Importance of terrestrial subsidies for estuarine food webs in contrasting East African catchments

Abrantes, Kátya G.; Barnett, Adam; Marwick, Trent R.; Bouillon, Steven

doi:10.1890/es12-00322.1

Cited by 61 publications

(63 citation statements)

References 93 publications

(101 reference statements)

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“…The environmental characteristics of each system are described in Table and more extensively in Abrantes et al . ().…”

Section: Methodsmentioning

confidence: 97%

“…Bayesian mixing models confirmed that C4 material from the catchment was the most important source for the highly turbid, C4‐dominated estuaries, whereas for the less turbid C3‐dominated estuaries terrestrial subsidies were not as important and consumers relied on a combination of terrestrial and aquatic sources (Abrantes et al . ). In the present study, the effect of environmental conditions such as dominant catchment vegetation and turbidity on estuarine food webs is further investigated.…”

Section: Introductionmentioning

confidence: 97%

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Stable isotope‐based community metrics as a tool to identify patterns in food web structure in east African estuaries

2013

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Summary1. Quantitative tools to describe biological communities are important for conservation and ecological management. The analysis of trophic structure can be used to quantitatively describe communities. Stable isotope analysis is useful to describe trophic organization, but statistical models that allow the identification of general patterns and comparisons between systems/ sampling periods have only recently been developed. 2. Here, stable isotope-based Bayesian community-wide metrics are used to investigate patterns in trophic structure in five estuaries that differ in size, sediment yield and catchment vegetation cover (C3/C4): the Zambezi in Mozambique, the Tana in Kenya and the Rianila, the Betsiboka and Pangalanes Canal (sampled at Ambila) in Madagascar. 3. Primary producers, invertebrates and fish of different trophic ecologies were sampled at each estuary before and after the 2010-2011 wet season. Trophic length, estimated based on d 15 N, varied between 3Á6 (Ambila) and 4Á7 levels (Zambezi) and did not vary seasonally for any estuary. Trophic structure differed the most at Ambila, where trophic diversity and trophic redundancy were lower than at the other estuaries. Among the four open estuaries, the Betsiboka and Tana (C4-dominated) had lower trophic diversity than the Zambezi and Rianila (C3-dominated), probably due to the high loads of suspended sediment, which limited the availability of aquatic sources. 4. There was seasonality in trophic structure at Ambila and Betsiboka, as trophic diversity increased and trophic redundancy decreased from the prewet to the postwet season. For Ambila, this probably resulted from the higher variability and availability of sources after the wet season, which allowed diets to diversify. For the Betsiboka, where aquatic productivity is low, this was likely due to a greater input of terrestrial material during the wet season.5. The comparative analysis of community-wide metrics was useful to detect patterns in trophic structure and identify differences/similarities in trophic organization related to environmental conditions. However, more widespread application of these approaches across different faunal communities in contrasting ecosystems is required to allow identification of robust large-scale patterns in trophic structure. The approach used here may also find application in comparing food web organization before and after impacts or monitoring ecological recovery after rehabilitation.

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“…The environmental characteristics of each system are described in Table and more extensively in Abrantes et al . ().…”

Section: Methodsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 97%

Stable isotope‐based community metrics as a tool to identify patterns in food web structure in east African estuaries

2013

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“…Terrestrial forest plants typically have isotope values similar to mangroves (Abrantes et al 2013), so any contribution of terrestrial matter to the food webs, for example via riverine input (Wissel and Fry 2005), cannot be separated from that of mangroves. This possibility could be important for management of land-uses in coastal catchments and could be pursued in future with additional biomarkers capable of separating mangroves from terrestrial plants (e.g., Dittmar et al 2006).…”

Section: Carbon Sourcesmentioning

confidence: 99%

Spatial analysis of carbon isotopes reveals seagrass contribution to fishery food web

Connolly

Waltham

2015

Ecosphere

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Citation: Connolly, R. M., and N. J. Waltham. 2015. Spatial analysis of carbon isotopes reveals seagrass contribution to fishery food web. Ecosphere 6(9):148. http://dx.doi.org/10.1890/ES14-00243.1Abstract. Despite the widespread use of carbon stable isotopes to distinguish among potential energy pathways in food webs, their usefulness is limited where potential basal carbon sources are numerous and diverse. We measured carbon isotope values of the major fisheries species, the mostly carnivorous Scylla serrata (giant mud crab), and potential basal, autotrophic sources supporting the food web. Conventional mixing modelling of autotroph and crab isotope data could not differentiate contributions from different sources. Pooling of modelled contributions from sources with similar isotope values indicated a role for organic matter from seagrass meadows or saltmarshes, but still did not define contributions well. Crab isotope data from a subsequent, spatially explicit survey of 14 sites, selected to represent different distances from key habitats, were analyzed using multiple regression. Crab isotope values showed a significant relationship with distance from seagrass (R 2 ¼ 0.87), but not with distance from mangroves or saltmarsh grass. Alongside seagrass meadows, crabs had very enriched isotope values, demonstrating their reliance on sources with enriched isotope values (seagrass and algae epiphytic on seagrass, 65-90% of their energy intake). At the site furthest from seagrass (21 km), crabs assimilated carbon primarily from depleted sources such as mangroves and terrestrial organic matter from coastal catchments (70-85%). Explicit spatial analysis of isotope data following a comprehensive survey revealed energy pathways not evident in conventional analyses.

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“…Supporting this view are a number of recent stable isotope studies suggesting that allochthonous DOC can provide a significant subsidy to pelagic zooplankton and fish in lakes (Cole et al ; Karlsson et al ; Tanentzap et al ) and estuarine and coastal systems (Hoffman et al ; Abrantes and Sheaves ; Hitchcock et al ; Von Biela et al ). Significantly, many of these studies have identified that the magnitude of allochthonous subsidy varies with environmental conditions, especially hydrological events (Abrantes et al ). For example, Hoffman et al () showed in the York River estuary, U.S.A., that the contribution of allochthonous carbon to cladocera and copepod diets increased during wet years, while Atwood et al () showed that terrestrial carbon made a significant contribution to zooplankton biomass following storms in the tropical estuary of Hilo Bay, Hawaii.…”

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confidence: 99%

Terrestrial dissolved organic carbon subsidizes estuarine zooplankton: An in situ mesocosm study

et al. 2015

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Freshwater inflows play an important role in delivering dissolved organic carbon (DOC) to estuaries. Episodic inputs of DOC may support increased bacterial production. However, the role of DOC in supporting zooplankton production is widely debated. To evaluate this role we performed an in situ mesocosm experiment in the Bega River estuary, Australia. We added a DOC leachate derived from terrestrial vegetation to 400 L mesocosm bags as treatments of +1.5, +3, and +16 mg C L−1 and monitored changes in carbon, nitrogen, phosphorus, bacteria, chlorophyll a (Chl a), and zooplankton over 22 d. Bacterial biomass peaked at day 2 and was highest in the +16 mg C L−1 treatment. Chl a was not significantly different between treatments. Mesozooplankton was dominated by copepodites of Gladioferens pectinatus and Sulcanus conflictus between days 5–9 and by adults between days 9–15. Significantly higher numbers of copepods were present in the +16 treatment followed by the +3 mg C L−1 treatment compared with the controls. Stable carbon isotope signatures of copepods in the +16 mg C L−1 treatment were significantly different from the control and showed leachate carbon supported between 29.3% and 55.8% of copepod biomass. These results suggest that the impact of allochthonous DOC loading events on estuarine zooplankton occurs over short periods, and that the magnitude of response is, in part, controlled by the quantity of bioavailable DOC loaded to the system. Our findings underscore the importance of microbial dynamics stimulated by DOC loading events from freshwater inflows as a trophic path in estuarine food webs.

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Importance of terrestrial subsidies for estuarine food webs in contrasting East African catchments

Cited by 61 publications

References 93 publications

Stable isotope‐based community metrics as a tool to identify patterns in food web structure in east African estuaries

Stable isotope‐based community metrics as a tool to identify patterns in food web structure in east African estuaries

Spatial analysis of carbon isotopes reveals seagrass contribution to fishery food web

Terrestrial dissolved organic carbon subsidizes estuarine zooplankton: An in situ mesocosm study

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