The ecology of free-living nematodes in nearshore marine and estuarine sediments of the microtidal lower west coast of Australia.

The overarching aim of this thesis was to describe the ecology of the assemblages of free-living nematodes in the sediments of nearshore marine and estuarine waters on the microtidal lower west coast of Australia. The thesis also provides descriptions of ten previously undescribed species as well as develops and tests a habitat classification scheme for the Swan River Estuary using these biotic assemblages. The first section of my thesis has determined the ways in which the characteristics of the nematode assemblages in nearshore marine waters along the microtidal lower west coast of Australia are related to habitat type, time of year and shore-perpendicular zones. Three habitat types, which had previously been identified on the basis of a suite of enduring environmental characteristics, could be broadly described as highly sheltered from wave activity and containing dense seagrass (habitat type 1), moderately sheltered from wave activity and with sparse seagrass (habitat type 2) and relatively exposed to wave activity and with no seagrass (habitat type 6). Sampling in five consecutive seasons yielded > 15 000 nematodes, representing 75 species. The number of species and densities in habitat type 1, and particularly those in its subtidal zone, were far greater than those in the other two habitat types. Both of these biotic variables underwent marked seasonal changes, declining to low levels during winter. The compositions of the assemblages differed significantly among the three habitat types, with the differences between habitat types 1 and 6 being particularly marked. Paracomesoma sipho, Dichromadora sp., Marylynnia annae and Pomponema sp., which, on the basis of their buccal cavity morphology, are assumed to feed primarily on benthic diatoms, were particularly abundant at the most sheltered habitat type, whereas Gonionchus australis, Theristus sp. and Bathylaimus australis, which are assumed to be deposit feeders, were relatively abundant at the most highly exposed habitat type. The compositions of the assemblages differed among seasons and were most discrete in spring, due to marked increases in the densities of certain species. However, differences in the compositions in the different zones of each habitat type were relatively small, presumably reflecting the influence of the small tidal regime of this region. The second component of this thesis has determined the ways in which the density, number of species, species composition and trophic structure of free-living nematode assemblages in the subtidal waters of a large microtidal estuary change spatially and temporally, and has explored whether those four biotic characteristics are related to certain environmental factors. Based on data derived from samples collected seasonally at 12 sites throughout the estuary, the densities and number of species of nematodes decreased progressively with distance from estuary mouth, to reach a minimum at sites where salinities were most variable, and then increased slightly in the uppermost part of the estuary where salinities were least. Densities were also generally greatest in spring, due largely to increases in the abundance of epistrate-grazing species at the time when the amount of primary food (microphytobenthos) peaked. The spatial distribution of the composition of the nematode assemblages was closely correlated with salinity and, to a lesser extent, grain-size composition and amount of particulate organic material in the sediment (%POM). Although species composition changed sequentially along the estuary, the change was particularly pronounced between sites above and below the area where salinities started to decline markedly and become more variable and %POM increased markedly. This reflected, in particular, far greater abundances of Spirinia parasitifera at the six downstream sites, and of Theristus sp. 1 at the six sites further upstream. Species composition underwent pronounced seasonal cyclical changes at all sites, presumably reflecting interspecific differences in the timing of peak reproduction and thus of recruitment. The trophic structure of the nematode assemblages changed both spatially and temporally in relation to the relative abundance of different food sources. Thus, for example, non-selective deposit feeders, such as Theristus sp. 1, dominated samples in the upper estuary, where %POM was by far the greatest, and was rare or absent at downstream sites. Conversely, epistrate grazers, such as species of the Chromadoridae, were most abundant at downstream sites in spring, when the density of the microphytobenthos reached its maximum. The data for the nematode assemblages in nearshore subtidal marine sediments of the lower west coast of Australia were compared with those in nearshore subtidal sediments in the upper and lower regions of the Swan River Estuary. The densities and average species richness in cores from the marine environment were much lower than in cores from both estuarine regions. However, the total number of species found in the marine environment was much greater than in the estuary. The compositions of the nematode assemblages were more variable in marine than estuarine sediments. The assemblages from the two estuarine regions were far more similar to each other than to those from the marine region at a species level, and also, but to a lesser extent, at the generic and family levels. While the trophic compositions of the nematode assemblages in the upper estuarine region was dominated by non-selective deposit feeding species and those of the lower estuarine region were dominated by epistrate grazing species during spring and non-selective deposit feeding species in other seasons, the dominant functional feeding groups varied among the sites representing the marine region. That variability presumably reflects differences in the relative contributions of the different potential food sources. Surprisingly, the trophic composition in the upper estuarine region, i.e. comprising predominantly non-selective deposit feeders, was similar to that at the very different environment of the most exposed marine site. The dominance of this feeding group at the marine site is assumed to be attributable to the fact that the only food source of any note is POM and, even then, it occurs in only small amounts. Taxonomic descriptions have been produced for ten new species of nematodes found during the ecological studies of the free-living aquatic nematofaunas of south-western Australia. These species were chosen because they were members of families for which the other species had been described and, in a number of cases, were important for distinguishing between the compositions of a priori groups. They comprised four species of Axonolaimidae, representing the genera Ascolaimus, Parascolaimus, Odontophora and Parodontophora, and six species of Desmodoridae, representing single species of Bolbonema, Eubostrichus, Catanema and Leptonemella and two species of Onyx. As a complement to the nematological study of the Swan River Estuary, a novel habitat classification system was developed and then applied in this environment. This system was based on enduring environmental characteristics and employed the relatively new multivariate statistical routines SIMPROF and LINKTREE. The applicability of habitat types produced by this classification system to biotic assemblages was tested using the data for the estuarine nematode assemblages described above. The results demonstrate that the compositions of the assemblages differed significantly among each of the habitat types defined by the classification system. While there were also significant differences between the compositions of the nematofaunas at sites belonging to the same habitat type, the extent of these differences were generally less than those between habitat types. A significant and strong correlation was also found between the spatial pattern exhibited by the environmental characteristics used to define habitat types, and that of the nematofauna

Review of the exploitation of marine resources of the Australian Indian Ocean Territories: the implications of biogeographic isolation for tropical island fisheries

The small islands of the Indian Ocean Territories are isolated reefs in an expanse of open ocean of abyssal depth. The majority of marine species that live on their reefs and lagoons have settled there from remote locations. Colonising individuals are presumed to have come to the island as the result of unusual weather and current conditions and form populations that are, necessarily, largely self-sustaining. The isolated populations that make up many of the fish and invertebrate stocks at the Cocos (Keeling) and Christmas Islands rely almost exclusively on larvae returning to their home reef to settle, grow and ultimately reproduce to maintain their numbers. This insularity is, in many cases, a direct implication of the constraints imposed on species by their own biology and reproductive strategy. In the event that a species is lost from either of the islands, recolonisation is dependent on reoccurrence of the unusual colonisation events. The vulnerability of these stocks is further exacerbated by the tiny size of the islands. The small reefs and lagoon only have the capacity to sustain small stocks of fish and invertebrates, ones that are very much at risk to chance events such as localised overfishing, anoxia events or over predation

Human Capacity Building for Introduced Marine Pest Monitoring in Western Australia FRDC Report – Project 2009/319 Tactical Research Fund

OBJECTIVES: 1. To identify gaps in the Western Australian skill and knowledge base for the monitoring of introduced marine pests. 2. To establish a centralised source of skills and knowledge in W.A. to facilitate the planning, evaluation, and quality control of activities relating to Introduced Marine Pest (IMP) monitoring. 3. To provide an Australian best practice example and knowledge base to facilitate the consistent, effective and efficient implementation of the National Monitoring system for IMPs

6500 BP Oldsquaw Duck (Clangula hyemalis) from Northern Ellesmere Island, Arctic Archipelago, Canada

A nearly complete skeleton, including partially preserved feathers, of an Oldsquaw duck (Clangula hyemalis L.) was recovered from Holocene marine deposits in Clements Markham Inlet, Ellesmere Island, N.W.T., Canada. The specimen was 2 m lower in the section than allochthonous terrestrial plants previously dated at 6400 ± BP (Sl-4314) and is estimated to be 6500 years old. These deposits represent a marine, prodeltaic sedimentary environment that emerged from the fiord as the result of postglacial isostatic uplift. Comparison of the specimen's present elevation and age with the inlet's emergence curve indicates the duck was buried in a paleowater depth of 38 m. Isostatic uplift is ubiquitous in the Canadian Arctic, exposing ocean bottoms and prodeltas. The deposits from these environments deserve closer scrutiny for fossils by Quaternary scientists, as they can contribute to a better understanding of the biologic development of the Canadian Arctic.

Likelihood of Marine Pest introduction to the Indian Ocean Territories

The introduction of new species to environments in which they did not evolve has been widely recognised as one of the top five threats to marine ecosystem function and to biodiversity (Millennium Ecosystem Assessment, 2005)

Ecological Risk Assessment for the State-wide Small Pelagic Scalefish Resource

In July 2021, the Department of Primary Industries and Regional Development convened an ecological risk assessment (ERA) of the fisheries that access the State-wide Small Pelagic Scalefish Resource. The ERA considered the potential ecological impacts of the West Coast Purse Seine Fishery, South Coast Purse Seine Fishery, Purse Seine Development Zones and the recreational fishers who catch small pelagic scalefish. The assessment evaluated the impact of each fishing sector/method on all relevant retained and bycatch species, endangered, threatened and protected species, habitats and the broader environment

Ecological Risk Assessment for the Temperate Demersal Elasmobranch Resource

In March 2021, the Department of Primary Industries and Regional Development (Department) convened an ecological risk assessment (ERA) of the fisheries that access the Temperate Demersal Elasmobranch Resource (Resource). ERAs are conducted by the Department as part of its Ecosystem Based Fisheries Management framework