Large-scale ecosystem engineering by flamingos and fiddler crabs on West-African intertidal flats promote joint food availability

El Hacen M. El-Hacen*, Tjeerd J. Bouma, Puck Oomen, Theunis Piersma, Han Olff

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Although the ecosystem engineering concept is well established in ecology, cases of joint engineering by multiple species at large scales remain rare. Here, we combine observational studies and exclosure experiments to investigate how co-occurring greater flamingos Phoenicopterus roseus and fiddler crabs Uca tangeri promote their own and each other's food availability by creating a spatially complex mosaic of depressions (bowls, gullies) and hummocks (plateaus, mounds) in the intertidal zone. This results in a mosaic of microhabitats with different tidal inundation regimes. These microhabitats are spatially organized with labyrinth-like patterns in the high intertidal zone and spotted patterns in the lower intertidal, both of which likely arise from biophysical interactions between these organisms and hydrodynamic forces. We show that the resulting spatial complexity is vital for biofilm production. The depression microhabitats were wetter and richer in organic matter and biofilms compared with hummocks. Excluding flamingos and crabs resulted in an increase in biofilm biomass over the shorter term (six months), but a decrease over the longer term (after one year). Moreover, our results strongly suggest that these biogeomorphological microhabitats in the mosaics were maintained by the feeding activities of flamingos and to a lesser extent crabs. During a period of flamingo exclusion, all the spotted patterns filled up with sediment, while the exclusion of crabs led to gradual sediment accumulation in the labyrinth-like patterns. Collectively, these findings provide empirical evidence for large-scale joint promotion of food availability by multiple taxa in a marine ecosystem.

Original languageEnglish
Pages (from-to)753-764
Number of pages12
JournalOikos
Volume128
Issue number5
DOIs
Publication statusPublished - 1 May 2019

Funding

Acknowledgements – We thank the authority of the Parc National du Banc d’Arguin (PNBA), Mauritania, for permission to carry out the research and for their logistic support. The experimental setup and data collection were greatly assisted by Lenze Hofstee, Petra de Goeij, Greg Fivash, Laura Govers, Mohamed Salem El Hadi, Mohamed Chedad, Babah Ould M’Bareck, Sidi Yahya Lemrabot, Sall Abdel Rahmane, Laura Soissons, Oscar Franken and Ahmed Ould Sidi Mohamed. We are grateful to all of them. Special thanks for Ruth Howison for helping in the field and for the valuable feedbacks on the MS. Finally, the manuscript was improved by editing from Esther R. Chang. Funding – This study was funded by a PhD scholarship from the MAVA Foundation, Switzerland. Author contributions – HO, EME, TP and TB conceived the ideas and designed methodology; EME, HO, PO and TB collected the data; EME, PO and HO analysed the data; EME, HO, TP and TB led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.

Keywords

  • Banc d'Arguin-Mauritania
  • biofilms
  • biogeomorphic
  • ecological autocatalysis
  • facilitation
  • feedback loop
  • spatial patterns

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