Fluorescent organic exudates of corals and algae in tropical reefs are compositionally distinct and increase with nutrient enrichment

Zachary A Quinlan,Thomas A Oliver,Kristina Remple,Nyssa J Silbiger,Hollie M Putnam,Craig A Carlson,Megan J Donahue,Craig E Nelson,Michael D Fox,Linda Wegley Kelly

doi:10.1002/lol2.10074

Abstract

AbstractDissolved organic matter (DOM) composition influences microbial community metabolism and benthic primary producers are a source of DOM in coral reefs. As reef benthic communities change, in part due to nutrient pollution, understanding impacts on reef microbial processes requires knowledge of DOM sources and composition. We conducted a multi‐week mesocosm experiment dosing four coral reef benthic constituents with three levels of nitrate and phosphate to contrast exudate composition and quantify the effects of nutrient enrichment on exudate release. Moderate nutrient enrichment enhanced bulk dissolved organic carbon exudation by all producers. Corals exuded rapidly accumulating DOM with a markedly high concentration of aromatic amino acid‐like fluorescent DOM components that clearly distinguishes them from algal exudates, which were dominated by humic‐like fluorescent components and did not accumulate significantly. Our results indicate that corals and algae release DOM of different quality and the quantity of DOM release increases with inorganic nutrient availability.

Highlights

Coral reefs are highly productive ecosystems that thrive in relatively oligotrophic tropical waters, in part by intense recycling of limited nutrients through a highly diverse and active microbial community (Raina et al 2009; Cardini et al 2015)
There was a significant effect of both reef constituent and nutrient addition on bulk dissolved organic carbon (DOC) and all fluorescent DOM (fDOM) components (FDR p < 0.05), except tyrosine-like components which were not affected by nutrients
Our results demonstrate that dominant benthic producer constituents on coral reefs release Dissolved organic matter (DOM) (Figure 2), that exudation generally increases with modest stable nutrient enrichment (Figures 2, 5, S3), and that corals release fDOM that is distinct from other benthic reef constituents (Figure 2c, 4, 5)

Summary

Introduction

Coral reefs are highly productive ecosystems that thrive in relatively oligotrophic tropical waters, in part by intense recycling of limited nutrients through a highly diverse and active microbial community (Raina et al 2009; Cardini et al 2015). The composition of exudates released by different primary producers on reefs is a key determinant of the structure of the microbial communities that drive the microbial loop, including both bacterioplankton (Nelson et al 2013; Haas et al 2016) and and likely the diverse and abundant microbial consortia that associate with reef organisms and surfaces (Ritchie and Smith 1995; Lee et al 2016). The metabolic activity of coral and algal-associated microbial communities directly influences competition between these benthic holobionts (Barott and Rohwer 2012). Determining how exudate DOM production and composition varies among different benthic taxa is fundamental to understanding coral reef ecology

Methods

Results

Conclusion