Recruitment of juvenile mbuna (Pisces: Cichlidae) to experimental rock shelters in Lake Malawi, Africa

Abstract

Mbuna are species of small cichlids that inhabit the rocky shoreline of Lake Malawi. They are mouthbrooders and do not guard their young. Recruitment to the community first occurs when the female deposits free-swimming young, approximately 11 mm standard length, among the rocks. Juvenile mbuna recruit to any refuge in the rock habitat and in this study, small rock shelters were monitored daily to follow the recruitment and subsequent persistence of young. Initial mortality rate was high; less than 10% of the fish survived more than 3 weeks after deposition by the female. At the two locations studied, recruitment was greater at West Thumbi Island (11 fish per day) than at Otter Point (8 fish per day). However, fewer recruits persisted as residents at Thumbi Island because mbuna young at Thumbi were capable of excluding subsequent recruits to their shelter. Similar priority effects were not observed at Otter Point. Mbuna lack pelagic stages in the life-cycle and the species composition of local adult assemblages is an important determinant of the number and type of subsequent recruits. Priority effects may help maintain stochastic influences on recruitment success and reduce the importance of deterministic processes that are directly linked to community structure.