ABSTRACT
Periodic outbreaks of crown‐of‐thorns starfish have led to severe coral reef degradation, with onehypothesized cause being eutrophication. Phosphorus (P) is one of the driving factors for eutrophication, butresearches on the spatiotemporal distributions of P in coral reefs are limited, impeding our understanding of theP cycling in coral reefs and its correlation with starfish outbreaks. This study undertook an analysis of various Pspecies, migration and transformation in seawater, sediments, and crown‐of‐thorns starfish within the coral reefsof the Xisha Islands, northern South China Sea. The results show that in seawater, P predominantly existed in thedissolved phase, with organic P constituting the largest fraction (>67%). Conversely, in sediments, P primarilyexisted as inorganic form (43%-95%), with calcium‐bound P comprising the majority (26%-46%). Notably,exchangeable P accounted for a relatively smaller fraction (9%-20%) but played a significant role as a source ofP released from sediments into seawater (0.01-0.17 mmol m-2hr-1). During starfish outbreaks, starfish (1,000individuals per hectare) assimilated P from seawater via phytoplankton or corals, resulting in substantialaccumulation of both organic and inorganic P in their tissues (69-315μmolg-1). Meanwhile, starfish excretionreleased P back into the seawater, which contributes to the migration and transformation of various P forms.Historical data also show a close relationship between P content and starfish density. These findings highlightthe interactions between starfish and P cycling within coral reefs, and provide valuable insights intoconservation and restoration on coral reefs, especially those severely affected by starfish outbreaks.
