Interactive influences of the marine yabby (Trypaea australiensis) and mangrove (Avicennia marina) leaf litter on benthic metabolism and nitrogen cycling in sandy estuarine sediment

Abstract

A previous study has demonstrated that in sandy sediment the marine yabby (Trypaea australiensis) stimulated benthic metabolism, nitrogen regeneration and nitrification, but did not stimulate denitrification, as the intense bioturbation of the yabbies eliminated anoxic microzones amenable to denitrification. It was hypothesised that organic matter additions would alleviate this effect as the buried particles would provide anoxic microniches for denitrifiers. To test this hypothesis a 55-day microcosm (75 cm 9 36 cm diameter) experiment, comprising four treatments: sandy sediment (S), sediment ? yabbies (S ? Y), sediment ? A. marina litter (S ? OM) and sediment ? yabbies ? A. marina litter (S ? Y ? OM), was conducted. Trypaea australiensis significantly stimulated benthic metabolism, nitrogen regeneration, nitrification and nitrate reduction in the presence and the absence of litter additions. In contrast, the effects of litter additions alone were more subtle, developed gradually and were only significant for sediment oxygen demand. However, there was a significant interaction between yabbies and litter with rates of total nitrate reduction and denitrification being significantly greater in the S ? Y ? OM than all other treatments, presumably due to the decaying buried litter providing anoxic micro-niches suitable to nitrate reduction. In addition, both T. australiensis and litter significantly decreased rates of DNRA and its contribution to nitrate reduction.

Direct contribution of clams (Ruditapes philippinarum) to benthic fluxes, nitrification, denitrification and nitrous oxide emission in a farmed sediment

“…N-excretion by the clams in this study could account for on average 80 ± 7% of benthic N-regeneration, indicating that the clams physiological rates were the major factor regulating organic matter turnover in the sediment. Given the very high biomass of clams in the farmed sediment, this estimate is in line with other estimates of the contribution of infauna N-excretion to sediment-water column NH þ 4 or DIN fluxes, where animal NH þ 4 excretion accounted for 10e90% of NH þ 4 or DIN effluxes (Blackburn and Henriksen, 1983;Gardner et al, 1993;Pelegri and Blackburn, 1995;Magni et al, 2000;Dunn et al, 2009Dunn et al, , 2012 with the highest contribution being for a Japanese tidal flat where the bivalves Ruditapes philippinarum and Muscilista senhousia dominated the faunal community (Magni et al, 2000). Overall, the potentially large contribution of clam respiration and N-excretion rates to SOD and N-regeneration rates, indicates not only that clams are a major influence on these rates, but that this effect is largely mediated by their own metabolism rather than through stimulation microbial respiration and N-mineralisation rates due to biodeposition of organic matter.…”

“…In this study estimated nitrification and denitrification (N 2 þ N 2 O) rates were significantly correlated to the biomass density of clams. Infauna have been proposed to enhance rates of nitrification by increasing the volume of oxic sediment amenable to ammonium oxidation by forming burrows and irrigating these with oxygenated water (Satoh et al, 2007;Stief, 2013), and denitrification by enhancing the supply of NO x from both nitrification and the overlying water, and by increasing the area of interface between oxic and anoxic sediment zones Welsh, 2003;Webb and Eyre, 2004;Dunn et al, 2012). In the case of Ruditapes philippinarum direct transfer of oxygen and NO x from the water column to the burrow wall sediments would be limited to periods when the animal's withdraw their siphons during movement or in response to a perceived threat.…”

“…The construction of burrows increases the area of the sediment-water interface by up to 500% promoting solute exchanges (Welsh, 2003;Stief, 2013). Burrow ventilation introduces oxygen from the overlying water leading to the development of oxic and suboxic sediment zones, which are amenable to nitrification and denitrification (Welsh, 2003;Nielsen et al, 2004;Robertson et al, 2009;Stief, 2013).These activities have been shown to enhance rates of benthic metabolism, N-regeneration, nitrification and denitrification (Howe et al, 2004;Jordan et al, 2009;Dunn et al, 2009Dunn et al, , 2012Nizzoli et al, 2007Nizzoli et al, , 2011.…”

Effects of the Bioturbating Marine Yabby Trypaea australiensis on Sediment Properties in Sandy Sediments Receiving Mangrove Leaf Litter

“…Sediment, yabbies (T. australiensis) and mangrove (A. marina) leaf litter were collected during 2007 from the Gold Coast Broadwater (Australia) and maintained as described in Dunn et al [32]. The study region is characterised by bioturbating infauna including T. australiensis, which is one of the dominant macrofauna species [26].…”

“…On day three after all yabbies had formed burrows, OM additions (0.125 g wet wt day −1 A. marina leaf litter with a mean C content of 39% dry wt. and C:N ratio of 36.9 ± 2.4 [32]) were initiated in S+OM and S+Y+OM treatments and were repeated daily until the completion of the incubations. Leaf litter additions were equivalent to 4.5 t ha −1 y −1 , which corresponds to the average annual leaf fall for A. marina within Moreton Bay [37].…”