Ecological Effects Of Fouling Organisms On Shellfish And Coastal Environment

Biofouling is defined as the attachment and subsequent growth of a community of plants and animals on structures exposed to the seawater environment (Aziset al., 2001). Biofuling is common phenomenon in the cultivation of bivalves worldwide. Many net pens are made of multi-filament netting materials which are ideal substrates for bio-fouling. Biofouling influence bivalves'cultivation and water column in many ways. In this paper, the successional development of fouling communities on the scallop cultivation alntern nets and their ecological effects on the cultured scallop Chlamys farreri and the ambient water column characteristics were studied. The main resultes are as follows:The ecological succession of fouling communities on the experimental panels of net material at the scallop and kelp polyculture site was studied from May 2007 to April 2008. Seasonal succession of fouling on the scallop cultivation net and scallop shell were also investigated. The biomass of fouling organisms on the 1-month panels were positively correlated with water temperature, ranged from 3¹210 g·m^-2. The wet weight of biofouling was lowest during February and highest in August. The biofouling on 3-month panels was most abundant on the summer and lowest during the winter, with a wet weight of about 2.20 and 0.65 g·m^-2, respectively. Fouling quantities on both lantern nets and scallop shells were characterized by a pronounced seasonal pattern. Fouling on lantern nets peaked in September with an average wet weight of 1.94 kg and dropped precipitously in October, followed by a slight increase in November. Similarly, shell fouling declined from September to October, and re-increased in November. The mean weights were 1.47 g, 0.49 g and 2.09 g, respectively. Fouling community on scallop nets and shells is a complex assemblage composed by several taxonomic groups, including Alga, Ascidiacea, Bryozoa, Annelida, Colenterata, Annelida, Mollusa, Crustacea and Spongia. Twenty-three macro-fouling species were identified. In September, the most abundant fouling was ascidians, C. intestinalis and S. clava. In October, the fouling community was predominated by C. intestinalis and blue mussel, M. edulis. The M. edulis was the dominant fouling in November.The artificial fouling which was three times of the upper valve mass did not negatively affect the survival and growth performance (e.g. shell length, muscle, and remaining soft tissue) of the scallop. Under culture conditions, the wet weight of fouling organisms on C. farreri shell was about 28.16(±38.60) % of the mass of the upper valve in September and the dry mass of fouling on P. yessoensis shell was approximately 7.82 (±2.38) % of the dry mass of the upper valve in August, which were much lower than the mass of artificial fouling in this study. Thus, it is unlikely that the mass of natural fouling would exert markedly negative effects on the growth or survival of C. farreri and P. yessoensis.The in situ biodepostion rates of two ascidians C.intestinalis or S.clava were 32.14 and 90.06 mg·ind^-1·d^-1 (or 858.99 and 467.76 mg·gdw^-1·d^-1), respectively, in September, under a water temperature of 24℃.The organic matter contents were 14.34% and 13.77%, respectively, and the organic carbon contents were 24.72% and 23.74%. The nitrogen contents were 0.27% and 0.25%, respectively. The C.intestinalis and S.clava on one scallop cultivation net may produce 4.14 and 2.55 mg nitrogen one day. In September, the ascidians which fouled on the scallop cultivation nets produced 2588.16 tons biodeposition, including 363.77 tons organic matter, 6.99 tons nitrogen and 1.79 tons phosphorus. The present experiment results indicated that the biodeposition of ascidians may strongly enhance the pelagic-benthic coupling and play an important role in the nutrient regeneration. Thus, the ascidians should be considered as an important component in the bay's ecological processes ecosystem.The POM uptaked by C.intestinalis and S.clava in Sepember were 14.30 and 17.01 mg·h^-1·ind^-1, respectively. The POM consumed by C. intestinalis or S. clava of one lantern net was equal 312 scallops. The dissolved oxygen consumed by C. intestinalis or S. clava were 0.32 and 0.18 mg·h^-1·ind^-1, the oxygen consumed by the ascidians on the lantern net was equivalent to the oxygen consumed by 75 scallops. The ammonium excretion rates of C. intestinalis, S. clava and M. edulis were 117.90 and 35.52 and 28.08 ug NH₄-N·g^-1·h^-1, respectively. The C. intestinalis, S. clava and M. edulis contribute 654.08 kg NH₄ -N·d^-1 to the bay in September, which equal to the NH₄-N excreted by 1019 tons of scallop (DTW). The ascidians and blue mussel on lantern nets would provide 2.75% of N demands for primary production and can support a production of kelp about 1204 tons.The assemblage of scallop in one cultivation net and the organisms which fouled on cultivation net and scallop shell was defined as scallop culture unit (called, SCU). The assemblage of oyster on a culture rope and organism on rope and oyster shells was defined as oyster culture unit (called, OCU). From June to September the uptake of POM by SCU ranged from 43.13 to 98.94 mg·h^-1, with a mean value of 74.05 mg·h^-1. The excretion of NH₄ -N ranged from 125.59 to 1432.23μmol·h^-1, and the excretion of PO₄-P ranged from 76.2-252.89μmol·h^-1, from June to September, which means the SCU contribute 211.09 tons N and 83.79 tons. The uptake of POM by OCU in June, August and September ranged from 5 to 41.43 mg·h^-1 indicating that the OCU consume 535.68 tons of POM from the bay. The oxygen consumption of OCU ranged from 16.54 to 41.76 mg·h^-1,from May to September. The OCU consume 955.58 tons dissolved oxygen from May to September. The excretion of NH₄ -N by OCU ranged from 35.56 to 489.34μmol·h^-1. The excretion of PO₄-P by OCU ranged from 9.92-16.68μmol·h^-1, which means the OCU contribute 62.37 tons N and 15.50 tons PO₄ -P to Sanggou Bay, from June to September.