Assessment of spatio-temporal variations of macroalgal canopies and fish schools before and after coastal desertification using acoustic methods.

Macroalgal canopies, which provide nutrients and habitats for many invertebrates and fishes in coastal waters, are disappearing worldwide. The simultaneous assessment of changes in macroalgae and fish distribution before and after coastal desertification, including deeper coastal waters where beyond macroalgae growth need attention. Therefore, we investigated their spatial distribution in the coastal waters off southwestern Japan in late autumn and winter using the acoustic method combined with visual observation. The number of fish schools was higher in late autumn than in winter, while they had similar acoustic backscattering strength (Sv) and school size, tended to be distributed in shallower waters. The number was lower after the macroalgae disappeared in both seasons, while the average Sv was higher, and the size was larger. They were distributed in similar water depths during the winter season. Fewer fish schools and higher Sv were observed in deeper waters after the macroalgae disappeared. We concluded that more fishes moved to shallower waters in the autumn than in the winter because of higher water temperatures. Macroalgae benefited small juvenile fishes in both shallow and deep coastal waters. Further studies on the distribution of specific species are expected for the assessment and restoration of the macroalgal ecosystem. [ABSTRACT FROM AUTHOR]