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Ghost crabs can be abundant at beaches where sea turtles nest, but the food web dynamics are poorly understood. Using multiple dietary methods, our research aimed to characterise the diet of the golden ghost crab Ocypode convexa at rookeries of the loggerhead turtle Caretta caretta on the west coast of Australia, with a focus on determining the importance of sea turtle eggs and hatchlings to its diet. We achieved this through combining complementary methods: gut content analysis (GCA); DNA analysis of gut contents; stable isotope analysis (SIA); and controlled feeding experiments. GCA showed that O. convexa is a facultative scavenger with an omnivorous diet comprising high contributions (> 55%) of abundant beach-cast leafy brown algae. However, DNA analysis identified C. caretta in ≥ 20% of crab guts, and stable isotope mixing models suggested that sea turtle contributed 40–62% of assimilated C and N for male and 21–40% for female ghost crabs during the nesting season, while other animal and algal sources were also likely to be consumed when sea turtle eggs and hatchlings were absent or present. Aquarium-based feeding assays showed that ghost crabs prefer sea turtle and fish carrion over leafy brown algae (0.81 vs 0.10 vs 0.03 g/h consumed). Sea turtles provide large amounts of nutrients to consumers in the form of eggs and hatchlings, and golden ghost crabs benefit substantially from this pulsed resource along the Ningaloo coast, a World Heritage Area. Through the combined use of SIA, GCA, DNA, and feeding trials, this study highlights the important roles of both sea turtles and ghost crabs in energy fluxes and nutrient cycling at generally nutrient-poor sandy beach ecosystems. However, high consumption rates in the region can possibly put the long-term survival of the C. caretta population at risk. [ABSTRACT FROM AUTHOR]

Context: The distribution of animals is influenced by a complex interplay of landscape, environmental, habitat, and anthropogenic factors. While the effects of each of these forces on fish assemblages have been studied in isolation, the implications of their combined influence within a seascape remain equivocal. Objectives: We assessed the importance of local habitat composition, seascape configuration, and environmental conditions for determining the abundance, diversity, and functional composition of fish assemblages across a tropical seascape. Methods: We quantified fish abundance in coral, macroalgal, mangrove, and sand habitats throughout the Dampier Archipelago, Western Australia. A full-subsets modelling approach was used that incorporated data from benthic habitat maps, a hydrodynamic model, in situ measures of habitat composition, and remotely sensed environmental data to evaluate the relative influence of biophysical drivers on fish assemblages. Results: Measures of habitat complexity were the strongest predictors of fish abundance, diversity, and assemblage composition in coral and macroalgal habitats, with seascape effects playing a secondary role for some functional groups. Proximity to potential nursery habitats appeared to have minimal influence on coral reef fish assemblages. Consequently, coral, macroalgal, and mangrove habitats contained distinct fish assemblages that contributed to the overall diversity of fish within the seascape. Conclusions: Our findings underscore the importance of structural complexity for supporting diverse and abundant fish populations and suggest that the value of structural connectivity between habitats depends on local environmental context. Our results support management approaches that prioritise the preservation of habitat complexity, and that incorporate the full range of habitats comprising tropical seascapes. [ABSTRACT FROM AUTHOR]

Understanding predator-prey interactions at the vulnerable egg and hatchling stage of sea turtles is crucial to effectively manage these threatened marine species. Our research quantified ghost crab predation on loggerhead turtles Caretta caretta at Gnaraloo Bay and Bungelup Beach, two of the four principal nesting sites for this species in the Southeast Indian Ocean. We counted ghost crab burrows along belt transects as a proxy for crab densities. We used start- and end-of-season nesting inventories to determine egg predation rates, in-situ accelerometers to measure predation activity in nests, and infrared videography to assess predation rates on emerging hatchlings. Ghost crab densities and egg predation rates at Gnaraloo Bay were almost twice those at Bungelup Beach. Egg predation was most prevalent at night and in the first and third trimesters of incubation. We did not observe any hatchlings emerging from nests at Gnaraloo Bay, while we observed predation, mainly by ghost crabs and to a lesser extent by seagulls, on 43% of hatchlings at Bungelup Beach. The alarmingly high rate of mortality due to native predators highlights a need for immediate management actions to mitigate this threat to a globally important loggerhead turtle stock. Our multi-method approach provides a holistic estimation of reproductive success from when eggs were laid to when hatchlings reached the relative safety of the ocean. [ABSTRACT FROM AUTHOR]

Habitat complexity and connectivity can influence the number of species and their diversity across a landscape. For the surf zones of ocean-exposed beaches, globally one of the longest habitat interfaces, the assumed low structural complexity, and apparent homogeneity, of the sandy seafloor habitats predicts low taxonomic and functional diversity. Here, we assessed how the configuration of the seascape and the context of different beach structure functional diversity and functional niche space of fish assemblages in surf zones. We expected that beaches that were well connected with highly productive and complex estuarine and reef habitats would support a greater level of functional diversity, and a greater degree of functional complementarity within different niches. We sampled surf zones at twenty-five beaches along 50 km of coastline in southeast Queensland, Australia. We calculated functional diversity and functional niche space using variation in the functional traits of fish assemblages. We found that increased proximity with nearby subtidal rocky reefs was the key feature of the coastline shaping functional diversity and functional niche space in surf zone fishes. These effects resulted in increased functional complementarity within a number of fish functional group niches when rocky reefs were nearby. We provide empirical evidence that habitat proximity can structure functional diversity and complementarity in the surf zones of ocean beaches, a system traditionally viewed as having low habitat heterogeneity. Our results highlight the focus management must take in conserving these highly connected ecosystems to avoid negative functional consequences. [ABSTRACT FROM AUTHOR]

Estuaries are productive ecosystems that provide important ecosystem functions such as the storage and cycling of dissolved organic matter (DOM) and nutrients. Intermittently closed/open lakes and lagoons (ICOLLs) can significantly impact biogeochemical processing and release of terrestrial nitrogen and carbon into the coastal environment due to longer residence times that can extend nutrient processing within the ICOLL. Pulses of nutrient release then occur when there is connectivity between the catchment and coastal waters. It remains unclear how modifications to estuaries and their catchments impact internal processes. To better understand the balance between autochthonous and allochthonous nutrients in a heavily modified ICOLL, multiple stable isotopes (δ13C, δ15N) of dissolved nutrients were used to evaluate seasonal and spatial changes to nitrogen sources and sinks in a southwest Australian ICOLL. The eutrophic status of water bodies has traditionally been based on concentrations of inorganic nitrogen (DIN) (particularly NH4+ and NOx) due to its presumed higher bioavailability and association with anthropogenic pollution. However, both NH4+ and NOx concentrations were low (0 – 12.5 µM) throughout the study area in both wet and dry seasons. Despite low surface water DIN concentrations, the system suffers from eutrophication issues such as algal blooms, low dissolved oxygen, and fish kills. The differences between the surface and porewater dissolved organic nitrogen (DON) and carbon (DOC) pools decreased in the wet season (high connectivity), suggesting that internal DOM turnover sustains eutrophication. This work demonstrates that including DON and its isotopic signature can be an effective way to study N in waterbodies with low DIN concentrations. It also highlights the need for DON, as a major constituent of total dissolved nitrogen, to be included in N studies and ultimately may have significant impact on the current understanding of the global N budget. [ABSTRACT FROM AUTHOR]

Spatial subsidies often occur from highly productive donor ecosystems to recipient systems with low productivity, but little is known about subsidies between highly productive ecosystems. Here, we investigated whether the kelp Ecklonia radiata, which is frequently dislodged from reefs, provides spatial subsidies in adjacent seagrass meadow where in situ productivity is already high. We clarified the pathways of the allochthonous kelp as a spatial subsidy by adding 15N-enriched kelp to Posidonia sinuosa seagrass meadows, tracing the uptake of kelp-derived nitrogen by seagrass epiphytes and epifauna. We observed a 32.5–52.2% loss of kelp biomass (wet weight), representing almost 13,000 μg of 15N from the labelled kelp. This corresponded with an increase in δ15N and 15N biomass of detritivores and epiphytes, showing either a direct or indirect (via epiphytes) assimilation of kelp-derived nutrients. The densities and biomass of the gastropod Strigosella lepidus and shrimps were higher in seagrass plots with input of E. radiata, but not for amphipods or the biomass of epiphytes. We estimate that the detritivores and epiphytes in the seagrass plots assimilated about 3% of the 15N released from the labelled kelp, and based on a data from previous study, the seagrass itself could have assimilated up to a further 6% of the released kelp 15N. Our findings show that in a highly productive seagrass ecosystem, where autochthonous food sources are available, the input of allochthonous resources such as kelp can supplement those resources and appears to play an important a role as a vector for a spatial subsidy. [ABSTRACT FROM AUTHOR]

Hybridisation among species of coral-reef fish was previously considered to be rare. However, recent studies have revealed that hybridisation is prevalent in coral-reef fish, highlighting the need to understand the causes of this process. The angelfishes (family Pomacanthidae) have the greatest proportion (~ 30%) of hybridising species to date, with 26 species reported to hybridise. The aim of this study was to examine ecological factors (rarity of parent species and niche overlap) that promote hybridisation in terrestrial environments and to test these factors in the marine environment by examining hybridising angelfishes at Christmas Island (Indian Ocean). Three species of pygmy angelfish (Centropyge flavissima, C. eibli, and C. vrolikii) and their hybrids were investigated to address three objectives: (1) to determine temporal and spatial patterns in abundance and whether these patterns are linked to environmental factors; (2) to test for overlapping patterns in habitat use; and (3) to test for overlapping patterns in diet. Based on 14 yr of surveys, C. flavissima was abundant (4.53 individuals per 250 m2 ± 0.66), whereas C. eibli, C. vrolikii, and all hybrid combinations were consistently rare (average abundance < 0.3 per 250 m2 ± 0.03). Parent species and their hybrids were more abundant at 20 m depth compared to 5 m. All species and their hybrids had similar patterns of abundance around Christmas Island, with significantly high abundances evident at the most sheltered sites. Parent species and their hybrids also had similar diets that comprised a mix of green, red, and brown algae. The rarity of parent species, their niche overlap, and the haremic reproductive strategy likely promote hybridisation in angelfishes at Christmas Island. This study provides empirical evidence that hybridisation in reef fishes conforms to terrestrial-based hypothesis, and thus advances our understanding of the processes underlying hybridisation in coral-reef systems. [ABSTRACT FROM AUTHOR]

Food webs on sandy beaches rely heavily on spatial subsidies of macroalgae and other detritus. Invasive macroalgal species are modifying many ecosystems worldwide, so the potential exists for them to alter the quantity and quality of food available to sandy beach consumers. We evaluated the suitability of the invasive kelp Undaria pinnatifida as a food for the talitrid amphipod Bellorchestia quoyana, an abundant consumer on sandy beaches in southern New Zealand. U. pinnatifida had similar gross nutritional and biomechanical properties to the three native macroalgal species (the kelps Macrocystis pyrifera and Durvillaea antarctica, and the green Ulva spp.). B. quoyana consumed U. pinnatifida at similar or higher rates than the native kelps in laboratory feeding assays (choice and no-choice assays with fresh tissues, and choice assays with tissue reconstituted into agar foods to remove structural properties). Our results indicate that U. pinnatifida is a usable alternative food source for B. quoyana and could, therefore, contribute to the local sandy beach food web. Understanding the role that invasive macroalgae play as a food source for beach consumers is essential to better comprehend how they may affect these subsidy-dependent ecosystems. [ABSTRACT FROM AUTHOR]

Key to understanding the impacts of invasive macroalgae on local food webs is determining the extent to which native herbivores consume the invasive macroalga. We used multiple-choice feeding assays to ascertain the relative feeding preferences of four subtidal grazers (the amphipod Aora typica, the isopod Batedotea elongata and the gastropods Cookia sulcata and Haliotis iris) for the invasive macroalga Undaria pinnatifida and six native macroalgae ( Macrocystis pyrifera, Durvillaea antarctica, Carpophyllum flexuosum, Cystophora scalaris, Marginariella boryana and Ulva spp.) that are all abundant along the Otago coast of southern New Zealand. Multiple-choice feeding assays were run under laboratory conditions during the austral autumn (April and June) of 2013. The relative abundances of the macroalgae in the field were also determined. All of the grazers ate U. pinnatifida at rates comparable to most of the native macroalgae, except for B. elongata, which barely consumed it. This indicates that U. pinnatifida, which was shown to be more abundant than native macroalgae in subtidal habitats, has the potential to contribute organic matter to the local food web and may be an undesirable food for some group of grazers. We suggest that U. pinnatifida could potentially alter existing trophic relationships. [ABSTRACT FROM AUTHOR]

Nutrients and energy derived from marine autotrophs subsidize shore ecosystems, increasing productivity and affecting food web dynamics and structure. In this study we examined how the inland reach of such inflow effects depends on vectors carrying the marine inflow inland and on landscape structure. We used stable isotopes of carbon and nitrogen to examine the roles of arthropod vectors in carrying marine-derived nutrients inland in two very different shore ecosystems: shore meadows in Sweden with marine inflows of algae and emerging chironomid midges; and sandy beaches and shore dunes in south-western Australia with marine inflows of algae and seagrass. In a colonization experiment, we found that deposited wrack on the beach is quickly colonized by both grazers and predators. However, in both systems we found a larger inland reach of the marine subsidy than could be accounted for by deposited macrophytes on shores alone, and that dipterans and spiders potentially functioned as vectors for the inflow. Our results indicate that marine inflows are important for near-shore terrestrial ecosystems well above the water's edge, and that this effect is largely due to arthropod vectors (mainly dipterans and spiders) in both low-productivity sandy beach ecosystems at the Indian Ocean coast of Australia, and more productive shore meadows on the Baltic Sea coast of Sweden. Our findings also suggest that the type of vector transporting marine material inland may be as important as the productivity contrast between ecosystems for explaining the degree of marine influence on the terrestrial system. [ABSTRACT FROM AUTHOR]

Allorchestes compressa is the dominant macroinvertebrate species in wrack accumulations on surf zones of south-western Australia. These amphipods were provided with a choice of macrophyte material representing brown and red algae and seagrass in a series of preference experiments in the laboratory and field. Feeding experiments showed that A. compressa exhibited a strong preference for particular types of macrophytes ( P < 0.01). Amphipods primarily consumed brown algae, with 69–98% of the biomass of Ecklonia radiata and 64% of the biomass of Sargassum sp. lost over the experiments. This study has shown that the amphipod A. compressa exhibits a clear preference for brown algae over red algae and seagrass as food. In terms of habitat preference, tank experiments using a series of pair-wise comparisons showed that, in the absence of fish predators, A. compressa selected seagrass as its preferred habitat over the other types of wrack ( P < 0.001). When satiated or starved, between 68 and 83 and 79 and 98% of amphipods were found in Amphibolis and Posidonia, respectively. In contrast, field-cage experiments revealed that A. compressa preferred either mixed wrack, brown algae or red algae over seagrass as a habitat ( P < 0.01). The contrasts between results from the laboratory and field suggest that other factors such as the presence of predators, water flow and light could influence habitat choice in the surf zone. This study shows that allochthonous material transported to surf zones from other habitats therefore play different roles in driving secondary production in this shoreline habitat. [ABSTRACT FROM AUTHOR]

Sandbar sharks, Carcharhinus plumbeus, collected from commercial shark fisheries in Western Australia were aged by examination of sectioned vertebrae and analysis of tag-recapture data. Growth curves were derived from consensus counts of growth bands from the vertebrae of 238 individuals ranging in size between 47 and 154 cm fork length (FL). The annual periodicity of growth band formation was validated using vertebrae from tagged sharks, which were injected with oxytetracycline ( n = 9) and calcein ( n = 23) and were at liberty for up to 8.1 years. The oldest female was estimated to be 25 years of age and the oldest male was 19 years. The ages at which 50% of female and male sharks were mature were estimated to be 16.2 and 13.8 years, respectively. Growth increment data from 104 tagged C. plumbeus, which were at liberty for up to 7.4 years, were used to construct growth curves for comparison with those derived from vertebral analysis. The two methods yielded noticeably different results. Based on a known size at birth of 42.5 cm FL, von Bertalanffy parameters estimated using length at age data from vertebral analysis were: K = 0.039 year−1 and L ∞ = 245.8 cm; K = 0.044 year−1 and L ∞ = 226.3 cm; and K = 0.040 year−1 and L ∞ = 239.6 cm for females, males and both sexes combined. The von Bertalanffy parameters derived from tag-recapture data were: K = 0.153 year−1 and L ∞ = 142.0 cm for combined sexes. However, as sharks longer than 142.0 cm were commonly encountered during sampling, these estimates appear to be biologically unrealistic. Also, given the high variability in growth rates of tagged sharks, compared to those derived from the larger vertebral analysis dataset, vertebral ageing was concluded to provide a better description of age and growth in this study. These results confirm that C. plumbeus is a slow-growing and late maturing species and thus recovery times from periods of overexploitation would be considerable. [ABSTRACT FROM AUTHOR]

We examined the diets of 12 morphologically diverse syngnathid species in shallow seagrass-dominated marine waters of south-western Australia to determine whether they differed among species that varied in body form, size and snout morphology, and in particular whether species with long snouts ingested more mobile prey. Although all species consume mainly small crustaceans, the dietary compositions of these species often vary markedly. We suggest that these differences are related to factors that influence both their foraging capabilities and/or locations. Those species with long snouts (e.g. the common seadragonPhyllopteryx taeniolatusand long-snouted pipefishVanacampus poecilolaemus) consume far more relatively mobile prey than species with short snouts. Species with short snouts (e.g. the pug-nosed pipefishPugnaso curtirostrisand Macleay’s crested pipefishHistiogamphelus cristatus) mainly consume slow moving prey. Spotted pipefish,Stigmatopora argus,and wide-bodied pipefish,Stigmatopora nigra, restrict their diets to planktonic copepods, probably because their small gape size limits their ability to feed on alternative larger prey. Both the short-snouted seahorse,Hippocampus breviceps, and West Australian seahorse,Hippocampus subelongatus, ingest mainly slow-moving prey, even though the latter species possesses a moderately long snout. This may reflect the fact that seahorses are weak swimmers that anchor themselves to vegetation or the substrate with a strongly prehensile tail and rarely venture into open water to pursue mobile prey. In contrast, the relatively largeP. taeniolatus, which resides above, rather than within, the macrophyte canopy, consumes mysids, which aggregate in open water above the seabed. Those pipefishes with characters that imply relatively enhanced mobility, such as well developed caudal fins and non-prehensile tails, are trophically diverse, suggesting that they are able to feed either on the sediment or phytal surfaces or in the water column. [ABSTRACT FROM AUTHOR]

Discusses the age, growth and reproduction of Sillago schomburgkii in nearshore waters of south-western Australia. Basis of the conclusion that Sillago schomburgkii is a multiple spawner; Patterns of growth of Sillago species; Comparisons of life history styles of a suite of Sillago species.

Understanding the sources of primary production supporting marine food webs is important for conserving critical habitats. However, the importance of allochthonous versus autochthonous production is often unclear. We identify the sources of primary production supporting three species of predatory fish (Lutjanus carponotatus, Lutjanus fulviflamma, and Lethrinus punctulatus) in the Dampier Archipelago, Western Australia. The proportions of mangrove, seagrass, macroalgae, and suspended particulate organic matter (SPOM) assimilated by fish of different life-history stages and from different habitats were determined using stable isotopes and Bayesian mixing models. While contributions of sources varied among species and habitats, we found that SPOM was an important energetic resource for both adults and juveniles of all three fish species. Juvenile L. carponotatus and L. punctulatus inhabiting macroalgal habitats assimilated more seagrass- and macroalgae-derived material than fish from coral or mangrove habitats, while reliance on mangrove carbon was generally limited overall. Assimilation of macrophyte-derived material decreased throughout ontogeny for L. carponotatus, while L. fulviflamma relied on a combination of SPOM and seagrass into adulthood. The contribution of macroalgae and SPOM to the diets of juvenile L. punctulatus and L. carponotatus from macroalgal habitats varied spatially but was unrelated to seascape configuration, habitat quality, or hydrodynamic conditions. While mixing models suggested a modest degree of trophic connectivity, cross-habitat trophic subsidies provided by macrophytes play a minor role in supporting the studied fish of either life-history stage. Instead, microalgal production predominantly fuels the productivity of predatory fish in this turbid, macrotidal system. [ABSTRACT FROM AUTHOR]