Species habitat associations are often complex, making it difficult to assess their influence on populations. Among coral reef fishes, habitat requirements vary among species and with ontogeny, but ...the relative importance of nursery and adult-preferred habitats on future abundances remain unclear. Moreover, adult populations may be influenced by recruitment of juveniles and assessments of habitat importance should consider relative effects of juvenile abundance. We conducted surveys across 16 sites and 200 km of reef to identify the microhabitat preferences of juveniles, sub-adults and adults of the damselfish Pomacentrus moluccensis. Microhabitat preferences at different life-history stages were then combined with 6 years of juvenile abundance and microhabitat availability data to show that the availability of preferred juvenile microhabitat (corymbose corals) at the time of settlement was a strong predictor of future sub-adult and adult abundance. However, the influence of nursery microhabitats on future population size differed spatially and at some locations abundance of juveniles and adult microhabitat (branching corals) were better predictors of local populations. Our results demonstrate that while juvenile microhabitats are important nurseries, the abundance of coral-dependent fishes is not solely dependent on these microhabitats, especially when microhabitats are readily available or following large influxes of juveniles.
The dynamic nature of coral reefs offers a rare opportunity to examine the response of ecosystems to disruption due to climate change. In 1998, the Great Barrier Reef experienced widespread coral ...bleaching and mortality. As a result, cryptobenthic fish assemblages underwent a dramatic phase-shift. Thirteen years, and up to 96 fish generations later, the cryptobenthic fish assemblage has not returned to its pre-bleach configuration. This is despite coral abundances returning to, or exceeding, pre-bleach values. The post-bleach fish assemblage exhibits no evidence of recovery. If these short-lived fish species are a model for their longer-lived counterparts, they suggest that (1) the full effects of the 1998 bleaching event on long-lived fish populations have yet to be seen, (2) it may take decades, or more, before recovery or regeneration of these long-lived species will begin, and (3) fish assemblages may not recover to their previous composition despite the return of corals.
Scientists and managers rely on indicator taxa such as coral and macroalgal cover to evaluate the effects of human disturbance on coral reefs, often assuming a universally positive relationship ...between local human disturbance and macroalgae. Despite evidence that macroalgae respond to local stressors in diverse ways, there have been few efforts to evaluate relationships between specific macroalgae taxa and local human‐driven disturbance. Using genus‐level monitoring data from 1205 sites in the Indian and Pacific Oceans, we assess whether macroalgae percent cover correlates with local human disturbance while accounting for factors that could obscure or confound relationships. Assessing macroalgae at genus level revealed that no genera were positively correlated with all human disturbance metrics. Instead, we found relationships between the division or genera of algae and specific human disturbances that were not detectable when pooling taxa into a single functional category, which is common to many analyses. The convention to use percent cover of macroalgae as an indication of local human disturbance therefore likely obscures signatures of local anthropogenic threats to reefs. Our limited understanding of relationships between human disturbance, macroalgae taxa, and their responses to human disturbances impedes the ability to diagnose and respond appropriately to these threats.
Scientists and managers rely on indicator taxa such as macroalgal cover to evaluate the effects of human disturbance on coral reefs, often assuming a universally positive relationship between local human disturbance and macroalgae. We use genus‐level monitoring data from 1205 sites to test this assumption. We found relationships between the division or genera of algae and specific human disturbances that were not detectable when pooling taxa into a single functional category, suggesting that the convention to use percent cover of macroalgae as an indication of local human disturbance likely obscures signatures of local anthropogenic threats to reefs.
Macroalgae‐dominated reefs are a prominent habitat in tropical seascapes that support a diversity of fishes, including fishery target species. To what extent, then, do macroalgal habitats contribute ...to small‐scale tropical reef fisheries? To address this question we: (1) Quantified the macroalgae‐associated fish component in catches from 133 small‐scale fisheries, (2) Compared life‐history traits relevant to fishing (e.g. growth, longevity) in macroalgal and coral‐associated fishes, (3) Examined how macroalgae‐associated species can influence catch diversity, trophic level and vulnerability and (4) Explored how tropical fisheries change with the expansion of macroalgal habitats using a case study of fishery‐independent data for Seychelles. Fish that utilised macroalgal habitats comprise 24% of the catch, but very few fished species relied entirely on macroalgal or coral habitats post‐settlement. Macroalgal and coral‐associated fishes had similar life‐history traits, although vulnerability to fishing declined with increasing contribution of macroalgae association to the catch, whilst mean trophic level and diversity peaked when macroalgal‐associated fish accounted for 20%–30% of catches. The Seychelles case study revealed similar total fish biomass on macroalgal and coral reefs, although the biomass of primary target species increased as macroalgae cover expanded. Our findings reinforce that multiple habitat types are needed to support tropical fishery stability and sustainability. Whilst coral habitats have been the focus of tropical fisheries management, we show the potential for macroalgae‐associated fish to support catch size and diversity in ways that reduce vulnerability to overfishing. This is pertinent to seascapes where repeated disturbances are facilitating the replacement of coral reef with macroalgal habitats.
Within the complex food webs that occur on coral reefs, mesopredatory fish consume small-bodied prey and transfer accumulated biomass to other trophic levels. We estimated biomass, growth and ...mortality rates of three common mesopredators from Ningaloo Reef in Western Australia to calculate their annual turnover rates and potential contribution to local trophic dynamics. Biomass estimates of the serranid
Epinephelus rivulatus
(4.46 ± 0.76 g m
−2
) were an order of magnitude greater than two smaller-bodied mesopredatory fishes,
Pseudochromis fuscus
(0.10 ± 0.03 g m
−2
) and
Parapercis clathrata
(0.23 ± 0.31 g m
−2
). Growth parameters generated from a von Bertalanffy growth function fitted to size-at-age data, however, indicated that mortality rates for the three mesopredators were similar and that 32–55 % of fish survived each year. Consequently, interspecific differences in annual turnover rates among
E. rivulatus
(1.9 g m
−2
yr
−1
),
Pa. clathrata
(0.10 g m
−2
yr
−1
) and
Ps. fuscus
(0.07 g m
−2
yr
−1
) were an artefact of differences in local biomass estimates. The rapid turnover estimates for
E. rivulatus
suggest this species is an important conduit of energy within the isolated patch reef habitat where it is typically found, while
Ps. fuscus
and
Pa. clathrata
channel smaller amounts of energy from specific habitats in the Ningaloo lagoon. Apparent differences in habitat, diet and turnover rates of the three species examined provide an insight into the different roles these species play in coral reef food webs and suggest that life-history traits allow for variability in the local and spatial contribution of these species at Ningaloo Reef. Moreover, calculating turnover rates of a broader suite of fish species from a range of trophic groups will help better define the role of fishes in coral reef trophic dynamics.
The distribution and abundance of small cryptic reef fishes were quantified among microhabitats and reef zones at both exposed and sheltered sites at Lizard Island, Great Barrier Reef. A total of ...1042 individuals from 44 species in 8 families were sampled. Marked variation in abundance, species numbers, size-class distribution and species composition were displayed among reef zones at exposed sites; in contrast, comparatively little variation was found in sheltered sites. The exposed, wave-swept front flat reef zone was clearly the most depauperate and species-poor zone with calmer back reef, lagoonal and reef base zones containing the highest numbers of individuals and species. Larger, heavier individuals predominated in exposed wave-swept reef zones whereas smaller, lighter individuals were commonly found in calmer waters. Sheltered sites exhibited little variation among zones. In these sites, microhabitat appeared to play a much greater role in shaping community composition. Overall, 68.5% of all individuals (70.1% at exposed and 65.4% at sheltered sites) were collected from sand/rubble microhabitats as opposed to 31.5% from open reef microhabitats. Assemblages at exposed and sheltered sites exhibited little taxonomic overlap, even of highly abundant species. These results indicate that wave energy plays a significant role in structuring small cryptic coral reef fish communities, with microhabitat type playing a key role in the absence of wave energy.
Accelerating coastal development and shipping activities dictate that dredging operations will intensify, increasing potential impacts to fishes. Coastal fishes have high economic, ecological, and ...conservation significance and there is a need for evidence‐based, quantitative guidelines on how to mitigate the impacts of dredging activities. We assess the potential risk from dredging to coastal fish and fisheries on a global scale. We then develop quantitative guidelines for two management strategies: threshold reference values and seasonal restrictions. Globally, threatened species and nearshore fisheries occur within close proximity to ports. We find that maintaining suspended sediment concentrations below 44 mg/L (15–121 bootstrapped CI) and for less than 24 hours would protect 95% of fishes from dredging‐induced mortality. Implementation of seasonal restrictions during peak periods of reproduction and recruitment could further protect species from dredging impacts. This study details the first evidence‐based defensible approach to minimize impacts to coastal fishes from dredging activities.
Hawkfishes (family: Cirrhitidae) are small conspicuous reef predators that commonly perch on, or shelter within, the branches of coral colonies. This study examined habitat associations of ...hawkfishes, and explicitly tested whether hawkfishes associate with specific types of live coral. Live coral use and habitat selectivity of hawkfishes was explored at six locations from Chagos in the central Indian Ocean extending east to Fiji in the Pacific Ocean. A total of 529 hawkfishes from seven species were recorded across all locations with 63% of individuals observed perching on, or sheltering within, live coral colonies. Five species (all except Cirrhitus pinnulatus and Cirrhitichthys oxycephalus) associated with live coral habitats. Cirrhitichthys falco selected for species of Pocillopora while Paracirrhites arcatus and P. forsteri selected for both Pocillopora and Acropora, revealing that these habitats are used disproportionately more than expected based on the local cover of these coral genera. Habitat selection was consistent across geographic locations, and species of Pocillopora were the most frequently used and most consistently selected even though this coral genus never comprised more than 6% of the total coral cover at any of the locations. Across locations, Paracirrhites arcatus and P. forsteri were the most abundant species and variation in their abundance corresponded with local patterns of live coral cover and abundance of Pocilloporid corals, respectively. These findings demonstrate the link between small predatory fishes and live coral habitats adding to the growing body of literature highlighting that live corals (especially erect branching corals) are critically important for sustaining high abundance and diversity of fishes on coral reefs.
Monitoring changes in coral cover and composition through space and time can provide insights to reef health and assist the focus of management and conservation efforts. We used a meta-analytical ...approach to assess coral cover data across latitudes 10-35 degree S along the west Australian coast, including 25 years of data from the Ningaloo region. Current estimates of coral cover ranged between 3 and 44% in coral habitats. Coral communities in the northern regions were dominated by corals from the families Acroporidae and Poritidae, which became less common at higher latitudes. At Ningaloo Reef coral cover has remained relatively stable through time (28%), although north-eastern and southern areas have experienced significant declines in overall cover. These declines are likely related to periodic disturbances such as cyclones and thermal anomalies, which were particularly noticeable around 1998/1999 and 2010/2011. Linear mixed effects models (LME) suggest latitude explains 10% of the deviance in coral cover through time at Ningaloo. Acroporidae has decreased in abundance relative to other common families at Ningaloo in the south, which might be related to persistence of more thermally and mechanically tolerant families. We identify regions where quantitative time-series data on coral cover and composition are lacking, particularly in north-western Australia. Standardising routine monitoring methods used by management and research agencies at these, and other locations, would allow a more robust assessment of coral condition and a better basis for conservation of coral reefs.
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