Underwater Photogrammetry Captures the Initial Recovery of a Coral Reef at Lalo Atoll

Atsuko Fukunaga,Ashley R Pugh,John H R Burns,Randall K Kosaki,Kailey H Pascoe

doi:10.3390/d14010039

Abstract

Recovery of coral reefs after physical damage sustained from storm events can be affected by various factors. Here, we examined the initial recovery of a coral reef at the southern end of uninhabited Lalo Atoll of Papahānaumokuākea Marine National Monument after its complete destruction by Hurricane Walaka in 2018. While the site was still mostly (98%) covered by a mixture of rubble and sand, surveys utilizing underwater photogrammetry allowed for detailed quantitative assessments of benthic cover and confirmed colonization of coral (Pocillopora meandrina and Porites lobata), macroalgae and sponges. The proportion of sand in the rubble–sand mixture also decreased from the level observed in 2019. Visual fish surveys confirmed the presence of 35 reef fish species, a large increase from no reef fish in 2019, despite the low biotic benthic cover. Overall, the colonization of benthic organisms and the return of reef fish, which is potentially supported by the benthos and cryptofauna in the rubble bed, offer positive signs of reef recovery. The photogrammetric surveys in the present study captured the subtle changes in the benthic cover and provided us with a procedure to continue monitoring the succession of the site. Continuous monitoring of the site should reveal whether the reef returns to the original state of Acropora coral dominance or progresses towards a coral assemblage with a different composition.

Highlights

Published: 8 January 2022Coral reefs are vulnerable to physical damage from extreme weather events such as hurricanes and cyclones
Benthic cover changed from ~70% Acropora coral reef fish prior to the hurricane damage [7,8]
While the benthic cover was still dominated by rubble and sand, there were a slight decrease from 99.7% in the previous survey in 2019 [6] and, more importantly, an increase in the rubble-to-sand ratio from 67.9–31.8% in 2019 [6] to

Summary

Introduction

Coral reefs are vulnerable to physical damage from extreme weather events such as hurricanes and cyclones. TheWhile area it is difficult to determine the exact spatial extent of the hurricane damage to coral reefs except for a single shark [6]. Reef might be relatively localized term monitoring sites in 2019 suggest that the extensive damage found at Rapture Reef (K.H.P.bepersonal observation). Rapture Reef is located at approximately 26 m depth and was home to high cover of Acropora table coral and an abundant and diverse population of reef home to high cover of Acropora table coral and an abundant and diverse population of fish prior to the hurricane damage [7,8]. Benthic cover changed from ~70% Acropora coral reef fish prior to the hurricane damage [7,8].

Fish and Benthic Photogrammetry Surveys

Generation and Analysis of 3D Models

Results and Discussion