http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:22797 Seagrasses are exposed to the constant risk of structural damage due to abiotic factors, such as waves and currents, and biotic factors, e.g. herbivory. Leaf mechanical resistance is therefore essential in protecting plants from structural failure and may also have ecological consequences. For example, mechanical traits of seagrass leaves may play an important role in plantherbivore interactions and food-preferences of herbivores in these ecosystems, as widely reported for terrestrial plants. However, little is known about leaf mechanical resistance against structural damage in seagrasses and how it varies with other traits such as their nutritional value. We analysed the correlation between fracture properties relevant to herbivory and the nutritional value of seagrass leaves, testing the general assumption that species that invest heavily in mechanical resistance (toughening of the leaves) will present low nitrogen and high carbon and fibre contents. Direct measurements of leaf traits were conducted on 9 seagrass species from south-western Australia: (1) leaf-fracture properties from shearing and tearing tests, (2) nutritional values (carbon to nitrogen ratio and fibre content) and (3) morphological and structural traits (specific leaf area and leaf thickness). Results showed that leaf-fracture properties in seagrasses were tightly correlated to their C:N ratio, which reflects their nutritional value, thus supporting the general assumption that C investment is inversely correlated to N content. This close correlation suggested that patterns of seagrass consumption may be influenced not only by the C:N ratio but also by the leaf-fracture properties. Among co-existing seagrasses, we found a continuous spectrum of mechanical and nutritional traits across species, which provides fundamental information about species assembly, herbivore behaviour and ecosystem functions. 2012-11-13T02:40:36.363Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:21651 Most fish are ectotherms and for this reason, water temperature is thought to be one of the main physical determinants of behaviour. We tested the hypothesis that behavioural thermoregulation occurs in 4 species of reef sharks (n = 58), where water temperature influences patterns of long-term (>1 yr) movement, by analysing acoustic monitoring and environmental datasets. We also used biotelemetry to measure the body temperature of 5 adult female blacktip reef sharks Carcharhinus melanopterus in response to changes in water temperature, to test whether they participate in inshore aggregations potentially to increase metabolic rates. We found that water temperature had the greatest influence on shark presence at each of our study sites (deviance explained = 3.7?54.6%), when compared to other variables. On average, body temperatures of female blacktip reef sharks were consistently warmer than average (±SE) water temperature by 1.3 ± 0.57°C, providing support for behavioural thermoregulation. The maximum body temperature of blacktip reef sharks while at the aggregation site corresponded to peak daily water temperatures. The average hourly body temperature varied little among individuals. Our models showed that the relationship between water temperature and the presence of female blacktip reef sharks was strongest at the aggregation site relative to other sites. These results suggest that reef shark movements are influenced by water temperature and provide additional support for the behavioural thermoregulation hypothesis. Such data are necessary for predicting how sharks might be affected by climate change and other human modifications to water temperature patterns. 2012-09-26T12:53:10.616Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:21379 Invasive primary producers can dramatically reorganize food webs through detrital subsidies. This study assessed (1) contributions of the invasive alga Caulerpa taxifolia to detrital resources of temperate Australian estuaries, and (2) effects of these contributions on sediment-dwelling invertebrates. In an invaded estuary, sampling of an intertidal shore indicated C. taxifolia fragments were consistently present in organic matter deposits and were particularly abundant following storms. Sampling of the alga across 6 invaded estuaries showed that the ratio of organic carbon to nitrogen (C:N) in fresh tissue varied between 7 and 16. To determine how C. taxifolia detritus influences benthic macrofaunal assemblages and whether this influence depends on the quantity and C:N ratio of C. taxifolia detritus, a manipulative field experiment was performed. On a sheltered intertidal mudflat, 0.25 m2 plots of sediment were experimentally enriched with either a high (90 g DW) or low (30 g) loading of high C:N (14) or low C:N (7) C. taxifolia detritus. Experimental enrichment negatively affected the total abundance and species richness of macroinvertebrates relative to controls, and these effects increased with detrital loading. For some macrofauna, reducing the C:N ratio tended to exacerbate negative effects on abundances, whereas it moderated these effects for other species. Given that organic matter derived from invasive species can be transported beyond the distribution of live invaders, greater consideration should be given to the potential broad-scale effects of invasive primary producers on detrital pathways. 2012-09-12T18:30:27.296Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20690 Manipulations of fully grown (>60.0 mm) detritivorous Sydney mud whelks Pyrazus ebeninus Brugiere 1972 suggest that the species serves as a ‘trophic cul-de-sac’, limiting flow of carbon from producers to top consumers. However, although large P. ebeninus individuals experience negligible predation, smaller individuals that do not cause the same depletion of primary and secondary producers may suffer predatory losses. To assess the role that predation on the small whelks might play in weakening the trophic cul-de-sac provided by larger conspecifics, we investigated size- and habitat-specific patterns of predation on P. ebeninus through a series of field and laboratory experiments. Field tethering of 3 size classes of snail indicated that irrespective of seasonal differences in predation intensity, small (30.1 to 40.0 mm shell height, SH) individuals experienced significantly greater predatory mortality (25% over 7 wk) than medium (50.1 to 60.0 mm SH: 7.5%) or large (70.1 to 80.0 mm SH: 2%) conspecifics. Predatory mortality was largely attributable to naticid predators, although several tethered snails were crushed, perhaps by elasmobranchs, toadfish or crabs. For some size classes there were differences in predatory mortality between low shore mudflats and higher shore mangrove forests, but the direction of these differences varied between autumn and spring, and the differences disappeared altogether when densities of predators were held constant, indicating that they were not driven by habitat per se. In laboratory experiments, the relative contributions of small, medium and large P. ebeninus individuals to the total prey consumed by the naticid gastropod Conuber sordidus Swainson 1821 were similar between choice and no-choice experiments, and even in the absence of small prey items, large P. ebeninus snails were not consumed. Thus, even when there is depletion of small size classes of P. ebeninus, it is unlikely that common benthic predators would consume sufficient numbers of large snails to prevent deleterious effects of this species on primary and secondary production. To the contrary, predatory mortality of small P. ebeninus individuals may ensure that its populations continue to be dominated by the large, damage-causing size classes. 2012-08-08T14:51:58.346Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20698 Under climate change, enhanced storminess may increase the magnitude and rate of detrital loading to the benthos, potentially altering sediment chemistry and/or physical disturbance of sediments. To assess whether the impact of detrital loading on invertebrates in intertidal sediment sparsely vegetated by seagrass is negatively affected by increasing the frequency and/or intensity of the disturbance, high (90 g dry weight) or low (30 g dry weight) quantities of shredded Zostera capricornii were added to experimental plots at high (intervals of 8 wk, on a total of 3 occasions) or low (added once) frequency. Macroinvertebrate assemblages were sampled 8, 16 and 24 wk after the first detrital enrichment. Plots subjected to frequent detrital addition contained up to 50% fewer macroinvertebrates, representing 50% fewer taxa than plots disturbed only once. This pattern was independent of disturbance intensity and emerged after only 2 detrital additions. Only at the low frequency of addition did the increased quantity of detritus influence macroinvertebrate assemblage composition, halving the number of animals by Week 24. Physical disturbance, not sediment chemistry, drove the frequency effect. Generally negative impacts of frequent detrital enrichment on infaunal populations occurred despite small positive effects of high detrital enrichment on the biomass of microphytobenthos, the food source of many sediment-dwelling invertebrates. These results suggest that, even though climate warming may increase the amount of detritus that is washed up onto intertidal sediments, its greater effect on soft-sediment communities is likely to come through increasing the frequency of storms. 2012-08-08T14:51:46.102Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20577 In urbanised coastal environments, where shoreline migration is impeded by hard structures, sea-level rise is expected to impact decomposition processes by changing the patterns of tidal inundation. We assessed how tidal elevation directly (by determining the decomposition environment) and indirectly (by determining leaf traits) influences the decay of the south-east Australian seagrass Zostera muelleri. First, we assessed how the standing biomass and quality of Z. muelleri leaves varied across a tidal elevation gradient. Second, we used a litter-bag experiment to assess how the effects of tidal elevation on leaf traits and the decompositional environment interact to influence the decomposition rate. Surveys of 3 estuaries revealed that the size and stiffness of seagrass blades increased with depth, and the carbon and fibre content of blades was greater at subtidal and low intertidal zones than at high intertidal elevations. The differences in leaf traits among tidal elevations were, however, less important than the differences in aerial exposure for controlling the decomposition rate. The litter bags incubated at subtidal and low intertidal elevations had a faster rate of decomposition than those incubated in the high intertidal, irrespective of litter quality. Across elevations, the decay rates of the intertidal seagrass and the stiffer subtidal Zostera were similar. These results suggest that sea-level rise will influence decay processes by changing the decompositional environment rather than by changing tissue quality. Studies investigating differences in litter production among tidal elevations and the capacity of hydrodynamic processes to transport excess litter are now required to facilitate ecosystem-level predictions of the effects of sea-level rise. 2012-07-26T17:42:17.225Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20578 Simple ecological models that predict trophic responses to bottom-up forcing are valuable tools for ecosystem managers. Traditionally, theoretical ecologists have used resource-dependent functional responses to explain the modification of food chains exposed to bottom-up perturbations. These models predict alternating positive, negative and zero responses at each trophic level. More recently, ratio-dependent functional response models that predict proportional increases at each level have challenged this paradigm. The present study tested the predictions of the 2 hypotheses empirically by comparing the relative biomasses of 4 trophic levels of an estuarine seagrass food chain in relatively undisturbed, low-nutrient catchments and 'developed' catchments subjected to a prolonged period of nutrient enrichment. We found that nutrient-enriched sites had significantly greater biomass of both epiphytic algae and grazing invertebrates; however, the bottom- up forcing of nutrients was attenuated at higher trophic levels (occupied by juvenile and piscivorous fish), with no significant effect of catchment development. This disconnect in the upward cascade of energy may be due to a number of possible reasons including high levels of diversity and omnivory, trophic subsidy within the system or the strength or nature of perturbations. Although the predictions of both hypotheses failed to hold across all trophic groups, ratio dependence was prevalent at the lower levels of the food chain, which has implications for catchment management. 2012-07-26T17:42:11.795Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20580 Short-term experiments exposing calcifying organisms to acidification have revealed altered growth and strength of their exoskeletons. We tested the hypothesis that multi-generational exposure to sustained estuarine acidification from runoff from acid sulphate soils (ASS) would: (1) reduce the shell strength of sessile or relatively immobile wild benthic invertebrates and (2) as a consequence render these invertebrates that rely on armour for anti-predator defence more susceptible to generalist benthic predators. First, we compared the force required to break the exoskeletons of Saccostrea glomerata, Bembicium auratum, and Heloecius cordiformis be - tween replicate south-east Australian mangrove forests close to (acidified) and away from (reference) major ASS outflow drains. Second, we assessed differences in the susceptibility of oysters from acidified and reference forests to predation by the generalist muricid gastropod Morula marginalba. Mollusc shells were significantly weaker at ASS-Affected than at reference sites, but the strength of crab carapaces was not influenced by acidification. Oysters from acidified sites were consumed by M. marginalba at a faster rate than oysters from reference sites in choice and nochoice experiments because M. marginalba required less time to drill through weaker shells. Many other predators such as crabs are generalist feeders th at consume prey at rates inversely proportional to their shell strength. Hence, in the absence of effects of acidification on the ability of these predators to consume prey, molluscs at acidified sites may also be more susceptible to other such predators. This study highlights how human stressors can rapidly alter predator-prey interactions that have evolved over many years. 2012-07-26T17:42:00.850Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:18903 During the last 2 centuries, southern right whales Eubalaena australis were hunted to near extinction, and an estimated 150 000 were killed by pre-industrial whaling in the 19th century and illegal Soviet whaling in the 20th century. Here we focus on the coastal calving grounds of Australia and New Zealand (NZ), where previous work suggests 2 genetically distinct stocks of southern right whales are recovering. Historical migration patterns and spatially variable patterns of recovery suggest each of these stocks are subdivided into 2 stocks: (1) NZ, comprising NZ subantarctic (NZSA) and mainland NZ (MNZ) stocks; and (2) Australia, comprising southwest and southeast stocks. We expand upon previous work to investigate population subdivision by analysing over 1000 samples collected at 6 locations across NZ and Australia, although sample sizes were small from some locations. Mitochondrial DNA (mtDNA) control region haplotypes (500 bp) and microsatellite genotypes (13 loci) were used to identify 707 individual whales and to test for genetic differentiation. For the first time, we documented the movement of 7 individual whales between the NZSA and MNZ based on the matching of multilocus genotypes. Given the current and historical evidence, we hypothesise that individuals from the NZ subantarctic are slowly recolonising MNZ, where a former calving ground was extirpated. We also suggest that southeast Australian right whales represent a remnant stock, distinct from the southwest Australian stock, based on significant differentiation in mtDNA haplotype frequencies (FST = 0.15, p < 0.01; ΦST = 0.12, p = 0.02) and contrasting patterns of recovery. In comparison with significant differences in mtDNA haplotype frequencies found between the 3 proposed stocks (overall FST = 0.07, ΦST = 0.12, p < 0.001), we found no significant differentiation in microsatellite loci (overall FST = 0.004, G′ST = 0.019, p = 0.07), suggesting ongoing or recent historical reproductive interchange. 2012-04-30T05:10:37.644Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:18679 We examined the movement characteristics and seasonality of feeding behaviour for an endemic Australian otariid, the Australian sea lion Neophoca cinerea. By combining tracking data and stable isotope analysis of serially subsampled vibrissae from 20 adult females at 7 colonies, we were able to characterise individual foraging specialisation across 80% of the species range. Adult females expressed long-term temporal consistency in both foraging site (offshore vs. inshore) and prey selection. When seasonality in foraging behaviour was detected (n = 7), there was no consistency in variation of isotope ratios between individuals or colonies. Offshore-foraging sea lions fed at higher trophic levels than inshore foragers. Potentially, inshore foragers could be subdivided into those which targeted heterogeneously distributed seagrass meadows or calcarenite reef sys tems for different payoffs. This data highlights the importance of understanding individual specialization and the dangers of generalising behaviour at the colony level. Individual specialisation in foraging behaviour may be a mechanism that reduces intra-specific competition, but its effectiveness will be a function of the temporal stability of individual differences. The present study is the first to identify multi-s eason consistency of individual foraging behaviour for any otariid. Given the long-term stability of adult female foraging behaviour, categorising individuals using a proxy measure such as whisker isotopic signature appears robust, economical, and appropriate. Such data is critical to modeling population response to anthropogenically driven fine-scale habitat modification. 2012-04-16T08:50:14.179Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:18583 Most models predicting changes to species distributions under future climate scenarios ignore dispersal processes, despite their importance in determining community structure in both terrestrial and aquatic systems ('supply-side ecology'). In the marine environment, facilitation of long-distance dispersal of coastal organisms by macrophytic rafts may be severely modified by climate impacts on raft supply, quality, and persistence, and on transport processes. Increasing storminess in the coastal zone, higher water temperatures, and changes in water circulation represent some of the key mechanisms that will directly affect rafts, while increases in herbivore metabolism due to higher water temperatures are likely to indirectly reduce raft longevity through raft consumption. Accurate predictions of climate impacts on coastal biodiversity will be con - tingent on resolution of factors influencing rafting so that this and other dispersal mechanisms can be incorporated into species distribution models. 2012-04-10T15:31:16.491Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:18321 Declines in marine predator populations have been attributed to anthropogenic activity and environmental change. Southern elephant seals Mirounga leonina are major consumers of biomass in the eastern region of the Southern Ocean and have been declining in numbers since the 1960s. Previous studies have identified evidence for habitat and diet partitioning over a range of spatial and temporal scales between juveniles and adults in the Macquarie Island population. We first analysed the stable isotopes (SI) of 6 entire vibrissae from a dead adult female southern elepha nt seal from Kerguelen Islands to determine moult and growth patterns. Secondly we analysed the SI from the vibrissae of 102 juvenile southern elephant seals to investigate diet. The results from the growth pattern analysis indicated that vibrissae do not grow or moult simultaneously. However, it is likely that at least part of the vibrissae will have been produced sometime during the most recent trip to sea and will give a broad indication of diet. The subsequent SI analysis confirmed that juveniles are consuming greater proportions of fish species, and identified myctophids as the primary component of juvenile diet. Myctophids are also consumed by king penguins Aptenodytes patagonicus which have greatly increased in numbers recently in the Macquarie Island area. This may have presented the juvenile southern elephant seals with increased competition and may influence survival. 2012-03-26T16:00:33.569Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:17344 Predators and prey are occasionally observed to comingle in close proximity on coral reefs. Both lethal and non-lethal (i.e. behavioral) effects of predators on prey are well documented. However, observations of apparent predator-prey interactions between the piscivorous twinspot snapper Lutjanus bohar and the herbivorous surgeonfish Acanthurus triostegus suggest that the nature of their association may be context-dependent. The context-dependent nature of some species interactions is well-known, and in some cases a single species has been shown to act as both predator and facilitator to its prey. We present incidental in situ observations suggesting that, in the context of voraciously grazing schools of A. triostegus, this species pair may also engage in a facultative mutualistic relationship. Specifically, we propose that within this context, both species may indirectly derive a benefit through changes in the behavior and/or density of territorial damselfishes driven by both L. bohar and A. triostegus. We provide prescriptions for rigorously testing this hypothesis and suggest that re-evaluation of this, and possibly other, ostensibly exclusive predator-prey pairs in marine systems may reveal unexpected relationships. Given the relative lack of examples of such interactions involving the same predator acting as both facilitator and predator from marine versus terrestrial systems, coupled with this preliminary evidence, we propose that this topic is ripe for exploration. 2012-02-05T17:21:00.441Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:17343 The quantification of spatial and temporal movement patterns of coral reef sharks is important to understand their role in reef communities and to aid the design of conservation strategies for this predatory guild. We observed 4 species of reef sharks aggregating in an inshore bay in the north of Western Australia for over 2 yr, using acoustic telemetry and visual censuses to examine how they partitioned this site in space and time. We fitted 58 sharks with acoustic transmitters: Carcharhinus melanopterus (36), C. amblyrhynchos (11), Negaprion acutidens (7) and Triaenodon obesus (4). Aggregations consisted primarily of C. melanopterus, although C. amblyrhynchos and N. acu tidens were often present. We observed aggregations by visual census in summer (maximum of 44 sharks). Detections were highest during warmer months (Sep to Mar) for all species, although some individuals showed year-round residency. C. melanopterus, C. amblyrhynchos and N. acutidens had strong diel patterns of attendance at the aggregation site. Peak daily detections occurred from 13:00 to 14:00 h local time for C. melanopterus and C. amblyrhynchos; juvenile C. melanopterus and N. acutidens peaked at 05:00 and 10:00 h, respectively. There was considerable spatial overlap of core areas of use (50% kernel density estimates) at the northern end of the bay by all species; the southern end was used primarily by C. melanopterus and N. acutidens. Aggregations of C. mela nop terus and C. amblyrhynchos consisted mainly of adult females, some of them pregnant. Courtship behaviour in C. melanopterus and T. obesus suggests that these aggregations are related to reproduction. All species displayed inter-annual site fidelity. The long-term presence of juvenile C. melanopterus and N. acutidens also suggests that this bay provides suitable conditions for younger age classes. 2012-02-05T17:20:57.657Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:17346 Animal movement is a central topic in ecology, as movements are crucial to habitat selection, foraging and spatial population ecology. Movement is a primary mechanism coupling animals to their environment, as organisms respond to environmental heterogeneity at different spatio-temporal scales. The fjord system in southern Chile is highly heterogeneous and sustains poorly known dolphin species, including the sympatric Chilean Cephalorhynchus eutropia and Peale's Lagenorhynchus australis dolphins. Focal dolphin group follows were undertaken between January and April 2007, 2008 and 2009 to assess the fine-scale movement patterns of these 2 species in southern Chile. Correlated random walk models (CRW) overpredicted dolphin paths for both species, indicating that dolphins displayed a resident type of movement. Only a small number of dolphin groups fitted a Lévy flight model, thus suggesting that dolphins undertake a non-random searching strategy. First-passage time (FPT) models for both species showed that dolphins spent a large proportion of their time in small localised areas of only 100 m radius. Generalized additive mixed models (GAMMs) demonstrated that Peale's dolphin movements were highly associated with kelp beds while Chilean dolphin movements were associated with rivers. Movement patterns of both species are very similar in scale and form, but they differ in relation to the associated ecological features. Movement models may be useful for developing holistic and more realistic predictions of how dolphins may respond to shifting resources as a consequence of environmental change with clear implications for conservation. 2012-02-05T17:20:53.034Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:17345 We compare vertebral microchemistry with previously described age-related movement patterns of bull sharks Carcharhinus leucas and pig-eye sharks C. amboinensis within coastal waters of north Australia. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) quantified the chemical signatures of nursery habitats within the vertebrae of juvenile and adult sharks. We examined evidence for adults returning to these habitats by applying LA-ICP-MS along a growth axis of their vertebrae. We transposed chemical signatures with growth increments in adult vertebrae to correlate with age estimates. Unique elemental signatures were i dentified in each of the fresh - water nurseries, but we did not find them in adult vertebrae. Age-specific changes in vertebral microchemistry in mature female bull sharks correlate with periodic returns every 1 to 2 yr to less saline environments to pup. We were unable to discriminate among natal habitats of pig-eye sharks using elemental fingerprints, and age-specific changes in vertebral microchemistry were also absent. We conclude that changes in vertebral microchemistry correlate with known habitat use patterns of the bull and pig-eye sharks, showing the potential of vertebral microchemistry to discern movement patterns in sharks. 2012-02-05T17:20:49.735Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15982 We measured biogenic silica (bSiO2) dissolution and production rates at 3 Southern Ocean sites with contrasting biogeochemical regimes (SAZ-Sense cruise, January to February 2007). Two sites were located in the Subantarctic Zone (SAZ) southeast and southwest of Tasmania, and 1 site was in the Polar Frontal Zone (PFZ). The measurements were repeated 3 times within a time frame of 4 to 7 d. In the PFZ and the western SAZ, the release of silicon from dissolving bSiO2, following a productive period, appeared sufficient to entirely sustain Si demand in surface waters. Biogenic silica dissolution was more efficient in the SAZ, likely owing to stronger microzooplankton grazing and bacterial activity. The degree of iron co-limitation correlated to bSiO2 growth rates (VSi, d-1). Highest rates were observed in the SAZ, southeast of Tasmania, a region influenced by iron-enriched East Australian Current water advecting through the Subtropical Front. The diatom communities appeared differently adapted and conditioned, in terms of uptake ability, for growth under low Si(OH)4 availability. Combining our results with existing bSiO2 dissolution and production data, we estimate a spring to summer net bSiO2 production for the circumpolar SAZ and PFZ regions of 7.4 and 3.6 Tmol yr-1, respectively, representing 4.3 and 2.1% of the global net bSiO2 production for each region. Furthermore, a clear seasonal pattern emerges with (1) higher bSiO2 production in spring (0.9 to 12.7 and 6.8 to 60.7 mmol Si m-2 d-1 for the SAZ and PFZ, respectively) compared to summer (0.1 to 6.6 and 0.3 to 9.1 mmol Si m-2 d-1 for the SAZ and PFZ, respectively) and (2) a bSiO2 dissolution to production ratio of <1 in spring (~0.4) and generally >1 in summer (~1.7). 2011-11-17T16:51:17.894Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15117 When resources are limited or patchy, a species may develop some degree of resource partitioning to reduce intra-specific competition. Development of intra-specific resource partitioning is more pronounced in species with clear phenotypic variation among individuals (e.g. age or sex). Southern elephant seals Mirounga leonina have pronounced sexual dimorphism and range widely in size and foraging range between juvenile and adult stages. However, hypothesized diet-based resource partitioning has been less clear due to difficulties in sampling diet while seals are away from breeding islands. We analysed fatty acids (FAs) from blubber of 122 juvenile seals and compared them to FA profiles from blubber of 52 adult females, and to FA profiles from 51 prey species (grouped as fish and squid) to examine evidence for diet-based resource partitioning in the seals. FA signature analysis revealed physiological and dietary differences between ages. Principle components of the 21 FAs from seal blubber and prey parts distinguished prey from seals, and clearly separated prey species into fish and squid classes. FA profiles from adult females differed to those from juveniles, with the former more 'squid-like' and the latter more 'fish-like'. Variation in FA profiles of seals was also apparent between sexes and during different seasons. Differences in diet between juveniles and adult females suggest resource partitioning occurs in response to large metabolic and physiological differences with age that limit juvenile dispersal and diving abilities. By consuming a different suite of prey species relative to adult females, juvenile southern elephant seals may reduce intra-specific competition. 2011-09-29T06:51:36.002Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15124 Environmental conditions experienced in early life affect growth and influence life history strategies, especially in seasonal environments. We studied the seasonal and sexual variation in resource allocation in juvenile southern elephant seals to investigate whether they show a seasonal decline in growth. We also examined whether sexual differences in growth may lead to separate growth strategies that suit each sex in maximizing fitness. We examined the variation in length (as a measure of somatic growth), body mass and condition of 470 individual 1- to 4-yr-old elephant seals relative to their different growth strategies. Applying a novel growth function, we observed increased somatic growth in summer compared to winter. Males were larger, had higher proportions of lean tissue and grew faster than females, demonstrating the evolution of a male growth strategy of attaining maximum size quickly, and a female strategy of achieving primiparity at an early age. This evidence supports the idea that seasonal patterns reflect seasonal variation in prey availability and quality, and differential growth strategies promote optimal resource allocation and increase an individual's probability of survival and future breeding success in the highly dynamic and seasonal Southern Ocean. 2011-09-29T06:51:19.315Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12999 The Australian fur seal Arctocephalus pusillus doriferus is a temperate latitude species with a breeding distribution restricted to Bass Strait, Australia. Recent studies of the foraging behaviour of female Australian fur seals indicated that they feed demersally in the shallow continental shelf waters, a behaviour that is in contrast to the epipelagic foraging of females of most other arctocephaline (Southern Hemisphere fur seals) species and akin to that observed in sea lions. These studies, however, were conducted at one colony (Kanowna Island) located in central northern Bass Strait, and it was suggested that the observed foraging behaviour may have been due to the distance of this colony from the continental shelf edge (180 km), making it inefficient to forage beyond it. Here, the diet of lactating Australian fur seals was compared between 2 colonies to test if differing proximity to the continental shelf edge resulted in differences in foraging behaviour. The 2 breeding colonies studied, Kanowna Island and The Skerries, were 180 and 25 km from the nearest shelf edge, respectively. We analysed a total of 917 scat samples collected at the 2 colonies between 1997 and 2001. From faecal analysis, 45 primarily demersal on-shelf species of fishes and cephalopods were identified. Only 4 species had a frequency of occurrence greater than 10%: redbait Emmelichthys nitidus, jack mackerel Trachurus sp., red rock cod Pseudophycis bachus, and Gould’s squid Nototodarus gouldi. No seasonal, annual or spatial differences were found between the 2 colonies, indicating that proximity to the shelf edge does not influence diet. 2011-05-25T21:52:06.689Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:10202 The grazing activity of consumers causes shifts between alternative states in a variety of terrestrial and marine ecosystems. One of the best examples of a consumer-driven shift occurs on temperate marine reefs, where grazing by high densities of sea urchins results in a shift from a foliose algal- to a crustose algal-dominated state. In this study, we focussed on 2 largely untested but important issues during the transition from a foliose algal- to a crustose algal-dominated state: (1) whether sea urchins impact foliose algal community composition by differentially removing species and (2) whether any impacts of grazing vary with 2 different densities of aggregating sea urchins. We tracked the movement of a high-density front of the sea urchin Heliocidaris erythrogramma and then performed experimental manipulations of H. erythrogramma at 2 unusually high but naturally occurring densities. Non-metric multidimensional scaling (nMDS) followed by analysis of similarities (ANOSIM) showed differences in the foliose algal community composition, and therefore differential removal of species, between permanent plots before and during grazing (surveys), and between grazed and ungrazed plots (experiment). Of the 6 abundant foliose algae, 2 had relatively low survivorship (Amphiroa anceps and Zonaria diesingiana), while 2 had relatively high survivorship (Delisea pulchra and Corallina officinalis) when grazed by high densities of sea urchins. Grazing by different densities of H. erythrogramma resulted in differences in the foliose algal community composition and for the chemically-defended D. pulchra there appeared to be a threshold sea urchin density required before its removal. Our results show that an intermediate community state composed of grazer-resistant foliose algae and crustose algae can occur, which may have important consequences for community composition. 2010-10-27T05:05:17.732Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:9065 The fucalean macroalga Hormosira banksii facilitates diverse rocky intertidal communities. Along the east coast of Australia, the alga can also persist in mangroves as a free-living form trapped amongst pneumatophores. We investigated (1) whether the alga has an effect on molluscan species richness and abundance in mangroves similar to that on rocky shores, and (2) whether, in mangroves, the source (phenotypically distinct estuarine or rocky shore populations) of H. banksii influences the outcome of its interspecific interactions. Sampling of 3 rocky shore and 3 mangrove sites along the east coast of Australia revealed that patches of H. banksii consistently supported a greater species richness of molluscs than adjacent substratum. Whereas the alga increased the abundance of molluscs in the mangrove forest, it had no effect or decreased molluscan abundance on the rocky shore. Transplant of H. banksii from rocky shores and estuarine tidal flats into the mangrove indicated that the source of the algae influenced the magnitude of effects. Although all algae enhanced molluscan abundance and species richness, estuarine H. banksii, which had larger vesicles and a longer thallus, supported more molluscs of more species than rocky shore H. banksii. These results support the growing consensus that the influence of foundation species at the community level is dependent on environmental conditions. As human activities place increasing pressure on coastal ecosystems, it will be important to understand the mechanisms and conditions that determine community-level effects of foundation species so that biodiversity may be conserved. 2010-08-02T11:30:31.990Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:139 This study examined how diet, foraging location and diving behaviour of female New Zealand fur seals Arctocephalus forsteri at Otago Peninsula, New Zealand (45° 52’ S, 170° 44’ E), varied in relation to prey abundance among seasons in 1994 and 1995. Time-depth recorders measured the diving behaviour of 24 lactating female fur seals, during summer, autumn or winter of 1994 and summer and autumn of 1995. Foraging locations were obtained by deploying satellite transmitters in summer, autumn and winter of 1994 only. Estimated biomass of prey items was determined from 690 scats and 166 regurgitates collected over summer, autumn and winter of both years, and compared with abundance data from research trawls in the same area. Foraging trip duration increased during the cooler seasons. Female fur seals showed a clear bout structure in dive behaviour, with the relative proportion of 3 main bout types (Long, Shallow, Deep) varying with season. Time between bouts (IBI) and bout duration varied with season, suggesting that prey distribution and prey encounter rate also varied. Linear discriminant analysis of the dive and foraging trip characteristics of individual females demonstrated clear seasonal differences. Females foraged on or near the continental slope in summer and farther offshore in autumn. Satellite telemetry locations and diet suggest principally inshore foraging during winter. Fur seals ate predominantly arrow squid Nototodarus sloanii during summer and autumn of both years, although fish, particularly myctophids, were persistent in the diet. Arrow squid were less common in winter when diet was more varied, and an inshore, benthic fish, ahuru Auchenoceros punctatus was dominant. There was no relationship between the annual changes in abundance of major prey species as measured by research trawls and their occurrence in seal diet. Overall, changes in dive behaviour may reflect changes in prey selection as prey abundance and availability change among seasons. 2010-03-22T06:20:06.725Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5989 For many marine organisms, including large, long-lived predators, the factors affecting connectivity between populations are still largely unknown. We assessed levels of genetic differentiation and dispersal patterns of bottlenose dolphins Tursiops sp. across Spencer Gulf and coastal areas west of the gulf in the Great Australian Bight, South Australia (SA), using data from mitochondrial DNA control region sequences and 6 microsatellite loci. Marked genetic differentiation and low migration were detected between dolphins of Spencer Gulf and those inhabiting coastal areas west of the gulf. We hypothesise that the restriction to dolphin gene flow is influenced by an oceanographic front at the mouth of Spencer Gulf that builds up over the austral summer and exhibits strong differences in water temperatures and salinity levels. It appears that the genetic subdivision reported here is a recent phenomenon, a finding consistent with the known geomorphologic history of the region. Coastal bottlenose dolphins from SA are evolutionarily divergent from other bottlenose dolphin species and are potentially under threat due to ongoing human-related mortality. The information from this study can, therefore, be used for the development of much-needed conservation management strategies. 2010-01-27T22:23:38.640Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:6891 Despite the importance of fine-scale spatial use in understanding an animal's foraging ecology, these data cannot readily be collected for free-ranging marine mammals. We used an acoustic positioning system to quantify, for the first time, the fine-scale 3-dimensional (3D) spatial use of free-ranging Weddell seals swimming under ice. Unlike many other phocid species, lactating Weddell seals spent up to 25% of their time diving. Given the limited foraging range imposed on the seals by the fast ice upon which they breed, this could lead to prey depletion and even inter-specific competition. The seals focused their underwater activity on a relatively small region associated with a steep bottom contour, using the entire water column, with very little time spent at the bottom. This behaviour is consistent with feeding on bentho-pelagic prey such as Pleurogramma antarcticum. The 3D profile of individual dives consisted of the seals making simple, directed dives which gradually converged with the ocean floor. There was some variation from this pattern, usually associated with increased searching time. Such focused foraging activity may result in local prey depletion and intra-specific competition. 2010-01-27T22:11:58.148Z ]]>