Biology of Parrotfishes


  • Chapter 1: Cranial Specializations of Parrotfishes, Genus Scarus (Scarinae, Labridae) for Scraping Reef Surfaces 
  • By Kenneth W. Gobalet

The heads of parrotfishes possess distinctive features that enable them to feed on the algae, bacterial mats, and other materials that encrust calcareous and rocky reef surfaces. Using five sympatric species of parrotfishes within two genera (Scarus and Nicholsina) that inhabit the Gulf of California as foci, this chapter chapter discusses the details of the head anatomy of that enable these fishes to consume a diet that includes massive amounts of abrasive substrate scraped from resistant surfaces. Facilitating this behavior are oral jaws that constantly regenerate through replacement of tiny teeth. The jaws contain durable ligaments that resist stresses, are shortened to enhance their mechanical advantage, and contain a mandible that includes a noteworthy second joint at its midpoint. The positioning of the muscles that contribute to the jaw apparatus are interpreted as is the architecture of the skeleton that accommodates the musculature, joints, levers, and connective tissue elements. Among these features are cruciate ligaments, serrated joints, menisci, and a specialized elastic ligament interconnecting the ascending process of the premaxilla of the upper jaw with the braincase.

  • Chapter 2: Innovation and Diversity of the Feeding Mechanism in Parrotfishes 
  • By Peter C. Wainwright, Samantha A. Price

Parrotfishes feed by scraping hard rocky surfaces to obtain material that they grind into a fine slurry with their pharyngeal jaws. Their unique role as disruptors of benthic communities and bioeroders of the reef is closely linked to three major innovations of the feeding apparatus that are described here. The parrotfish pharyngeal jaws include elaboration of the fourth epibranchial bones to stabilize extensive anterior-posterior movements of the upper jaws during the milling actions. The oral jaws of most parrotfish species are armed with a cutting, beak-like edge that allows the distinctive scraping action during feeding. Within one group of parrotfish there is a novel intra-mandibular joint that substantially alters the mechanics of jaw movements. Patterns of morphological diversity of the feeding apparatus of parrotfishes reveal a major axis of diversity that contrasts species with large muscles, high jaw protrusion and a wide mouth, with species with small structures. Studies show that the rates of evolution of oral jaw traits are elevated in the clade that exhibits the intra-mandibular joint, indicating a role for this innovation in spurring additional functional diversity.

  • Chapter 3: Nutritional Ecology of Parrotfishes (Scarinae, Labridae) 
  • By Kendall D. Clements, J. Howard Choat

A focus on nutrition is generally central to the study of trophodynamics and resource partitioning in terrestrial assemblages. In contrast, the study of trophic diversification in herbivorous fishes on coral reefs has focused on the effects of feeding, rather than its causes. The dietary substrata of parrotfishes are therefore understood largely in terms of where parrotfishes feed, not what they ingest. In this chapter an existing framework of parrotfish feeding is used to generate predictions on potential dietary resources, and evaluated these in terms of nutritional composition. The extent to which various resource targets matched predictions based on feeding behaviour and digestive mechanisms are then examined. Finally, the assimilation of nutrients by parrotfishes is assessed in light of data from biochemical analyses. All studied parrotfish appeared to utilise a diet that contained proportions of protein, lipid and carbohydrate inconsistent with either epilithic turf algae or macroalgae. Parrotfish have a specialised branchial feeding mechanism that appears designed to harvest and selectively retain microscopic particles in the pharynx. Biochemical data indicated a diet of bacteria and/or cyanobacteria distinct from that used by other large grazing fishes. The hypothesis that parrotfishes are microphages that target protein-rich epilithic, endolithic and epiphytic microscopic phototrophs provides a synthetic, unified explanation consistent with all available nutritional evidence.

  • Chapter 4: Dynamic Demography: Investigations of Life-history Variation in the Parrotfishes 
  • By Brett M. Taylor, Elizabeth D.L. Trip, J. Howard Choat

Parrotfishes represent a major coral reef-associated fishery resource to most tropical nations globally. However, this chapter highlights the scarcity of age-based information that has been completed for this group, work that would directly inform fisheries management across many scales. Despite this, much has been uncovered regarding variation in life-history traits between different species as well as within individual species, spanning from regional to near-global scales. Investigations of spatial patterns from available data demonstrate strong and predictable effects on life-history trait values linked to ocean basin history (largest spatial scale), changes in water temperature and seasonality across latitudinal gradients (intermediate scale), and unexpected patterns across small spatial scales driven by habitat, benthic productivity, density-dependent and other biotic or abiotic processes. Because parrotfish assemblages are generally speciose and variably targeted by fishers, detailed age-based life-history information provides a powerful path for understanding species' relative vulnerability to overexploitation. Future studies regarding the demography of parrotfishes are warranted from many regions globally, but this will also require enhanced coordination and collaboration between fisheries research programs.

  • Chapter 5: Vision and Colour Diversity in Parrotfishes 
  • By Ulrike E. Siebeck

Parrotfishes are a group of fishes which exhibit highly diverse colours and colour patterns. This chapter provides a comprehensive summary of current knowledge on parrotfish coloration as well as on the visual system of this group of fish. In order to understand the functions of the colours, it is important to evaluate the colours not from the perspective of humans but rather from that of the intended receiver, e.g. other parrotfish. This chapter therefore includes information about the various parameters necessary to evaluate how a parrotfish might see another parrotfish. The physical properties of fish colours, the mechanisms of different modes of colour changes and the functions of fish colours are discussed, as well as the properties of the underwater light spectrum and the different components of the visual system required for the detection of fish colour patterns. This general review then forms the context within which to better interpret parrotfish colour diversity and vision.

  • Chapter 6: Feeding in Parrotfishes: The Influence of Species, Body Size, and Temperature
  • By Andrew S. Hoey

Parrotfishes are commonly classified into three main feeding modes, or functional groups, based largely on differences in the osteology and myology of the oral and pharyngeal jaws: excavators, scrapers, and browsers. These functional groups have provided a useful framework for assessing the disturbance impact of parrotfish assemblages of the reef substratum, however such approaches often obscure important variation among species. This chapter explores how the disturbance impacts (or effects) of parrotfish feeding on benthic reef communities vary among species, and with body size and temperature. The chapter starts by describing differences in the morphology of the feeding apparatus of parrotfishes and relate these to differences in feeding rate and feeding impact among species. It then explores the influence of body size on the rate of feeding, and the disturbance of individual bites on the reef surface, both among and within species. The evidence presented in this chapter reveal the overwhelming effect of body size on the amount of material that is scraped or excavated from reef surfaces, and questions the commonly accepted functional classification of this group. The chapter concludes that incorporating species- and size-specific metrics of feeding, together with the influence of environmental conditions (e.g., temperature) and nutrition will greatly expand our understanding of the causes and consequences of feeding among parrotfishes

  • Chapter 7: Functional Variation Among Parrotfishes: are they Complementary or Redundant?
  • By Deron E. Burkepile, Douglas B. Rasher, Thomas C. Adam, Andrew S. Hoey, Mark E. Hay

Herbivory is a critical process that underpins coral reef structure and function. Parrotfishes play significant roles in the herbivore guild by removing macroalgae, promoting coral settlement and growth, producing sediment by bioeroding carbonate substrates, and preying on corals. This chapter addresses patterns in functional variation among parrotfishes and how species of parrotfishes are either complementary or redundant to other members of the herbivore guild. Herbivore and parrotfish diversity is critical for maintaining ecosystem function because herbivores differ in sensitivity to algal chemical, morphological, and structural defenses. In addition to complex patterns in complementarity in diet selection, parrotfish species are diverse in their spatial foraging patterns, life history strategies, habitat use, and responses to predators. This functional variation and complementarity within parrotfishes and among other herbivorous species results in important positive impacts of herbivore diversity on coral reefs. Increasing parrotfish and herbivorous fish diversity often results in increased macroalgal consumption and increased success of corals. Thus, the complementary roles that parrotfishes play are important for the ecosystem function of coral reefs.

  • Chapter 8: The Role of Parrotfishes in the Destruction and Construction of Coral Reefs
  • By Jennie Mallela, Rebecca J. Fox

Viewing parrotfish through the lens of geological and morphological reef development, this chapter discusses the critical role that parrotfishes play in the development of the physical, calcium carbonate, structure of coral reef ecosystems. It shows how, as ecosystem engineers, parrotfish feeding and carbonate recycling activities impact on reef growth exploring the relative contributions of parrotfishes to both coral reef destruction (via bioerosion) and construction (sediment production and reworking). These processes are then considered within a "carbonate budget" framework, to illustrate how parrotfish bioerosion and sediment production roles sit within the overall battle of constructive and destructive forces that determine the outcome for coral reef development. The reader is then shown how factors associated with global change are likely to impact on reef carbonate budgets, with a view to understanding how the contribution of parrotfishes to reef construction and destruction might influence the dynamic balance of reef development in a changing world. Finally, the chapter sets out the overall prognosis for reef development under future climate projections and the roles that parrotfish bioerosion and sediment production are likely to play under such conditions.

  • Chapter 9: The Good, the Bad, and the Ugly: Parrotfishes as Coral Predators
  • By Roberta M. Bonaldo, Randi D. Rotjan

Parrotfishes (Scarinae, Labridae) are widely regarded as herbivores because of their frequent feeding on reef surfaces covered by benthic algae. The robust jaws of the parrotfishes, however, makes them one of the most versatile fish groups in tropical reefs; enabling them to feed on almost all reef surfaces, including live coral colonies. Coral predation, nevertheless, is not uniform among the parrotfishes, as most corallivorous parrotfishes are large bodied, typically excavating, species that bite deeper into the coral skeleton. Corallivory by parrotfishes may affect the growth and morphology of coral colonies, the distribution of adult colonies of preferred prey species, and the survivorship of coral recruits. Partial mortality of coral colonies by parrotfish grazing is a common and direct effect of the removal of live coral tissue and portions of the underlying skeleton, but total colony mortality events appear to be rare. This chapter reviews parrotfish corallivory, with special focus to: (1) identify the main characteristics, drivers and consequences of coral predation by parrotfishes; (2) the likely implications of anthropogenic disturbances and reef degradation to parrotfishes, and to their roles as coral predators; and (3) the identification of current knowledge gaps in parrotfish corallivory and areas for future research.

  • Chapter 10: Geographic Variation in the Composition and Function of Parrotfishes
  • By Michel Kulbicki, Alan M. Friedlander, David Mouillot, Valeriano Parravicini

Parrotfishes are a diverse group, with 100 species distributed across the world's tropical and subtropical oceans. There are very few endemic parrotfish species as most species have a wide geographical range. Unlike many other fish groups whose distributions and species richness are shaped by evolutionary history and habitat size, parrotfish species richness is nearly equally controlled on a global scale by sea temperature (SST), and isolation, as well as habitat size and evolutionary history. Over smaller spatial scales, the species richness, abundance and biomass of parrotfish is dependent on the regional species pool, island size, and fishing with further influence of reef type and within reef habitats. Importantly, there are major differences in parrotfish assemblages between the Atlantic and Indo-Pacific, with assemblages in the Atlantic dominated by browsing species, smaller individuals and higher abundances, but lower biomasses than the Indo-Pacific. Parrotfish are also frequently found in adjacent biotopes (mangroves, seagrass, algal beds) in the Atlantic, mainly as juveniles, whereas they are not abundant in these biotopes in the Indo-Pacific. Differences in the structure of parrotfish assemblages and their relationship to environmental variables at different scales, suggest the ecological role of parrotfish may vary across regions.

  • Chapter 11: Phenological Aspects of Parrotfish Ecology on Coral Reefs
  • By Yohannes Afeworki, Henrich Bruggemann

Spatial and temporal variation in resources exerts a strong influence on population processes in coral reef fishes. Seasonality in food resources will propagate through the food web, but they are likely to be most pronounced in the lower trophic levels, such as grazers. In the chapter ‘Phenological aspects of parrotfish ecology on coral reefs’ the effects of temporal changes in benthic algal communities on the nutritional ecology, habitat use and aspects of the life-history of parrotfishes are reviewed. Seasonality affects the availability of preferred high-yield food resources and parrotfishes can only partly compensate this by consuming less preferred food items. As a consequence, food intake varies seasonally, which in turn affects body condition, growth and reproductive activity. It is argued that in, order to maximize reproductive output, parrotfishes may defer reproductive activity to lean periods of the year. A better understanding of parrotfish phenology enables making predictions of their responses to climatic and human disturbances of coral reefs.

  • Chapter 12:The Ecology of Parrotfishes in Marginal Reef Systems
  • By Andrew S. Hoey, Michael L. Berumen, Roberta M. Bonaldo, John A. Burt, David A. Feary, Carlos E.L. Ferreira, Sergio R. Floeter, Yohei Nakamura

Climate change is having a dramatic effect on coral reefs, and is leading to the poleward range expansions of coral reef organisms and the tropicalization of marginal reef communities. These changes have led to suggestions that marginal reefs may act as refugia from climate change. We already know that parrotfishes are essential for the health of tropical reefs, but are they equally important on marginal reefs? This chapter provides an overview of what is currently known of the ecology of parrotfishes on these marginal, high latitude reefs. The chapter starts with a description of the biotic and abiotic conditions that characterize high latitude reefs, and how these may influence various aspects of parrotfish ecology within these systems. It then uses case studies from four marginal reef systems (the Arabian Peninsula, eastern Australia, southern Japan, and Brazil) to explore the ecology of parrotfishes in these unique environments in greater detail. Together, these case studies highlight that declines in the abundance and diversity of parrotfishes with increasing latitude are widespread, and pronounced among excavating parrotfishes. While parrotfishes often dominate herbivore biomass on low latitude reefs, they appear to be relatively minor players on marginal reefs.

  • Chapter 13: The Ecology of Parrotfishes on Low Coral Cover Reefs
  • By Rebecca J. Fox

This chapter delves further into the relationship between parrotfish and coral reef structure, exploring the special role that parrotfish play on reefs that have low levels of coral cover. Leading the reader through the story of 'low coral cover' reefs around the world and how they have come to be defined as such, the chapter goes on to explore the nature and scale of functional impact that parrotfishes have on these types of reef ecosystems, and the challenges and opportunities that low coral cover environments present for parrotfishes. The chapter closes with the sobering message that, as global change continues to degrade the world's coral reefs, there is a real risk that the ecology of parrotfishes on 'low coral cover' reefs will become the rule, rather than the special case.

  • Chapter 14: No-take Marine Reserve Effects on Parrotfish and Parrotfish-benthos Interactions
  • By Sarah-Lee A. Questel, Garry R. Russ

Feeding by parrotfish is considered to play a critical role in maintaining coral cover on coral reefs. Concern exists that overfishing of parrotfish may cause benthic phase-shifts from coral to macroalgal dominated states. No-Take Marine Reserves (NTMRs) are advocated widely as one potential solution to overfishing. NTMRs are hypothesized to increase density and biomass of parrotfish targeted by fishing and subsequently reverse effects of fishing on coral reef benthos. This chapter examined evidence for both direct and indirect effects of NTMRs on parrotfish density and biomass and how NTMR protection affects interactions between parrotfish and the benthos that were top-down (parrotfish effects on benthos) and bottom-up (benthic effects on parrotfish). Evidence suggests that parrotfish density and biomass generally increased in NTMRs relative to fished areas over time, but only where fishing targeted parrotfish. Evidence that NTMRs could subsequently modify the ways in which parrotfish exert top-down control on the benthos was rare and equivocal. In contrast, bottom-up processes (benthic effects on parrotfish) influence density of parrotfish strongly, often independently of NTMR status. To assess recovery of parrotfish and parrotfish-benthos interactions inside NTMRs relative to fished areas, more well-designed Before-After-Control-Impact-Pair studies that incorporate decadal-scale monitoring are required.

  • Chapter 15: Differential Vulnerabilities of Parrotfishes to Habitat Degradation
  • By Michael J. Emslie, Morgan S. Pratchett

Habitat degradation has detrimental effects on ecological assemblages, and on coral reefs it is manifest as declines in the cover of habitat forming scleractinian corals. The causes of coral reef degradation are many and vary geographically. These impacts are very concerning as millions of people rely on coral reefs for food and livelihoods, and chronic habitat degradation is threatening goods and services provided by these systems. Parrotfishes are a conspicuous and important component of coral reef fish faunas that are considered fundamental to the resilience and functioning of coral reefs. However, there are conflicting reports about the vulnerability of the group to the chronic degradation of coral reefs. This chapter explores species specific differences in the vulnerability of parrotfishes to different disturbances by firstly compiling published data on the changes in parrotfish abundance during disturbances that have caused coral loss. This is then complemented with new data from long-term and spatially extensive surveys across the Great Barrier Reef to explicitly examine responses of parrotfishes to temporally and spatially discrete disturbance events. Parrotfishes are generally resilient to coral depletion and habitat degradation caused by major disturbances affecting contemporary reef environments (e.g., cyclones, coral bleaching, and outbreaks of crown-of-thorns starfish), though parrotfishes (like most reef fishes) are sensitive to widespread or significant loss of topographic complexity, which may occur due to extensive coral loss. Currently however, the major threat to parrotfishes is fisheries exploitation, which is of considerable concern given their importance to coral reef resilience.

  • Chapter 16: FAQs about Caribbean Parrotfish Management and their Role in Reef Resilience
  • By Alastair R. Harborne, Peter J. Mumby

Parrotfishes have an important role in the functioning of Caribbean coral reefs, particularly through the removal of macroalgae that is detrimental to coral populations. By removing these algae, abundant parrotfish on a reef can significantly aid the recovery of a reef after disturbances, such as a hurricane or coral bleaching event. Although this role of parrotfishes is intuitively obvious, it encompasses many subtleties relating to the dynamics of reef communities, the controls of macroalgal growth, and the effects of fishing and conservation initiatives. These nuances have led to some confusion among researchers, managers, and the public about how parrotfish affect reef resilience, and how resilience is affected by overfishing. This chapter aims to address this confusion. The chapter is structured by considering 17 frequently asked questions related to the biology, functional role, and management of parrotfishes. Each question is then answered by reviewing the literature and providing guidance to readers on where there is consensus, why some studies appear to conflict, and where the major gaps in knowledge remain. Management of parrotfishes is a critical conservation issue in the Caribbean, and the chapter aims to address what such management can and can't achieve, and how it might be most effective.

  • Chapter 17: Parrotfishes, are We Still Scraping the Surface? Emerging Topics and Future Research Directions
  • By Andrew S. Hoey, Brett M. Taylor, Jessica Hoey, Rebecca J. Fox

Parrotfish are found on almost every coral reef of the world. It is this ubiquity, coupled with their unique functional impact, which makes them one of the most important, and most researched, groups of fishes on coral reefs. This chapter provides an overview of what is known of the ecology of parrotfishes, highlights promising and emerging topics of research, and suggests future research directions. Parrotfishes are largely viewed in terms of their top-down impacts on benthic communities. There is a clear need to change our thinking to consider how bottom-up processes may shape parrotfish populations and assemblages. This will require a shift from the current focus on the consequences of feeding to a holistic approach to understanding both the causes and consequences of parrotfish feeding, how changes in reef condition may influence foraging decisions, and an understanding of ontogenetic shifts in habitat requirements. Studies investigating the physiology, thermal tolerance and potential for behavioural thermoregulation represent exciting research directions. With coral reefs in global decline, thoughts turn to what the future holds for parrotfish populations. We already know parrotfish are essential for healthy reef ecosystem, but are healthy reefs essential for parrotfishes?

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