Variability of Polychaete Secondary Production in Intertidal Creek Networks along a Stream-Order Gradient

<div><p>Dendritic tidal creek networks are important habitats for sustaining biodiversity and ecosystem functioning in salt marsh wetlands. To evaluate the importance of creek heterogeneity in supporting benthic secondary production, we assess the spatial distribution and secondary production of a representative polychaete species (<i>Dentinephtys glabra</i>) in creek networks along a stream-order gradient in a Yangtze River estuarine marsh. Density, biomass, and secondary production of polychaetes were found to be highest in intermediate order creeks. In high order (3rd and 4th) creeks, the density and biomass of <i>D. glabra</i> were higher in creek edge sites than in creek bottom sites, whereas the reverse was true for low order (1st and 2nd) creeks. Secondary production was highest in 2nd order creeks (559.7 mg AFDM m⁻² year⁻¹) and was ca. 2 folds higher than in 1st and 4th order creeks. Top fitting AIC models indicated that the secondary production of <i>D. glabra</i> was mainly associated with geomorphological characters including cross-sectional area and bank slope. This suggests that hydrodynamic forces are essential factors influencing secondary production of macrobenthos in salt marshes. This study emphasizes the importance of microhabitat variability when evaluating secondary production and ecosystem functions.</p></div

Density, biomass of <i>Dentinephtys glabra</i> at bottom and edge sampling locations in creeks of different orders.

<p>Error bars represent standard error (n = 36). The same capital letters denote non-significant differences and different capital letters represent a significant difference (<i>P</i><0.05) between bottom and edge locations for creeks of the same order. The same lowercase letters denote non-significant differences and different letters represent a significant difference (<i>P</i><0.05) among creek orders for each sampling location.</p

Creeks sampled on the Jiuduansha Island.

<p>Samples were collected at two locations (bottom and edge) in each creek.</p

Estimation of the total <i>Dentinephtys glabra</i> production in Jiuduansha creeks on an order by order basis with one-way ANOVA results showing the effect of creek order.

<p>Different superscript letters (a and b) represent a significant difference (<i>P</i><0.05) among creeks of different orders.</p

Density and biomass of <i>Dentinephtys glabra</i> in creeks of different orders.

<p>Error bars represent standard error (n = 72). The same letters above the bars denote non-significant differences and different letters represent a significant difference (<i>P</i><0.05) among creek orders.</p

Results of model selection using Akaike's information criterion (AIC) for the relationship between secondary production of <i>Dentinephtys glabra</i> and environmental factors.

<p>Only the top five models with Akaike weight (<i>w_i</i>) and R² values are shown. Regression coefficients were expressed as Z values (estimate/SE).</p><p>Factors are abbreviated as Cond (conductivity), Cross (cross-sectional area), Slope (bank slope), Water (Water content), Chl <i>a</i> (Chl <i>a</i> concentration), Temp (temperature), Clay (clay-silt content).</p

Monthly density and biomass of <i>Dentinephtys glabra</i> in creeks of different orders.

<p>Error bars represent standard error (n = 6). The same letters above the bars denote non-significant differences and different letters represent a significant difference (<i>P</i><0.05) among creek orders in each month.</p

Physicochemical parameters and geomorphological characters in creek of each order with one-way ANOVA results showing the effect of creek order.

<p>Shown are Fisher's <i>F</i>-ratio (<i>F</i>) and <i>P</i>-values of ANOVA for testing differences of each variable among creeks of different orders. Different superscript letters (a, b and c) represent a significant difference (<i>P</i> < 0.05) among creeks of different orders.</p

Trophic Dynamics of Filter Feeding Bivalves in the Yangtze Estuarine Intertidal Marsh: Stable Isotope and Fatty Acid Analyses

<div><p>Benthic bivalves are important links between primary production and consumers, and are essential intermediates in the flow of energy through estuarine systems. However, information on the diet of filter feeding bivalves in estuarine ecosystems is uncertain, as estuarine waters contain particulate matter from a range of sources and as bivalves are opportunistic feeders. We surveyed bivalves at different distances from the creek mouth at the Yangtze estuarine marsh in winter and summer, and analyzed trophic dynamics using stable isotope (SI) and fatty acid (FA) techniques. Different bivalve species had different spatial distributions in the estuary. <i>Glauconome chinensis</i> mainly occurred in marshes near the creek mouth, while <i>Sinonovacula constricta</i> preferred the creek. Differences were found in the diets of different species. <i>S</i>. <i>constricta</i> consumed more diatoms and bacteria than <i>G</i>. <i>chinensis</i>, while <i>G</i>. <i>chinensis</i> assimilated more macrophyte material. FA markers showed that plants contributed the most (38.86 ± 4.25%) to particular organic matter (POM) in summer, while diatoms contributed the most (12.68 ± 1.17%) during winter. Diatoms made the largest contribution to the diet of <i>S</i>. <i>constricta</i> in both summer (24.73 ± 0.44%) and winter (25.51 ± 0.59%), and plants contributed no more than 4%. This inconsistency indicates seasonal changes in food availability and the active feeding habits of the bivalve. Similar FA profiles for <i>S</i>. <i>constricta</i> indicated that the bivalve had a similar diet composition at different sites, while different δ¹³C results suggested the diet was derived from different carbon sources (C₄ plant <i>Spartina alterniflora</i> and C₃ plant <i>Phragmites australis</i> and <i>Scirpus mariqueter</i>) at different sites. Species-specific and temporal and/or spatial variability in bivalve feeding may affect their ecological functions in intertidal marshes, which should be considered in the study of food webs and material flows in estuarine ecosystems.</p></div

Relative percentages of fatty acid markers (diatom, bacteria, dinoflagellates, vascular plants and zooplankton) from <i>Sinonovacula constricta</i> and <i>Glauconome chinensis</i> in summer.

<p>Different superscript letters (<i>a</i>, <i>b</i>) refer to significant differences between two bivalve species (Tukey HSD test, <i>P</i> < 0.05).</p