Incidence of mussel culture on biogeochemical fluxes at the sediment-water interface

Abstract

Upward nutrient fluxes at the sediment-water interface were studied in a mussel farming zone (Carteau, Gulf of Fos, France) in order to estimate the impact of organic matter input from biodeposition. Nitrate, nitrite, ammonia, silicate, phosphate and oxygen were measured. Fluxes were estimated by means of polyacrylate benthic chambers placed at sites located under (UM) and outside (OM) the rope hanging structures. Transformation of biodeposited organic matter increases phosphate, silicate and ammonia fluxes. No variation in nitrite fluxes could be detected and only minor differences were observed in nitrate and the oxygen production/consumption equilibrium at the two stations. Phosphate and silicate fluxes, which were always higher at the UM than at the OM site, decreased from spring to winter. Ammonia fluxes were very high under mussel cultures in May and September and lower in November. The fact that ammonia flux was always higher at the UM than at the OM sites might be explained by degradation of mussel biodeposit, as well as by benthic macrafauna excretion. Discrepancies between fluxes of the nutrients studied at the UM and OM sites increased as organic particulate matter in the water column decreased. Variations of oxygen flux followed a different pattern, since they were correlated with presence and abundance of photosynthetic microphytes on the bottom and in the water. Bottom respiration exceeded production of oxygen only in May 1988 at the UM station.As it now stands, biodeposit input into the sediment under mussel ropes does not affect the ecosystem, although the flow of nutrients towards the water column is higher than in other areas.

Effects of shellfish farming on the benthic environment

“…These range from significant impact such as extensive bacterial mats underneath mussel longlines (Dahlbäck and Gunnarsson, 1981) and changes in benthic community composition under shellfish culture structures (Tenore et al, 1982) to minimal effects (e.g. Baudinet et al, 1990;Buschmann et al, 1996). Most studies on organic enrichment of the seabed from shellfish farming have concluded that the effect is small, and much less than that caused by finfish farming.…”

Influence of intertidal Manila clam Venerupis philippinarum aquaculture on biogeochemical fluxes

“…Nutrient regeneration from benthic sediments to the water column occurs through mineralization of organic material through aerobic and anaerobic processes (Glud 2008), both being stimulated by clam biodeposition (Kaspar et al 1985, Baudinet et al 1990, Bartoli et al 2001, Nizzoli et al 2007). Clam metabolic activity and bioirrigation due to clam movements may also release various nutrients (Bartoli et al 2001, Welsh & Castadelli 2004, Nizzoli et al 2007.…”

“…Nevertheless, suspension-feeding bivalves play important functional roles in aquatic ecosystems, since they may affect various physical and biological processes in both the water column and the benthic environment (Newell 2004, Nizzoli et al 2006a). Numerous studies have described the influence of bivalve culture on various components of the environment, including nutrient cycling (Doering et al 1987, Baudinet et al 1990, Nizzoli et al 2006a,b, Richard et al 2006, 2007b, Thouzeau et al 2007), localized organic loading (Mattsson & Lindén 1983, Weise et al 2009), benthic macrofaunal communities (Kaiser et al 1996, Spencer et al 1996, Jie et al 2001, Callier et al 2008, and seston (Newell 2004, Guyondet et al 2013. High densities of infaunal filter-feeding bivalves may influence benthic environments either directly, through their metabolic activity (e.g.…”

“…High densities of infaunal filter-feeding bivalves may influence benthic environments either directly, through their metabolic activity (e.g. oxygen consumption and ammonium production) and feeding, or indirectly, by modifying biogeochemical processes at the water−sediment interface (Doering et al 1987, Baudinet et al 1990, Magni et al 2000. Only a portion of the food captured by bivalves is ingested and used for respiration, growth, and reproduction; the other fraction is released postdigestion as faeces or, if rejected prior to ingestion, as consolidated particles, termed pseudofaeces (Navarro & Thompson 1997).…”

“…Pseudofaeces and faeces are collectively known as biodeposits. Biodeposition by cultured bivalves may lead to accumulation of organic matter within farm areas (Jie et al 2001), and related high concentrations of benthic organic matter may induce mineralization processes and stimulate both aerobic and anaerobic metabolism and nutrient recycling (Kaspar et al 1985, Baudinet et al 1990). Benthic processes are more complicated when farmed bivalves are infaunal species (as compared to farming bivalves in suspended and off-bottom culture), such as Manila clams, because they not only increase biodeposition locally but also live within the sediments (Bartoli et al 2001), with both factors potentially influencing benthic processes.…”