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

Abstract

Invasive primary producers can dramatically reorganize food webs through detrital subsidies. This study assessed (1) contributions of the invasive alga Caulerpa taxifolia to detrital resources of temperate Australian estuaries, and (2) effects of these contributions on sedimentdwelling invertebrates. In an invaded estuary, sampling of an intertidal shore indicated C. taxifolia fragments were consistently present in organic matter deposits and were particularly abundant following storms. Sampling of the alga across 6 invaded estuaries showed that the ratio of organic carbon to nitrogen (C:N) in fresh tissue varied between 7 and 16. To determine how C. taxifolia detritus influences benthic macrofaunal assemblages and whether this influence depends on the quantity and C:N ratio of C. taxifolia detritus, a manipulative field experiment was performed. On a sheltered intertidal mudflat, 0.25 m 2 plots of sediment were experimentally enriched with either a high (90 g DW) or low (30 g) loading of high C:N (14) or low C:N (7) C. taxifolia detritus. Experimental enrichment negatively affected the total abundance and species richness of macroinvertebrates relative to controls, and these effects increased with detrital loading. For some macrofauna, reducing the C:N ratio tended to exacerbate negative effects on abundances, whereas it moderated these effects for other species. Given that organic matter derived from invasive species can be transported beyond the distribution of live invaders, greater consideration should be given to the potential broad-scale effects of invasive primary producers on detrital pathways. KEY WORDS: Detritus · Caulerpa taxifolia · Food quality · Invasion · Nitrogen content · Spatial subsidy Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 420: [73][74][75][76][77][78][79][80][81] 2010 sources, typically degrades rapidly and produces a short-term nutritional source to fast growing consumers (Tenore 1977). Although the C:N ratio of detritus can change during degradation (Anderson 1973, Suberkropp et al. 1976, the starting C:N ratio is a good predictor of decomposition rate (Enriquez et al. 1993).Invasive primary producers are an increasingly large component of detrital pools (Kennedy & Hobbie 2004, Rodil et al. 2008 and have the potential to markedly alter their value. Many successful invaders have rapid individual growth, early maturity, a short life span, high fecundity, minimal structural defence and extensive dispersal capacity (Lodge 1993, Schaffelke et al. 2006. Consequently, invasive primary producers tend to generate large amounts of labile detritus with a low C:N ratio, which is more readily decomposed than is litter from native species (Vitousek et al. 1987, Ashton et al. 2005. Whereas small amounts of refractory detritus may fuel productivity, large quantities of labile detritus may induce sediment anoxia (Pearson & Rosenberg 1978). This phenomenon may be exacerbated in areas of nutrient enrichment where invasive primary producer...

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