Phytoplankton as a principal diet for callianassid shrimp larvae in coastal waters, estimated from laboratory rearing and stable isotope analysis

Abstract

Running page head: Umezawa et al.: Field diet of callianassid shrimp larvae ABSTRACT: The field diet of meroplanktonic decapod crustacean larvae is poorly known, despite standard use of microzooplankton as food in laboratory culture. Using callianassid shrimp Nihonotrypaea harmandi larvae collected from a 65 m deep inner-shelf location off mid-western Kyushu, Japan, between June and August 2012 and 2013 and mass-reared in the laboratory, phytoplankton-based diet through larval development (zoeae I−VI to decapodid) was demonstrated. When the pure-cultured diatom Chaetoceros gracilis was fed to zoeae, survival rate to decapodids was 3.4 to 3.9% in 26 to 40 d at 22°C, which was comparable to previous rearing results for zoeae fed microzooplankton. Trophic enrichment factors (TEFs) 1 from stable isotope (SI) analysis of zoeal whole-body tissue in the laboratory were 2.0‰ for δ C and 1.9‰ for δ 15 N. In the field water column, diatoms dominated the nano-to micro-sized plankton, accounting for 38 to 81% of the biovolume, followed by heterotrophic protists. The trophic position (TP) estimated from amino acid-specific δ 15 N values for the field-collected zoeae VI was 2.1 (TPGlu/Phe) or 2.7 (TPAla/Phe), suggesting that those zoeae fed on mixtures of phytoplankton and heterotrophs including protists. Bulk SI analyses were performed for particulate organic matter (POM; proxy for phytoplankton), microzooplankton (mainly calanoid copepods), and shrimp zoeae to elucidate the diet of larvae in the water column. A shift in SI from fresh to degraded POM was determined through the incubation of field-collected POM. Based on this shift during degradation and larval TEFs, phytoplankton and their sinking detritus with heterotrophic protists were estimated to be the principal diet for those larvae residing mostly below the chlorophyll maximum layer.

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

“…3. Because LDDs of N. harmandi reared at 20.8 ± 0.5 C (mean; SD) and 24.0 ± 0.0 C in the laboratory were close to those at 22.2 ± 0.1 and 22.3 ± 0.1 C (Tamaki et al, 2013, unpublished data;Umezawa et al, 2018), the LDDs mentioned in the item (2) were applied to the PLDs through the reproductive season of 1994, when water temperatures at 40-m depth of "Stn 2" (Figure 1a) were estimated to range from 20.0 to 24.5 C during the main larval developmental period (Data S2g). Assuming no mortality through zoeal development, the probability distribution of the daily emerging maximally available candidate (newly-metamorphosed) decapodids derived from the EDS-III embryos on any one date (as a proxy for newly-released zoeae-I at the immediate night of that date) was depicted, with both the numerical proportions of the two normal-distribution groups in the embryo volume and the two decapodid groups' mean preceding LDD (± SD) values retained.…”

“…The boundary between the two groups was defined as the crossing point of the corresponding normal‐distribution curves. Each sampling date in 1992 was applied to the respective nearest dates during the reproductive season of 1994, where the two mean (± SD ) LDD values derived from the corresponding embryo groups (the shorter and longer LDDs from the larger‐ and smaller‐volume groups, respectively) were assumed constant throughout the dates, and the numerical proportions for the two LDD groups varied among the dates according to those for the two corresponding embryo‐volume groups. Because LDDs of N. harmandi reared at 20.8 ± 0.5°C (mean; SD ) and 24.0 ± 0.0°C in the laboratory were close to those at 22.2 ± 0.1 and 22.3 ± 0.1°C (Tamaki et al, , unpublished data; Umezawa et al, ), the LDDs mentioned in the item (2) were applied to the PLDs through the reproductive season of 1994, when water temperatures at 40‐m depth of “Stn 2” (Figure 1a) were estimated to range from 20.0 to 24.5°C during the main larval developmental period (Data S2g). Assuming no mortality through zoeal development, the probability distribution of the daily emerging maximally available candidate (newly‐metamorphosed) decapodids derived from the EDS‐III embryos on any one date (as a proxy for newly‐released zoeae‐I at the immediate night of that date) was depicted, with both the numerical proportions of the two normal‐distribution groups in the embryo volume and the two decapodid groups’ mean preceding LDD (± SD ) values retained.…”

“…The principal diet for those zoeae was estimated to be phytoplankton (Somiya, Suzuki, & Tamaki, ; Umezawa et al, ). In a laboratory rearing in which cultured diatoms ( Chaetoceros gracilis ) alone were fed to a larval assemblage derived from several females at a water temperature of 22°C, decapodids emerged in two groups, with peak abundances in 29 and 35 days after hatching (Umezawa et al, ). 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, ).…”

“…2. The probability distribution of daily emerging decapodids reared at 22 C in the laboratory comprised two normal distributions over dates, which reflected the two normal distributions in the initial EDS-I embryo volume (Umezawa et al, 2018). For the present study, the two distributions, with time, of decapodids derived from the two separate rearing tanks in that paper were combined into a single probability distribution, which was separated into two new normal distributions with a mean LDD of 29.3 days (± 1.6 SD) for the larger embryos and 35.1 days (± 2.4 SD) for the smaller embryos (n = 302; figure not shown).…”

“…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.…”