Polymorphic color vision in white-faced capuchins (Cebus capucinus): Is there foraging niche divergence among phenotypes?

Many species of platyrrhine primates are characterised by sex-linked color vision polymorphism. This presents an opportunity to study the biology and ecology of individuals with different phenotypes living in the same group. Several evolutionary processes could maintain polymorphic genes in populations. In this study, we evaluate the hypothesis that foraging niche divergence among monkeys explains the presence of multiple color vision phenotypes. Specifically, we test whether dichromats and trichromats differ in foraging time devoted to cryptic vs brightly colored resources. We did not find any differences in foraging time spent on different food types by dichromatic and trichromatic monkeys in two groups of white-faced capuchins (Cebus capucinus) living in a tropical dry forest. We conclude that in so far as these variables are concerned, niche divergence does not likely explain color vision polymorphism in our study population.     

Light levels used during feeding by primate species with different color vision phenotypes

The intensity of available light is important in determining how well a diurnal animal can distinguish color. Primates with different types of color vision may exhibit behaviors that maximize visual contrast during critical activities such as feeding. We hypothesized that (1) trichromatic taxa will feed in a wide range of light conditions because color constancy permits stabilized color appearance across changes in illumination, and (2) that taxa with a high proportion of dichromatic individuals will tend to feed at higher light levels to increase color contrast. We recorded light levels during feeding bouts of seven primate taxa with varying degrees of color vision: the dichromatic Lemur catta, two polymorphic species, Propithecus v. verreauxi and Ateles geoffroyi, and the routine trichromats, Alouatta palliata, Colobus guereza, Piliocolobus badius, and Cercopithecus ascanius. Results were equivocal for our hypotheses. While routinely trichromatic taxa used varying light levels, the pattern of results did not differ from the dichromatic Lemur catta. However, polymorphic taxa not only sought the highest light, but females, which are the only individuals in polymorphic taxa that can be trichromatic, fed in higher light levels than males when eating non-green foods. This result is consistent with selection operating to maintain a balanced polymorphism in these taxa, though the connection between light levels and color vision type for the females is unclear. Our results further suggest that trichromatic vision may afford a selective advantage because it permits foraging under a greater range of light levels.     

A rapid ontogenetic shift in the diet of juvenile yellowfin tuna from Hawaii

Within the tropical and subtropical oceans, tuna forage opportunistically on a wide variety of prey. However, little is known about the trophic ecology of the smallest size classes which play an important role in stock assessments and fisheries management. The foraging behavior of yellowfin tuna, Thunnus albacares (23.5–154.0 cm FL), collected from nearshore Fish Aggregating Devices (FADs) around Oahu was studied using stable isotope and stomach contents analyses. Emphasis was placed on small juveniles. Yellowfin tuna changed their diets significantly between 45 and 50 cm forklength (ca. 1.5 kg). Smallest size classes fed on planktonic organisms inhabiting the shallow mixed layer, primarily larval stomatopod and decapod crustaceans, whereas larger tuna fed on teleosts and adult Oplophorus gracilirostris, a vertically migrating mesopelagic species of shrimp. When interpreting the variation in prey δ ¹⁵N values, we considered both their relative trophic position and δ ¹⁵N values of the nitrogen at the base of the food web. Based on the distinct diet shift of the yellowfin tuna, demonstrated by both isotope and stomach content analyses, we propose a critical mass threshold was reached at about 45 cm FL that enabled sufficient endothermic capability to allow tuna to access prey dwelling in deeper, colder water. These ontogenetic changes in foraging range and commensurate shift in diet of small tunas would affect their vulnerability to fishing pressure.     

Polymorphism in gigantobacterial symbionts in the guts of surgeonfish (Acanthuridae: Teleostei)

The morphology and partial cytology of a group of bacteria-related organisms from the guts of surgeonfish are described. These gigantobacteria symbionts are encountered in the guts of various species of this fish family throughout the Indo-Pacific region and the Red Sea. They have been tentatively grouped and placed in a “family”, Epulopiscidae, according to the first species described, Epulopiscium fishelsoni Montgomery and Pollak, 1988. In addition to a morphological comparison between the various forms from different species of surgeonfish, suggestions are presented with regard to their possible morphological diversification during evolutionary and host-species specificity. Received: 10 June 1998 / Accepted: 29 October 1998     

Chemical defense in pelagic octopus paralarvae: Tetrodotoxin alone does not protect individual paralarvae of the greater blue-ringed octopus (Hapalochlaena lunulata) from common reef predators

Some pelagic marine larvae possess anti-predator chemical defenses. Occasionally, toxic adults imbue their young with their own defensive cocktails. We examined paralarvae of the greater blue-ringed octopus (Hapalochlaena lunulata) for the deadly neurotoxin tetrodotoxin (TTX), and if present, whether TTX conferred protection to individual paralarvae. Paralarvae of H. lunulata possessed 150 ± 17 ng TTX each. These paralarvae appeared distasteful to a variety of fish and stomatopod predators, yet food items spiked with 200 ng TTX were readily consumed by predators. We conclude that TTX alone does not confer individual protection to paralarvae of H. lunulata, and that they possess an alternative defense. In larger doses, tetrodotoxin is a deterrent to the predatory stomatopod Haptosquilla trispinosa (mean dose = 3.97 μg/g). This corresponds to 12–13 paralarvae per predator based on the TTX levels of the clutch we examined. Thus, the basic assumption that individual paralarvae of H. lunulata are defended by TTX alone was disproved. Instead, functionality of TTX levels in paralarvae may arise through alternative selective pathways, such as deterrence to parasites, through kin selection, or against predator species not tested here.     

Bioluminescence spectra of shallow and deep-sea gelatinous zooplankton: ctenophores, medusae and siphonophores

We have examined the variability and potential adaptive significance of the wavelengths of light produced by gelatinous zooplankton. Bioluminescence spectra were measured from 100 species of planktonic cnidarians and ctenophores collected between 1 and 3500 m depth. Species averages of maximal wavelengths for all groups ranged from 440 to 506 nm. Ctenophores (41 species) had characteristically longer wavelengths than medusae (34 species), and the wavelengths from siphonophores (25 species) had a bimodal distribution across species. Four species each produced two different wavelengths of light, and in the siphonophore Abylopsistetragona these differences were associated with specific body regions. Light from deep-dwelling species had significantly shorter wavelengths than light from shallow species in both ctenophores (p = 0.010) and medusae (p = 0.009). Although light production in these organisms was limited to the blue-green wavelengths, it appears that within this range, colors are well-adapted to the particular environment which the species inhabit. Received: 27 April 1998 / Accepted: 27 October 1998     

Chemical mimicry in an incipient leaf-cutting ant social parasite

Some social parasites of insect societies are known to use brute force when usurping a host colony, but most use more subtle forms of chemical cheating either by expressing as few recognition cues as possible to avoid being recognized or by producing similar recognition cues to the host to achieve positive discrimination. The former “chemical insignificance” strategy represents a more general adaptive syndrome than the latter “chemical mimicry” strategy and is expected to be characteristic of early evolutionary stages of social parasitism. We tested this hypothesis by experimentally analyzing the efficiency by which Acromyrmex echinatior leaf-cutting ants recognize intruding workers of the incipient social parasite Acromyrmex insinuator. The results were consistent with the parasite being “chemically insignificant” and not with the “chemical mimicry” hypothesis. Gas chromatography–mass spectrometry analysis of cuticular hydrocarbon profiles showed that social parasite workers produce significantly fewer hydrocarbons overall and that their typical profiles have very low amounts of hydrocarbons in the “normal” C29–C35 range but large quantities of unusually heavy C43–C45 hydrocarbons. This suggests that the C29–C35 hydrocarbons are instrumental in normal host nestmate recognition and that the C43–C45 compounds, all of which are dienes and thus more fluid than the corresponding saturated compounds, may reinforce “chemical insignificance” by blurring any remaining variation in recognition cues.     

Comparative study of behavioral-sensitivity thresholds to near-UV and blue-green light in deep-sea crustaceans

The behavioral sensitivities of five species of deep-sea crustaceans (order Decapoda: Acanthephyra curtirostris, A. smithi, Notostomus gibbosus, Janicella spinacauda and Oplophorus gracilirostris) to near-UV and blue-green light were studied during a research cruise off the coast of Hawaii in 1993. Two of the five species have electrophysiologically-measured spectral sensitivity peaks at 400 and 500 nm, while the remaining three species have a single sensitivity peak at 490 to 500 nm. In the current study, behavioral mean threshold sensitivities (defined as the lowest irradiance change to which the shrimp would give a behavioral response) were determined for tethered specimens of each species at two wavelengths, 400 and 500 nm. The mean behavioral threshold sensitivities of the two species with putative dual visual-pigment systems were approximately the same to near-UV and blue-green light, while the other three species were significantly less sensitive to near-UV vs blue-green light. Results from these experiments indicate that (1) behavioral information obtained from tethered shrimp accurately reflects their spectral sensitivity, and (2) the sensitivity of the putative dichromats to near-UV light is sufficiently low to detect calculated levels of near-UV light remaining in the down-welling field at their daytime depth of 600 m. Possible functions of this high sensitivity to short wavelength light are discussed.     

Feeding ecology and evolutionary survival of the living coelacanth Latimeria chalumnae

One concept of evolutionary ecology holds that a living fossil is the result of past evolutionary events, and is adapted to recent selective forces only if they are similar to the selective forces in the past. We describe the present environment of the living coelacanth Latimeria chalumnae Smith, 1939 at Grande Comore, western Indian Ocean and report depth-dependent cave distribution, temperature, salinity and oxygen values which are compared to the fish's distribution and its physiological demands. We studied the activity pattern, feeding behaviour, prey abundance and hunting success to evaluate possible links between environmental conditions, feeding ecology and evolutionary success of this ancient fish. Transmitter tracking experiments indicate nocturnal activity of the piscivorous predator which hunts between approximately 200 m below the surface to 500 m depth. Fish and prey density were measured between 200 and 400 m, both increase with depth. Feeding tracks and feeding strikes of the coelacanth at various depths were simulated with the help of video and laser techniques. Along a 9447 m video transect a total of 31 potential feeding strikes occurred. Assuming 100% hunting success, medium-sized individuals would obtain 122 g and large females 299 g of prey. Estimates of metabolic rates revealed for females 3.7 ml O₂ kg⁻¹ h⁻¹ and for males 4.5 ml O₂ kg⁻¹ h⁻¹. Today coelacanths are considered to be a specialist deep-water form and to inhabit, with their ancient morphology, a contemporary environment where they compete with advanced, modern fish. Received: 5 July 1999 / Accepted: 11 November 1999     

A trade-off between prey- and predator-induced polyphenisms in larvae of the salamander Hynobius retardatus

Organisms in natural habitats participate in complex ecological interactions that include competition, predation, and foraging. Under natural aquatic environmental conditions, amphibian larvae can simultaneously receive multiple signals from conspecifics, predators, and prey, implying that predator-induced morphological defenses can occur in prey and that prey-induced offensive morphological traits may develop in predators. Although multiple adaptive plasticity, such as inducible defenses and inducible offensive traits, can be expected to have not only ecological but also evolutionary implications, few empirical studies report on species having such plasticity. The broad-headed larval morph of Hynobius retardatus, which is induced by crowding with heterospecific anuran (Rana pirica) larvae, is a representative example of prey-induced polyphenism. The morph is one of two distinct morphs that have been identified in this species; the other is the typical morph. In this paper, we report that typical larval morphs of Hynobius can respond rapidly to a predatory environment and show conspicuous predator-induced plasticity of larval tail depth, but that broad-headed morphs cannot respond similarly to a predation threat. Our findings support the hypothesis that induction or maintenance of adaptive plasticity (e.g., predator-induced polyphenism) trades off against other adaptive plastic responses (e.g., prey-induced polyphenism). For a species to retain both an ability to forage for larger prey and an ability to more effectively resist predation makes sense in light of the range of environments that many salamander larvae experience in nature. Our results suggest that the salamander larvae clearly discriminate between cues from prey and those from predators and accurately respond to each cue; that is, they adjust their phenotype to the current environment.     

Mechanism of egg recognition in defenses against conspecific brood parasitism: American coots (<Emphasis Type="Italic">Fulica americana</Emphasis>) know their own eggs

Hosts of avian brood parasites use a variety of defenses based on egg recognition to reduce the costs of parasitism; the most important of which is rejecting the parasitic eggs. Two basic recognition mechanisms are possible: “true recognition”, whereby hosts recognize their own eggs irrespective of their relative frequency in the clutch, and minority recognition (or “recognition by discordancy”), whereby hosts respond to the minority egg type. The mechanism of recognition has been experimentally studied in a handful of species parasitized by interspecific brood parasites, but the mechanism used in defenses against conspecific brood parasitism is unknown. I experimentally determined the mechanism of egg recognition in American coots (Fulica americana), a species with high levels of conspecific brood parasitism, egg recognition, and rejection. I swapped eggs between pairs of nests to alter frequencies of host and “parasite” eggs and then used two criteria for recognition: egg rejection and nonrandom incubation positions in the clutch. Eight of 12 nests (66%) given equal frequencies of host and parasite eggs showed evidence of true recognition. In contrast, only one of eight (12.5%) nests where host eggs were in the minority showed evidence of recognition by discordancy. The nonrandom incubation positions of parasitic eggs indicates that birds sometimes recognize parasitic eggs without rejecting them and provides a means of assessing recognition on a per nest basis in species with large clutches. Adaptive recognition without rejection may also be an important evolutionary stepping stone to the evolution of egg rejection in some taxa.     

Diel migration of phytoplankton and spectral light field in the Ría de Vigo (NW Spain)

Diel migration of Mesodinium rubrum, Eutreptiella sp., Scrippsiella trochoidea, Dinophysis acuminata and Ceratium furca throughout a 24 h cycle is described for a stable, well-stratified estuary (Ría de Vigo, NW Spain). Daily changes in light quantity and in spectral light ratios i.e. red:far-red, blue:red, green:red and blue:green have been analysed. The spectral light ratios changed at twilight and around noon at various depths. Some of the downward migrations were well predicted by Stokes' law, while other migrations were faster and deeper than calculated. The coincidence of these movements with abrupt changes in red:far-red, green:red and blue:green light ratios is discussed. Some species are able to migrate through the pycnocline, whereas others do not seem to be able to do so. Several species are present in maximum numbers at depth at night, while others display upward migration independent of light, suggesting the existence of endogenous rhythms. Upward migration at dusk began with dispersal of populations, with renewed aggregation at the sea surface coincident with an increase in the red:far-red ratio at 6 m and the green:red ratio at 6 and 10 m. Based on direct evidence for the control of flagellar mobility by light quality reported by other authors from laboratory studies, it is suggested that, together with other cues, spectral light ratios of different light qualities modulate vertical phytoplanktonic migration. Received: 18 July 1997 / Accepted: 17 October 1997     

Genetic connectivity among color morphs and Pacific archipelagos for the flame angelfish, <Emphasis Type="Italic">Centropyge loriculus</Emphasis>

Color variation is used in taxonomic classification of reef fishes, but it may not reliably indicate evolutionary divergence. In the central Pacific, there are three color morphs of the flame angelfish, Centropyge loriculus: a red morph that occurs primarily in the Hawaiian archipelago, the endemic Marquesan color morph with reduced black markings, and an orange morph that occurs throughout the rest of Oceania. The red and orange morphs co-occur at Johnston Atoll (1,300 km south of Hawai’i), but intermediate forms have not been reported. To determine whether the three color morphs represent distinct evolutionary lineages, we compared 641 base pairs of mitochondrial cytochrome b. Forty-one closely related haplotypes were observed in 116 individuals. Analysis of molecular variance (AMOVA) indicated no significant genetic structure among color morphs (Φ_ST = 0.011, P = 0.147). Likewise, there was no significant pairwise structure between sampling locations, separated by up to 5,700 km, after a Bonferroni correction (Φ_ST = 0.000–0.080, P = 0.0130–0.999). Genetic studies in conjunction with larval distribution data indicate that Centropyge species are highly dispersive. While there is a strong geographic component to the distribution of color morphs in C. loriculus, we find no evidence for corresponding genetic partitioning. We do not rule out an adaptive role for color differentiation, but our data do not support emerging species.     

Light environment and mating behavior in Trinidadian guppies (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>)

Male guppies, Poecilia reticulata, have color patterns that result from a balance between natural selection for crypsis to avoid predators and sexual selection for bright, complex patterns that attract females. Males use displays to show off these patterns to potential mates, but their conspicuousness also depends on the light environment in which they are viewed. We investigated variation in natural underwater guppy light environments in Trinidad, West Indies, and found that mating behavior is correlated with both the ‘quantity’ (total irradiance) and ‘quality’ (spectral composition) of light: light intensity and the proportion of ultraviolet light were negatively related to display rates. Experimental manipulation of light environment to mimic natural daily changes demonstrated that these relationships are causal and are independent of time of day effects. At lower light levels, when guppies are less detectable by visually hunting predators, females had more opportunity for active mate choice, because males displayed more. However, these light conditions may reduce the ability of females to accurately discriminate between males. Guppy mating behavior is therefore strongly affected by light environment, and this may have important effects on sexual selection.     

Three party symbiosis: acoelomorph worms,corals and unicellular algal symbionts in Eilat (Red Sea)

Epizoic worms were found to occur on certain coral colonies from reefs off the coast of Eilat (Red Sea). We identified 14 coral species infested by acoelomorph worms at a depth range of 2–50 m. The host corals were all zooxanthellate and included both massive and branching stony corals and a soft coral. Worms from all hosts were identified as belonging to the genus Waminoa and contained two distinct algal symbionts differing in size. The smaller one was identified as Symbiodinium sp. and the larger one is presumed to belong to the genus Amphidinium. Worm-infested colonies of the soft coral, Stereonephthya cundabiluensis, lacked a mucus layer and exhibited distinct cell microvilli, a phenotype not present in colonies lacking Waminoa sp. In most cases, both cnidarian and Acoelomorph hosts displayed high specificity for genetically distinctive Symbiodinium spp. These observations show that the epizoic worms do not acquire their symbionts from the “host” coral.     

Ultraviolet absorption in transparent zooplankton and its implications for depth distribution and visual predation

The use of transparency as camouflage in the epipelagic realm is complicated by the presence of ultraviolet radiation, because the presence of UV-protective pigments decreases UV transparency and may reveal transparent zooplankton to predators and prey with UV vision. During July 1999, September 1999, and June 2000, transparency measurements (from 280 to 500 nm) were made on living specimens of 15 epipelagic (collection depth: 0–20 m, average: 11 ± 1 m) and 19 mesopelagic (collection depth: 150–790 m, average: 370 ± 40 m) species of transparent zooplankton from Oceanographer Canyon and Wilkinson Basin in the Northwest Atlantic Ocean. In addition, measurements of downwelling irradiance (from 330 to 500 nm) versus depth were made. The tissues from epipelagic zooplankton had lower UV transparency than those from mesopelagic zooplankton, while the average visible transparency (at 480 nm) of the two groups was not significantly different. Percent transparency was positively correlated with wavelength over most of the measured range, with a rapid decrease below a certain cutoff wavelength. In mesopelagic tissues, the cutoff wavelength was generally 300 nm. In epipelagic tissues, the cutoff wavelength was between 300 and 400 nm. Twelve out of 19 epipelagic tissues had transparencies at 320 nm that were half or less than their 480 nm transparency values, versus only 4 out of 21 mesopelagic tissues. The effects of UV absorption on UV visibility and minimum attainable depth were modeled using contrast theory and the physics of light attenuation. Because UV absorption was generally significantly greater in the UVB than in the UVA spectrum (where UV vision occurs), and because the highest UV absorption was often found in less transparent individuals, its modeled effects on visibility were slight compared to its effects on minimum attainable depth. Received: 14 April 2000 / Accepted: 16 November 2000     

Ecological role of stomatopods (mantis shrimps) and potential impacts of trawling in a marine ecosystem of the southeast coast of India

Ecosystems are balanced by nature and each component in the system has a role in the sustenance of other components. A change in one component would invariably have an effect on others. Stomatopods (mantis shrimps) are common and ecologically important predatory crustaceans in tropical marine waters. The ecological role of mantis shrimps and potential impacts of trawling in a marine ecosystem were estimated using Ecopath with Ecosim (EwE) Version 5.0 software, by constructing a mass balanced Ecopath model of Parangipettai (Porto Novo) ecosystem. Based on fisheries information from the region, 17 ecological groups were defined including stomatopods. Both primary and secondary data on biomass, P/B, Q/B and diet composition were used as basic inputs. The mass balanced model gave a total system throughput of 14,756 t km⁻² year⁻¹. The gross efficiency of 0.000942 indicated higher contribution of lower food chain groups in the fishery though the mean trophic level was 3.08. The immature and developing stage of the ecosystem was indicated by the ratio of total primary production and total respiration (1.832) and the net system production (2643.30 t km⁻² year⁻¹). Key indices (flow to detritus, net efficiency and omnivory index), split mortality rates and mixed trophic impact of different ecological groups were obtained from the model. A flow diagram was constructed to illustrate the trophic interactions, which explained the biomass flows in the ecosystem with reference to stomatopods. Two temporal simulations were made, with 10 year durations in the mass balanced Ecopath model by using ecosim routine incorporated in EwE software. The effect of decrease in biomass of stomatopods in the ecosystem was well defined, in the first run with increase in stomatopod fishing mortality, and the group showed a high positive impact on benthopelagic fish biomass increase (129%). The simulation with increase in trawling efforts resulted in the biomass decline of different ecological groups as elasmobranchs to 1%, stomatopods to 2%, crabs and lobsters to 36%, cephalopods to 63%, mackerel to 78%, and shrimps to 89%. Present study warns stomatopod discards and further increase in trawling efforts in the region and it explained the need for ecosystem based fisheries management practices for the sustainability of marine fisheries.     

Evidence for behavioral sensitivity to near-UV light in the deep-sea crustacean Systellaspis debilis

The role of UV light in the deep-sea environment has been discounted in the past, due to the assumptions that (1) there is insufficient UV light available for vision and, therefore (2) deep-sea organisms would not be sensitive to these wavelengths. A recent study that employed electrophysiological techniques on dark-captured deep-sea crustaceans demonstrated that several species of deep-sea crustaceans possess very high sensitivity to near-UV light. The current study was undertaken to determine if near-UV light would also elicit a behavioral response from these species. The species studied was Systellaspis debilis, an oplophorid shrimp whose daytime depth ranges from 600 to 700 m. A method for tethering shrimp was developed which allowed them to freely orient in response to changes in the ambient light field. Behavioral responses to changes in ambient light included changes in body tilt with respect to the horizontal plane, changes in swimming speed, and movement of the feeding appendages. These experiments, the first of their kind on a deep-sea organism, demonstrate that behaviorally, S. debilis is equally sensitive to very low intensities of blue-green and near-UV light.     

Evolutionary relationships of deep-sea hydrothermal vent and cold-water seep clams (Bivalvia: Vesicomyidae): results from the mitochondrial cytochrome oxidase subunit I

Phylogenetic relationships among vesicomyid clams (Bivalvia: Vesicomyidae) and their placement within the order Heterodonta were examined using mitochondrial encoded cytochrome oxidase subunit I (COI) DNA sequences. The presently analyzed vesicomyids represent a recent monophyletic radiation that probably occurred within the Cenozoic. Nucleotide phylogenetic analyses resolved discrete clades that were consistent with currently recognized species: Calyptogena magnifica, C. ponderosa, Ectenagena extenta, C. phaseoliformis, Vesicomya cordata, Calyptogena n. sp. (Gulf of Mexico), C. kaikoi, C. nautilei, C. solidissima and C. soyoae (Type-A). However, specimens variously identified as: V. gigas, C. kilmeri, C. pacifica, and V. lepta comprised two “species complexes”, each composed of multiple evolutionary lineages. Most taxa are limited to hydrothermal-vent or cold-seep habitats, but the “vent” versus “seep” clams do not constitute separate monophyletic groups. Current applications of the generic names Calyptogena, Ectenagena, and Vesicomya are not consistent with phylogenetic inferences. Received: 24 July 1997 / Accepted: 22 August 1997     

Heavy metal contamination and physiological variability in the Brazilian mangrove crabs Ucides cordatus and Callinectes danae (Crustacea: Decapoda)

 Physiological studies were made on the crabs Ucides cordatus (L.) and Callinectes danae sampled from populations living in “polluted” mangroves on the southeast littoral of Brazil. Analysis of Cu, Cd, Zn, and Fe of sediments and crab tissues showed interspecific differences in tissue concentrations, and significantly higher levels of Cu, Cd, and Zn in “polluted” populations compared to “unpolluted” crabs living in uncontaminated mangrove in the same geographical area. Individuals of both species from the polluted site showed significantly greater capacities for regulating blood osmotic concentrations at low salinity (9‰). However, U. cordatus showed a reduced hypo-regulatory ability in 34‰S. Differences in ionoregulation were also seen. “Polluted”C. danae showed significantly higher Na/ K-ATPase levels in posterior gills compared to “unpolluted” crabs. Oxygen consumption rates (M˙ _O2) were elevated in U. cordatus, but depressed in C. danae from the “polluted” population. Individuals of both species from this site showed significantly lower O:N ratios, mainly because of an increased net efflux of ammonia. Adenylate energy charge (AEC) values of muscle and hepatopancreas in “unpolluted” and “polluted” populations of both species were not significantly different. These physiological differences are discussed in relation to the known acute physiological and metabolic effects of heavy metals in crustaceans, and interpretated in the light of possible adaptive changes following long-term exposure to contamination. Received: 6 August 1999 / Accepted: 22 June 2000