Abstract
Coral reefs are typified by their benthic components, and reef diversity and productivity are traditionally ascribed to the symbiotic association between corals and zooxanthellae, and other macroalgal forms. Less understood is the role of plankton and adjacent pelagic areas in contributing to reef productivity. Half of the reef benthos are filter or particle feeders, while a significant proportion of reef fishes are planktivorous. These organisms can serve as bridges between adjacent oceanic areas to the reef proper, and the pelagic and benthic realm. Here, we investigate the plankton trophic dynamics in two reef systems in the West Philippine Sea. Physico-chemical data, phytoplankton and mesozooplankton samples were collected from stations spanning offshore to reef areas per site. These were subjected to microscopic and stable isotope analysis to determine variability in plankton distribution, phytoplankton and zooplankton interactions, and gain insights into the trophic dynamics and productivity of reefs. Results showed distinct variations in plankton biomass and assemblage from offshore to reef areas, as well as between the reef systems. Phytoplankton distributions pointed toward filtering out of cells across the fore reef and reef flat areas, while mesozooplankton distributions could be mediated more by other factors. Isotopic signatures of δ13C and δ15N indicated the influence of different nutrient sources for phytoplankton and that mesozooplankton relied only partly on phytoplankton for food in most areas of the reefs. The mesozooplankton likely also obtain food from other sources such as the microbial and detrital pathways. More in-depth spatio-temporal studies on these bentho-pelagic interactions are recommended, which can provide more robust estimates of the trophic dynamics of these reefs that are situated in important fishing grounds and key biodiversity areas.
Highlights
Coral reefs are one of the most biologically diverse and productive coastal ecosystems
Previous work have focused on characterizing gross hydrodynamic features in the deeper waters of the West Philippine Sea (WPS) and South China Sea (SCS), and there are no studies that we are aware of describing oceanographic patterns across time and space at a similar atoll scale featured in this study
Phytoplankton biomass is considered to be generally low in waters surrounding coral reef ecosystems, characterized by typical concentrations of chl a at approximately 0.2–0.6 μg/L (Nakajima et al, 2016) owing to a low concentration of inorganic nutrients (Hearn et al, 2001)
Summary
Coral reefs are one of the most biologically diverse and productive coastal ecosystems They are geographically located in shallow oligotrophic waters in the inter-tropical regions at 30◦N–30◦S, and these reefs occupy less than 0.1% of the world’s oceans (Lesser, 2004). Plankton Trophic Relationships WPS taxonomic organization and spatial and temporal distribution These marine ecosystems play a role in the exchange of organic and non-organic matter with the adjacent ocean and lagoon (Hamner et al, 2007). Hamner et al (2007) illustrated the spatial variation of available zooplankton from the oceanic side to the lagoon in the barrier reef of Palau This and other studies (Morales and Murillo, 1996; Gruber et al, 2018) highlight the interaction between the open ocean and coral reefs through the import and export of plankton. Morais and Bellwood (2019) estimated that 41% of the fish productivity in a windward reef on the Great Barrier Reef derived from pelagic subsidies, while McMahon et al (2016) found that pelagic productivity can contribute greater than 70% to C consumed and assimilated by fish in oceanic reefs in the Red Sea
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