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

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.

Cobble community DNA as a tool to monitor patterns of biodiversity within kelp forest ecosystems

“…Moreover, abalone show a strong positive relationship with a coralline alga from Lithophylloideae and Corallinales; yet, PISCO do not record coralline alga and no do find this relationship in their analysis (Figure ). O’Leary et al () demonstrated that some species of CCA induce a settlement response more strongly than others, indicating preference and specificity for cues associated with abalone (see also Morse, Hooker, Duncan, & Jensen, ).…”

“…Crustose coralline algae (CCA; Rhodophyta, Corallinaceae) and other red algae found growing on cobbles have been shown to be one of the primary inducers of settlement and metamorphosis in several invertebrate species (e.g. sea urchins, abalones and limpets; O’Leary et al, ). We found the presence of red abalone ( Haliotis rufescens ) on 60% of the cobbles (59/97) with the highest occurrence at Hopkins (23) and at Lovers Point (21), while Point Pinos (15) showed the least detection.…”

“…The kelp forest floor includes bedrock and cobbles spread throughout or partly imbedded in the kelp bed over a range of depths (Lieberman, John, & Lieberman, ). These natural substrates are typically covered with red algae, including the coralline algae that have been shown to prompt larval settlement for many species (reviewed in O’Leary et al, ). Along the coast of California, cobbles are used as replicable sampling units for monitoring during annual abalone recruitment surveys (Rogers‐Bennett et al, ).…”

Trophic control of cryptic coralline algal diversity

“…Coralline algae play essential roles in marine ecosystems and are ubiquitous in most rocky reef habitats (10,23). Corallines cement coral reefs together (37), act as a substrate for algae and surf grass (38), facilitate kelp recruitment (39,40), and chemically induce larval settlement of a wide phylogenetic range of invertebrates (41)(42)(43)(44)(45). However, our ability to effectively differentiate coralline species has been obscured by deceptively simple morphologies, rampant convergent evolution, and misunderstood phenotypic variation (46,47).…”

“…DNA barcoding techniques allow for the accurate identification of species and have demonstrated that some of the most common species under the morphological species concept in fact represent several to more than a dozen distinct genetic species (46,48,49). Widespread cryptic diversity is potentially problematic for ecologists because coralline species can differ in growth rate (43,50), competitive ability (28,32,33), resistance to environmental stress (51,52), and their effects on invertebrate recruitment (43,53). Therefore, changes in the diversity of coralline assemblages could influence their contributions to ecosystem function, yet shifts could easily go undetected due to the cryptic nature of coralline taxa.…”