Elemental composition (C,N,H) in larval and crab-1 stages of Pagurus bernhardus (Decapoda,Paguridae) and Carcinus maenas (Decapoda,Portunidae)

Analyses of individual content of carbon (C), nitrogen (N), and hydrogen (H) were carried out for all larval stages of Pagurus bernhardus and Carcinus maenas, and for newly metamorphosed crabs. Maximum range in total larval development is 12.8 to 165.8 g C, 3.2 to 35.1 g N, and 1.9 to 24.9 g H in P. bernhardus and 3.1 to 43.2 g C, 0.7 to 10.1 g N, and 0.4 to 6.3 g H in C. maenas. From these data energy equivalents were calculated. Maximum range in total larval life is 0.43 to 6.38 J ind. ^-1 in P. bernhardus and 0.1 to 1.49 J ind. ^-1 in C. maenas. There is a 32.4% mean loss of energy in P. bernhardus megalopa development; this seems to describe the normal developmental pattern in this stage. Biomass was determined as fresh and dry weight respectively. Individual dry weight is about 3.6 to 5.6 times higher in P. bernhardus (44 to 340 g) than in C. maenas (12 to 93 g) larvae.Contribution to research project Experimentelle marine Ökosystemanalyse sponsored by Bundesministerium für Forschung und Technologie, Bonn (Grant No. MFU-0328/1)     

Respiratory metabolism of Pagurus bernhardus (Decapoda: Paguridae) megalopa

Individual oxygen consumption was determined during the megalopa development of Pagurus bernhardus at 18°C in 1983. The maximum observed range was from 0.101 to 0.343 l O₂ h^-1 ind^-1. Individual respiration rate dropped by about 33% during the first two days and continued to remain at that level throughout the moult cycle. The results are discussed together with data on biomass and the fact that P. bernhardus megalopa do not feed.     

Patterns of larval and early juvenile growth in a semiterrestrial crab, Armases angustipes (Decapoda: Sesarmidae): comparison with a congener with abbreviated development

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.     

Developmental changes in body weight and elemental composition of laboratory-reared larvae of the red frog crab,Ranina ranina (Decapoda: Brachyura)

Ranina ranina larvae were reared at 29°C from hatching to the megalopa stage to measure daily changes in body weight, water content and elemental composition. Energy, estimated from carbon content, was also examined. The water content was 85 to 92% of body weight immediately after ecdysis but decreased with days after ecdysis. Gains in body weight, carbon, nitrogen, hydrogen and energy during each instar ranged from 52 to 245% and increased with instar after instar II (body weight and carbon), instar III (hydrogen and energy), and instar IV (nitrogen). Cumulative gains of these elements from hatching to 2 d before metamorphosis into megalopa ranged from 11 567% (carbon) to 12 209% (energy). Most cumulative gains (57 to 59%) in elemental composition were contributed by instar VII. Carbon, nitrogen and hydrogen content in body weight decreased to a minimum on the day of ecdysis and increased on the subsequent days. C:N ratios after instar IV were lowest on the day after ecdysis and reached a plateau by the second day. Energy, estimated as J mg^-1 dry weight (DW), decreased with instar and within a molt cycle, and was at a minimum on the day after ecdysis. Gains in elemental composition could be described by an exponential function of days after hatching and by a quadratic function in each instar.     

Larval development of the hermit crab Clibanarius albidigitus (Crustacea: Anomura: Diogenidae) reared under laboratory conditions

The larval development of Clibanarius albidigitus Nobili is described and illustrated from laboratory-reared specimens. At 30°C, this species passes through four zoeal stages before molting to the megalopa. Of the 120 individual larvae reared, survival was high, with 88% reaching the megalopal stage. Zoeal stage durations varied from 3 to 18 d. Rearing was terminated after 45 d, and at that time no megalopae had molted to the firstcrab stage. Among known larvae of Clibanarius species, C. albidigitus is immediately distinguished by the presence of dorsomedial and dorsolateral carapace keels.     

Growth and elemental composition (C,N, H) in Inachus dorsettensis (Decapoda: Majidae) larvae reared in the laboratory

Larvae of the spider crab Inachus dorsettensis were reared in the laboratory at constant 12 °C. Development lasted 8 to 10 d in the Zoea I, 10 to 12 d in the Zoea II and 14 to 20 d in the megalopa stage. During this time, larval growth was measured in samples taken every 2 to 4 d as dry wt (W), carbon (C), nitrogen (N), and hydrogen (H); energy content (E) was calculated from C. Biomass and energy (per individual) increased in each larval stage as a parabola-shaped function of age, which could be fitted by a power equation. C, H, and E show a higher percentage gain (relative to the initial values at hatching) than W or N, suggesting that proportionally more lipid than protein is accumulated during larval development. There are cyclical changes in the relative (per unit of W) biomass and energy figures, corresponding to the larval moult cycles: immediately after each ecdysis all these values decrease, presumably due to rapid uptake of water and minerals, then they increase again due to tissue growth and remain high until the next moulting occurs. Cyclical changes in the C/N ratio suggest that proportionally more lipid than protein is accumulated during the initial (postmoult) phase of the moult cycle, followed by a period of balanced or protein-dominated gain during the intermoult and premoult phases. These patterns of growth and elemental composition observed during the complete larval development and in single moult cycles of I. dorsettensis are compared with those described in the literature for other decapod species. This comparison suggests a high degree of similarity in biochemical composition and growth characteristics of larval decapod crustaceans.     

Influence of limited starvation periods on growth and elemental composition (C,N,H) of Carcinus maenas (Decapoda: Portunidae) larvae reared in the laboratory

Zoea-1 larvae of Carcinus maenas L. (Decapoda: Brachyura: Portunidae) were from Helgoland in March 1984 and reared in the laboratory at 18°C through ecdysis. Dry weight (DW) and elemental composition of carbon (C), nitrogen (N), and hydrogen (H) were analyzed in newly hatched zoea-1, after different initial starvation periods, and in newly moulted zoea-2. Continually starved zoea-1 lost biomass and energy steadily, and logarithmic functions show best fit of empirical and predicted data. Biomass and energy equivalents of newly moulted zoea-2 are significantly correlated with starvation periods in the zoea-1, showing lower values with longer initial starvation. After about 25 to 34% individual biomass and energy losses, larvae exceed the point-of-noreturn (PNR), and do not recover or moult to the zoea-2, even if re-fed. When starvation ceases before the PNR, larvae moult to the zoea-2, and develop with lower average growth rates (AGR) after prolonged periods of initial food deprivation. The later larvae were re-fed, the less absolute amounts of DW, C, H, and individual energy, but more DW-related energy equivalents and N accumulated during subsequent feeding towards ecdysis. It is suggested that lipid, rather than protein, is the main source of energy controlling the maintenance of larval moult cycles. After lipid reserves are depleted, zoea-1 larvae live on body protein, and lose the ability to absorb and restore sufficient lipid if re-fed later than the PNR.Contribution to research project An-145/1-1 granted by the Deutsche Forschungsgemeinschaft (DFG)     

Accumulation and loss of biomass inLiocarcinus holsatus larvae during growth and exuviation

Liocarcinus holsatus (Fabricius) larvae, of females originating from the Elbe Estuary, FRG, were reared in the laboratory at constant 15°C in May 1988. For each larval stage, developmental time was measured by individual cultures (Zoea I: 6.7±0.7d; Zoea II: 5.0±0.6d; Zoea III: 4.8±0.7 d; Zoea IV: 5.3±0.6d; Zoea V: 6.1±1.1d; Megalopa: 10.45±0.7d). During the entire period of development, dry weight (W), carbon (C), nitrogen (N), and hydrogen (H) were measured daily (Zoea I to V) or every second day (Megalopa). The energy content (E) was estimated from C. Biomass and energy (per individual) increased in each larval stage as a parabolic function of age and is described by power functions. C, H, and E exhibit a higher percentage gain (relative to initial values at the time of hatching) than W and N. It is suggested that proportionally more lipid than protein is accumulated during larval development. Cyclical changes in the relative biomass (% W) correspond to the larval moult cycle, indicating a rapid uptake of water and minerals immediately after hatching and a later increase in tissue growth. Changes in the C:N ratio suggest that during the first period more lipid than protein is accumulated. These patterns of growth and elemental composition are compared with literature data and a high degree of similarity in the growth characteristics of decapod larvae is seen. In addition W, C, N, and H values as well as E were measured for the exuviae of Zoea I to V and Megalopa. The percentage loss of growth rate by exuviae for each larval instar were higher in W (12 to 16%) and C (8 to 12%), and varied between 5 and 10% for N, H, and E.     

Endogenous swimming rhythms in estuarine crab megalopae: implications for flood-tide transport

Up-estuary migration of crab larvae to adult habitats is thought to be accomplished by selective tidal transport in which late-stage larvae enter the water column on flood tides and remain on or near the bottom on ebb tides. This study measured endogenous rhythms in swimming by the last larval stage (megalopa) of blue crabs Callinectes sapidus and fiddler crabs Uca spp. Previous field studies found that megalopae of both species were only abundant in the estuarine water column on nocturnal rising tides. Megalopae were collected from the Newport River Estuary, North Carolina (34°41N; 76°40W) during August–September 1992 and swimming activity was recorded for 4.5 to 7 d under constant conditions with a video system. Rhythms exhibited by both genera in the laboratory were not identical to those recorded in the field. Uca spp. displayed a circatidal rhythm, with maximum swimming occurring near the time of high tide in the field. Rhythm amplitude increased when crushed oyster shells were present, which suggested that megalopae bury or cling to the substrate during quiescent periods. In contrast, C. sapidus had a circadian rhythm in which maximum swimming coincided with the day phase in the field. In most trials, the activity of blue crab megalopae was unrelated to the expected tidal cycle. It was concluded that a tidal rhythm in swimming was the behavioral basis of flood-tide transport for fiddler crab larvae. The endogenous rhythm in blue crabs does not participate in transport, which probably results from behavioral responses to environmental cues associated with flood tide.     

Laboratory study of effects of temperature and salinity on survival and larval development of a population of Rhithropanopeus harrisii from the Mondego River estuary,Portugal

Rhithropanopeus harrisii (Gould) is an introduced species in the estuary of the Mondego River (Portugal): it was first recorded from the Iberian Peninsula in 1989. The larval development of this population was studied under laboratory conditions at different temperatures and salinities, and showed a larval development pattern very similar to that reported for American estuarine populations of this species. Larval development was negatively correlated with temperature. Time to megalopa varied between 7 and 35 d; the first crab (C₁) was reached after a maximum of 11 to 43 d. Larval development was optimum at 25°C and 15S. Larval survival was maximum at 10, 15 and 20S at all three temperatures studied (20, 25 and 30°C). The percentage of abnormal megalopae increased with increasing salinity to a maximum (100%) at 30S; incidence of abnormality was not affected by temperature.     

Larval development of Ocypode quadrata (Brachyura: Crustacea) under laboratory conditions

The larvae of Ocypode quadrata (Fabricius) have been reared in the laboratory, from hatching to megalopa stage, at 35 S, 25°C. The five zoeal stages and the megalopa are described, including functional appendages of each stage. On the basis of morphological characteristics, the first zoeal and megalopa stages of O. quadrata can be distinguished from similar stages of closely related Ocypodinae. At 25°C, the megalopa appeared in a minimum of 34 days following hatching.     

Changes of respiration and biomass of spider crab (Hyas araneus) larvae during starvation

The influence of starvation on respiration (R), dry weight (W), carbon (C), nitrogen (N), hydrogen (H), and energy content (E; calculated fromC) of spider crab (Hyas araneus L.) larvae was studied in the laboratory. In all larval stages (zoea I and II, megalopa)W increased during postmoult, independent of food, and decreased subsequently. The final reduction inW after continued starvation increased from stage to stage (9, 13, and 20% respectively), but it was always much lower than the decrease inC (44 to 52%),N (42 to 46%),H (50 to 58%), andE (53 to 62%). Individual (R) and weight-specific respiration rates (QO ₂) were reduced by 83 to 88%. The time-dependence of these reductions in metabolism and biomass as well as the rates of change in all parameters studied were described with non-linear regression models and differential equations, respectively. Rates and total amounts of energy lost during starvation were independently calculated fromC andR values, and similar results were mostly obtained. Only in the megalopa stage was there a conspicuous difference between the two estimates: higher losses were calculated fromR. This shows that further (biochemical) data are required for a more complete understanding of the energetics of this stage. Estimates of total protein (fromN) and lipid (fromC) suggest that both constituents serve as metabolic substrates during starvation, but most of the energy originates from the breakdown of protein.Supported by the Deutsche Forschungsgemeinschaft (An 145/1-1)     

Costs of extended brood protection in the Antarctic sea star, Neosmilaster georgianus (Echinodermata: Asteroidea)

Changes in size, morphology, and biochemical composition in adults and embryos of a brooding sea star, Neosmilaster georgianus (Sladen), were studied in a population adjacent to Anvers Island, Antarctic Peninsula (64°46′S; 64°04′W) during the austral spring, 1991. Five morphological stages of development were designated in 24 broods, and for each the weight and biochemical composition of the brooding adults and their embryos were determined. Between Stage 1 and 2, the dry weight (dw) and organic weight (ow) of the embryo did not change. From Stage 2 to 3, the dw and ow increased significantly by 10%. Stage 2 and 3 embryos were in clusters of a few (2 to 10) to as many as 40 individuals. In the smaller clusters, individual embryos were attached by tissue cords to another, sometimes atrophied, brood member. In the larger clusters, they were attached to a central mass of tissue containing remnants of embryos. We interpret these interactions as a form of cannibalism which may account for the weight gains between Stage 2 and 3. During Stages 4 and 5, as juvenile form was approached, the dw and ash weight of the young increased significantly and the ow decreased significantly. The calculated energy content for the juvenile (Stage 5) was not significantly different from the energy content of the earliest undifferentiated stage (Stage 1), an indication that most of the organic matter in the egg is the primary contribution to the large juvenile. In brooding females, pyloric caeca indices declined by 52% from Stage 1 to Stage 5 and pyloric energy stores declined by 63% due to proportionately equivalent declines in protein and lipid. The ovary index was low and increased only slightly during brood protection, while the size of the largest oocytes remained approximately 23% that of ova. Energy stores in the pyloric caeca of brooding N. georgianus thus become depleted over a long period of incubation during which the adults apparently starve. This may delay oocyte development and ultimately limit the frequency of individual reproduction. Received: 15 September 1998 / Accepted: 9 March 1999     

Comparative feeding ecology of two sympatric rockfish congeners,Sebastes caurinus (copper rockfish) and S. maliger (quillback rockfish)

Possible differences in the diet or metabolism of sympatric finback and humpback whales in the Gulf of St. Lawrence were investigated through analysis of their blubber fatty acids. Free-ranging finback (Balaenoptera physalus, n=19) and humpback (Megaptera novaeangliae, n=10) whales were sampled through biopsy during summer 1991. The two species differed in the chemical composition and stable carbon isotope distribution of fatty acids extracted from their outermost blubber layer. Finback blubber was slightly but significantly richer in its relative proportions of 12:0, 13:0, i14:0, 17:0, 18:1 n9, 18:1 n7, and 20:0 (probability of difference 99%), 18:2 n6, 18:0, and 19:0 (probability 95%), and 16:1 n5 and 16:0 (90%). The stable isotope ratio of finback total fatty acids averaged-25.5±0.4%. Humpbacks contained relatively more i16:0, 18:1 n5, 20:5 n3, and 22:6 n3 (probability 99%), 16:1 n7, i18:0, 20:4 n6, and 22:5 n3 (95%), and 20:4 n3 (>90%). Their fatty acid ¹³ averaged -25.8±0.5% (different from finbacks with a probability of 95%). There was no significant difference between the two species in the relative proportions of 14:1, 14:0, i15:0, a15:0, 15:0, i17:0, a17:0, 17:1, 20:1 n9, 20:1 n7, 22:1 n11, or 22:1 n9, which together made up one-third of total fatty acids. We used principal component and cluster analyses to integrate and visualize the differences in the chemometric data sets. The chemical and isotopic differences found in the present study are consistent with a slightly lower trophic position for humpbacks compared to finbacks in the Gulf of St. Lawrence, reflecting a difference in long-term, average diet.     

Response of mud crab (Panopeus herbstii) megalopae to cues from adult habitat

During the summer of 1995, we investigated the response of mud crab megalopae (Panopeus herbstii Milne-Edwards) to cues associated with adult habitat. Natural rock/shell substratum and the rock-associated seaweed, Fucus vesiculosus L., both induced metamorphosis of competent megalopae; natural sand substratum did not induce metamorphosis. Structural mimics of preferred substrata induced metamorphosis only when covered with natural biofilm. Clean mimics did not induce metamorphosis. Water-soluble exudates from preferred substrata showed weak induction of metamorphosis. Exudates from adult P. herbstii elicited a similar weak response. Exudates from another species of crab and from two fish predators did not induce metamorphosis. We conclude that water-soluble cues associated with major components of preferred adult habitat induce the metamorphic molt of P. herbstii megalopae. The three-dimensional structure of the substratum is not important in induction of metamorphosis, but the biofilm associated with preferred substratum plays a critical role. It is not clear whether the biofilm produces the water-soluble cue or simply provides a tactile stimulus that works in conjunction with the soluble cue.     

Larval growth in the estuarine crab Chasmagnathus granulata: the importance of salinity experienced during embryonic development, and the initial larval biomass

The importance of salinity experienced during embryonic development and initial larval biomass on larval growth was studied in the South American estuarine crab Chasmagnathus granulata. Ovigerous females were maintained at three salinities (15, 20, and 32‰) from egg laying to hatching of zoea l. Larvae from all treatments were reared under constant conditions of photoperiod (12∶12), temperature (18°C), and salinity (first instar at 20‰, subsequent instars at 32‰). Biomass was measured as dry weight, carbon, and nitrogen content per individual at egg laying, hatching of zoea l, premoult zoea l, and zoea 4, and in 8-day-old megalopa. From hatching to premoult zoea 4, biomass was higher for larvae from prehatching salinities of 15 and 32‰. There was a significant positive correlation between biomass at hatching and at premoult zoea l and zoea 4. Accumulated biomass during zoeal stages tended to be higher for larvae from broods with higher biomass at hatching, although this trend was not always significant. Zoea 4 either directly metamorphosed to megalopa or moulted to zoea 5, following, respectively, a short or long developmental pathway. The proportion of zoea 4 that followed the long pathway was negatively correlated with biomass of zoeal stages. Biomass at hatching was correlated with biomass of megalopae developed through the short pathway, although it was not correlated with the accumulated biomass at this stage. Megalopae developed through the long pathway (i.e. metamorphosed from zoeae 5) had higher biomass than those from the short pathway. The present results suggest that prehatching salinity and initial egg and larval biomass can be very important for larval growth. Published online: 9 August 2002     

Endogenous swimming rhythms of blue crab, Callinectes sapidus , megalopae: effects of offshore and estuarine cues

Larvae of the blue crab Callinectes sapidus Rathbun develop on the continental shelf. The postlarval stage (megalopa) occurs near the surface and is transported shoreward by wind-driven surface currents. It then uses selective tidal stream transport for migration up an estuary. Endogenous swimming rhythms were measured under constant dark conditions in the laboratory in megalopae collected from the Newport River Estuary (North Carolina), the Delaware Bay, and offshore from the Newport River Estuary. Megalopae from all areas had a similar circadian activity rhythm, in which they swam during the time of the day phase in the field and were inactive at night. This rhythm predicts the presence of a reverse, diel, vertical-migration pattern offshore which would contribute to the location of megalopae near the surface during the day. The rhythm lacks obvious ecological significance in estuaries because it does not contribute to selective tidal stream transport and would increase vulnerability to visual predators during the day. Attempts to entrain a circatidal rhythm in swimming by cyclic and step changes in salinity were unsuccessful, as the circadian rhythm persisted. The rhythm also continued in the presence of the eelgrass Zostera marina, which is a site of settlement and metamorphosis in the field. Thus, megalopae enter estuaries with a solar day rhythm in activity. This rhythm, however, is not expressed, because light inhibits swimming during the day upon exposure to estuarine water. Since this light inhibition is removed in offshore waters, the rhythm would be expressed if, after entering an estuary, megalopae were transported back to offshore areas. Received: 19 December 1995 / Accepted: 2 August 1996     

Growth, carbon, nitrogen and caloric content of Solea senegalensis (Pisces: Soleidae) from egg fertilization to metamorphosis

Eggs and larvae of the Senegal sole, Solea senegalensis Kaup, were reared from fertilization until the end of metamorphosis, which occurs by Day 17 after hatching at 19.5 °C. Changes in energy content and biomass quality were studied in terms of dry weight and of carbon, nitrogen and energy content. S. senegalensis spawned eggs of about 1 mm diameter which hatched 38 h after fertilization. Average dry weight of individual eggs was 46 μg, the chorion accounting for about 18% of total dry weight. Gross energy of recently fertilized sole eggs was approximately 1 J egg⁻¹. From fertilization to hatching, eggs lost 8% of their total energy (chorion not included). After hatching, larvae lost 14% of their initial energy until the start of feeding which occurred about 48 h afterwards. The principal components catabolized during embryogenesis were carbon-rich compounds that decreased by 26%, while nitrogen-rich compounds decreased by only 10% and were practically unaltered from hatching to the start of feeding. Feeding larvae displayed constant growth during the period studied (specific growth rate on a dry weight basis was 0.26 d⁻¹). The relative proportion of carbon and nitrogen content revealed an accumulation of high energy compounds in the days before metamorphosis. By Day 14, the energy content reached values similar to those of recently hatched embryos, but decreased again during metamorphosis. Received: 10 June 1998 / Accepted: 28 January 1999     

Influence of extracts of adult crabs on molting of fiddler crab megalopae (<Emphasis Type="Italic">Uca pugnax</Emphasis>)

Larvae of many benthic invertebrates metamorphose in response to habitat cues, which include the presence of adult conspecifics. Prior research showed that fiddler crab [Uca pugnax (Smith)] megalopae advance molting to the first crab stage in seawater in which conspecific adult crabs were maintained. In the present study, extracts of adult crabs were prepared and the specificity and protein content were characterized. U. pugnax megalopae were reared in the laboratory to minimize their prior exposure to potential molting cues. Then they were presented with extract solutions (in 1995, 1996, 1997, and 2000) to determine the specificity of the molting response to extracts of several crab species and the effects of the protein concentration of the extract, age of the megalopae at exposure to extract, and the duration of exposure on the molting response. Megalopae of U. pugnax molted sooner in seawater containing extract from adult conspecifics than in filtered seawater without extract or in seawater containing extract from the congener U. minax. Extract from the mud crab Dyspanopeus sayi retarded molting of U. pugnax megalopae. The stimulatory effect of U. pugnax extract on molting of megalopae was dependent on extract concentration. U. pugnax megalopae did not respond to extract until 6 days after molting, and only 1 day of exposure was sufficient to stimulate molting. The boiled extract was effective after being frozen (–15°C) for 2 years. The preparation of stable extract provides a uniform stimulus for multiple experiments examining the specificity of molting cues for brachyuran crustacean larvae and the onset of receptivity to cues.Communicated by J.P. Grassle, New Brunswick     

Diurnal and lunar patterns of larval recruitment of Brachyura into a mangrove estuary system in Ranong Province, Thailand

The present study followed the temporal recruitment pattern of brachyuran larvae in a mangrove tidal creek on the Andaman Sea coast of Ranong Province, Thailand, based on the assumption that the processes governing recruitment are important for the overall population dynamics of mangrove brachyuran crabs. Plankton net samples were taken on five occasions: on two new moon spring tides, one waxing moon neap tide, one full moon spring tide and one waning moon neap tide during October and November 1997. In addition collectors for larval crab megalopae were employed every 3 days through one dry season and one wet season (March–October 1998). Both the plankton net samples and collector samples revealed four major brachyuran groups in three families: Ocypodidae, Grapsidae and Portunidae. The grapsid group was further separated into two morphotypes which were identified as Metaplax and sesarmid species. Identified group mean numbers per cubic metre were ocypodids 3.0, sesarmids 0.8 and Metaplax 0.5, while portunid megalopae were very scarce (≪0.1 m⁻³). Further analysis of plankton net samples showed that when considering the parameters date, depth, current direction and the diel cycle, Metaplax and ocypodids distribute differently in the tidal and lunar cycle. Metaplax recruitment dominates on flood tides and on bottom layers, followed by middle and surface layers. Conversely, ocypodid abundance varied significantly with date only. Notably recruitment was not dependent on the diel cycle for either group. The collector samples of megalopae showed that recruitment of ocypodids, Metaplax and sesarmids occurred on full and new moon spring tides, while portunid megalopae preferred to settle on full moon spring tides. Since tidal currents were related to the lunar cycle megalopa groups are also cross-correlated with tidal amplitude, except for the portunid group. It is concluded that megalopae recruit in a similar manner to what has been found in other regions of the world, except that the abundance of ocypodids and Metaplax is not influenced by the diel cycle. Received: 14 February 2000 / Accepted: 24 November 2000