Bronwyn M. Gillanders

The Identification, Conservation, and Management of Estuarine and Marine Nurseries for Fish and Invertebrates

Michael W. Beck, Kenneth L. Heck, Jr., Kenneth W. Able, Daniel L. Childers, David B. Eggleston, Bronwyn M. Gillanders, Benjamin Halpern, Cynthia G. Hays, Kaho Hoshino, Thomas J. Minello, Robert J. Orth, Peter F. Sheridan and Michael P. Weinstein

Reconstructing migratory patterns of fish based on environmental influences on otolith chemistry

The analysis of elements in calcifiedstructures of fish (e.g., otoliths) todiscriminate among fish stocks and determineconnectivity between populations is becomingwidespread in fisheries research. Recently, theconcentrations of elements in otoliths arebeing analysed on finer scales that allow thedetermination of a continuous record of otolithchemistry over a fishs entire life history.These elemental concentrations can potentiallybe used to reconstruct migration patterns,based upon the influence that water chemistry,temperature, and salinity have on otolithchemistry. In doing so, assumptions are madeabout how environmental and biological factorsinfluence the concentration of elements in fishotoliths. However, there have been fewexperiments that have tested crucialassumptions regarding what influences elementaluptake and incorporation into fish otoliths.Specifically, knowledge regarding interactionsamong environmental variables, such as theambient concentration of elements in water,temperature, and salinity, and how they mayaffect otolith chemistry, is limited.Similarly, our understanding of the rate atwhich elements are incorporated into otolithsand the implications this may have forinterpretations is lacking. This reviewdiscusses methods of determining movement offish, the development of otolith research, andsome physiological aspects of otoliths (e.g.,pathways of elemental uptake). The types ofanalysis techniques that will lead to reliableand accurate migratory reconstructions areoutlined. The effects that have on otolith chemistry arereviewed with the specific aim of highlightingareas lacking environmentalvariables in experimental data. Theinfluences of the rate of elementalincorporation and ontogeny on otolith chemistryare also addressed. Finally, future researchdirections are suggested that will fill thegaps in our current knowledge of otolithchemistry. Hypotheses that need to be tested inorder to reconstruct the migratory histories offish are outlined, in a bid to clarify thedirection that research should take beforecomplex reconstructions are attempted.

Approaches to resolving cephalopod movement and migration patterns

Cephalopod movement occurs during all phases of the life history, with the abundance and location of cephalopod populations strongly influenced by the prevalence and scale of their movements. Environmental parameters, such as sea temperature and oceanographic processes, have a large influence on movement at the various life cycle stages, particularly those of oceanic squid. Tag recapture studies are the most common way of directly examining cephalopod movement, particularly in species which are heavily fished. Electronic tags, however, are being more commonly used to track cephalopods, providing detailed small- and large-scale movement information. Chemical tagging of paralarvae through maternal transfer may prove to be a viable technique for tracking this little understood cephalopod life stage, as large numbers of individuals could be tagged at once. Numerous indirect methods can also be used to examine cephalopod movement, such as chemical analyses of the elemental and/or isotopic signatures of cephalopod hard parts, with growing interest in utilising these techniques for elucidating migration pathways, as is commonly done for fish. Geographic differences in parasite fauna have also been used to indirectly provide movement information, however, explicit movement studies require detailed information on parasite-host specificity and parasite geographic distribution, which is yet to be determined for cephalopods. Molecular genetics offers a powerful approach to estimating realised effective migration rates among populations, and continuing developments in markers and analytical techniques hold the promise of more detailed identification of migrants. To date genetic studies indicate that migration in squids is extensive but can be blocked by major oceanographic features, and in cuttlefish and octopus migration is more locally restricted than predictions from life history parameters would suggest. Satellite data showing the location of fishing lights have been increasingly used to examine the movement of squid fishing vessels, as a proxy for monitoring the movement of the squid populations themselves, allowing for the remote monitoring of oceanic species.

Spatial variation in elemental composition of otoliths of three species of fish (family Sparidae)

Determining the nursery habitat of fishes that have moved from estuarine nursery habitats is difficult. The elemental fingerprints of otoliths of three species of sparids were determined to investigate their utility as a natural tag of the nursery habitat. Juvenile Pagrus auratus (snapper), Rhabdosargus sarba (tarwhine) and Acanthopagrus australis (bream) were collected from two sites in each of 15, six and three estuaries, respectively, and their otoliths analysed by solution-based inductively coupled plasma-mass spectrometry. Significant differences in otolith chemistry were found for all three species of juveniles collected from different estuaries. The same patterns among estuaries were not seen for all species, although it was not possible to sample the same sites within an estuary for all species. For bream, significant differences in otolith chemistry were found among all three estuaries, whereas for tarwhine the six estuaries were separated into three groups. For snapper, a number of estuaries could be separated, but there was some overlap for other estuaries. All three species were collected from the same site within one estuary and their otoliths analysed. Significant differences were found among species, but the implication of this finding remains unclear as the three species show differences in microhabitat use and may also differ in age. Because the elemental fingerprints of juveniles vary among estuaries or groups of estuaries, the nursery or recruitment estuary of adult fish could now be determined by analysing the juvenile region of adult otoliths. Thus, connectivity between estuaries and open coastal populations could be determined. Such information will have major implications for fisheries management because it will provide information on the distance that fish have moved from their recruitment estuary and the number of estuaries that contribute to each adult population.

Potential effects of climate change on Australian estuaries and fish utilising estuaries: a review

Estuaries are especially vulnerable to the impacts of climate change because changes in climatic and hydrologic variables that influence freshwater and marine systems will also affect estuaries. We review potential impacts of climate change on Australian estuaries and their fish. Geographic differences are likely because southern Australian climates are predicted to become warmer and drier, whereas northern regions may see increased precipitation. Environmental factors, including salinity gradients, suspended sediment, dissolved oxygen and nutrient concentrations, will be influenced by changing freshwater input and other climate variables. Potential impacts will vary depending on the geomorphology of the estuary and the level of build-up of sand bars across estuarine entrances. Changes to estuarine fish assemblages will depend on associated changes to salinity and estuarine-mouth morphology. Marine migrants may be severely affected by closure of estuarine mouths, depending on whether species ‘must’ use estuarine habitat and the level of migratory v. resident individuals. Depending on how fish in coastal waters locate estuaries, there may be reduced cues associated with estuarine mouths, particularly in southern Australia, potentially influencing abundance. In summary, climate change is expected to have major consequences for Australian estuaries and associated fish, although the nature of impacts will show significant regional variation.

Climate change and Australian marine and freshwater environments, fishes and fisheries: synthesis and options for adaptation

Anthropogenic climate change is already apparent and will have significant, ongoing impacts on Australian fishes and their habitats. Even with immediate actions to reduce greenhouse gases, there will be sustained environmental changes. Therefore, it is necessary to consider appropriate adaptations to minimise detrimental impacts for both fishes and the human populations that utilise them. Climate change will have a range of direct effects on the physiology, fitness, and survivorship of Australia’s marine, estuarine and freshwater fishes, but also indirect effects via habitat degradation and changes to ecosystems. Effects will differ across populations, species and ecosystems, with some impacts being complex and causing unexpected outcomes. The range of adaptation options and necessary levels of intervention to maintain populations and ecosystem function will largely depend on the vulnerability of species and habitats. Climate change will also have an impact on people who depend on fishes for food or livelihoods; adapting to a new climate regime will mean trade-offs between biological assets and socioeconomic drivers. Models can be used to help predict trends and set priorities; however, they must be based on the best available science and data, and include fisheries, environmental, socioeconomic and political layers to support management actions for adaptation.

Fish and Invertebrate Assemblages in Seagrass, Mangrove, Saltmarsh, and Nonvegetated Habitats

Many studies compare utilization of different marine habitats by fish and decapod crustaceans; few compare multiple vegetated habitats, especially using the same sampling equipment. Fish and invertebrates in seagrass, mangrove, saltmarsh, and nonvegetated habitats were sampled during May–August (Austral winter) and December–January (Austral summer) in the Barker Inlet-Port River estuary, South Australia. Sampling was undertaken using pop nets in all habitats and seine nets in seagrass and nonvegetated areas. A total of 7,895 fish and invertebrates spanning 3 classes, 9 orders, and at least 23 families were collected. Only one fish species,Atherinosoma microstoma, was collected in all 4 habitats, 11 species were found in 3 habitats (mangroves, seagrass, and nonvegetated), and 13 species were only caught in seagrass and nonvegetated habitats. Seagrass generally supported the highest numbers of fish and invertebrates and had the greatest species richness. Saltmarsh was at the other extreme with 29 individuals caught from two species. Mangroves and nonvegetated habitats generally had more fish, invertebrates, and species than saltmarsh, but less than seagrass. Analyses of abundances of individual species generally showed an interaction between habitat and month indicating that the same patterns were not found through time in all habitats. All habitats supported distinct assemlages although seagrass and nonvegetated assemblages were similar in some months. The generality of these patterns requires further investigation at other estuaries. Loss of vegetated habitats, particularly seagrass, could result in loss of species richness and abundance, especially for organisms that were not found in other habitats. Although low abundances were found in saltmarsh and mangroves, species may use these habitats for varying reasons, such as spawning, and such use should not be ignored.

Spatial and habitat-related patterns of temperate reef fish assemblages: implications for the design of Marine Protected Areas

Patterns of rocky reef fish assemblages (composition and relative abundance of species) were examined to provide data on the design of Marine Protected Areas (MPAs), which aim to protect these organisms. A hierarchical design was used to investigate changes in fish assemblages at scales of metres to kilometres along-shore, and among reef habitat types within two 10-km areas on the central coast of New South Wales, Australia. Influences of physical and biological attributes of a reef on assemblages of fish were also examined. The greatest variation in fish assemblages occurred at scales of 2–6 km along-shore. Eighty percent of species recorded were found within a 6-km section of coastline. The most predictable differences in assemblages were found between reef habitats (urchin-grazed barrens, Ecklonia forest and sponge habitat), and between depths. Marine Protected Areas should ideally incorporate all available habitats over the entire depth range at which they occur. This may require MPAs larger than 2–6 km, or multiple MPAs that have been specifically located to include these features, as representation of habitats was found to vary at scales of kilometres to tens of kilometres along shore.

Consistency of patterns between laboratory experiments and field collected fish in otolith chemistry: an example and applications for salinity reconstructions

Elemental concentrations within fish otoliths can track movements and migrations of fish through gradients of environmental variables. Tracking the movements of fish relies on establishing links between environmental variables and otolith chemistry, with links commonly made using laboratory experiments that rear juvenile fish. However, laboratory experiments done on juvenile fish may not accurately reflect changes in wild fish, particularly adults. We tested the hypotheses that: (1) the relationship between ambient (water) and otolith chemistry is similar between laboratory-reared black bream (Acanthopagrus butcheri) and wild black bream; and (2) ontogeny does not influence otolith chemistry. Field-collected and laboratory-reared fish showed similar effects of ambient strontium : calcium (Sr : Ca) on otolith Sr : Ca concentrations. However, ambient and otolith barium : calcium concentrations (Ba : Ca) differed slightly between laboratory-reared and field-collected fish. Importantly, fish reared in stable environmental variables showed no influence of ontogeny on Sr : Ca or Ba : Ca concentrations. Natural distributions of ambient Sr : Ca showed no clear relationship to salinity, yet, ambient Ba : Ca was inversely related to salinity. The distribution of ambient Sr : Ca and Ba : Ca in estuaries inhabited by black bream, suggest that these elements can answer different questions regarding environmental histories of fish. Reconstructing salinity histories of black bream using otolith Ba : Ca concentrations seems plausible, if adequate knowledge of Ba : Ca gradients within estuaries is obtained.

Accelerometry estimates field metabolic rate in giant Australian cuttlefish Sepia apama during breeding

1. Estimating the metabolic rate of animals in nature is central to understanding the physiological, behavioural and evolutionary ecology of animals. Doubly labelled water and heart-rate methods are the most commonly used approaches, but both have limitations that preclude their application to some systems. 2. Accelerometry has emerged as a powerful tool for estimating energy expenditure in a range of animals, but is yet to be used to estimate field metabolic rate in aquatic taxa. We combined two-dimensional accelerometry and swim-tunnel respirometry to estimate patterns of energy expenditure in giant Australian cuttlefish Sepia apama during breeding. 3. Both oxygen consumption rate (Vo2) and swimming speed showed strong positive associations with body acceleration, with coefficients of determination comparable to those using similar accelerometers on terrestrial vertebrates. Despite increased activity during the day, field metabolic rate rarely approached Vo2, and night-time Vo2 was similar to that at rest. 4. These results are consistent with the life-history strategy of this species, which has a poor capacity to exercise anaerobically, and a mating strategy that is visually based. With the logistical difficulties associated with observation in aquatic environments, accelerometry is likely to prove a valuable tool for estimating energy expenditure in aquatic animals.