Ole Bjørn Brodnicke, Camilla Hansen, Jonathan Huie, Simon Brandl, Katrine Worsaae
This is a plain language summary of a Functional Ecology research article which is published here.
On tropical coral reefs, patches of seemingly barren sand are commonly found between the corals. These patches harbour a diverse and productive community of tiny (microscopic) invertebrates (called meiofauna), as well as small fishes that feed by taking in entire mouthfuls of sand to extract small prey (known as sand-sifting).
Little is known about how these sand-sifting fish affect their microscopic prey and which specializations enable them to do so. Therefore, we experimentally investigated the feeding behaviour of the two small tropical fishes, blueband goby (Valenciennea strigata) and sixspot goby (Valenciennea sexguttata). We documented how their feeding behaviour impacts the abundance and diversity of their meiofaunal prey and the means by which they are able to extract them from the sand. During aquarium experiments, both goby species drastically reduced the abundance of meiofauna by up to 46 %, but did not affect the overall diversity. The fish especially reduced the number of copepods and segmented worms. Our morphological work, using advanced imaging techniques, revealed that the sand-sifting gobies have anatomical features in their mouths (including protruding taste buds) that help them to detect, separate and retain their microscopic prey from the sand. Their feeding behaviour and specialized feeding structures enable sand-sifting gobies to exploit a productive and abundant prey source, which few other fish can access. This function of acquiring sand derived energy supports the fast growth of these fish, which have short lifespans due to high predation-imposed mortality by other fish.
In conclusion, these sand-sifting fishes appear to be morphologically specialized for feeding on tiny invertebrates in the sand and, in doing so, may efficiently transfer energy through the coral reef food web from microscopic prey to larger fish predators.