the dry season month September 2010, with the opposite pattern during the wet season month February 2011.

Bottom Line: The nutrient content and ratios of the analyzed invertebrates did not significantly vary among seasons with the exception of the copepod Pseudodiaptomus spp. (C:N) and the tanaid Apseudes digitalis (%N, C:N).These changes did not track the seasonal variations of the suspended or sediment particulate matter.As climate change scenarios for the east coast of South Africa predict increased rainfall as a higher number of rainy days and days with higher rainfall, our results suggest that future changes in rainfall and river inflow will have measurable effects on the nutrient content and stoichiometry of food sources and possibly also in estuarine consumers.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, Westville Campus, University of KwaZulu-Natal, Durban, South Africa.

ABSTRACT
This study aimed to determine the variability of carbon and nitrogen elemental content, stoichiometry and diet proportions of invertebrates in two sub-tropical estuaries in South Africa experiencing seasonal changes in rainfall and river inflow. The elemental ratios and stable isotopes of abiotic sources, zooplankton and macrozoobenthos taxa were analyzed over a dry/wet seasonal cycle. Nutrient content (C, N) and stoichiometry of suspended particulate matter exhibited significant spatio-temporal variations in both estuaries, which were explained by the variability in river inflow. Sediment particulate matter (%C, %N and C:N) was also influenced by the variability in river flow but to a lesser extent. The nutrient content and ratios of the analyzed invertebrates did not significantly vary among seasons with the exception of the copepod Pseudodiaptomus spp. (C:N) and the tanaid Apseudes digitalis (%N, C:N). These changes did not track the seasonal variations of the suspended or sediment particulate matter. Our results suggest that invertebrates managed to maintain their stoichiometry independent of the seasonality in river flow. A significant variability in nitrogen content among estuarine invertebrates was recorded, with highest % N recorded from predators and lowest %N from detritivores. Due to the otherwise general lack of seasonal differences in elemental content and stoichiometry, feeding guild was a major factor shaping the nutrient dynamics of the estuarine invertebrates. The nutrient richer suspended particulate matter was the preferred food source over sediment particulate matter for most invertebrate consumers in many, but not all seasons. The most distinct preference for suspended POM as a food source was apparent from the temporarily open/closed system after the estuary had breached, highlighting the importance of river flow as a driver of invertebrate nutrient dynamics under extreme events conditions. Moreover, our data showed that estuarine invertebrates concentrated C and N between 10-100 fold from trophic level I (POM) to trophic level II (detritivores/deposit feeders) and thus highlighted their importance not only as links to higher trophic level organisms in the food web, but also as providers of a stoichiometrically homeostatic food source for such consumers. As climate change scenarios for the east coast of South Africa predict increased rainfall as a higher number of rainy days and days with higher rainfall, our results suggest that future changes in rainfall and river inflow will have measurable effects on the nutrient content and stoichiometry of food sources and possibly also in estuarine consumers.

No MeSH data available.


Related in: MedlinePlus