Macroinvertebrate diet in intertidal seagrass and sandflat communities: A study using C, N, and S stable isotopes

Abstract

Most seagrass community food-web studies using stable isotopes have been carried out in subtidal habitats during one sampling event. We used C, N, and S stable isotopes to characterise the diet of the dominant macroinvertebrates found in intertidal Zostera capricorni and sandflat communities of southern New Zealand in late summer and winter. The range of δ 13 C and δ 34 S values for Z. capricorni was wide (>5‰), which highlights the importance of accounting for spatial and temporal variability in primary producer isotopic signatures. The range of δ 15 N values for Z. capricorni was comparatively small (<l‰). Mixing models based on δ 13 C and δ 15 N signatures suggested that Z. capricorni was a potentially important contributor (24-99%) to the diet of most consumers sampled at the seagrass site, whereas microphytobenthos dominated the diet of the same consumers at the sandflat site. The main exception was the bivalve Austrovenus stutchburyi, which had a diet consisting mostly (up to 85%) of Ulva and Polysiphonia spp. at both sites. S isotopes proved to be of limited use owing to the difficulty of sampling microphytobenthos and to potential nondietary sources of 34 S-depleted sulfur to consumers.

Distribution and abundance ofAbarenicola affinis(Arenicolidae, Polychaeta) in tidal inlets of Otago, New Zealand

“…Chlorophyll a was measured to indicate biomass of microphytobenthos (Jones et al 2011), which had been identified as an important food source for A. affinis (Leduc et al 2006). Comparatively higher microphytobenthos biomass may be related to fewer lugworms feeding at the sediment surface, while sediment chlorophyll a measurements may have also been a weak indicator of microphytobenthos production in muddy areas of this inlet (Jones et al 2011) where low permeability causes a reduction in turnover of algal biomass due to decreased light penetration, solute and particle fluxes (Blanchard et al 2001;Billerbeck et al 2007).…”

“…The latter two parameters were used to indicate potential food sources for lugworms (i.e. total available organic material in surface and subsurface sediment, and microphytobenthos biomass in surface sediment, respectively; Longbottom 1970; Leduc et al 2006;Jones et al 2011). For sediment granulometry, samples were wet sieved to extract the fines fraction (B 63 mm), dried to constant weight (60 8C, 48 h) and mechanically sieved to obtain grain size fractions (63Á125, 125Á250, 250Á500, 500Á1000 mm; McManus 1988).…”

“…These patterns can be influenced by sediment grain size composition, which has been found to affect burrow maintenance and feeding processes (Longbottom 1970;Baumfalk 1979;Beukema & de Vlas 1979), and availability of food (e.g. meiofauna and microfauna, detritus, microphytobenthos) as indicated by organic matter and chlorophyll a content of the sediment (Longbottom 1970;Beukema & de Vlas 1979;Zebe & Schiedeck 1996;Andresen & Kristensen 2002;Leduc et al 2006).…”

“…The lugworm Abarenicola affinis (Ashworth 1903) is endemic to New Zealand, where it occurs sparsely in North Island, but in several locations in South Island, such as in tidal inlets of the Otago coast (Wells 1963;Leduc et al 2006;Glasby et al 2009). Relatively little is known about the biology and ecology of A. affinis and there are no published quantitative data on this species.…”

Lugworm (Abarenicola affinis) in seagrass and unvegetated habitats

“…In southeastern New Zealand, the lugworm Abarenicola affinis (Ashworth 1903) is common in tidal inlets and estuaries, where it co-occurs with the seagrass Zostera muelleri (Irmisch ex Ascherson 1867) in a number of habitats (Wells 1963;Leduc et al 2006;Goerlitz et al 2013). Zostera muelleri is a short-bladed seagrass (5-15 cm blade length), which is common on intertidal flats throughout New Zealand, where it often exhibits a patchy distribution (Turner 2007).…”