Landscape edges shape dispersal and population structure of a migratory fish

Many freshwater organisms have a life-history stage that can disperse through seawater. This has obvious benefits for colonization and connectivity of fragmented sub-populations, but requires a physiologically challenging migration across a salinity boundary. We consider the role of landscape boundaries between freshwater and seawater habitats, and evaluate their potential effects on traits and developmental histories of larvae and juveniles (i.e., dispersing life-history stages) of an amphidromous fish, Galaxias maculatus. We sampled juvenile fish on their return to 20 rivers in New Zealand: 10 rivers had abrupt transitions to the sea (i.e., emptying to an open coastline); these were paired with 10 nearby rivers that had gradual transitions to the sea (i.e., emptying into estuarine embayments). We reconstructed individual dispersal histories using otolith microstructure, otolith microchemistry, and stable isotope analysis. We found that fish recruiting to embayment rivers had distinct dispersal and foraging histories, were slower growing, smaller in size, and older than fish recruiting to nearby non-embayment rivers. Our results indicate that landscape edges can affect dispersal capabilities of aquatic organisms, potentially leading to divergent life-history strategies (i.e., limited- versus widespread-dispersal). Patterns also suggest that dispersal potential among landscape boundaries can create heterogeneity in the traits of individuals, with implications for metapopulation dynamics.

Building blue infrastructure: Assessing the key environmental issues and priority areas for ecological engineering initiatives in Australia's metropolitan embayments

Ecological engineering principles are increasingly being applied to develop multifunctional artificial structures or rehabilitated habitats in coastal areas. Ecological engineering initiatives are primarily driven by marine scientists and coastal managers, but often the views of key user groups, which can strongly influence the success of projects, are not considered. We used an online survey and participatory mapping exercise to investigate differences in priority goals, sites and attitudes towards ecological engineering between marine scientists and coastal managers as compared to other stakeholders. The surveys were conducted across three Australian cities that varied in their level of urbanisation and environmental pressures. We tested the hypotheses that, relative to other stakeholders, marine scientists and coastal managers will: 1) be more supportive of ecological engineering; 2) be more likely to agree that enhancement of biodiversity and remediation of pollution are key priorities for ecological engineering; and 3) identify different priority areas and infrastructure or degraded habitats for ecological engineering. We also tested the hypothesis that 4) perceptions of ecological engineering would vary among locations, due to environmental and socio-economic differences. In all three harbours, marine scientists and coastal managers were more supportive of ecological engineering than other users. There was also greater support for ecological engineering in Sydney and Melbourne than Hobart. Most people identified transport infrastructure, in busy transport hubs (i.e. Circular Quay in Sydney, the Port in Melbourne and the Waterfront in Hobart) as priorities for ecological engineering, irrespective of their stakeholder group or location. There were, however, significant differences among locations in what people perceive as the key priorities for ecological engineering (i.e. biodiversity in Sydney and Melbourne vs. pollution in Hobart). Greater consideration of these location-specific differences is essential for effective management of artificial structures and rehabilitated habitats in urban embayments.

Contrasting patterns in habitat selection and recruitment of temperate reef fishes among natural and artificial reefs

Artificial reefs, a common management tool for stock enhancement of recreational fisheries and marine habitat restoration, have been deployed all over the world. However, little is known about the attractiveness of artificial compared to natural reefs to reef fishes. Here we investigated the habitat preferences of three reef fish species: Trachinops caudimaculatus, Vincentia conspersa and Trinorfoklia clarkei through the observation of recruitment patterns to three study habitats: Reef Ball reefs, custom-designed artificial reefs, and natural reefs in Port Phillip Bay, Victoria, Australia. Additionally, we examined habitat preferences of new recruits of T. caudimaculatus and V. conspersa using laboratory-based habitat choice experiments. In general, T. caudimaculatus recruitment was at least twice as high on natural reefs compared to both artificial reefs, whereas V. conspersa recruitment was almost three times greater on Reef Ball reefs compared to the other two habitats. T. clarkei recruited in equal numbers across all habitats. However, in the laboratory experiments T. caudimaculatus recruits selected the Reef Ball reef almost three times as often as the other two habitats, while V. conspersa exhibited no habitat preference. Little is known about the growth, condition, survival or reproduction of individuals that occupy artificial reefs. In areas where habitat is not limiting, the higher preference or equal attractiveness of some artificial habitats may negatively influence fish populations, if larvae are redirected to poorer quality artificial reef habitat, that lead to lower fitness advantages.

Independent estimates of marine population connectivity are more concordant when accounting for uncertainties in larval origins

Marine larval dispersal is a complex biophysical process that depends on the effects of species biology and oceanography, leading to logistical difficulties in estimating connectivity among populations of marine animals with biphasic life cycles. To address this challenge, the application of multiple methodological approaches has been advocated, in order to increase confidence in estimates of population connectivity. However, studies seldom account for sources of uncertainty associated with each method, which undermines a direct comparative approach. In the present study we explicitly account for the statistical uncertainty in observed connectivity matrices derived from elemental chemistry of larval mussel shells, and compare these to predictions from a biophysical model of dispersal. To do this we manipulate the observed connectivity matrix by applying different confidence levels to the assignment of recruits to source populations, while concurrently modelling the intrinsic misclassification rate of larvae to known sources. We demonstrate that the correlation between the observed and modelled matrices increases as the number of observed recruits classified as unknowns approximates the observed larval misclassification rate. Using this approach, we show that unprecedented levels of concordance in connectivity estimates (r = 0.96) can be achieved, and at spatial scales (20-40 km) that are ecologically relevant.

Born at the right time? A conceptual framework linking reproduction, development, and settlement in reef fish

Parents are expected to make decisions about reproductive timing and investment that maximize their own fitness, even if this does not maximize the fitness of each individual offspring. When offspring survival is uncertain, selection typically favors iteroparity, which means that offspring born at some times can be disadvantaged, while others get lucky. The eventual fate of offspring may be further modified by their own decisions. Are fates of offspring set by birthdates (i.e., determined by parents), or can offspring improve upon the cards they've been dealt? If so, do we see adaptive plasticity in the developmental timing of offspring? We evaluate these questions for a coral reef fish (the sixbar wrasse, Thalassoma hardwicke) that is characterized by extreme iteroparity and flexible larval development. Specifically, we monitored larval settlement to 192 small reefs over 11 lunar months and found that most fish settled during new moons of a lunar cycle (consistent with preferential settlement on dark nights). Settlement was significantly lower than expected by chance during the full moon and last quarter of the lunar cycle (consistent with avoidance of bright nights). Survival after settlement was greatest for fish that settled during times of decreasing lunar illumination (from last quarter to new moon). Fish that settled on the last quarter of the lunar cycle were ~10% larger than fish that settled during other periods, suggesting larvae delay settlement to avoid the full moon. These results are consistent with a numerical model that predicts plasticity in larval development time that enables avoidance of settlement during bright periods. Collectively, our results suggest that fish with inauspicious birthdates may alter their developmental trajectories to settle at better times. We speculate that such interactions between parent and offspring strategies may reinforce the evolution of extreme iteroparity and drive population dynamics, by increasing the survival of offspring born at the "wrong" time by allowing them to avoid the riskiest times of settlement.

The nose knows: linking sensory cue use, settlement decisions, and post-settlement survival in a temperate reef fish

Habitat selection by animals that migrate or disperse ultimately determines the biotic and abiotic environment they will experience in subsequent life stages. Intuitively, for habitat selection to be adaptive, animals should respond positively to cues produced by habitat characteristics that will enhance their fitness in the new environment. However, there are many examples of dispersing animals where individuals are attracted to cues produced by factors that reduce their fitness after arrival. In this study, we use a temperate reef fish to examine the relative importance of habitat-associated cues in habitat selection decisions, and assess whether use of these cues is adaptive across early life stages. We used a series of laboratory- and field-based manipulative experiments to test: (1) what habitat-associated cues are likely used to locate suitable habitat; (2) whether in situ settlement patterns reflect the cue response tested in the laboratory; and (3) whether the aspects of the habitat that stimulate settlement are the same as those that maximize survival. We observed a positive response to multiple habitat-associated cues, with conspecific cues eliciting the strongest behavioral response in laboratory choice experiments, and a strong inverse density-dependent relationship at settlement. Macroalgal cues also elicited a positive response at settlement, but were associated with higher mortality after settlement, suggesting that habitat selection decisions are not always adaptive. We argue that this non-intuitive behavior may still be adaptive if it improves fitness at an earlier life stage, as habitat selection behavior is the result of tradeoffs in fitness costs across multiple stages.

Rapid growth causes abnormal vaterite formation in farmed fish otoliths

Sagittal otoliths are essential components of the sensory organs that enable all teleost fish to hear and maintain balance, and are primarily composed of calcium carbonate. A deformity, where aragonite (the normal crystal form) is replaced with vaterite, was first noted over 50 years ago but its underlying cause is unresolved. We evaluated the prevalence of vateritic otoliths from two captive rearing studies which suggested that fast growth, due to environmental rather than genetic control, led to vaterite development. We then tested this by varying light and temperature to create phenotypes with different growth rates, which resulted in fast growers (5x larger) having 3 times more vaterite than slow growers. A decrease in either the ratio of otolith matrix proteins (otolin-1/OMM-64) or [Ca2+]/[CO32–] may explain why fast growth causes vaterite deposition. As vaterite decreases hearing sensitivity, reducing growth rates in hatcheries may improve the welfare of farmed fish and increase the success of conservation efforts.

High prevalence of vaterite in sagittal otoliths causes hearing impairment in farmed fish

The rapid growth of aquaculture raises questions about the welfare status of mass-produced species. Sagittal otoliths are primary hearing structures in the inner ear of all teleost (bony) fishes and are normally composed of aragonite, though abnormal vaterite replacement is sometimes seen in the wild. We provide the first widespread evaluation of the prevalence of vaterite in otoliths, showing that farmed fish have levels of vaterite replacement over 10 times higher than wild fish, regardless of species. We confirm this observation with extensive sampling of wild and farmed Atlantic salmon in Norway, the world's largest producer, and verify that vateritic otoliths are common in farmed salmon worldwide. Using a mechanistic model of otolith oscillation in response to sound, we demonstrate that average levels of vaterite replacement result in a 28-50% loss of otolith functionality across most of a salmonid's known hearing range and throughout its life cycle. The underlying cause(s) of vaterite formation remain unknown, but the prevalence of hearing impairment in farmed fish has important implications for animal welfare, the survival of escapees and their effects on wild populations, and the efficacy of restocking programs based on captive-bred fish.

Influence of freshwater flows on the distribution of eggs and larvae of black bream Acanthopagrus butcheri within a drought-affected estuary

This study tested the hypothesis that variable freshwater flow in the Gippsland Lakes, Australia, influences the location and extent of environmental conditions suitable for spawning and larval development of black bream, Acanthopagrus butcheri. Freshwater flow had a large influence on the salinity and level of stratification (difference between bottom and surface salinity) in the Gippsland Lakes. Freshwater flows throughout this study varied from no or low flows through to major flooding in 2007. Eggs of A. butcheri were found in similar concentrations throughout the lakes and rivers. More than 99% of larvae, however, were collected from within rivers, with very few larvae being collected from the lakes. A comparison of two spawning seasons revealed that the year with higher freshwater flows also had greater spawning activity and higher concentrations of larvae. Interestingly, there was a significant relationship between the distribution of eggs and larvae with the level of stratification. The highest concentrations of larvae occurred at sites with a difference in bottom and surface salinities of 15-20. This study demonstrates that despite A. butcheri spawning in the lakes and rivers, it is only locations with a halocline that function as larval nursery habitat.

Extended incubation affects larval morphology, hatching success and starvation resistance in a terrestrially spawning fish, Galaxias maculatus (Jenyns 1842)

The effect of extended incubation (delayed hatching) on larval morphology in the terrestrially spawning common galaxias Galaxias maculatus was investigated by inducing larvae to hatch 1 and 2 weeks after the normal 2 week incubation period. After 1 week of extended incubation, larvae were larger (longer in standard length, L(S), and greater in body depth) compared to controls (larvae that experienced normal incubation durations). After 2 weeks of extended incubation, larvae were smaller (shorter in L(S) and smaller in body depth) than larvae that experienced 1 week of extended incubation. Furthermore, eye area increased while yolk-sac size decreased monotonically with increasing incubation duration. These results suggest that larvae experiencing long periods of extended incubation are using somatic tissue to meet their metabolic demands. Larvae that experienced 2 weeks of extended incubation succumbed to starvation sooner than control larvae, but hatching success was not significantly different. Temperature mediated the effect of extended incubation on the morphology of larvae at hatching, most likely, through its effects on developmental rate and efficiency of yolk utilization. This study demonstrates some of the consequences of terrestrial spawning with extended incubation, which will assist in determining why this intriguing behaviour has evolved several times in a diverse range of taxa.

Post-settlement migratory behaviour and growth-related costs in two diadromous fish species, Galaxias maculatus and Galaxias brevipinnis

The physiological challenges incurred during the transition from sea to fresh water and the constraints they place on the rate at which the common galaxiid Galaxias maculatus and the climbing galaxiid Galaxias brevipinnis can migrate from marine to freshwater habitats were examined. The duration of the marine to freshwater transition, the relationship between post-settlement age (PSA) and standard length (L(S)) as a proxy for energetic costs incurred during settlement and the potential effects of estuary geomorphology on migratory behaviour was investigated. Rate of upstream migration after settlement was not uniform. Upstream migration rate was slowest directly after settlement and increased with increasing PSA and distance from the river mouth, indicating a delay in upstream migration by newly recruited galaxiids. L(s) did not increase with age, at least within the first 21 days post settlement. These patterns were consistent for both species, in spite of differences in their life histories, across the recruitment season, despite seasonal variation in recruit size, and among estuaries with different properties. The results suggest that the timing and speed of migratory behaviour primarily reflect physiological constraints. Given the duration of residency of these species in estuaries, this study indicates that estuaries are critical transitional habitats for diadromous fishes during their migration from marine to freshwater habitats.

Life history, pathology, and description of Kudoa ovivora n. sp. (Myxozoa, Myxosporea): an ovarian parasite of Caribbean labroid fishes

We describe Kudoa ovivora n. sp. from ovaries of bluehead wrasse, Thalassoma bifasciatum, and record its presence in 6 species (Labroidei) collected in the San Blas Islands. Panama. Kudoa ovivora spores are quadrate with rounded edges in apical view, oval-shaped with apical valve extensions in side view (mean spore dimensions: length 6.5 microns, width 7.7 microns, thickness 6.9 microns; mean polar capsule dimensions: length 2.1 microns, width 1.5 microns). This is the first Kudoa species from gonads of fishes. Prevalence of infection varied among labrids (Thalassoma bifasciatum, Halichoeres bivittatus, Halichoeres garnoti, Halichoeres poevi), with T. bifasciatum exhibiting the greatest prevalence. Density of infection, measured as percent infected eggs, also varied among species with highest densities occurring in H. garnoti. Kudoa ovivora may not require an intermediate host because fishes fed infected tissue developed more infections than unfed fish. Infected eggs are inviable and larger and heavier than uninfected eggs. Infected eggs contain more organic and inorganic material, indicating that K. ovivora increases resource allocation to eggs. Therefore, infected females may have reduced growth, fecundity, and/or spawning activity. Because males were uninfected and all identified hosts are protogynous sequential hermaphrodites, further studies of K. ovivora may provide new insights on the costs/benefits of sex change.

Social Control of Sex Change in the Bluehead Wrasse, Thalassoma bifasciatum (Pisces: Labridae)

While the bluehead wrasse has long been used as a test species in sex allocation theory, there is no published evidence that sex change in this species is socially controlled. Here we show that removal of large terminal color phase (TP) males from local populations leads to sex and color change in the largest initial color phase (IP) females. In contrast, no sex changes occurred in control populations in which the TP males were handled but replaced, and in which only the IP males were removed. The response to removals was quite precise, resulting in a nearly one-to-one replacement of TP males. Large individuals that had been seen spawning as female males on the day prior to the manipulation, initiated male behaviors within minutes of the removal of the TP males and spawned in the male role the same day. Color changes were noted within a day and were distinct within four days. Sex change was verified by histological examination of the gonads of the changing individuals. All had functional testes, and all showed evidence of recent transition from the ovarian condition. Mature sperm can be produced in as little as eight days after the initiation of sex change.