Identification and characterization of olfactory receptor genes and olfactory perception in rapa whelk Rapana venosa (Valenciennes, 1846) during larval settlement and metamorphosis.

The rapa whelk Rapana venosa, an economically important marine fishery resource in China but a major invader all over the world, changes from a phytophagous to a carnivorous form following settlement and metamorphosis. However, the low settlement and metamorphosis rates (<1%) of larvae limit the abundance of R. venosa. This critical step (settlement and metamorphosis) remains poorly characterized but may be related to how larvae perceive the presence of shellfish, their new source of food. Here, we report that larvae may use olfactory perception to sense shellfish. Olfactory receptor (OR) genes are involved in odor sensing in animals. We identified a total of 463 OR genes, which could be grouped into nine clades based on phylogenetic analysis. When assessing the attraction of larvae at different developmental stages to oyster odor, R. venosa showed active settlement and metamorphosis behavior only at the J4 stage (competent larva, 1000-1500 µm shell length) and in the presence of shellfish odor at the same time. Expression of OR gene family members differed between stage 2 (four-spiral whorl stage) and stage 1 (single- to three-spiral whorl stage), indicating significant changes in the olfactory system during larval development. These findings broaden our understanding of olfactory perception, settlement, and metamorphosis in gastropods and can be used to improve R. venosa harvesting, as well as the sustainable development and utilization of this resource.

[Carbon, nitrogen, and phosphorus budgets of bottom-cultured clam Ruditapes philippinarum].

In order to elucidate the role of bottom-cultured clams in the coastal nutrient cycle, the seasonal filtration, ingestion and biodeposition rates were in situ measured and carbon (C), nitrogen (N) and phosphorus (P) budgets of Ruditapes philippinarum among four seasons were modeled. The results showed that the scope for growth of R. philippinarum in carbon (SFG(C)), nitrogen (SFG(N)), and phosphorus (SFG(P)) all varied significantly among seasons, with the highest values in spring. Meanwhile, SFG(C) was negative in summer, SFG(N) and SFG(P) were always positive throughout the year. The seasonal variations of SFG(C), SFG(N) and SFG(P) were -3.94-49.82 mg C x ind(-1) x d(-1), 0.72-9.49 mg N x ind(-1) x d(-1), and 0.15-3.06 mg P x ind(-1) x d(-1), respectively. The net growth efficiencies in carbon (K(C2)), nitrogen (K(N2)), and phosphorus (K(P2)) also showed a distinct seasonal pattern among seasons, and ranked as K(P2) > K(N2) > K(C2). The C, N, and P budgets illustrated that the R. philippinarum population relatively used more N and P than C for growth and efficiently transferred the pelagic primary production to a higher trophic level. The current study suggested that R. philippinarum bottom-cultured at large scale might play a dominant role in the nutrient cycle of the coastal ecosystem and should be considered as an important ecological component in coastal areas.

[Self-pollution in Ruditapes philippinarum bottom-cultured area of Zhuanghe coast].

By using sediment trap and closed respirator, a year-round in situ investigation was made on the bio-deposition rate, ammonia excretion rate, and phosphate excretion rate in the Ruditapes philippinarum bottom-cultured area of Zhuanghe coast. The three test rates of R. philippinarum all showed obvious seasonal variability, with the bio-deposition rate ranged in 0.15-1.47 g x ind(-1) x d(-1) (annual average 0.61 g x ind(-1) x d(-1)), ammonia excretion rate ranged in 0.02-0.40 mg x ind(-1) x d(-1) (annual average 0.17 mg x ind(-1) x d(-1)), and phosphate excretion rate ranged in 0.01-0.39 mg x ind(-1) x d(-1)(annual average 0. 13 mg x ind(-1) x d(-1)). Based on these, it was estimated that the annual bio-deposit production by the bottom-cultured R. philippinarum in Zhuanghe coast could reach as high as 5.46 x 10(7) t dry mass, amounting to 9.07 x 10(6) t organic matter (OM), 1.00 x 10(6) t organic carbon (OC), or 1.18 x 10(5) t organic nitrogen (ON), and the annual NH4+ -N and PO4(3-)-P productions were 1.49 x 10(4) t and 1.15 x 10(4) t, respectively. Our results suggested that for the large scale and high density bivalve culture in China coasts, the potential impacts of self-pollutants by filter-feeding bivalves on the environment should not be neglected.

[Bioremediation potential of Apostichopus japonicus (Selenka) in coastal bivalve suspension aquaculture system].

Suspension aquaculture of filter-feeding bivalves can produce large amount of faeces and pseudofaeces (biodeposits) that may impact aquaculture environment, while deposit-feeding sea cucumbers may effectively utilize such particulate wastes and act as a scavenger in mariculture system. In this paper, the ingestion, growth, and excretion of deposit-feeder Apostichopus japonicus were investigated in situ seasonally to evaluate its bioremediation potential of a suspension aquaculture system of filter-feeding bivalves. The results showed that A. japonicus could grow well in newly designed culture nets, with its maximum specific growth rate being 0.34% d(-1). The A. japonicus could effectively use the biodeposits generated by co-cultured bivalves, and the ingestion rate at 21.2 degrees C in summer, 19.2 degrees C in autumn, and 7.7 degrees C in winter was 0.1746, 0.0989, and 0.0050 g g(-1) d(-1), respectively. A. japonicus could promote the regeneration of nutriens in biodeposits via the excretion of considerable amount of dissolved N and P, and the excretion also showed obvious seasonal fluctuation. The extrapolation based on the in situ investigation results showed that when co-cultivated with bivalves in lantern nets, A. japonicus would ingest 4.5-159.6 kg hm(-2) d(-1) of dry biodeposits and excrete 1,382.5-3,678.1 mmol hm(-2) d(-1) of NH4(+)-N and 74.6-335.7 mmol hm(-2) d(-1) of PO4(3-)-P, indicating that the deposit-feeding A. japonicus had a great bioremediation capability in suspension aquaculture systems. The integrated model of deposit-feeding A. japonicus and filter-feeding bivalve could not only benefit the economy, but also sustain the environment.