Aim Propagule size and output are critical for the ability of a plant species to colonize new environments. If invasive species have a greater reproductive output than native species (via more and/or larger seeds), then they will have a greater dispersal and establishment ability. Previous comparisons within plant genera, families or environments have conflicted over the differences in reproductive traits between native and invasive species. We went beyond a genus-, family-or habitat-specific approach and analysed data for plant reproductive traits from the global literature, to investigate whether: (1) seed mass and production differ between the original and introduced ranges of invasive species; (2) seed mass and production differ between invasives and natives; and (3) invasives produce more seeds per unit seed mass than natives.Location Global. MethodsWe combined an existing data set of native plant reproductive data with a new data compilation for invasive species. We used t -tests to compare original and introduced range populations, two-way ANOVAs to compare natives and invasives, and an ANCOVA to examine the relationship between seed mass and production for natives and invasives. The ANCOVA was performed again incorporating phylogenetically independent contrasts to overcome any phylogenetic bias in the data sets. ResultsNeither seed mass nor seed production of invasive species differed between their introduced and original ranges. We found no significant difference in seed mass between invasives and natives after growth form had been accounted for. Seed production was greater for invasive species overall and within herb and woody growth forms. For a given seed mass, invasive species produced 6.7-fold (all species), 6.9-fold (herbs only) and 26.1-fold (woody species only) more seeds per individual per year than native species. The phylogenetic ANCOVA verified that this trend did not appear to be influenced by phylogenetic bias within either data set. Main conclusionsThis study provides the first global examination of both seed mass and production traits in native and invasive species. Invasive species express a strategy of greater seed production both overall and per unit seed mass compared with natives. The consequent increased likelihood of establishment from longdistance seed dispersal may significantly contribute to the invasiveness of many exotic species.

Abstract:The National Oceanic and Atmospheric Administration's Coral Reef Watch program developed and operates several global satellite products to monitor bleaching-level heat stress. While these products have a proven ability to predict the onset of most mass coral bleaching events, they occasionally miss events; inaccurately predict the severity of some mass coral bleaching events; or report false alarms. These products are based solely on temperature and yet coral bleaching is known to result from both temperature and light stress. This study presents a novel methodology (still under development), which combines temperature and light into a single measure of stress to predict the onset and severity of mass coral bleaching. We describe here the biological basis of the Light Stress Damage (LSD) algorithm under development. Then by using empirical relationships derived in separate experiments conducted in mesocosm facilities in the Mexican Caribbean we parameterize the LSD algorithm and demonstrate that it is able to describe three past bleaching events from the Great Barrier Reef (GBR). For this limited example, the LSD algorithm was able to better predict differences in the severity of the three past GBR bleaching events, quantifying the contribution of light to reduce or exacerbate the impact of heat stress. The new Light Stress Damage algorithm we present here is potentially a significant step forward in the evolution of satellite-based bleaching products.

Cumulative impacts assessments on marine ecosystems have been hindered by the difficulty of collecting environmental data and identifying drivers of community dynamics beyond local scales. On coral reefs, an additional challenge is to disentangle the relative influence of multiple drivers that operate at different stages of coral ontogeny. We integrated coral life history, population dynamics, and spatially explicit environmental drivers to assess the relative and cumulative impacts of multiple stressors across 2,300 km of the world's largest coral reef ecosystem, Australia's Great Barrier Reef (GBR). Using literature data, we characterized relationships between coral life history processes (reproduction, larval dispersal, recruitment, growth, and mortality) and environmental variables. We then simulated coral demographics and stressor impacts at the organism (coral colony) level on >3,800 individual reefs linked by larval connectivity and exposed to temporally and spatially realistic regimes of acute (crownof-thorns starfish outbreaks, cyclones, and mass coral bleaching) and chronic (water-quality) stressors. Model simulations produced a credible reconstruction of recent (2008-2020) coral trajectories consistent with monitoring observations, while estimating the impacts of each stressor at reef and regional scales. Overall, simulated coral populations declined by one-third across the GBR, from an average of ~29% to ~19% hard coral cover. By 2020, <20% of the GBR had coral cover higher than 30%, a status of reef health corroborated by scarce and sparsely distributed monitoring data. Reef-wide annual rates of coral mortality were driven by bleaching (48%) ahead of cyclones (41%) and starfish predation (11%). Beyond the reconstructed status and trends, the model enabled the emergence of complex interactions that compound the effects of multiple stressors while promoting a mechanistic understanding of coral cover dynamics. Drivers of coral cover growth were identified; notably, water quality (suspended sediments) was estimated to delay recovery for at least 25% of inshore reefs. Standardized rates of coral loss and recovery allowed the integration of all cumulative impacts to determine the equilibrium cover for each reef. This metric, combined with maps of impacts, recovery potential, water-quality thresholds, and reef state metrics, facilitates strategic spatial planning and resilience-based management across the GBR.

Ocean acidification (OA) is predicted to reduce reef coral calcification rates and threaten the long-term growth of coral reefs under climate change. Reduced coral growth at elevated pCO2 may be buffered by sufficiently high irradiances; however, the interactive effects of OA and irradiance on other fundamental aspects of coral physiology, such as the composition and energetics of coral biomass, remain largely unexplored. This study tested the effects of two light treatments (7.5 versus 15.7 mol photons m−2 d−1) at ambient or elevated pCO2 (435 versus 957 µatm) on calcification, photopigment and symbiont densities, biomass reserves (lipids, carbohydrates, proteins), and biomass energy content (kJ) of the reef coral Pocillopora acuta from Kāne‘ohe Bay, Hawai‘i. While pCO2 and light had no effect on either area- or biomass-normalized calcification, tissue lipids gdw−1 and kJ gdw−1 were reduced 15% and 14% at high pCO2, and carbohydrate content increased 15% under high light. The combination of high light and high pCO2 reduced protein biomass (per unit area) by approximately 20%. Thus, under ecologically relevant irradiances, P. acuta in Kāne‘ohe Bay does not exhibit OA-driven reductions in calcification reported for other corals; however, reductions in tissue lipids, energy content and protein biomass suggest OA induced an energetic deficit and compensatory catabolism of tissue biomass. The null effects of OA on calcification at two irradiances support a growing body of work concluding some reef corals may be able to employ compensatory physiological mechanisms that maintain present-day levels of calcification under OA. However, negative effects of OA on P. acuta biomass composition and energy content may impact the long-term performance and scope for growth of this species in a high pCO2 world.

Many animal populations that are endangered in mainland areas exist in stable island populations, which have the potential to act as an ''ark'' in case of mainland population declines. Previous studies have found neutral genetic variation in such species to be up to an order of magnitude lower in island compared to mainland populations. If low genetic variation is prevalent across fitnessrelated loci, this would reduce the effectiveness of island populations as a source of individuals to supplement declining mainland populations or re-establish extinct mainland populations. One such species, the black-footed rock-wallaby (Petrogale lateralis lateralis), exists within fragmented mainland populations and small island populations off Western Australia. We examined sequence variation in this species within a fitness-related locus under positive selection, the MHC class II DAB b1 locus. The mainland populations displayed greater levels of allelic diversity (4-7 alleles) than the island population, despite being small and isolated, and contained at least two DAB gene copies. The island population displayed low allelic diversity (2 alleles) and fewer alleles per individual in comparison to mainland populations, and probably possesses only one DAB gene copy. The patterns of DAB diversity suggested that the island population has a markedly lower level of genetic variation than the mainland populations, in concordance with results from microsatellites (genotyped in a previous study), but preserved unique alleles which were not found in mainland populations. Where possible, conservation actions should pool individuals from multiple populations, not only island populations, for translocation programs, and focus on preventing further declines in mainland populations.

Ocean acidification changes the carbonate chemistry of seawater in a manner that reduces the biomineralisation rate of reef-building corals. Other effects of acidification on coral physiology are less well-explored, and recent debate has focused on whether ocean acidification causes a change in Symbiodinium densities within tropical and subtropical reef-building corals. Within the framework of null-hypothesis significance testing, some aquaria experiments have provided evidence for a decrease in symbiont densities within coral tissue under ocean acidification (whilst others have suggested an increase). However, null-effects have prevailed in the majority of such experiments, and so the question has remained unresolved. This study attempted to resolve this question using a meta-analytic framework, by establishing the effect sizes for symbiont density change under ocean acidification from a structured search of the literature. A regression of effect size (Hedge's d) versus level of ocean acidification revealed a statistically significant negative relationship, with symbiont 1 density per cm 2 decreasing as the level of ocean acidification increased. The decline amounted to an additional 0.07 standard deviations of difference in symbiont density between corals in control (near present day) and acidified seawater with every 100 μatm of increase in partial pressure of CO 2 in seawater (a relationship with an r 2 of 0.24). A further unresolved question is whether ocean acidification will synergistically exacerbate (or diminish) symbiont density reductions caused by elevated temperature. An analysis of covariance did not reveal a greater decline in symbiont densities with increasing acidification at elevated temperature compared to non-stressful temperature, though this latter analysis should be viewed as exploratory due to a lower sample size.The well-supported evidence for a decline in symbiont densities in tropical and subtropical corals under ocean acidification now provides an impetus for sustained investigation of the consequences of such a change for holobiont functioning and the broader function of the coral reef ecosystem.

Coral bleaching can have widespread impacts on reefs leaving many areas in need of coral recovery. While the long-term mitigation of bleaching requires transitioning to a low carbon economy, local management has focused on approaches that seek refugia from or tolerance to bleaching stressors, reduce additional stressors, or facilitate coral recovery. Here, we describe a tactical response to coral bleaching events that seeks to identify the most important reefs for driving imminent recovery. A bleaching recovery algorithm is described that identifies those reefs that provide the most important sources of coral larvae that supply many reefs in the early stages of post-bleaching recovery (i.e., reefs in need of coral larval supply). We describe the algorithm with a simple toy example and then apply it to the Great Barrier Reef, which has experienced three mass bleaching events in the last 5 yr. Once such reefs have been identified it makes practical sense to undertake a vulnerability assessment and if necessary reduce manageable stressors, such as outbreaks of crown-of-thorns starfish or anchor damage, so that critical sources of coral recovery are not depleted further. In short, algorithms like this can help managers target finite management resources, including restoration, to where they might be most effective in facilitating natural processes of recovery.

Cumulative impacts assessments on marine ecosystems have been hindered by the difficulty of collecting environmental data and identifying drivers of community dynamics beyond local scales. On coral reefs, an additional challenge is to disentangle the relative influence of multiple drivers that operate at different stages of coral ontogeny. We integrated coral life history, population dynamics and spatially-explicit environmental drivers to assess the relative and cumulative impacts of multiple stressors across 2,300 km of the world's largest coral reef ecosystem, Australia's Great Barrier Reef (GBR). Using literature data, we characterized relationships between coral life history processes (reproduction, larval dispersal, recruitment, growth and mortality) and environmental variables. We then simulated coral demographics and stressor impacts at the organism (coral colony) level on >3,800 individual reefs linked by larval connectivity, and exposed to temporally- and spatially-realistic regimes of acute (crown-of-thorns starfish outbreaks, cyclones and mass coral bleaching) and chronic (water quality) stressors. Model simulations produced a credible reconstruction of recent (2008-2020) coral trajectories consistent with monitoring observations, while estimating the impacts of each stressor at reef and regional scales. Overall, corals declined by one third across the GBR, from an average ~29% to ~19% hard coral cover. By 2020, less than 20% of the GBR had coral cover higher than 30%. Global annual rates of coral mortality were driven by bleaching (48%) ahead of cyclones (41%) and starfish predation (11%). Beyond the reconstructed status and trends, the model enabled the emergence of complex interactions that compound the effects of multiple stressors while promoting a mechanistic understanding of coral cover dynamics. Drivers of coral cover growth were identified; notably, water quality (suspended sediments) was estimated to delay recovery for at least 25% of inshore reefs. Standardized rates of coral loss and recovery allowed the integration of all cumulative impacts to determine the equilibrium cover for each reef. This metric, combined with maps of impacts, recovery potential, water quality thresholds and reef state metrics, facilitates strategic spatial planning and resilience-based management across the GBR.