Larvae Of Hyas Araneus Research Articles

Detection of phytoplankton pigments by HPLC in Hyas araneus larvae (crustacea, decapoda): Comparison of field and laboratory samples

The ingestion of phytoplankton by Hyas araneus larvae was shown by light- and scanning electron microscopic examination of faeces and HPLC analysis of larvae collected from the field (zoea I) or cultivated in the laboratory (zoea I, II). To date these larvae have been considered to be carnivorous. Three phytoplankton pigments were detected by HPLC: chlorophyll a (marker pigment for phytoplankton in general), fucoxanthin (marker pigment for Bacillariophyceae) and peridinin (marker pigment for Dinophyceae); also present were the degradation products of chlorophyll a (phaeophytin a and phaeophorbide a). The pigment composition of larvae collected from field samples showed that dinoflagellates were ingested in addition to diatoms. The pigment concentration in larvae from field samples was lower than in laboratory-reared larvae, which may be due to lower algal concentrations in the field. The chlorophyll a concentration in the larvae from the field ranged from 0.05 to 0.5 ng·larvae −1, phaeophytin a from 2.1 to 8.2 ng·larvae −1 and phaeophorbide a from 0.1 to 0.4 ng larvae -1. The fucoxanthin and peridinin concentrations varied from 0.2 to 3.8 ng·larvae −1 and from 0.0 to 0.3 ng larvae -1, respectively. Similar values of dry weight and elemental composition in the zoea I were found in field samples and laboratory cultures fed with diatoms exclusively.

Energetics, moult cycle and ecdysteroid titers in spider crab (Hyas araneus) larvae starved after the D0 threshold

Zoea I larvae of Hyas araneus L. (Decapoda: Brachyura: Majidae) were dredged in January 1986 from the German Bight and reared in the laboratory at constant 12°C, until they reached the transition of stages C/D0 of the moult cycle (4 d after hatching). This developmental stage had previously been found to correspond with the point of reserve saturation (PRS) which allows autonomous (food-independent) development through the rest of the moult cycle and hence, was termed the “D0 threshold”. One part of the larvae was continually fed (control), another group was starved from the D0 threshold until moulting to the zoea II instar. In these two experimental groups, as well as in the two groups of zoea II larvae obtained from the different feeding conditions, the course of the moult cycle, biomass (dry weight, W; carbon, C; nitrogen, N; hydrogen, H; energy, E; the latter estimated from C), and ecdysteroid titers (measured with a radio-immuno-assay as ecdysone equivalents) were investigated. When the larvae reached the PRS, they had gained 90% in W, 72% in C, 32% in N, 53% in H, and 65% in E, since hatching, corresponding to an accumulation of 87% of final W and 62 to 69% of C, N, and H reached later, at the end of the mould cycle in the control. The period of starvation caused a 2.5-d delay of the moult cycle, mainly in late premoult, and significant losses of biomass and energy. Starved and fed larvae secreted similar amounts of moulting hormone per individual, but with a reduced rate in the starved group, thus causing developmental delay. Zoea II larvae moulting after starvation contained less than half of the control biomass and energy, and even less than a freshly hatched zoea I. Growth rate was only slightly enhanced in these zoea II larvae as compared to the fed control, but losses of biomass, mainly of lipids, were partly compensated by a 4-d prolongation of their moult cycle, chiefly (3 d) in stage C. Biomass curves were almost parallel in the two experimental groups of zoea II larvae, with significantly higher values in the control during all stages of the moult cycle. However, similar relative proportions (74 to 89%) of late premoult biomass and energy were reached at the D0 threshold, regardless of different feeding history and initial or final values in a given group. The ecdysteroid titer curve of the zoea II which had moulted from starved zoea I was very similar to that in control larvae, but with a 3-d delay in the occurrence of premoult peak concentration (in both groups in stage D1). Regulation and coordination of moult cycle, ecdysteroid titers, and growth in the larval development of decapod crustaceans are discussed, with special reference to the D0 threshold.