Baselines and Degradation of Coral Reefs in the Northern Line Islands

TLDR

Coral reefs are heavily degraded by local human activities and global change, making it hard to distinguish their separate impacts, and rigorous baselines of pristine conditions are needed for effective conservation. The study surveyed reefs on uninhabited and increasingly populated atolls in the northern Line Islands to establish a baseline of community structure and document human‑activity‑associated changes. The authors surveyed reef community structure on uninhabited atolls (Kingman, Palmyra) and increasingly populated atolls (Tabuaeran, Kiritimati) in the northern Line Islands. Reefs on unpopulated atolls were dominated by top predators and reef‑building organisms, with inverted biomass pyramids and lower coral disease, whereas reefs on populated atolls were dominated by small planktivorous fishes and fleshy algae, exhibited bottom‑heavy biomass pyramids, higher coral disease, and lower recruitment, indicating that protection from overfishing and pollution enhances reef resilience to global warming.

Abstract

Effective conservation requires rigorous baselines of pristine conditions to assess the impacts of human activities and to evaluate the efficacy of management. Most coral reefs are moderately to severely degraded by local human activities such as fishing and pollution as well as global change, hence it is difficult to separate local from global effects. To this end, we surveyed coral reefs on uninhabited atolls in the northern Line Islands to provide a baseline of reef community structure, and on increasingly populated atolls to document changes associated with human activities. We found that top predators and reef-building organisms dominated unpopulated Kingman and Palmyra, while small planktivorous fishes and fleshy algae dominated the populated atolls of Tabuaeran and Kiritimati. Sharks and other top predators overwhelmed the fish assemblages on Kingman and Palmyra so that the biomass pyramid was inverted (top-heavy). In contrast, the biomass pyramid at Tabuaeran and Kiritimati exhibited the typical bottom-heavy pattern. Reefs without people exhibited less coral disease and greater coral recruitment relative to more inhabited reefs. Thus, protection from overfishing and pollution appears to increase the resilience of reef ecosystems to the effects of global warming.