What ecological role do soft-substrate tide pools play for fishes? Difference in community structures between estuarine and coastal tidal flats in subtropical Japan

Abstract

Soft-substrate tide pools are considered important habitats for fishes from an ecological perspective. However, the ecological roles of such pools and use patterns by fish remain unclear, especially regarding differences between estuarine and coastal tidal flats. In this study, quantitative sampling using the quadrat method was performed in the estuarine and coastal tidal flats on Okinawa-jima Island of subtropical Japan during four seasons. Ecological roles of soft-substrate tide pools were classified as follows: (1) permanent habitat for residents; (2) nursery ground for transients; and (3) waiting area until high tide for accidental species. Within these classifications, the ecological role and value of tide pools for transient fishes varied between the tidal flat types. The habitat value of tide pools is higher for residents than for transient species because the habitat is not replaceable for residents because of their specific ability to survive there. By contrast, transient and accidental species use the tide pools as temporary habitats; however, their high diversity affects the variation in community structure on Okinawa-jima Island. Our results suggest that we should consider not only species diversity, but also habitat use patterns of individual species, together with their life history, when evaluating habitat value with regard to conservation and management of each tidal flat.

First Records of an Estuarine Goby <i>Acentrogobius ocyurus</i> (Gobiiformes: Gobiidae) from Japan and the Sulu Sea in the Philippines

“…The order Gobiiformes is one of the most diverse fish taxa that includes at least 2310 species belonging to 324 genera found globally in various habitats ranging from freshwater to deep sea (Patzner et al 2011;Nelson et al 2016;Parenti 2021). In the western Pacific Ocean, tidal mudflats are dominated by gobies throughout the climate divisions including northern Australia (Chargulaf et al 2011), temperate Japan (Okazaki et al 2012), and subtropical Japan (Kunishima and Tachihara 2020). The genus Acentrogobius Bleeker, 1874 is one of the typical taxa found on tidal mudflats within or close to mangroves of the western Pacific Ocean (Allen 2015), however, its diversity, distribution, microhabitat, life history, and phylogeny are yet to be well understood.…”

Soft-bottom tidepools within mixed reefs of native mussels and introduced oysters – refuge for associated species and parasites?

“…However, tidepools also occur in intertidal soft-bottom coastal systems (Kunishima & Tachihara, 2020), where they are depressions in tidal flats that develop depending on local hydrography, bottom topography and sediment composition (Brenha-Nunes et al ., 2016). Tidepools in sedimentary coastal ecosystems can also be formed by habitat-structuring epibenthic organisms on the sediment surface when seawater is retained by these structures at ebb-tide conditions or when these structures initiate morphological changes of the bottom, that indirectly lead to the development of tidepools.…”

Benthic macrofauna under extremes

“…The formation of these depressions in the tidal flat can be attributed to mutual effects of currents and sediment properties (Perillo, 2019), movements of bioturbators such as crabs Neohelice granulate and shellfish Meretrix meretrix (Shi et al, 2020;Toniolo et al, 2021), or anthropogenic activities like bait digging and collections (Meager et al, 2005). Water pools may provide temporary habitats for various marine organisms during low tide (Dethier, 1984;Kunishima & Tachihara, 2020). Moreover, tidal pools could potentially provide refuges to organisms during heatwaves, because a higher pore water content can attenuate thermal diffusion on tidal flats (Kim et al, 2007;Thomson, 2010).…”