The combined effect of temperature and salinity changes on osmoregulation and haemocyanin concentration in Saduria entomon (Linnaeus, 1758)

Global warming is having an impact on the temperature and salinity of Baltic Sea waters. Therefore, it is important to determine the conditions in which animals can exist and how these changes may influence their functioning. Hence, the purpose of this research was to determine the broad tolerance limits of temperature and salinity of the glacial relict Saduria entomon by studying its behaviour, osmoregulatory ability and haemocyanin concentration. This effect of temperature was confirmed in the laboratory for individuals acclimated to different salinity and temperature regimes. Changes in the physiological parameters of S. entomon at various temperatures (5.5–21.5°C) and salinity levels (1–15 PSU) were recorded. There were statistically significant differences in haemolymph osmotic pressure under the influence of salinity and temperature. The mean haemolymph osmotic pressures were the lowest at 1 PSU at all the temperatures examined and the highest at 15 PSU and high temperatures 16.5 and 21.5°C. The haemocyanin concentration decreased significantly with increasing temperature at 1 PSU. There was a significant difference in haemocyanin concentration due to salinity at temperatures of 5.5 and 10.0°C (the haemocyanin concentration decreased with increasing salinity). The results showed that, although S. entomon is classified as a cold-water animal, it can survive at high temperatures above 16.5°C at least for a short time, as it is capable of osmoregulation. The tolerance to temperature changes was better than expected.     

Effects of salinity on larval and early juvenile growth of an extremely euryhaline crab species,Armases miersii (Decapoda: Grapsidae)

The neotropical crab Armases miersii (Rathbun, 1897) breeds in supratidal rock pools, where great salinity variations occur. In laboratory experiments, all larval stages and the first juveniles were reared at six different salinities (5–55 PSU, intervals of 10 PSU). In five series of experiments, exposure to these conditions began either from hatching (Zoea I) or from the onset of successively later stages (Zoea II, III, Megalopa, Crab I). Growth was measured in terms of dry weight, carbon, nitrogen and hydrogen content. At osmotically extreme conditions (5 and 55 PSU, resp.), all stages showed minimum biomass accumulation; this was consistent with maximum mortality and longest duration of development (data presented in a separate paper). Successively later exposure to these salinities tended to reduce these effects. Lowest mortality and shortest time of development occurred generally at 15–25 PSU, indicating an optimum at moderately reduced salinities. This response pattern, however, was not congruent with that observed in growth. Biomass accumulation was initially maximum within a wide range of salinities (15–45 PSU), but in the Zoea II and III stages, this range tended to narrow and to shift towards higher salinities (35–45 PSU). These trends reversed in the Megalopa and Crab I, where maximum growth occurred again in a wider range and at lower salinities (15–35 PSU). The reduction of zoeal growth in moderately dilute media (15–25 PSU), which were optimal for survival and development, is interpreted as an energetic cost of hyper-osmoregulation, which begins already at hatching. Five PSU caused hypo-osmotic stress, exceeding in the long term the larval capacity for hyper-regulation. Poor zoeal survival and growth at 55 PSU are interpreted as effects of hyper-osmotic stress. In the Megalopa and Crab I, reduced growth at salinities 35 PSU may reflect the energetic costs of hypo-osmoreguation beginning in these stages. Our data suggest that the physiological adaptations of larval and early juvenile A. miersii allowing for survival and development in a physically harsh and unpredictable habitat imply a trade-off with reduced growth, due to energetic costs of osmoregulation.     

Effects of large Saduria entomon (Isopoda) on spatial distribution of their small S. entomon and Monoporeia affinis (Amphipoda) prey

We performed laboratory experiments to investigate the effects of predator avoidance and numerical effects of predation on spatial distribution of small Saduria entomon (Isopoda) and Monoporeia affinis (Amphipoda), with large S. entomon as predators. The horizontal distribution and mortality of the prey species, separately and together, were studied in aquaria with a spatial horizontal refuge. We also estimated effects of refuge on mortality of small S. entomon and M. affinis by experiments without the refuge net. In addition, we investigated whether predation risk from large S. entomon influenced the swimming activity of M. affinis, to clarify the mechanisms behind the spatial distribution. Both small S. entomon and M. affinis avoided large S. entomon. The avoidance behaviour of M. fffinis contributed about 10 times more to the high proportion in the refuge than numerical effects of predation. Due to the low mortality of small S. entomon the avoidance behaviour of this species was even more important for the spatial distribution. The combined effect of avoidance behaviour and predation in both species was aggregation, producting a positive correlation between the species in density. M. affinis showed two types of avoidance behaviour. In the activity experiments they reduced activity by 36% and buried themselves in the sediment. In the refuge experiments we also observed avoidance behaviour with the emigration rate from the predator compartment being twice the immigration rate. The refuge did not lower predation mortality in M. affinis, probably due to the small scale of the experimental units in relation to the mobility of the species. Predation mortality in small S. entomon was higher in absence of a refuge and especially high in absence of M. affinis.     

Influence of salinity and cadmium on the survival and osmoregulation of Callianassa kraussi and Chiromantes eulimene (Crustacea: Decapoda)

This study investigated the influence of salinity and cadmium on the survival and osmoregulatory capability of two decapod crustaceans, Callianassa kraussi and Chiromantes eulimene. Callianassa kraussi was able to survive in salinities of 5–55 over 96 h, whilst C. eulimene survived in 0–55 over the same time period. The 96-hour cadmium LC₅₀ for both species decreased progressively at salinities above and below their respective isosmotic conditions, with the decrease being slightly more pronounced below compared to above isosmotic salinity. A hypo-iso-osmoregulatory strategy was followed by C. kraussi as it hyper-osmoregulated at salinities between 5 and 25 and osmoconformed at salinities greater than 25. Chiromantes eulimene followed a hyper-hypo-osmoregulatory strategy; it hyper-regulated in salinities from 0 up to isosmotic conditions at about 28 (c. 780 mOsm kg^?1), followed by hypo-regulation up to 55. The effect of cadmium exposure on the osmoregulatory capacity of C. kraussi was more pronounced at hyper-regulating salinities (5–25) whilst on C. eulimene the influence was more pronounced at salinities above the isosmotic point (28). The influence of salinity and cadmium on both survival and osmoregulation of the two crustaceans are discussed by outlining the chemical and physiological mechanisms involved.     

The effects of different temperature and salinity levels on the acute toxicity of zinc in the Pink Shrimp (Farfantepenaeus paulensis)

The purpose of this study was to measure the acute toxicity of zinc (Zn) on Farfantepenaeus paulensis at different salinities and temperatures by monitoring oxygen consumption. This aspect of the effect of zinc has not been studied in this important commercial species before. First, we examined the acute toxicity of zinc in F. paulensis at 24, 48, 72, and 96?h medium lethal concentration (LC₅₀). One hundred and fifty shrimp were employed for the routine metabolism measurement utilizing sealed respirometers. Ten shrimp were subjected to oxygen consumption measurements in one of the four concentrations of zinc (control, 0.5, 1.0, 2.0, and 3.0 mg?L^?1) at three salinities (36, 20, and 5) and three temperatures (25°C, 20°C, and 15°C). Zinc was significantly more toxic at a salinity of 5 than at 20 or 36. The oxygen consumption was estimated through experiments performed on each of the 12 possible combinations of three temperatures (25°C, 20°C, and 15°C) and three salinities (36, 20, and 5). The shrimp showed a significant reduction in oxygen consumption at a salinity of 5. The results show that the oxygen consumption decreases with respect to the zinc concentration in all temperatures studied. At the highest zinc concentration employed (3.0?mg?L^?1), the salinity 5 and the temperature at 25°C, oxygen consumption decreases 60.92% in relation to the control. The results show that zinc is more toxic to F. paulensis at lower salinities. The significance of the findings for the biology of the species close to sources of zinc is discussed.     

Effect of salinity on the distribution of Ponto-Caspian gammarids in a non-native area – environmental and experimental study

The native area of gammarids from the so-called ‘Caspian complex’, Pontogammarus robustoides (G.O. Sars, 1894), Obesogammarus crassus (G.O. Sars, 1894), Dikerogammarus haemobaphes (Eichwald, 1841) and D. villosus (Sowinsky, 1894), is associated with brackish waters. Over the last several decades they have colonized the European inland waters and part of the brackish Baltic Sea. It is believed that anthropogenic increase in the salinity of inland waters facilitated their expansion. However, the influence of salinity on the dispersal of gammarid species outside their native area is not fully understood. We tested the hypothesis that salinity was a major factor in determining distribution, based on the abundance of Gammaridae in three coastal areas of low salinity (brackish Baltic), i.e. 0.3, 3.4 and 7.3 PSU, successfully inhabited by them. Additionally, for the first time, the effect of water salinity on the osmoregulatory capacity of O. crassus was examined under laboratory conditions, for the salinities given above. The experiments showed that similarly as in the case of other Caspian complex species, salinity values of about 7 PSU create better conditions for osmoregulation in O. crassus than lower salinities (i.e. 0.3 and 3.4 PSU). In the environmental part of the study, we observed that only D. villosus achieved a significantly higher abundance in the area of 7.3 PSU. Thus, we concluded that in the range of 0.3–7.3 PSU, salinity is not a key factor governing the distribution of Ponto-Caspian gammarids.     

The combined effects of temperature and salinity on the survival of Euterpina acutifrons (Dana) (Copepoda, Harpacticoida) from the New Zealand and Brazilian coasts

The combined effects of temperature and salinity on the survivalof non ovigerous female Euterpina acutifrons from the south-easternNew Zealand and southern Brazilian coasts were studied. Sixsalinities (6, 20, 34, 48, 62 and 76 ) and five temperatures(5, 10, 15, 20 and 25°C) were used for New Zealand specimenswhile six temperatures (5, 10, 15, 20, 25 and 30°C) andthe same salinities were employed for the Brazilian specimens.The mortality data were analysed statistically using multipleregression techniques. Animals from New Zealand showed greatertolerance to cold, less to high temperatures and more resistanceto both high and low salinities than those from Brazil, Animalsfrom both areas were slightly more tolerant of low temperaturein high salinities and of high temperature in low salinities.These striking differences observed between New Zealand andBrazilian populations of E. acutifrons imply the existence ofdifferent physiological races in this species.     

Cocoon deposition of Rhyacodrilus hiemalis Ohtaka (Tubificidae) in Lake Biwa,Japan

The larval stages of the mud prawn Upogebia africana were reared in the laboratory, from hatchings of females collected in the Mgazana estuary, South Africa. The larvae were tested for the combined effects of temperature and salinity in a factorial designed experiment, using 3 females and 2 replicates of 10 larvae per combination. Combinations were made from 5 temperatures (15, 20, 25, 30 and 35 °C) and 4 salinities (15, 25, 35 and 45). Results were tested by ANOVA and multiple regression was applyed to generate contour models by polynomial equation. Results showed that U. africana develops optimally in near to sea water salinity at around 25 °C, with slightly wider tolerance to low salinity in zoeal stage I, and with increased moult rate at lower salinity in late stages. A comparison with similar experimental results for other species is made, namely in view of the life cycle strategies for dispersal and return migration.     

The effect of salinity on larval survival and development in the sea urchin Echinometra lucunter

Summary

Reductions in salinity can have adverse effects on larval development and larval survival in some invertebrate taxa but not others. Salinity tolerance of larvae may be particularly important in echinoderms because they are both poor ion regulators and stenohaline. I examined the effect of six levels of salinity (15, 18, 21, 24, 27 and 33 PSU) on survival and rate of development of larvae in the subtropical sea urchin Echinometra lucunter. In the short-term, mortality rate was significantly lower in 33 PSU than in all other salinities except 27 PSU, and it was significantly greater in 15 and 18 PSU than in all higher salinities. In the long-term, daily and cumulative mortality were significantly greater in 15 PSU than in most other salinities over 11 days of development (except for cumulative mortality in 18 PSU). They were significantly greater in 18 PSU than in 21 PSU or 33 PSU over a period of 13 days. Furthermore, daily mortality was significantly greater in 18 PSU than in 24 PSU or 27 PSU at 13 d after fertilization. Daily and cumulative mortality were significantly lower in 33 PSU than in 21, 24 or 27 PSU over a period of 17 days. Although in the control (33 PSU) 75% of larvae completed development to the 8-arm stage at 35 d, no larvae developed further than the 4-arm stage in 18, 21, 24 or 27 PSU; in 15 PSU, ~60% of larvae did not develop further than swimming blastulae. Since prolonged exposure to salinities as high as 27 PSU (frequently recorded in the adult habitat) can result in great larval losses, adaptive behaviours that prevent larvae from entering water layers of low salinity will enhance their chance for survival.     

Hot and salty: the temperature and salinity preferences of a temperate estuarine shrimp larva, Upogebia pusilla (Decapoda: Thalassinidea)

At a time when global climate changes are forcing life to adapt to a warming and salinity-changing environment, it is essential to understand how future changes in ocean chemistry will affect species. This study evaluates the combined effects of temperature and salinity on survival and development of Upogebia pusilla larvae. Combinations were made from three temperatures (18, 23, and 28°C) and three salinities (15, 25, and 35). Survival, larval duration and megalopa size were compared between treatments. U. pusilla larvae developed optimally in the highest salinity (35) and higher temperatures (23–28°C). Low salinities and temperatures did not support larval survival and development, with salinity being the main restricting factor for survival, while temperature affected mainly the duration of the larval stages. Larvae at higher temperatures (23–28°C) presented a higher development rate but no differences were found in megalopa size.     

Growth and survival of the invasive alga, <Emphasis Type="Italic">Caulerpa taxifolia</Emphasis>, in different salinities and temperatures: implications for coastal lake management

The alga Caulerpa taxifolia is an invasive pest species in many parts of the world and has recently become established in several estuaries in south eastern Australia. A major infestation has occurred in Lake Conjola, an intermittently open and closed coastal lagoon in southern NSW. Short term (1 week) laboratory experiments were carried out to investigate growth and survival of fragments of C. taxifolia collected from this outbreak, under a range of salinities (15–30 ppt) and water temperatures (15–30°C). Fronds, stolons and thalli of the alga all displayed similar responses. Many of the algal fragments doubled in size over the week and a maximum growth rate of 174 mm/week was recorded. Fragments showed good growth (> 20 mm/week) at salinities > 20 ppt and temperatures > 20°C. Almost total mortality occurred at salinities lower than 20 ppt and temperatures less than 20°C. Historical records of water quality demonstrate that prior to entrance manipulation in 2001, salinities in Lake Conjola had often dropped to below 17 ppt for extended periods (up to 2 years). This suggests that management of the alga may be improved if the lake was allowed to undergo its normal cycles of opening and closing to the ocean, and that entrance manipulation may be one factor that has influenced the success of this invasive species.     

Direct and indirect effects of predation by Saduria entomon (Isopoda) on the size-structure of Monoporeia affinis (Amphipoda)

We performed a 6-month laboratory experiment to investigate the direct and indirect effects of predation by the benthic invertebrate predator Saduria entomon on the growth and survival of Monopreia affinis prey individuals in different age-cohorts at low and high prey densities. The experimental results were compared with changes of growth and abundance in corresponding age-cohorts of M. affinis at sites with different S. entomon and M. affinis densities in the deep sublittoral zone of the Bothnian Sea during the same year. In the experiment, the presence of S. entomon reduced growth rate of M. affinis in the 1-year and 2-year age-cohorts at low amphipod density. Increased refuge use by M. affinis, expressed as a decrease in swimming activity in the presence of S. entomon, is suggested to have reduced feeding rate and therefore growth of the amphipods. The recruitment of M. affinis offspring was reduced in presence of S. entomon. In the field, the growth rate of amphipods in the 1-year cohort increased with increasing S. entomon density at low amphipod density. We found no corresponding increase of M. affinis growth in the 2-year cohort. The positive effect on 1-year amphipod growth indicated that predation reduced intra-cohort competition of M. affinis and increased growth of surviving prey at high predator density. In both the experiment and the field data we found indications of size-selective predation on smaller M. affinis specimens. This was because of the changed ratio between number of individuals in the juvenile age-cohorts and lower recruitment of amphipod offspring connected to S. entomon density. The experimental results and field data suggest that predation by S. entomon may have both direct and indirect effects on the size-structure of M. affinis populations. Received: 22 June 1998 / Accepted: 15 March 1999     

The effect of salinity and temperature on the larval development of clibanarius vittatus (Bosc) (crustacea: decapoda: diogenidae)

Clibanarius vitatus (Bosc) larvae were reared in twenty combinations of four salinities (15, 20, 25, and 30%) and five temperatures (15, 20, 25, 30 and 35%°C). No development was observed in any salinity at 15°C, but partial development occurred in all other test conditions. Metamorphosis to juvenile crabs was noted only at salinities of 25 and 30A% in combination with temperatures of 25 and 30°C. In general, development times were decreased at higher temperatures; no trend was evidence for salinity. Mortality of zoeae was usually highest at the time of the first molt and greatest overall mortality occurred during the megalopa stage prior to metamorphosis. Previous experiments (unpubl.) have shown that C. vittatus adults can tolerate temperature down to 5°C. It is suggested that geographic distribution of C. vittatus (Virginia, southward) is limited not by adult tolerances but by the inability iof the species to establish a breeding population. Larvae require two months at 25°C or above to metamorphose, and this condition is not met in areas north of Virginia.     

Plasma osmolality and oxygen consumption of perch Perca fluviatilis in response to different salinities and temperatures

The present study determined the blood plasma osmolality and oxygen consumption of the perch Perca fluviatilis at different salinities (0, 10 and 15) and temperatures (5, 10 and 20° C). Blood plasma osmolality increased with salinity at all temperatures. Standard metabolic rate (SMR) increased with salinity at 10 and 20° C. Maximum metabolic rate (MMR) and aerobic scope was lowest at salinity of 15 at 5° C, yet at 20° C, they were lowest at a salinity of 0. A cost of osmoregulation (SMR at a salinity of 0 and 15 compared with SMR at a salinity of 10) could only be detected at a salinity of 15 at 20° C, where it was 28%. The results show that P. fluviatilis have capacity to osmoregulate in hyper‐osmotic environments. This contradicts previous studies and indicates intraspecific variability in osmoregulatory capabilities among P. fluviatilis populations or habitat origins. An apparent cost of osmoregulation (28%) at a salinity of 15 at 20° C indicates that the cost of osmoregulation in P. fluviatilis increases with temperature under hyperosmotic conditions and a power analysis showed that the cost of osmoregulation could be lower than 12·5% under other environmental conditions. The effect of salinity on MMR is possibly due to a reduction in gill permeability, initiated to reduce osmotic stress. An interaction between salinity and temperature on aerobic scope shows that high salinity habitats are energetically beneficial during warm periods (summer), whereas low salinity habitats are energetically beneficial during cold periods (winter). It is suggested, therefore, that the seasonal migrations of P. fluviatilis between brackish and fresh water is to select an environment that is optimal for metabolism and aerobic scope.     

Effects of reduced salinity on the biochemical composition (lipid, protein) of zoea 1 decapod crustacean larvae

Effects of reduced salinities on dry weight (DW) and biochemical composition (total lipid and protein contents) of zoea 1 larvae were evaluated in four decapod crustacean species differing in salinity tolerance (Cancer pagurus, Homarus gammarus, Carcinus maenas, Chasmagnathus granulata). The larvae were exposed to two different reduced salinities (15‰ and 25‰ in C. granulata, 20‰ and 25‰ in the other species) for a long (ca. 50% of the zoea 1 moulting cycle) or a short period (16 h, starting at ca. 40% of the moulting cycle), while a control group was continually maintained in seawater (32‰).In general, the increments in dry weight, lipid and protein content were lower at the reduced salinities than in the control groups. In the zoea 1 of H. gammarus (stenohaline) and C. pagurus (most probably also stenohaline), the lipid and protein contents varied greatly among treatments: larvae exposed to low salinities exhibited very low lipid and protein contents at the end of the experiments compared to the controls. In some cases, there were negative growth increments, i.e. the larvae had, after the experimental exposure, lower lipid and protein contents than at the beginning of the experiment. C. maenas (moderately euryhaline) showed a lower variation in protein and lipid content than the above species. The zoea 1 of C. granulata (fairly euryhaline) showed the lowest variability in dry weight, protein and lipid content. Since salinity tolerance (eury- v. stenohalinity) is associated with the osmoregulatory capacity, our results suggest a relationship between the capability for osmoregulation and the degree of change in the biochemical composition of larvae exposed to variable salinities.Besides larval growth of these species should be affected by natural reductions of salinity occurring in coastal areas at different time scales. These effects may be potentially important for population dynamics since they should influence the number and quality of larvae reaching metamorphosis.     

Laboratory Studies of Parasite Transmission Aspects between Hydrobia spp. (Gastropoda) and Corophium volutator (Amphipoda)

Aspects of parasite transmission between Hydrobia spp. and Corophium volutator, first and second intermediate host of digenetic trematodes, were investigated under laboratory conditions. H. ventrosa is used as an intermediate host by several trematode species. Under laboratory conditions the most frequently observed emergence from H. ventrosa was of cercariae of Maritrema subdolum. The number of cercariae shed per day varied considerably. It was observed that 30 cercariae on average and up to 450 cercariae at maximum can emerge from a single H. ventrosa per day. Cercarial production continued until the death of the snails. The life-span of cercariae of the species M. subdolum decreased as the water temperature increased. It can be concluded that under natural conditions the cercariae, after emerging, have a maximum period of 1 day in which to seek out their second intermediate host C. volutator. Almost all specimens of C. volutator exposed to cercariae of the species M. subdolum died within the test period of 6 days. High average cercarial densities caused short life-spans (<50 h), while at lower densities longer survival times were possible. For cercariae of other Trematoda species, we were unable to find any equally clear evidence of a reduction in the survival rate of C. volutator within the test period. Mortality of C volutator, and other effects of infestation, as observed in our experiment, can be assumed to be a result of the penetration process of the cercariae but they also can be attributed to the mesocercariae.     

Effects of salinity on growth, photosynthesis and respiration in a freshwater alga Rhizoclonium riparium (Chlorophyceae, Cladophorales)

A freshwater green alga, Rhizoclonium riparium (Roth) Harvey, was found to grow in diluted seawater with salinities (PSU) from 0.1 to 34.0 (0.1–34.0 S). It grew best at 13.6 S and least at 0.1 S which was the least salinity reported in its habitat. Net photosynthetic oxygen production of R. riparium rose with salinity up to 34.0. However, in the medium adjusted at pH 8.1. the net photosynthesis rose at low ranges of salinity and was almost at the same level in all ranges of salinities examined. The net photosynthesis was increased by the addition of bicarbonate in the medium. Respiratory oxygen consumption did not rise with the increase of external salinities from 0.1 to 34.0. The results indicate that R. riparium can grow by increasing net photosynthesis in diluted seawater in which the pH value is suitable for effective bicarbonate supply to photosynthesis.     

Effects of temperature and salinity on the growth of the red tide flagellates Heterocapsa circularisquama (Dinophyceae) and Chattonella verruculosa (Raphidophyceae)

Growth responses of the red tide flagellates, Heterocapsa circularisquama(Dinophyceae) and Chattonella verruculosa (Raphidophyceae),were examined with 36 different combinations of temperature(5–30°C) and salinity (10–35 PSU). Heterocapsacircularisquama did not grow at or below a temperature of 10°C.The maximum growth rate of H.circularisquama (1.3 divisionsday^–1) was obtained with a combination of 30°C and30 PSU. In contrast, C. verruculosa did not grow at 10 PSU andat temperatures of 25°C or more. The maximum growth rateof C. verruculosa (1.74 divisions day^–1) was obtainedwith a combination of 15°C and 25 PSU. A significant temperature-salinityinteraction on growth was found by factorial analysis. Basedon the physiological characteristics obtained in the presentstudy, these novel flagellates have a potential for future outbreaksof red tides in pre viously unaffected waters.     

Effects of salinity on the growth rate,carrageenan yield,and cellular structure of <Emphasis Type="Italic">Kappaphycus alvarezii</Emphasis> (Rhodophyta,Gigartinales) cultured in vitro

Kappaphycus alvarezii was cultured in vitro under salinities ranging from 15 to 55 psu for 35 days to determine the differential effect on growth rate, carrageenan yield, and cellular structure. Plants kept in 15 psu died after 3 days, while plants cultured in 55 psu presented low growth rates during the entire experimental period (0.28% day⁻¹). Plants cultured in 25, 35, and 45 psu showed growth rates normally associated with this species (between 3% and 4% day⁻¹) and similar cellular morphology. Carrageenan yield was significantly higher in plants cultured in 25 psu in relation to the other treatments. As observed by light microscopy, plants cultured in 15 psu showed cellular turgidity and increased cell wall thickness, both consequences of hyposalinity. Chloroplasts and other membranous organelles underwent rupture and considerable disorganization in ultrastructure. Although branches from the 55 psu samples showed plasmolysis, cells were able to maintain chloroplast integrity, despite their rudimentary features. In high salinities, great concentrations of floridean starch grains were observed in subcortical cells, indicating their probable participation in osmoregulation. Based on these results, we defined the range of 25 to 45 psu as the limits of saline tolerance for K. alvarezii. While new field studies are required to confirm these results, it can be concluded that new sites, such as inactive or abandoned shrimp tanks with salinities up to 25 psu, could be considered for commercial farming.