Niche differentiation of ammonia-oxidising archaea (AOA) and bacteria (AOB) in response to paper and pulp mill effluent.

Sediment organic loading has been shown to affect estuarine nitrification and denitrification, resulting in changes to sediment biogeochemistry and nutrient fluxes detrimental to estuarine health. This study examined the effects of organic loading on nutrient fluxes and microbial communities in sediments receiving effluent from a paper and pulp mill (PPM) by applying microcosm studies and molecular microbial ecology techniques. Three sites near the PPM outfall were compared to three control sites, one upstream and two downstream of the outfall. The control sites showed coupled nitrification-denitrification with minimal ammonia release from the sediment. In contrast, the impacted sites were characterised by nitrate uptake and substantial ammonia efflux from the sediments, consistent with a decoupling of nitrification and denitrification. Analysis of gene diversity demonstrated that the composition of nitrifier communities was not significantly different at the impacted sites compared to the control sites; however, analysis of gene abundance indicated that whilst there was no difference in total bacteria, total archaea or ammonia-oxidising archaea (AOA) abundance between the control and impacted sites, there was a significant reduction in ammonia-oxidising bacteria (AOB) at the impacted sites. The results of this study demonstrate an effect of organic loading on estuarine sediment biogeochemistry and highlight an apparent niche differentiation between AOA and AOB.

Fine-scale spatial and temporal variations in diets of the pipefish Stigmatopora nigra within seagrass patches.

Diets of the pipefish Stigmatopora nigra were analysed to determine if food availability was causing S. nigra to distribute according to habitat edge effects. Gut analysis found little difference in the diets of S. nigra at the edge and interior of seagrass patches, regardless of time of day or season. Fish diets did, however, vary with seagrass density: S. nigra in denser seagrass consumed more harpacticoid copepods and fewer planktonic copepods. The lack of difference in prey eaten by S. nigra at the edge and interior of patches suggests either that food was not determining S. nigra distribution patterns within patches or that differences in fish densities across patches meant that relative fish-prey densities were similar at edge and interior positions. Alternatively, any edge effects in diet might be masked by gradients in seagrass structure.

Phenotype-environment mismatches reduce connectivity in the sea.

The connectivity of marine populations is often surprisingly lower than predicted by the dispersal capabilities of propagules alone. Estimates of connectivity, moreover, do not always scale with distance and are sometimes counterintuitive. Population connectivity requires more than just the simple exchange of settlers among populations: it also requires the successful establishment and reproduction of exogenous colonizers. Marine organisms often disperse over large spatial scales, encountering very different environments and suffering extremely high levels of post-colonization mortality. Given the growing evidence that such selection pressures often vary over spatial scales that are much smaller than those of dispersal, we argue that selection will bias survival against exogenous colonizers. We call this selection against exogenous colonizers a phenotype-environment mismatch and argue that phenotype-environment mismatches represent an important barrier to connectivity in the sea. Crucially, these mismatches may operate independently of distance and thereby have the potential to explain the counterintuitive patterns of connectivity often seen in marine environments. We discuss how such mismatches might alter our understanding and management of marine populations.

Roles of larval supply and behavior in determining settlement of barnacles in a temperate mangrove forest.

Recruitment is often a major influence on the spatial distribution of populations of benthic marine invertebrates, but the contributions of different components of recruitment are not well known, with the added complication that the relative importance of various life-history processes may be scale-dependent. Previously, we have shown that over a large scale across a mangrove (Avicennia marina) forest in southeastern Australia, settlement of the barnacle Elminius covertus explained its patterns of recruitment, which in turn explained the distribution of adults on mangrove pneumatophores. Post-settlement mortality had little influence on this pattern. In contrast, small-scale vertical distributions of adult barnacles along individual pneumatophores were determined by the pattern of recruitment, which differed from the pattern of settlement, so post-settlement mortality determined the vertical patterns of adults.In this study, we tested whether larval supply and/or settlement behavior influence the observed settlement patterns of E. covertus across a forest (from seaward to landward zones). We also tested whether larval supply could explain the vertical settlement patterns along the pneumatophores. A pumping system was used to collect cypris larvae from seaward, mid and landward zones of a mangrove forest and an adjacent, unvegetated shore and from three heights above the sediment surface. We also used transplantation of wooden stakes bearing microbial films and barnacle recruits between horizontal zones of the forest to determine whether settlement was influenced by these films or recruits.Both cyprid supply and cyprid behavior were important factors in determining the patterns of settlement of E. covertus across the forest. Cyprid supply was a result of three-fold differences in immersion times of different (landward, mid and seaward) zones across the forest and a decrease in density of cyprids in the water column from the seaward zone of the forest to the landward sections. In the absence of mangroves immediately adjacent to the forest, there was no temporally consistent difference in cyprid density across the shore and even the differences in immersion time did not produce consistent differences in cyprid supply across the shore. Wooden substrata that had been immersed at seaward sections of the forest attracted consistently more settlers than substrata immersed initially at other sections of the forest and settlement could be induced beyond the normal distribution of adults of E. covertus by stakes transplanted from the seaward zone.The vertical settlement pattern could not be explained by the supply of cyprids, suggesting that larval behavior must determine the vertical settlement pattern.