Facultative commensalism of a free-burrowing urothoid amphipod with a deep burrow-dwelling callianassid shrimp in intertidal sand

Abstract

25Species of the free-burrowing amphipod genus, Urothoe, are common macrobenthos on open sandy 26 beaches. On intertidal sandflats, some species are associated with burrows or tubes of large infauna. 27How this link is formed under sheltered settings was examined. On an intertidal sandflat emersed for 28 300 m seaward in mid-western Kyushu, Japan, U. carda co-occurred with the deep burrow-dwelling 29 callianassid shrimp, Nihonotrypaea harmandi. Amphipods resided in the surface 5-cm sediment 30 outside shrimp burrows, as confirmed by sediment coring and burrow casting. In the summertime 31 during 1980 to 1981, the shrimp and amphipod populations were confined to the upper shore at 32 mean densities of 182 and 701 inds m -2 , respectively. In winter to spring, when the sediment surface 33 mixing was caused by seasonal wind-induced waves, only the amphipod extended distribution to the 34 lowest shore. By 1983, the shrimp increased mean density by 2.5 times and distribution range to the 35 lowest shore. In the summers of 1984, 2010, and 2015, the amphipod extended distribution to the 36 lowest shore, with small variations in population size. Three marked changes in substrate properties 37 were associated with the shrimp inhabitation: thicker oxidized layer (proxy for oxygenated layer) in 38 the sediment column; looser surface sediment, as evaluated with vane shear strength; and coarser 39 and better-sorted surface sediment with less mud content. At least the former two changes were 40 attributable to shrimp bioturbation, which could provide the amphipod with more permeable and 41 softer substrates, leading to the formation of facultative commensalism. 42

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>

“…The undisturbed sediment sampling was conducted using a core sampler with an internal diameter of 60 mm and a thickness of 50 mm, according to the procedures described in Sassa & Watabe (2007). The hardness of surficial sediments was assessed by vane shear strength τ * (Amos et al 1988, Sassa & Watabe 2007, Kuwae et al 2010, Sassa et al 2011, 2014, Seike et al 2018, Tamaki et al 2018. The vane shear strengths were measured using a compact vane shear testing apparatus (FTD-S; TOH-NICHI, Japan) with intersecting vane blades of 40 mm width, 10 mm depth, and 0.5 mm thickness (Fig.…”

Sexual dimorphism in the gammaridean amphipod, Urothoe carda Imbach, 1967, from an intertidal sandflat in southern Japan

“…The lowest proportion of U. carda mature males on the Tomioka sandflat population might be ascribed to a greater predation rate for them while in the water column. Frequent shuffling their dwelling sites on the sandflat may occur (Tamaki et al., ), which could be during nocturnal submergence periods.…”

“…The Tomioka sandflat is located on the north‐western corner of Amakusa‐Shimoshima Island [130.037°E and 32.521°N; Tamaki et al. (), Figure ]. The maximum emersed area of the sandflat during low tide in spring‐tide periods spans 3.5 km alongshore and 150–550 m cross‐shore.…”

“…The maximum emersed area of the sandflat during low tide in spring‐tide periods spans 3.5 km alongshore and 150–550 m cross‐shore. The specimens of Urothoe carda for quantifying sexual dimorphism were collected during low tide on 21 March, 3 June, 1 August, and 28 October in 2015 (Tamaki et al., ). Sediment samples to a depth of 10 cm were passed through a 0.5‐mm mesh sieve, and the residue was fixed with 10% neutralized formalin solution.…”

“…Urothoe carda was originally described for the specimens collected from fine to coarse sand bottoms at depths of 15–19 m in Nha Trang Bay, south‐eastern Vietnam (Imbach, ). The species occurred on an intertidal flat of Iriomote Island in Japan (situated 200 km east of Taiwan; Matsumoto, Okuda, Itani, & Ariyama, ) and on an intertidal sandflat located in mid‐western Kyushu, Japan (Tomioka sandflat; Tamaki et al., ). In the amphipod assemblage on subtidal sediments of a large estuary near the Tomioka sandflat (i.e.…”