Abstract
Many aquatic ecosystems are sustained by detrital subsidies of leaf litter derived from exogenous sources. Although numerous studies have examined the effects of litter species richness and identity on decomposition processes, it remains unclear how these effects extend to associated invertebrate communities or how these effects vary spatially according to local environmental context. Using field enrichment experiments, we assessed how the species richness, assemblage composition, and supply of detrital litter resources interact to affect benthic communities of three temperate Australian estuarine mudflats. Our experiments utilized eight litter sources that are presently experiencing human-mediated changes in their supply to estuarine mudflats. Contrary to predictions, we did not detect effects of the species richness of detrital mixtures on benthic communities. Macroinvertebrate community structure and, in particular, abundance were, instead, influenced by the assemblage composition of detrital mixtures. At two of the three sites, plots receiving the most labile detrital mix, containing the ephemeral algae Chaetomorpha and Ulva, supported the fewest macroinvertebrates of all the experimental enrichments. The large effect of detrital mix identity on macroinvertebrate communities is of concern given present trends of proliferation of macroalgae at the expense of more refractory seagrasses and marsh grasses. As such environmental degradation continues, it will be important to more fully understand under what environmental contexts such compositional changes in detrital resources will have the most detrimental effects on important prey resources for commercially important fish and wading shorebirds.
Highlights
The dynamics and food web structure of many ecological systems are determined not by endogenous processes but by the supply of materials, energy, and organisms they receive from other ecosystems (Polis et al 1997)
Ecology and Evolution published by John Wiley & Sons Ltd
We predicted that macroinvertebrates communities, which include functional groups that directly consume detritus and those that consume microalgae stimulated by detrital breakdown (Rublee 1982), would be more abundant and species rich in sediments receiving a greater species richness of phytodetritus because of the greater resource base available
Summary
The dynamics and food web structure of many ecological systems are determined not by endogenous processes but by the supply of materials, energy, and organisms they receive from other ecosystems (Polis et al 1997). Of the studies that have considered the spatial subsidy litter represents to the faunal communities of aquatic habitats, most have considered only the effects of the supply of a single litter source (e.g., Kelaher and Levinton 2003; Olabarria et al 2007). Several studies have demonstrated effects of different litter species on individual consumers (Duggins and Eckman 1994, 1997), but very few have examined how changes in the composition of detritus affect the structure of whole communities (but see Bishop and Kelaher 2008; Bishop et al 2010; Olabarria et al 2010) It is poorly understood how changes in the supply and quality of litter will vary according to environmental context. To test the hypothesis that effects of enrichment would be consistent across sites of similar landscape setting, we replicated our experiments across three sites, each situated in a different estuary within the same biogeographical area
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