Valter Amaral

The proteomes of Sydney rock oysters vary spatially according to exposure to acid sulfate runoff

Runoff from acid sulfate soils (ASS) has severe environmental and economic impacts on estuarine ecosystems. Oysters display reduced abundance, growth rate and shell thickness when exposed to ASS runoff, yet the molecular underpinnings of their responses have not been explored. We hypothesised that the proteomes of wild Sydney rock oysters, Saccostrea glomerata, would differ between populations recurrently exposed to ASS compared with those unaffected by runoff from ASS. We used two-dimensional electrophoresis to compare protein abundances in the gills of S. glomerata collected from two sites close to (acidified) and two sites away from (reference) major ASS outflow drains in a south-east Australian estuary. Approximately 5% of the proteome was differentially expressed between oysters from acidified and reference sites, with five protein spots more abundant and one less abundant at the sites close to drains. Another protein spot was present only in oysters from reference sites. This study is the first screening of spatial variation in the protein expression of S. glomerata with respect to discharge from ASS. Altered protein expression may underpin short-term inducible responses to ASS runoff, or genetic resistance acquired through recurrent exposure of populations to the stressor.

Effect of runoff from acid-sulfate soils on pneumatophores of the grey mangrove, Avicennia marina

Runoff from acid-sulfate soils (ASS) is increasingly threatening the structure and function of estuarine ecosystems worldwide. Along the eastern coast of Australia, sulfuric acid is known to affect the growth and survival of mangrove saplings; however, impacts of ASS runoff on the structure and function of established mangrove trees are unclear. Pneumatophores, the aerial roots produced by some species of mangrove, are critical sites of gas exchange, allowing these species to persist in waterlogged soils. They also provide physical structure in estuarine sediments, facilitating communities of algae, invertebrates and, at high tide, fish. We tested the hypotheses that Avicennia marina (Forsk.) Vierh. pneumatophores would be less abundant, shorter, thinner and weaker close to major ASS outflow drains. Sampling at sites close to and away from drains within each of two estuaries of New South Wales, Australia, showed no effect of exposure to runoff on pneumatophore density or thickness. Pneumatophores were, however, shorter (~2 cm) and weaker (up to two-fold) at ASS-affected than reference sites. Although the reduced length and strength of pneumatophores at acidified sites may limit the number of epifaunal molluscs they can support, the persistence of dense pneumatophores indicates that the capacity to benefit invertebrates and fish remains.

Implications of habitat-specific growth and physiological condition on juvenile crab population structure

Post-settlement processes can regulate the size and structure of marine invertebrate and fish populations. Faster growth and better physiological condition generally increase the survival potential of early juveniles, being usually associated with structurally complex habitats. Successive cohorts of early juvenile Carcinus maenas were followed in sandy and seagrass (Zostera noltii) habitats in the Mira Estuary, Portugal, to estimate growth and physiological condition (evaluated by RNA/DNA ratio) of juvenile populations. Mean cohort growth was similar in both habitats. However, in the sandy habitat, population size structure progressed to cohorts of larger carapace width (CW) and the RNA/DNA ratio was always higher than in the Z. noltii habitat. In this habitat, cohorts of low CW prevailed throughout and RNA/DNA ratio only increased after ~5.0 mm CW. Higher densities characterising seagrass areas may result in higher competition for resources, limiting growth and condition and leading to dispersal to less populated habitats. Larger juveniles had the best physiological condition, especially early in the season. Seagrass habitats do not necessarily yield enhanced growth rates and physiological condition of early juvenile crabs in relation to sandy areas. Knowledge of such trends is vital to understand distribution and abundance patterns of fish and marine invertebrate populations.

Wild populations of Sydney rock oysters differ in their proteomic responses to elevated carbon dioxide

This study tested the proteomic responses of three spatially distinct Sydney rock oyster populations to elevated pCO2. Oysters were collected from environmentally different sites, two chronically affected by acid sulfate soil. Oysters from each of the three populations were exposed to ambient (380µatm) or elevated (856 and 1500µatm) pCO2 for 4 weeks. Subsequent proteomic analysis from haemolymph revealed that (1) there were differences between the proteomes of the three populations after exposure to ambient pCO2, and (2) the different oyster populations mounted significantly different responses to elevated pCO2. Proteins that differed significantly in concentration between pCO2 treatments fell into five broad functional categories: energy metabolism, cellular stress responses, the cytoskeleton, protein synthesis and the extracellular matrix. This is consistent with the hypothesis that environmental stress in oysters leads to a generic response involving increased mitochondrial energy production to maintain cellular homeostasis. Proteins involved in the cytoskeleton and energy metabolism were the most differentially expressed and were seen in all three oyster populations. Differences between populations in their proteomic responses suggested that the local environments from which oysters originate may affect their capacity to respond to ocean acidification.