Spawning aggregation behavior and reproductive ecology of the giant bumphead parrotfish, Bolbometopon muricatum, in a remote marine reserve.

Brian J Zgliczynski,Bradford Z Teer,Joseph L Laughlin,Roldan C Muñoz

doi:10.7717/peerj.681

Abstract

The giant bumphead parrotfish (Bolbometopon muricatum) has experienced precipitous population declines throughout its range due to its importance as a highly-prized fishery target and cultural resource. Because of its diet, Bolbometopon may serve as a keystone species on Indo-Pacific coral reefs, yet comprehensive descriptions of its reproductive ecology do not exist. We used a variety of underwater visual census (UVC) methods to study an intact population of Bolbometopon at Wake Atoll, a remote and protected coral atoll in the west Pacific. Key observations include spawning activities in the morning around the full and last quarter moon, with possible spawning extending to the new moon. We observed peaks in aggregation size just prior to and following the full and last quarter moon, respectively, and observed a distinct break in spawning at the site that persisted for four days; individuals returned to the aggregation site one day prior to the last quarter moon and resumed spawning the following day. The mating system was lek-based, characterized by early male arrival at the spawning site followed by vigorous defense (including head-butting between large males) of small territories. These territories were apparently used to attract females that arrived later in large schools, causing substantial changes in the sex ratio on the aggregation site at any given time during the morning spawning period. Aggression between males and courtship of females led to pair spawning within the upper water column. Mating interference was not witnessed but we noted instances suggesting that sperm competition might occur. Densities of Bolbometopon on the aggregation site averaged 10.07(±3.24 SE) fish per hectare (ha) with maximum densities of 51.5 fish per ha. By comparing our observations to the results of biennial surveys conducted by the National Oceanic and Atmospheric Administration (NOAA) Coral Reef Ecosystem Division (CRED), we confirmed spatial consistency of the aggregation across years as well as a temporal break in spawning activity and aggregation that occurred during the lunar phase. We estimated the area encompassed by the spawning aggregation to be 0.72 ha, suggesting that spawning site closures and temporal closures centered around the full to the new moon might form one component of a management and conservation plan for this species. Our study of the mating system and spawning aggregation behavior of Bolbometopon from the protected, relatively pristine population at Wake Atoll provides crucial baselines of population density, sex ratio composition, and productivity of a spawning aggregation site from an oceanic atoll. Such information is key for conservation efforts and provides a basic platform for the design of marine protected areas for this threatened iconic coral reef fish, as well as for species with similar ecological and life history characteristics.

Highlights

Human impacts to terrestrial and marine communities are widespread and typically begin with the local extirpation of large-bodied animals (Pandolfi et al, 2003; Morrison et al, 2007)
All research was conducted in accordance with the Animal Welfare Act (AWA) and with the U.S Government Principles for the Utilization and Care of Vertebrate Animals Used in Testing, Research, and Training (USGP) OSTP CFR May 20, 1985, Vol 50, No 97
Wake Atoll (19◦18′N,166◦37′E) is a U.S Pacific Remote Island, National Wildlife Refuge, and Marine National Monument co-managed by the National Oceanic and Atmospheric Administration (NOAA) and the U.S Fish and Wildlife Service (USFWS), but with access controlled by the U.S Department of Defense (DOD)

Summary

Introduction

Human impacts to terrestrial and marine communities are widespread and typically begin with the local extirpation of large-bodied animals (Pandolfi et al, 2003; Morrison et al, 2007). Large-bodied species play an important ecological role and many are key species that may be critical for maintaining long-term ecosystem stability (Bellwood, Hoey & Choat, 2003; Sadovy et al, 2003; Pandolfi et al, 2005). Large predators can shape the number, distribution, and behavior of their prey, while large herbivores can act as ecological engineers by shaping the structure and species composition of plant or algal communities (Morrison et al, 2007; McCauley et al, 2010). The challenge of understanding how large-bodied species contribute to ecosystem structure and community organization is often confounded by their rarity.

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