Settlement of oyster Magallana bilineata (Roding, 1798) spat in the natural environment: seasonality and substrate texture preference

This study determined the seasonality of Magallana bilineata spat settlement in a natural oyster bed and established surface texture preference of competent larvae by comparing the numbers of spat settling on the smooth and rough surfaces of ceramic tiles over a period of 31 months. This will guide farmers when to deploy cultches to maximise spat harvest. Regardless of tile orientation, spat numbers were significantly higher on the rough side (129.07 +/- 9.3 m(-2)) than on the smooth side (66.95 +/- 7.0 m(-2)). Spat collection was highest in March, June and July in each of 2015, 2016 and 2017. There was no significant correlation between the number of spat settling in each month with temperature, salinity, pH, dissolved oxygen (DO), sulphide, phosphate, nitrate, nitrite and ammonia concentrations, plankton density measured at deployment and retrieval of tiles, except for DO during deployment. The only significant correlations with mean shell length (SL) were with DO and ammonia during tile retrieval. Mean SL did not significantly differ between tile orientations and surfaces but differed between months, being highest in August 2015 and August 2016. From these results, it is best to deploy roughened cultches in this particular area in March, June and July.

Automated summary

This study determined the seasonality of Magallana bilineata spat settlement in a natural oyster bed and identified the surface texture preference of competent larvae. The study also analyzed the factors affecting spat settlement and found that there was no significant correlation with water quality factors. Based on the results, it is recommended to deploy cultches in March, June, and July to maximize spat harvest.