First record of an epibiosis between the sand crab Emerita analoga (Stimpson, 1857) (Decapoda: Hippidae) and the mussel Semimytilus algosus (Gould, 1850) (Bivalvia, Mytilidae) in southern Peru

Coastal zones of the Humboldt Current Upwelling System (HCUS) are composed both of rocky and sandy beaches inhabited by macrozoobenthic communities. These show oscillating changes in the dominance of species; the abundance of the sand crab Emerita analoga is linked to phases of the El Niño Southern Oscillation (ENSO). The biogenic surfaces of these crabs serve as substrate for opportunistic colonizers. This study is the first record of an epibiosis between E. analoga and the rock mussel Semimytilus algosus, detected at a southern Peruvian sandy beach. Mussels fouled a wide size-range of adult E. analoga (7.3%) but they themselves belonged to small-size classes. The largest S. algosus was 17.4 mm in length. Highest permanence of epibionts was found on larger sand crabs (maximum between 24 and 27 mm). Significantly more mussels were found on the ventral surface (39.4%) compared to 10 other surface areas of the sand crab. Possible benefits and disadvantages of the observed epibiosis for both the basibiont and the epibiont are discussed.     

Factors influencing aggregation patterns in the sand crab Emerita analoga (Crustacea: Hippidae)

Summary Aggregation patterns in Emerita analoga (in southern California) are delineated with respect to their spatial, daily, and seasonal components. Both abiotic and biotic factors are found to be associated with patterns of aggregation. Spatially, E. analoga aggregates from March through September to a significantly greater degree in the upper one-third area of the wash zone where exposure to wave shock and fish predation are probably decreased. Sand crabs are more aggregated on a daily basis during low tides than at high tides. This may be due to differential rates of migration caused by a decrease in the beach slope angle. Two seasonal peak periods of aggregation are present, one in the early spring, and one in the late summer. These periods occur during the times of highest reproductive female abundance. High seasonal intensities of aggregation probably function to facilitate mating through the maintenance of close proximity between males and females. Visual methods and/or quantitative sampling based on visual observations do not adequately reflect patterns of aggregation in E. analoga.     

Entrainment of the activity rhythm of the mole crab Emerita talpoida

The mole crab Emerita talpoida migrates with the tide in the swash zone of sand beaches. A circatidal rhythm in vertical swimming underlies movement, in which mature male crabs show peak swimming activity 1-2 h after the time of high tides at the collection site. In addition, there is a secondary rhythm in activity amplitude, in which crabs are maximally active following low amplitude high tides and minimally active following high amplitude high tides. The present study determined the phase response relationship for entrainment of the circatidal rhythm with mechanical agitation and whether the cycle in activity related to tidal amplitude could be entrained by a cycle in the duration of mechanical agitation at the times of consecutive high tides. After entrainment with mechanical agitation on an orbital shaker, activity of individual crabs was monitored in constant conditions with a video system and quantified as the number of ascents from the sand each 0.5 h. Mechanical agitation at the times of high tide, mid-ebb and low tide reset the timing of the circatidal rhythm according to the timing relationship to high tide. However, mechanical agitation during flood tide had no entrainment effect. In addition, a cycle in duration of mechanical agitation entrained the rhythm in activity amplitude associated with tidal amplitude. Both rhythms and entrainment effectiveness over the tidal cycle may function to reduce the likelihood of stranding above the swash zone.     

Grooming behavior and morphology of the caridean shrimp Pandalus danae Stimpson (Decapoda: Natantia: Pandalidae)

Grooming or cleaning is a frequent behaviorial activity of the shrimp Pandalus danae . Setal brushes on thoracic limbs scrape and rub other appendages and general surfaces of the exoskeleton. Chelate limbs nip and pick at edges of crevices in the cephalothoracic region. Scanning electron microscopy reveals that the setae composing the grooming brushes are equipped with characteristic tooth- and scale-like setules which serve as the actual rasping devices. Antennules, antennae and pereopods are frequently preened by the third maxillipeds and first pereopods, while large areas of the exoskeleton are cleaned by the third pair of walking legs and the chelate limbs.
Shrimp with the general cleaning limbs ablated develop significantly greater infestations of the epizoic suctorian Ephelota than animals allowed to groom. Olfactory hairs on the antennules of shrimp deprived of the third maxillipeds become fouled with diatoms and debris while those on controls do not. Grooming behavior clearly prevents a build-up of settling organisms between molts and repeated cleaning of sensory sites is essential in maintaining contact with the environment.     

The feeding behaviour of the sand crab Scopimera inflata (Decapoda, Ocypodidae)

A sequence of activities all related to the feeding of Scopimera inflata H. Milne-Edwards, 1873 can be distinguished during the daytime periods of low tide. Emergence begins one to two hours after a feeding area is uncovered, reaches a peak after a further three hours but some crabs are still emerging after the tide has turned. Before feeding commences the burrow is cleared of waste sand down to the water-table. While feeding S. inflata forms a feeding trench which acts as an escape route back to the hole and is defended against other crabs of the same species. Agonistic behaviour becomes evident as feeding progresses. Threat displays, fighting, displacement feeding, and agitation feeding are recognizable behaviour patterns which have been observed.     

Genetic differentiation in the mud crab Scylla serrata (Decapoda: Portunidae) within the Indian Ocean

Scylla serrata (Decapoda: Portunidae) is a swimming crab that is widespread in the Indo-Pacific region and commonly found in estuarine and mangrove waters. An extended planktonic larval phase suggests high dispersal potential and the possibility of extensive gene flow between conspecific populations at least on a geographic mesoscale (tens to hundreds of kilometres).Intraspecific variation of the mitochondrial DNA cytochrome oxidase subunit I (mtDNA COI) gene was investigated in 77 individuals from four representative mangrove swamps of the African tropics (Kenya and Zanzibar) by means of DNA sequencing. We examined 535 base pairs (bp) and identified 24 different haplotypes. Each population sample is characterised by a single most frequent haplotype, shared among all four populations, and a small number of rare ones, typically present in only one or two individuals and representative of a specific population.Analysis of molecular variance (AMOVA), F_ST statistics and χ² contingency analysis of spatial distribution of mtDNA haplotype frequencies revealed in toto a significant genetic differentiation among populations. These results could indicate that gene flow might be reduced, even between geographically close sites, despite the high potential for dispersal; anyway, at the recorded level of divergence and owing to the abundance of rare haplotypes and singletons in our data set, repeated sampling over time is necessary to establish whether the recorded pattern of genetic differentiation is stable and biologically significant.Finally, integration of our data with those reported by Gopurenko et al. [Mar. Biol. 134 (1999) 227] on S. serrata from South Africa, Red Sea and Mauritius Islands allowed to infer S. serrata population structure within a larger area of the Indian Ocean region.     

Developmental shift in the selective tidal-stream transport behavior of larvae of the fiddler crab Uca minax (LeConte)

Following hatching, larvae of the fiddler crab Uca minax (La Conte) are exported from the adult habitat in estuaries to coastal and shelf waters where they undergo development prior to re-entering estuaries as postlarvae (megalopae). Studies of the spatial distribution of both newly hatched zoeae (Stage I) and megalopae indicate they undergo rhythmic vertical migrations associated with the tides for dispersal and unidirectional transport (selective tidal-stream transport) both within estuaries and between estuaries and the nearshore coastal ocean. We tested the hypothesis that U. minax zoeae possess a circatidal rhythm in vertical migration that facilitates offshore transport in ebb tidal flows, while postlarvae (megalopae) return to estuaries using a similar flood-phased endogenous rhythm. We also determined if the expression of the rhythm was influenced by the salinity conditions zoeae and megalopae experience as they transition between low-salinity regions of estuaries and high-salinity coastal waters. Stage I zoeae were collected by holding ovigerous female crabs in the lab until hatching. Megalopae were collected from the plankton and identified to species using molecular techniques (PCR-RFLP). Under constant laboratory conditions, both zoeae and megalopae exhibited endogenous circatidal rhythms in swimming that matched the principal harmonic constituent of the local tides (12.39 ± 0.07 h; X¯ ± SE). Upward swimming in Stage I zoeae occurred 2.5-4 h after high tide near the time of expected maximum ebb currents in the field. Rhythmic swimming of megalopae occurred slightly earlier in the tide (2.5 ± 0.09 h after high tide; X¯ ± SE) but was not entirely synchronized with flood currents, as expected. Salinity conditions had no apparent effect on the expression or pattern of the rhythms. Results indicate that this circatidal rhythm forms the behavioral basis of selective tidal-stream transport (STST) in early stage U. minax zoeae, but does not undergo a sufficient phase shift to account for vertical distribution patterns exhibited by megalopae in the field.     

Developmental patterns of larval growth in the edible spider crab, Maja brachydactyla (Decapoda: Majidae)

The large edible spider crab Maja brachydactyla Balss, 1922, an overexploited coastal fishery resource in Galicia (NW Spain), is considered as a potential aquaculture candidate. Patterns of its larval growth were studied under controlled laboratory conditions (constant 18 ± 1 °C; 36‰ salinity; photoperiod ca. 12:12 h; lipid-enriched Artemia metanauplii provided as food). From hatching through complete larval development and metamorphosis to the first juvenile crab instar, changes in carapace size, dry weight (DW), ash content, elemental composition (carbon, hydrogen, nitrogen; CHN), and proximate biochemical composition (total proteins, lipids, carbohydrates; Pr, L, Ch) were measured in successive stages (zoea I, II, megalopa, crab I). Body size may be described as a linear function of the number of molting cycles, whereas the amounts of DW, CHN, Pr, L, and Ch per individual increased exponentially (3 to 9 fold). The highest growth rates were observed in L, C and H, the lowest in DW, Pr and N. As a consequence of these patterns, the C:N mass ratio as well as the fractions of L, C and H (in % of DW) increased significantly, while those of Pr and N decreased from 26% to 16% of DW. Throughout development, however, Pr remained the principal biochemical component of total DW. Positive correlations between biochemical and CHN data allow for estimates of Pr from N and of L from C values per individual. The patterns of larval growth observed in M. brachydactyla are, in general, similar to those previously described for other brachyuran crabs with a planktotrophic mode of larval development.     

Prey detection by fourth stage Coccinella transversoguttata larvae (Coleoptera: Coccinellidae)

The mode of prey detection is described for stage IV Coccinella transversoguttata larvae. The prolegs and possibly the head and mouthparts are more important than the stemmata for detecting prey. Prey are probably first noted by touch, but contact chemoreception, especially by the mouthparts, may also occur.     

Burrow structure and use in the sand fiddler crab, Uca pugilator (Bosc)

Uca pugilator, the sand fiddler crab, constructs two kinds of burrows in protected, sandy upper-intertidal and supratidal substrates on the west coast of Florida. Temporary burrows are built and used as a refuge by non-breeding crabs during high tide periods and at night when crabs cease feeding in the intertidal zone. Breeding burrows are constructed and defended by courting males and are the site of mating, oviposition and the incubation of eggs by females. Up to three ovigerous females may be accommodated in a single breeding burrow, each female sequestered in a separate terminal chamber. The construction and defence of burrows specialized for breeding may be an adaptive response by males to the preferences females exhibit when selecting a breeding site.     

Depth regulation of crab larvae in the absence of light

Behavioral responses to gravity and hydrostatic pressure have been investigated in two species of xanthid crabs Leptodius floridanus (Gibbes) and Panopeus herbstii Milne-Edwards to determine whether such responses provide a mechanism for depth regulation in the absence of light.In laboratory experiments, the four zoea stages and one megalopa stage of each species assume a differential vertical distribution in darkness, with succeeding stages showing a deeper overall distribution. Passive sinking rates increase in succeeding zoea stages and drop to an intermediate level after the molt to the megalopa stage. All zoea stages exhibit a negative geotaxis in the absence of light; the megalopa shows a positive geotaxis. The first zoea stage of Leptodius floridanus responds to an increase in hydrostatic pressure (up to 1 atmos above ambient) with an increase in swimming rate. This pressure response is shown to be reversible and not subject to short-term acclimation. The swimming rate of the last zoea stage does not increase in response to an increase in pressure.It is concluded that the responses of these larvae to gravity and hydrostatic pressure together with their characteristic passive sinking rates provide a mechanism for depth regulation in the absence of light that varies during ontogeny.     

Oxygen consumption and the respiratory responses to declining oxygen tension in the crab Ebalia tuberosa (Pennant) (Crustacea: Decapoda: Leucosiidae)

Oxygen consumption and its relationship to body weight and activity have been examined in Ebalia tuberosa (Pennant). Ebalia showed only very limited ability to regulate their oxygen consumption under conditions of declining P_O2. Respiratory independence was markedly affected by the level of activity of the animals. When inactive, respiratory independence was maintained down to a critical P_O2 of only about 130 mm Hg while when active, the crabs behaved as perfect conformers. Inactive Ebalia responded to a decrease in PO₂ by increasing the pumping activity of the scaphognathites and heart. This increased activity continued even at oxygen tensions lower than the P_c. The rate of reversals of the ventilatory currents did not change with decreasing P_O2. In the active crabs, the pumping activity of the scaphognathites and heart, and the rate of current reversals were higher than in the inactive animals, and a decrease in PO₂, did not bring about any further change in any of these responses. When exposed to hypoxic conditions for long periods initially inactive crabs survived longer than did active animals.     

The larvae of the spider crab Pisoides bidentatus (A. Milne-Edwards, 1873) (Decapoda: Majoidea: Pisidae) reared under laboratory conditions

Larval development of the spider crab, Pisoides bidentatus (A.Milne-Edwards, 1873) (Decapoda: Majoidea: Pisidae), inhabitingthe Russian waters of the Sea of Japan is described and illustratedfor the first time from larvae reared in the laboratory. Thedevelopment included two zoea and one megalopa, thus followingthe typical pattern in the Majoidea. At a temperature of 20–22°Clarval development of P. bidentatus took from 9 to 13 days.The comparative analysis revealed that the larvae of two Pisoidesspecies differ in numerous characters whereas zoea of P. bidentatusand Pugettia quadridens belonging to different families arenearly identical. According the larval characters, P. bidentatusand P. quadridens should be assigned to one genus. The larvaldata lend the support to revision the taxonomic position ofP. bidentatus.     

Sexual and seasonal variations in osmoregulation and ionoregulation in the estuarine crab Chasmagnathus granulatus (Crustacea, Decapoda)

The estuarine crab Chasmagnathus granulatus (Crustacea, Decapoda, Brachyura) inhabits salt marshes along the South Atlantic coast from Rio de Janeiro (Brazil) to Patagonia (Argentina). In the present study, salinity tolerance (0-45‰; 16-1325 mOsm/kg H₂O) and hemolymph osmotic and ionic (Na⁺, Cl⁻, and K⁺) regulation in both female and male C. granulatus were analyzed in summer and winter. Results showed that both female and male C. granulatus are euryhaline. Mortality was only observed in extremely low salinity (0‰; 16 mOsm/kg H₂O) for both sexes. For females, the LT₅₀ at 0‰ salinity was similar in summer (20.1 h) and winter (17.4 h). Males were more tolerant to salinity than females in both seasons, and mortality was observed only in summer (LT₅₀ = 50.9 h). Results from freshly collected crabs or long-term (16-day) osmotic and ionic regulation experiments in the laboratory showed that male C. granulatus is a better hyper-osmoregulator than female in summer and winter. However, a hypo-osmoregulatory ability was only observed in females experimentally subjected to salinity 40‰ (1176 ± 11 mOsm/kg H₂O) in both seasons. In both sexes, hyper-osmotic regulation was achieved by hyper-regulating hemolymph Na⁺, Cl⁻, and K⁺ concentration. In females, hypo-osmotic regulation was achieved by hypo-regulating hemolymph Na⁺ and Cl⁻ concentration. Long-term (16-day) osmotic and ionic regulations in different salinities were similar in males or females collected and tested in summer and winter. Despite this lack of a seasonal effect on hemolymph osmoregulatory and ionoregulatory patterns in males or females, a marked seasonal difference in the dynamics of these processes was observed for both sexes. In the first 2 days after hypo-osmotic shock (20‰→5‰; 636→185 mOsm/kg H₂O), variations in female osmolality and ion (Na⁺ and Cl⁻) concentration were larger and faster in winter than in summer, while in males the opposite was observed. Furthermore, a seasonal effect on the crab response to hyper-osmotic shock (20‰→40‰; 636→1176 mOsm/kg H₂O) was only observed in males. A new osmolality and ion (Na⁺ and Cl⁻) concentration steady state was faster achieved in winter than in summer. Regarding sexual differences, females showed a better capacity to hypo-regulate the hemolymph osmolality and Na⁺ concentration than males, even after a sudden increase in salinity (hyper-osmotic shock) in both seasons. On the other hand, males showed a better capacity to hyper-regulate the hemolymph osmolality and Na⁺ concentration than females, even after a sudden decrease in salinity (hypo-osmotic shock), especially in winter. Taken together, results reported in the present study suggest the need to consider both sex and collection season as important factors in future osmotic and ionic regulation studies in estuarine crabs.     

The role of haemocytes from the crab Carcinus aestuarii (Crustacea,Decapoda) in immune responses: A first survey

For the first time, a functional study of haemocytes from the crab Carcinus aestuarii was performed in order to evaluate their involvement in immune responses. Total haemocyte count (THC), phagocytosis, haemolymph opsonisation properties, hydrolytic and oxidative enzyme activities, and production of intracellular superoxide anion were evaluated. A great variability in THC was recorded among individuals, and haemocyte mean number was 6.4 (×10⁶) cells/ml haemolymph. Although only hyalinocytes were able to phagocytose yeast cells or Zymosan, phagocytic index was low (3%) and did not increase significantly (4%) after pre-incubation of yeast and Zymosan in cell-free haemolymph, suggesting that haemolymph did not have opsonising properties. All haemocyte types produced superoxide anion, whereas only granulocytes were positive to the hydrolytic enzymes assayed. In addition, only granulocytes were positive to phenoloxidase activity. Both Petri dish and spectrophotometric assays revealed a very low lysozyme-like activity in cell-free haemolymph (CFH) and haemocyte lysate (HL), although enzyme activity was higher in CFH than in HL. Interestingly, normalisation of data as to total protein content in CFH and HL resulted in an opposite situation, lysozyme-like activity being higher in HL than in CFH. This demonstrated that haemolymph of C. aestuarii has a high quantity of total proteins, functional properties of which need to be better investigated in future studies. Overall, the results obtained in the present study indicated that C. aestuarii haemocytes are not very active phagocytic cells, but they are more active in terms of both hydrolytic and oxidative enzyme activities and superoxide anion production.     

Respiration,energy balance and development during growth and starvation of Carcinus maenas L. larvae (Decapoda:Portunidae)

In all larval stages of Carcinus maenas L. oxygen consumption was measured at three temperatures (12,18,25 °C). Values increased during development and were in the range of 0.037 ± 0.01 (zoea-1, 12°C, $\text{x}\text{?}\text{± 95\% CL}$) to 0.734 ± 0.047 μl O₂ · h^?1 · ind^?1 (megalopa, 25 °C). Growing larvae showed temperature dependent trends in weight specific respiration rates (referred to dry wt; DW), with values between ≈2.4 and 9.4 μl O₂· h^?1·mg DW^?1. Increase in oxygen consumption of megalops did not differ much at temperatures between 18 and 25 °C. This points to an exceptional physiological position of this stage. Fed zoea-1 of C. maenas (18 °C) revealed growth rates in terms of 40% DW, 20% carbon (C), 30% nitrogen (N) and 65% hydrogen (H). At the same time larvae gained individual energy by 13% (J · ind^?1), while weight specific energy dropped by ≈ 19% (J · mg DW^?1) during the first day and remained constant until the moult. Starved zoea-1 of C. maenas (18 ° C) gained ≈ 20 % in DW through the first day, probably caused by inorganic salts which enter the organism after the moult of the prezoea. DW dropped to ≈ 25 % of initial value, when starvation continued. Single components decreased by ≈50% (C), 54% (N), 57% (J · ind^?1). Weight specific energy (J · mg DW^?1) decreased by 40% during the first 4 days of starvation, remaining constant thereafter. Individual respiration rate (R) dropped by 61 %, weight specific respiration rate (QO₂) by 55 %. Individual energy loss in starved zoea-1 was 0.077 J over a period of 11 days. In this period ≈ 9.3 μl O₂·ind^?1 were consumed. Thus effective oxygen capacity was lower than in growing larvae. It dropped to 5.3 J·mlO₂^?1 after 4 days and remained constant if starvation continued, i.e. 65 % of possible energy loss occurred during the first 4 days. Decrease in requirement for oxygen and its effective capacity were both recognized as independent components of survival during starvation. Partitioning of energy through individual larval development of C. maenas was investigated for all five larval stages. The cumulative budget could be calculated: consumption (C) = 28.23 J, growth (G) = 0.92 J, exoskeleton (Ex) = 0.20 J, metabolism (M) = 5.30 J, egestion and excretion (E) = 21.82 J. Mean gross and net growth efficiency were, K₁ = 3.3% and K₂ = 14.8%, respectively.     

Developmental changes in the structure and function of mouthparts of phyllosoma larvae of the packhorse lobster, Jasus verreauxi (Decapoda: Palinuridae)

Mouthpart morphology and feeding behaviour of Jasus verreauxi phyllosomas (instars 1-13) were examined using scanning electron microscopy and video analysis, respectively, to better understand ingestion and processing mechanisms and to identify developmental changes in feeding biology. The density, robustness and complexity of mouthpart setation increased with development, oral field increased and there were a greater number of spinose projections on maxillae 1 in mid and late instar phyllosomas. The second and third maxillipeds were able to sweep a larger area due to their increased length, which effectively increased the size of the oral field. Changes in feeding behaviour were consistent with these morphological differences between instars. In late instars, the shredding and tearing efficiency of maxillae 1 increased, larger pieces of prey were pushed between the mandibles, and the mandibles were able to effectively grind food due to a slight rotation away from the transverse plane. Both morphological and behavioural observations suggests that the absolute size range of prey increases with phyllosoma body size and the prey processing (i.e. ability to capture, manipulate and grind prey) becomes more efficient with development. We suggest early instar phyllosoma are most suited to a diet comprising softer prey items, whereas later-instar phyllosoma are better equipped to deal with larger, fleshier prey.