Abstract: To understand whether calcium content in substrate of artificial reefs could affect oyster spat settlement, we designed a twofactor randomized experiment with calcium carbonate in different contents (four treatment levels: 5%, 20%, 40%, 60%) and oyster larvae abundances (low treatment group: 1 ind·mL^-1, high treatment group: 7-8 ind·mL^-1). The density and shell height of oyster spats attached onto experimental substrates were measured. The results showed that both calcium content and planktic larvae abundance significantly affected the density of settled oyster spats (P<0.05). Planktic larvae abundance in seawater had a significant effect on the shell height of settled oyster spats (P<0.05), but calcium content did not significantly affect the shell height of settled oyster spats (P>0.05). The substrate with calcium carbonate content of 20% showed the greatest inducing ability to settlement of oyster larvae, and attracted significantly greater oyster settlement than the experimental group of 60% (P<0.05). The density of settled oyster spats was greater in the high abundance of oyster larvae than in the low abundance (P<0.05) regardless of calcium carbonate content, while the contrast result was found for the shell height: high larval abundance treatment < low larval abundance treatment (P<0.05).

Key words: Gueldenstaedtia verna, spatial distribution pattern, microtopography, subalpine meadow, Geranium wilfordii