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Modeling reef fish biomass, recovery potential, and management priorities in the Western Indian Ocean

Modeling reef fish biomass, recovery potential, and management priorities in the Western Indian Ocean

Three targets for planning fisheries are therefore the mid-range estimate for sustainable pro- duction (~450 kg/ha), the point where fish diversity declines (~600 kg/ha), and where reef states and processes begin to change (~1150 kg/ha). With these targets and knowledge of the fish biomass or benefits and recovery times or costs, models can optimize the selection of reefs for fisheries restrictions. Previous studies have shown that human population density and par- ticularly distance to markets are good predictors of fish biomass and functional groups [13 – 15]. Recovery rates are also being increasingly understood from studies of well-enforced long- term fisheries closures [7, 16, 17]. Similar patterns of recovery are emerging in disparate loca- tions, with rate and duration depending on the initial biomass and rates of increase for various functional groups [7]. This emerging information makes it possible to map the distribution of reef fish biomass using proxies for fishing pressure, and to predict recovery rates based on local demography and management conditions. Recovery time can then be evaluated as a cost — the lost opportunity to capture fish–and can be minimized to develop regional fisheries and con- servation prioritization plans.

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Visual versus video methods for estimating reef fish biomass

Visual versus video methods for estimating reef fish biomass

Differences in biomass estimates between the two methods are also apparent among some key taxa. Serranids are targeted by fishers on may corals reefs, including Ningaloo (Sadovy de Mitcheson et al. 2013; Ryan et al. 2015), and their abundance is often monitored to assess the effects of fishing (Russ et al. 2008). We found that biomass estimates of serranids from DOV were low compared to UVC, primarily due to fewer fish being detected on video. Most serranids are closely associated with the benthos, where they hide in small crevices and caves (Sluka 2000). This cryptic behaviour means abundance of these, and other benthic species, is generally low on DOVS, especially when the technique precludes extensive searching of the reef (Pelletier et al. 2011; Holmes et al. 2013). Encouragingly abundance of lethrinids and lutjanids, which are also often targeted by fishers, were similar, though size estimates were obtained for very few of the schooling lutjanids in DOVS. Inability to measure all fish in a school may not be a problem if fish are of a similar size and at least some can be measured. Moreover, abundance of schooling fish is often estimated or rounded off when using UVC and size estimates are grouped. Hence idiosyncrasies associated with each method contribute to inaccuracy and methodological differences of biomass estimates of schooling fish.

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Bright spots among the world’s coral reefs

Bright spots among the world’s coral reefs

Drawing on a broad body of theoretical and empirical research in the social sciences 24,26,27 and ecology 2,6,28 on coupled human-natural systems, we quantified how reef fish biomass (panel a) was related to distal social drivers such as markets, affluence, governance, and population (panels b,c), while controlling for well-known environmental conditions such as depth, habitat, and productivity (panel d) (Extended Data Table 1, Methods). In contrast to many global studies of reef systems that are focused on demonstrating the severity of human impacts 6 , our examination seeks to uncover potential policy levers by highlighting the relative role of specific social drivers. Critically, the strongest driver of reef fish biomass (i.e. the largest standardized effect size) was our metric of potential interactions with urban centres, called market gravity 29 (Extended Data Fig. 1, 2, 3; Methods). Specifically, we found that reef fish biomass decreased as the size and accessibility of markets increased (Extended Data Fig. 2b, and Extended Data Fig. 3). Somewhat counter-intuitively, fish biomass was higher in places with high local human population growth rates, likely reflecting human migration to areas of better environmental quality 30 -a phenomenon that could result in increased degradation at these sites over time. We found a strong positive, but less certain

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Bright spots among the world's coral reefs

Bright spots among the world's coral reefs

Drawing on a broad body of theoretical and empirical research in the social sciences 24,26,27 and ecology 2,6,28 on coupled human-natural systems, we quantified how reef fish biomass (panel a) was related to distal social drivers such as markets, affluence, governance, and population (panels b,c), while controlling for well-known environmental conditions such as depth, habitat, and productivity (panel d) (Extended Data Table 1, Methods). In contrast to many global studies of reef systems that are focused on demonstrating the severity of human impacts 6 , our examination seeks to uncover potential policy levers by highlighting the relative role of specific social drivers. Critically, the strongest driver of reef fish biomass (i.e. the largest standardized effect size) was our metric of potential interactions with urban centres, called market gravity 29 (Extended Data Fig. 1, 2, 3; Methods). Specifically, we found that reef fish biomass decreased as the size and accessibility of markets increased (Extended Data Fig. 2b, and Extended Data Fig. 3). Somewhat counter-intuitively, fish biomass was higher in places with high local human population growth rates, likely reflecting human migration to areas of better environmental quality 30 -a phenomenon that could result in increased degradation at these sites over time. We found a strong positive, but less certain

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Weak compliance undermines the success of no-take zones in a large government-controlled marine protected area

Weak compliance undermines the success of no-take zones in a large government-controlled marine protected area

The effectiveness of marine protected areas depends largely on whether people comply with the rules. We quantified temporal changes in benthic composition, reef fish biomass, and fishing effort among marine park zones (including no-take areas) to assess levels of compliance following the 2005 rezoning of the government-controlled Karimunjawa National Park (KNP), Indonesia. Four years after the rezoning awareness of fishing regulations was high amongst local fishers, ranging from 79.567.9 (SE) % for spatial restrictions to 97.761.2% for bans on the use of poisons. Despite this high awareness and strong compliance with gear restrictions, compliance with spatial restrictions was weak. In the four years following the rezoning reef fish biomass declined across all zones within KNP, with .50% reduction within the no-take Core and Protection Zones. These declines were primarily driven by decreases in the biomass of groups targeted by local fishers; planktivores, herbivores, piscivores, and invertivores. These declines in fish biomass were not driven by changes in habitat quality; coral cover increased in all zones, possibly as a result of a shift in fishing gears from those which can damage reefs (i.e., nets) to those which cause little direct damage (i.e., handlines and spears). Direct observations of fishing activities in 2009 revealed there was limited variation in fishing effort between zones in which fishing was allowed or prohibited. The apparent willingness of the KNP communities to comply with gear restrictions, but not spatial restrictions is difficult to explain and highlights the complexities of the social and economic dynamics that influence the ecological success of marine protected areas. Clearly the increased and high awareness of fishery restrictions following the rezoning is a positive step. The challenge now is to understand and foster the conditions that may facilitate compliance with spatial restrictions within KNP and marine parks worldwide.

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Shape learning and discrimination in reef fish

Shape learning and discrimination in reef fish

Different sensory modalities have different detection ranges. The useful range of a particular signal is determined by both intrinsic receptor sensitivity and signal disruption in the transmission medium (reef waters, in this case). Acoustic signals can be detected over large distances due to the fast speed of sound in water (5 times faster than in air); however, their directionality is rapidly lost due to multiple reflection and refraction boundaries (e.g. surface of water, 3-D reef structure). Olfactory cues are slow and become distorted by water movement, meaning that odour plumes have to be slavishly tracked to their source. Visual cues are fast and highly directional but are limited in range due to the absorption and scattering properties of water. This attenuation of light causes a blurring of edges and a loss of contrast, and is wavelength specific resulting in changes in colour signals with distance and depth (Jerlov, 1976). Despite these challenges, many aquatic animals have a very well developed visual sense (Lythgoe, 1972; Collin et al., 2003; Kröger and Katzir, 2008) including colour vision capabilities such as those described in stomatopods (Marshall et al., 1996) and damselfish (Siebeck et al., 2008). In the clear waters around coral reefs, visual signals may be visible

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Colour vision in coral reef fish

Colour vision in coral reef fish

Over many millions of years, sea creatures have developed a range of light reflectance properties. One example is the large variation in the patterns and colours of fish inhabiting the worldʼs coral reefs. Attempts to understand the significance of the colouration have been made, but all too often from the perspective of a human observer. A more ecological approach requires us to consider the visual system of those for whom the colours were intended, namely other sea life. A first step is to understand the sensitivity of reef fish themselves to colour. Physiological data has revealed wavelength-tuned photoreceptors in reef fish, and this study provides behavioural evidence for their application in colour discrimination. Using classical conditioning, freshly caught damselfish were trained to discriminate coloured patterns for a food reward. Within 3–4·days of capture the fish selected a target colour on over 75% of trials. Brightness of the distracter and target were systematically varied to confirm that the fish could discriminate stimuli on the basis of chromaticity alone. The study demonstrates that reef fish can learn to perform two- alternative discrimination tasks, and provides the first behavioural evidence that reef fish have colour vision.

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Regional endothermy in a coral reef fish?

Regional endothermy in a coral reef fish?

For gastro-intestinal metabolism to elevate the internal thermal environment, any heat generated must be locally retained. Physiological mechanisms have evolved in all fish lineages that exhibit regional endothermy, to reduce the loss of metabolic heat [16,38]. Vascular counter-current heat exchange systems have arisen to retain metabolically generated heat in the brain and eyes of billfishes and in the red muscle blocks of tunas [16,36,39]. It is possible that a simplified version of such counter-current heat exchange may exist in the vascular systems supplying the peritoneal cavity of C. microrhinos, resulting in localized retention of heat generated from digestive processes. Alternatively, a relatively basic counter-current heat exchange mechanism may already exist in the vascular system of fishes. The parallel arrangement of the arteries and veins may act as a site for heat transfer, retaining some visceral heat which would otherwise be lost from venous blood as it moves towards the gills [40–41].

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Reef fish foraging associations: "nuclear-follower" behavior or an ephemeral interaction?

Reef fish foraging associations: "nuclear-follower" behavior or an ephemeral interaction?

Nuclear-following associations are common among reef fishes, whereas species can act as nuclear or followers (Karplus 1978; Dubin 1982; Lukoschek and McCormick 2000; Sazima et al. 2007; Araújo et al. 2009). Other reef animals are also known to engage in such interactions performing the "nuclear" function (Strand 1988; Gibran 2002; Sazima et al. 2004; Sampaio et al. 2007; Machado and Barreiros 2008). The nuclear species are believed to maintain interaction cohesion by facilitating feeding, allowing the species to rely on items that would be otherwise not accessible, and/or anti-predator pay off, reducing predation risk while feeding in groups (Diamant and Shpigel 1985; Strand 1988; Srinivasan et al. 2010). Therefore, such interaction plays a significant role on reef trophodynamics, as they are frequent and usually benefit the follower species (Bshary et al. 2006).

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Drivers of reef shark abundance and biomass in the Solomon Islands

Drivers of reef shark abundance and biomass in the Solomon Islands

The indigenous people of the Solomon Islands, like other Melanesian countries, have complex systems of customary marine tenure (CMT) under which fishing rules can be flexi- bly applied and adjusted to regulate access to marine resources [14], though the nature of CMT systems and those involved in decision-making vary across the country [15]. Since the 1990s, community-based resource management (CBRM) and community-based co-man- agement approaches have been promoted to build on CMT arrangements to manage small- scale coral-reef fisheries, including reef sharks [10,16]. While CBRM measures around the western Pacific have demonstrated some success in maintaining fish populations [17], pro- tection of highly vulnerable and mobile shark populations is likely to require additional top- down controls, such as no-take areas or catch bans [18]. Some top down controls are being considered by the Solomon Islands Government, who have developed a draft National Plan of Action for sharks. For example, the draft plan makes recommendations for: catch restric- tions where monitoring data indicate populations are threatened; and consideration of mor- atoria during breeding seasons or no-take areas over known breeding habitats (S. Jupiter, pers. comm.).

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Temporal Variation of Fish Diversity and Assemblages and Their Associations to Environmental Variables in the Mangrove of Qinzhou Harbor, Guangxi Province, China

Temporal Variation of Fish Diversity and Assemblages and Their Associations to Environmental Variables in the Mangrove of Qinzhou Harbor, Guangxi Province, China

A dataset including all the species collected in mangrove was constructed. Similarities among fish communities collected in different months were estimated using a Bray-Curtis similarity coefficient, which was conducted basing on the presence (1) or absence (0) of each species in each sampling. The agglomerative method, using an un-weighted pairgroup average, was used to do a clustering analysis of the matrix (Li et al., 2012; Clarke et al., 2006), and an ordination plot of nonmetric multidimensional scaling (NMDS) was constructed to separate the fish fauna in time and in different tidal type. One way analysis of similarities (ANOSIM) was used to determine whether the fish assemblage separted by NMDS ordination differed significantly. All multivariate analyses were performed with the Plymouth Routines in Multivariate Ecological Research (PRIMER v5.0) software. Initially, a global R statistic is calculated to determine whether significant differences exist between all groups (analogous to the global F test in ANOVA). If differences are significant at a global level, then pairwise comparisons between sample groups are conducted to test for differences between pairs. In global test, the null hypothesis was rejected at a significance level of P<0.05 (Smith, 2003). All multivariate analyses were performed with the PRIMER 5.0 computer package. No species was removed from the analysis with PRIMER because all species, including uncommon or rare species are responding to environmental conditions and are thus important in revealing environmental changes (Cao et al., 1998).

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Reef odor: a wake up call for navigation in reef fish larvae

Reef odor: a wake up call for navigation in reef fish larvae

Orientation behavior. The bearings were first used to assert the directionality of each individual, i.e., the concentration of the fish larva positions relative to the center of the arena around an average heading, using the Rayleigh test of uniformity (first order analysis [31] (Fig. 4). The rotation of the DISC measured by the compass allowed us to convert the larval positions in the chamber’s frame of reference (before correction by the compass’ readings) to their positions in the cardinal reference (after correction by the Figure 1. The Drifting In Situ Chamber (DISC). A) schematic view of the Lagrangian observational system. The hardware includes a main underwater unit [red rectangle] composed of a cylindrical frame (H 1.2 m6 0.63 m) made of clear acrylic bars (a) holding a behavioral mesh chamber ( 0.38 m, mesh-size ,1 mm) (b), a pressure enclosure (c) housing an electronic compass and the imaging system composed of a camera with high capacity memory card, a time lapse, and a large battery, allowing for up to 8 hours of continuous recording at 1 HD frame per second. Other instruments include an analog compass (d) and a mini-CTD (e) that senses the ambient conductivity, temperature, and depth. The underwater unit is locked into the current by a drogue (f) and connected to a surface float (g) and Global Positioning System (GPS) (h) by a 3 mm-diameter nylon line attached with three stainless steel bridles (i) to the top ring of the underwater unit; the length of the line is adjusted the target deployment depth. B) In situ view of the DISC deployed off One Tree Island (OTI), Great Barrier Reef. The immersed underwater unit is symmetrical and becomes transparent, minimizing visual disturbances to the tested larva. Graphic courtesy of Bellamare LCC [drogue and surface float not to scale]; photo credit M. Kingsford.

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Market access, population density, and socioeconomic development explain diversity and functional group biomass of coral reef fish assemblages

Market access, population density, and socioeconomic development explain diversity and functional group biomass of coral reef fish assemblages

The majority of studies that have explored the effect of human activity on coral reef fish diversity and function have shown that these assemblage characteristics are explained by either fishing pressure (Jennings et al., 1995; Jennings and Polunin, 1996; DeMartini et al., 2008) or human population density (Jennings and Polunin, 1997; Bellwood et al., 2003; Dulvy et al., 2004a,b; Mora, 2008; Williams et al., 2008, 2011; Stallings, 2009) (Table 1). While it is clear that local human population density and direct fishing effects are important in explaining ecological gradients, we have shown here that trade, measured as distance to market, is also important (Fig. 2). In the Solomon Islands trade likely affects fish diversity and function through small-scale commercial fishing to supply urban markets, whereas population density likely affects diversity and function through semi-subsistence based fishing to supply local needs. Trade allows societies to acquire resources from further afield, externalizing environmental footprints beyond local human–environment systems (Arrow et al., 1995; Berkes et al., 2006; Shandra et al., 2009). Resource management and biodiversity conservation initiatives must recognize that trade and local population pressure represent different drivers of ecological degradation, and should therefore consider applying different strategies to address their different effects on ecosystems. For example, strong governance of markets through sustainable harvesting certification, and market-specific gear and species restrictions, will become increasingly important if coral reef fish continue to be a readily traded commodity (Berkes et al., 2006).

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Effects of elevated water temperature and food availability on the reproductive performance of a coral reef fish

Effects of elevated water temperature and food availability on the reproductive performance of a coral reef fish

Climate change is predicted to increase average water temperature and affect food supply for marine fishes, but how these changes will influence reproduc- tive performance is still poorly understood. We found that both temperature and food level had substantial effects on some reproductive attributes and physical condition of a common reef fish, Acanthochromis poly- acanthus. Most noticeably, increases in water temper- ature caused a substantial reduction in reproduction, with complete reproductive failure at elevated temper- atures and low food supply. Fish that reproduced at higher temperatures produced smaller eggs, which has important implications for juvenile success (Donelson et al. 2008). There was no indication of plasticity in the timing of reproduction relative to water temperature, with individuals at all temperatures commencing breeding within a week of each other. Although the lack of breeding in some pairs may represent a delay in reproduction, and thus some plasticity in this trait, the loss of a season’s breeding in a population with aver- age ages of 2 to 8 yr would represent a significant loss of individual fitness. Given the apparent lack of plas- ticity in the timing of reproduction, the present results suggest that reproductive failures and declines in A. polyacanthus populations are likely to occur as the ocean warms.

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Deep-reef fish assemblages of the Great Barrier Reef shelf-break (Australia)

Deep-reef fish assemblages of the Great Barrier Reef shelf-break (Australia)

growing body of comparable work in disparate locations, such as Hawaii, Brazil, Puerto Rico and the Caribbean. Our study is the first to characterize the diversity of deep-reef fish assemblages in the GBR. These depth patterns are similar to other deeper marine systems where the fish community shows strong zonation and declining spe- cies richness and abundance with the depth gradient (e.g. refs 19, 36, 49, 69–71). Some species show narrower depth ranges, while others are less restricted, and this has important implications for the future management of these resources. For instance, conservation planners can set aside representative areas based on depth to max- imize protection of mesophotic reefs and species. Fishery managers can better define optimal targeted fishing depths and designate “Essential Fish Habitat” based on depth 72 , such as the designated Bottomfish Restricted

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Exploring movement patterns of an exploited coral
reef fish when tagging data are limited

Exploring movement patterns of an exploited coral reef fish when tagging data are limited

Study species. Lethrinus miniatus is a generalist pre- dator consuming a wide range of fishes and inverte- brates (Walker 1978) and is one of the largest emperor species, attaining a maximum fork length (FL) of around 600 mm (Williams et al. 2003, 2007b). L. minia- tus generally inhabits coral reefs (Carpenter 2001) but also is encountered commonly on deeper shoal areas between reefs to depths of more than 100 m (Newman & Williams 1996). The distribution of L. miniatus is restricted compared with other emperor species, with populations found only in waters around Australia, New Caledonia, Norfolk Island and the Ryuku Islands of southern Japan (Carpenter 2001). The largest popu- lations of L. miniatus are found along the east coast of Queensland on the GBR between approximately 17.5 and 24.5° S, where it is one of the most important com- mercial and recreational species in the coral reef finfish fishery (Mapstone et al. 1996, 2004, Williams 2002).

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Responses of reef fish communities to coral declines on the Great Barrier Reef

Responses of reef fish communities to coral declines on the Great Barrier Reef

While resilience of coral reef ecosystems to major disturbances has been documented (Sano 2000, Hal- ford et al. 2004), many reef systems have shifted from coral to algal dominance and are perceived to be in a degraded state (Hughes et al. 2007). This change has been partly attributed to insufficient herbivory by reef fishes as a result of overfishing. A range of herbivorous fish taxa that graze upon algal turfs (i.e. species within the Acanthuridae and Scaridae) are likely to inhibit phase shifts to algal dominance following coral de- clines and enhance conditions for settlement of coral larvae (Bellwood et al. 2004, Hughes et al. 2007). Other ‘nominal herbivores’ that feed on detritus are often very abundant on shallow coral reefs (particularly the acanthurid Ctenochaetus spp.; Wilson et al. 2003), yet their role in preventing phase shifts is unclear, while the few species that actually consume fleshy macroal- gae have the potential to reverse phase shifts (Pratch- ett et al. 2008). Coral mortality creates space for algae to colonize, but responses of fish herbivores to the increased algal supply have included increases, no change and decreases in abundance (Birkeland & Lucas 1990, Wilson et al. 2006). In one case, abundance of herbivores increased immediately after a bleaching event, but then decreased markedly as habitat eroded (Garpe et al. 2006). Increases in herbivore abundance to exploit greater food availability are likely to reflect either migration (Wilson et al. 2006) or enhanced re- cruitment, the latter being contingent upon favourable oceanographic conditions for the fish larvae (Birkeland & Lucas 1990).

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Spatial Ecology of Reef Fish in Backreef and Coral Reef Habitats.

Spatial Ecology of Reef Fish in Backreef and Coral Reef Habitats.

Given that recreational (e.g. tourist) divers collect the majority of the REEF fish data, we suspect that, at any given island, REEF survey sites (1) are preferentially located on the most structurally complex available reefs with the highest local fish densities and diversities, and (2) likely do not equally sample reefs near and far from backreef nursery areas. If this is true, then locally enhanced adult densities of nursery-associated fish species (Table 5, #1) could easily be missed due to (1) the absence of survey data from reefs near nursery habitat, or (2) averaging the results from many sites far from and relatively few sites near nursery habitats. Under the same set of assumptions (i.e., diver bias towards structurally complex reefs, and regional variability in reef structural complexity), any difference between islands’ reef structural complexity (Table 5, #2) and fish response to that structural complexity, would be identified by the REEF data. In addition, REEF survey methods and differences in island-wide reef structural complexity would explain (1) the failure to observe a significant association between nursery-associated fish abundance and island-wide quantity of nursery habitat, and (2) the predominant pattern of positive correlation between individual nursery- and reef-associated fish species abundance scores observed in this study.

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Marine reserves and reproductive biomass: a case study of a heavily targeted reef fish

Marine reserves and reproductive biomass: a case study of a heavily targeted reef fish

statuses were somewhat indistinct, adult density and spawner biomass were an order of magnitude greater in protected sites. Spawner biomass at Achang Marine Preserve greatly exceeded all other sites. Piti also demonstrated a high reproductive potential, despite having a relatively low total abundance. Conversely, spawner biomass and adult density estimates for East Agan˜a were based on only two individuals above the size at maturity recorded from ninety independent transects. While increased biomass of target species within protected sites is frequently demonstrated in the primary literature [47,48,49,50], the magnitude of difference between protected and fished sites in our study is among the highest estimates published to date (reviewed in [5]). This is likely a result of Guam’s history of intense exploitation of marine resources and the heavy reliance on unsustainable fishing practices such as monofilament gill netting [43]. In addition, ratios of spawner to total biomass differed considerably between levels of protection status, giving further indication that the size-selective effects of fishing have had a major impact on the demographic signature of these populations. The benefits of increased reproductive potential within protected sites to adjacent areas are logistically difficult to demonstrate in situ [5], and empirical evidence of enhanced larval transport for coral-reef fishes is sparse. However, these proposed benefits have been established via modeling [1,11,51,52] which show that, given appropriate environmental and biological conditions, exploited fish populations can be significantly en- hanced through larval export.

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Natural bounds on herbivorous coral reef fishes

Natural bounds on herbivorous coral reef fishes

Notably, detritivores and browsers showed opposing responses to SST, with browser biomass being negatively and detritivore biomass positively related to SST. Similar decreases in the biomass of browsing fishes with decreasing latitude, and hence SST, are evident in both the Atlantic [25] and southern Pacific Ocean [86]. Temperature fundamentally constrains the metabolic processes of ectotherms, and various hypotheses have been proposed to explain how temperature might impact the performance and fitness of individuals [87]. For instance, the temperature–size rule predicts ectotherms to be smaller in warmer waters, owing to reduced mean body size, earlier matu- ration, and increased initial growth rates [88–90]. While the temperature-constraint hypothesis relates to the interacting effects of temperature and food quality on fish physiology [25,91]. Here, we found increased browser biomass in cooler waters and increased detritivore biomass in warmer waters. Whether these trends in the standing stock of these functional groups relate to larger individuals and/or intraspecific variabil- ity in life-history characteristics across the temperature gradients surveyed would require location-specific, age-based studies on individual species.

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