Normal Delayed Establishment of a Semilunar Brooding and Larval Release Cycle in the Course of the Reproductive Season of the Ghost Shrimp Population on a Warm Temperate Intertidal Sandflat

Semilunar postlarval settlement periodicity ensuing from semilunar larval release cycle in the Nihonotrypaea harmandi (Crustacea, Decapoda, Axiidea, Callianassidae) population on an intertidal sandflat in an open marine coastal embayment

“…4). From third to eighth batches of females with EDS‐III embryos during the reproductive season of 1994 (Section 2.3), the peak female density in each batch exactly or nearly coincided with the corresponding syzygy date (Tamaki et al, , fig. 19D,E).…”

“…19D,E). Thus, although the period at EDS‐III ranges from Day 9 to Day 14 after the first date at EDS‐I (Tamaki, Tanoue, Itoh, & Fukuda, ), the females with EDS‐III embryos in the above six batches in 1994 were regarded as those releasing larvae at each immediate night (Tamaki et al, ). Following this, in the present study, the density of newly‐released larvae from the females contained in a unit sandflat area [2,000 cm 2 : unit corer area (100 cm 2 ) × 20 cores] on each sampling date was represented by the density of EDS‐III embryos carried by all females in that area.…”

“…The Tomioka sandflat faces north to northeast and is disturbed by northerly wind‐induced waves especially during mid‐October to mid‐April (Tamaki, ). The mean (± SD ) significant wave heights on the sandflat during June 6–September 22, September 23–October 15 and October 16–November 5 in 2010 were 3.8 ± 1.9, 5.8 ± 5.4 and 10.6 ± 7.3 cm, respectively (Tamaki et al, ). Winds drive upwelling/downwelling in some coastal waters.…”

“…In the plankton samples for 15-m depth of the water column on the same date, decapodids first emerged around high tide after sunset (Figure 5a,b). The decapodid density decreased from the highest value at F I G U R E 6 Daily nighttime-and vertically-averaged (i.e., over 14 depth points from 4 to 17 m) tidal current velocity vectors at Stn C in Tomioka Bay (Figure 1b) reproduced for the period from June through November in 1994, based on tidal harmonic analysis for the ADCP data during October 14 to November 13 in 2009 [nighttime was defined as the period from sunset to sunrise times (database for these times is given in Tamaki et al, 2018)]; averaged value for every 10-min record during the nighttime was plotted at 00:00 hr:min on each date. The maximum current velocity and its occurrence date in every group of velocity vectors directed at the ESE coming in a 2-week cycle is indicated in red colors.…”

“…The reproductive season of the N. harmandi population on the Tomioka sandflat is from June through October (Tamaki et al, ), during which eight distinct larval (zoea‐I) releases occur basically in a semilunar cycle (Tamaki et al, ). Those zoeae‐I are transported to the coastal ocean, further going through five zoeal and one decapodid stages mainly in a 60–80‐m deep Amakusa‐nada area 10–20 km north and west of the sandflat (Tamaki et al, ; Tamaki & Miyabe, ).…”