A 3D perspective on sediment turnover and feeding selectivity in blennies. (July 2022) - Bowden, Casey L.
Abstract: Sediments in algal turfs can modify a wide variety of key ecological processes on coral reefs. While some larger reef fishes can remove these turf-bound sediments, the role of small, yet abundant, cryptobenthic fishes is currently unclear. To address this knowledge gap, we explored the extent to which the blenny, Ecsenius stictus, can shape sediment dynamics on coral reefs by quantifying their sediment ingestion and space use. Per unit body mass, E. stictus process sediments at comparable rates to key parrotfish and surgeonfish species. However, in absolute terms, E. stictus has a negligible influence on net sediment dynamics, despite their abundance. Behavioural observations and 3D photogrammetry reveal that E. stictus preferentially feed and rest on elevated surfaces; potentially because of low sediment loads on these surfaces. Overall, E. stictus may be responding to sediment loads rather than manipulating them; it is a passenger rather than a driver in reef processes. Highlights: The blenny, Ecsenius stictus turns over 11% of their body mass in sediment daily. Yet a small body size renders their overall impact on sediment dynamics negligible. Despite their abundance, E. stictus ingest <1% of daily on-reef sediment influx. Feeding was focussed on small core areas on elevated substrata. Selective feeding of E. stictus could be related to avoiding high-sediment areas.