Micro-photoautotroph predation as a driver for trophic niche specialization in 12 syntopic Indo-Pacific parrotfish species

Parrotfish are key agents of bioerosion and sediment production in coral reef ecosystems; however, their dietary targets and therefore potential sources of variation in carbonate cycling lack resolution. Here we address this knowledge shortfall in our current understanding of parrotfish diets by testing the concept that protein-rich micro-photoautotrophs are the target prey for many Scarinine parrotfishes. We focus at fine spatial scales on the feeding substrata of 12 syntopic Indo-Pacific parrotfish species at mid-shelf sites around Lizard Island, Great Barrier Reef, Australia. We followed individual parrotfish on snorkel until biting was observed, and then extracted a reef core around each bite. The surface of each bite core was scraped to similar to 1 mm for quantitative microscopic analysis (up to 630 x magnification) and for 16S and 18S rRNA metabarcoding. The most dominant photoautotrophic group in terms of surface cover was filamentous cyanobacteria, followed by crustose coralline algae. Epiphytic, epilithic, endophytic and endolithic filamentous cyanobacteria were consistent bite core biota. Although the density of filamentous cyanobacteria on bite cores was largely consistent among the 12 parrotfish species, the quantitative microscopic data and rRNA metabarcoding revealed distinct differences between parrotfish species in the taxonomic composition of core biota. Our data provide further evidence that these syntopic parrotfish species partition feeding resources.