Impact of mussel (Mytilus galloprovincialis) raft-culture on benthic macrofauna, in situ oxygen uptake, and nutrient fluxes in Saldanha Bay, South Africa

Abstract

Culture of the mussel Mytilus galloprovincialis in a South African bay created organic enrichment and anoxia in sediments. Particulate organic matter (POM) was high under rafts versus the references, especially in the first 10 cm (C = 7.5 versus 0.4%, N = 0.7 versus 0.08%). Total reducible sulphides (TRS) increased threefold downcore (from 0.04 to 0.12%). High C:N ratios (12–15) indicated accumulation of refractory POM, derived mainly from faeces and decaying mussels and foulers. Although O2 uptake by raft sediments was the lowest, rates could not conclusively be separated from the references. Ammonium dominated N efflux, the highest and most variable rates being under mussels (825 ± 500 µmol NH4·m–2·h–1). Phosphate efflux (25–140 µmol·m–2·h–1) could not be ascribed to culture biodeposition, but there was an inconclusive trend for the molar N:P ratio to be highest in these sediments. Macrofauna biomass was reduced and trophic groups and taxa altered. Under rafts, macrofauna and organic debris were linked to O2 uptake rates, whereas at the reference sites, macrofauna appeared to be the major O2 consumer. It was concluded that POM and TRS in sediment as well as macrofauna biomass, and potentially molar N:P ratios, were more sensitive indicators of benthic impact from mussel culture than O2 uptake rates or nutrient fluxes.

Influence of filtering and biodeposition by the cultured scallop Chlamys farreri on benthic-pelagic coupling in a eutrophic bay in China

“…This is in agreement with other studies (Grant et al 1995, Chamberlain et al 2001, Crawford et al 2003. Although a shift toward anaerobic metabolism at bivalve culture sites may exist, the impact of the build-up of discarded cultured organisms, and fouling algae or ascidians beneath longline culture sites, is more noticeable than any impacts from bivalve biodeposition (Grant et al 1995, Zhou 2000, Stenton-Dozey et al 2001. In some cases, however, the accumulation of biodeposits in suspended cultures may result in a locally anoxic environment and faunal impoverishment (Haven & MoralesAlamo 1966, Dahlbäck & Gunnarsson 1981, StentonDozey et al 2001, Waite et al 2005.…”

“…Grant 1999). As more living biomass is accumulated, the proportion of primary production available for further growth of bivalve biomass decreases , and the biodeposition by dense bivalve populations may be so intense that the stimulated microbial respiration can result in anoxia in underlying sediments (Dahlbäck & Gunnarsson 1981, Stenton-Dozey et al 2001. In recent years, there have been an increasing number of studies on the impacts of cultured bivalves on coastal ecosystems, as the aquaculture industry grows (Kaiser et al 1998, Newell 2004.…”

The impact and control of biofouling in marine aquaculture: a review

“…Conversely, biofouling increases food availability to shellfish through enhanced net primary production (Lodeiros et al 2002;Ross et al 2002;Le Blanc et al 2003). Biofoulers also greatly contribute to the already high biodeposition beneath aquaculture farms (Stenton-Dozey et al 2001). For example, Giles et al (2006) report that of the total deposition under a farm, only 14% can be attributed to mussel biodeposits, suggesting that the remaining 86% is deposited by other sources including biofouling.…”

Benthic community respiration in areas impacted by the invasive mollusk Crepidula fornicata

“…Chl a concentration in the water column positively influenced CR DO . Chl a concentration is an indicator of phytoplankton biomass in the water column and reflects the delivery of fresh organic matter to the sediments (Stenton-Dozey et al 2001, Eyre & Ferguson 2005. The feeding activities of C. fornicata (filtration + biodeposition) are also related to phytoplankton biomass, as well as the subsequent biodeposit remineralization (Stenton-Dozey et al 2001).…”

“…C. fornicata also influences carbon fluxes in the benthic community by stimulating the bacterial decomposition processes through its high biodeposition , Ragueneau et al 2002. Increased benthic respiration and mineralization can decrease dissolved oxygen (DO) concentration, inducing shifts to hypoxic conditions in sediments (Stenton-Dozey et al 2001). However, the impact of C. fornicata on DO and carbon fluxes has never been assessed at the community level.…”