Osmoregulation in Larvae of the Land-Crab, Cardisoma guanhumi Latreille

Daily studies were made of the osmoregulatory abilities of Cardisomaguanhumi from hatching to the end of larval development. Theseresults were compared to those of similar research on osmoregulationby larvae and megalopa of four species of estuarine, littoral,and sub-littoral crabs. The comparison shows that larvae ofC. guanhumi possess the same kinds of adaptations for waterintake at the time of molt that were found in Rhithropanopeusharrisii. Land-crab larvae hyperregulated in 10 p.p.t. sea waterand hyporegulated in water of 40 p.p.t. for experimental periodsfor 2 hr during the first one-third of their development. Duringthe remainder of larval life, they hyporegulated against 15p.p.t. in intermolt periods and became isosmotic with, or hyporegulatedagainst, 10 p.p.t. at the time of molting. From the time ofhatching, the osmoregulatory pattern of developing C. guanhumifits them for deep penetration of estuaries and for crossingsteep saline gradients. This pattern is evidence for a strongerand more enduring control of water balance, especially at thetime of molting, than we have found in non-terrestrial species.     

Accumulation of Uric Acid in the Land Crab, Cardisoma guanhumi

Variable amounts of white particulate matter occur in the hemocoelof the land crab, Cardisoma guanhumi. This material, mainlyuric acid, accounts for 0.2–15.9% of the total dry weightof a series of crabs. The material appears to increase duringintermolt. Concentrations of uric acid in the blood varied from0.2 to 13.2 mg/100 ml. Urine and feces contained little or nouric acid. Estimates of NH₃-N (3.9 mg/100 ml) in the blood of C. guanhumiare higher, and those of non-protein N (10.2 mg/100 ml) arelower, than corresponding values reported for other decapods.The crab's rate of nitrogen release (0.4 mg/10 g/day) into wateris similar to that reported for other terrestrial crustaceans.About one-third of this is released as NH₃. The urine of C.guanhumi is frequently nearly free of nitrogen, and its stomachfluid contains about five to seven times as much as does itsblood. Implications of these findings in the crab's metabolismand excretion are discussed.     

Adaptive significance of hatching rhythms and dispersal patterns of estuarine crab larvae: avoidance of physiological stress by larval export?

Estuarine crabs commonly display two larval dispersal patterns in which larvae are either exported from or retained within estuaries. The semiterrestrial fiddler crab Uca minax (LeConte, 1855) hatches on nocturnal spring high tides in the upper estuary and larvae are rapidly transported downstream. The mud crab Rhithropanopeus harrisii (Gould, 1841) hatches on nocturnal high tides of any amplitude and larvae are retained behaviorally in the upper estuary throughout development. If larvae are exported from the estuary to avoid environmental stress, then exported larvae should be less tolerant of high temperatures and low salinities than retained larvae. Larvae of these two species of estuarine crabs were hatched at 20‰ and 25 °C and subjected to salinities of 0, 5, 10,20, and 30‰, temperatures of 25 and 35 °C, and exposure times of 2, 6, 12, and 48 h. Larvae of both species reared at 30 or 20‰ survived well, while those reared in fresh water all died within 2 h regardless of temperature. Mud crab larvae reared at 5 and 10‰ survived better at the lower temperature (25 °C), higher salinity, and shorter exposure times. There was no significant effect of temperature or salinity on the survival of fiddler crab larvae, although survival decreased with increasing exposure time. Thus, the hypothesis that fiddler crab larvae are exported into stable coastal waters to reduce physiological stress is not supported. However, fiddler crab larvae may have evolved to be very tolerant of extreme temperature and salinity stress because they, unlike mud crabs, often release their larvae into shallow creeks. Most fiddler crab larvae are released on nocturnal spring high tides, which facilitates dispersal from tidal creeks. However, freshwater runoff and heat transferred from the marsh surface to flooding waters may still create stressful conditions for larvae soon after they are released. Larval release on spring high tides may facilitate dispersal from tidal creeks.     

The effect of salinity and temperature on the larval development of Mithrax caribbaeus Rathbun, 1920 (Brachyura: Majidae) reared in the laboratory

Larvae of Mithrax caribbaeus were reared in the laboratoryin a factorial experiment employing three temperatures (22,25 and 28°C) and three salinities (32, 35 and 38). Survivaland duration of larval stages were recorded. Ovigerous femalesof M.caribbaeus were collected from the south-eastern coastof Margarita Island, Venezuela, and maintained in individualaquaria until hatching. Eggs from three of the females hatchedin the laboratory. Larvae from each hatching were subdividedinto groups of 10 and reared in plastic bowls containing 200ml filtered and UV-irradiated sea water at different temperature–salinitycombinations. Larvae were transferred daily to clean bowls withnewly hatched Artemia nauplii, and the number of molts and mortalitywithin each bowl was recorded. Complete larval development ofM.caribbaeus occurred under all experimental conditions. Salinityhad the greatest effect on percentage survival of each larvalstage and complete development up to the first crab stage. Thefirst zoeal stage exhibited the highest survival rate. Maximumsurvival for this stage occurred at 25°C, 32–35. Survivalin the second zoeal stage and the megalopa was affected onlyby salinity. Effects of temperature and salinity on survivaldecreased with advance in development. The duration of the twozoeal stages, the megalopa, and development to the first crabstage showed a gradual reduction with increasing temperature.Salinity showed an effect on the duration of zoeal stages butnot on the megalopal stage. Development from hatching to thefirst crab stage required 8–18 days, depending on thetemperature–salinity combination, and was inversely relatedto temperature, averaging 14.3 days at 22°C, 11.8 days at25°C and 9.2 days at 28°C.     

Survival and development of horseshoe crab (Limulus polyphemus) embryos and larvae in hypersaline conditions

The horseshoe crab Limulus polyphemus spawns in the mid- to upper intertidal zone where females deposit eggs in nests below the sediment surface. Although adult crabs generally inhabit subtidal regions of estuaries with salinities from 5 to 34 ppt, developing embryos and larvae within nests are often exposed to more extreme conditions of salinity and temperature during summer spawning periods. To test whether these conditions have a negative impact on early development and survival, we determined development time, survival, and molt cycle duration for L. polyphemus embryos and larvae raised at 20 combinations of salinity (range: 30-60 ppt) and temperature (range: 25-40 degrees C). Additionally, the effect of hyperosmotic and hypoosmotic shock on the osmolarity of the perivitelline fluid of embryos was determined at salinities between 5 and 90 ppt. The embryos completed their development and molted at salinities below 60 ppt, yet failed to develop at temperatures of 35 degrees C or higher. Larval survival was high at salinities of 10-70 ppt but declined significantly at more extreme salinities (i.e., 5, 80, and 90 ppt). Perivitelline fluid remained nearly isoosmotic over the range of salinities tested. Results indicate that temperature and salinity influence the rate of crab development, but only the extremes of these conditions have an effect on survival.     

Effect of Eyestalk-Ablation on Circulating Ecdysteroids in Hemolymph of Snow Crabs, Chionoecetes opilio: Physiological Evidence for a Terminal Molt

Bering Sea snow crabs (Chionoecetes opilio) are a commerciallyimportant crab harvested in the Bering Sea. Optimal managementof this species requires an understanding of the biology ofthis crab that is currently incomplete. Fisheries managers applya continuous growth model in their management of snow crab,which assumes that male crabs increase in size throughout theirlifespan. Male snow crabs undergo a morphometric molt that leadsto a disproportionate increase in chelae size and it is stilldebated whether this molt is associated with a terminal molt.This study was conducted to determine whether adult male C.opilio are anecdysic. Using current knowledge of the hormonalregulation of crustacean growth, snow crab physiology was manipulatedto induce an increase in molting hormones (ecdysteroids). Sincefemale snow crabs are known to undergo a terminal molt afterattaining reproductive maturity, we compared ecdysteroid levelsin eyestalk-ablated terminally molted females, small-clawedmales and large-clawed males. Snow crabs were collected fromthe Bering Sea and maintained in circulating seawater at approximately6°C. Animals were either eyestalk-ablated or left intact.Ecdysteroid levels in hemolymph were quantified using an enzyme-linkedimmunosorbant assay (ELISA). Circulating ecdysteroids were significantlyhigher in small-clawed male crabs when compared to large-clawedmales or terminally molted females. Eyestalk-ablation increasedcirculating ecdysteroids in small-clawed males, but had no significanteffect on circulating ecdysteroids in large-clawed males orin terminally molted females.     

Effects of temperature, salinity and food level on the life history traits of the marine rotifer Synchaera cecilia valentina, n. subsp.

A strain of the marine rotifer Synchaeta cecilia valentina,n. subsp., isolated from the Hondo of Elche Spanish Mediterraneancoastal lagoon at 22 salinity, was cultured in the laboratoryin 20 ml test tubes and fed with the alga Tetrasemis suecica.The effect of two temperatures (20 and 24°C), four salinities(20,25,30 and 37) and two food levels (15 000 and 25000 cellsml^–1) on the life history traits of this rotifer werestudied in life tables performed with replicated individualcultures. Temperature and salinity had a significant negativeeffect (P < 0.001) on the average lifespan (LS) and on thenumber of offspring per female (R₀) The effect of food levelon LS is unclear, whereas R₀ is greater at 20°C with thelower concentration of algae and at 24°C with the higheralgal concentration. The maximum values of LS and R₀, 5.6 daysand 9.2 offspring per female, respectively, were recorded at20°C, 25o salinity and low food concentration. There isalso a clear negative effect on the intrinsic growth rate (r)due to salinity. The effect of temperature depends on the foodlevel and, as occurs with R₀ the maximum values of r occur withthe lower algal concentration at 20°C, whereas at 24°Cthey are obtained with the higher algal concentration. Theser values, from 1.04 to 1.10 day^–1, were reached at 24°C,salinities of 20–25 and with high food concentration.     

Some Thermal Requirements of Fiddler Crabs of the Temperate and Tropical Zones and Their Influence on Geographic Distribution

Thermal stress is one environmental parameter that has greatlyinfluenced the migration of crustaceans from the sea to land.Since a greater number of species of terrestrial crabs are foundin the tropics than in the temperate zone, comparative studiesof the influence of temperature on latitudinally separated populationswere undertaken. Two tropical species, U. rapax and U. thayeri,may occur as far north as St. Augustine, Florida, or, followinga severe winter, may be rare north of Cape Kennedy. The lethaleffect of the low temperatures recorded during one severe winter(1957–58) is supported by laboratory studies in whichLD₅₀, deaths occurred in 4.5 days at 10°C for U. rapax acclimatedto 18°C. The experiment demonstrates that U. rapax cannotacclimate to and survive low temperatures. This contrasts markedlywith the situation in semi-terrestrial crabs of the temperatezone, which are able to acclimate to cold. The distribution of Uca around Cape Cod Bay correlates wellwith the coastal hydrographic thermal gradient and supportsPassano's suggestion that temperatures below 20° may belimiting as they inhibit proecdysis in U. pugnax. Such an inhibitionis found experimentally in U. pugilator and in the tropicalspecies, U. rapax. It is hypothesized that a shift in the thermodynamicsof the processes underlying molting has not occurred in Ucaof the temperate zone. The paucity of semi-terrestrial Brachyurain the temperate zone may be due to the failure of many speciesto evolve capacity-adaptations to carry out all requisite lifeprocesses at temperatures below 20°, or the resistance-adaptationsnecessary to survive the low temperatures of winter.     

QUANTIFICATION OF THE PHYSIOLOGICAL RESPONSES OF THE EUROPEAN FLAT OYSTER OSTREA EDULIS L. TO TEMPERATURE AND SALINITY

Physiological stress was quantified in specimens of the Europeanflat oyster Ostrea edulis, acclimated to a matrix of temperature(5–25°C) and salinity (16–34%o) conditions,using the Scope for Growth (SFG) index. Variations in the indexwere interpreted from the responses of its components, absorptionefficiency, filtration rate, respiration and ammonia excretionrates, to external conditions. Mean SFG values were most influencedby acclimation temperature but significant differences werefound between animals at different salinities over the rangetested. There was a severe reduction in SFG when high temperaturewas combined with reduced salinity (     

Effects of growth medium, temperature, salinity and seawater source on the growth of Gymnodinium catenatum (Dinophyceae) from Bahia Concepcion, Gulf of California, Mexico

Laboratory studies were performed to determine the effect oftemperature, salinity, seawater sources and culture media onthe vegetative growth of clonal cultures of Gymnodinium catenatumisolated from Bahía Concepción, Mexico. Theseisolates were heterothallic and isogamous. Exponential growthrates of G. catenatum in f/2 with different selenium concentrationsand soil extract and GSe media were moderate. Maximum cell yieldswere obtained in GSe and f/2 media with selenium (10^–8and 10^–7 M), while in f/2 medium with soil extract cellyields were considerably lower. The highest percentage of longchains was found in f/2 media supplied with selenium (10^–8M). The optimal temperature range for growth was 11.5–30°C,with the highest growth rates between 21 and 29°C. The rangeof salinity tolerated by G. catenatum changed with seawatersource. With seawater from Vineyard Sound (Massachusetts, USA),G. catenatum grew at salinities from 15 to 36, with an optimalgrowth rate obtained at salinities between 26 and 30. With seawaterfrom Bahía Concepción, this species toleratedsalinities from 25 to 40, with optimal growth at salinitiesbetween 28 and 38. Ecophysiological measurements reported hereare consistent with the environment of the bay, which has limitedinput of humic materials from runoff and high salinity and temperature.These data, when viewed with data from studies of globally distributedG. catenatum, demonstrate the ability of this species to livein a broad array of habitats.     

Effects of increasing salinity on a cyanobacteria bloom in the Potomac River estuary

From June through August, 1985, a bloom of the cyanobacteriumMicrocyslis aeruginosa was observed in the upper Potomac Riverreaching densities of 193 x 10⁶ cells 1^–1 and 83% of totalcells in the surface mixed layer. However, in regions typifiedby salinities of 1–2 p.p.t. immediately down-river, thealga disappeared from the phytoplankton assemblage, never contributing>17% of total phytoplankton numbers. In an attempt to determinethe effect of increasing salinity on limiting horizontal distributionsof cyanobacteria blooms in the Potomac River estuary, threelaboratory experiments were conducted. Bloom samples collectedfrom the river were exposed to daily salinity increases of 1–2p.p.t. through the addition of NaCl or a complement of fullsea salts. Relative to samples receiving no salt supplement,densities of Microcyslis spp. declined in salinity-stressedsamples. However, total cyanobacteria remained constant or increaseddue to rapid growth of Aphanizomenon. The addition of a mixtureof full sea salts favored aggregation of cyanobacteria, yieldingan average of 132 cells colony^–1; 36 cells colony^–1were observed in populations maintained in river water and NaCl-supplementedsamples. Chlorophyll concentrations declined slightly relativeto assemblages receiving no salt additions while carbon fixationwas reduced in salinity-stressed assemblages. These resultssuggest that salinities from 0.5 to 7 p.p.t., typical of theoligohaline region of the Potomac River, could limit the distributionof Microcystis-dominated blooms down-estuary. In addition, increasingsalinities should result in the aggregation of photosyntheticallyinhibited cells and, through prolonged exposure to increasingosmotic stress, produce large, rapidly sinking detrital particlessupporting microbial decomposition in oligohaline and mesohalineregions of the lower Potomac River estuary, perhaps perpetuatinghigh microbial oxygen demand and anoxia in this portion of theriver/estuary.     

Comparison of low salinity tolerance in Callinectes sapidus Rathbun and Callinectes similis Williams postlarvae upon entry into an estuary

Planktonic larvae of estuarine crabs are commonly exported to the continental shelf for development and then return to coastal and estuarine areas as postlarvae (megalopae). Megalopae returning to estuaries must be adapted to survive in brackish water whereas those of coastally distributed species should not need such adaptations. We investigated 1) whether megalopae of the estuarine crab Callinectes sapidus and the coastal crab Callinectes similis undergo changes in salinity tolerance upon entry into an estuary and 2) what factors induce those changes. Megalopae were collected at a coastal site and a nearby estuarine site and exposed to a range of salinities (5, 10, 15, 20 and 30) for 6 h. Percent survival was determined after 24 h reintroduction to the collection site water. We also investigated 1) whether increased salinity tolerance was induced by reduced salinity or estuarine chemical cues, 2) the time to acclimation and 3) the salinity necessary for acclimation. C. sapidus megalopae from the estuarine site were more likely to survive exposure to low salinities than those from the coastal site. C. sapidus megalopae from the coastal site exhibited increased survival after acclimation to salinities of 27 and 23 for 12 h. Estuarine chemical cues had no effect on salinity tolerance. C. similis megalopae were less likely to survive at low salinities and did not exhibit an acclimation response upon exposure to reduced salinities. These results suggest that megalopae of C. sapidus are physiologically adapted to recruit to estuaries whereas megalopae of C. similis are unable to acclimate to low salinity conditions.     

The effect of abrupt salinity change on oxygen consumption in crab megalopae of Chincoteague Bay,USA

Variability in salinity is an environmental stressor that crab megalopae encounter as they are carried by tides and currents throughout Chincoteague Bay. We exposed blue crab (Callinectes sapidus) and fiddler crab (Uca spp.) megalopae to abrupt salinity changes from 10 to 31 ppt and measured their oxygen usage. It was hypothesized that the megalopae would cope with the changes in a manner reflective of the documented abilities and tolerances of adult crabs. It was also hypothesized that lower salinities would have a particularly detrimental effect on the megalopae reflected by both increased oxygen usage and mortality. The megalopae of both species did exhibit an increase in oxygen use at lower salinities, although the effect was more pronounced during the initial transition and decreased during acclimation. The megalopae mirrored the adult responses, with blue crab larvae consuming more oxygen per mg of wet weight at lower salinities, whereas fiddler crab larval oxygen consumption was relatively uniform at all salinities. Mortality of some blue crab postlarvae was observed at 10 ppt while all larval fiddler crabs survived. Coupled with the introduction of additional fresh water into the global water system, these results indicate that further investigation into this subject is necessary.     

Acclimation of Intertidal Crabs

SVXOPSIS. Intertidal crabs are subjected to marked fluctuationsin environmental factors. Temperature and salinity influencethe distribution of organisms both on a latitudinal basis andalong a subtidal to terrestrial gradient. These factors areoperative on all stages of the life history. Resistance-adaptations. Adult fiddler crabs (genus Uca) fromthe temperate zone are more resistant to low temperature thantropical species. Also, the tolerance to low temperature ofcrabs from the temperate zone is greatly influenced by thermalacclimation, i.e. cold-acclimated crabs are more resistant thanwarm-acclimated animals. In contrast, tropical species havelimited adaptive ability. At elevated temperatures no consistentdifference in the lethal limits of crabs from tropical and temperatezones is observed. In contrast with the adults, larvae of tropicalspecies are cold-resistant. However, the larvae of all speciestested are more sensitive to reduced salinities than are theadults. Capacity-adaptatioyis. Subtidal species of crabs tend to havea lower level of respiratory performance, as measured by variousindices, than crabs from the intertidal zone. The metabolicresponse of fiddler crabs from the temperate zone is more labileat low temperature than in species from the tropical zone. Atelevated temperature the reverse response is observed. On aninterspecific basis, differences in the metabolictemperaturepatterns of acclimation of latitudinally separated populationsof U. pugilator are observed when based on the hypotheticalschemes of Bullock, Precht, and Prosser.     

Physiological evaluation of temperature effect on the growth processes of the mysid, Neomysis intermedia Czerniawsky

Ingestion, respiration, and molting loss rates were measuredover the 3 – 29°C range in Neomysis intermedia. Weightspecific rates of these physiological processes ranged from2 to 140% body C day^–1 for ingestion, from 2 to 15% bodyC day^–1 for respiration, and from 0.1 to 5% body C day^–1for molting loss. All weight-specific rates showed a logarithmicdecrease with a logarithmic increase in body weight, and a logarithmicincrease with a linear increase in temperature below 20 or 25°C.The effect of temperature, however, was different between thephysiological rates, with a large temperature dependency foringestion (Q₁₀ = 2.6 –3.9) and molting loss (Q¹⁰ = 2.9– 3.6) and a moderate temperature dependency for respiration(Q₁₀ = 1.9 – 2.1). Calculated assimilation efficiencychanged with body size, but was constant over the temperaturerange examined. Allocation of assimilated materials varied witha change in temperature, reflecting the different temperaturedependence between physiological processes. It was deduced thatthe strong temperature dependency of the growth rate in N. intermediaobserved in the previous studies resulted from the large temperatureeffect on ingestion and assimilation rates, superimposed bythe different allocation of assimilated materials. ¹Present address: Department of Botany, University of Tokyo,Hongo, Tokyo 113, Japan     

The Role of Carbonic Anhydrase in Blood Ion and Acid-Base Regulation

The role of carbonic anhydrase (CA) in ion transport processesof aquatic and terrestrial arthropod species is reviewed. Inboth insects and crustaceans CA is found in a variety of iontransporting tissues. The bulk of CA activity in crustaceansis concentrated in the posterior gills, which are morphologicallyand biochemically adapted for ion transport. The enzyme canbe specifically localized to gill lamellae which contain largepopulations of salt transporting chloride cells. Enzyme activityin the posterior gills of species having the ability to regulateblood ion concentrations increases when these organisms areacclimated to environmental salinities in which they ion regulate.In stenohaline, ion conforming species branchial CA activityis uniformly low, being only 5–10% that in regulatingspecies. Studies on the blue crab, Callinectes sapidus, usingthe specific CA inhibitor acetazolamide have shown that theenzyme is indeed important in blood ion regulation. Blood Na^$and Cl^– concentrations are both severely lowered in drug-treatedanimals acclimated to low salinity, while they remain virtuallyunaffected in animals acclimated to high salinity, in whichthe animal is an ion conformer. High salinity acclimated crabstreated with acetazolamide do not survive transfer to low salinity,and mortality is related to a breakdown in the ion regulatorymechanism. Branchial CA most likely functions in the hydrationof respiratory CO₂ to H^$ and HCO₃^–, which serve as counterionsfor the active uptake of Na^$ and Cl^–, respectively. Interrestrial species the role of CA is unclear and merits furtherinvestigation.     

Seasonal species composition of barnacle larvae (Cirripedia: Thoracica) in Rhode Island waters, 1977-1978

Cirripede larvae can occur year-round in temperate and tropicalwaters, often in significant numbers, yet the species compositionof the ‘Balanus sp.’ component is rardy studied.Weekly plankton samples were analyzed qualitatively for larvalcirripede species and stage over a year (1977–1978) attwo Rhode Island stations. Six species of larvae were foundin Lower Narragansett Bay (30° salinity). Semibalanus balanoidesand Balanus balanus have a single winter brood. S. balanoidesis the predominant winter breeder with a minor release of naupliiin early December and major release in March followed by cypridsin mid-April.B. balanus populations release all larvae in Marchwith cyprids in mid-April. Balanus crenatus is mainly a winterbreeder, but has multiple broods; it does not breed in July-Septemberwhen the water temperature is above 18°C. Balanus venustusis the predominant summer breeder, and larvae were observedfrom May through December (water >8°C). Larvae of Chthamalusfragilis and Balanus eburneus occur in low numbers from May-October.At the Pettaquamscutt River site (12 salinity), Balanus improvisuslarvae predominate and early stage nauplii (I-II) occur in samplesyear round (0–27°C). Two peaks of later stage naupliiand cyprids occur in late spring (May) and early winter (Nov.-Jan.).Continued temperatures bdow 5°C or above 20°C appearto inhibit larval development. Comparison of results with existing literature reveals severalsignificant findings. The bimodal rdease of S. balanoides larvaeis unusual and may be in response to the phytoplankton dynamicsof the year; however, the existence of distinct races of S.balanoides may also be a factor. Larvae of B. venustus predominatein the lower bay during the summer, yet this species is unreportedin past studies. B. improvisus nauplii are more cold tolerantthan previously reported. Comparison of findings with reportedbreeding patterns in Florida indicate significant differencesin temperature responses between northern and southern populations. ¹Contribution No. 188 from EPA Environmental Research Laboratory,South Ferry Rd., Narragansett, RI 02882     

Influence of salinity on the larval development of the fiddler crab <Emphasis Type="Italic">Uca vocator</Emphasis> (Ocypodidae) as an indicator of ontogenetic migration towards offshore waters

Larvae of many marine decapod crustaceans are released in unpredictable habitats with strong salinity fluctuations during the breeding season. In an experimental laboratory study, we investigated the influence of seven different salinities (0, 5, 10, 15, 20, 25 and 30) on the survival and development time of fiddler crab zoea larvae, Uca vocator, from northern Brazilian mangroves. The species reproduces during the rainy season when estuarine salinity strongly fluctuates and often reaches values below 10 and even 5. Salinity significantly affected the survival rate and development period from hatching to megalopa, while the number of zoeal stages remained constant. In salinities 0 and 5, no larvae reached the second zoeal stage, but they managed to survive for up to 3 (average of 2.3 days) and 7 days (average of 5.1 days), respectively. From salinity 10 onwards, the larvae developed to the megalopal stage. However, the survival rate was significantly lower (5–15%) and development took more time (average of 13.5 days) in salinity 10 than in the remaining salinities (15–30). In the latter, survival ranged from 80–95% and development took 10–11 days. Given the 100% larval mortality in extremely low salinities and their increased survival in intermediate and higher salinities, we conclude that U. vocator has a larval ‘export’ strategy with its larvae developing in offshore waters where salinity conditions are more stable and higher than in mangrove estuaries. Thus, by means of ontogenetic migration, osmotic stress and resulting mortality in estuarine waters can be avoided.     

Effects of Temperature and Water Loss on Terrestrial Locomotor Performance in Land Crabs: Integrating Laboratory and Field Studies

SYNOPSIS. Terrestrial and semi-terrestrial crustaceans are exposedto fluctuations in ambient temperature and conditions that favorevaporative water loss. These environmental stresses alter performancelimits in the laboratory and behavior in the field. The maximalrate of oxygen consumption, maximum aerobic speed, and endurancecapacity are greater at a body temperature (T_b) of 24°Cthan at 15°C or 30°C in the ghost crab, Ocypode quadrata.The total metabolic cost to move at the same relative speedis greater at a T_b of 24°C than at 15°C. Slower aerobickinetics at 15°C result in a smaller relative contributionof oxidative metabolism to total metabolic cost. However, therelative contributions from accelerated glycolysis are similarat both temperatures. When locomotion is intermittent, the totaldistance traveled before fatigue can be similar at Tbs of 15and 24°C but result from different movement and pause durationsat these temperatures. Performance limits of the ghost crabare negatively affected by dehydration and are sensitive torates of water loss. In the laboratory, endurance capacity ofthe fiddler crab, Uca pugilator, is greater at a T_b of 30°Cthan at 25°C. In the field, freely moving fiddler crabswith a T_b of 30°C travel at faster mean preferred speeds,as determined by motion analysis, than crabs at 25°C. Datafor land crabs support and advance general ectothermic modelsfor the effects of temperature and dehydration on locomotorperformance.     

Effects of temperature, salinity and irradiance on the growth of the harmful red tide dinoflagellate Cochlodinium polykrikoides Margalef (Dinophyceae)

The effects of temperature, salinity and irradiance on the growthof the harmful red tide dinoflagellate Cochlodinium polykrikoideswere examined in the laboratory. From 60 different combinationsof temperature (10–30°C) and salinity (10–40)under saturated irradiance, C. polykrikoides exhibited its maximumspecific growth rate of 0.41 day^-1 at a combination of 25°Cand salinity of 34. Optimum growth rates of >0.3 day^-1 wereobserved at temperatures ranging from 21 to 26°C and atsalinities from 30 to 36. The organism did not grow at temperatures10°C and only grew at salinities >30 if the temperaturewas >15°C. It was able to grow in temperatures rangingfrom 15 to 30°C and at salinities from 20 to 36. These valuesclosely resembled those observed for this species in situ. Itappears as if C. polykrikoides is a stenohaline organism thatprefers high salinities, indicative of offshore waters. Temperaturehad the greatest influence on the growth rate, followed by salinity,and then the interaction between temperature and salinity. Theoptimum irradiance for growth was >90 µmol m^-2 s^-1.Photoinhibition did not occur at 230 µmol m^-2 s^-1, whichwas the maximum irradiance used in this study.