Morphological character changes through decapodid-stage larva and juveniles in the ghost shrimp Nihonotrypaea harmandi from western Kyushu, Japan: Clues for inferring pre- and post-settlement states and processes

Abstract

Authors' contributions: AT supervised the study and wrote the manuscript. YS and SO undertook the laboratory experiments. JI undertook the field experiment. YH and SS conducted the larval sampling at sea. ST assisted in analyzing data and interpretation of results.

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

“…The two decapodid groups can be tracked back to the respective normal-distribution groups in both newly-fertilized embryo volume-and newly-hatched zoea-I total length-frequency distributions (Umezawa et al, 2018). These two LDDs were comparable to those for larvae mass-reared mainly with microzooplankton foods [rotifer and brine shrimp, with the addition of a diatom (C. gracilis) only for zoea-I] at water temperatures of 21 and 24 C (Tamaki et al, 2013).…”

“…The three samples from seabed towing around the Tomioka Bay mouth (Stn B; Figure 1) during the daytime on September 21, 1995 contained 5, 12, and 27 decapodids of N. harmandi, respectively. Linea thalassinica in the carapace was absent for all individuals, indicating that they were before metamorphosis into the juvenile (see Tamaki et al, 2013). 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).…”

“…Of the N. harmandi individuals collected from the Tomioka sandflat in 1994 and assigned to the juvenile category by their TLs (Section 2.4), the decapodids or juveniles that were newly settled during the most frequent interval (3 days) in each set of two successive sampling dates [hereafter termed (new) settlers] were extracted to keep the duplicate count of settler numbers between the dates to a minimum. Settler traits for this purpose are summarized from Tamaki et al (): (a) longest duration of the decapodid stage in the water column was estimated at 6 days; (b) shortest duration for a newly‐metamorphosed decapodid to become the juvenile was 3 days; (c) after their settlement on the sandflat, 0–2 days old settlers stay at the (post‐settlement) decapodid stage at least for 3–1 days, respectively; (d) pre‐settlement decapodids retained exopods in their pereiopods, while settlers had lost them; (e) the combination of rostrum length and pereiopods’ exopod state could partially determine the settler age; (f) age (in days) of a settler from the start of its decapodid stage is different from the time lapse for a settler from its settlement time [i.e., x d after settlement ( x = 0–2) by a y ‐days old pre‐settlement decapodid ( y = 0–6)]; (g) pre‐settlement decapodids were most probably non‐feeding, whereas settlers resumed feeding on microalgae, growing at a mean rate of 0.2‐mm TL day −1 ; and (h) TLs of the 0‐day‐old settlers ranged from 4.1 to 4.7 mm, which would become 4.7–5.3 mm in 3 days (i.e., on the next sampling date in most cases). Tamaki et al () proposed 4.9‐mm TL as a largest‐size threshold to most accurately estimate the number of settlers occurring during the 3‐day interval from one sampling date to the next.…”

“…In the summer of 2006, at a 65‐m deep water column (gray star point in Figure 1b), zoeae resided mainly in the 20–50‐m deep segment with temperatures ranging from 21 to 24°C, and decapodids performed a normal DVM, staying on or close to the seabed during the daytime and spreading over the whole depths during the nighttime (Tamaki et al, ). In laboratory larval rearings at water temperatures of 21–24°C, decapodids emerged in two groups, with peaks in one lunar duration and the longer one after hatching (Tamaki et al, ; Umezawa et al, ). It remains to be elucidated (a) how decapodids around the Tomioka Bay mouth are finally transported by nighttime flood tidal currents to the sandflat, (b) how that transport is modified by wind‐driven currents, and (c) how the consequent temporal change in newly‐settled decapodid densities over the reproductive season is brought about.…”

A peculiar reworking ofOphiomorphashafts in the Miocene Nangang Formation, Taiwan

“…If this is the case, then no brooding chambers would be expected. Many species of ghost shrimp disperse their larvae in the open water where they may migrate shorter or longer distances before returning to the shelf waters for reproduction in later stages of their life cycles (Tamaki et al, 2010(Tamaki et al, , 2013. In some species, the juveniles have been seen to return to the adult's burrow system where they produce a set of smaller side burrows within the adult system before producing their own system (Kornienko, 2013;Shimoda & Tamaki, 2004;Tamaki, Ikebe, Muramatsu, & Ingole, 1992).…”