Spatial variation in the morphological traits of Pocillopora verrucosa along a depth gradient in Taiwan.

Derek Soto,Vianney Denis,Chaolun Allen Chen,Stephane De Palmas,Ming Jay Ho,Mónica Medina

doi:10.1371/journal.pone.0202586

Abstract

Pocillopora verrucosa is a widely distributed depth-generalist coral that presents plasticity in its skeletal macro- and microstructure in response to environmental gradients. Light and water movement, which covary with depth, are the main environmental drivers of morphological plasticity in this genus; however, assessing environmentally-induced plasticity may be confounded by the extent of interspecific variation in Pocillopora. We examine the morphology of 8 typed P. verrucosa specimens collected along a depth gradient ranging from 7 to 45 meters and comprising 3 sites throughout Ludao, Taiwan. We measured 36 morphological characters, 14 which are novel, in 3 regions on the corallum—the apex, branch and base—in order to quantify their relationship to site and depth. We found significant correlation between depth and 19 morphological characters, notably branch verruca area, branch verruca height, base verruca spacing, base spinule length, and branch corallite area. 60% of microstructural characters and 25% of macrostructural characters showed a correlative relation to depth, suggesting that depth acclimatization is manifested primarily at the microstructural level. Canonical discriminant analysis of all morphometric characters by depth supports clustering into 3 groups: an overlapping 7m and 15m group, a 23-30m group, and a 38-45m group. Canonical discriminant analysis by site supports clustering into low- and high-current sites, differentiated primarily by branch septa width, base septa width, pre-terminal branch width, terminal branch maximum length, and terminal branch minimum length. We conclude that distinctive patterns of morphological variation in mesophotic specimens of P. verrucosa could reflect the effects of abiotic parameters such as light and water flow. Elucidating the mechanisms behind the morphological changes that occur in response to environmental gradients can help clarify the role that physiological plasticity plays in the acclimatization of corals to the unique environmental settings of mesophotic coral ecosystems.

Highlights

Scleractinian coral taxonomy is traditionally based on descriptions of skeletal micro- and macrostructures, yet these characteristics can be altered in novel environments or in response to environmental change [1] through a phenomenon known as plasticity [2,3,4,5]
Despite its relevance to taxonomy and coral ecology, studies on morphological plasticity in corals— along environmental gradients—are uncommon; out of more than 1300 extant scleractinian species, relatively few have been investigated for plastic responses [6]
Out of 28 microstructural characters (Fig 4) and 8 structural characters (Fig 5) measured, significant correlation coefficients were found for 19 characters: apex spinule length, apex spinule spacing, apex verruca area, apex verruca height, base spinule length, base spinule width, base corallite area, base corallite spacing, base verruca area, base verruca spacing, branch spinule length, branch spinule width, branch spinule spacing, branch septa length, branch corallite area, branch verruca area, branch verruca height, terminal branch maximum width, and terminal branch minimum length (Table 3)

Summary

Introduction

Scleractinian coral taxonomy is traditionally based on descriptions of skeletal micro- and macrostructures, yet these characteristics can be altered in novel environments or in response to environmental change [1] through a phenomenon known as plasticity [2,3,4,5]. Morphological plasticity, which often transcends species boundaries, is a source of considerable confusion in the identification and taxonomy of many scleractinian corals [4, 6, 7] and may lead to the inclusion of misidentified species in a study [8]. In comparison to corals from shallow waters, corals that inhabit mesophotic environments may possess unique characteristics that optimize light harvesting and photosynthetic efficiency [15,16,17] and reduce oxidative stress [18, 19]. Even though the interaction between light and depth on coral traits is well documented [32,33,34,35,36,37,38], the acclimatory potential of zoxanthellate scleractinian corals inhabiting MCEs remains poorly understood [39,40,41]

Methods

Results

Conclusion