Trapping of microplastics and other anthropogenic particles in seagrass beds: Ubiquity across a vertical and horizontal sampling gradient.

Seagrass beds can trap large amounts of marine debris leading to areas of accumulation, known as 'sinks', of anthropogenic particles. While the presence of vegetation can enhance accumulation, less is known about how the trapping effect changes from vegetated to less vegetated patches. To test this, vegetation and sediment were sampled along a vegetation percent cover gradient from the centre of seagrass beds to nearby less vegetated patches. To determine whether trapped particles can lead to increased accumulation in associated fauna, gastropods were also collected from the transects laid across this gradient. Extracted anthropogenic particles were counted and characterised. Particles were detected in all sample types and reached quantifiable limits in at least 50% of sediment and gastropod samples. There was no significant difference in the distribution of particles found in seagrass beds compared to less vegetated patches, suggesting other factors contribute to the trapping efficiency of biogenic habitats besides simply the presence or absence of vegetation.

Differential tolerance of species alters the seasonal response of marine epifauna to extreme warming.

Marine heatwaves are occurring with greater frequency and magnitude worldwide and can significantly alter community structure and ecosystem function. Predicting changes in community structure in extreme temperatures requires an understanding of variation among species in their thermal tolerance, and how potential acclimatization to recent temperatures influences survival. To address this, we determined the tolerance to extreme temperatures in a crustacean epifaunal assemblage that inhabits macroalgae in the southeast Australian ocean warming hotspot. Amphipods were the most abundant group and the thermal tolerance of the most abundant species (two in winter and four in summer) was tested to determine their thermal limits and probability of survival in near-future extreme temperatures. Survival, measured as time to immobilization, was compared across species, sexes, life stage and body size. The greatest variation in tolerance to extreme temperatures was among species (not body sizes or life stages), indicating that heatwaves could shift the composition of the macroalgal associated epifaunal assemblage. Comparison of recent thermal history (between 18 °C to 22 °C) revealed greater thermal tolerance of warm acclimatized individuals. Our results indicate that the impacts of a marine heatwave will depend on local species composition and their timing relative to recent climate conditions.

Thermal tolerance in the amphipod Sunamphitoe parmerong from a global warming hotspot, acclimatory carryover effects within generation.

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.

Sublethal effects of contaminants on marine habitat-forming species: a review and meta-analysis.

Contaminants may affect ecosystem functioning by reducing the fitness of organisms and these impacts may cascade through ecosystems, particularly if the sensitive organisms are also habitat-forming species. Understanding how sub-lethal effects of toxicants can affect the quality and functions of biogenic habitats is critical if we are to establish effective guidelines for protecting ecosystems. We carried out a global systematic review and meta-analysis critically evaluating contaminant effects on properties of habitat-formers linked to ecosystem functioning. We reviewed a total of 95 publications. However, 40% of publications initially captured by the literature search were identified as having flaws in experimental design and ~11% did not present results in an appropriate way and thus were excluded from the quantitative meta-analysis. We quantitatively reviewed 410 studies from 46 publications, of which 313 (~76%) were on plants and seaweeds, that is macro-algae, saltmarsh plants and seagrasses, 58 (~14%) studied corals and 39 (~10%) looked at toxicant impacts on bivalves, with 70% of those on mussels and the remaining studies on oysters. Response variables analysed were photosynthetic efficiency, amount of chlorophyll a (as a proxy for primary production) and growth of plants, seaweeds and corals as well as leaf area of plants. We also analysed filtration, growth and respiration rates of bivalves. Our meta-analysis found that chemical contaminants have a significant negative impact on most of the analysed functional variables, with the exception of the amount of chlorophyll a. Metals were the most widely harmful type of contaminant, significantly decreasing photosynthetic efficiency of kelps, leaf area of saltmarsh plants, growth of fucoids, corals and saltmarsh plants and the filtration rates of bivalves. Organic contaminants decreased the photosynthetic efficiency of seagrass, but had no significant effects on bivalve filtration. We did not find significant effects of polycyclic aromatic hydrocarbons on any of the analysed functional variables or habitat-forming taxa, but this could be due to the low number of studies available. A meta-regression revealed that relationships between concentrations of metal contaminants and the magnitude of functional responses varied with the type of metal and habitat-former. Increasing concentrations of contaminants significantly increased the negative effects on the photosynthetic efficiency of habitat-formers. There was, however, no apparent relationship between ecologically relevant concentrations of metals and effect sizes of photosynthetic efficiency of corals and seaweeds. A qualitative analysis of all relevant studies found slightly different patterns when compared to our quantitative analysis, emphasising the need for studies to meet critical inclusion criteria for meta-analyses. Our study highlights links between effects of contaminants at lower levels of organisation (i.e. at the biochemical and/or physiological level of individuals) and ecological, large-scale impacts, through effects on habitat-forming species. Contaminants can clearly reduce the functioning of many habitat-forming marine species. We therefore recommend the adoption of routine measures of functional endpoints in monitoring and conservation programs to complement structural measures.

Temperature effects on a marine herbivore depend strongly on diet across multiple generations.

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.