Ecosystem-Scale Effects of Nutrients and Fishing on Coral Reefs

Abstract EN

Nutrient pollution and fishing are the primary local causes of coral reef decline but their ecosystem-scale effects are poorly understood.

Results from small-scale manipulative experiments of herbivores and nutrients suggest prioritizing management of fishing over nutrient pollution because herbivores can control macroalgae and turf in the presence of nutrients.

However, ecological theory suggests that the opposite occurs at large scales.

Moreover, it is unclear whether fishing decreases herbivores because fishing of predators may result in an increase in herbivores.

To investigate this paradox, data on the fish and benthic communities, fishing, and nutrients were collected on Kiritimati, Kiribati.

Oceanographic conditions and a population resettlement program created a natural experiment to compare sites with different levels of fishing and nutrients.

Contrary to theory, herbivores controlled macroalgae in the presence of nutrients at large spatial scales, and herbivores had greater effects on macroalgae when nutrients were higher.

In addition, fishing did not increase herbivores.

These results suggest that protecting herbivores may have greater relative benefits than reducing nutrient pollution, especially on polluted reefs.

Reallocating fishing effort from herbivores to invertivores or planktivores may be one way to protect herbivores and indirectly maintain coral dominance on reefs impacted by fishing and nutrient pollution.