| Summary |
Network models (Ecopath) are used to explore fisheries food webs and possible impacts of fishery harvests. The goal of this study was to create a network model for the Calabash Caye, Belize, marine ecosystem. Network models of carbon flow are composed of compartments (species or groups of species) and flows of energy (measured as biomass) between the compartments. A comprehensive, multi-species Ecopath food web model of the Puerto Rico-Virgin Islands (PRVI) coral reef ecosystem was used as the structural and comparative model for the Calabash Caye ecosystem. The PRVI model was constructed solely from literature values, whereas the Calabash Caye model used site-specific data to parameterize the Calabash Caye model, data regarding compartmental biomass, production-to-biomass ratio, consumption-tobiomass ratio, assimilation efficiency and diet composition. To obtain the fish biomass data for the fish compartments Calabash Caye model, visual censuses at both dawn and dusk were conducted in the coral reef, seagrass and mangrove habitats surrounding the island. As the PRVI model did not consider biomass shifts between time of day or habitat, the Calabash model was created as one entity. The primary study determined that time of day did not have an impact upon numerical abundance and that the coral reef had a significantly higher numerical abundance than the seagrass and mangrove habitats. The latter finding reveals that the current Calabash Caye Ecopath model can be reconfigured into separate habitat models. Effective trophic levels, mixed trophic impacts and weighted connectance diagrams of both unadjusted models were analyzed and compared. The Calabash model revealed that the ecosystem contained lower biomasses of carnivores and higher biomasses of herbivores than the PRVI ecosystem as well as one fish compartment (grunts and snappers) showing signs of movement between the three habitats during the course of the day. The information revealed by this baseline study will be beneficial to those officials and academics visualize natural and anthropogenic effects on the reef, seagrass and mangrove areas. |
