Cross-habitat impacts of species decline: response of estuarine sediment communities to changing detrital resources

Abstract

Food webs of many ecosystems are sustained by organic matter from other habitats. Human activities and climatic change are increasingly modifying the quality and supply of these resources, yet for most ecosystems it is unknown how the taxonomic composition of organic matter influences community composition. Along the coastline of Sydney, Australia, the once abundant habitat-forming macroalga, Phyllospora comosa, is now locally extinct. Shallow reefs are now primarily occupied by Sargassum sp. and, to a lesser extent, the kelp Ecklonia radiata. We experimentally manipulated the supply of P. comosa, Sargassum sp. and E. radiata to estuarine sediments to assess responses by macroinvertebrate communities to: (1) changing the identity of the dominant detrital resource; and (2) varying the ratio of input of different macrophytes. Estuarine sediments dosed with P. comosa supported greater abundances of macroinvertebrates than sediments receiving Sargassum sp. or the kelp E. radiata. Whereas plots receiving Sargassum sp. or E. radiata had fewer macroinvertebrates than controls, plots receiving a moderate (120 g dry weight per m(2)) loading of P. comosa had more. Mixtures of detritus dominated by P. comosa supported similar macroinvertebrate communities to monocultures of the alga. Communities in sediments receiving detritus comprised of less than one-third P. comosa were, however, distinctly different. Our study provides evidence that the ecological ramifications of species decline can extend to spatially removed ecosystems, subsidized by allochthonous materials. Even prior to extinction of detrital sources, small changes in their provision of organic matter may alter the structure of subsidized communities.

Impacts of detritus from the invasive alga Caulerpa taxifolia on a soft sediment community

“…and the mangrove Avicennia marina did not reduce macroinvertebrate abundance over a similar 2 mo period (Bishop et al 2007, Bishop & Kelaher 2008. Other algal sources (Ecklonia radiata, Sargassum sp., or Phyllospora comosa) reduced abundances by only 10 to 30% (Bishop et al 2010), not the 70% seen here following loading with C. taxifolia. In the present study, the reduction of abundances in experimental plots receiving C. taxifolia were unanticipated as plots never exhibited any evidence of surface anoxia, such as black patches or the presence of white, sulphurreducing bacteria.…”

Towards Restoration of Missing Underwater Forests

“…This seaweed influences local biodiversity in other systems as well. Wrack from detached and decomposing Phyllospora is an important source of detritus to soft sediment systems nearby and supports a more diverse assemblage of invertebrates than detritus originating from other macroalgae [27]. Thus, its disappearance has likely had major consequences for local ecosystems.…”

Decline and local extinction of Fucales in French Riviera: the harbinger of future extinctions?

“…Some taxa have been driven to regional extinction (Thibaut et al, 2005;Coleman et al, 2008;Phillips & Blackshaw, 2011) or are threatened by climate warming that might drive them toward areas where retreat is impossible (Wernberg et al, 2011). These impacts are leading to shifts in habitat structure from a state with canopy forming species to alternative states, in the worst case to barren grounds composed of filamentous and encrusting species (Micheli et al, 2005;Connell et al, 2008;Perkol-Finkel & Airoldi, 2010;Sala et al, 2012;Filbee-Dexter & Scheibling, 2014), with flow-on effects on adjacent communities (Bishop et al, 2010).…”