Rekrutmen Box Mussel, Septifer Bilocularis L. Efek Substratum Dan Kepadatan Dewasa

An intertidal population of Septifer bilocularis L. was studied in Tongkeina, North Sulawesi, Indonesia. Open and closed cages were applied in field experiments to study the effects of four types of substrata on settling of S. bilocularis: live shells of adults, dead shells, coral rubble, and sand. Each substratum was tested with four levels of adult mussel density: 0, 10, 50, 100 individuals per compartment. The number of recruits as a function of cage, substratum, and adult density was analysed using Two-way ANOVA. The experiment showed that new recruits were affected by the substratum but not by the density of adults. The surface of adult box mussels was the most attractive substratum for recruits

Protective refuges for seeded juvenile scallops (Placopecten magellanicus) from sea star (Asterias spp.) and crab (Cancer irroratus and Carcinus maenas) predation

We examined two methods to provide refuge for seeded juvenile sea scallops (Placopecten magellanicus) from sea star (Asterias spp.) and crab (Cancer irroratus and Carcinus maenas) predation by considering (i) initial density of seeded scallops and (ii) presence of an alternative prey species (blue mussel (Mytilus edulis)). In the seeding density experiment, underwater plots were seeded with different densities of scallops (1, 6, and 69·m–2). In the alternative prey experiment, plots were seeded with one density of scallops (5·m–2) and different densities of mussels (0, 5, and 30·m–2). Animal densities were monitored over time, and predation rate was estimated using tethered scallops. In the seeding density experiment, scallop density in plots initially seeded with 6 scallops·m–2 decreased at the slowest rate. Estimated predation rate of scallops in all plots tended to increase with prey density. In the alternative prey experiment, mussel density decreased immediately after seeding, while scallop density decreased after approximately 1 week. Estimated predation rate of scallops decreased with increasing mussel density. Also, sea stars aggregated in plots containing scallops and mussels. In both experiments, 17%–58% of seeded scallops were lost to dispersal, and final scallop density was approximately 1·m–2, independent of treatment.

[NO TITLE AVAILABLE]

Cultivated mussels (Perna perna) were studied to test for the effects of cleaning on their growth. These effects were examined by experimentally cleaning mussels and by changing mussel density. Treatment was performed twice, at two and four months after immerging the ropes. Two months after the first treatment and three months after the second treatment, mussels were harvested and measured (weight, length, width and thickness). Analysis of variance showed that none of the treatments resulted in increased growth of the mussels, nor did increased density result in decreased growth when compared with the control. It was concluded that it was not necessary to clean the shells to increase harvest.