Data-RSOS

Data-RSO

Data from: Suction-induced habitat selection in sand bubbler crabs

We show that a decapod crustacean, the sand bubbler crab (SBC) Scopimera globosa, utilizes suction, which is the tension of moisture in the sediment, to select habitats at normal times and at the time of disaster events, through a range of controlled laboratory experiments and field observations at various sandflats in Japan. When SBCs are released on fields with no spatial suction gradient, their direction of movement is random. However, the situation clearly changes with increasing suction gradients, in which case the SBCs move to suitable zones for burrowing. Predictions based on suction–burrowing relationships coupled with the knowledge of geophysical state changes induced by suction dynamics are consistent with the observed formation of habitats throughout the seasons. Such suction-induced habitat selection in SBCs manifest themselves in a robust way even following sudden events such as typhoons, where erosion and deposition processes distinctly alter the geomorphological profiles, as well as the states of suction, yet consistently yielding habitats at the newly formed, suitable suction environments. Such suitable suction environments cause repeated battles over burrows, with the competition rate more than seven times as high as that in a critical suction environment for burrowing

Burrowing criteria and burrowing mode adjustment in bivalves to varying geoenvironmental conditions in intertidal flats and beaches.

The response of bivalves to their abiotic environment has been widely studied in relation to hydroenvironmental conditions, sediment types and sediment grain sizes. However, the possible role of varying geoenvironmental conditions in their habitats remains poorly understood. Here, we show that the hardness of the surficial intertidal sediments varies by a factor of 20-50 due to suction development and suction-induced void state changes in the essentially saturated states of intertidal flats and beaches. We investigated the response of two species of bivalves, Ruditapes philippinarum and Donax semigranosus, in the laboratory by simulating such prevailing geoenvironmental conditions in the field. The experimental results demonstrate that the bivalve responses depended strongly on the varying geoenvironmental conditions. Notably, both bivalves consistently shifted their burrowing modes, reducing the burrowing angle and burial depth, in response to increasing hardness, to compensate for the excessive energy required for burrowing, as explained by a proposed conceptual model. This burrowing mode adjustment was accompanied by two burrowing criteria below or above which the bivalves accomplished vertical burrowing or failed to burrow, respectively. The suitable and fatal conditions differed markedly with species and shell lengths. The acute sensitivities of the observed bivalve responses to geoenvironmental changes revealed two distinctive mechanisms accounting for the adult-juvenile spatial distributions of Ruditapes philippinarum and the behavioral adaptation to a rapidly changing geoenvironment of Donax semigranosus. The present results may provide a rational basis by which to understand the ensuing, and to predict future, bivalve responses to geoenvironmental changes in intertidal zones

Long-term changes in a trochid gastropod population affected by biogenic sediment stability on an intertidal sandflat in regional metapopulation context

Although destabilization and stabilization of soft sediments by macro-infauna are regarded as key to understanding benthic community dynamics, how component populations are affected concurrently by both agents was poorly investigated. On an intertidal sandflat, Kyushu, Japan during 1979 − 2014 (previous study) and 2015 − 2019, monitoring was made of the populations of the filter-feeding gastropod, Umbonium moniliferum, the burrow-dwelling ghost shrimp, Neotrypaea harmandi (destabilizer), and the tube-building polychaete, Mesochaetopterus minitus (stabilizer). Results revealed that gastropod population changes were driven by an interplay of shrimp, polychaete, and the stingray, Hemitrygon akajei, foraging for shrimp by sediment excavation. The gastropod went through high abundance (1100 m−2) in 1979, extinction during 1986 − 1997, two marked recoveries with peaks in 2001 and 2009, a slight recovery in 2016, and near extinction in 2019. These changes largely followed the fluctuation in shrimp density across a threshold of 160 m−2 inhibiting gastropod recruitment. The polychaete exhibited intermittent outbreaks with peaks in 2000, 2007, and 2016, with maximum densities of 15,000 − 24,000 m−2. Sandflat topography and sedimentary variables were measured during 2015 − 2017. Sediment stabilization by polychaete aggregations at the mid-tidal zone is suggested to have boosted gastropod recruitment. Release at sea and retrieval on shore of drift cards mimicking gastropod larvae with 3- to 9-day planktonic duration was conducted in 2008 − 2009 to specify source populations sending larvae to the present population. Potential source populations were censused in 1998 and 2017 − 2018. Their recent virtual extinction appears responsible for the present population’s decline from 2011. This raises the need for metapopulation perspective to understand local dynamics

Model selection results for (A) burrowing depth z^* and (B) burrowing angle <i>θ</i> on <i>Ruditapes philippinarum</i> and <i>Donax semigranosus</i>.

<p>A generalized linear model (GLM) with a binomial error distribution to examine the effect of species, shell length, and sediment hardness on burrowing depth z* and burrowing angle <i>θ</i>. Only the best fitted models (the smallest AIC models) are shown.</p

Protocol for burrowing experiments on <i>Ruditapes philippinarum</i>.

<p>W.L. : Water level, G.W.L. : Groundwater level, <i>s</i> : Suction, <i>D</i>_r : Sediment relative density, τ* : Sediment hardness, L : Shell length.</p><p>Air temp. : 20.2±0.2°C, Water temp. : 19.1±0.4°C, Salinity : 27 psu.</p><p>a( ): Case of L = 30, 50 mm.</p><p>Symbols <i>a</i>, <i>b</i>, and <i>c</i> denote the observed results. The symbol <i>a</i> means that the individual completed vertical burrowing (z* = −1, <i>θ</i> = 90±10°). The symbol <i>b</i> means that the individual exhibited inclined burrowing (0<<i>θ</i><80°) and/or partial burrowing (−1c means that the burrowing was impossible (z* = 0 and <i>θ</i> = 0). Air and water temperatures are mean values ± SE.</p

Sediment hardness as assessed by the vane shear strength.

<p>(A) High-resolution vane shear testing system in the laboratory. Sediments with prescribed sediment relative densities <i>D</i>_r were formed in an acrylic cylindrical chamber set in a larger water tank. Suctions <i>s</i> at the level of the sediment surface were varied by changing the water level in the tank. The vane shear testing was performed by inserting and rotating the vane blade in the uppermost layer of the given sediment. (B) Results of the vane shear testing. The peak value of the measured vane shear stresses represents the vane shear strength τ*, namely the sediment hardness. (C) Field vane shear testing apparatus for surficial sediments. The apparatus directly measures τ*. (D) Sediment hardnesses simulated in the laboratory as functions of suctions and sediment relative densities of the intertidal sediments taken at the Nojima tidal flat. Data in (D) were obtained using both apparatuses shown in (A) and (C) and represent mean values ± SE.</p

Burrowing criteria and burrowing mode adjustment in <i>Donax semigranosus</i>.

<p>Measured normalized burrowing depth z^* and burrowing angle <i>θ</i> versus sediment hardness for L = 10 mm. The sediment hardnesses τ* were varied by changing suctions <i>s</i> and sediment relative densities <i>D</i>_r at 40%, 60%, 80%, as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025041#pone-0025041-t002" target="_blank">Table 2</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025041#pone-0025041-g001" target="_blank">Figure 1D</a>. Data represent mean values ± SE. The results of the related statistical analyses (GLM) are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025041#pone-0025041-t003" target="_blank">Table 3A,B</a>.</p