Evaluation of the green mussel floating cage related to the enlightenment aspect through the analysis of the Perna viridis spat settlement & population structure

Abstract

Abstract A floating cage is one of the methods of cultivating green mussels that can potentially be used as a medium for maritime education because it is easily accessible to people of various age groups, especially in green mussel cultivation related to mangrove ecotourism. This study aims to analyze the design of floating cages from light and shaded zones based on the spat density and the population structure. The research was conducted in floating cages operated in the Java Sea, Banyuurip Village, Ujungpangkah District at coordinates 06°52’18.84” South Latitude and 112°29’41.19” East Longitude. The spat density was calculated per collector rope per depth (1-4m). When the green mussels were harvested in five-month cultivation from each zone, the population structure was analyzed with Excel 2010 software and measured for the population frequency distribution to investigate the percentage of mussels that reached consumer size. The differences between open and shaded population variables were evaluated by t-test (α=5%). The results of this study show that the density of spat attachment to the collector in the open space was 17.044±724 individuals/m2, and in the shaded area was 16.085±4634 individuals/m2. The density of the spat at a depth of 1m (22,538±4,536 individuals/m2) was significantly different (p<0.05, with three observations) from the density at a depth of 4m (10,830±1,016 individuals/m2) in a light area. However, the spat settlement between each depth was not significantly different in the shaded area. The population structure of green mussels in both areas had seven length classes (class I-VII) with a 7.8 mm interval. The percentage of the class VI population (47.4-55.20 mm) in the light area (31%) was significantly different (p<0.05) from the shaded area (25.79%). It means that the portion of green mussels suitable for harvest (length 40-80 mm) in the light zone is more than in dark zone. We conclude that lighting is an essential aspect of the rate of spat attachment, survival, and growth. The proportion and position of the shaded area in the floating cages must be adjusted so that the growth of the spat is not blocked.