Histopathology of Growth Anomaly Affecting the Coral, Montipora capitata: Implications on Biological Functions and Population Viability

John H R Burns,Misaki Takabayashi,Howard Browman

doi:10.1371/journal.pone.0028854

Abstract

Growth anomalies (GAs) affect the coral, Montipora capitata, at Wai'ōpae, southeast Hawai'i Island. Our histopathological analysis of this disease revealed that the GA tissue undergoes changes which compromise anatomical machinery for biological functions such as defense, feeding, digestion, and reproduction. GA tissue exhibited significant reductions in density of ova (66.1–93.7%), symbiotic dinoflagellates (38.8–67.5%), mesenterial filaments (11.2–29.0%), and nematocytes (28.8–46.0%). Hyperplasia of the basal body wall but no abnormal levels of necrosis and algal or fungal invasion was found in GA tissue. Skeletal density along the basal body wall was significantly reduced in GAs compared to healthy or unaffected sections. The reductions in density of the above histological features in GA tissue were collated with disease severity data to quantify the impact of this disease at the colony and population level. Resulting calculations showed this disease reduces the fecundity of M. capitata colonies at Wai'ōpae by 0.7–49.6%, depending on GA severity, and the overall population fecundity by 2.41±0.29%. In sum, GA in this M. capitata population reduces the coral's critical biological functions and increases susceptibility to erosion, clearly defining itself as a disease and an ecological threat.

Highlights

Reports of coral diseases have increased over the last several decades along with concerns that changing environmental conditions are promoting disease susceptibility [1,2,3]
Coral Growth anomalies (GAs) lesions are identified on the basis of gross morphology as they develop into pale protuberant masses, but the etiology, pathogenesis, and physiological impacts of this disease are poorly understood [6,32,17]
The central and peripheral tissues of healthy colonies were compared to determine if histological differences between GA and non-GA tissue might be due to spatial location within a colony

Summary

Introduction

Reports of coral diseases have increased over the last several decades along with concerns that changing environmental conditions are promoting disease susceptibility [1,2,3]. A substantial effort has been made to describe coral diseases around the globe, comprehensive pathological characterizations, ecological drivers, and the associated threat to particular populations or communities is undetermined in many cases [3,4,5,6]. As environmental stressors in coastal areas are predicted to intensify, increasing disease prevalence may exacerbate synergistic threats to coral reef ecosystems [7,3,8]. It is critical to characterize coral diseases comprehensively to determine their impacts on organismal function, population viability, and coral reef ecosystem integrity. Growth anomaly (GA) is a coral disease first recorded in 1965 that has been identified in multiple species from reefs throughout the world [9,10,11]. Transmissibility, pathogenesis, and mortality associated with this disease in most coral species remain largely uncharacterized [13,19,10,17]

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