Universality of the linkage between geoenvironment and the distributions of three <i>Haustorioides</i> amphipods: <i>H. japonicus</i>, <i>H. munsterhjelmi</i>, and <i>H. koreanus</i>

Abstract

It is known that suction, namely, the tension of moisture in sediments, governs the distribution of the sandy beach amphipod Haustorioides japonicus, which occurs on the intertidal zones of open sandy beaches. Against this background, field studies were conducted to investigate whether there is a universal linkage between the suction and the distributions of three Haustorioides species, H. japonicus, H. munsterhjelmi, and H. koreanus, and to clarify the relationship between the distribution of these three species on shores and the variation in suction associated with the tide-induced variation in groundwater level. The study sites were as follows: Maze and Gokahama beaches, located on the coast of the Sea of Japan in Honshu, Japan and Tsuyazaki beach on the coast of the Genkai Sea in Kyushu, Japan for H. japonicus; Shari beach in Hokkaido, Japan for H. munsterhjelmi; and Samyang beach on Jeju Island, South Korea for H. koreanus. The field sites had different tidal ranges, from 0.2 to 2.81 m. The obtained results showed that the suction governed the variations of the habitat geophysical environments (degree of saturation, sediment compaction, water content, and sediment hardness) of surficial sediments in sandy beaches, and the distributions of the three Haustorioides species are associated with particular suctions, irrespective of the differences among the three Haustorioides species, the differences in tidal ranges, and the variations in tidal level. In addition, the tidal migrations of H. japonicus and H. munsterhjelmi were caused by shifts in their suitable zones for burrowing.

Cross‐shore distributions of peracarid crustaceans after changes in beach morphology: The importance of suction as a key geoenvironmental variable

“…In addition, both the suction development and suction dynamics‐induced sediment compaction give rise to a marked increase in sediment hardness in the essentially saturated zone (Figures 2c and 3c). As the sediments become unsaturated, the suction dynamics‐induced sediment compaction becomes less pronounced and weaker (Sassa et al, 2014; Yang et al, 2019). As a consequence, the sediment hardness decreases markedly.…”

“…The observed variations of general characteristics in the geophysical environments can be summarized and explained consistently by the respective conceptual models shown in Figures 2 and 3. In the essentially saturated zones ( s ≤ s aev ), the tide‐ and wave swash‐induced suction dynamics bring about distinct cyclic elastoplastic sediment contraction (Sassa & Watabe, 2007), leading to an increase in the density of the cyclically exposed yet saturated sediments (Sassa et al, 2014; Yang et al, 2019). Thus, the water contents decrease gradually according to the relation between water content w and void ratio e in Equation ) (Figures 2b and 3b).…”

“…Observation stations were set up at 1 m intervals in the intertidal zone and at 2 m intervals in the supratidal zone along the cross‐shore transect where there was no debris, to minimize any impact of debris on the distribution of macroinfauna. At the observation stations, we performed Global Navigation Satellite System (GNSS) surveying, using TRIMBLE R4 GNSS System (Trimble), to quantify the monsoon‐induced beach profile changes, and measured suction, as a relevant physical variable that represents the geophysical states of intertidal and supratidal sandy sediments (Sassa et al, 2011, 2014; Sassa & Watabe, 2007, 2008; Sassa & Yang, 2019a, 2019b; Yang et al, 2019), using tensiometers (HG‐2100AEL, mol, Inc., Japan) along the cross‐shore transect of the beaches. The tensiometer had a porous ceramic cup (diameter 0.039 m, height 0.04 m) at the tip, which was filled with deaired water.…”

“…In addition, to investigate the variations of geophysical environments of sandy beach sediments before and after monsoonal storm‐induced morphological changes in beach profiles, undisturbed duplicate samples of surficial sediment were collected along the cross‐shore transect of the beaches using a core sampler with an internal diameter of 60 mm and a thickness of 50 mm, according to the procedures of Sassa and Watabe (2007), in October 2015, October 2018, March 2019 and April 2019 at Maze, and in October 2016, October 2018, March 2019 and April 2019 at Gokahama. The hardness of surficial sediments was assessed by vane shear strength τ * (Sassa et al, 2011; Sassa & Yang, 2019a; Yang et al, 2019). The vane shear strengths were measured using a compact vane testing apparatus (FTD‐S; TOHNICHI, Japan) with intersecting vane blades of 40 mm width, 10 mm depth and 0.5 mm thickness (Sassa et al, 2011, Figure 1), by keeping the rotation speed of the vane at less than 60°/min 1 .…”

“…Recently, Sassa and Watabe (2007) and Sassa, Watabe, Yang, and Kuwae (2011) demonstrated that the dynamics of suction, associated with tide‐ and swash‐induced fluctuations in groundwater level, play a substantial role in controlling the geophysical environment of habitats. In addition, it has been found that the suction governs suitable and critical conditions for the burrowing activities of diverse intertidal macroinfauna, such as bivalvia, polychaeta, decapoda and amphipoda, the physiological activity of isopoda, and the foraging activity of wading birds dunlin inhabiting intertidal flats and sandy beaches (Kuwae, Miyoshi, Sassa, & Watabe, 2010; Sassa et al, 2011, 2014; Sassa & Watabe, 2008; Sassa & Yang, 2019a, 2019b; Yang, Sassa, & Takada, 2019).…”