Calcifying algae maintain settlement cues to larval abalone following algal exposure to extreme ocean acidification

Jennifer K O’Leary,Fiorenza Micheli,James P Barry,Donald C Potts,Stephen R Palumbi,Laura Rogers-Bennett,Paul W Gabrielson

doi:10.1038/s41598-017-05502-x

Abstract

Ocean acidification (OA) increasingly threatens marine systems, and is especially harmful to calcifying organisms. One important question is whether OA will alter species interactions. Crustose coralline algae (CCA) provide space and chemical cues for larval settlement. CCA have shown strongly negative responses to OA in previous studies, including disruption of settlement cues to corals. In California, CCA provide cues for seven species of harvested, threatened, and endangered abalone. We exposed four common CCA genera and a crustose calcifying red algae, Peyssonnelia (collectively CCRA) from California to three pCO2 levels ranging from 419–2,013 µatm for four months. We then evaluated abalone (Haliotis rufescens) settlement under ambient conditions among the CCRA and non-algal controls that had been previously exposed to the pCO2 treatments. Abalone settlement and metamorphosis increased from 11% in the absence of CCRA to 45–69% when CCRA were present, with minor variation among CCRA genera. Though all CCRA genera reduced growth during exposure to increased pCO2, abalone settlement was unaffected by prior CCRA exposure to increased pCO2. Thus, we find no impacts of OA exposure history on CCRA provision of settlement cues. Additionally, there appears to be functional redundancy in genera of CCRA providing cues to abalone, which may further buffer OA effects.

Highlights

Predictions of marine ecosystem function under future ocean acidification (OA) suggest that the acidification rate[1,2,3] is likely to overwhelm the capacity of many species to respond[4] because Ocean acidification (OA) is creating conditions organisms may not have experienced in their evolutionary history[5]
The few studies that have focused on the effects of OA on Crustose coralline algae (CCA) cues provided to settlers have focused on corals, and acidification of CCA led to reductions in coral settlement of up to 86% due to changes in settlement cues[25, 26]
Upwelling regions have highly variable pCO2 conditions that can result in periodic exposure to pH well below normal[38, 39]

Summary

Introduction

Predictions of marine ecosystem function under future ocean acidification (OA) suggest that the acidification rate[1,2,3] is likely to overwhelm the capacity of many species to respond[4] because OA is creating conditions organisms may not have experienced in their evolutionary history[5]. CCA are widespread and abundant (forming 25–70% of the benthos in tropical and temperate reefs15–17), and play important ecological roles including substrate consolidation, providing food for grazers, and providing space and cues for invertebrate larval settlement[15, 18, 19]. The role CCA (and potentially other red algal crusts) play in providing cues for invertebrate larval settlement is critical: loss or change in coralline crusts can cause dramatic reduction in recruitment[15, 22], indirectly altering invertebrate population dynamics. At least one type of non-coralline red algae induces abalone larval settlement (Hildenbrandia dawsonii)[23].changes in the settlement cues provided by crustose calcifying red algae (CCRA, including both CCA and other calcifying red crusts) may have ecosystem-level consequences, mediated by changes in settlement of invertebrate species[19, 24]. Exposure of tropical CCRA to OA has led to changes in both larval recruitment rate and larval preference for algal substrates[25]

Methods

Results

Discussion

Conclusion