The relation between salinity and copper complexing capacity of natural estuarine waters and the uptake of dissolved 64Cu by Macoma balthica

Abstract

The radiotracer ⁶⁴Cu was used to assess the influence of natural organic ligands on the bioavailability of copper. Biological availability of the ⁶⁴Cu-complexes was measured by accumulation in the bivalve Macoma balthica. The experiments were carried out in April as well as in February with water from the relatively clean Oosterschelde Sea arm and the relatively polluted Westerschelde estuary. Adsorption onto shells, as well as uptake in tissues was assessed at salinities of 10‰ and 30‰. Simultaneously with the exposure experiments, ligand characteristics of the natural waters were assessed. High ligand concentrations, as occurring in the Westerschelde around February, reduced ⁶⁴Cu (320 nM) uptake by more than 50%, in spite of the much lower salinity in the Westerschelde water. At the low salinity, uptake was increased slightly in Westerschelde water, but considerably in Oosterschelde water. This implies that at low ambient ligand concentrations (during the whole year in Oosterschelde water and in the summer period also in Westerschelde water) the influence of salinity on ⁶⁴Cu uptake is more pronounced.     

The salinity tolerance of Ophiothrix angulata (Say) (Echinodermata: Ophiuroidea) in latitudinally separate populations

Ophiothrix angulata (Say) from an estuary in South Carolina were less tolerant of reduced salinity than those from an estuary in Florida. Animals from North Inlet, South Carolina, became incapacitated more rapidly after exposure to a reduced salinity, and were less able to recover after return to normal salinity. This difference probably results from the more severe selection for salinity tolerance at Cedar Key, Florida. The Florida estuary has a lower average salinity (25‰) than that in South Carolina (30‰), and has more frequent extended periods of reduced salinity. The two populations are of different color varieties and size; there may be differences in the breeding seasons as well. The South Carolina and Florida populations of Ophiothrix angulata may represent different races.     

Copper binding ability of the extracellular organic matter released by Skeletonema costatum

Abstract

The copper complexing ability of the exudates produced during the exponential growth phase by Skeletonema costatum has been investigated by a ligand-competition technique involving copper sorption onto C-18 Sep-Pak cartridges. Two ligands with different affinity for copper were required for the best fit of the copper complexation data in seawater with and without exudates: a strong ligand with a log K close to 13 and a weaker ligand with a log K close to 9. The culture increased both L₁ and L₂ ligand concentrations, already present in seawater, by a factor close to 4 after the first 72 hours of growth. The presence of class 1 stronger ligands in copper binding organics produced by the diatom is discussed in relation to natural copper speciation in the sea.     

Speciation of copper(II) in natural waters in the presence of ligands of high and intermediate strength

Abstract

A new procedure is presented for the determination of the ligands of copper(II) in natural waters, based on titration with the metal ion, monitored by measuring the concentration of copper(II) sorbed on the carboxylic resin Amberlite CG 50. The data are treated by the Ruzic linearization method to obtain the concentration of the ligands and the conditional stability constant of the complexes. Ligands with reaction coefficient α_M higher than 0.1 K*w/V are detected, where K* is the ratio of the concentration of sorbed metal to the concentration of free metal in solution, which can be evaluated from the sorption equilibria of copper(II) on Amberlite CG 50, w is the amount of water in the resin phase, and V the volume of the solution phase. Some natural waters at high and low salinity were examined. The ligand concentration determined in these samples ranged from around 50 to 2000 nM, while the original copper concentrations from 11 to 130 nM. The ligand concentration was always much higher than that of copper(II). The conditional stability constants were very high, particularly in low salinity waters, where values as high as K’= 10^15.7 were obtained. In high salinity waters values around 10⁹ were found for the complex formation constant of the ligands titrated with copper(II). The investigation was also extended to a model solution, containing EDTA, obtaining K’ = 10^15.5, in acceptable agreement with that evaluated from the literature values.     

Fluctuating salinity improves survival of the invasive freshwater golden mussel at high salinity: implications for the introduction of aquatic species through estuarine ports

In order to evaluate the resistance to salinity as a factor enhancing freshwater invasiveness, we assessed the tolerance of the mussel Limnoperna fortunei to salinity conditions mimicking changes in an estuary. We tested mussel mortality in 30-day exposures to constant and fluctuating salinities at different temperatures in the laboratory. Test conditions simulated different seasons of the year and locations with increasing influence of marine waters in Río de la Plata, Argentina. Significant mortality (31 % after 30 days) was observed at a constant salinity of 2 ‰, increasing to 45 and 57 % at 5 and 10 ‰, respectively. In contrast, considerably greater tolerances were observed when conditions in the experimental chamber fluctuated between salt water and fresh water. No significant mortality was observed in mussels exposed to a salinity cycle with abrupt salinity changes ranging 1–23 ‰ (mean 2.68 ‰) over a month. Tolerance to this type of regime was unaffected by different temperatures within ambient ranges. Tests at constant salinity underestimate the tolerance of this and probably other freshwater nonindigenous species (NIS) to short-term saltwater exposures. Estuarine ports account for ca. 2/3 of non-marine ports globally, thus constituting donor and recipient hotspots for the spread of NIS propagules into continental aquatic ecosystems via shipping vectors. The tolerance of L. fortunei to estuarine conditions likely contributes to the species’ remarkable invasive success. These results highlight the need to determine causes of invasiveness and to study NIS traits not alone but in combination with transport network properties.     

Osmotic and ionic regulation in the western rock lobster Panulirus longipes (Milne-Edwards)

The western rock lobster, Panulirus longipes (Milne-Edwards) is poikilosmotic over its tolerated salinity range, 25–45 ‰. Blood sodium is accumulated while chloride concentration is reduced. Sodium and chloride vary directly with the external salinity, although maintaining their differences in the same proportions as at normal salinity (36.0 ‰). Calcium is accumulated, ranging from over 150% at salinity 20 ‰ to about 117% at salinity 45 ‰. Potassium concentration is equivalent to the external at normal salinity, but is increased with lowered and decreased with raised salinity. Magnesium is reduced to about one-third that of the external concentration over the salinity range 20–40 ‰, but regulation begins to break down at 45 ‰. Individual ions exhibit, therefore, a range of regulation types, from poikilosmotic to homoiosmotic.Equilibrium for sodium, chloride, and calcium is attained in 10 h at salinities of 25, 30, 40 and 45 ‰ respectively. Rate constants for this exchange are linearly related to salinity differential, and rapid osmotic adjustment is by high permeability, equal in both directions, probably mainly via the gills. Muscle appears to act as a salt pool for sodium, chloride, and potassium but not for magnesium and calcium. Salt-loading causes a slight salt diuresis, the salts being excreted, probably via the gills. Except for calcium, there is no excretion of salt into the gut, but there is evidence of an exchange of chloride with another anion. Magnesium excretion is slow, and in the absence of osmotic stress possibly occurs via the antennal glands. All the ions examined appear to be regulated independently.     

Copper complexing capacity in fresh-waters using the catechol-cathodic stripping voltammetric method

Abstract

The catechol-cathodic stripping voltammetric (CSV) method for measurement of the copper complexing capacity of marine and estuarine waters, has been modified and applied to fresh-waters. The optimum catechol concentration needed was the major difference between the two methods. It was found necessary to separately optimise the catechol concentration for each of the three fresh-water samples tested, presumably because of the much greater differences in the concentration of complexing ligands in fresh-water compared with marine or estuarine waters. This limits the usefulness of the CSV method for the determination of the complexing capacity of fresh-waters.

The total ligand concentration ([L_t]) and conditional stability constants (*K) derived for the three fresh-waters are compared with similar data obtained using an anodic stripping voltammetric (ASV) method. The set of copper-binding ligands determined using the CSV method were slightly lower in concentration, but stronger binding, than those obtained using the ASV method (CSV: [L_t] 0.04–0.06 μM, log K(pH 6) 8.9–9.4; ASV: [L_t] 0.11–0.17 μM, log *K(pH 6) 7.9–8.1).     

Responses of Embryos and Larvae of the Starfish <Emphasis Type="Italic">Asterias amurensis</Emphasis> to Changes in Temperature and Salinity

We studied the effects of different combinations of temperature (5, 10, 14, 17, 20, and 22°C) and salinity (from 32 to 8‰) on the development of the starfish Asterias amurensis Lutken from Vostok Bay, Sea of Japan. Embryonic development is the most vulnerable stage; it passes successfully at 10–17°C and the salinity range of 32 to 26‰. Blastulae are the most tolerant of changing environmental factors. They survive and develop at the temperatures of 5–17°C and in the salinity range of 32–18‰. Gastrulae and bipinnariae survive under higher temperature values and salinity from 32 to 20‰. The tolerance for decreased salinity during the process of fertilization and in the latest stage of development, the brachiolaria with the developing juvenile starfish, was confined to the salinity range of 32–22‰, which agrees with the tolerance of adult starfish Asterias amurensis. Thus, for normal development of the Amur starfish in the early stages, some particular conditions of temperature and salinity are required. This is, probably, due to adaptive capabilities of each developmental stage and the peculiarities of the ecological conditions at particular depths.     

Carbonate Mineralogy Along a Biogeochemical Gradient in Recent Lacustrine Sediments of Gallocanta Lake (Spain)

Three sedimentary subenvironments, palustrine (GP), marginal lacustrine (GML) and central lacustrine (GCL), were compared regarding water chemistry and microbial activity in order to explain the differences in the carbonate mineralogical composition of the upper sediment layer in Gallocanta Lake, a shallow hypersaline environment in Northeastern Spain. Horizontal heterogeneity was considerable, salinity ranged from 5 to 116 (‰) for the GP and GCL subenvironments respectively. Sulfate, Mg ^{2 +} , and Ca ^{2 +} concentrations covaried among them and with salinity. The relative abundance of Mg-bearing carbonates, including high-Mg calcite, dolomite and hydrated Ca-magnesite, increased with the salinity. They were absent from the GP subenvironment, where only calcite precipitates, and maximum abundances were found in the GCL subenvironment (61%), where salinity, sulfate, and Mg ²⁺ concentrations were highest. Every subenvironment presented specific microecological characteristics. The microbial community of the GCL subenvironment lacked of oxygenic photosynthesis, while the microbial communities of GML and GP subenvironments were photosynthetically active. Vertical profiles of sulfide and pH at the water-sediment interface revealed clear differences between the GCL and GML subenvironments as well. Sulfide was detected below the oxic layer in the GCL subenvironment and increased with depth, but it was undetected in the GML subenvironment. The precipitation of Mg-bearing carbonates with different Mg:Ca proportions occurs at different stage along a biogeochemical gradient, where increasing salinity and sulfate content favour the anaerobic oxidation of organic carbon by dissimilatory sulfate reduction.     

Effect of heavy metals on samples and model population of rotifers <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> muller at different salinity

Effect of Cu²⁺ and Cr⁶⁺ on samples and on model populations of rotifers Brachionus plicatilis Muller in chronic conditions at different salinity was investigated. The LC₅₀ (48 h) at salinities 10, 20, and 30‰ were 53.9, 0.25, and 0.1 mg Cr/l, respectively. The concentrations of 0.3 mg Cu/l and more led to the death of 100% of rotifers in 48 h in salinities 10 and 20‰, but at 30‰ the concentration 0.1 mg Cu/l was lethal. LC₅₀ (48 h) at salinities 10, 20, and 30‰ were 7.06, 0.07, and 0.01 mg Cu/l, respectively. The toxicity of Cr and Cu for samples became higher with increasing salinity. For the model populations, the salinity influenced toxicity only at high concentrations of Cr (20 mg/l). The effect of Cr was higher on samples than on model populations.     

Effects of temperature and salinity on the larvae of two species of rhizocephalan (Crustacea: Cirripedia)

Summary

Responses of larvae of two rhizocephalan species to changes in seawater temperature and salinity were studied under laboratory conditions. Peltogasterella gracilis parasitizes the hermit crab Pagurus pectinatus, which occurs at stable salinity and gradually changing temperature in summer. Sacculina polygenea is a parasite of the crab Hemigrapsus sanguineus, which lives in the intertidal zone in summer where salinity and temperature can fluctuate during the day. The development of both species is comprised of five naupliar stages and the cyprid stage, and it was considered successful if more than 50% of the nauplii attained the cyprid stage. P. gracilis nauplii successfully developed at 12–20°C and 30–34‰, but at 22°C successful development occurred in a narrower salinity range (32–34‰). All nauplii died both at 25°C and in 26‰. S. polygenea nauplii successfully reached the cyprid stage at higher temperatures (18–25°C) and a wider salinity range (18–34‰) than P. gracilis nauplii, but at 12°C and 16‰ larval development of S. polygenea was suppressed. Under favorable conditions, naupliar development lasted 3.5 days in P. gracilis and 2–3 days in S. polygenea. The cyprids of both rhizocephalan species demonstrated a greater resistance to temperature and salinity changes than nauplii. However, P. gracilis cyprids were active in a narrower salinity range (16–34‰), as compared to S. polygenea cyprids (8–34‰). Under favorable conditions the cyprids of both species survived for 6 to 10 days.     

The effects of salinity,and calcium and potassium variations on the growth of two estuarine red algae

The effects of varying salinity and calcium and potassium concentrations on the growth of two species of estuarine Rhodophyta, Bostrychia radicans Montagne and Caloglossa lepricurii (Montagne) J. Agardh, were examined in unialgal culture. Inocula of settled tetraspores on glass coverslips were incubated in six concentrations of potassium (0. 100, 200, 300, 400 and 500 mg/l) at five salinities (0, 5, 15, 25, and 35%) in the presence of calcium. Growth responses of each alga were determined from the average cell number of 75 tetrasporelings after 4 days in Ott's synthetic sea-water medium. The concentrations of dissolved potassium and calcium in sea water along a salinity gradient in an estuary were determined with atomic absorption spectrophotometry. Four-day-old tetrasporeling of Bostrychia and Caloglossa demonstrated growth over wide ranges of potassium concentrations with growth maxima at 400 500 and 200 400 mg/l, at the optimal salinities for growth of 25 and 15%, respectively. These studies indicate also that the presence of calcium is essential for appreciable growth of both species at each salinity and the effects of variations in potassium are dependent upon the presence of calcium. The abundance of both species in the Mullica River estuary. New Jersey, appears to be a response to a total osmotic effect along the salinity gradient because sufficient levels of the major cations are present. However, the upper limit of both species towards the head of the Mullica River estuary may be determined by combinations of low salinity and low levels of dissolved calcium and potassium rather than by low salinity alone.     

Hydrogen isotope response to changing salinity and rainfall in Australian mangroves

Hydrogen isotope ratios (²H/¹H, δ²H) of leaf waxes covary with those in precipitation and are therefore a useful paleohydrologic proxy. Mangroves are an exception to this relationship because their δ²H values are also influenced by salinity. The mechanisms underlying this response were investigated by measuring leaf lipid δ²H and leaf and xylem water δ²H and δ¹⁸O values from three mangrove species over 9.5 months in a subtropical Australian estuary. Net ²H/¹H fractionation between surface water and leaf lipids decreased by 0.5–1.0‰ ppt^?1 for n‐alkanes and 0.4–0.8‰ ppt^?1 for isoprenoids. Xylem water was ²H depleted relative to surface water, reflecting ²H discrimination of 4–10‰ during water uptake at all salinities and opportunistic uptake of freshwater at high salinity. However, leaf water ²H enrichment relative to estuary water was insensitive to salinity and identical for all species. Therefore, variations in leaf and xylem water δ²H values cannot explain the salinity‐dependent ²H depletion in leaf lipids, nor the 30‰ range in leaf lipid δ²H values among species. Biochemical changes in direct response to salt stress, such as increased compatible solute production or preferential use of stored carbohydrates, and/or the timing of lipid production and subsequent turnover rates, are more likely causes.     

Inhibitory effects of cadmium on carbonic anhydrase activity and ionic regulation of the estuarine crab Chasmagnathus granulata (Decapoda,Grapsidae)

This work was aimed at evaluating the gill carbonic anhydrase (CA) activity of the estuarine crab Chasmagnathus granulata exposed in vivo to cadmium, at different salinities. The in vivo effect of the specific inhibitor acetazolamide (AZ) was also assayed. Besides, the inhibition of CA activity by different heavy metals (cadmium, copper, zinc) and AZ were evaluated under in vitro conditions. For the in vivo assays, adult males were acclimated to salinities of 2.5 or 30‰. The corresponding 96-h LC₅₀ of cadmium was 2.69 mg l⁻¹ at 2.5‰, and >50 mg l⁻¹ at 30‰. Cadmium only caused a significant lower CA activity than control at 2.5‰. EC₅₀ for CA inhibition was estimated to be 1.59 mg l⁻¹ at 2.5‰. Statistical differences in Na⁺ hemolymphatic levels (P<0.05) were only detected at 2.5‰, between 0 and 1.25 mg l⁻¹ of cadmium, but no statistical differences were observed for Cl⁻ levels at any assayed salinity. As CA inhibition registered at 2.5‰ was followed by only changes in Na⁺ concentration, it is likely that cadmium exposure could differentially affect ions permeability, among others factors. The concentrations that inhibited in vitro 50% of enzymatic activity (IC₅₀) were 2.15×10⁻⁵, 1.62×10⁻⁵, 3.75×10⁻⁶ and 4.4×10⁻¹⁰ M for cadmium, copper, zinc and AZ, respectively. The comparison with IC₅₀ values of other aquatic species, indicates a higher CA sensitivity for C. granulata to pollutants.     

Salinity influence on the ecology of phytoflagellate blooms in lower new york bay and adjacent waters

The possible rôle of salinity in phytoflagellate blooms in New York Harbor estuarine and oceanic waters was examined by culture studies of the dominant species. Massartia rotundata (Lohmann) Schiller (=Katodinium rotundatum (Lohmann) Loeblich III) grew best in the range 24–30‰, Olisthodiscus luteus Carter in the range 10–36‰, and Prorocentrum micans Ehrenberg in the range 27–36‰. The optimum ranges for all three species sufficiently match the characteristic bay-ocean range (17–32‰) to eliminate salinity tolerance as a major factor in bloom development. Laboratory simulation of the change from brackish-river to ocean water salinities, by culture preconditioning at 20‰ or at 30‰ before inoculation into a salinity gradient, shows stress effects on growth, especially in Massartia rotundata and Olisthodiscus luteus. It is speculated that salinity stress may temporarily affect the development of particular blooms of these two species.     

Virus and microbial loop dynamics over an annual cycle in three contrasting Antarctic lakes

1. Viral and microbial loop dynamics were investigated over an annual cycle in three contrasting saline Antarctic lakes – Highway Lake (salinity 4‰), Pendant Lake (salinity 19‰) and Ace Lake, a meromictic system (with a mixolimnion salinity of 18‰) in order to assess the importance of viruses in extreme, microbially dominated systems. 2. Virus like particles (VLP) showed no clear seasonal pattern, with high concentrations occurring in both winter and summer (range 0.89 × 10⁷ ± 0.038 to 12.017 × 10⁷ ± 1.28 mL^?1). VLP abundances reflected lake productivity based on chlorophyll a concentrations. Bacterial abundances and biomass did not correlate with VLP numbers except in Pendant Lake, the most productive of the three lakes studied. 3. Pendant Lake supported the highest bacterial biomass (range Highway: 18.44 ± 1.35 to 59.43 ± 2.80 ng C mL^?1; Ace: 14.42 ± 2.69 to 68.39 ± 2.95 ng C mL^?1; Pendant: 31.36 ± 3.94 to 115.95 ± 4.49 ng C mL^?1) so that virus to bacteria ratios (VBR) (range 30.48 ± 7.96 to 96.67 ± 8.21) were higher in Ace Lake (range 30.58 ± 3.98 to 80.037 ± 1.60) and Highway Lake (range 18.63 ± 3.12 to 126.74 ± 6.50). 4. Negative correlations occurred between VLP and cryptophytes (dominant phototrophic nanoflagellates), suggesting that they were not hosts to lytic viruses. Among the other protists only the heterotrophic nanoflagellates of Highway Lake (dominated by the marine choanoflagellate Diaphanoeca grandis) showed a positive correlation with VLP. 5. The VLP was negatively correlated with photosynthetically active radiation (PAR) and temperature, both of which increased with ice thinning and breakout, increasing viral decay. In winter VLP probably persisted in cold, dark water. 6. High VLP concentrations and high VBR (values at the upper end of those reported for marine and lacustrine systems) indicated that viruses, most of which were probably bacteriophage, are a major element within the microbial communities in extreme, saline lakes.     

Covariance Analysis of Chlorophyll Distribution in the Sundays River Estuary,Eastern Cape

Summary

An analysis of covariance performed on chlorophyll a distribution data from the Sundays River estuary identified five persistent water masses with significantly different chlorophyll a contents. These corresponded to different hydrodynamic regions within the estuary. The relationship between salinity and chlorophyll a was used to identify a transition zone between the low-salinity upper estuary and the brackish riverine inflow. Chlorophyll a concentrations ranged from <6 μg 1^?1 near the mouth to >100 μg 1^?1 in the middle and upper reaches. High variance of chlorophyll a data in this region was the result of temporal chlorophyll a fluctuations in two time scales. The first related to the daily ebb/tide and the second to the lunar spring/neap tidal cycle. Unlike its importance in larger and deeper estuaries, light played only a minor role in the horizontal distribution of chlorophyll a. The presence of a chlorophyll a maximum in the turbid low salinity region is explained in terms of the relatively constant photic depth/mixed depth ratio along the estuary and the high residence time of water in this region.     

Temperature and salinity effects on the respiratory metabolism of the first zoeal stage of Macrobrachium holthuisi Genofre & Lobão (decapoda: Palaemonidae)

Oxygen consumption rates of stage I Macrobrachium holthuisi Genofre & Lobão zoeae were measured in 24 different temperature and salinity combinations using Cartesian diver microrespirometers. Metabolic rates varied little with salinity at 15°C while at 20°C a marked elevation occurred in 0 and 35‰ At 25°C, a slight elevation occurred in 0‰; rates remained constant, however, in the other salinities. At 30°C, respiratory rates were similar to those recorded at 25°C except for decreases at 0 and 28‰ salinity. Q₁₀ values in the different salinities were usually highest between 15 and 20°C. Statistical analyses showed that while both temperature, salinity and their interaction significantly influenced larval respiratory rates, temperature had the more pronouced effect. Larval metabolism is salinity independent over the salinity range encountered in the larval biotope (7–21‰) at temperatures of 15–30°C.     

Particulate phosphorus in the Humber estuary

The biogeochemical controls on particulate phosphorus distribution in the Humber estuary have been investigated with regard to salinity and season. Surveys of the Humber were conducted in August 1991 and January, March and June 1992. Samples were collected for particulate phosphorus, dissolved phosphorus, suspended load and salinity analysis. Particulate phosphorus forms 16 to 93% of the total phosphorus present in the water column of the Humber estuary. Total particulate phosphorus concentrations in the Humber ranged from 1 to 45 μmol l⁻¹. This range is comparable to that observed in similar sized industrialized estuaries of the U.S.A. and northern Europe. Flocculation at low salinities was found to be a major influence on particulate phosphorus concentrations. Highest concentrations of particulate phosphorus were found in reaches below a salinity of 5 and may result in phosphorus being trapped in the sediments of the estuary. There is evidence that this phosphorus may be released as oxygen concentrations decrease during the summer. Suspended load, adsorption/desorption equilibrium and external inputs were also found to influence the particulate phosphorus concentrations.     

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.