Fish predation is important in shaping populations and community structure in aquatic systems. These predator-prey interactions can be influenced by environmental, behavioural and morphological factors. Morphological constraints influence the feeding performance of species, and interspecific differences can thus affect patterns of resource use. For piscivorous fishes that swallow prey whole, feeding performance has traditionally been linked to three key morphological constraints: oral gape, pharyngeal gape, and the cleithral gape. However, other constraints may be important. We therefore examine 18 potential morphological constraints related to prey capture and processing, on four predatory species (Cephalopholis urodeta, Paracirrhites forsteri, Pterois volitans, Lates calcarifer). Aquarium-based experiments were then carried out to determine capture and processing behaviour and maximum prey size in two focal species, C. urodeta and P. forsteri. All four species showed a progressive decrease in gape measurements from anterior to posterior with oral gape ≥ buccal ≥ pharyngeal ≥ pectoral girdle ≥ esophagus ≥ stomach. C. urodeta was able to process prey with a maximum depth of 27% of the predators’ standard length; for P. forsteri it was 20%. C. urodeta captured prey head-first in 79% of successful strikes. In P. forsteri head-first was 16.6%, mid-body 44.4%, and tail-first 38.8%. Regardless of capture mode, prey were almost always swallowed head first and horizontally in both focal species. Most internal measurements appeared too small for prey to pass through. This may reflect the compressibility of prey, i.e. their ability to be dorsoventrally compressed during swallowing movements. Despite examining all known potential morphological constraints on prey size, horizontal maxillary oral gape in a mechanically stretched position appears to be the main morphological variable that is likely to affect maximum prey size and resource use by these predatory species.

The reef flat is one of the largest and most distinctive habitats on coral reefs, yet its role in reef trophodynamics is poorly understood. Evolutionary evidence suggests that reef flat colonization by grazing fishes was a major innovation that permitted the exploitation of new space and trophic resources. However, the reef flat is hydrodynamically challenging, subject to high predation risks and covered with sediments that inhibit feeding by grazers. To explore these opposing influences, we examine the Great Barrier Reef (GBR) as a model system. We focus on grazing herbivores that directly access algal primary productivity in the epilithic algal matrix (EAM). By assessing abundance, biomass, and potential fish productivity, we explore the potential of the reef flat to support key ecosystem processes and its ability to maintain fisheries yields. On the GBR, the reef flat is, by far, the most important habitat for turf‐grazing fishes, supporting an estimated 79% of individuals and 58% of the total biomass of grazing surgeonfishes, parrotfishes, and rabbitfishes. Approximately 59% of all (reef‐wide) turf algal productivity is removed by reef flat grazers. The flat also supports approximately 75% of all grazer biomass growth. Our results highlight the evolutionary and ecological benefits of occupying shallow‐water habitats (permitting a ninefold population increase). The acquisition of key locomotor and feeding traits has enabled fishes to access the trophic benefits of the reef flat, outweighing the costs imposed by water movement, predation, and sediments. Benthic assemblages on reefs in the future may increasingly resemble those seen on reef flats today, with low coral cover, limited topographic complexity, and extensive EAM. Reef flat grazing fishes may therefore play an increasingly important role in key ecosystem processes and in sustaining future fisheries yields.

Teeth are crucial in elucidating the life history of vertebrates. However, most studies of teeth have focused on mammals. In heterodont mammals, tooth function is based on tooth shape and position along the jaw. However, the vast majority of vertebrates are homodont, and tooth function might not be based on the same principles (in homodonts, tooth shape is broadly similar along the jaw). We provide a quantitative framework and establish dentition-based morphotypes for piscivorous fishes. We then assess how these morphotypes relate to key functional feeding traits. We identified three broad morphotypes: edentulate, villiform and macrodont, with edentulate and villiform species displaying considerable functional overlap; macrodont species are more distinct. When analysing macrodonts exclusively, we found a major axis of variation between ‘front-fanged’ and ‘back-fanged’ species. The functional interpretations of this axis suggest that tooth-based functional decoupling could exist, even in homodont vertebrates, where teeth have similar shapes. This diversity is based not only on tooth shape but also solely on the position along the jaw.