Differential Effects of Substrate Type and Genet on Growth of Microfragments of Acropora palmata

Erin Papke,Bailey Wallace,Sarah Hamlyn,Robert Nowicki

doi:10.3389/fmars.2021.623963

Abstract

Global decline of coral reefs has led to a widespread adoption of asexual propagation techniques for coral restoration, whereby coral colonies are fragmented and allowed to re-grow before being returned to the reef. While this approach has become increasingly popular and successful, many questions remain regarding best practices to maximize restoration speed, efficiency, and survival. Two variables that may influence growth and survival of asexually fragmented colonies include coral genet and growth substrate. Here, we evaluate the effects of genet and substrate (commercially available ceramic vs. in-house made cement) on the survival and growth of 221 microfragments of elkhorn coral Acropora palmata over 193 days. All corals survived the experimental period, and doubled their initial size in 45 days, with an average growth of 545% over the study duration. Growth was generally linear, though the growth of some corals more closely matched logistic, logarithmic, or exponential curves. Both genet and substrate had significant effects on coral growth, though the two factors did not interact. Genet had a stronger influence on coral growth than substrate, with the fastest genet growing at 216% the rate of the slowest genet. Corals on cement substrate grew at 111.9% the rate of those grown on ceramic. This represents both a significant cost savings and elimination of logistical challenges to restoration practitioners, as the cement substrate ingredients are cheap and globally available. Our work shows that both genet and substrate should be considered when undertaking asexual restoration of Acropora palmata to maximize restoration speed and efficiency.

Highlights

Coral reefs, often characterized as underwater rainforests, are among the most biodiverse ecosystems on Earth (Reaka-Kudla, 1997; Jaap, 2000) and perform critical ecological and economic functions for millions worldwide (e.g., Moberg and Folke, 1999; Ferrario et al, 2014)
This model was more parsimonious than models which included a ramet effect that varied by genet or substrate (Supplementary Table 1)
Numerous factors can impact the outcomes of coral restoration including coral growth, success/survivorship, and cost-efficiency of coral propagation

Summary

Introduction

Often characterized as underwater rainforests, are among the most biodiverse ecosystems on Earth (Reaka-Kudla, 1997; Jaap, 2000) and perform critical ecological and economic functions for millions worldwide (e.g., Moberg and Folke, 1999; Ferrario et al, 2014). Dramatic declines in coral cover globally over the past several decades (Gardner et al, 2003; Côté et al, 2005; De’ath et al, 2012) have eroded the functionality of these ecosystems and gravely threaten them and the services they provide (Jones et al, 2004; Alvarez-Filip et al, 2011) These declines have been driven by both natural and anthropogenic stressors such as overfishing, disease, storms, nutrient pollution, coastal development, and climate change (e.g., Gladfelter, 1982; Hughes, 1994; Bruno et al, 2007; Burke et al, 2011; Walton et al, 2018). Because species such as A. palmata have experienced relatively rapid declines over the last several decades (Bruckner, 2002; Miller et al, 2002; Sutherland and Ritchie, 2004), it is important for practitioners to grow corals quickly and efficiently to reach goals of population enhancement

Methods

Results

Conclusion