Herbivorous Reef Fishes Research Articles

Herbivore functions in the hot-seat: Resilience of Acanthurus triostegus to marine heatwaves.

Herbivorous fishes play a crucial role in the conservation of coral reefs threatened by thermal stress (e.g., marine heatwaves and long-term ocean warming) by helping to maintain reefs in a coral-dominated state via the removal of algae. However, as thermally sensitive ectotherms, rising thermal stress may also pose a serious threat to these fishes and the critical ecosystem functions they deliver. Here we evaluate the consequences of thermal stress on the capacity of a common herbivorous coral reef fish (Acanthurus triostegus) to control finely filamentous matrices of Caulerpa sertularioides and C. verticillata algae in Hawai'i, by characterizing in-vivo changes in metabolic demands, diurnal foraging rates, activity patterns and individual condition in a laboratory setting during winter (24.0±0.1°C), summer (27.5±0.1°C), and at the peak of a representative marine heatwave, (31.0±0.1°C). Rising temperatures caused significant increases in standard metabolic rate (from ~135 O2 kg-1 h-1 in winter to 224 O2 kg-1 h-1 at the peak of a marine heatwave), but not in the proportion of time spent active (~83-96%) or foraging (~2.4 bites min-1). Consequently, A. triostegus gained body mass during summer and winter, but lost ~0.8% body mass per day during the marine heatwave. Given marine heatwaves can last for weeks to months, these results indicate that while herbivorous coral reef fishes may continue to remove algae during periods of thermal stress, their ability to control many macroalga may be limited due to precipitous reductions in individual performance. Therefore, in addition to algal types, the thermal sensitivity in herbivorous reef fishes will need to be considered for the successful implementation of coral-algal management strategies in a warmer world.

Analysis of coral reef health based on the abundance of herbivorous reef fish in the waters of Krueng Raya, Aceh Besar

Analysis of coral reef health based on the abundance of herbivorous reef fish in the waters of Krueng Raya, Aceh Besar

The Abrolhos Nominally Herbivorous Coral Reef Fish Acanthurus chirurgus, Kyphosus sp., Scarus trispinosus, and Sparisoma axillare Have Similarities in Feeding But Species-Specific Microbiomes

Coral reefs rely heavily on reef fish for their health, yet overfishing has resulted in their decline, leading to an increase in fast-growing algae and changes in reef ecosystems, a phenomenon described as the phase-shift. A clearer understanding of the intricate interplay between herbivorous, their food, and their gut microbiomes could enhance reef health. This study examines the gut microbiome and isotopic markers (δ13C and δ15N) of four key nominally herbivorous reef fish species (Acanthurus chirurgus, Kyphosus sp., Scarus trispinosus, and Sparisoma axillare) in the Southwestern Atlantic’s Abrolhos Reef systems. Approximately 16.8 million 16S rRNA sequences were produced for the four fish species, with an average of 317,047 ± 57,007 per species. Bacteria such as Proteobacteria, Firmicutes, and Cyanobacteria were prevalent in their microbiomes. These fish show unique microbiomes that result from co-diversification, diet, and restricted movement. Coral-associated bacteria (Endozoicomonas, Rhizobia, and Ruegeria) were found in abundance in the gut contents of the parrotfish species Sc. trispinosus and Sp. axillare. These parrotfishes could aid coral health by disseminating such beneficial bacteria across the reef. Meanwhile, Kyphosus sp. predominantly had Pirellulaceae and Rhodobacteraceae. Four fish species had a diet composed of turf components (filamentous Cyanobacteria) and brown algae (Dictyopteris). They also had similar isotopic niches, suggesting they shared food sources. A significant difference was observed between the isotopic signature of fish muscular gut tissue and gut contents, pointing to the role that host genetics and gut microbes play in differentiating fish tissues.

Graph-theoretic modeling reveals connectivity hotspots for herbivorous reef fishes in a restored tropical island system

ContextSeascape connectivity refers to how the spatial configuration of marine habitats facilitates or hinders the movement of organisms, nutrients, materials or energy. Predicting and ranking potential connectivity among habitat patches for coral reef fishes helps to understand how reef fishes could utilize and connect multiple habitat types through the flow of nutrients, energy and biomass across the wider seascape during foraging movements.ObjectivesTo advance a spatially explicit understanding of connectivity linkages within a tropical atoll system by modeling, mapping and quantifying potential seascape connectivity for two locally abundant herbivorous reef fish species, the parrotfish, Chlorurus spilurus (pahoro hohoni or pa’ati pa’apa’a auahi), and the surgeonfish, Acanthurus triostegus (manini).MethodsWe applied a two-step modeling approach by first mapping habitat suitability for the focal species. A graph-theoretic modeling technique was then applied to model and measure the contribution of benthic habitat patches to species-specific potential connectivity within the seascape.ResultsHabitat suitability was higher and less fragmented for C. spilurus than for A. triostegus. Potential ecological connectivity estimates for C. spilurus were higher across the entire seascape, with differences between species likely driven by local-scale benthic habitat patch configuration and species home ranges. Hotspots of ecological connectivity across the atoll were mapped for both species.ConclusionsDespite advances in the application of graph-theoretic techniques in the coastal environment, few marine conservation and restoration measures currently integrate spatial information on ecological connectivity. This two-step spatial modeling approach holds great potential for rapid application of connectivity modeling at multiple spatial scales, which may predict ecological responses to conservation actions including active habitat restoration.

Drivers of nutrient intakes from fisheries in French Polynesia

ABSTRACT Small-scale fisheries provide nutrients to hundreds of millions of people worldwide, with yields dependent on the condition of marine habitats such as coral reefs. Small-scale fisheries are a particularly important food source in societies with nutrient deficiencies and where unhealthy food alternatives are widely available. Using data from coral reef surveys around two islands in French Polynesia (Moorea and Raiatea), we show how the availability of nutrients to fisheries changed in relation to the condition of coral habitat. Fish biomass and nutrient availability were highest when coral cover was low around both islands, driven predominantly by abundant herbivorous reef fish. We also investigated the importance of fish in people’s diets, to determine if fish consumption was aligned with available fisheries resources on local reefs and if nutrient intakes from fish could be explained by people’s socioeconomic background. People ate a higher diversity of reef fish in Raiatea, however nutrient intakes from fish were higher in Moorea. Most people ate more fish than meat on both islands, however fish consumption declined over generations. People from fishing households had higher nutrient intakes from reef and pelagic fish, and people from farming households had higher intakes from reef fish. Preference for eating reef fish over pelagic fish was also associated with higher total nutrient intakes. Promoting traditional diets rich in fish could be key to meeting people’s nutritional needs in French Polynesia while reducing diet-related health issues linked to the overconsumption of fat. French and Tahitian versions of the are available in Supplementary Material.

Distribution and abundance of herbivorous reef fishes on a barrier reef system in the Florida Keys and Dry Tortugas, Florida

Herbivorous reef fishes control algal growth and are critical for maintaining reef health. Grazing effects vary due to community composition, so a diverse herbivore community is important for preventing phase shifts from coral to algal-dominated reefs. However, herbivore communities and grazing effects vary spatially, resulting in non-uniform distribution of algal mitigation across the seascape. Therefore, understanding how habitat influences herbivore communities is essential for predicting the spatial distribution of these species' ecological services. This study used underwater visual surveys (n = 5455) to examine how habitat influences spatial patterns of herbivorous fish densities and species richness in the Florida Keys and Dry Tortugas, Florida. Herbivorous fishes were ubiquitous, and communities were dominated by small herbivores such as damselfishes (Pomacentridae), gobies (Gobiidae), surgeonfishes (Acanthuridae), and small- to medium-bodied parrotfishes (subfamily Scarinae). A suite of factors influenced herbivorous fish communities but boosted regression tree results showed that habitat relief, depth, and spatial location within the Florida Keys and Dry Tortugas were the most important factors. In general, herbivore occurrence, density, and species richness increased as percent of low relief hardbottom habitat (<0.2 m high) decreased. In addition, density and occurrence of herbivores generally increased at shallower depths. Spatial location influenced the density of herbivores with potential hotspots predominantly located in the Upper Keys and the Dry Tortugas Bank. These data provide a valuable understanding of the spatial distribution of herbivorous reef fishes, and aid management decisions regarding the protection and sustainability of herbivore resources and the ecosystems that rely on them.

Herbivorous Reef Fish Interaction with the Habitat and Physicochemical Variables in Coral Ecosystems in the Mexican Tropical Pacific

Herbivorous fish can mediate spatial competition between algae and corals, which is crucial for coral ecosystems. However, in areas with limited coral coverage like the Mexican tropical Pacific (MTP), this dynamic is not fully understood. This study, using a functional trait approach and ordination analysis, explores whether herbivorous reef fish assemblage influences the benthic habitat components or if physicochemical factors define the habitat variability in the MTP’s Cleofas and Marietas insular systems. We analyzed if this relationship persisted across systems and over time, and identified species traits tied to habitat variability. Island comparison analyses between Cleofas and Marietas reveal that both herbivorous reef fish and physicochemical variables shape the habitat. Cleofas had larger mobile herbivorous fish that formed groups related mostly to macroalgae cover. In contrast, temporal analysis of Marietas shows that the habitat is primarily shaped by physicochemical variables with herbivorous fish being mainly small farmer species related to branching corals. Notably, these closely situated insular systems present varied ecosystem mediators, influenced by diverse drivers including fish traits and environmental factors. This study underscores the potential of employing a framework of ecological species traits combined with ordination methods to unravel the distinct site dynamics that contribute to the persistence of coral ecosystems within the MTP.

Comparison of feeding preferences of herbivorous fishes and the sea urchin Diadema antillarum in Little Cayman.

On Caribbean coral reefs, losses of two key groups of grazers, herbivorous fishes and Diadema antillarum, coincided with dramatic increases in macroalgae, which have contributed to decreases in the resilience of these coral reefs and continued low coral cover. In some locations, herbivorous reef fishes and D. antillarum populations have begun to recover, and reductions in macroalgal cover and abundance have followed. Harder to determine, and perhaps more important, are the combined grazing effects of herbivorous fishes and D. antillarum on the structure of macroalgal communities. Surprisingly few studies have examined the feeding preferences of D. antillarum for different macroalgal species, and there have been even fewer comparative studies between these different herbivore types. Accordingly, a series of in-situ and ex-situ feeding assays involving herbivorous fishes and D. antillarum were used to examine feeding preferences. Ten macrophytes representing palatable and chemically and/or structurally defended species were used in these assays, including nine macroalgae, and one seagrass. All species were eaten by at least one of the herbivores tested, although consumption varied greatly. All herbivores consumed significant portions of two red algae species while avoiding Halimeda tuna, which has both chemical and structural defenses. Herbivorous fishes mostly avoided chemically defended species while D. antillarum consumed less of the structurally defended algae. These results suggest complementarity and redundancy in feeding by these different types of herbivores indicating the most effective macroalgal control and subsequent restoration of degraded coral reefs may depend on the recovery of both herbivorous fishes and D. antillarum.

Mixed-species groups of herbivorous reef fishes show variable responses to ecosystem perturbations in the Lakshadweep Islands, India.

Herbivorous reef fishes provide a vital function in reef ecosystems by removing algae and making space available to coral recruits. The high abundance of herbivores in the reefs of the Lakshadweep islands has potentially aided in reef recovery and helped avoid a phase shift to an algal-dominated system, despite most areas having suffered massive coral losses. Mixed-species grouping in herbivores could potentially benefit both the participant species and the reef ecosystem by improving foraging efficiency. We examined the grouping propensity and species richness for three types of herbivore groups after a mass-bleaching event in 2010 and a mass recruitment event in 2015. The species richness and number of parrotfish groups, as well as the grouping propensity of common species, declined starkly across years, indicating that these groups may have formed in response to the mass-bleaching event, slowly diminishing as the reefs recovered. Conversely, large surgeonfish, which varied in richness and propensity across islands and aspect, are probably influenced by local processes. Small surgeonfish only increased in species richness and number in 2015, which may have been in response to the recruitment event. Thus, herbivorous fishes may respond differently to local ecosystem perturbations and play different roles in reef recovery. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Dynamics of Herbivorous Fish and Its Role in Controlling Algal Coverage in Coral Reef Restoration Area Affected by the Bleaching Phenomenon in 2016

Coral reefs in the waters of Liukangloe Island were reported to have experienced a bleaching phenomenon in May 2016 and rehabilitation efforts were carried out in 2019. This study aimed to analyze the structure of the herbivorous fish community and its role in controlling algal cover in the rehabilitation area. Observations of herbivorous fish were carried out using visual census techniques on an area of ​​4m2 and observation of algae in 0.5x0.5 m2 transects on several coral attachment media from dead coral substrates. The results showed that the proportion of herbivorous fish species in the transplant area ranged from 15.81-58.67% and the proportion of individuals ranged from 12.51-34.62%. The dynamics of the number of species and abundance of herbivorous reef fish did not show significant differences between substrates and had the same dynamic pattern in all substrates uses but varied temporally according to the time of observation. The exception is the rubble area which continues to increase until the end of the observation. A high number of herbivorous fish species richness was observed in the branching and natural coral substrates and low in the rubble substrate. The abundance of herbivorous reef fish showed a significant and negative relationship to algal cover and confirmed that the presence of herbivorous reef fish could control or reduce the value of algal cover.

A functional perspective on the meaning of the term ‘herbivore’: patterns versus processes in coral reef fishes

Herbivorous fishes are a key functional group in coral reef ecosystems and have been the focus of a vast body of research. While substantial progress has been made in research, challenges persist, especially in respect to quantifying patterns versus processes. Despite this challenge being recognised over 40 years ago. To help clarify such challenges, and work towards solutions, in this perspective we explore how the definition of ‘herbivorous reef fishes’ precludes an easy translation between patterns of herbivore abundance and the process of herbivory. Indeed, if herbivorous fishes are defined as, a fish in which the diet is predominantly based on plant material, then this encompasses a diverse suite of fishes which all remove primary producers to varying extents and have markedly different impacts on reef functioning. Given this situation, we explore how our approaches to directly quantifying herbivory on reefs have progressed. We highlight how lessons learnt from macroalgal assays could be applied to the direct quantification of herbivory from algal turfs in the epilithic algal matrix (EAM); a community of primary producers that are invariably difficult to work with and quantify. Nevertheless, given the abundance of turfs on coral reefs, and their relative importance in herbivore dynamics, widespread process-based assessment of EAM herbivory represents an avenue for expanding future research. Recognising the difficulty of translating patterns in herbivore abundance to the process of herbivory, and an enhanced focus on EAM herbivory, will be necessary to comprehensively quantify the process of herbivory on Anthropocene coral reefs.

Community Structure of Herbivore Reef Fishes in Lagonoy Gulf, Eastern Philippines

Reef herbivory is a critical ecological process that can control community structure in a reef and can determine recovery potential; therefore, herbivores are an important input in coral reef resiliency. In Lagonoy Gulf, herbivorous reef fishes were surveyed from 22 sampling stations with 93 transects of which 149 species belonging to 14 families were recorded. Although no differences between stations were detected among their biomasses, sizes, abundance and number of species; clustering of stations showed significant differences between clusters. Functional grouping suggests that almost all reefs experienced overfishing as average biomasses were relatively low, with grazers weighing only 112 kg ha-1, scrapers with 56 kg ha-1, browsers 14 kg ha-1, and territorial damselfish 70 kg ha-1. Marine Protected Areas (MPA) were noted to have no impact on reefs’ herbivore community structure since it was almost similar with outside-MPAs and non-MPAs, but then, MPAs have higher overall values than the two other areas. Generally, presence of herbivore fishes in Lagonoy Gulf is a good indicator of the reef’s potential recovery before and after a disturbance event. Furthermore, the diverse herbivore population of the Gulf enhances functional redundancy.

Seasonal variation in diet and isotopic niche of nominally herbivorous fishes in subtropical rocky reefs

Herbivorous fishes can be sensitive to environmental fluctuations, which influence both availability of food resources and metabolic rate, and thus nutritional requirements. Impacts on herbivore nutritional ecology may result from seasonal variations in temperature and meteoceanographic shifts such as wind-induced upwelling events. We evaluated the effects of seasonal changes on the nutritional ecology of 3 nominally herbivorous fishes (Acanthurus chirurgus, Sparisoma axillare and Kyphosus vaigiensis) in a subtropical rocky reef on the southeastern Brazilian coast using a combination of gut content analysis (at 2 scales of magnification) and stable isotope analysis. Sampling of in situ water temperature covered both patterns of seasonal variation in sea surface temperature, and seasonal occurrence of upwelling. Local upwelling occurred throughout the year but less frequently in winter. Diet and isotopic niche displayed little seasonal variation. Species-specific patterns of seasonal variation indicated distinct responses to environmental fluctuations. Temperature alone cannot explain the locality-specific variation in the nutritional ecology of herbivorous reef fish, and contrary to predictions that digestion in herbivorous fishes is impaired by cooler temperatures, no significant shifts in species’ nutritional ecology were detected.

Early successional trajectory of benthic community in an uninhabited reef system three years after mass coral bleaching

Severe thermal stress events occurring on the backdrop of globally warming oceans can result in mass coral mortality. Tracking the ability of a reef community to return to pre-disturbance composition is important to inform the likelihood of recovery or the need for active management to conserve these ecosystems. Here, we quantified annual, temporal changes in the benthic communities for the three years following mass coral mortality at Jarvis Island—an uninhabited island in the Pacific Remote Islands Marine National Monument. While Jarvis experienced catastrophic coral mortality in 2015 due to heat stress resulting from the 2015/16 El Niño, significant annual shifts were documented in the benthic community in the three years post-disturbance. Macroalgal and turf dominance of the benthos was temporary—likely reflecting the high biomass of herbivorous reef fishes post-bleaching—giving way to calcifiers such as crustose coralline algae and Halimeda, which may facilitate rather than impede coral recovery. By 2018, indications of recovery were detectable in the coral community itself as juvenile densities increased and stress-tolerant genera, such as Pavona, exceeded their pre-disturbance densities. However, densities of Montipora and Pocillopora remain low, suggesting recovery will be slow for these formerly dominant taxa. Collectively, the assemblage and taxon-specific shifts observed in the benthic and coral community support cautious optimism for the potential recovery of Jarvis Island’s coral reefs to their pre-disturbance state. Continued monitoring will be essential to assess whether reassembly is achieved before further climate-related disturbance events affect this reef system.

Differences of Macroalgal Consumption by Eight Herbivorous Coral Reef Fishes From the Xisha Islands, China

Herbivorous fishes play an important role in preventing the overabundance of macroalgae on coral reefs. Understanding the feeding selectivity and consumption of macroalgae by herbivorous fishes can be challenging in studies of their ecological role in the preservation and recovery of coral reefs. Coral reef decline, macroalgal overgrowth and overfishing are clearly visible in the Xisha Islands, China. However, there are seldom studies on the feeding behaviors of herbivorous fishes in this area. We used microscopy, 18S rRNA high-throughput sequencing, and stable isotope analyses to comprehensively examine the diet of eight herbivorous reef fish species common in the Xisha Islands, including one parrotfish, two chub, two unicorn fish, and three rabbitfish. Based on microscopic examination,Siganus argenteusfed on the highest number of macroalgae species (five species), followed byNaso unicornis(four species).Kyphosus cinerascens,K. vaigiensis,N. unicornisandS. punctatissimusfed on the entire macroalgal thallus, indicating their greater ecological importance compared with species that only consume algal fronds. According to the 18S rRNA high-throughput sequencing of fish intestinal contents, cluster analysis revealed that consumed macroalgae composition from the eight fishes always grouped together based on the fish species, but with low similarity.K. vaigiensisremoved the highest diversity of macroalgae species as well as the greatest quantity of macroalgae.Calotomus carolinuscan consume the red algaPneophyllum conicum, which is widely distributed on Indo-Pacific coral reefs and can overgrow and kill live corals.N. unicorniswas found to occupy the lowest trophic position based on stable isotope analysis. Multi-technique analyses revealed thatK. vaigiensis,N. unicornisandS. argenteusshowed a high consumption potential of macroalgae, suggesting that they are the key browsers that should receive priority protection in the Xisha Islands. A diverse herbivorous fish fauna is also very important in the Xisha coral reefs. These results not only demonstrated the various functions of different herbivorous fish species in macroalgal removal, but also provided insights into the management of herbivorous fishes on the coral reefs of the South China Sea.

Local Overfishing Patterns Have Regional Effects on Health of Coral, and Economic Transitions Can Promote Its Recovery.

Overfishing has the potential to severely disrupt coral reef ecosystems worldwide, while harvesting at more sustainable levels instead can boost fish yield without damaging reefs. The dispersal abilities of reef species mean that coral reefs form highly connected environments, and the viability of reef fish populations depends on spatially explicit processes such as the spillover effect and unauthorized harvesting inside marine protected areas. However, much of the literature on coral conservation and management has only examined overfishing on a local scale, without considering how different spatial patterns of fishing levels can affect reef health both locally and regionally. Here, we simulate a coupled human-environment model to determine how coral and herbivorous reef fish respond to overfishing across multiple spatial scales. We find that coral and reef fish react in opposite ways to habitat fragmentation driven by overfishing, and that a potential spillover effect from marine protected areas into overfished patches helps coral populations far less than it does reef fish. We also show that ongoing economic transitions from fishing to tourism have the potential to revive fish and coral populations over a relatively short timescale, and that large-scale reef recovery is possible even if these transitions only occur locally. Our results show the importance of considering spatial dynamics in marine conservation efforts and demonstrate the ability of economic factors to cause regime shifts in human-environment systems.

Species differences drive spatial scaling of foraging patterns in herbivorous reef fishes

Herbivory is a core ecosystem function that is delivered heterogeneously across space. Disentangling the drivers of foraging patterns is key to understanding the functional impact of herbivores. Because intrinsic drivers of foraging like metabolism, nutritional requirements and movement costs scale allometrically, foraging movement patterns in terrestrial herbivores have been shown to also scale positively with body size. However, spatial patterns of herbivory can also be explained by orthogonal factors such as trophic position, competition and functional groupings. Here, we investigate body size and species traits as drivers of the spatial scaling of foraging patterns in herbivorous coral reef fishes. We quantified foraging patterns of 119 individuals from nine common herbivorous species using focal individual surveys. Body size, species identity, feeding substrata, social grouping and functional group were tested as predictors of three foraging metrics: foraging area, inter‐foray distance and tortuosity. Our resulting model revealed that species identity overshadowed body size as a predictor in models for all foraging metrics. While foraging area was explained best by species only, the resulting tortuosity and mean inter‐foray distance models included a small effect of body size that explained within‐species variation. We do not find strong support for size‐scaling of foraging patterns in our study species. These findings indicate that foraging allometry based on Optimal foraging theory cannot be generally applied to reef fish assemblages due to a diversity of foraging strategies, such as spatial partitioning and territoriality. Our work reveals the importance of behavioural ecology and taxonomic diversity in understanding herbivory, especially given the functional differences across species. With coral reefs under threat across the world, this is an important step to disentangling the spatial delivery of a core ecosystem function.

Intensive catched parrotfish Chlorurus bleekeri (de Beaufort, 1940) in Wallace Line, Makassar Strait, Indonesia

Bleeker’s Parrotfish Chlorurus bleekeri (de Beufort, 1940) is a Scaridae lives in coral reef ecosystems in tropical and subtropical waters. Bleeker’s Parrotfish is very abundant in the Indo-Pacific region. Bleeker’s Parrotfish can be found from shallow water to a depth of 30 meters. Bleeker’s Parrotfish is a herbivorous fish. Herbivorous reef fish are important in the coral reef ecosystem because ecologically they can control the coral competitor. Therefore, the exploitation of Bleeker’s Parrotfish needs to be regulated keep sustainable use of Bleeker’s Parrotfish. This study aims to analyze the growth, mortality, and exploitation rate of Bleeker’s Parrotfish in the Wallace Line, Makassar Strait, Indonesia. Fish samples were obtained from the catch of fishermen landed at Fish Landing Port, Makassar City, South Sulawesi, Indonesia. Length frequency data is converted into group data using the Bhattacharya method. Growth parameters were estimated using the von Bertalanffy growth equation. The total mortality (Z) was estimated using the Beverton and Holt equations. The natural mortality rate (M) was estimated using the Pauly empirical formula. Fishing mortality rate (F) was estimated using the equation F = Z − M. The exploitation rate (E) was estimated using the Beverton and Holt equations, E=F/Z. The growth rate was Lt = 40[1-exp−0.15(t+1.05)]. The total mortality rate was 2.56 year−1, the natural mortality rate was 0.96 year−1, the fishing mortality rate was 1.60 year−1, and the exploitation rate was 0.63 year−1. Exploitation rates greater than 0.50 indicate that the Bleeker’s Parrotfish in the Wallace line was catched intensively.

Resource‐to‐consumer ratio determines the functional response of an herbivorous fish in a field experiment

In theoretical ecology, the quantity of resource consumed by a consumer per unit of time, defined as functional response, is of paramount importance. To better understand species interactions over time it is necessary to analyze whether consumer's functional response depends on resource density alone (which is the reference assumption) or on both resource and consumer densities. There are few field studies that, by varying the resource and consumer densities, provide solid empirical evidence to indicate the most suitable model of functional response in complex systems, such as coral reefs. We performed a field experiment with an herbivorous surgeonfish and their resource, a red seaweed, in a near‐pristine reef ecosystem. We measured algal consumption while varying densities of consumers and resources. We fit nine alternative functional response models, which either included or excluded consumer‐dependence. The model selection and the parameter estimation indicated that the functional response of the herbivorous surgeonfish depended on the ratio of seaweed to herbivorous fish densities. These results imply that, within a given density, surgeonfish can share resources but individual's consumption rate decrease with higher fish densities. These results also suggest that mutual intraspecific interference exists at herbivorous fish densities generally observed in the field and it should be considered in predicting consumption rates by herbivorous reef fishes. Finally, this study indicates that models incorporating consumer‐dependence must be considered for understanding herbivorous fish and algae population dynamics when placed in the context of the most biodiverse ecological communities, such as reef ecosystems.

Ecological Traits Influencing Anthropogenic Debris Ingestion by Herbivorous Reef Fishes

One of the most conspicuous marks of the Anthropocene worldwide is the ubiquitous pollution by long lifespan materials (e.g., plastic). In marine habitats, anthropogenic debris are observed from floating on the surface to deposited on the substrate or ingested by wildlife at different food web levels. However, the link between feeding strategy types and debris ingestion by reef fishes remains poorly explored. We analyzed the gut contents of three nominally herbivorous fishes along the Brazilian coast: the doctorfish Acanthurus chirurgus, the parrotfish, Sparisoma axillare, and the chub Kyphosus vaigiensis. Individual [i.e., total length (TL)] and species-level functional traits, as well sites with distinct environmental features (i.e., tourism activity intensity, fishing pressure, and distance from the coast), were tested as predictors of the concentration of debris found inside individual fish guts. Debris found were quantified, measured, and classified accordingly to color and shape. We found debris in 52.7% of individuals. Debris ranged from 0.10 to 11.75 mm, and the frequency of occurrence and ingestion rate (number of debris per individual) varied among species, being higher for the scraper species S. axillare (95.7% and 4.9 ± 1.2, respectively) and A. chirurgus (74.6% and 1.64 ± 0.34), than for the browser K. vaigiensis (55.8% and 0.83 ± 0.24). TL, scraping feeding mode, and the most impacted location were positively related to debris ingestion rate. Our work revealed a higher vulnerability of an ecologically important trophic group to debris ingestion and of an already threatened species according to Brazilian red list. Besides the increasing number of species contaminated by anthropogenic debris, its effect on fish biology and physiology remains poorly understood. Understanding these links would improve conservation planning as species contamination could act as a proxy for environmental pollution on marine habitats.