Parrotfish sex ratios recover rapidly in Bermuda following a fishing ban

Parrotfishes are an ecologically and commercially important teleost group whose grazing contributes to maintaining coral-dominated states on hermatypic reefs. However, overfishing has skewed sex ratios of Atlantic parrotfishes because fishing has disproportionate impacts on larger individuals, and males are generally larger than females. Whether protection from fishing may allow sex ratios to return to equilibrium is unknown, as fishing can induce irreversible ecological and/or evolutionary shifts. Bermuda banned trap fishing in 1990, creating a unique opportunity to analyse long-term responses of Atlantic parrotfishes to release from fishing. We found that sex ratios of four common parrotfishes were initially skewed, with male proportions ranging from 0.04 to 0.18. However, male proportions rebounded within 3–4 yr, equilibrating at values ranging from 0.36 to 0.54, similar to those reported at unfished sites in the region. Our results are encouraging for regional efforts to recover lost grazing function by restoring overfished herbivore populations.     

Direct and indirect effects of nursery habitats on coral‐reef fish assemblages,grazing pressure and benthic dynamics

Migrating species are common within seascapes, but the potential for these movements to alter the populations and functional roles of non‐migrating species (e.g. by increasing predation) is rarely investigated. This study considers whether the presence of nursery habitats (mangroves and seagrass) simply enhances the abundance of nursery‐using parrotfishes and piscivores on nearby coral reefs, or also affects other parrotfishes. Data from 131 reef sites and multiple seascape configurations across 13 degrees of latitude were used to model correlations between biophysical variables, including nursery habitat connectivity, and the abundance and grazing pressure of both nursery‐using species and other parrotfishes and piscivore biomass. Connectivity to mangroves and dense seagrass was positively correlated with the biomass of nursery‐using species, but was also negatively correlated with non‐nursery parrotfish populations. This reduction may be caused indirectly by nursery habitats increasing confamilial competition and predation by nursery‐using piscivores, particularly affecting small parrotfishes settling directly onto reefs. As key reef grazers, parrotfishes affect coral demographics. Consequently, a spatial simulation model predicted the impacts after five years of changes in grazing pressure because of nursery habitat connectivity. The model demonstrated that high nursery connectivity was correlated to changes in grazing pressure on nearby reefs that could potentially lead to differences in coral cover of ～3–4% when compared to low connectivity reefs. However, the direction of this change depended on the seascapes’ characteristics. Historically, large‐bodied, nursery‐using parrotfish would have increased grazing in all nursery‐rich seascapes. Overfishing means that nursery availability may have spatially variable impacts on coral cover, influencing reserve design. This study suggests that nursery availability may directly and indirectly modify an ecological process, and alter an ecological cascade (migrating species increase predator and competitor abundances, affecting other grazers and consequently corals). Therefore, elucidating the multi‐species impacts of animal movements is required to better understand ecosystem functioning.     

Herbivore abundance and grazing intensity on a Caribbean coral reef

Herbivory is a primary factor in determining the structure of coral reef communities. Spatial variation among reef habitats in the intensity of herbivory has been documented, but underlying variation in species composition and abundance within the herbivore guild has received little attention. The distribution and relative abundances of herbivorous fishes and sea urchins across several habitats were studied on the Belizean barrier reef off the Caribbean coast of Central America. Marked variation in total herbivore density as well as major changes in the composition of the herbivore guild were found across reef habitats. Acanthurids (surgeonfishes) predominated in shallow areas (< 5 m) while scarids (parrotfishes) were dominant in deeper habitats. Significant differences among habitats in an experimental assay of grazing intensity were strongly correlated with herbivore abundance. The spatial distribution of herbivorous fishes across reef habitats does not appear to be simply explained by differences in reef topography, but may depend on complex interactions among proximity to nearby shelter, predator abundance, density of territorial competitors, and local availability of food resources.     

Complex interactions in the control of coral zonation on a Caribbean reef flat

Summary This study uses short-term assays and long-term transplant experiments to document the potential importance of fish predation and herbivory to the distribution and abundance of reef-building corals in a Caribbean back-reef system. Experimental manipulations of fish access reveal that the zonal patterns of the two reef-building corals Porites astreoides and P. porites f. furcata, dominant on shallow back-reef habitats, are strongly associated with the feeding intensity of parrotfishes. Differential palatability of the two corals to parrotfishes, the proximity of protective cover for large grazers and the availability of small refugia to harbor a cryptic grazer fauna are suggested as major features contributing to the observed patterns. A model predicting the interactions of various algivore/corallivore guilds on the relative dominance of Porites and algal populations is presented.     

Sleeping functional group drives coral-reef recovery

The world's coral reefs are in decline, with many exhibiting a phase shift from coral to macroalgal dominance . This change is often associated with habitat loss and overharvesting of herbivorous fishes, particularly parrotfishes and surgeonfishes . The challenge is to reverse this decline and enhance the resilience of coral-reef ecosystems . We demonstrate, by using a large-scale experimentally induced phase shift, that the rapid reversal from a macroalgal-dominated to a coral- and epilithic algal-dominated state was not a result of herbivory by parrotfishes or surgeonfishes. Surprisingly, phase-shift reversal was primarily driven by a single batfish species (Platax pinnatus), a fish previously regarded as an invertebrate feeder. The 43 herbivorous fishes in the local fauna played only a minor role, suggesting that biodiversity may not offer the protection we hoped for in complex ecosystems. Our findings highlight the dangers faced by coral reefs and other threatened complex ecosystems: Species or functional groups that prevent phase shifts may not be able to reverse phase shifts once they occur. Nevertheless, reversal is possible. The critical issue is to identify and protect those groups that underpin the resilience and regeneration of complex ecosystems.     

Parrotfish predation on massive Porites on the Great Barrier Reef

Parrotfish grazing scars on coral colonies were quantified across four reef zones at Lizard Island, Northern Great Barrier Reef (GBR). The abundance of parrotfish grazing scars was highest on reef flat and crest, with massive Porites spp. colonies having more parrotfish grazing scars than all other coral species combined. Massive Porites was the only coral type positively selected for grazing by parrotfishes in all four reef zones. The density of parrotfish grazing scars on massive Porites spp., and the rate of new scar formation, was highest on the reef crest and flat, reflecting the lower massive Porites cover and higher parrotfish abundance in these habitats. Overall, it appears that parrotfish predation pressure on corals could affect the abundance of preferred coral species, especially massive Porites spp, across the reef gradient. Parrotfish predation on corals may have a more important role on the GBR reefs than previously thought.     

Habitat selection in a variable environment

A Monte Carlo simulation scheme was utilized to determine optimal strategies of habitat utilization in a variable environment. The model allows for differences in quality among habitats at any one time and for varying levels of environmental variance and autocorrelation. When habitats are on the average equal in quality, tracking of temporal fluctuations in environment through variable habitat selection is universally advantageous with the gain in fitness limited by environmental variance, autocorrelation, and number of available habitats. Average differences in quality among habitats will restrict the advantage of variable habitat utilization (over complete usage of the average better habitat) to cases of high environmental autocorrelation or high ratios of enviromental variance to mean habitat separation. Extending an earlier prediction of Levins (1965), the average heterozygosity per individual in a natural population should increase with increasing environmental variance.     

Sexual development and reproductive demography of the green humphead parrotfish (Bolbometopon muricatum) in the Solomon Islands

An investigation of the reproductive biology of the green humphead parrotfish (Bolbometopon muricatum) from three areas in the Western Province of the Solomon Islands revealed that B. muricatum exhibits several features that differ from the pattern of reproductive development observed in most parrotfishes. Unlike most parrotfishes, histological evidence suggests that the sexual pattern of B. muricatum is essentially gonochoristic with high incidences of anatomical but non-functional hermaphroditism. B. muricatum also differs from other parrotfishes in that all males pass through an immature female (or bisexual) phase as demonstrated by all adult testis retaining the ex-ovarian lumen and peripheral sperm sinuses in the gonad wall. However, a protogynous diandric reproductive strategy cannot be excluded given that sampling may have missed transitional individuals. Marked variation in the demography of male B. muricatum between the three locations examined is considered to reflect variation in historical fishing effort.     

Analysis of urban impacts on aquatic habitats in the central Amazon basin: Adult odonates as bioindicators of environmental quality

Thirty streams were surveyed in urban and natural settings in the municipality of Manaus in the central Amazon basin (Brazil) with the objective of identifying the species of adult odonates that can be used as bioindicators of environmental quality. The data collected were used to test the hypothesis that species in the suborder Zygoptera are indicators of better-preserved environments due to their smaller body sizes and reduced tolerances to habitat modification, whereas species in the suborder Anisoptera were presumed to be indicators of impacted habitats with no vegetation. The habitats were classified as preserved, intermediate, and degraded, based on their environmental characteristics. A total of 908 specimens were collected, representing 60 species. The results of the indicator value (IndVal) identified 13 species as indicators of environmental quality, of which nine were typical of preserved habitats, two of intermediate habitats, and four of modified habitats (intermediate or degraded). Odonate species richness declined with increasing urbanization, a pattern also presented by the zygopterans, although anisopteran species richness was higher in intermediate habitats. Zygopteran species showed high fidelity/specificity for preserved habitats, although a small number of the species of this suborder showed a similar relationship with intermediate or degraded habitats, whereas anisopterans were associated only with disturbed habitats (intermediate and degraded). Overall, the results indicate that the diagnosis of the adult odonate community can provide a rapid and effective tool for evaluation of environmental quality. As many species are stenotopic, they can be used as indicators of good habitat quality, whereas some of the more eurytopic species can indicate disturbed habitats.     

Contribution of habitat type to residency and dispersal choices by overwintered and summer adult Colorado potato beetles

The walking and flight dispersal of marked overwintered and summer Colorado potato beetles (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), released in field box‐plots was monitored simultaneously in six habitats over a period of 4 days. The emigration out of plots by walking beetles was calculated from the catch in linear pitfall traps completely surrounding each box‐plot and emigration flight was estimated from the number of beetles missing from the plot or captured by the trap. Overwintered beetles dispersed sooner after release than summer beetles. Overall, the mean number of beetles retained by the habitat was significantly higher in the host habitat (potato) than in any non‐host habitat tested (soybean, pasture, bare ground, water, woodland). Unexpectedly, there was no or little difference in overall beetle retention between non‐host habitats except for higher retention in the water habitat. No difference in the ratio of flight over walking could be detected by the study between overwintered and summer CPB except in the water and woodland habitats. Twenty‐four hours after release, the highest ratios were obtained in the water and woodland habitats and the lowest in the bare‐ground habitat, but ratios were similar for all habitats, except water, after 96 h. As a population, under these experimental conditions, 96 h after release, it seems that CPB displayed a slight preference for flight over walking, with walking as a default mode. A fed and starved pre‐release treatment had no effect on dispersal rates or mode of dispersal. Essentially, our results showed that over a 96‐h period, northeastern North American CPB emigrated at similar rates from the various non‐host habitats encountered, except for water, using walking as much as flight. The host habitat retained CPB significantly longer than non‐host habitats but with a mode of dispersal ratio similar to that in non‐host habitats. The impact on dispersal of the various habitats encountered by CPB in the agro‐ecosystem was less important than expected suggesting that the interaction of environmental parameters is likely to have the most significant impact in determining dispersal rates and dispersal modes.     

Global ecological success of Thalassoma fishes in extreme coral reef habitats

Phenotypic adaptations can allow organisms to relax abiotic selection and facilitate their ecological success in challenging habitats, yet we have relatively little data for the prevalence of this phenomenon at macroecological scales. Using data on the relative abundance of coral reef wrasses and parrotfishes (f. Labridae) spread across three ocean basins and the Red Sea, we reveal the consistent global dominance of extreme wave‐swept habitats by fishes in the genus Thalassoma, with abundances up to 15 times higher than any other labrid. A key locomotor modification—a winged pectoral fin that facilitates efficient underwater flight in high‐flow environments—is likely to have underpinned this global success, as numerical dominance by Thalassoma was contingent upon the presence of high‐intensity wave energy. The ecological success of the most abundant species also varied with species richness and the presence of congeneric competitors. While several fish taxa have independently evolved winged pectoral fins, Thalassoma appears to have combined efficient high‐speed swimming (to relax abiotic selection) with trophic versatility (to maximize exploitation of rich resources) to exploit and dominate extreme coral reef habitats around the world.     

水蚀风蚀交错区柠条锦鸡儿叶片比叶面积和营养元素变化动态

通过对黄土高原水蚀风蚀交错区主要生长月份柠条锦鸡儿(Caragana korshinlii Kom.)叶片比叶面积(SLA)和矿质元素含量的测定,探讨其对生境条件及生长时间的响应规律,结果表明:不同生境柠条锦鸡儿叶片SLA随生长月份的变化趋势基本一致,但变化差异不显著;不同生境叶片有机碳(C)含量变化差异不显著;叶片全氮(N)含量、全钾(K)含量对生长月份的变化响应明显,变异幅度较大,而随生境条件发生的变异较小;叶片全磷(P)含量在不同生境随着生长月份发生的变异较大。不同生境叶片N/P随月份发生的变异较大、C/P的变异较小;叶片C/N、C/K在不同生境间无明显差异,但均随生长月份而产生较大变化,叶片N、P、K的含量与SLA相关性不明显。所以,生境条件和生长时间是柠条锦鸡儿叶片结构特性和养分组成发生变化的重要原因,其叶片比叶面积与矿质养分含量受外界环境因子和自身发育状况的共同调控。     

Context-dependent corallivory by parrotfishes in a Caribbean reef ecosystem

This study assesses the patterns of corallivory by parrotfishes across reefs of the Florida Keys, USA. These reefs represent a relatively unique combination within the wider Caribbean of low coral cover and high parrotfish abundance suggesting that predation pressure could be intense. Surveys across eight shallow forereefs documented the abundance of corals, corallivorous parrotfishes, and predation scars on corals. The corals Porites porites and Porites astreoides were preyed on most frequently with the rates of predation an order of magnitude greater than has been documented for other areas of the Caribbean. In fact, parrotfish bite density on these preferred corals was up to 34 times greater than reported for corals on other reefs worldwide. On reefs where coral cover was low and corals such as Montastraea faveolata, often preferred prey for parrotfishes, were rare, predation rates on P. porites and P. astreoides, and other less common corals, intensified further. The intensity of parrotfish predation increased significantly as coral cover decreased. However, parrotfish abundance showed only a marginal positive relationship with predation pressure on corals, likely because corallivorous parrotfish were abundant across all reefs. Parrotfishes often have significant positive impacts on coral cover by facilitating coral recruitment, survival, and growth via their grazing of algae. However, abundant corallivorous parrotfishes combined with low coral cover may result in higher predation on corals and intensify the negative impact that parrotfishes have on remaining corals.     

Transformation of algal turf by echinoids and scarid fishes on French Polynesian coral reefs

The respective roles of regular echinoids and scarid fishes in the transformation of turf algae, the main food resource for reef herbivores, were investigated on French Polynesian coral reefs. The role of one species of parrotfish (Scarus sordidus) was compared with that of four species of echinoids. The degree and ways of degradation of the algal matter were determined by the organic matter percentage, the composition of the sugar fraction, and the concentration and composition of chlorophylltype pigments as assayed by HPLC analysis. Chemical analyses were performed on anterior and posterior intestines for scarids, intestinal contents and faeces for echinoids, and on fresh algal turf as a control of initial food quality. A decrease in mean percentage of organic matter in gut content was observed from intestine (9.7%) to faeces (7%) in sea urchins, but not in parrotfishes. The total sugar fraction decreased from fresh algal turf (32% of total organic matter) to echinoid (28%) to scarid (18%) gut contents. The ratio of insoluble to soluble sugars (I/S ratios) was higher in echinoids (2.6) than in scarid gut contents (1.0). A decrease in the total pigment concentration was measured from fresh algal turf to echinoid and it was found to be even lower in scarid gut contents. Chromatograms showed that the composition of chlorophyll-type pigments in scarid intestines was very similar to fresh algal turf, with a dominance of native forms, mainly chlorophyll a and b. On the contrary, degraded pigment forms dominated in echinoids. The main degraded products were pheophorbides in sea urchins, and chlorophyllides in parrotfishes. These results provided evidence for differentiation in digestive processes occurring in the two types of grazers. Echinoids released higher degraded algal material than did scarids. Thus, these two types of grazers play different roles in the recycling of organic matter on coral reefs.     

Intraspecific phenotypic variability of plant functional traits in contrasting mountain grasslands habitats

Empirical studies that link plants intraspecific variation to environmental conditions are almost lacking, despite their relevance in understanding mechanisms of plant adaptation, in predicting the outcome of environmental change and in conservation. Here, we investigate intraspecific trait variation of four grassland species along with abiotic environmental variation at high spatial resolution (n = 30 samples per species trait and environmental factor per site) in two contrasting grassland habitats in Central Apennines (Italy). We test for phenotypic adaptation between habitats, intraspecific trait-environment relationships within habitats, and the extent of trait and environmental variation. We considered whole plant, clonal, leaf, and seed traits. Differences between habitats were tested using ANOVA and ANCOVA. Trait-environment relationships were assessed using multiple regression models and hierarchical variance partitioning. The extent of variation was calculated using the coefficient of variation. Significant intraspecific differences in trait attributes between the contrasting habitats indicate phenotypic adaptation to in situ environmental conditions. Within habitats, light, soil temperature, and the availability of nitrate, ammonium, magnesium and potassium were the most important factors driving intraspecific trait-environment relationships. Leaf traits and height growth show lower variability than environment being probably more regulated by plants than clonal traits which show much higher variability. We show the adaptive significance of key plant traits leading to intraspecific adaptation of strategies providing insights for conservation of extant grassland communities. We argue that protecting habitats with considerable medium- and small-scale environmental heterogeneity is important to maintain large intraspecific variability within local populations that finally can buffer against uncertainty of future climate and land use scenarios.     

Rhythms of gene expression in a fluctuating intertidal environment

The physiological strategies that enable organisms to thrive in habitats where environmental factors vary dramatically on a daily basis are poorly understood. One of the most variable and unpredictable habitats on earth is the marine rocky intertidal zone located at the boundary between the terrestrial and marine environments. Mussels dominate rocky intertidal habitats throughout the world and, being sessile, endure wide variations in temperature, salinity, oxygen, and food availability due to diurnal, tidal, and climatic cycles. Analysis of gene-expression changes in the California ribbed mussel (Mytilus californianus) at different phases in the tidal cycle reveals that intertidal mussels exist in at least four distinct physiological states, corresponding to a metabolism and respiration phase, a cell-division phase, and two stress-response signatures linked to moderate and severe heat-stress events. The metabolism and cell-division phases appear to be functionally linked and are anticorrelated in time. The magnitudes and timings of these states varied by vertical position on the shore and appear to be driven by microhabitat conditions. The results provide new insights into the strategies that allow life to flourish in fluctuating environments and demonstrate the importance of time course data collected from field animals in situ in understanding organism-environment interactions.     

VARIATION IN SEX EXPRESSION IN CANADA YEW (TAXUS CANADENSIS)

Sex expression was measured in several Canada yew (Taxus canadensis Marsh.) populations of the Apostle Islands of Wisconsin and southeastern Minnesota to determine the extent of variation within and among populations. Sex expression was recorded qualitatively (monoecious, male, or female) and quantitatively (by male to female strobilus ratios or standardized phenotypic gender). No discernible trends in differences in sex expression among populations or habitats were recorded. Trends in sex expression of individuals within populations were complex. Small yews tended to be male or, if monoecious, had female-biased strobilus ratios. Large yews were monoecious but had male-biased strobilus ratios. Phenotypic gender, recorded as relative maleness, however, was negatively, but weakly, correlated with plant size. Gender distribution in four of five populations was bimodal, suggesting that cosexual populations consist of male and female morphs. Strobilus ratios of individuals in Apostle Island populations showed significant annual variation, but gender for these same plants was significantly correlated from year to year. Annual adjustments in gender were most pronounced in small yews. The results indicate that relative investment in male and female reproductive structures by Canada yew individuals is responsive to environmental variation, but sex expression also has a proximate genetic component.     

Drivers of protogynous sex change differ across spatial scales

The influence of social demography on sex change schedules in protogynous reef fishes is well established, yet effects across spatial scales (in particular, the magnitude of natural variation relative to size-selective fishing effects) are poorly understood. Here, I examine variation in timing of sex change for exploited parrotfishes across a range of environmental, anthropogenic and geographical factors. Results were highly dependent on spatial scale. Fishing pressure was the most influential factor determining length at sex change at the within-island scale where a wide range of anthropogenic pressure existed. Sex transition occurred at smaller sizes where fishing pressure was high. Among islands, however, differences were overwhelmingly predicted by reefal-scale structural features, a pattern evident for all species examined. For the most abundant species, Chlorurus spilurus, length at sex change increased at higher overall densities and greater female-to-male sex ratios at all islands except where targeted by fishermen; here the trend was reversed. This implies differing selective pressures on adult individuals can significantly alter sex change dynamics, highlighting the importance of social structure, demography and the selective forces structuring populations. Considerable life-history responses to exploitation were observed, but results suggest potential fishing effects on demography may be obscured by natural variation at biogeographic scales.     

Human activity selectively impacts the ecosystem roles of parrotfishes on coral reefs

Around the globe, coral reefs and other marine ecosystems are increasingly overfished. Conventionally, studies of fishing impacts have focused on the population size and dynamics of targeted stocks rather than the broader ecosystem-wide effects of harvesting. Using parrotfishes as an example, we show how coral reef fish populations respond to escalating fishing pressure across the Indian and Pacific Oceans. Based on these fish abundance data, we infer the potential impact on four key functional roles performed by parrotfishes. Rates of bioerosion and coral predation are highly sensitive to human activity, whereas grazing and sediment removal are resilient to fishing. Our results offer new insights into the vulnerability and resilience of coral reefs to the ever-growing human footprint. The depletion of fishes causes differential decline of key ecosystem functions, radically changing the dynamics of coral reefs and setting the stage for future ecological surprises.     

Individual variation in feeding habitat use by adult female green sea turtles (Chelonia mydas): are they obligately neritic herbivores?

Satellite telemetry and stable isotope analysis were used to confirm that oceanic areas (where water depths are >200 m) are alternative feeding habitats for adult female green sea turtles (Chelonia mydas), which have been thought to be obligate herbivores in neritic areas (where depths are <200 m). Four females were tagged with satellite transmitters and tracked during post-nesting periods from Ogasawara Islands, Japan. Three females migrated to neritic habitats, while transmissions from another female ceased in an oceanic habitat. The overall mean nighttime dive depths during oceanic swimming periods in two females were <20 m, implying that the main function of their nighttime dives were resting with neutral buoyancy, whereas the means in two other females were >20 m, implying that they not only rested, but also foraged on macroplankton that exhibit diel vertical migration. Comparisons of stable carbon and nitrogen isotope ratios between 89 females and the prey items in a three-source mixing model estimated that 69% of the females nesting on Ogasawara Islands mainly used neritic habitats and 31% mainly used oceanic habitats. Out of four females tracked by satellite, two females were inferred from isotope ratios to be neritic herbivores and the two others oceanic planktivores. Although post-nesting movements for four females were not completely consistent with the inferences from isotope ratios, possibly due to short tracking periods (28–42 days), their diving behaviors were consistent with the inferences. There were no relationships between body size and the two isotope ratios, indicating a lack of size-related differences in feeding habitat use by adult female green turtles, which was in contrast with loggerhead sea turtles (Caretta caretta). These results and previous findings suggest that ontogenetic habitat shifts by sea turtles are facultative, and consequently, their life histories are polymorphic.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.