Size-related and seasonal patterns of egg collar production in Polinices pulchellus (Gastropoda: Naticidae) Risso 1826

Polinices pulchellus held in the laboratory produced egg collars all year round. Egg collar production was greatest during July and August and only occurred in females >8-10 mm shell length. The largest individuals (14-16 mm shell length) had the highest fecundity and ceased egg-laying in late September, whilst 8-14 mm individuals laid egg collars until November. Small females (4-6 mm) grew rapidly during the warmer, summer months (April to August), became sexually mature and began laying egg collars in mid-September. Both the range of egg collar wet weights and the maximum wet weight of an individual egg collar increased with female size class. Temperature strongly affected the length of time between the laying of egg collars and the hatching of larvae (9-10 days at 19-20 °C and 14-15 days at 13-14 °C). A close relationship was also found between egg collar wet weight and the number of veliger larvae released.     

Embryonic encapsulation and maternal incubation: Requirements for survival of the early stages of the estuarine gastropod Crepipatella dilatata

During their reproductive period, females of Crepipatella dilatata deposit their embryos in capsules that they then brood in the pallial cavity until juveniles emerge several weeks later, after passing through a transient veliger “larval” stage. Artificially excapsulated veligers of this species experimentally exposed to a wide range of salinities (5, 10, 15, 20, 25, and 30 psu) for six hours showed reduced activity at salinities of 15 and 20 psu, whereas encapsulated veligers exposed to those same salinities showed no reduction of activity. Artificially excapsulated veligers showed high mortality at salinities of 5 and 10 psu; encapsulated embryonic stages also showed high mortalities at 5 psu and serious sublethal effects at 10 psu in tests excluding maternal protection, showing that encapsulation alone does not provide complete protection from low salinity stress. Natural tidal cycles in the Quempillén River estuary also reduced embryonic survival at salinities of ≤ 10 psu when the capsules were exposed without maternal protection. In contrast, encapsulated embryos protected by their mothers survived well regardless of the salinity to which they were exposed, under both natural and laboratory-simulated estuarine tidal cycles. C. dilatata are able to develop in the estuary only because of maternal protection, since salinity levels in this environment sometimes decline to as low as 7 psu. Successful embryonic development in this estuary reflects the capacity of C. dilatata adults to detect dangerously low salinity levels and then seal themselves off from the environment for up to 50 hrs (O. Chaparro pers. obs.) when the salinity drops below 22.5 psu, allowing salinity to remain above this level within the pallial cavity despite continued salinity declines in the surrounding seawater.     

Behavioral aspects of cold tolerance in blackchin tilapia,Sarotherodon melanotheron,at different salinities

Synopsis Cold tolerance and behavioral responses of blackchin tilapia, Sarotherodon melanotheron, to rapidly decreasing temperatures were investigated at salinities of 5, 15, and 35 parts per thousand (ppt). Cold tolerance did not significantly differ with salinity or social rank. Mean temperatures were 10.7° C for beginning loss of equilibrium, 9.6° C for complete loss of equilibrium, and 6.9° C for death at all salinities. Behavioral activity declined with decreasing temperature and ceased between 10–12° C. Certain behavioral actions were significantly more frequent at 15 or 35 ppt salinity than at 5 ppt. The northward range expansion by introduced populations of the blackchin tilapia in the United States probably will be limited by its lower lethal temperature limits, but may also be affected by temperatures at which social behavior becomes disrupted.     

The effect of spawning salinity on eggs of spotted seatrout (Cynoscion nebulosus, Cuvier) from two bays with historically different salinity regimes

Spotted seatrout are capable of spawning in a wide range of salinities. Along the Texas Gulf Coast, bay salinities increase from an average of 14 ppt in Galveston Bay to an average of 40 ppt in Lower Laguna Madre due to the negative gradient of freshwater inflow from north to south. Tagging studies have shown that the majority of spotted seatrout do not migrate between adjacent bay systems. Spawning salinity has been shown to affect many properties of eggs including the diameter and salinity of neutral buoyancy. Spotted seatrout from two historically different salinity regimes (Matagorda Bay (MB) and Upper Laguna Madre (ULM)) were kept in the laboratory and induced to spawn in three salinities: 20, 30, and 40 ppt. The purpose of this study was to evaluate eggs at each of the three salinities and between the two bay systems. Two-way ANOVA showed a significant effect on the egg diameter of bay and spawning salinity, and a significant interaction between bays and spawning salinity. No significant difference in size at hatch was found between spawning salinities or between bays. Hatch rates in spawning salinity were >90% in all cases. Regression of wet weight on spawning salinity was highly significant for both bays. Eggs spawned in 20 ppt have the largest wet weight and eggs spawned in 40 ppt have the smallest wet weight, irrespective of parental bay origin. Percentage of water varied between 92% for 20 ppt spawned eggs and 86% in 40 ppt spawned eggs. Neutral Buoyancy Salinity (NBS) of eggs increased with increasing spawning salinity. Eggs spawned by the Upper Laguna Madre fish held at 20 ppt were not positively buoyant at 20 ppt. The results of this study suggest that spotted seatrout are locally adapted to the prevailing salinity regime within an estuary.     

The combined influence of sub-optimal temperature and salinity on the in vitro viability of Perkinsus marinus, a protistan parasite of the eastern oyster Crassostrea virginica

Perkinsus marinus is a major cause of mortality in eastern oysters along the Gulf of Mexico and Atlantic coasts. It is also well documented that temperature and salinity are the primary environmental factors affecting P. marinus viability and proliferation. However, little is known about the effects of combined sub-optimal temperatures and salinities on P. marinus viability. This in vitro study examined those effects by acclimating P. marinus at three salinities (7, 15, 25 ppt) to 10 °C to represent the lowest temperatures generally reached in the Gulf of Mexico, and to 2 °C to represent the lowest temperatures reached along the mid-Atlantic coasts and by measuring changes in cell viability and density on days 1, 30, 60 and 90 following acclimation. Cell viability and density were also measured in 7 ppt cultures acclimated to each temperature and then transferred to 3.5 ppt. The largest decreases in cell viability occurred only with combined low temperature and salinity, indicating that there is clearly a synergistic effect. The largest decreases in cell viability occurred only with both low temperature and salinity after 30 days (3.5 ppt, 2 °C: 0% viability), 60 days (3.5 ppt, 10 °C: 0% viability) and 90 days (7 ppt, 2 °C: 0.6 ± 0.7%; 7 ppt, 10 °C: 0.2 ± 0.2%).     

Toxic effects of mercury on the hard clam,Meretrix lusoria,in various salinities

1. The 96-hr lc₅₀ values for juvenile hard clams, Meretrix lusoria, were 328, 392 and 194 μg/l Hg in 10, 20 and 30 ppt salinities at 25 ± 1°C, respectively; for adult hard clams 341 and 140 μg/l Hg in 20 and 30 ppt salinities, respectively.2. Acclimatizing the adult clams to low salinity of 10 ppt lessened the toxicity of mercury. However, juvenile animals appeared to be more sensitive to mercury poisoning after 96 hr exposure in 10 ppt salinity.3. All embryos exposed to 40 μg/l Hg and above died within 30 hr. In the control, 44% of hatched embryos had developed into D-stage larvae, while those exposed to 20 μg/l Hg were still in the trochophore stage. Most of the retarded larvae developed into abnormal forms within 30 hr at 28°C in 15 ppt salinity.4. In order to maintain water quality and protect natural resources, the recommended safe level of mercury is 0.046 (0.039–0.053) μg/l Hg, based on the estimated 30-hr EC₅₀ for the clam embryos, with an application factor of 0.01.     

Effects of salinity, temperature and individual variability on the reproduction of Eurytemora affinis (Copepoda; Calanoida) from the Seine estuary: A laboratory study

The brackish water copepod Eurytemora affinis is the most abundant copepod species in the low salinity zone (2-15) of the Seine estuary. Despite its ecological importance, little is known about its population dynamics in the Seine. We studied the effects of temperature (10 °C and 15 °C) and salinity (5, 15 and 25) on reproduction under non-limiting food conditions. We used experiments to determine multiple reproductive parameters for E. affinis. In all experiments, we fed E. affinis a mixture of Rhodomonas marina and Isochrysis galbana. Couples of pre-adult females (C5) and adult males were mated until the female extruded a clutch of eggs and then individual females were observed every 6-12 hours until death to determine (a) embryonic development time, (b) inter clutch time and (c) clutch size throughout their adult lifespan. All reproductive parameters were negatively affected by low temperature (10 °C) and by high salinity (25). At 10 °C and a salinity of 25, mortality during the post-embryonic period was extremely high (85%). Differences in all reproductive parameters between salinities 5 and 15 were minimal. From 15 °C to 10 °C mean latency time (time between hatching of eggs and extrusion of new ones) increased from 0.8 to 2.25 days, the mean embryonic development time from 2.2 to 3.2 days and the mean clutch size decreased from 38 to 22 eggs female^- 1. The mean clutch size decreased when females reached a critical age. The hatching success was high (near 95%) under all conditions except at high salinity. Egg production rates showed no significant differences between salinities 5 and 15 and were significantly higher at 15 °C (13 eggs female^- 1 day^- 1 at salinity 5 and 15) than at 10 °C (4 eggs female^- 1 day^- 1). These values at 15 °C were higher compared to those from other populations of E. affinis in estuaries or lakes. The high reproductive potential of E. affinis from the Seine estuary at 15 °C and low salinities explain its high densities in the low salinity zone during spring and early summer.     

Age-linked changes in salinity tolerance of larval spotted seatrout (Cynoscion nebulosus, Cuvier)

Acute salinity tolerance limits for the estuarine spawning spotted seatrout, Cynoscion nebulosus (Cuvier). were evaluated by examining 18 h survival of larvae in an extensive range of salinity treatments (0 to 56 ppt). Larvae from eggs spawned in two different salinities (24 and 32 ppt) as well as larvae acclimated in hypersaline and brackish waters were compared. Both upper and lower salinity tolerance limits showed an age-linked pattern, decreasing to a minimum tolerance range (6.4 to 42.5 ppt) at age 3 days after hatching (at 28 o C) and increasing to the widest range tolerated (1.9 to 49.8 ppt) on the last day tested (age 9 days). Acclimation to hyposaline conditions was demonstrated by larvae spawned at 32 ppt although significant hypersaline acclimation could not be demonstrated. Altered upper limits to the range tolerated by larvae from different spawning salinities indicated parental and/or early acclimation effects are important. Consistently greater vulnerability to both hyper- and hyposaline conditions at age 3 days after hatching was observed in all tests conducted. Exposures related to the onset of feeding at this time are likely explanations for this reduced tolerance.     

Effect of temperature, salinity and delayed attachment on development of the solitary ascidian Styela plicata (Lesueur)

The solitary ascidian Styela plicata (Lesueur) is a common member of epibenthic marine communities in Hong Kong, where seawater experiences extensive seasonal changes in temperature (18-30 °C) and salinity (22-34‰). In this investigation, the relative sensitivity of different developmental stages (i.e., duration of embryonic development, larval metamorphosis and post-larval growth) to various temperature (18, 22, 26 and 30 °C) and salinity (22‰, 26‰, 30‰ and 34‰) combinations is reported. Fertilized eggs did not develop at lower salinities (22‰ and 26‰). At higher salinities (30‰ and 34‰), the duration of embryonic development increased with decreasing temperature (18 °C: 11.5±0.3 h; 30 °C: 8.5±0.3 h). More than 50% of larvae spontaneously attached and metamorphosed at all the levels of temperature and salinity tested. At higher temperatures (22, 26 and 30 °C) and salinities (30‰ and 34‰), functional siphon developed in about 72 h after hatching, whereas at low temperature (18 °C), siphon developed only in <30% of individuals in about 90 h. However, none of the metamorphosed larvae developed subsequently at low salinity (22‰). When forced to swim (or delayed attachment), larvae lost about 0.27 mJ after 48 h (about 22% of the stored energy). Such a drop in energy reserves, however, was not strong enough to cause a significant impact on post-larval growth. This study suggests that temperature and salinity reductions due to seasonal monsoon may have significant effect on the embryo and post-larval growth of S. plicata in Hong Kong.     

Development and mortality of the first naupliar stages of Eurytemora affinis (Copepoda, Calanoida) under different conditions of salinity and temperature

As a prevalent species complex in temperate estuaries and salt marshes of the Northern Hemisphere, populations of Eurytemora affinis that inhabit these environments must be adapted to salinity fluctuations. Some populations have invaded freshwater environments. In this work, we focus on the combined effects of temperature and salinity fluctuations on mortality rates and development time of the first naupliar stages under starvation. Two temperatures (10 and 15 °C) and eight salinities, ranging from 0 to 35 psu are investigated. We show (i) that among all experimental conditions the optimal temperature and salinity for naupliar survival and development are 15 psu and 15 °C, and (ii) that only the most extreme salinities (i.e. 0 and 35 psu) have a negative effect on naupliar survival. Nauplii develop faster and reach a higher developmental stage at 15 than at 10 °C, independent of salinity. The relevance of this metabolic adaptive pattern is discussed in the general framework of in situ behavior, tidal forcing and biogeographic variability, as well as the potential sources of the observed individual variability.     

Preliminary studies on cryopreservation of snakehead (Channa striata) embryos

This paper reports the findings of the ongoing studies on cryopreservation of the snakehead, Channa striata embryos. The specific objective of this study was to collect data on the sensitivity of C. striata embryo hatching rate to low temperatures at two different developmental stages in the presence of four different cryoprotectants. Embryos at morula and heartbeat stages were selected and incubated in 1 M dimethyl sulfoxide (Me₂SO), 1 M ethylene glycol (EG), 1 M methanol (MeOH) and 0.1 M sucrose solutions at different temperatures for a period of time. Embryos were kept at 24 °C (control), 15 °C, 4 °C and −2 °C for 5 min, 1 h and 3 h. Following these treatments, the embryos were then transferred into a 24 °C water bath until hatch to evaluate the hatching rate. The results showed that there was a significant decrease of hatching rate in both developmental stages following exposure to 4 °C and −2 °C at 1 h and 3 h exposure in each treatment. Heartbeat stage was more tolerant against chilling at −2 °C for 3 h exposure in Me₂SO followed by MeOH, sucrose and EG. Further studies will be conducted to find the best method to preserve embryos for long term storage.     

Acute osmotic tolerance of cultured cells of the oyster pathogen Perkinsus marinus (Apicomplexa : Perkinsida)

Cultured Perkinsus marinus cells were exposed for 24 hr to salinities of 0, 3, 6, 9, 12 and 22 ppt at temperatures of 1, 5, 10, 15 and 28°C in artificial seawater (ASW) and to the same salinities at 28°C in ASW with the osmotic concentration adjusted with sucrose to the equivalent of 22 ppt. At 28°C mortality increased as salinity decreased below 22 ppt. Mortality was greater than 99% at 0 ppt and greater than 90% at 3 ppt. Mortality was 70% at 6 ppt, 43% at 9 ppt and 20% at 12 ppt. Mortality was low (<5%) and equal to that at 22 ppt in all treatments where osmotic concentration was maintained with sucrose. Mortality occurred rapidly, within 5 min of exposure to experimental conditions. In the region where mortality was most sensitive to salinity changes (6–12 ppt), lower temperature caused an increase in mortality, but the temperature effect was significant only at 9 ppt.     

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.     

Hypoxia, low salinity and lowered temperature reduce embryo survival and hatch rates in black bream Acanthopagrus butcheri (Munro, 1949)

Embryo survival and hatch rates were measured in black bream Acanthopagrus butcheri exposed to different treatments of dissolved oxygen: hypoxic and normoxic, three salinities: 15, 23 and 35 and two temperatures: 16 and 20° C. Hypoxic conditions (50% saturation) reduced 1 day embryo survival by up to 15% ( P < 0·05) compared to embryos held in normoxic (>80% saturation) conditions. Temperature had no effect on the survival of embryos in these treatments, however, lowered salinity significantly reduced embryo survival at 20° C, but not at 16° C. Mean hatch rates were reduced by 10–28% in hypoxic treatments ( P < 0·05) and lowered salinity treatments ( P < 0·05). Hatching was delayed by up to 24 h at 16° C and very low (or zero) hatching occurred in hypoxic treatments at salinities of 15 and 23. These results confirm that environmental conditions in estuaries are important factors in determining spawning success of black bream and are discussed in relation to global warming and climate change that are likely to alter the physical conditions in southern Australian estuaries.     

Life history divergence of sympatric diploid and polyploid populations of brine shrimp Artemia parthenogenetica

In order to study how polyploidy affects life history patterns in animals, we have examined sympatric diploid and polyploid brine shrimp (Artemia parthenogenetica) from China, Italy and Spain under laboratory conditions. At optimal temperature and salinity (25°C and 90 ppt), diploids from the three populations had much higher intrinsic rates of increase, higher fecundity, faster developmental rates, and larger brood sizes than their sympatric polyploids. The Chinese and Italian populations were selected for further analysis to determine the life history responses of diploids and polyploids to temperature and salinity changes. Under intermediate and high salinities, Chinese and Italian polyploids produced most of their offspring as dormant cysts while their sympatric diploids produced most of their offspring as nauplii. This relationship is reversed in the Spanish diploid-polyploid complex. For the Chinese population at 25° C, pentaploid clones had higher developmental rates than diploid clones at 35 ppt; at 90 ppt, diploid clones had higher developmental rates than the pentaploids. Italian diploids and tetraploids had different responses to variation in both temperature (25° C and 31° C) and salinity (30 ppt and 180 ppt). Our results demonstrate that relative fitness of the two cytotypes is a function of environmental conditions and that sympatric diploids and polyploids respond differently to environmental changes. Chinese and Italian polyploids are expected to have lower fitness than their sympatric diploids when the physical environment is not stressful and when intraspecific competition is important. However, polyploids may have advantages over sympatric diploids in stressful habitats or when they encounter short-term lethal temperatures. These results suggest that polyploid Artemia have evolved a suite of life-history characteristics adapting them to environments that contrast to those of their sympatric diploids.     

Multigenerational analysis of temperature and salinity variability affects on metabolic rate,generation time,and acute thermal and salinity tolerance in Daphnia pulex

Climate change, sea level rise, and human freshwater demands are predicted to result in elevated temperature and salinity variability in upper estuarine ecosystems. Increasing levels of environmental stresses are known to induce the cellular stress response (CSR). Energy for the CSR may be provided by an elevated overall metabolic rate. However, if metabolic rate is constant or lower under elevated stress, energy for the CSR is taken from other physiological processes, such as growth or reproduction. This study investigated the examined energetic responses to the combination of temperature and salinity variability during a multigenerational exposure of partheogenetically reproducing Daphnia pulex. We raised D. pulex in an orthogonal combination of daily fluctuations in temperature (15, 15–25, 15–30 °C) and salinity (0, 0–2, 0–5). Initially metabolic rates were lower under all variable temperature and variable salinity treatments. By the 6th generation there was little metabolic variation among low and intermediate temperature and salinity treatments, but metabolic suppression persisted at the most extreme salinity. When grown in the control condition for the 6th generation, metabolic suppression was only observed in D. pulex from the most extreme condition (15–30 °C, 0–5 salinity). Generation time was influenced by acclimation temperature but not salinity and was quickest in specimens reared at 15–25 °C, likely due to Q₁₀ effects at temperatures closer to the optima for D. pulex, and slowest in specimens reared at 15–30 °C, which may have reflected elevated CSR. Acute tolerance to temperature (LT₅₀) and salinity (LC₅₀) were both highest in D. pulex acclimated to 15–30 °C and salinity 0. LT₅₀ and LC₅₀ increased with increasing salinity in specimens raised at 15 °C and 15–25 °C, but decreased with increasing salinity in specimens raised at 15–30 °C. Thus, increasing temperature confers cross-tolerance to salinity stress, but the directionality of synergistic effects of temperature and salinity depend on the degree of environmental variability. Overall, the results of our study suggest that temperature is a stronger determinant of metabolism, growth, and tolerance thresholds, and assessment of the ecological impacts of environmental change requires explicit information regarding the degree of environmental variability.     

Temperature and salinity effects on growth, survival, reproduction, and potential distribution of two non-indigenous botryllid ascidians in British Columbia

Two non-indigenous botryllid ascidian species - Botryllus schlosseri (golden star tunicate) and Botrylloides violaceus (violet tunicate) - have become established in British Columbia (BC), Canada. One species, B. schlosseri, is native to Europe while the other, B. violaceus, is native to Asia. Environmental tolerances of both species are poorly understood. We examined the effects of temperature and salinity on growth, survival, and reproduction of these species in the laboratory in order to characterize their environmental tolerances and preferences. Laboratory-raised juvenile colonies were studied using a two-factorial experimental design with five levels of temperature (5, 10, 15, 20, 25 °C) and five levels of salinity (14, 20, 26, 32, 38‰). Both B. schlosseri and B. violaceus possessed broad temperature and salinity tolerances, but B. schlosseri was slightly more euryhalinal than B. violaceus. Generally, B. schlosseri survived environmental conditions of 10-25 °C and 14-38‰, exhibited positive growth at 10-25 °C and 20-38‰, and attained its largest colony sizes at 15-20 °C and 20-38‰. Botrylloides violaceus tolerated environmental conditions between 5-25 °C and 20-38‰, demonstrated positive growth at 15-25 °C and 26-38‰, and attained its largest colony sizes at 20-25 °C and 26-38‰. Results from the laboratory experiment were then used in a modeling exercise to determine the coastal areas of BC that these organisms might be likely to exist in or invade, based on near-surface temperatures and salinities. The model predicted that no areas were totally unsuitable for survival and growth of either species (based solely on temperature and salinity tolerances), with the most suitable locations being along the west coast of Vancouver Island, a region with significant shellfish aquaculture activity.     

The effects of environmental factors on the embryonic survival of the Patagonian squid Loligo gahi

Seawater temperature and salinity are environmental variables that impose physiological limits for the embryonic development of marine invertebrates. For cephalopod species, these limits have rarely been established. This work presents experimental results on the embryonic survival of the Patagonian squid Loligo gahi, which is the last decades' most important loliginid species in terms of volume of commercial catches worldwide, as a function of seawater temperature and salinity. Reference magnitudes of surface seawater temperature and salinity within the area of distribution of the species were explored by analysis of satellite databases and published information. Embryos were incubated under eight constant regimes of temperature within 4-22 °C and four constant salinity regimes within 20-34.33‰ (12 °C). Also, to determine the effects of sudden temperature changes on embryonic survival, embryos were incubated at four variable regimes of temperature, with thermal shifts (6-day long 2-°C magnitude alterations of the incubation temperature) applied both at early and late stages of embryonic development. Embryonic survival was zero in incubations at constant temperature regimes ≤5° and at 22 °C, low at 6 °C, and high within 8-20 °C. A function was fitted by nonlinear regression to relate embryonic survival and mean incubation temperature. Thermal shifts applied in incubations at 20-22-20 °C variable regime of temperature provoked low embryonic survival compared to that observed in incubation at 20 °C constant regime. Embryonic survival was zero in incubations conducted at 20.0‰ and 34.3‰ salinity, and high at 26.4‰ and 32.8‰ salinities.     

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.     

Effects of temperature on development and growth in the tick,Haemaphysalis longicornis

As a part of ecological studies onHaemaphysalis longicornis, the effects of controlled temperatures (12, 15, 20, 25 and 30°C; 100% RH) on development and growth of the tick were investigated and the critical low temperature for each stage in the life cycle was estimated. As the temperature became low, the periods of preoviposition, oviposition, egg hatching (incubation) and moulting were prolonged. At 12°C, however, oviposition, egg hatching and moulting of the larva and nymph did not occur. The critical low temperatures for oviposition, egg hatching (developmental zero) and larval and nymphal moulting which were calculated theoretically from the regression equations, were 11.1, 12.2, 10.2 and 11.8°C, respectively. The temperature also affected the egg productivity and hatch-ratio. The number of deposited eggs per mg of body weight decreased markedly at 15°C, and the hatch-ratio was lowered with dropped temperatures.