A description of larval and early juvenile development in Paralomis spinosissima (Decapoda: Anomura: Paguroidea: Lithodidae) from South Georgia waters (Southern Ocean)

The early life history of the sesarmid crab Chiromantes ortmanni (Crosnier, 1965) was studied at constant laboratoryconditions, and the complete larval and early juvenile development are described. Chiromantes ortmanni showsintraspecific variability in the pattern of larval development, which typically includes 5 or, less frequently, 6 zoeal stagespreceding the megalopa. The regular pathway (with 5 zoeal stages) required ca 18–20 days. During this time span, zoealsize (carapace length) increased by a factor of 2.2 from 0.33 to 0.73 mm, while biomass (measured as zoeal dry mass andcontents of carbon, nitrogen and hydrogen) showed an 8-fold increment. The megalopa moulted after 10–12 days to thefirst juvenile crab stage, the total larval development from hatching to metamorphosis taking approximately one month(or ca. 4 days longer in larvae passing through an additional zoeal stage). First egg-laying was observed 8.5 months later,at a female carapace width of 14.4 mm. After an embryonic development time of 26–27 days, a total of 3,470 larvaehatched during two subsequent nights. Hence, the minimum generation time (from hatching to first offspring release)comprised slightly more than 10 months. Unlike the regular zoeal stages, the supernumerary stage VI showed atypicalcharacters for Sesarmidae larvae, especially in the setation pattern of the first maxilliped and the segmentation of theendopod of the second maxilliped. Some characteristics presented an intermediate morphology between that of the zoeaV and the megalopa. The first juvenile stage (crab I) is described in detail, while only the most relevant morphologicalchanges and sexual differentiation are highlighted for subsequent crab stages (II–IX). Males and females can bedistinguished from instar V onward, based on sexual dimorphism in the pleopods and the presence of gonopores in thefemales. The morphological characters of all larval stages and of the first juvenile crab are compared with those of other Chiromantes spp.

Growth rate of sterlet larvae and juveniles during 2008 and 2009 was studied under experimental and farming conditions in the Czech Republic. The embryos hatched when reaching a mean total length (TL) of 9.0 mm. Larvae were fed by living food, with a gradual transition to dry diet. The exogenous feeding and the larval period of ontogeny started at DAH 9 (day after hatching) reaching TL of 15–17 mm accompanied by melanin plug exclusion. Towards the end of larval period (DAH 39–43, TL 50–58 mm), the embryonic finfold disappeared and the formation of fin apparatus was nearly completed. During the larval and early juvenile development, daily increments of TL and weight (w) ranged between 0.33–4.23 mm.d−1 and 0.0018–1.6400 g.d−1, respectively. The specific growth rate (SGR) ranged from 25.65 to 2.73 %.d−1. Growth intensity and length parameters are similar to the Starry sturgeon, lower than those of the Siberian sturgeon and Russian sturgeon and significantly lower than at Beluga sturgeon. Sterlet’s Fulton weight condition factor (FWC) was higher than in the Siberian and Starry sturgeon. The development was also observed on the basis of morphological changes. The larval development could be divided into six steps.

Changes in biomass and chemical composition during lecithotrophic larval development of the southern king crab, Lithodes santolla (Molina)

Egg production, hatching rates, and abbreviated larval development of Campylonotus vagans Bate, 1888 (Crustacea: Decapoda: Caridea), in subantarctic waters

In a semiterrestrial and estuarine tropical crab, Armases angustipes Dana (Grapsoidea: Sesarmidae), changes in biomass (measured as dry mass, W; carbon, C; nitrogen, N; and hydrogen, H; per individual) and relative elemental composition (C, N, H, in percent of W; C:N mass ratio) were studied during development from an early egg stage through hatching, the complete larval phase, metamorphosis and the first juvenile crab stage (CI). In the megalopa and CI, growth was measured also within the moulting cycle, and biomass and elemental composition were determined in cast exuviae. From an early egg stage to the freshly hatched larva, A. angustipes lost about 20% of W, 29% of C, 5% of N and 32% of H. Proportionally higher losses in C than in N were reflected also in a significantly decreasing C:N mass ratio (from 5.02 to 3.74). These results indicate that lipids mobilised from yolk reserves represented the principal metabolic substrate for embryonic energy production, while proteins were catabolised at a much lower rate. The present data of growth and exuviation are compared with previously published data from a congener, A. miersii Rathbun, which has an abbreviated and facultatively lecithotrophic mode of larval development (with three instead of four zoeal stages; stages I and II in principle independent of food). When growth is measured as an increase in the final (premoult) biomass of successive developmental stages, both species show an exponential pattern. Within the moulting cycles of the megalopa and the first juvenile, both species show parabola-shaped growth curves, with a rapid biomass increase in postmoult and intermoult stages, and losses in the premoult phase. Thus, the two Armases species show, in general, similar patterns of larval and early juvenile growth. However, the initial size of eggs and larvae is about four times larger in A. miersii, and its biomass remains higher throughout the period of larval and early juvenile development. A. angustipes is able to partially make up for this difference, as it has an additional zoeal stage, and its megalopa and CI stages show higher relative biomass increments (in percent of initial values). Due to this compensatory growth pattern, A. angustipes reaches in its CI stage about half the biomass of a juvenile A. miersii. When exuvial losses of megalopae and juveniles are compared between these two species, A. miersii shows higher biomass losses per individual (corresponding with its larger size), but lower relative losses (C, N, H, in percent of late premoult body mass or in percent of previously achieved growth increments). Differences in larval and early juvenile growth and in the exuvial losses of megalopae and juveniles of these two congeners are discussed in relation to their differential ecology, life history and reproductive strategy.

Paralomis granulosa Jacquinot is a commercially fished lithodid crab species living in subantarctic and cold-temperate regions of southern South America. Its larval stages (Zoea I, II, Megalopa) are fully lecithotrophic, developing in the complete absence of food from hatching through metamorphosis; first feeding occurs in the first juvenile crab stage. In laboratory rearing experiments conducted at constant 1, 3, 6, 9, 12, and 15°C, we studied rates of larval and early juve- nile survival and development in relation to temperature. At 1°C, many larvae (52%) reached the Megalopa stage almost 2 mo after hatching, but all died subsequently without passing through meta- morphosis. Larval development was successfully completed at all other temperatures, with maximum survival at 6 to 9°C. The time of non-feeding larval development from hatching to metamorphosis lasted, on average, from 24 d (at 15°C) to almost 4 mo (117 d, at 3°C). When the experiment was ter- minated 1 yr after hatching, the 3rd (3°C) to 8th (15°C) juvenile crab instar had been reached. The relationship between the time of development through individual larval or juvenile stages (y) and temperature (T) was described as a power function (y = a × T b , or log(y) = log(a) + b · log(T); the same regression model was also used to describe the temperature-dependence of cumulative periods of development from hatching. The wide thermal tolerance window for successful larval development (at least 3 to 15°C) and the broad geographic range of this species show that the early life-cycle stages of P. granulosa are cold-eurythermal. This physiological trait together with larval independence of food indicate that this lithodid crab species is well adapted to severe conditions of cold in com- bination with the food-limitation in subantarctic regions. Since similar traits have been also observed in other Lithodidae, we suggest that early life-history adaptations to low temperatures and low plank- tonic productivity may explain the high number of lithodid species occurring at high latitudes and in the deep sea, i.e. in conditions under which other Decapoda show strongly reduced diversity.

Summary The freshwater crab Sesarma fossarum (Decapoda, Brachyura, Sesarmidae) was only recently described as a new species. As in most other endemic Jamaican crabs that have radiated in limnic and terrestrial environments, its early life history has been largely unknown. In an experimental laboratory study this species was reared through embryonic, larval, and early juvenile development, and ontogenetic changes in biomass (contents of carbon, nitrogen, and hydrogen) were measured. The duration of egg development varied greatly within a single brood, such that larval hatching occurred through an extended period (12 d). Larval development invariably consisted of two non-feeding (fully lecithotrophic) zoeal stages and a facultatively lecithotrophic megalopa, followed by metamorphosis to the first juvenile crab stage (always feeding). The zoeal phase lasted on average 4–5 d, while the megalopa required 8–10 d. This abbreviated and largely food-independent mode of development is interpreted as a life-history adaptation to conditions of food limitation in the breeding habitat of this species (presumably maternal burrows dug in river banks). This strategy is based on an enhanced maternal energy investment in the production of large, yolk-rich eggs (ca. 1.4 mm size, 0.6–0.7 mg dry mass). The megalopa shows a highly flexible nutritional strategy where the appearance of a functional feeding system allows for exploitation of external energy sources, while its development remains, in principle, independent of scarcely available food. However, when megalopae were reared without any food, the first juvenile crab stage showed an enhanced mortality and a reduced body size. Decreasing C, H, and C:N values indicate that the fully endotrophic (embryonic and zoeal) phase is principally based on a utilization of lipid reserves; the same applies to the development of megalopae reared in a continued absence of food. In fed megalopae, increasing N and decreasing C:N values indicate that dietary energy was primarily invested in protein synthesis, required for the construction of new tissues and organs. Similarity in the reproductive, developmental, and bioenergetic traits of S. fossarum and other limnic or terrestrial crabs from Jamaica suggest that food limitation during the early larval phase has been one of the principal selection factors driving the evolution of the endemic non-marine clade of sesarmids towards increasing egg size and larval lecithotrophy.

Changes in biomass, lipid, fatty acid and elemental composition during the abbreviated larval development of the subantarctic shrimp Campylonotus vagans

Editor's evaluation: Antagonistic role of the BTB-zinc finger transcription factors Chinmo and Broad-Complex in the juvenile/pupal transition and in growth control

Larval development of the subantarctic squat lobster Munida subrugosa (White, 1847) (Anomura: Galatheidae), reared in the laboratory

Fecundity, hatching rhythm, and the planktotrophic larval development of the hermit crab Pagurus comptus from sub-Antarctic waters of the Beagle Channel (Tierra del Fuego) were studied under controlled laboratory conditions of temperature, light cycle, food supply, and salinity. Fecundity was low, ranging from 134 to 848 eggs per female (cephalotoraxic shield length, SL, 2.3–5.0 mm). Hatching observed in the laboratory ranged from 6 to 30 d. The larval development was studied in laboratory cultures fed with Artemia sp. nauplii and kept at constant 7.0±0.5°C. Larvae invariably passed through four zoeal instars and one megalopa stage. Mean durations of the zoeal stages I to IV were 14.3±1.8, 16.7±4.6, 23.2±6.5, 33.4±9.2 d, respectively. Combined with the 43.8±5.6 d recorded for the survived megalopae, we suggest that the complete larval development lasts about four months. Starved larvae, on average, survived for 22±8.1 d (maximum 38 d) by far exceeding the zoea I duration in fed larvae, but did not reach the moult to the zoea II stage. Unlike other sub-Antarctic decapods, which show a tendency towards abbreviated or endotrophic larval developments at high latitudes, hermit crabs, at their southernmost distributional limit on Earth, show an extended and fully planktotrophic larval development and thus need to synchronize larval release with short periods of high primary production.

Summary Four regular zoeal, the megalopal and first two crab stages of Lopholithodes mandtii Brandt were reared under laboratory conditions. Additionally one specimen passed through a fifth zoeal stage. All stages are described and illustrated.

Morphological variations in the two zoeal stages and megalopa of a lecithotrophic population of Paralomis granulosa (Jacquinot) reared under laboratory conditions are reviewed. Attention is also directed to certain aspects of their development not previously considered. More importantly, the first three juvenile stages are described and illustrated for the first time. Specific consideration is given to the structural changes in the abdominal tergites during the transformation from megalopa to third crab, and ancillary information on abdominal plate development in juvenile stages four and five is provided. Total pleopod loss in both sexes and subsequent reappearance in females is discussed.

Energetic changes throughout lecithotrophic larval development in the deep-sea lithodid crab Paralomis spinosissima from the Southern Ocean

Effects of ocean warming on larvae development of Patella tenuis crenata in the Canary Islands