Movement of carbon among estuarine habitats and its assimilation by invertebrates

Abstract

We measured the extent of movement of carbon and its assimilation by invertebrates among estuarine habitats by analysing carbon stable isotopes of invertebrates collected along transects crossing the boundary of two habitats. The habitats were dominated by autotrophs with distinct isotope values: (1) mudflats containing benthic microalgae (mean -22.6, SE 0.6 per thousand) and (2) seagrass and its associated epiphytic algae (similar values, pooled mean -9.8, 0.5 per thousand). Three species of invertebrates were analysed: a palaemonid shrimp, Macrobrachium intermedium, and two polychaete worms, Nephtys australiensis and Australonereis ehlersi. All species had a similar narrow range of isotope values (-9 to -14 per thousand), and showed no statistically significant relationship between position along transect and isotope values. Animals were relying on carbon from seagrass meadows whether they were in seagrass or on mudflats hundreds of metres away. Particulate organic matter collected from superficial sediments along the transects had similar values to animals (mean -11.1, SE 1.3 per thousand) and also showed no significant relationship with position. The isotope values of these relatively immobile invertebrates and the particulate detritus suggest that carbon moves from subtidal seagrass meadows to mudflats as particulate matter and is assimilated by invertebrates. This assimilation might be direct in the case of the detritivorous worm, A. ehlersi, but must be via invertebrate prey in the case of the carnivorous worm, N. australiensis and the scavenging shrimp, M. intermedium. The extent of movement of carbon among habitats, especially towards shallower habitats, is surprising since in theory, carbon is more likely to move offshore in situations such as the current study where habitats are in relatively open, unprotected waters.

Food web of a SW Atlantic shallow coastal lagoon: spatial environmental variability does not impose substantial changes in the trophic structure

“…Invertebrates also presented similar isotopic values to earlier studies, except for Palaemonetes argentinus, which was also δ 13 C depleted (i.e. Kwak & Zedler 1997, Vizzini & Mazzola 2003, Connolly et al 2005, Wissel & Fry 2005, Abreu et al 2006. In turn, fish in LR tended to be δ 13 C depleted, but δ 15 N enriched with respect to other studies (Hughes & Sherr 1983, Kwak & Zedler 1997, Abreu et al 2006, Garcia et al 2007.…”

Monsoons and habitat influence trophic pathways and the importance of terrestrial‐marine linkages for estuary sharks

“…Such subsidies may include dissolved or particulate organic matter, including leaf litter from rivers and mangroves (Paterson andWhitfield 1997, Mfilinge et al 2005), as well as marinederived organic matter from offshore plankton and adjacent habitats such as seagrass meadows and kelp forests (Boschker et al 2000, Norderhaug et al 2003, Bouillon et al 2004. The complex dynamics of trophic subsidies and relative importance of terrestrial and marine carbon sources in most estuarine habitats are, however, case-specific (Chanton and Lewis 2002, Connolly et al 2005, Heck et al 2008), varying at multiple temporal and spatial scales, and according to the feeding ecologies of specific marine assemblages (Darnaude et al 2004, Mcleod and Wing 2009). …”

Spatial variation of chlorophyll on estuarine mudflats determined by field-based remote sensing

“…In contrast, other studies have shown that benthic grazers do not feed directly on MPB (e.g. Connolly et al 2005). Defaecation by benthic animals (Thrush et al 2006), burrowing by animals such as crabs (Warren & Underwood 1986) and variations associated with microtopography of the surface of the sediment (Plante et al 1986), and indirect effects through shading may also affect distribution of MPB at small scales.…”