Context-Specific Bioturbation Mediates Changes to Ecosystem Functioning
- 677 Downloads
Species are often grouped according to their biological or functional traits to better understand their contribution to ecosystem functioning. However, it is becoming clear that a single species can perform different roles in different habitats. Austrohelice crassa, a burrow-building mud crab shifts its primary bioturbational role to that of a vertical mixer in non-cohesive sediments as frequent burrow collapse greatly enhances sediment reworking. We conducted in situ crab density manipulations in two sediment environments (a non-cohesive sand and a cohesive muddy-sand) to examine if the context-specific functional roles were linked to changes in solute fluxes across the sediment–water interface. Across both habitats, we show that A. crassa regulated nutrient cycling, creating strong density driven effects on solute exchanges. Increasing crab density increased sediment O2 demand and the flux of NH4 + from the sediment, indicating much of the response was physiologically driven. Clear interactions between A. crassa and microphytobenthos were also detected in both habitats. Despite lowering microphyte standing stock through deposit feeding, A. crassa increased benthic primary production per unit of chlorophyll a. Our experiment also revealed important context-specific differences, most notably for NH4 + fluxes, which were higher where burrows and their associated microbial communities were most stable (muddy-sand). This study highlights the need to integrate interactions between organism behavior and habitat type into functional group studies to broaden conceptual frameworks and avoid oversimplification of highly complex organism–sediment interactions.
Key wordsbenthic–pelagic coupling Austrohelice crassa crab intertidal density solute flux ecosystem processes
We thank Dudley Bell, Luca Chiaroni, Branwen Hughes, Anna John, Hannah Jones, Deniz Özkundakci, Warrick Powrie, and Julia Simpson for field support and Kerry Allen, Scott Edhouse, Bruce Patty, and Jacinta Parenzee for laboratory assistance. The subject-matter editor Karen McGlathery and two anonymous reviewers provided constructive and insightful comments that greatly improved the manuscript. This research was supported by a NIWA PhD scholarship funded through the Foundation for Research, Science and Technology (FRST) project no. C01X0501.
- Aller RC, Yingst JY. 1978. Biochemistry of tube dwellings: a study of the sedentary polychaetes Amphirtite ornate (Leidy). J Mar Res 36:201–54.Google Scholar
- Arar E, Collins G. 1997. Method 445.0: in vitro determination of chlorophyll a and phaeophytin a. Marine and freshwater algae by fluorescence. Revision 1.2. Cincinnati (OH): US Environmental Protection Agency.Google Scholar
- Asmus H, Asmus R. 1985. The importance of grazing food chain for energy flow and production in three intertidal sand bottom communities of the northern Wadden Sea. Helgol Mar Res 39:273–301.Google Scholar
- Day P. 1965. Particle fractionation and particle-size analysis. In: Black CA et al., Eds. Methods of soil analysis part 1. Madison, WI: American Society of Agronomy. p 545–67.Google Scholar
- Dean W. 1974. Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss on ignition: comparison with other methods. J Sediment Petrol 44:242–8.Google Scholar
- Heip CHR, Goosen NK, Herman PMJ, Kromkamp J. 1995. Production and consumption of biological particles in temperate tidal estuaries. Oceanogr Mar Biol 33:1–149.Google Scholar
- Henriksen K, Rasmussen MB, Jensen A. 1983. Effect of bioturbation on microbial nitrogen transformations in the sediment and fluxes of ammonium and nitrate to the overlaying water. Ecol Bull 35:193–205.Google Scholar
- Kristensen E. 1985. Oxygen and inorganic nitrogen exchange in a Nereis virens (Polychaeta) bioturbated sediment–water system. J Coast Res 1:109–16.Google Scholar
- Williamson RB, Wilcock RJ, Wise BE, Pickmere SE. 1999. Effect of burrowing by the crab Helice crassa on chemistry of intertidal muddy sediments. Environ Toxicol Chem 18:2078–86.Google Scholar