Herbivorous damselfishes expand their territories after causing white scars on Porites corals

Hiroki Hata,Shota Takano,Hiroyuki Masuhara

doi:10.1038/s41598-020-73232-8

Abstract

Turf algae become the most abundant benthic group on coral reefs after mass coral bleaching. By defending feeding territories, damselfishes enhance the growth of turf algae in so-called algal farms and affect coral communities both directly and indirectly. We found several white scars (i.e., bite lesions) on massive Porites colonies around feeding territories. In this study, we examined the occurrence of white scars on corals and their function in coral–algal competition at the boundaries between algal farms of two damselfish species—the intensive farmer Stegastes nigricans, and the intermediate farmer S. lividus—and adjacent Porites corals for 3 years around Okinawa Island, Japan. White scars occurred on Porites colonies only adjacent to the territories of both damselfish species. Of the white scars on corals around S. nigricans territories, 73% of the area was covered by algae within 2 weeks, while the remaining was re-covered by Porites tissues. The coral–algal boundaries encroached further into areas of coral when the area of white scars were larger. These results suggest that both intensive and intermediate farmers bite adjacent Porites colonies causing white scars on corals, and expand their territories onto corals using algae-covered white scars as stepping stones.

Highlights

Turf algae become the most abundant benthic group on coral reefs after mass coral bleaching
We focus on an intensive farmer, S. nigricans, and an intermediate farmer, S. lividus, to compare different farming strategies
White scars on Porites were found only adjacent to the territories of S. nigricans and S. lividus (Fig. 4a,c,e)

Summary

Introduction

Turf algae become the most abundant benthic group on coral reefs after mass coral bleaching. We examined the occurrence of white scars on corals and their function in coral–algal competition at the boundaries between algal farms of two damselfish species—the intensive farmer Stegastes nigricans, and the intermediate farmer S. lividus—and adjacent Porites corals for 3 years around Okinawa Island, Japan. On Okinawa’s reefs, one territorial damselfish, Stegastes nigricans, maintains turf algae inside its territory as an algal farm on live coral colonies, such as massive Porites corals. On corals neighbouring these territories, white scars of about 1 cm in diameter have been observed. Intermediate farmers do not weed but they keep mixed turfs as algal farms[15] In this way, territorial damselfish species vary in their farming strategies and may have different impacts on coral reef resilience. We observed the coral–algal boundaries around and outside the territories of herbivorous damselfishes, the occurrence of white scars on corals adjacent to these boundaries, and algal colonization and coral recovery over the course of a 3-year period

Objectives

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Conclusion