Prevalence,geographic distribution,and fitness effects of Microphallus turgidus (trematoda: Microphallidae) in grass shrimp (Palaemonetes spp.) from coastal Georgia

Grass shrimp, Palaemonetes pugio Holthuis and P. vilgaris (Say), were collected at 11 localities along the coast of Georgia and surveyed for digenetic trematode metacercariae. The effect of trematode infection on grass shrimp fitness was also examined. Microphallus turgidas (Leigh) was the only trematode observed. The prevalence of metacercarial cysts of this parasite in P. pugio (75%) was higher than in P. vulgaris (24%), as were the mean intensity, abundance, and population density (no. cysts/cm host body length) of the parasite. Infected shrimp were found at every collection locality and parasite prevalence and density were greatest in P. pugio from higher salinity localities (> or = 20 parts per thousand [ppt]). There was no relation between host body size and parasite density in P. vulgaris, and parasite density increased with host body size in P. pugio, suggesting that the parasite does not affect host survival. There was no relation between parasite density and shrimp egg mass, but nonovigerous female P. pugio were more heavily infected than ovigerous ones. In addition, 1 metacercaria of M. turgidus in each of 2 specimens of P. vulgaris was parasitized by the haplosporidian Urosporidium crescens De Turk. This represents a new shrimp host record for this hyperparasite.     

Maximum standard metabolic rate corresponds with the salinity of maximum growth in hatchlings of the estuarine northern diamondback terrapin (Malaclemys terrapin terrapin): Implications for habitat conservation

I evaluated standard metabolic rates (SMR) of hatchling northern diamondback terrapins (Malaclemys terrapin terrapin) across a range of salinities (salinity = 1.5, 4, 8, 12, and 16 psu) that they may encounter in brackish habitats such as those in the Maryland portion of the Chesapeake Bay, U.S.A. Consumption of O₂ and production of CO₂ by resting, unfed animals served as estimates of SMR. A peak in SMR occurred at 8 psu which corresponds closely with the salinity at which hatchling growth was previously shown to be maximized (salinity ∼ 9 psu). It appears that SMR is influenced by growth, perhaps reflecting investments in catabolic pathways that fuel anabolism. This ecophysiological information can inform environmental conservation and management activities by identifying portions of the estuary that are bioenergetically optimal for growth of hatchling terrapins. I suggest that conservation and restoration efforts to protect terrapin populations in oligo-to mesohaline habitats should prioritize protection or creation of habitats in regions where average salinity is near 8 psu and energetic investments in growth appear to be maximized.     

Branchial carbonic anhydrase activity and ninhydrin positive substances in the Pacific white shrimp, Litopenaeus vannamei, acclimated to low and high salinities

The Pacific white shrimp, Litopenaeus vannamei, acclimated to 30 ppt salinity, was transferred to either low (15 and 5 ppt), or high (45 ppt) salinity for 7 days. Hemolymph osmolality, branchial carbonic anhydrase activity, and total ninhydrin-positive substances (TNPS) in abdominal muscle were then measured for each condition. Hemolymph osmotic concentration was regulated slightly below ambient water osmolality in shrimp acclimated to 30 ppt. At 15 and 5 ppt, shrimp were strong hyper-osmotic regulators, maintaining hemolymph osmolality between 200 and 400 mOsm above ambient. Shrimp acclimated to 30 ppt and transferred to 45 ppt salinity were strong hypo-osmotic and hypo-ionic regulators, maintaining hemolymph osmolality over 400 mOsm below ambient. Branchial carbonic anhydrase (CA) activity was low (approximately 100 micromol CO(2) mg protein(-1) min(-1)) and uniform across all 8 gills in shrimp acclimated to 30 ppt, but CA activity increased in all gills after exposure to both low and high salinities. Anterior gills had the largest increases in CA activity, and levels of increase were approximately the same for low and high salinity exposure. Branchial CA induction appears to be functionally important in both hyper- and hypo-osmotic regulations of hemolymph osmotic concentrations. Abdominal muscle TNPS made up between 19 and 38% of the total intracellular osmotic concentration in shrimp acclimated to 5, 15, and 30 ppt. TNPS levels did not change across this salinity range, over which hemolymph osmotic concentrations were tightly regulated. At 45 ppt, hemolymph osmolality increased, and muscle TNPS also increased, presumably to counteract intracellular water loss and restore cell volume. L. vannamei appears to employ mechanisms of both extracellular osmoregulation and intracellular volume regulation as the basis of its euryhalinity.     

Rapid evolution of body fluid regulation following independent invasions into freshwater habitats

Colonizations from marine to freshwater environments constitute among the most dramatic evolutionary transitions in the history of life. Colonizing dilute environments poses great challenges for acquiring essential ions against steep concentration gradients. This study explored the evolution of body fluid regulation following freshwater invasions by the copepod Eurytemora affinis. The goals of this study were to determine (1) whether invasions from saline to freshwater habitats were accompanied by evolutionary shifts in body fluid regulation (hemolymph osmolality) and (2) whether parallel shifts occurred during independent invasions. We measured hemolymph osmolality for ancestral saline and freshwater invading populations reared across a range of common-garden salinities (0.2-25 PSU). Our results revealed the evolution of increased hemolymph osmolality (by 16-31%) at lower salinities in freshwater populations of E. affinis relative to their saline ancestors. Moreover, we observed the same evolutionary shifts across two independent freshwater invasions. Such increases in hemolymph osmolality are consistent with evidence of increased ion uptake in freshwater populations at low salinity, found in a previous study, and are likely to entail increased energetic costs upon invading freshwater habitats. Our findings are consistent with the evolution of increased physiological regulation accompanying transitions into stressful environments.     

Salinity tolerance and osmoregulation of the arctic marine amphipods Onisimus litoralis (Kroyer) and Anonyx nugax (Phipps)

Summary The gammarid amphipod Onisimus litoralis, which inhabits arctic and subarctic intertidal and under-ice habitats, is a euryhaline hyperosmotic regulator. It survives 10 d exposures to salinities from 5 to 55 ppt. It hyperregulates its hemolymph osmolality during 3 h exposures to dilutions of 33 ppt seawater and remains hyperosmotic for at least 2 w. The hemolymph is isosmotic to the medium after 12 h exposures to salinities higher than 33 ppt. The gammarid amphipod Anonyx nugax, which inhabits arctic and subarctic subtidal areas, tolerates salinities from 23 to 45 ppt with little mortality. Unlike Onisimus, however, it is an osmoconformer and its hemolymph becomes isosmotic to all dilute salinities within its tolerance range after 12 h and to concentrated media after 3 h. The salinity tolerances and osmoregulatory abilities of both species are reflected in their distributions in the field.     

Effects of increases in salinity on phytoplankton in the Broadwater of the Myall Lakes, NSW, Australia

The Broadwater of the Myall Lakes system is highly susceptible to cyanobacterial bloom formation after heavy rain events. During prolonged low flow periods, saline intrusion from the lower Myall River increases salinity levels and effectively controls some bloom forming algal taxa. To assess the effect of low-to-moderate increases in salinity (up to 4 ppt) on phytoplankton chlorophyll a, cell abundance, diversity and assemblage structure, salinity enhancement experiments were conducted on Broadwater samples collected in June 2005 (salinity 1.5 ppt), October 2005 (4 ppt) and January 2006 (12 ppt). Natural phytoplankton assemblages were incubated in the laboratory for 10 days, under different treatments of salinity (no addition, +2 ppt, + 4 ppt) and nutrient conditions (no addition, excess N+P). The greatest impact of salinity enhancement in N+P enriched samples was observed in June (1.5–5.5 ppt); chlorophyll a was significantly reduced in samples with the highest salinity treatment, and the taxon most negatively affected by an elevation in salinity to 5.5 ppt was Anabaena circinalis. Taxonomic richness and diversity (Shannon–Wiener index) were unexpectedly significantly higher at 5.5 ppt than at 1.5 ppt. This result, in part, explains the observed significant differences in phytoplankton assemblage structure over this salinity range. In October, the main effect of elevating salinity levels from 4 ppt to 8 ppt was a reduction in the abundance of chlorophytes, particularly Scenedesmus. Phytoplankton samples that were collected when the lake salinity level was 12 ppt were little affected by salinity increases of 2 ppt and 4 ppt, most likely because field samples were already relatively high in salt content. We suggest that further investigations focus on phytoplankton responses to salinity under a range of nutrient regimes that are common to coastal lakes.     

Effects of low-salinity on the growth and development of spotted halibut Verasper variegatus in the larva-juvenile transformation period with reference to pituitary prolactin and gill chloride cells responses

Low-salinity adaptability was investigated in a flatfish spotted halibut Verasper variegatus during the period from late metamorphic larvae to early juveniles by a 20-day rearing experiment under different salinity regimes (1, 4, 8, 16 and 32 ppt). Effects of low-salinity on growth and development were examined and the changes in the prolactin (PRL) production level in the pituitary and the gill chloride cell morphology were examined as physiological backgrounds for low salinity adaptation. PRL cells and chloride cells were identified by immunocytochemistry with a specific antiserum for PRL₁₈₈ and Na⁺,K⁺-ATPase. Most of the fish exposed to over 4 ppt survived for 20 days, but all the fish exposed to 1 ppt died within 5 days. Fish kept in intermediate salinities (8, 16 ppt) grew significantly better than those in the control group (32 ppt). Fish exposed to 4 ppt attained almost the same body length as the control group at 20 days after transfer, although these fish showed an abnormally dark body color as well as delayed development. These results suggested that spotted halibut has a high-adaptability to low-salinity environments and prefers an intermediate salinity near iso-osmolality (about 12 ppt) from the late metamorphic larval stage, but does not completely adapt to a hypoosmotic of 4 ppt salinity or less than half of the osmolality. The percentage of PRL-cell volume to pituitary volume was significantly higher at 4 ppt than in the control group. The chloride cells in gill filaments were significantly larger at 4 ppt than in the control group. These results suggest that juveniles could adapt to a low-salinity environment due to the activation of PRL production and enlargement of chloride cells. These laboratory findings suggest that late metamorphic larvae and early juveniles of spotted halibut may utilize a low salinity environment such as estuarine tidal flats or very shallow coastal areas as their nursery grounds in the sea.     

Effects of eyestalk ablation on carbonic anhydrase activity in the euryhaline blue crab Callinectes sapidus: neuroendocrine control of enzyme expression

Carbonic anhydrase (CA) activity in the gills of the euryhaline blue crab, Callinectes sapidus, was measured in response to acute low-salinity transfer and treatment with eyestalk ablation (ESA) in an attempt to elucidate potential regulatory mechanisms of salinity-mediated CA induction. ESA alone resulted in an approximate doubling of CA activity in the posterior, ion-transporting gills of crabs acclimated to 35 ppt. Transfer of intact crabs to 28 ppt, a salinity at which the blue crab is still an osmotic and ionic conformer, had no effect on CA activity, but treatment with ESA prior to transfer resulted in a 5-fold increase. Hemolymph osmolality was unaffected by ESA. There was a 7-fold induction of CA activity in posterior gills of intact crabs transferred from 35 to 15 ppt, and this was potentiated by about 100% by ESA. Hemolymph osmolality was slightly elevated in the ESA-treated crabs. CA activity in anterior gills did not increase in response to any treatment. Hemolymph concentrations of methyl farnesoate (MF) were measured for all experimental animals. MF concentrations were undetectable in all intact crabs, regardless of salinity. Treatment with ESA resulted in elevated levels of hemolymph MF, but these levels were still relatively low and unrelated to salinity. These results suggest that CA induction is under the control of a regulatory substance located in the eyestalk. This substance appears to be a CA repressor, keeping CA expression at low levels in the gills of crabs acclimated to high salinity. Exposure to low salinity, or treatment with ESA, removes the effects of this putative repressor and allows CA induction to occur.     

Seed germination traits of two plant functional groups in the saline deltaic ecosystems

Aims Salt stress resulting from soil salinization is one of the driving forces of the land degradation throughout the world. The modern Yellow River delta is one of the most saline areas in China. Phytoremediation can be an effective way to restore the salinized ecosystems, which requires selecting appropriate plant species. This study explored the germination responses of common plant species from contrasting habitats in the Yellow River delta to varying salinity, offering experimental information for ecosystem restoration in the Yellow River delta.Methods In this study, 15 common plant species from the Yellow River delta were divided into two groups (high-salinity and low-salinity groups) by their natural habitats using Canonical Correlation Analysis. Seeds of each species were treated with five salinity levels (0, 5, 10, 20 and 30 ppt), using a randomized complete block design, and germinated seeds were counted and removed daily for 28 days to calculate the final germination proportion and mean time to germination. The germination responses of seeds to salinity treatments were compared between the two groups.Important findings In relation to salinity, seed germination behavior of the test species was closely related to the salinity level of the habitats over which they were distributed. Species from the habitats with higher salinity had generally higher final germination proportion but shorter mean time to germination than those from the habitats with lower salinity in all of five salinity treatments used. The final germination proportion and mean time to germination of low-salinity group species were more sensitive to salinity than those of high-salinity group species. Selecting the species with high final germination proportion and short mean time to germination is important for restoration of salinized land.     

Salinity tolerance in Hyalophysa chattoni (Ciliophora, Apostomatida), a symbiont of the estuarine grass shrimp Palaemonetes pugio

The apostome ciliate Hyalophysa chattoni, a symbiont of the estuarine grass shrimp Palaemonetes pugio, was tested for its growth and reproductive ability in a wide range of salinities from 0.1 to 55 ppt. Shrimp, with their attached ciliates, were slowly acclimated to different salinities in order to assess protozoan cell size and division. The trophont and tomont stages of the ciliate life cycle were analyzed. In both stages, cell size increased with salinity from 0.1 to 20 ppt. Cell size leveled in the 20-35 ppt range, and decreased at higher salinities. The number of daughter cells produced per tomont cyst correlated with increased cell size, and also correlated with increased salinity. Additionally, increased salinity correlated with an increase in the percentage of cells able to divide and excyst as tomite stages. These results indicate that H. chattoni is able to grow and divide more effectively at salinities closer to seawater than in the estuarine environment from which they were collected. Though able to survive salinities from 0.1 to 55 ppt, the species is better adapted for an existence in the higher salt concentrations.     

Salinity-mediated carbonic anhydrase induction in the gills of the euryhaline green crab, Carcinus maenas

The euryhaline green crab, Carcinus maenas, is a relatively strong osmotic and ionic regulator, being able to maintain its hemolymph osmolality as much as 300 mOsm higher than that in the medium when the crab is acclimated to low salinity. It makes the transition from osmoconformity to osmoregulation at a critical salinity of 26 ppt, and new acclimated concentrations of hemolymph osmotic and ionic constituents are reached within 12 h after transfer to low salinity. One of the central features of this transition is an 8-fold induction of the enzyme carbonic anhydrase (CA) in the gills. This induction occurs primarily in the cytoplasmic pool of CA in the posterior, ion-transporting gills, although the membrane-associated fraction of CA also shows some induction in response to low salinity. Inhibition of branchial CA activity with acetazolamide (Az) has no effect in crabs acclimated to 32 ppt but causes a depression in hemolymph osmotic and ionic concentrations in crabs acclimated to 10 ppt. The salinity-sensitive nature of the cytoplasmic CA pool and the sensitivity of hemolymph osmotic/ionic regulation to Az confirm the enzyme's role in ion transport and regulation in this species. CA induction is a result of gene activation, as evidenced by an increase in CA mRNA at 24 h after transfer to low salinity and an increase in protein-specific CA activity immediately following at 48 h post-transfer. CA gene expression appears to be under inhibitory control by an as-yet unidentified repressor substance found in the major endocrine complex of the crab, the eyestalk.     

Comparative life history of female mosquito fish,Gambusia affinis,in tidal freshwater and oligohaline habitats

Synopsis Female Gambusia affinis were collected from low salinity/near-neutral pH and tidal freshwater/low pH localities to document life history variation between these two habitats. Mosquito fish were 2.7 times more abundant in low salinity/near-neutral pH (2.37 ± 0.72 ppt; pH = 5.73 ± 0.11) than in tidal freshwater/low pH (0.27 ± 0.19 ppt; pH = 4.46 ± 0.18) habitats in Old Fort Bayou, a black-water tidal river of the Biloxi Bay estuary, Mississippi. Fish were common in both areas from June 1985 through February 1986. There were no significant differences between habitats in the length-weight relationships during the reproductive season with the exception of February. However, there were significant differences in life histories, although the areas were only 4 km apart. Ovarian recrudescence was observed in fish from both areas in February, but ovaries of low salinity fish were more developed than ovaries of freshwater fish. All fish from both areas had regressed ovaries by late September. The monthly slopes of the brood size vs. standard length regressions were significantly different between areas throughout the reproductive season with the exception of June. Although freshwater fish produced heavier tail-free embryos, fish from low salinity had significantly higher GSI values and brood size throughout the reproductive season. These observations suggest that Gambusia affonis may have a greater reproductive effort in low salinity/near-neutral pH environments than in freshwater/low pH habitats.     

The role of the antennal glands in ion and body volume regulation of cannulated Penaeus monodon reared in various salinity conditions

Urinary production rate and the osmotic and ionic concentrations in both urine and hemolymph were measured in cannulated intermolt Penaeus monodon which were either abruptly transferred from 45 ppt seawater to 15 ppt seawater (Experiment 1) or acclimated to 5, 25 and 45 ppt seawater (Experiment 2). In Experiment 1, urinary magnesium concentration fell dramatically from 228 to 30 mEq/l within 4 h post-transfer, but 8 h after transfer, U/H (urine/hemolymph) ratios stabilized at between 1.0 and 2.5. Sodium was higher in urine than in hemolymph during the first 24 h after transfer, while potassium was lower in urine than in hemolymph until 72 h after transfer, which suggests that sodium and potassium concentrations are regulated by the antennal gland after an abrupt change in media. In Experiment 2, the urinary production rate of P. monodon decreased as salinity increased, suggesting that the antennal glands also regulate body volume. In the acclimated shrimps of Experiment 2, the antennal glands did not appear to regulate osmolarity or the concentration of chloride, sodium, potassium, and calcium ions, but as salinity increased, U/H ratios of magnesium increased from 2.3 to 13.5, and active secretion by the antennal gland accounted for 57 approximately 93% of the total magnesium excretion through urine. These results suggest that active secretion of magnesium by the antennal gland enable this shrimp to maintain hypoionic levels of magnesium in the hemolymph.     

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.     

Critical salinity, sensitivity, and commitment of salinity-mediated carbonic anhydrase induction in the gills of two euryhaline species of decapod crustaceans

Two euryhaline species of decapod crustaceans, Carcinus maenas and Callinectes sapidus, were subjected to a series of acute low-salinity challenges, and changes in carbonic anhydrase (CA) activity in the gills were monitored in order to characterize the nature of salinity-sensitive CA induction. CA activity is uniformly low in all gills of both species at high salinity, but at a critical salinity of 27 ppt, CA induction occurs in the posterior, ion-transporting gills, with CA activity approximately doubling. This salinity occurs right at, or slightly above, the point at which these species make the transition from osmoconformity to osmoregulation. The regulatory mechanism that controls the levels of CA expression after the initial induction has occurred is also very sensitive. Changes in CA activity occur in response to changes in salinity as small as 20 milliosmoles. CA induction only occurs after a critical minimum amount of time of exposure to low salinity (48-72 hr in C. maenas and 12 hr in C. sapidus), but once induction is begun, it continues regardless of subsequent salinity changes. The timing is most likely due to the time it takes for changes in gene expression and resultant increases in CA mRNA to occur in response to low-salinity exposure, and the delay in CA induction could be an adaptation to avoid making metabolically expensive responses to potentially short-term environmental changes.     

Light limiting thresholds for submerged aquatic vegetation in a blackwater river

Field-based monitoring data were used to estimate the limiting light threshold for Vallisneria americana, the dominant species, in the St. Johns River, Florida. There was a considerable range of threshold estimates (0.5–35% of surface light) among individual observations. Light threshold calculations were divided into low- and high-salinity groups of sites. The field-based mean threshold for 1998–2004 was 9% for low-salinity (<0.5 ppt annual mean) sites. Sites with higher salinity (>0.5 ppt annual mean) had a higher mean light threshold of 14%. A separate analysis of the freshwater Crescent Lake suggested a light threshold of 9%. Increased epiphyte biomass during the drought may have accounted for the majority of the higher light requirements in the freshwater reach of the river. Light requirement values in this study were similar to other studies focusing on V. americana.     

Field observations of four Aurelia labiata jellyfish behaviours: swimming down in response to low salinity pre-empted swimming up in response to touch,but animal and plant materials were captured equally

Jellyfish live in complex environments and must continually make behavioural choices. In field observations, adult Aurelia labiata were confronted with a conflict between swimming up elicited by touch of the manubrium and swimming down elicited by low salinity. Following a touch, downward-swimming medusae (1.5–2.0 m deep) turned and swam to within 0.5 m of the surface when the salinity in the top 1.5 m of the water column was greater than 20 ppt but medusae uniformly refused to swim up into the top 1.25 m when the salinity was less than 20 ppt even after being touched three times. The central nervous system of A. labiata appears to have neural circuitry that specifies their response when medusae encounter stimuli that elicit incompatible behaviours. Upward-swimming adult medusae had animal, vegetable or cellulose (paper) material dispersed ahead of them. Medusae captured each material on the bell margin and transported it to a gastric pouch. Medusae displayed only minor behavioural differences in the process. Having sensory, neural and muscular systems organized to capture and pass to the stomach, a huge variety of materials allows medusae to survive in different seasons and environments.     

Effects of low salinity on metamorphosis in estuarine colonial ascidians

Abstract. We studied the effects of brackish water on larval attachment, events of metamorphosis, and juvenile mortality in three colonial ascidian species that live in a Florida coastal lagoon. Eudistoma olivaceum and Eudistoma hepaticum are restricted in their adult distribution to areas of relatively high and constant salinity near inlets, whereas Ecteinascidia turbinata extends more than 20 km into the Indian River, where salinity can be much more variable. In all three species, metamorphosis proceeded more quickly at 33 ppt than at lower salinities. The thresholds for successful metamorphosis differed among species in a manner that corresponded to the adult distributions, with E. turbinata being capable of completing metamorphosis at salinities as low as 22 ppt, E. hepaticum as low as 24 ppt, and E. olivaceum as low as 26 ppt. Larvae of both Eudistoma species delayed settlement in very low salinity water, whereas those of E. turbinata settled very quickly, then failed to complete metamorphosis. Juvenile mortality at salinities lower than 22 ppt was 100% for all three species. Survival in salinities higher than 22 ppt was strongly correlated with salinity in E. olivaceum and E. hepaticum , but not E. turbinata.     

Larval development of Aedes aegypti and Aedes albopictus in peri-urban brackish water and its implications for transmission of arboviral diseases

Aedes aegypti (Linnaeus) and Aedes albopictus Skuse mosquitoes transmit serious human arboviral diseases including yellow fever, dengue and chikungunya in many tropical and sub-tropical countries. Females of the two species have adapted to undergo preimaginal development in natural or artificial collections of freshwater near human habitations and feed on human blood. While there is an effective vaccine against yellow fever, the control of dengue and chikungunya is mainly dependent on reducing freshwater preimaginal development habitats of the two vectors. We show here that Ae. aegypti and Ae. albopictus lay eggs and their larvae survive to emerge as adults in brackish water (water with <0.5 ppt or parts per thousand, 0.5-30 ppt and >30 ppt salt are termed fresh, brackish and saline respectively). Brackish water with salinity of 2 to 15 ppt in discarded plastic and glass containers, abandoned fishing boats and unused wells in coastal peri-urban environment were found to contain Ae. aegypti and Ae. albopictus larvae. Relatively high incidence of dengue in Jaffna city, Sri Lanka was observed in the vicinity of brackish water habitats containing Ae. aegypti larvae. These observations raise the possibility that brackish water-adapted Ae. aegypti and Ae. albopictus may play a hitherto unrecognized role in transmitting dengue, chikungunya and yellow fever in coastal urban areas. National and international health authorities therefore need to take the findings into consideration and extend their vector control efforts, which are presently focused on urban freshwater habitats, to include brackish water larval development habitats.