• Energy Research

To predict impacts of ocean acidification and warming on the responses of marine populations, it is important to determine an organism’s capacity for phenotypic plasticity and genetic adaptation. We determined the effects of near-future acidification and warming across the life cycle of Heliocidaris erythrogramma from fertilisation to metamorphosis in the progeny of 16 sire-dam crosses. Sources of variation in tolerance to warming (+3°C) and acidification (-0.3 to –0.5 pH units) were investigated for fertilisation, larvae and juveniles. Across all life stages, maternal legacy was important, with dam identity significantly interacting with stressors. Across the genotypes tested, fertilisation was negatively affected by increased temperature, but not low pH. Larval development was compromised by low pH, but not increased temperature. By the juvenile stage, no impact of warming or acidification was evident, likely due to selective mortality of sensitive individuals, indicating the presence of a subset of resilient progeny. Across all treatments, the juveniles exhibited a similar ability to calcify. The impact of treatments on development was influenced by parental identity, with the offspring of some sire-dam pairs more sensitive than others. That the progeny of some sire-dam pairs showed high stress tolerance indicates the potential for selection of resistant genotypes and adaptation that could facilitate the persistence of H. erythrogramma populations. Performance of progeny was not consistent across development, with the impact of stressors differing depending on developmental stage. This shows the importance of assessing climatic change across multiple stages in the life cycle.

The thermal response of the amphipod Sunamphitoe parmerong was contrasted between unacclimated 'wild' and acclimated populations. Brooding females were allocated to 17 °C or 23 °C treatments and their progeny developed to adulthood at the same temperature. Tolerance to acute thermal challenge (26-36 °C) was determined. The 17 °C and 23 °C acclimated S. parmerong had a 0.45 and 0.64 risk of death compared to the unacclimated individuals. The upper lethal temperature (LT50) was 27.4 °C for the unacclimated group and 29.6 °C and 30.4 °C for the 17 °C and 23 °C acclimated groups, respectively. Acclimation shifted their LT50 by 2.2 °C and 3 °C, respectively. The wild population exhibited high variability in thermal tolerance, potentially due to their environmental history and greater diversity of genotypes. After acclimation S. parmerong had decreased variability in thermal tolerance and that of the 23 °C group shifted by 1 °C compared with the 17 °C group. These results indicate developmental phenotypic plasticity or differential survival of resilient progeny as potential mechanisms to facilitate persistence in a warming ocean.

Increasing sea surface temperatures are predicted to alter marine plant-herbivore interactions and, thus, the structure and function of algal and seagrass communities. Given the fundamental role of host plant quality in determining herbivore fitness, predicting the effects of increased temperatures requires an understanding of how temperature may interact with diet quality. We used an herbivorous marine amphipod, Sunamphitoe parmerong, to test how temperature and diet interact to alter herbivore growth, feeding rates, survival, and fecundity in short- and long-term assays. In short-term thermal stress assays, S. parmerong was tolerant to the range of temperatures that it currently experiences in nature (20-26 °C), with mortality at temperatures > 27 °C. In longer term experiments, two generations of S. parmerong were reared in nine combinations of temperature (ambient, + 2, + 4 °C) and diet (two high- and one low-quality algal species) treatments. Temperature and diet interacted to determine total numbers of amphipods in the F1 generation and the potential F2 population size (sum of brooded eggs and newly hatched juveniles). The size and development rate of F1 individuals were affected by diet, but not temperature. Consumption rates per capita were highest at intermediate temperatures but could not explain the observed differences in survival. Our results show that predicting the effects of increasing temperature on marine herbivores will be complicated by variation in host plant quality, and that climate-driven changes to plant availability will affect herbivore performance, and thus the strength of plant-herbivore interactions.

Climate-driven changes in biotic interactions can profoundly alter ecological communities, particularly when they impact foundation species. In marine systems, changes in herbivory and the consequent loss of dominant habitat forming species can result in dramatic community phase shifts, such as from coral to macroalgal dominance when tropical fish herbivory decreases, and from algal forests to ‘barrens’ when temperate urchin grazing increases. Here, we propose a novel phase-shift away from macroalgal dominance caused by tropical herbivores extending their range into temperate regions. We argue that this phase shift is facilitated by poleward-flowing boundary currents that are creating ocean warming hotspots around the globe, enabling the range expansion of tropical species and increasing their grazing rates in temperate areas. Overgrazing of temperate macroalgae by tropical herbivorous fishes has already occurred in Japan and the Mediterranean. Emerging evidence suggests similar phenomena are occurring in other temperate regions, with increasing occurrence of tropical fishes on temperate reefs.

Significance Consumption transfers energy and materials through food chains and fundamentally influences ecosystem productivity. Therefore, mapping the distribution of consumer feeding intensity is key to understanding how environmental changes influence biodiversity, with consequent effects on trophic transfer and top–down impacts through food webs. Our global comparison of standardized bait consumption in shallow coastal habitats finds a peak in feeding intensity away from the equator that is better explained by the presence of particular consumer families than by latitude or temperature. This study complements recent demonstrations that changes in biodiversity can have similar or larger impacts on ecological processes than those of climate.

In this study, we used a trait-based approach to quantify morphological varability in subtidal rocky reefs dominated by the algal genus Sargassum along a latitudinal gradient, from subtropical to cool temperate sites, in south-eastern Australia (~900 km). We tested whether large-scale variation in sea surface temperature (SST), site exposure and nutrient availability can predict algal biomass and individual morphology. Morphological traits of Sargassum collected across 6 degree of latitude along the south-eastern coast of Australia

Thousands of species have been introduced to new ranges worldwide. These introductions provide opportunities for researchers to study evolutionary changes in form and function in response to new environmental conditions. However, almost all previous studies of morphological change in introduced species have compared introduced populations to populations from across the species' native range, so variation within native ranges probably confounds estimates of evolutionary change. In this study, we used microsatellites to locate the source population for the beach daisy Arctotheca populifolia that had been introduced to eastern Australia. We then compared four introduced populations from Australia with their original South African source population in a common-environment experiment. Despite being separated for less than 100 years, source and introduced populations of A. populifolia display substantial heritable morphological differences. Contrary to the evolution of increased competitive ability hypothesis, introduced plants were shorter than source plants, and introduced and source plants did not differ in total biomass. Contrary to predictions based on higher rainfall in the introduced range, introduced plants had smaller, thicker leaves than source plants. Finally, while source plants develop lobed adult leaves, introduced plants retain their spathulate juvenile leaf shape into adulthood. These changes indicate that rapid evolution in introduced species happens, but not always in the direction predicted by theory.