| Popis: |
Herbivorous fishes have consistently been found to have a significant positive impact on the resilience of coral reefs. Their feeding and foraging actions shape the capacity of reefs to both resist, and recover from, disturbance. Relatively little is known, however, about which ecological features in particular influence their distributions, movements, and foraging behaviours. Furthermore, the manner in which their biomass is altered by human actions remains poorly understood. Understanding and appreciating these key factors may help improve global management strategies of fisheries and coral reef habitats. Overall, this thesis provides a framework to establish the ecological functions of commercially important herbivorous fishes. This will not only help authorities establish effective management strategies to curb fishing pressure, but will also provide an indication of the capacity of reefs to resist or recover from disturbances that lead to algal dominance.At present, there is a noticeable gap in the literature pertaining to the ecological role that individual herbivorous fish species play; contemporary research instead focusses on their overall contribution. To bridge this gap and to render this research relevant to management efforts in the Seychelles, this thesis explored the distribution, ecological functions, and spatial ecology of key rabbitfish species in this archipelago of the Indian Ocean. Rabbitfishes are a crucial food source to the majority of the Western Indian Ocean region, comprising the bulk of their artisanal fisheries. In the Seychelles, in particular, they constitute over 60% of the total artisanal catch and, notably, there are no measures aimed at management of stocks currently being implemented or enforced.This thesis demonstrates that the overall distribution of herbivorous fishes is shaped by the habitat characteristics of individual reefs, and not by the presence of marine reserves. Species level analyses on rabbitfishes reveal that they were also influenced by the features of reef habitats, but not the conservation status of individual reefs. Furthermore, this research reveals that fishes from different functional groups occupy distinct reef habitats, suggesting that this may lead to spatial separation in the distribution of different forms of herbivory, and possibly reef resilience, in the Seychelles.This thesis investigated the ecological functions of rabbitfishes, focussing on their foraging rates and substrate preference, among diverse sites with varying benthic habitats. It reveals that rabbitfishes display both browsing and grazing traits, indicating possible functional complementarity between species. This is an important distinction as it implies that the conservation of different species may result in distinct shifts in the competitive dominance of coral and algae.Finally, this thesis examines the spatial ecology of the most commercially important fish species of the artisanal fishery in the Seychelles: the shoemaker spinefoot (Siganus sutor); it investigated whether they act as a mobile link between networked habitats, and whether their movements differed between day and night. Detection patterns reveals them to be diurnal herbivores, with only rare nocturnal movements. Furthermore, their movements are influenced by seagrass and coral abundance. Identification of such links between networked habitats are relevant for the purposes of implementing effective fisheries and habitat management strategies, and have a crucial bearing on sites around the archipelago which are to be declared marine reserves. |
