Brenton Knott

Ancient androdioecy in the freshwater crustacean Eulimnadia

Among the variety of reproductive mechanisms exhibited by living systems, one permutation—androdioecy (mixtures of males and hermaphrodites)—is distinguished by its rarity. Models of mating system evolution predict that androdioecy should be a brief stage between hermaphroditism and dioecy (separate males and females), or vice versa. Herein we report evidence of widespread and ancient androdioecy in crustaceans in the genus Eulimnadia, based on observations of over 33 000 shrimp from 36 locations from every continent except Antarctica. Using phylogenetic, biogeographical and palaeontological evidence, we infer that androdioecy in Eulimnadia has persisted for 24–180 million years and has been maintained through multiple speciation events. These results suggest that androdioecy is a highly successful aspect of the life history of these freshwater crustaceans, and has persisted for orders of magnitude longer than predicted by current models of this rare breeding system.

Morphological changes in external and internal feeding structures during the transition phyllosoma‐puerulus‐juvenile in the Western Rock Lobster (Panulirus cygnus, Decapoda: Palinuridae)

External and internal feeding structures of the pelagic final phyllosoma, the transitional puerulus, and the benthic juvenile Western Rock Lobster, Panulirus cygnus, were studied by means of scanning electron microscopy. The study revealed that the external feeding structures of phyllosomata are well equipped for capture and mastication of food. The foregut, however, is not clearly divided into pyloric and cardiac regions and a gastric mill is absent, although a comb row and gland filter are present. Juveniles, on the other hand, have a well‐developed gastric mill and gastric teeth, and a cardiopyloric valve separates the foregut into cardiac and pyloric regions. External mouthparts of juveniles are suitable for mastication of solid food particles and bear numerous setae. In contrast, external mouthparts of pueruli are largely non‐setose. Furthermore, although the foregut is differentiated into pyloric and gastric regions and a gland filter and comb row are present, a functional gastric mill is absent during the puerulus stage. Absence of such structures indicates that the puerulus may be a non‐feeding stage. It is postulated that absence of (or reduced) feeding may be a response to an increased risk of predation rather than a result of the considerable morphological changes taking place during the transition from a planktonic to a benthic lifestyle, as has been previously proposed.

The fauna of thrombolitic microbialites, Lake Clifton, Western Australia

A total of 30 microbialites at two sites in Lake Clifton, Yalgorup National Park, Western Australia, were sampled by coring to quantify the associated fauna with these organo-sedimentary structures. Twenty five species of aquatic fauna were recorded from the cores, comprising 20 species of metazoan, predominantly Crustacea (including Melita kauerti (Amphipoda), Exosphaeroma cf. serventii (Isopoda); and Cyprideis australiensis(Ostracoda); Polychaeta (Capitella cf. capitata); nematodes; and five species of Foraminifera (Protista). Multivariate analysis of the five numerically most abundant taxa (amphipods, isopods, ostracods, polychaetes, nematodes) separated microbialites by season and submergence. Numbers of all taxa, particularly polychaetes and amphipods, were much higher in spring than in autumn, and in permanently-inundated than in seasonally-inundated microbialites. The exception was higher numbers of juvenile polychaetes in seasonally-inundated microbialites at the northern site in spring. This study showed that modern thrombolitic microbialites can co-exist with a diverse invertebrate fauna and serves as a baseline for future studies of interactions between microbialites and fauna.

ONTOGENETIC CHANGES IN THE STRUCTURE AND FUNCTION OF THE MOUTHPARTS AND FOREGUT OF EARLY AND LATE STAGE PANULIRUS ORNATUS (FABRICIUS, 1798) PHYLLOSOMATA (DECAPODA: PALINURIDAE)

Abstract Structure of the mouthparts and foregut of Panulirus ornatus phyllosomata (stages I-VI hatchery reared, IX-X wild caught) were examined using scanning electron microscopy and histology to gain an understanding of ingestive and digestive processing mechanisms, to identify potential shifts in diet during development, and to suggest appropriate physical characteristics for the development of a suitable formulated diet for commercial aquaculture of this species such as size, texture, and buoyancy. Mouthpart and foregut structure indicates that P. ornatus phyllosomata are capable of ingesting zooplankton of any hardness during this life history stage and are only limited by their ability to capture and manipulate prey as the mandibular molars are well developed to masticate prey further. Mouthpart morphology changes little during development, however, the disposition of the mouthparts and size of the mouth aperture increases with each successive stage of development, suggesting a greater capacity to manipulate and ingest larger prey. The foregut of all developmental stages consists of a single chamber, with well-developed grooves, channels and setae, but lacks a gastric mill. Presence of well-developed main brushes, lateral setae, and development of a functional filter press at stage IV suggests an increased ability to triturate and filter prey internally, reducing both the time spent externally manipulating prey with the mouthparts and the vulnerability to predation in the open ocean. The results presented here suggest that formulated diets larger than > 428 μm, with a firm/hard consistency that allow the dactyli of the second and third maxillipeds to penetrate the diet without causing fouling of the setae would be suitable.

The recent spread of Artemia parthenogenetica in Western Australia

In Western Australia, populations of Artemia parthenogenetica in coastal salt lakes at Rottnest Island and Lake Hayward, and in salterns at Port Hedland and Shark Bay, are widely accepted to have been introduced by humans. Further, within the past 10 years, populations of A. parthenogenetica have been found in inland playa salt lakes in the wheatbelt of south-west Western Australia, where none had been recorded in previous salt lake studies. Here we hypothesise that birds act as transport vectors for Artemia cysts both within Australia and between the Asian and Australian continents. Allozyme analysis was used to identify clonal types (multi-locus genotypes), clonal frequencies, genotypic diversities and genotypic identity of six populations (three coastal, three inland).Overall, the inland populations displayed almost identical genotypic structure to the coastal population from Lake Hayward, indicating that Lake Hayward could be the major source for dispersal and colonisation of inland populations. Results support the hypothesis of dispersal inland by nomadic bird species. Furthermore, evidence suggests that the inland and Lake Hayward populations may be an example of a metapopulation.The greater variety of genotypes present in the Rottnest population indicates that this population has received a large number of small immigrations, or that it received one large introduction. The former may indicate a long period of suitable salinities, providing a greater time-span over which migration and succession of clonal types could occur in comparison to other populations. While we cannot rule out the possibility of human introduction of A. parthenogenetica to Rottnest, the hypothesis of cyst dispersal along the Austral-Asian flyway remains possible.

Denitrification activity in sediment surrounding polychaete (Ceratonereis aequisetis) burrows

The effect of burrow-dwelling fauna on sediment denitrification within the Swan River Estuary, Western Australia, was assessed by determining the spatial profile of potential denitrification activity surrounding individual burrows of a polychaete. This activity was described for Ceratonereis aequisetis and compared with uninhabited sediment. Potential porewater denitrification activity was measured as N’2O production in the presence of acetylene (which blocks N2O reduction and NH4+ oxidation) and supplementary NO3-(provided as a substrate for denitrification). Snap-freezing of sediment cores in liquid nitrogen allowed easy sectioning in both the vertical (perpendicular depth from surface sediment) and radial (depth from burrow wall) planes. Overall, potential denitrification activity was significantly greater in inhabited sediment than in uninhabited sediment, although uninhabited sediment had higher surficial (0–10 mm) potential denitrification activity. Potential denitrification activity was also greater closer to the burrow wall (0–9 mm) rather than further into the sediment (9–13 mm). Greater sampling resolution would be required to determine whether a thin oxygenated surface layer (of either the vertical or radial plane) exists in which denitrification is inhibited. Although this study accurately demonstrates the spatial effect of C. aequisetis on sediment potential denitrification, the reported denitrification intensity may not reflect the rate in situ.

Spatial and temporal variation in lipid and fatty acid profiles of western rock lobster pueruli at first settlement: biochemical indicators of diet and nutritional status.

Rock lobster species are found worldwide and have a life history that includes development through a planktonic phyllosoma followed by a nektonic non-feeding puerulus that relies on stored energy during recruitment into near-shore habitats. Recruitment to adult populations of western rock lobster (Panulirus cygnus) is highly variable and is likely to be strongly influenced by shelf width and oceanic conditions affecting cross-shelf transport and nutrition. Since the nutritional status of newly settled pueruli will reflect the phyllosoma feeding environment and distance swum, we studied levels of lipid, fatty acid (FA) and protein of 422 pueruli and 79 first instar juveniles from four Western Australian locations. Lipid levels generally were inversely related to shelf width but were variable, suggesting pueruli may travel complex trajectories to coastal settlement. Lipid and FA composition of pueruli were consistent with spatial and seasonal variation in Leeuwin Current and coastal productivity regimes. Seasonal differences in FA composition occurred regardless of the year of settlement. Pueruli had lower lipid levels during ENSO years, when recruitment tends to be lower also. Measures of puerulus nutritional status appear to provide valuable insights into the processes underpinning recruitment in Panulirus cygnus and other commercially and ecologically important species.

Aggressive interactions between freshwater turtle, Chelodina oblonga, hatchlings and freshwater crayfish, Cherax spp.: implications for the conservation of the critically endangered western swamp turtle, Pseudemydura umbrina

Interactions between turtle hatchlings of Chelodina oblonga and the marron, Cherax tenuimanus, the gilgie, C. quinquecarinatus, the koonac, C. preissii (freshwater crayfish native to Western Australia) and the introduced yabby, Cherax. sp., were observed in laboratory-based trials in uncluttered aquaria. Marron, koonacs and yabbies, but not gilgies, showed aggressive and predatory behaviour towards the hatchlings. In total, 59 attacks were observed in 26 of the 80 trials. On 12 occasions, crayfish captured hatchlings in their chelae. On two occasions, the attack of the crayfish was so quick that the hatchling was killed instantly. Compared with movement when alone, movement of hatchlings was significantly greater in the presence of koonacs and yabbies, but significantly less in the presence of marron and gilgies. The range of non-native yabbies currently is expanding into Ellen Brook Nature Reserve which harbours the last naturally persisting population of the critically endangered western swamp turtle, Pseudemydura umbrina. No native crayfish occur in the habitat of P. umbrina in this reserve. The possible invasion by the ecological generalist yabby poses a new threat to the survival of P. umbrina.

Artemia parthenogenetica in Lake Hayward, Western Australia. II. Feeding biology in a shallow, seasonally stratified, hypersaline lake

Primary production in Lake Hayward, Western Australia, is dominated by benthic microbial communities, with limited planktonic primary production. This study investigated the question of how Artemia, commonly regarded as simple, obligate, non-selective filter feeders, were able to survive in this system. Bacteria (heterotrophic and autotrophic, filamentous and unicellular) were the major components in the diet of the Artemia in Lake Hayward. These bacteria were derived from bacterial aggregates in the water column and also from benthic mat material (both still attached to the substrate and from pieces floating in the water column). Benthic diatoms were a substantial dietary component of animals living in the unstratified shallow regions. Photosynthetic eukaryotic nanoplankton comprised a minor component of the diet of this Artemia population. Gut contents of a large number of animals and the results of a simple laboratory test indicated that these animals utilise substrate-bound food resources. The results of the present study raises the question of the ecological significance of surface grazing by brine shrimps in other shallow, benthos dominated saline systems.

Effects of recent increases in salinity and nutrient concentrations on the microbialite community of Lake Clifton (Western Australia): are the thrombolites at risk?

The Yalgorup lakes, a groundwater-fed system in south-western Australia recognized as a Ramsar wetland, hold significant scientific and conservation value due to the presence of a unique range of lake systems, resident waterfowl and, on the eastern shore of Lake Clifton, the presence of the only thrombolite reef in the southern hemisphere. Recent concern over changing physico-chemical conditions in the lakes, particularly an increase in salinity, prompted this study: the current status of the inherent thrombolite community is unknown. Salinity, total phosphorous (TP), phosphate, total nitrogen (TN), nitrate, chlorophyll-a and relative abundance of the thrombolite microflora were measured in Lake Clifton to analyse changing conditions in this lake and to determine the effect of these water parameters on the thrombolite community. Comparisons with historical data revealed a significant increase in salinity since 1985 and a possible increase in phosphorus concentrations in the lake in the recent decade, although historical nutrient data are rather sparse. The increased salinity may be due to concentration of lake water through a combination of high evaporation, long-term reduction in rainfall and increased groundwater abstraction. Comparison of the composition of the thrombolite community with historical data indicates a large reduction in relative abundance of Scytonema sp. and other filamentous cyanobacterial species, which are believed to be fundamental for the thrombolite structure. It is concluded the changing physico-chemical environment of the Yalgorup Lakes may have led to the decline in important genera in the thrombolite community; however, the mechanisms underlying this change remain unknown.