Mollusk species composition and quantity distribution of intertidal zone in Nanji Islands Marine Nature Reserve

Based on the mollusks’ data which were obtained by biological resources quantitative and qualitative investigation in seven sections of the intertidal zone of Nanji Islands in November 2013, February, May and August 2014, this paper studied the species composition and quantitative distribution of mollusks in this area. The results are as follows: (1) A total of 63 species of mollusks were identified, which belong to 3 classes, 13 orders, 34 families and 52 genera. The numbers of species that appeared in spring, summer, autumn and winter were 48, 48, 45 and 41, respectively. (2) The numbers of mollusks resources was different in different seasons. As for the number of individuals: spring> autumn> winter> summer; As for the weight: spring> autumn> summer> winter; the average individual number and biomass of mollusks are 506.5/m² and 801.54 g/m², and the maximum was in spring and the minimum was in winter, respectively. (3) The average numbers of mollusks varied in different tidal areas: middle tidal zone> low tidal zone> high tidal zone. The differences in biomass were also apparent: low tidal zone> middle tidal zone> high tidal zone. (4) The dominant species varied greatly in different seasons, butSeptifer virgatus was the first dominant species throughout the year. Because of the influence of environmental factors, such as currents, topography and wind waves, the distribution of mollusks in Nanji Islands varied greatly in different seasons and sections. At the same time, compared with the past data, the kinds of and the number of mollusks in Nanji Islands have decreased to some extent in recent 20 years.