Abstract
Phytoplankton production drives marine ecosystem trophic-structure and global fisheries yields. Phytoplankton biomass is particularly influential near coral reef islands and atolls that span the oligotrophic tropical oceans. The paradoxical enhancement in phytoplankton near an island-reef ecosystem—Island Mass Effect (IME)—was first documented 60 years ago, yet much remains unknown about the prevalence and drivers of this ecologically important phenomenon. Here we provide the first basin-scale investigation of IME. We show that IME is a near-ubiquitous feature among a majority (91%) of coral reef ecosystems surveyed, creating near-island ‘hotspots' of phytoplankton biomass throughout the upper water column. Variations in IME strength are governed by geomorphic type (atoll vs island), bathymetric slope, reef area and local human impacts (for example, human-derived nutrient input). These ocean oases increase nearshore phytoplankton biomass by up to 86% over oceanic conditions, providing basal energetic resources to higher trophic levels that support subsistence-based human populations.
Highlights
Phytoplankton production drives marine ecosystem trophic-structure and global fisheries yields
Mechanisms that act to promote nearshore phytoplankton biomass are critical for coral reef ecosystem development and persistence[5]
Using 35 coral reef islands and atolls spanning 43° of latitude and 60° of longitude (Fig. 2 and Supplementary Table 1) that cross multiple gradients in oceanic forcing[11], geophysical attributes[11], reef-community composition[5,12] and local human impacts[12], we quantify the prevalence of the Island Mass Effect (IME) across the tropical Pacific
Summary
Phytoplankton production drives marine ecosystem trophic-structure and global fisheries yields. The paradoxical enhancement in phytoplankton near an island-reef ecosystem—Island Mass Effect (IME)—was first documented 60 years ago, yet much remains unknown about the prevalence and drivers of this ecologically important phenomenon. Variations in IME strength are governed by geomorphic type (atoll vs island), bathymetric slope, reef area and local human impacts (for example, human-derived nutrient input). These ocean oases increase nearshore phytoplankton biomass by up to 86% over oceanic conditions, providing basal energetic resources to higher trophic levels that support subsistencebased human populations. The ecological impacts of enhanced phytoplankton biomass are especially acute near tropical coral reef islands and atolls as these ecosystems predominantly reside in nutrient impoverished waters that lack new production[4]. We show that the IME increases the nearshore standing stock of phytoplankton biomass by up to 85.6% over background oceanic conditions, providing basal energy sources for higher trophic levels across an otherwise barren ocean landscape
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