Community Structure and Spatio-Temporal Variability of Ichthyoplankton in Kenyan Coastal Waters.

Abstract

Temporal and spatial variability in abundance and distribution of fish larvae contributes to structuring populations of adults within coral reef habitats and influences connectivity of reef sites. However, few studies have examined this variability at different spatial and temporal scales in the Western Indian Ocean (WIO). In an effort to bridge this gap, this study examined patterns of fish larval supply in Malindi and Watamu Marine National Parks between March 2005 - March 2007. Additionally, the study examined large-scale spatial variations in larval assemblages along lagoonal reef sites at a span > 160 Kms, and the inter-annual variability in alongshore assemblages of fish larvae at this scale. Larvae were sampled using a combination of plankton nets and light-traps. A total of 56 families, 45 genera and 21 species of larvae were identified in Malindi Marine Park, while, 21 families, 14 genera and 6 species were sampled in Watamu Marine Park. The dominant taxa at both sites were; Blenniidae (Parablennius sp. and Omobranchus sp.), Engraulidae (Stolephorus commersonii), Gobiidae n.d, and Pomacentridae (Abudefduf sp.). Seasonality was found to have an effect on the occurrence of larvae over the two parks, with segregation of distinct larval groups within and between the parks on a small spatial scale. Inter-annual variations in distribution of larvae and larval assemblage structure suggested annual differences in spawning patterns. Correspondence Analysis, indicated differences in species-site associations between years. Data suggested overall spawning by fishes on the north Kenyan coast with subsequent likely transport of larvae to the south. Hatch dates derived from otolith analysis of commerson’s anchovy, Stolephorus commersonii, were; January - March 2005, August - September 2005, December - February 2006. Monthly growth rates for S. commersonii larvae and juveniles were highest in the northeast monsoon months of December (0.207 cm.day-1) and March 2005 (0.119 cm.day-1), and lowest in southeast monsoon months of July (0.056 cm.day-1), and April (0.0105 cm.day-1) 2006, respectively. Finescale temporal variation in larval supply to Malindi Marine Park indicated that larval supply to the park was mostly nocturnal, with a peak during spring tides. Time-series spectral analysis showed that larval supply to Malindi Marine Park occurred after a 30 day cyclical period associated with the new moon lunar phase. This study provides, for the first time, a synoptic account of the taxonomy, distribution and relative abundance of nearshore fish larval assemblages in lagoonal waters of coastal Kenya, and contributes in providing baseline data useful in understanding fish population replenishment in lagoonal reefs.