No abstract

Acropora millepora colony thriving under extreme low pH, low oxygen and highly variable temperatures of a Great Barrier Reef mangrove lagoon.

Coral nursery and outplanting practices have grown in popularity worldwide for targeted restoration of degraded "high value" reef sites, and recovery of threatened taxa. Success of these practices is commonly gauged from coral propagule growth and survival, which fundamentally determines the return-on-effort (RRE) critical to the cost-effectiveness and viability of restoration programs. In many cases, RRE has been optimized from past successes and failures, which therefore presents a major challenge for locations such as the Great Barrier Reef (GBR) where no local history of restoration exists to guide best practice. In establishing the first multi-taxa coral nursery on the GBR (Opal Reef, February 2018), we constructed a novel scoring criterion from concurrent measurements of growth and survivorship to guide our relative RRE, including nursery propagule numbers (stock density). We initially retrieved RRE scores from a database of global restoration efforts to date (n = 246; 52 studies) to evaluate whether and how success commonly varied among coral taxa. We then retrieved RRE scores for Opal Reef using initial growth and survivorship data for six key coral taxa, to demonstrate that RRE scores were high for all taxa predominantly via high survivorship over winter. Repeated RRE scoring in summer is therefore needed to capture the full dynamic range of success where seasonal factors regulating growth versus survivorship differ. We discuss how RRE scoring can be easily adopted across restoration practices globally to standardize and benchmark success, but also as a tool to aid decision-making in optimizing future propagation (and outplanting) efforts.

Re‐attaching or out‐planting coral as fragments, colonies, and on larval settlement devices to substrates is a major bottleneck limiting scalabilty and viability of reef restoration practices. Many attachment approaches are in use, but none that are low‐cost, opportunistic, rapid but effective, for integration into existing tour operations on the Great Barrier Reef (GBR) where staff and boat time is a major cost and chemical fixatives cannot be easily used. We describe a novel attachment device—Coralclip®—developed to meet this need and so aid maintenance and restoration of GBR tourism sites. Coralclip® is a stainless steel springclip attached by a nail integrated through the spring coil, and can be deployed with a coral fragment in as fast as 15 seconds. Initial laboratory tests demonstrated that Coralclip® secured coral fragments or larval settlement tiles under dynamic flow regimes characteristic of exposed reefs. Coral out‐planting from fragments of opportunity and from nurseries (n = 4,580; 0.3–1.9 coral/minute; US$0.6–3.0/coral deployed) or larval settlement tiles (n = 400; 2.5 tiles/minute; US$0.5 tile deployed−1) when deployed by divers from routine boat operations at Opal Reef confirmed highly effective attachment, with ≤15% failure of clips found after 3–7 months. We discuss how Coralclip® is a cost‐effective means to support reef maintenance and restoration practices.

Symbiosis between reef-building corals and unicellular algae (Symbiodiniaceae) fuels the growth and productivity of corals reefs. Capacity for Symbiodiniaceae to fix inorganic carbon (Ci) and translocate carbon compounds to the host is central to coral health, but how these processes change for corals thriving in environmental extremes remains largely unresolved. We investigate how a model coral -Pocillopora acuta -persists from a reef habitat into an adjacent extreme mangrove lagoon on the Great Barrier Reef. We combine respirometry and photophysiology measurements, Symbiodiniaceae genotyping, and 13 C labelling to compare P. acuta metabolic performance across habitats, in relation to the Ci uptake and 27 translocation capacity by symbionts' autotrophy. We show that differences in P. acuta 28 metabolic strategies across habitats align with a shift in dominant host-associated 29 Symbiodiniaceae taxon, from Cladocopium in the reef to Durusdinium in the mangroves. This 30 shift corresponded with a change in 'photosynthetic strategy', with P. acuta in the mangroves 31 utilising absorbed light for photochemistry over non-photochemical quenching. Mangrove 32 corals translocated similar proportions of carbon compared to the reefs, despite a lower Ci uptake. These trends indicate that coral survival in mangrove environments occurs through sustained translocation rate of organic compounds from coral symbionts to host. Introduction 36The ecological success of reef-building corals resides on their ability to establish and 37 maintain metabolic exchanges through an effective symbiotic association with dinoflagellates 38 from the family Symbiodiniaceae. Symbiodiniaceae fuel their hosts with organic carbon by fixing inorganic carbon (Ci) through photosynthesis (Davy et al. 2012). While Ci uptake rates by the algal symbionts have rarely been measured, they appear strongly regulated by environmental factors, such as availability of CO2 (pCO2) (Suggett et al. 2012b; Brading et al. 42 2013) and temperature (Oakley et al. 2014). Recent work on cultured Symbiodiniaceae 43 revealed that different environmental optima primarily drive variation in Ci uptake rates (Ros 44 et al. 2020). Within reef systems where Symbiodiniaceae are hosted within cnidarian tissues, symbiont cells are typically carbon-limited (Smith and Muscatine 1999; Doherty 2009; Towanda and Thuesen 2012); as such, cnidarians can exhibit a stimulated carbon metabolism under naturally higher pCO2 (more acidic) environments (Suggett et al. 2012b). The efficiency 48 of Symbiodiniaceae carbon metabolism across environments thus appears an important trait in 49 supporting their host's survival, and a means to cope with stressful conditions. 50 51 Associations between the cnidarian host and specific genera, species or strains of 52 Symbiodiniaceae profoundly influence the stress resilience of their coral host (Berkelmans and 53

No abstract

Coral reefs are deteriorating worldwide prompting reef managers and stakeholders to increasingly explore new management tools. Following back-to-back bleaching in 2016/2017, multi-taxa coral nurseries were established in 2018 for the first time on the Great Barrier Reef (GBR) to aid reef maintenance and restoration at a “high-value” location–Opal Reef–frequented by the tourism industry. Various coral species (n = 11) were propagated within shallow water (ca. 4-7m) platforms installed across two sites characterised by differing environmental exposure–one adjacent to a deep-water channel (Blue Lagoon) and one that was relatively sheltered (RayBan). Growth rates of coral fragments placed onto nurseries were highly variable across taxa but generally higher at Blue Lagoon (2.1–10.8 cm2 month-1 over 12 months) compared to RayBan (0.6–6.6 cm2 month-1 over 9 months). Growth at Blue Lagoon was largely independent of season, except for Acropora tenuis and Acropora hyacinthus, where growth rates were 15–20% higher for December 2018-July 2019 (“warm season”) compared to August-December 2018 (“cool season”). Survivorship across all 2,536 nursery fragments was ca. 80–100%, with some species exhibiting higher survivorship at Blue Lagoon (Acropora loripes, Porites cylindrica) and others at RayBan (A. hyacinthus, Montipora hispida). Parallel measurements of growth and survivorship were used to determine relative return-on-effort (RRE) scores as an integrated metric of “success” accounting for life history trade-offs, complementing the mutually exclusive assessment of growth or survivorship. RRE scores within sites (across species) were largely driven by growth, whereas RRE scores between sites were largely driven by survivorship. The initial nursery phase of coral propagation therefore appears useful to supplement coral material naturally available for stewardship of frequently visited Great Barrier Reef tourism (high-value) sites, but further assessment is needed to evaluate how well the growth rates and survival for nursery grown corals translate once material is outplanted.

Active chlorophyll a fluorometry is a well-established tool for noninvasively diagnosing coral functional state, but has not yet been developed as a rapid phenotyping (functional screening) platform as for agriculture and forestry. Here, we present a proof-of-concept using Light-Induced Fluorescence Transient-Fast Repetition Rate fluorometry (LIFT-FRRf) to identify coral photobiological-based phenotypes in the context of rapidly scaling coral propagation practices on the northern Great Barrier Reef. For example, resolving light niche plasticity to inform transplantation, and identifying functionally diverse colonies to maximize stock selection. We first used optically diverse laboratory-reared corals and coral endosymbiont (Symbiodiniaceae) isolates to develop a phenotyping approach integrating FRRf instantaneous kinetic parameters (light harvesting, electron turnover rates) and light-dependent parameters (dynamic "quenching" terms, saturating light intensity [E K ]). Subsequent field-based LIFT-FRRf phenotyping of coral from a selective (2-4 m depth) reef habitat revealed that widely topographically dispersed plating Acropora taxa exhibited broad light niche plasticity (E K variance) underpinned by multiple phenotypes that were predominantly differentiated by minimum electron turnover capacity; fluorometer configurations that cannot resolve kinetic parameters will thus likely have more limited capacity to resolve phenotypes. As such, plating Acropora have broad propagation potential in terms of multiple functional variants for stock and across diverse light environments (growth, transplantation). In contrast, coral taxa (Pocillopora verrucosa, Echinopora lamellosa) with relatively restricted topographic dispersion exhibited less light niche plasticity and only single phenotypes, thereby imposing more constraints for propagation. We discuss the core technical, operational, and conceptual steps required to develop more sophisticated coral phenotyping platforms.