Habitat conversion and species loss alters the composition of carbon sources to benthic communities

Abstract

Generalist fishes provide an effective measure of the composition of basal carbon source pools fueling benthic communities, by integrating inputs across major consumer groups. In Doubtful Sound, New Zealand, shallow water invertebrate communities differ from those in other areas in Fiordland due to low salinity caused by freshwater output of a hydroelectric power station. To investigate whether the composition of basal carbon sources supporting this benthic community differed from that in unaltered sites, we sampled a generalist wrasse, Notolabrus celidotus, from altered and unaltered habitats throughout Fiordland, and quantified its δ 13 C, δ 15 N, δ 34 S and the abundance of its fatty acids. N. celidotus from the altered sites in Doubtful Sound had significantly lower δ 13 C, δ 15 N and δ 34 S than those collected from similar habitats throughout the Fiordland region, indicating a higher proportion of chemosynthetically fixed organic matter for Doubtful Sound N. celidotus and the invertebrate community upon which they feed. Relatively high abundances of cis-vaccenic acid (18:1ω7c) in fish from Doubtful Sound and δ 13 C values that were ~-33 ‰ for 18:1 isomers confirmed the incorporation of chemosynthetic bacteria, and indicated that the original source of carbon was forest litter. Despite these differences in carbon supply to N. celidotus, analysis of otolith sections revealed no differences in growth rates among sites. The results of this study demonstrate that a shift in invertebrate composition can be indicated by higher order consumers. In Doubtful Sound, decreased abundance of filter-feeding bivalves has reduced the flux of marine derived carbon through the benthic community to higher trophic levels relative to more pristine sites in Fiordland.KEY WORDS: Notolabrus celidotus · Stable isotopes · Fatty acid biomarkers · Compound specific δ 13 C · Food web Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 411: [127][128][129][130][131][132][133][134][135][136] 2010 tures of fish muscle tissue integrate carbon source use by a community over months to years (e.g. Guelinckx et al. 2007, Suring & Wing 2009). We designed a sampling scheme to test whether anthropogenic modifications to the salinity environment in a New Zealand fjord had altered carbon routing in the benthic community. While the marine and terrestrial environments of the 15 fjords in southern New Zealand, collectively known as Fiordland, remain relatively pristine, Doubtful Sound receives an average of 450 m 3 s -1 of freshwater outflow from the Manapouri Hydroelectric Power Station. The resulting persistent shallow low salinity layer (Gibbs et al. 2000) has led to a reduction in the abundance of filter-feeding invertebrates including infaunal clams (Tallis et al. 2004, Rutger & Wing 2006, McLeod & Wing 2008 and mussels (Jack et al. 2009). The decreased biomass of filterfeeding bivalves could dramatically reduce the capture of particulate carbon (from both phytoplankton and eroded macroalg...

Niche partitioning in the Fiordland wrasse guild

“…Mytilus edulis galloprovincialis) and gastropods found in the diet of N. celidotus support the significantly higher dispersion of trophic levels for this species relative to N. fucicola and P. miles. Previous studies confirm that N. celidotus also feeds on chemoautotrophic prey sources in inner Doubtful Sound (McLeod et al 2010). The dietary plasticity of N. celidotus helps to explain its ability to exist in high abundance along the length of the fjord axis.…”

“…Salinity also changes substantially over the length of the fjord as a result of heavy rainfall and riverine input. Low inner fjord salinity levels have been associated with altered subtidal food web structure (Rutger & Wing 2006) that limits prey availability for wrasses (McLeod et al 2010). Consequently, outer fjord habitats are highly productive, using wave energy to support benthic production in Ecklonia radiata kelp forest-dominated subtidal communities, while the calm, semi-estuarine, low light environment in the inner fjord supports invertebrate and black coral Antipathes fiordensis dominated ecosystems where large kelps are less abundant and macroalgae are largely estuarine species growing in the low salinity layer ).…”

High incidence of invertebrate‐chemoautotroph symbioses in benthic communities of the New Zealand fjords

“…Chemoautotrophic bacteria that form symbioses with clams including Solemya spp. (Solemyidae), Lucinidae, and Thyasiridae have FA profiles that are distinct from heterotrophs, being dominated by cis-vaccenic acid (18:1v7c; Conway et al 1994;Fullarton et al 1995;McLeod and Wing 2007). This compound provides a tracer for chemoautotrophic bacteria in food web studies (McLeod and Wing 2007).…”

“…Fiordland therefore provides an excellent setting to study connectivity between intact terrestrial and marine environments in terms of spatial subsidies of organic matter (OM). Large inputs of forest litter into the fjords result in highly organic marine sediments (Glasby 1978;McLeod and Wing 2009;Smith et al 2010) and there are indications that widespread fermentation occurring within the sediment drives methanogenesis (Schlesinger 1997) and extensive production of hydrogen sulfide (Brewin et al 2008). In a descriptive study of macroinfauna inhabiting the deep basins (# 420 m) of the DoubtfulBradshaw fjord complex, Brewin et al (2008) reported the common yet patchy occurrence of taxa that are likely hosts to chemoautotrophic bacteria, including Solemyidae, Manzanellidae, Lucinidae, Thyasiridae (all Mollusca: Bivalvia) and Pogonophora.…”

“…Chemical tracer techniques including natural abundance of stable isotopes and fatty acids (FAs) provide a powerful means to detect and quantify relative inputs of sources of OM to marine food webs (Alfaro et al 2006;McLeod and Wing 2007 (Sargent et al 1987;Arts et al 2009). Chemoautotrophic bacteria that form symbioses with clams including Solemya spp.…”