Showing papers by "Gary A. Kendrick published in 2013"

Invasion Is a Community Affair: Clandestine Followers in the Bacterial Community Associated to Green Algae, Caulerpa racemosa, Track the Invasion Source

Abstract: Biological invasions rank amongst the most deleterious components of global change inducing alterations from genes to ecosystems. The genetic characteristics of introduced pools of individuals greatly influence the capacity of introduced species to establish and expand. The recently demonstrated heritability of microbial communities associated to individual genotypes of primary producers makes them a potentially essential element of the evolution and adaptability of their hosts. Here, we characterized the bacterial communities associated to native and non-native populations of the marine green macroalga Caulerpa racemosa through pyrosequencing, and explored their potential role on the strikingly invasive trajectory of their host in the Mediterranean. The similarity of endophytic bacterial communities from the native Australian range and several Mediterranean locations confirmed the origin of invasion and revealed distinct communities associated to a second Mediterranean variety of C. racemosa long reported in the Mediterranean. Comparative analysis of these two groups demonstrated the stability of the composition of bacterial communities through the successive steps of introduction and invasion and suggested the vertical transmission of some major bacterial OTUs. Indirect inferences on the taxonomic identity and associated metabolism of bacterial lineages showed a striking consistency with sediment upheaval conditions associated to the expansion of their invasive host and to the decline of native species. These results demonstrate that bacterial communities can be an effective tracer of the origin of invasion and support their potential role in their eukaryotic host's adaptation to new environments. They put forward the critical need to consider the 'meta-organism' encompassing both the host and associated micro-organisms, to unravel the origins, causes and mechanisms underlying biological invasions.

Aquaculture of Posidonia australis Seedlings for Seagrass Restoration Programs: Effect of Sediment Type and Organic Enrichment on Growth

Abstract: Seeds of the seagrass Posidonia australis are desiccation sensitive and as there is no seed dormancy seeds cannot be stored for use in restoration projects. To realize the restoration potential of seed-based restoration of Posidonia, this study investigated preconditioning seedlings of Posidonia in aquaculture facilities before transplanting to extend the restoration window from a few weeks (for fresh seed) to months or even years (for preconditioned seedlings). Here, we tested two levels of organic matter addition, 0 and 1.5% sediment dry weight and three sediment types; two heterogeneous sediments typical of low-energy marine environments (1) unsorted calcareous and (2) unsorted silica, and a homogeneous sediment typical of high-energy marine habitats (3) well-sorted silica. We then evaluated seedling survival, biomass and development over a period of 7 months in tank culture. There was 100% survival over the 7-month experimental period for seedlings. Seedling leaf, root, rhizome, and total biomass increased when organic matter was added to unsorted calcareous and unsorted silica sediment but not well-sorted silica sediment, although this increase was significant only after 7 months of growth. The characteristics of the sediment also influenced seedling root length and architecture. Root length and number of lateral root branches were greatest in unsorted sediments and when organic matter was present. This study demonstrates that tank culture of P. australis enabled seedlings to be available for restoration purposes for at least 7 months, and with modification of the sediment composition, larger P. australis seedlings with more substantial root systems can be produced.

Reproductive synchrony in a habitat-forming kelp and its relationship with environmental conditions

Abstract: Key biological processes such as the timing and synchrony of reproduction, are sensitive to fluctuations in the environment, as well as alterations in the physiology and behaviour of individuals and the ecology of populations. The main aim of this study was to identify patterns in reproductive timing and relationships with prevailing environmental conditions, for the major habitat-forming alga in temperate Australia, Ecklonia radiata (C. Agardh) J. Agardh. We observed strong synchronous patterns of zoospore production across spatial scales from hundreds of metres to tens of kilometres, with populations of E. radiata reproducing from mid-summer to the end of autumn. High zoospore densities were positively related to sea temperature and E. radiata released zoospores in temperatures well above previously documented thermal tolerance limits for other Laminariales. Reproductive timing was also negatively related to seasonal increase in wave exposure. We conclude that E. radiata undergoes synchronous reproduction which can be linked to its annual growth cycle and natural environmental fluctuations, to promote growth and survival of recruits.

Coastal fish assemblages reflect geological and oceanographic gradients within an Australian zootone.

Abstract: Distributions of mobile animals have been shown to be heavily influenced by habitat and climate. We address the historical and contemporary context of fish habitats within a major zootone: the Recherche Archipelago, southern western Australia. Baited remote underwater video systems were set in nine habitat types within three regions to determine the species diversity and relative abundance of bony fishes, sharks and rays. Constrained ordinations and multivariate prediction and regression trees were used to examine the effects of gradients in longitude, depth, distance from islands and coast, and epibenthic habitat on fish assemblage composition. A total of 90 species from 43 families were recorded from a wide range of functional groups. Ordination accounted for 19% of the variation in the assemblage composition when constrained by spatial and epibenthic covariates, and identified redundancy in the use of distance from the nearest emergent island as a predictor. A spatial hierarchy of fourteen fish assemblages was identified using multivariate prediction and regression trees, with the primary split between assemblages on macroalgal reefs, and those on bare or sandy habitats supporting seagrass beds. The characterisation of indicator species for assemblages within the hierarchy revealed important faunal break in fish assemblages at 122.30 East at Cape Le Grand and subtle niche partitioning amongst species within the labrids and monacanthids. For example, some species of monacanthids were habitat specialists and predominantly found on seagrass (Acanthaluteres vittiger, Scobinichthys granulatus), reef (Meuschenia galii, Meuschenia hippocrepis) or sand habitats (Nelusetta ayraudi). Predatory fish that consume molluscs, crustaceans and cephalopods were dominant with evidence of habitat generalisation in reef species to cope with local disturbances by wave action. Niche separation within major genera, and a sub-regional faunal break, indicate future zootone mapping should recognise both cross-shelf and longshore environmental gradients.

Environmental influences on kelp performance across the reproductive period: an ecological trade-off between gametophyte survival and growth?

Abstract: Most kelps (order Laminariales) exhibit distinct temporal patterns in zoospore production, gametogenesis and gametophyte reproduction. Natural fluctuations in ambient environmental conditions influence the intrinsic characteristics of gametes, which define their ability to tolerate varied conditions. The aim of this work was to document seasonal patterns in reproduction and gametophyte growth and survival of Ecklonia radiata (C. Agardh) J. Agardh in south-western Australia. These results were related to patterns in local environmental conditions in an attempt to ascertain which factors explain variation throughout the season. E. radiata was fertile (produced zoospores) for three and a half months over summer and autumn. Every two weeks during this time, gametophytes were grown in a range of temperatures (16–22°C) in the laboratory. Zoospore densities were highly variable among sample periods; however, zoospores released early in the season produced gametophytes which had greater rates of growth and survival, and these rates declined towards the end of the reproductive season. Growth rates of gametophytes were positively related to day length, with the fastest growing recruits released when the days were longest. Gametophytes consistently survived best in the lowest temperature (16°C), yet exhibited optimum growth in higher culture temperatures (20–22°C). These results suggest that E. radiata releases gametes when conditions are favourable for growth, and E. radiata gametophytes are tolerant of the range of temperatures observed at this location. E. radiata releases the healthiest gametophytes when day length and temperature conditions are optimal for better germination, growth, and sporophyte production, perhaps as a mechanism to help compete against other species for space and other resources.

High Sulfide Intrusion in Five Temperate Seagrasses Growing Under Contrasting Sediment Conditions

Abstract: Five temperate seagrasses (Amphibolis antartica, Halophila ovalis, Posidonia australis, Posidonia sinuosa and Zostera nigricaulis) were surveyed along the south-west coast of Western Australia. These morphological different seagrasses grow in contrasting sediments with large variations in sedimentary organic matter, carbonate and iron contents. We tested if sulfur composition in the plants responded to sulfur dynamics in the sediments and if plant morphology affected the sulfur composition of the plants. The sediments were characterized by low sulfate reduction rates (<9 mmol m−2day−1), low concentrations of dissolved sulfides in the pore waters (<74 μM) and low burial of sulfides (total reducible sulfur <0.8 mol m−2) in the sediments. However, all seagrasses showed high intrusion in the below-ground parts with up to 84 % of the sulfur derived from sedimentary sulfides. There were no direct links between sulfur in the plants and sulfur dynamics in the sediments, probably due to low iron contents in the sediments limiting the buffering capacity of the sediments and exposing the plants to sulfides despite low rates of production and low pools of sulfides. The intrusion was linked between plant compartments (roots, rhizomes and leaves) for the two small species (H. ovalis and Z. nigricaulis), whereas the intrusion into the leaves was limited for the larger species (P. australis and P. sinuosa) and for A. antarctica, where extensive rhizomes and roots and the long stem for A. antarctica separate the leaves from the sediment compartment. Elevated intrusion was observed at two study locations, where natural deposition of organic matter or nutrient enrichment may be contributing factors to enhanced sulfide pressure.

A genetic assessment of a successful seagrass meadow (Posidonia australis) restoration trial

Abstract: Seagrass meadows are in decline globally. Although numerous experimental methods have been implemented to restore meadows, few have been successful in the long term. Poor decisions on the sourcing of transplants from donor sites, including poor genetic integration and/or low genetic diversity, may impact on restoration success. However, despite evidence to suggest a positive association between genetic diversity and ecological resilience, there is usually little or no input from genetic data to inform on the genetic management of ecological restoration. Cockburn Sound has seen a 77% decline in seagrass cover since 1967. A transplant trial was conducted between 2004 and 2008 with sprigs of Posidonia australis being planted into a bare sand area. Survival was monitored annually, and in 2012, we compared genetic diversity in this transplant area with the original donor site. Genetic diversity in the restored meadow was very high and comparable to the donor site, with no genetic differentiation detected. The high level of genetic diversity and choice of site may have played an important role in the success of this restoration trial. The observed natural recruits around the site after establishment of transplants suggest that local restoration efforts may improve seafloor habitat and facilitate natural expansion of the meadow.

Nesting behaviour of a temperate damselfish (Parma mccullochi) and its influence on algae

Abstract: Many pomacentrid fishes spawn demersally, often onto nest sites of filamentous algae The temperate Western Australian pomacentrid P mccullochi spawns onto such nest sites During preliminary observations nest sites with visibly different algal structures were observed, with the filamentous algal cover of some nests being greatly reduced compared to others These observations led us to hypothesise that algal management by this species would lead to a large change in the algal structure of nest sites, through more intense disturbance processes than have been described in tropical herbivorous pomacentrids when maintaining their algal feeding areas Behavioural observations and collection of algae from nest sites revealed that in late spring and summer P mccullochi maintained and defended a nesting site that was populated by filamentous algae Fish with nests defended the territory more intensively than fish without nests, at a cost of reduced feeding rates The algae within the nest sites progressed throu