Changes in geochemical foreshore attributes as a consequence of intertidal shellfish aquaculture: a case study

Abstract

On the west coast of British Columbia (BC), Canada, the intertidal is under pressure by commercial farming of the non-native Manila clam Venerupis philippinarum. We applied a 3-tiered approach to determine how farming practices were affecting the geochemical attributes of the intertidal. We compared farmed and reference sites with respect to % silt, organic matter, ammonium, phosphorus, iron and manganese in surface (0 to 3 cm) and bulk (0 to 10 cm) sediments. Ammonium porewater profiles and sediment sorption coefficients were determined for 1 of the 3 regions where the greatest intensity of shellfish farming occurred (Tier I). Mesocosm studies were conducted in which intertidal species were manipulated to match the community composition on the farmed as compared to reference sites (Tier II). Microcosm studies were applied to determine how shifts in community structure as observed on farmed versus reference sites and as manipulated in the mesocosm studies, altered the rate of ammonium diffusion to overlying surface waters (Tier III). All geochemical attributes and ammonium sorption coefficients were greater in either surficial and/or bulk sediments of farmed as compared to reference beaches. Tier III studies indicated that the rate of ammonium diffusion from sediments to surface waters was less in microcosms with only bivalves compared to those with mussels, barnacles and bivalves. Tier I and II studies suggest that greater recovery of ammonium and phosphorus is related to increased bivalve density and % plant coverage on farmed versus reference sites. In contrast, greater amounts of organic matter and silt are due to the presence of antipredator nets. Farming practices that ensure well aerated sediments and support a diverse intertidal community would be advised so that important nutrient geochemical cycles are not altered such to be a detriment to the quality of habitat or to interfere with primary productivity.KEY WORDS: Intertidal · Community composition · Shellfish aquaculture · Nutrients · Organic matter · Nitrogen · Phosphorous · Iron Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 404: [91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107][108] 2010 Given the importance of the intertidal as the interface between terrestrial and oceanic processes, much attention has been given to the behaviour of nutrients within this region with possibly nitrogen being the most well studied of the nutrients required for primary productivity (e.g. Enoksson 1993, Twichell et al. 2002, Hou et al. 2003, Burgin & Hamilton 2007, Fulweiler et al. 2007, Serpa et al. 2007). Perhaps receiving less attention although no less important are iron and phosphorus (reviewed in Newell 2004). A review of the literature suggests that while the geochemical cycling of these elements on the intertidal is complex, amounts of organic matter and hence oxygen availability are key drivers in their geochemical transformations (e.g. Jensen et al. 1995, Gunnars & Blomqv...

Favored use of anti-predator netting (APN) applied for the farming of clams leads to little benefits to industry while increasing nearshore impacts and plastics pollution

“…A total of 16 paired farm and reference sites were sampled for both surficial (0-3 cm) a bulk (0-10 cm) sediments and analyzed for % silt, organic matter, ammonium, phosphorus, iron and manganese. In agreement with the studies of Sorokin et al, 1999;Bartoli et al, 2001;Beadman et al, 2004 andBendell-Young, 2006;Bendell et al (2010) found that all geochemical attributes and ammonium sorption coefficients were greater in either surficial and/or bulk sediments of farmed as compared to reference beaches. A possible explanation for the different outcomes of the study by Munroe and McKinley (2007) is that the region they chose for field manipulation has been intensively used for shellfish farming since 1940.…”

“…A unique finding was increased temperature under the nets, the nets acting as an insulator keeping intertidal sediments warmer as compared to those intertidal regions without nets. Bendell et al (2010) compared sediment characters of netted versus non-netted intertidal areas across three geographically distinct regions of BC. A total of 16 paired farm and reference sites were sampled for both surficial (0-3 cm) a bulk (0-10 cm) sediments and analyzed for % silt, organic matter, ammonium, phosphorus, iron and manganese.…”

Influence of Manila clam aquaculture on rates and partitioning of organic carbon oxidation in sediment of Keunso Bay, Yellow Sea

“…Ejected organic matter is larger and more prone to deposition on the sediment, since pseudo-feces and fecal pellets are excreted as mucus-bound aggregates (Giles & Pilditch 2004). Unlike oysters and mussels, which are generally cultivated in boxes or attached to longlines in the water column (Christensen et al 2003, Carlsson et al 2012, Hyun et al 2013, Manila clams are farmed directly in intertidal sediment after dispersion (Bendell et al 2010, Lavoie et al 2016. Accumulation of organic matter and intense sediment reworking (i.e.…”

Ecosystem goods and services from Manila clam culture in Puget Sound: a modelling analysis

“…Several authors have shown that similarly de ployed nets may in crease concentrations of organic matter to a limited extent (Munroe & McKinley 2007, Bendell et al 2010, and could imply shifts in community structure (Ben dell et al 2010), but in another experiment where predator nets were placed above net bags for hard clams, they also acted as artificial reefs and increase biodiversity and provide nursery grounds through macroalgal colonisation (Powers et al 2007). …”