Impact of wind and freshwater inputs on phytoplankton biomass in the coral reef lagoon of New Caledonia during the summer cyclonic period: a coupled three-dimensional biogeochemical modeling approach

Abstract

A coupled three-dimensional physical-biological model was developed in order to simulate the ecological functioning and potential impacts of land-derived inputs in the southwest lagoon of New Caledonia. This model considered pelagic biogeochemical cycling of organic matter, taking into account advection and diffusion processes driven mainly by local wind fields and freshwater discharges. Modeled phytoplankton dynamics were strongly correlated with both freshwater nutrient inputs and wind-driven hydrodynamic processes, the latter resulting in a large input of oceanic water from the southeast part of the lagoon under trade wind conditions. In situ data obtained during the summer (January 1998) under trade wind conditions supported predicted concentration gradients along several coast to reef transects and provided a validation of the coupled physical-biogeochemical model. An additional sensitivity analysis showed that the alteration of the biogeochemical parameters did not strongly affect the results of the model. Freshwater inputs of nutrients were simulated using a realistic scenario corresponding to the summer rainy season of 1997-1998 in New Caledonia. Despite occasional flooding events from the main rivers considered in these simulations, no significant meso-scale phytoplankton bloom was identified. Hydrodynamically driven dispersion and rapid uptake of nutrients by phytoplankton were sufficient to spatially constrain the impact of river inputs and maintain oligotrophic conditions. The fine spatial grid of our three-dimensional model demonstrated that eutrophication in the southwest lagoon of New Caledonia is confined to the most restricted coastal embayments, while most of the lagoon experiences sustained oligotrophic conditions

Chlorophylls and Phycoerythrins as Markers of Environmental Forcings Including Cyclone Erica Effect (March 2003) on Phytoplankton in the Southwest Lagoon of New Caledonia and Oceanic Adjacent Area

“…In normal conditions, precipitations and winds are the main environmental factors driving the spatiotemporal variations of phytoplankton biomass in New Caledonian waters [11,12] although anthropogenic influences could affect it locally, particularly around Nouméa [5,10]. From April 2002 to April 2003, trade winds blew over 75% of the time and, in agreement with the Douillet et al model [23], they created a northwest circulation in the SWL with output of lagoon waters by the different passes (Dumbéa, Boulari).…”

“…Andrews and Gentien [67] identify a broad scale of physical mechanisms which combine to deliver nutrient from the ocean to the Great Barrier Reef. In the three-dimensional-coupled physical-biological model, the ocean is considered as an oligotrophic vector for the SWL and productivity increase essentially associated to terrestrial and/or anthropogenic inputs [12]. This notion could be revised by an increase of research effort to identify more precisely climatic conditions which could enhance the role of the ocean in lagoon and coral reef productivity.…”

“…Winds, precipitations [9], anthropogenic activities [10], and hydrodynamics [11] are the main environmental factors that can explain the Tchl a variations in the SWL. A coupled three-dimensional physical-biological model was developed to simulate the Tchl a distribution in the SWL from freshwater input, trade winds intensity, and hydrodynamics [12]. This model demonstrated that eutrophication is limited to coastal bays and oligotrophic conditions prevailed in most part of the lagoon.…”

Detecting age-structured effects in growth performance of coral reef fish juveniles

“…1), were sampled. Located near a pass, Larégnère Islet is an offshore islet submitted to oceanic influence, whereas Canard Islet is submitted to the terrigeneous influence of the main island (Pinazo et al 2004).…”

“…and little difference in environmental conditions between stations compared with differences between islets (e.g. Pinazo et al 2004), fish from the same islet were pooled together. Upon collection, all individuals were anaesthetized in a benzocaine solution and immediately preserved in 95% methylated alcohol.…”