Can soil nematode community structure be used to indicate soil carbon dynamics in horticultural systems?

There is a need to develop indicators that relate the dynamics of soil organic carbon (SOC) with changes in land management of horticultural production systems. Soil nematode communities have been shown to be sensitive to land management changes, but often do not include plant-parasites in the calculation of soil nematode community indices. The concept of nematode functional guilds was used to estimate the proportion of carbon entering the soil ecosystem through different channels, such as through decomposition of organic material, the detrital channel, through the roots of plants, the root channel or recycled through the activity of predators, a predation channel. Calculations of the indices were developed and validated using case studies in the north Queensland banana industry. Firstly, a survey of organic and conventional banana farms found a greater proportion of C entering the soil ecosystem through the detrital channel and a reduced proportion of C originating through the root channel at the organic sites relative to conventional sites. Secondly, a field experiment comparing compost amendments, found application of fresh compost significantly increased the proportion of C entering the soil ecosystem through the detrital channel and decreased proportion of C originating from the root channel. Thirdly, a field experiment comparing 'conventional' banana production to an 'alternative' system which incorporated organic matter, found the proportion of C entering the soil ecosystem through the root channel was significantly greater in the conventional systems relative to the alternative system. This research demonstrates that nematode indices can be used to assess horticultural systems, by indicating the origins of SOC.

Spawning stock dynamics of two penaeid prawns, Metapenaeus bennettae and Penaeus esculentus, in Moreton Bay, Queensland, Australia

Spawning stock dynamics of 2 commercially important penaeid prawns, Metapenaeus bennettae and Penaeus esculentus, from 9 stations in Moreton Bay (27°15'S, 153°15'E), southeast Queensland, Australia, were examined. An egg production index (EPI), based on the relative abundance, proportion that were mature or ripe, and size of adult females, was used as a measure of egg production in the 2 populations. Egg production by M. bennettae was 20 to 30 higher than that by P. esculentus, extended over 7 to 8 mo each year and peaked from February to March (late summer to early autumn). Monthly patterns in egg production by M. bennettae varied between years. In contrast, P. esculentus produced most of its eggs in a single, clearly defined peak in October (spring), although production continued to March (early autumn) each year. The seasonal onset and subsequent decline in maturation in P. esculentus were rapid. Egg production by M. bennettae was several times higher at the 5 northern stations than at the 4 southern stations and negatively correlated with salinity during the main spawning period. Egg production by P. esculentus was less varied among stations and positively correlated with depth. P. esculentus appeared more likely than M. bennettae to experience recruitment overfishing because (1) the peak spawning period for P. esculentus was dependent on relatively few adult females spawning over a short period, and (2) the selectivity of trawl nets used in the bay was much higher for P. esculentus spawners than for those of M. bennettae. Compared with more northern populations, P. esculentus in Moreton Bay matured at a larger size, had lower incidences of insemination and mature or ripe females, and had a shorter spawning period. These results suggest the likelihood of recruitment overfishing in P. esculentus increases with increasing latitude.

Telomere dynamics in the Sydney rock oyster (Saccostrea glomerata): an investigation into the effects of age, tissue type, location and time of sampling.

Telomere length has been purported as a biomarker for age and could offer a non-lethal method for determining the age of wild-caught individuals. Molluscs, including oysters and abalone, are the basis of important fisheries globally and have been problematic to accurately age. To determine whether telomere length could provide an alternative means of ageing molluscs, we evaluated the relationship between telomere length and age using the commercially important Sydney rock oyster (Saccostrea glomerata). Telomere lengths were estimated from tissues of known age individuals from different age classes, locations and at different sampling times. Telomere length tended to decrease with age only in young oysters less than 18 months old, but no decrease was observed in older oysters aged 2-4 years. Regional and temporal differences in telomere attrition rates were also observed. The relationship between telomere length and age was weak, however, with individuals of identical age varying significantly in their telomere length making it an imprecise age biomarker in oysters.

Bacterial Community Structure in the Hindgut of Wild and Captive Dugongs (Dugong dugon)

Dugongs (Dugong dugon) are marine mammals that obtain nutrients through hindgut fermentation of seagrass, however, the microbes responsible have not been identified. This study used denaturing gradient gel electrophoresis (DGGE) and 454-pyrosequencing to profile hindgut bacterial communities in wild dugongs. Faecal samples obtained from 32 wild dugongs representing four size/maturity classes, and two captive dugongs fed on cos lettuce were screened using DGGE. Partial 16S rRNA gene profiles of hindgut bacteria from wild dugong calves and juveniles were grouped together and were different to those in subadults and adults. Marked differences between hindgut bacterial communities of wild and captive dugongs were also observed, except for a single captive whose profile resembled wild adults following an unsuccessful reintroduction to the wild. Pyrosequencing of hindgut communities in two wild dugongs confirmed the stability of bacterial populations, and Firmicutes (average 75.6% of Operational Taxonomic Units [OTUs]) and Bacteroidetes (19.9% of OTUs) dominated. Dominant genera were Roseburia, Clostridium, and Bacteroides. Hindgut microbial composition and diversity in wild dugongs is affected by ontogeny and probably diet. In captive dugongs, the absence of the dominant bacterial DNA bands identified in wild dugongs is probably dependent upon prevailing diet and other captive conditions such as the use of antibiotics. This study represents a first step in the characterisation of a novel microbial ecosystem-the marine hindgut of Sirenia.

Linking spatial stock dynamics and economics: Evaluation of indicators and fishery management for the travelling eastern king prawn (Melicertus plebejus)

Reduced economic circumstances have moved management goals towards higher profit, rather than maximum sustainable yields in several Australian fisheries. The eastern king prawn is one such fishery, for which we have developed new methodology for stock dynamics, calculation of model-based and data-based reference points and management strategy evaluation. The fishery is notable for the northward movement of prawns in eastern Australian waters, from the State jurisdiction of New South Wales to that of Queensland, as they grow to spawning size, so that vessels fishing in the northern deeper waters harvest more large prawns. Bio-economic fishing data were standardized for calibrating a length-structured spatial operating model. Model simulations identified that reduced boat numbers and fishing effort could improve profitability while retaining viable fishing in each jurisdiction. Simulations also identified catch-rate levels that were effective for monitoring in simple within-year effort-control rules. However, favourable performance of catch-rate indicators was achieved only when a meaningful upper limit was placed on total allowed fishing effort. The methods and findings will allow improved measures for monitoring fisheries and inform decision makers on the uncertainty and assumptions affecting economic indicators.

An overview on the role of Hexanchiformes in marine ecosystems: biology, ecology and conservation status of a primitive order of modern sharks

The large size, high trophic level and wide distribution of Hexanchiformes (cow and frilled sharks) should position this order as important apex predators in coastal and deep-water ecosystems. This review synthesizes available information on Hexanchiformes, including information not yet published, with the purpose of evaluating their conservation status and assessing their ecological roles in the dynamics of marine ecosystems. Comprising six species, this group has a wide global distribution, with members occurring from shallow coastal areas to depths of c. 2500 m. The limited information available on their reproductive biology suggests that they could be vulnerable to overexploitation (e.g. small litter sizes for most species and suspected long gestation periods). Most of the fishing pressure exerted on Hexanchiformes is in the form of commercial by-catch or recreational fishing. Comprehensive stock and impact assessments are unavailable for most species in most regions due to limited information on life history and catch and abundance time series. When hexanchiform species have been commercially harvested, however, they have been unable to sustain targeted fisheries for long periods. The potentially high vulnerability to intense fishing pressure warrants a conservative exploitation of this order until thorough quantitative assessments are conducted. At least some species have been shown to be significant apex predators in the systems they inhabit. Should Hexanchiformes be removed from coastal and deep-water systems, the lack of sympatric shark species that share the same resources suggests no other species would be capable of fulfilling their apex predator role in the short term. This has potential ecosystem consequences such as meso-predator release or trophic cascades. This review proposes some hypotheses on the ecology of Hexanchiformes and their role in ecosystem dynamics, highlighting the areas where critical information is required to stimulate research directions.

Early-season movement dynamics of phytophagous pest and natural enemies across a native vegetation-crop ecotone

There is limited understanding about how insect movement patterns are influenced by landscape features, and how landscapes can be managed to suppress pest phytophage populations in crops. Theory suggests that the relative timing of pest and natural enemy arrival in crops may influence pest suppression. However, there is a lack of data to substantiate this claim. We investigate the movement patterns of insects from native vegetation (NV) and discuss the implications of these patterns for pest control services. Using bi-directional interception traps we quantified the number of insects crossing an NV/crop ecotone relative to a control crop/crop interface in two agricultural regions early in the growing season. We used these data to infer patterns of movement and net flux. At the community-level, insect movement patterns were influenced by ecotone in two out of three years by region combinations. At the functional-group level, pests and parasitoids showed similar movement patterns from NV very soon after crop emergence. However, movement across the control interface increased towards the end of the early-season sampling period. Predators consistently moved more often from NV into crops than vice versa, even after crop emergence. Not all species showed a significant response to ecotone, however when a response was detected, these species showed similar patterns between the two regions. Our results highlight the importance of NV for the recruitment of natural enemies for early season crop immigration that may be potentially important for pest suppression. However, NV was also associated with crop immigration by some pest species. Hence, NV offers both opportunities and risks for pest management. The development of targeted NV management may reduce the risk of crop immigration by pests, but not of natural enemies.