No abstract

The position of meroplanktonic larvae in the water column with depth-dependent current velocities determines horizontal transport trajectories. For those larvae occurring in inner shelf waters, little is known about how combined diel and tidally-synchronized vertical migration patterns shift ontogenetically.

1 2 One notable type of bioturbation in marine soft sediments involves the excavation of large pits and 3 displacement of sediment associated with predator foraging for infaunal benthos. Batoids are among 4 the most powerful excavators, yet their impact on sediment has been poorly studied. For expansive 5 temperate tidal flats, only relatively small proportions of the habitat can be sampled due to physical 6 and logistical constraints. The knowledge of the dynamics of these habitats, including the spatial and 7 temporal distribution of ray bioturbation, thus remains limited. We combined the use of aerial 8 photogrammetry and in situ benthic sampling to quantify stingray feeding pits in Tomioka Bay, 9Amakusa, Japan. Specifically, we mapped newly-formed pits over an 11-ha section of an intertidal 10 sandflat over two consecutive daytime low tides. Pit size and distribution patterns were assumed to 11 scale with fish size and reflect size-specific feeding behaviors, respectively. In situ benthic surveys 12were conducted for sandflat-surface elevation and prey density (callianassid shrimp). The volume 13 versus area relationship was established as a logistic function for pits of varying sizes by 14 photographing and refilling them with sediment. This relationship was applied to the area of every 15 pit detected by air to estimate volume, in which special attention was paid to ray ontogenetic change 16 in space utilization patterns. In total, 18103 new pits were formed per day, with a mean individual 17 area of 1060 cm 2 . The pits were divided into six groups (G1 to G6 in increasing areas), with 18 abundances of G1, G2+G3, and G4−G6 being medium, high, and low, respectively. Statistical 19 analyses using generalized linear models revealed a marked preference for the higher prey-density 20 areas in G1 and the restriction of feeding grounds of G4−G6 to the lower shore, with G2+G3 being 21 generalists for prey density and sandflat elevation. The lower degrees of overall bioturbation by G1 22 and G4−G6 were spatially structured for the eight sub-areas demarcated by prey density and sandflat 23 elevation, while G2+G3 homogenized the state over the sandflat. The newly-formed pits' sub-areal 24 2 mean numerical, excavated-areal, and displaced-sediment-volume densities per day were confined to 25 small ranges: 0.14−0.17 m −2 , 132−223 cm 2 m −2 , and 551−879 cm 3 m −2 (latter two including 119 26 shallow non-pit excavations). These bioturbation rates are positioned at relatively high levels 27 compared with those by rays from other geographic regions. The present procedure is applicable to 28 the assessment of disturbance by any surface-sediment excavators on tidal flats if their pit 29 dimensions are discernible from the air. 30 31

To delineate a soft-shore trophic structure, macrobenthos was collected from an intertidal sandflat at the mouth of the Shirakawa River in the central part of Ariake Sound, Kyushu, Japan, on 3 occasions in 2003 (January, March, and June to July during the rainy season), and the isotopic compositions of animals and their potential food sources were analyzed. Food sources of animals were assessed based on the diet -tissue isotopic fractionation (δ 13 C = 0.6 to 2.0 ‰, δ 15 N = 3.4 to 3.9 ‰) of 3 main constituent species (the bivalves Mactra veneriformis and Ruditapes philippinarum and the ghost shrimp Nihonotrypaea japonica), which had been determined by an earlier laboratory experiment. The results revealed that (1) consumers were classified into 3 groups; a group consisting of 51 species including 4 main species (the above-mentioned species and the mud shrimp Upogebia major) that derived nutrition mainly from coastal phytoplankton, one consisting of 7 species that incorporated more 13 C-enriched material (e.g. benthic microalgae) and a group consisting of 4 species that incorporated more 13 C-reduced material (e.g. riverine organic matter); (2) the phytoplankton-based trophic structure was composed of 3 trophic levels; (3) M. veneriformis juveniles collected during the rainy season appeared to incorporate riverine organic matter; and (4) reeds from the flood plain, detrital terrestrial plant material, sewage effluents and seaweeds were not food sources for most consumers. We concluded that the high phytoplankton biomass and scarcity of benthic microalgae on this sandflat account for its phytoplankton-based trophic structure.KEY WORDS: Stable isotopes · Estuary · Intertidal sandflat · Trophic structure · Phytoplankton · Benthic microalgae Resale or republication not permitted without written consent of the publisher

No abstract

No abstract

On an intertidal sandflat in western Kyushu, Japan in 1979, the trochid gastropod, Umbonium (Suchium) moniliferum (Lamarck), and the thalassinidean ghost shrimp, Callianassa japonica Ortmann, densely inhabited the lower and upper zones, respectvely. Callianassa japonica subsequently expanded its distribution range considerably, having occupied almost the entire sandflat by 1983. Concurrently, the U. moniliferum population gradually declined, becoming extinct in 1986. Furthermore, the populations of 9 species associated with U. moniliferum (predators, an ectoparasite, and subsequent inhabitants of empty U. moniliferum shells) had disappeared by the end of 1992. The extinction processes of U. moniliferum and the two other most numerically dominant species, the ectoparasitic gastropod, Odostomia sp., and the hermit crab, Diogenes nitidimanus Terao, were described in detail. It is believed that the bioturbation of sediments by C. japonica was responsible for the extinctions, possible mechanisms involved being discussed. This is the first documented record of the extinction of a large part of a macrobenthic assemblage centering on a filter‐feeding Umbonium species which is characteristic of the benthic communities on many intertidal sandflats extending from Japanese to Southeast‐Asian waters.

No abstract