Use of mangroves by fish: new insights from in-forest videos

Even in some of the best-studied areas, there has been little direct evaluation of how extensively mangroves are used by fish, or the extent of their penetration through mangrove forests. As a result, paradigms about the utilisation and value of mangroves have not been fully tested. We used an array of unbaited underwater videos to investigate the extent to which fish used mangroves in north-eastern Australian estuaries. Only a small subset of estuarine species were observed entering the mangroves, and patterns of utilisation differed from those expected based on standard paradigms. In particular, trophic groups such as planktivores occurred rarely even 1 m inside the seaward mangrove margin, with utilisation dominated by a few species known to specialise on mangrove-associated prey. Of the species that did enter the mangroves, only a few penetrated through to the landward edge. The limited use of mangroves by fish in these systems suggests a need to reconsider the ways in which mangroves provide refuge and the extent to which they are used as foraging sites. The fact that mangrove use was more restricted than expected implies that the nursery value of these systems is likely to be conferred at a whole-ecosystem scale, and emphasises the need for a detailed, region-specific understanding of the specific values of the different components of mangrove ecosystems.