Influence of farmed pearl oysters and associated biofouling communities on nutrient regeneration in lagoons of French Polynesia

Abstract

Bivalve cultivation can significantly contribute to nutrient cycling in semi-enclosed ecosystems. We investigated the influence of suspended pearl oyster culture on nutrient regeneration in the water column of 3 oligotrophic lagoons in French Polynesia. The aim of this first study performed in a tropical area was to assess the seasonal variability of nutrient fluxes and to quantify the contribution of biofouling communities. In situ metabolic enclosure systems were used to measure nutrient uptake or release by 'cultivation units' (i.e. 4 pearl oysters with or without associated biofouling). In all 3 study lagoons (Tahiti, Mangareva, Ahe), nutrient fluxes produced by pearl oyster and associated biofouling communities (CR units) were 4-to 6-fold higher than those measured for cleaned pearl oysters. CR units can release dissolved inorganic nitrogen and soluble reactive phosphorus in the water column at a rate of 200 and 50 µmol h −1 , respectively. Trophic level and composition of biofouling communities may explain the variations of fluxes observed between the different islands. At the pearl farm scale (Ahe), pearl oyster long-lines may supply 70% of the inorganic nitrogen demand for primary production, with biofouling communities accounting for 60% of the total nutrient release. Pearl oyster culture enhances nutrient availability and alters stoichiometry, which can strongly modify the dynamics of the planktonic ecosystem.

Fate of 15N-enriched cyanobacteria feed for planktivorous fish in an enclosure experiment: a stable isotope tracer study

“…Nutrient concentration analyses indicated that TN and TP were about 4 times higher in the tilapia enclosure than in the silver carp enclosure due to the digestive capacity of Microcystis, which suggests that the ichthyoeutrophication potential of tilapia is greater than that of silver carp. 11.05 % of the 15 N was assimilated by the tilapia whereas 3.58 % of the 15 N was assimilated by the silver carp, suggesting that tilapia has a higher capacity to assimilate and retain Microcystis nitrogen than silver carp, although the absorptivities of both species were relatively low. At the end of the experiment, 8.48 % of the 15 N was detected in sedimentary detritus in the tilapia enclosure, as compared to 6.07 % of the 15 N in the silver carp enclosure, which suggests that only a small fraction of the Microcystisderived nitrogen sank to the bottom.…”

“…In addition, previous studies have indicated that shrimps can also excrete inorganic nitrogen into water bodies through their gills, mainly in the Abstract A tracer experiment using isotope 15 N was performed to study the assimilation and retention of nitrogen from feces by two planktivorous fish, silver carp Hypophthalmichthys molitrix and tilapia Oreochromis niloticus, in Lake Taihu (China). Microcystis was enriched with 15 N-NH 4 Cl, lyophilized to produce feed for fish, and traced to establish the fate of feces nitrogen. Samples of organisms and abiotic substances were analyzed for excess 15 N and nutrient concentrations in the water column were determined on days 0, 1, 5, 10, 15, and 20.…”

“…As a result, significant amounts of cyanobacterial detritus enter water bodies upon being excreted by fish [13]. In addition, previous studies have indicated that shrimps can also excrete inorganic nitrogen into water bodies through their gills, mainly in the Abstract A tracer experiment using isotope 15 N was performed to study the assimilation and retention of nitrogen from feces by two planktivorous fish, silver carp Hypophthalmichthys molitrix and tilapia Oreochromis niloticus, in Lake Taihu (China). Microcystis was enriched with 15 N-NH 4 Cl, lyophilized to produce feed for fish, and traced to establish the fate of feces nitrogen.…”

“…Microcystis was enriched with 15 N-NH 4 Cl, lyophilized to produce feed for fish, and traced to establish the fate of feces nitrogen. Samples of organisms and abiotic substances were analyzed for excess 15 N and nutrient concentrations in the water column were determined on days 0, 1, 5, 10, 15, and 20. Nutrient concentration analyses indicated that TN and TP were about 4 times higher in the tilapia enclosure than in the silver carp enclosure due to the digestive capacity of Microcystis, which suggests that the ichthyoeutrophication potential of tilapia is greater than that of silver carp.…”

First report on in situ biodeposition rates of ascidians (Ciona intestinalis and Styela clava) during summer in Sanggou Bay, northern China

“…They can form dense and heavy aggregations within suspended aquaculture operations, as culturing infrastructure (e.g. buoys, anchors, ropes, and lantern nets) and bivalve shells provide an abundance of hard substrata for them to colonize (Grant et al 1998, Costa-Pierce & Bridger 2002are abundant in coastal waters (Prins et al 1997, Newell 2004, Lacoste et al 2014. Like bivalves, ascidians have a relatively high filtration capacity (Randløv & Riisgård 1979, Lesser et al 1992, Petersen & Riisgård 1992.…”