Mihalitsis, Michalis, and Bellwood, David R. (2019) Morphological and functional diversity of piscivorous fishes on coral reefs. Coral Reefs, 38 (5). pp. 945-954.

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Abstract

Piscivory is a significant ecosystem function on coral reefs, with up to 53% of species on reefs being regarded as piscivorous. Despite this ecological importance, the species that contribute to this function have not been assessed in a broad comparative, morphological context. We therefore conducted a morphological assessment of piscivorous coral reef fishes based on a comparative analysis of 119 species, linking morphology with ecological traits (habitat and activity). After accounting for phylogenetic relationships, we found that head length, premaxilla–maxilla (pmx–mx) length, body depth, and eye size mark the primary axis of variation among species. Pmx–mx length is strongly correlated with both vertical and horizontal gape size. We identify three distinct ecomorphotypes: diurnal benthic, nocturnal, and pelagic piscivores. Benthic diurnal and nocturnal piscivores display a wide array of pmx–mx lengths, potentially reflecting the large array of prey sizes and shapes in benthic habitats. This diversity highlights the potential for niche partitioning based on maximum ingestible prey sizes. By comparison, pmx–mx lengths in pelagic piscivores are more restricted, suggesting limited variance in prey sizes or restrictions associated with their feeding mode. Fin shape was also a primary driver of variation between benthic and pelagic predators. The ecomorphotype of nocturnal piscivores suggests that although they are benthic-associated during daytime, these forms leave the reef at night to feed in more open habitats. When analyzing diurnal benthic piscivores alone, we found a major axis of variation between deep-bodied piscivores with large gapes and large head lengths versus fusiform piscivores with high fin aspect ratio values. This continuum appears to describe the relative strength of benthic associations. Overall, we provide a broad quantitative framework for understanding the morphology and potential functions of piscivorous fishes on coral reefs.

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