Spatial, seasonal, and ontogenetic variations in the significance of detrital pathways and terrestrial carbon for a benthic shark, Chiloscyllium plagiosum (Hemiscylliidae), in a tropical estuary

Abstract

Using a combination of stable isotope analyses (SIA), fatty acid profiling (FAP), and FA-specific SIA, we investigated the relative importance of terrestrial-and marine-derived carbon, and spatial (inshore vs. offshore), seasonal (wet vs. dry season), and ontogenetic variations, in the relative contribution of detrital pathways to the white-spotted bamboo shark, Chiloscyllium plagiosum in the Pearl River estuary. SIA and FAP suggested the sharks acquired carbon from both marine-and terrestrial-derived detritus via consumption of polychaetes and small crustaceans, with carbon from terrestrial sources being more important to juveniles (25-50 cm long) at inshore locations. Juveniles generally had significantly higher levels of diatom FA, bacterial FA, and long-chaincarbon-saturated FA biomarkers than adults (. 65 cm), especially during the wet season, suggesting that they relied on primary consumers which assimilated a mixture of autotrophic and detrital carbon sources. Levels of zooplankton and animal-derived FA biomarkers generally increased with shark size, indicating an ontogenetic dietary shift. Utilizing the results of FA-specific SIA (i.e., d 13 C values of individual bacterial FA of detritus) from four sources (i.e., terrestrial plant litter, macroalgae, phytoplankton, and sediments), Bayesian mixing models revealed juveniles in the inner estuary assimilated significantly higher amounts of terrestrial carbon (37-45%) than adults (22-37%) or sharks in the outer estuary (1-36%). The combined use of multiple dietary tracers effectively revealed the interaction of various detrital pathways to marine predators in the Pearl River estuary, and highlighted the importance of terrestrial-marine linkages for interpretation of energy flow in coastal ecosystems.

Fatty acids and stable isotopes as indicators of early-life feeding and potential maternal resource dependency in the bull shark Carcharhinus leucas

“…Mar Ecol Prog Ser 455: [245][246][247][248][249][250][251][252][253][254][255][256] 2012 man et , Torres-Rojas et al 2010, to molecular tools including stable isotope and lipid biomarker analysis (MacNeil et al 2005, Pethybridge et al 2010, Wai et al 2011. Although stomach content analysis can provide evidence for specific dietary items, biochemical approaches have the advantage of providing information on assimilated organic substrates and can be especially helpful in complex ecosystems with multiple organic carbon substrates (Dalsgaard et al 2003, Iverson et al 2004, Whiles et al 2010.…”

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

“…There, local primary production is often less than community respiration (Pace et al 2004, del Giorgio andPace 2008), and subsidies of allochthonous organic matter from terrestrial sources often supplement local autochthonous sources such as phytoplankton (Hoffman et al 2007(Hoffman et al , 2008, Van den Meersche et al 2009, Babler et al 2011. In contrast to temperate regions, however, the origins of the organic matter sustaining food webs and secondary production in most tropical estuaries are largely unknown (Blaber 2000, Barros et al 2010, Wai et al 2011a.…”

“…The importance of terrestrial carbon to higher trophic levels has recently been demonstrated for the white-spotted bamboo shark Chiloscyllium plagiosum (Hemiscylliidae), a common benthic predator in the PRE, and allochthonous energy was particularly important for juvenile C. plagiosum within the inner estuary nursery grounds (Wai et al 2011a). The spadenose shark, Scoliodon laticaudus (Carcharhinidae), is sympatric with bamboo sharks in the PRE, and occurs widely in the coastal waters of the Indo-West Pacific (White and Sommerville 2010).…”

“…A combination of three assimilation-based methods (stable isotope analyses (SIA), fatty acid profiling (FAP), and FA-specific SIA (FASIA)) were used to investigate the relative importance of terrestrial (i.e., leaf litter) and marine (i.e., macroalgae and phytoplankton) carbon sources and to elucidate the utilization of detritus derived from these sources, as has been revealed for the bamboo shark (see Wai et al 2011a). Given the substantial seasonal input of terrestrial organic matter from the PRE basin during the wet, summer monsoon, we predicted that the carbon utilization of prey and spadenose sharks would vary according to season (wet vs. dry season) and location (inner vs. outer estuary).…”

Importance of terrestrial subsidies for estuarine food webs in contrasting East African catchments

“…However, even with the use of stable isotopes, there is still some controversy related to the importance of allochthony, with some studies suggesting that terrestrial detritus is important for estuarine food webs (e.g., Abrantes and Sheaves 2010, Wai et al 2011), while most did not find evidence of incorporation of terrestrial detritus by aquatic consumers (e.g., Deegan andGarritt 1997, Chanton andLewis 2002) and suggest that transported material is not available to be assimilated by aquatic consumers as it is mostly refractory (Wiegner et al 2009). …”