Fish species richness decreases with salinity in tropical coastal lagoons

Aim To analyse the relationship between fish species richness and salinity, and to provide a simple linear model for fish diversity trends across salinity gradients in a tropical coastal lagoon that can be compared with other similar ecosystems and other communities. To reinforce our conclusions, the salinity–fish richness relationship was investigated at different spatial scales (sampling station, set of stations and whole lagoon) and for two different periods, separated by 18 years. Location The Terminos coastal lagoon, a shallow tropical lagoon (mean maximum depths ranging between 3.5 and 4.5 m), is located in the southern Gulf of Mexico (18.5–18.8° N, 91.3–91.9° W). The lagoon is 70 km long and 30 km wide, with a surface area of 1700 km². Methods Fish sampling, individual identification to the species level, and environmental variable measurements were carried out monthly at 17 sampling points. Multiple regression analysis with a backward selection procedure was used to relate fish species richness to environmental variables. Other statistical techniques, including cluster analysis and ancova , were applied to experimental data surveys. Results Among the different environmental variables, salinity was significantly and consistently related to fish species richness, whatever the period and the scale of observation. We found mainly significant negative correlations (P < 0.05) between fish species richness and salinity when sampling stations were analysed individually, and particularly for the river runoff zones with high variation in salinity throughout the year. For the entire lagoon, robust negative linear models were observed when fish species richness was organized into salinity ranges, with salinity explaining c. 8% of the variation in mean fish species richness (in a multiple regression analysis; 63–93% when considered in isolation). Main conclusions In the Terminos lagoon the relationship between fish species richness and salinity is mainly negative on any spatial scale. This result may be due partially to the penetration of freshwater fishes into estuarine areas following freshwater discharges, and partially to the dominance of estuarine taxa more able to tolerate low than high salinity values. Finally, we suggest that the ‘realized’ ecotone, where species from different origins really mix, is situated between 5 and 10‰, corresponding to the highest fish richness.     

Combinations of biological attributes predict temporal dynamics of fish species in response to environmental changes

Assessing species vulnerability to environmental changes is a major challenge for conservation. Combinations of biological attributes have already been successfully used for this purpose, allowing large-scale prediction of inter-specific differences in demographic parameters (e.g. abundance) or endangered status. However, studies investigating whether biological attributes could be used to predict the temporal demographic responses of species in a changing environment are still scarce. In this work, we tackled this issue by taking advantage of a multi-decadal survey of concomitant changes in fish communities and environmental conditions within the Terminos lagoon (Mexico). Based on this rare dataset, we first characterized changes in abiotic parameters that occurred in this ecosystem since the 80s. Then, we adapted a multivariate index accounting for changes in both species abundance and occurrence to assess concomitant demographic changes for the 25 dominant fish species in the lagoon, classifying them into five various types of trajectories (“Increasing”, “Decreasing”, “Constant”, “Hump-shape” and “U-shape”). Finally, we assessed the accuracy in prediction of these temporal responses for all possible combinations of 15 biological attributes including taxonomy, ecological and life-history traits.Our results showed that fish specific demographic changes over the last 30 years could be accurately predicted (72% accuracy) using a combination of five biological attributes (spawning season, order, maximum salinity, width of salinity range, oocyte size) among which three could be related to the increase in average salinity occurred in the lagoon over this period. Appropriate sets of complementary biological attributes could similarly allow prediction of inter-specific differences in demographic changes in other areas, thereby offering an additional pragmatic tool for ecosystem managers to identify vulnerable species at the local scale.     

Fish cell lines: Two new cell lines derived from explants of trunk musculature ofCynoscion arenarius

Summary Two cell lines were established from explants of trunk musculature of healthy, males sand seatrout,Cynoscion arenarius. One of the lines, designated CyA-1, has been carried through 150 subcultures during 6 yr. The other, designated CyA-2, has been carried through 100 subcultures during 2 yr. Both lines grow well in L15 medium adjusted to 0.150M NaCl and supplemented with 10% fetal bovine serum. Optimal growth occurs at temperatures between 24 and 30°C. The species of origin of both lines was confirmed by a cytotoxic antibody dye exclusion test. The karyotype of CyA-1 has not yet stabilized, showing a modal chromosome number of 120 at Passage 9, 89 at Passage 63, and 79 at Passage 100. The karyotype of CyA-2 is rather stable, with a modal chromosome number of 47 at Passage 1 and 49 at Passage 100. Chromosome morphology of CyA-2 is homogeneous (small, acrocentric), whereas the chromosomes of CyA-1 show considerable size variation (with small chromosomes possibly formed from fragmentation of original structures). Both lines were found to be free of bacterial or fungal contamination. Both lines supported replication of lymphocystis virus strains isolated fromBairdiella chrysura (the silver perch) and fromMicropogon undulatus (the Atlantic croaker) but were refractory to 11 other viruses (4 from fish, 1 from amphibians, and 6 from mammals). This study was supported in part by the National Oceanographic and Atmospheric Administration, Office of Sea Grant No. 04-3-158-58.     

Binding characteristics, hormonal regulation and identity of the sperm membrane progestin receptor in Atlantic croaker

Recently a novel cDNA was discovered in spotted seatrout ovaries encoding a protein with seven transmembrane domains that has the characteristics of the membrane progestin receptor (mPR) mediating maturation-inducing steroid (MIS) induction of oocyte maturation in this species. Preliminary results suggested the MIS also activates an mPR on the spermatozoa of spotted seatrout and a closely related species, Atlantic croaker, to stimulate sperm motility. We show here that plasma membranes of croaker sperm demonstrate high affinity (Kd approximately 20 nM), limited capacity (Bmax 0.08 nM), specific and displaceable binding for progestins that is characteristic of mPRs. The MIS (17,20beta,21-trihydroxy-4-pregnen-3-one, 20beta-S) displayed the greatest binding affinity for the sperm mPR among the steroids tested. Treatment of croaker testicular tissue in vitro with gonadotropin caused a several-fold increase in sperm mPR receptor concentrations that was partially blocked in the presence of cyanoketone, which suggests this action of gonadotropin is partially mediated by stimulation of steroidogenesis. Protein bands of the predicted sizes for the mPR and its dimer (40 and 80 kDa) were detected by Western blotting of croaker sperm membranes using a specific antibody to the novel seatrout mPR (mPRalpha). Immunocytochemistry of whole croaker spermatozoa with the mPRalpha antibody showed that staining was primarily localized on the midpiece, consistent with a role of the mPRalpha in mediating MIS stimulation of sperm motility. The results suggest that the mechanism of progestin action on fish sperm involving mPRs is basically similar to that in mammals and has been evolutionarily conserved amongst vertebrates.     

Behavioral specialization in developing sciaenids and its relationship to morphology and habitat

Behavioral development of three species of marine sciaenid fish larvae was examined and related to their sensory morphology and habitat. Anti-predator behavior of the larvae was examined under different experimental conditions to isolate the roles of vision and mechanoreception. Spotted seatrout larvae maintained high levels of responsiveness even without visual cues but performed very poorly without mechanoreception. Loss of visual cues had no impact on the distance at which seatrout responded to the stimulus. Atlantic croaker generally performed best when vision was available. This species had low responsiveness without visual stimuli, and had smaller reactive distances when unable to use vision. Red drum were the most flexible in their use of sensory systems. For almost the entire larva period, responsiveness of red drum was equally high regardless of which sensory system was not available. In addition, reactive distances were unaffected when either visual or mechanoreceptive stimuli were eliminated. Thus, seatrout and croaker are sensory specialists, and red drum are sensory generalists. This is corroborated by previous studies on the sensory morphology of these species which showed that seatrout had more mechanosensory specialization, croaker had more visual specialization, and red drum were intermediate, with some enhancement of both systems. Behavioral data are interpreted in terms of habitat usage of the three species. Seatrout have the most restricted distribution over seagrass beds, croaker have a somewhat more flexible distribution, encompassing more open water habitats, and red drum have the most flexible range of habitats, using both vegetated and unvegetated portions of the estuary. These results indicate that even closely related species can exhibit different behaviors in order to better exploit the habitats in which they occur.     

Analysis of fish parasitofauna in Vistula Lagoon (the Baltic Sea)

The characteristics of parasitofauna (81 species) of 15 fish species from Vistula Lagoon (the Baltic Sea) are given. Parasites with a direct developmental cycle dominate. Parasites with a complicated developmental cycle are represented mainly by species developed through zoobenthos. Some of the parasites testify to the deterioration of the ecological state of the lagoon. A zoogeographic analysis of fish parasitofauna has shown the presence of five faunistic complexes. In Vistula Lagoon freshwater species dominate, but marine species are also recorded. Species that appeared in the lagoon as a result of human commercial activity are also registered.     

Influence of environmental changes in the north-western Atlantic Ocean on a parasite, Echinorhynchus gadi (Acanthocephala) of Atlantic cod ( Gadus morhua) occurring off coastal Labrador, Canada

A study was conducted to determine the influence of environmental change on an endoparasite, Echinorhynchus gadi (Acanthocephala) of Atlantic cod (Gadus morhua) over a 30-year period off the coast of Labrador in the north-western Atlantic, North Atlantic Fisheries Organization subareas 2J-3K. Cod, once an abundant fish species that had been commercially exploited for many decades, declined precipitously during the mid-1980s onwards. This decline was attributed to climatic changes that affected the entire food chain from zooplankton to fish, sea birds and marine mammals. A monitoring programme was introduced, sampling cod by otter trawling using research vessels. The fish, after capture, were frozen at - 20 degrees C, subsequently thawed and the digestive tract removed and examined for the parasite in 2006. Data from samples taken in 1976, 1980-81, 1986, 1990, 2000 and 2003 were compared statistically with those collected in 2006. The results indicate a decline in the prevalence and mean abundance of E. gadi in 1986 with a minimum in 2000 but increasing gradually in 2003 and 2006. These changes were coincident initially with a decline of oceanic temperature and the entire food web, including capelin (Mallotus villosus), a preferred prey of cod and primary source of E. gadi. The increase in prevalence and mean abundance of the parasite in 2006 were associated with an increase of oceanic temperature and the return of small schools of capelin to offshore areas. Cod older than 4 years harboured a greater abundance of E. gadi than younger fish, while no difference was observed between the sexes. The results suggest that the abundance of E. gadi can be useful as a bioindicator of environmental changes in the north-western Atlantic.     

A dispersal-dependent zone of introgressive hybridization between weakfish, Cynoscion regalis, and sand seatrout, C. arenarius, (Sciaenidae) in the Florida Atlantic

Five diagnostic codominant nuclear DNA markers and a diagnostic mitochondrial DNA marker were used to survey weakfish (Cynoscion regalis) and sand seatrout (C. arenarius), with particular focus on heretofore uncharacterized juvenile populations along the Florida (FL) Atlantic coast. Geographic and reproductive ranges of weakfish and sand seatrout were shown to overlap on the Atlantic coast along north and central FL. An active bidirectional zone of introgressive hybridization exists between these taxa, centered in the St Johns River, FL. Strong patterns of Hardy-Weinberg, linkage, and cytonuclear disequilibrium and a bimodal hybrid index distribution were observed for juvenile cohorts in the zone center, coupled with narrow (～240 km) concordant clines. Parental forms had disparate habitat preferences; hybrid forms occurred predominantly in intermediate habitats. All genetic data were consistent with the hypothesis that the C. arenarius-C. regalis hybrid zone is maintained by a dynamic equilibrium between continued interspecific gene flow and one or more opposing forces. Cytonuclear analyses indicated that parental forms mate assortatively in the zone but that mate recognition was imperfect. Ethological mating dynamics are likely stabilized by some form of endogenous or exogenous postfertilization selection against hybrids such that parental taxa will likely continue to evolve independently.     

Biochemical studies on Brachionus plicatilis: hydrolytic enzymes,integument proteins and composition of trophi

In Terminos Lagoon, México, more than 80 fish species use the mangrove and seagrass habitats. We studied nekton dynamics in an inlet seagrass system and a more sheltered seagrass/mangrove system located behind a barrier island. Seasonal community biomass ranges from 0.6 to 5.2 g wet wt m^-2. For the two habitats together, there are 28 dominant species. Eleven species were common to both areas: Sphoeroides testudineus (Linnaeus, 1758), Archosargus rhomboidalis Linnaeus, 1758, A. probatocephalus (Walbaum, 1792), Arius felis (Linnaeus, 1766), A. melanopus (Gunther, 1864), Eucinostomus gula (Cuvier & Valenciennes, 1830), Bairdiella chrysoura (Lacépède, 1803), Orthopristis chrysoptera (Linnaeus, 1766), Chilomycterus schoepfi (Walbaum, 1792), Opsanus beta (Goode & Bean, 1879) and Lutjanus griseus (Linnaeus, 1758). Ten species used exclusively the inlet seagrass system: Urolophus jamaicensis (Cuvier, 1817), Haemulon aurolineatum (Cuvier, 1829), H. bonariense (Cuvier, 1830), H. plumieri (Lacépède, 1802), Anisotremus virginicus (Linnaeus, 1758), Odontoscion dentex (Cuvier, 1830), Corvula sanctae-luciae (Jordan, 1890), Nicholsina usta (Valenciennes, 1839), Stephanolepis hispidus (Linnaeus, 1766) and Diodon hystrix Linnaeus, 1758. Seven species were dominant only in the seagrass/mangrove system: Anchoa mitchilli (Cuvier & Valenciennes, 1848), Scorpaena plumieri Bloch, 1789, Cynoscion nebulosus (Cuvier & Valenciennes, 1830), Diapterus rhombeus (Cuvier & Valenciennes, 1830), Bairdiella ronchus (Cuvier & Valenciennes, 1830), Cichlasoma urophtalmus (Günther, 1862) and Acanthostracion quadricornis (Linnaeus, 1758). Comparative analysis showed that periodic variation in biomass and diversity of fish assemblages in seagrass and seagrass/mangrove habitats were synchronized with sizes and densities of population, season of the year (dry, wet, ‘nortes’), circulation pattern, and patterns of primary production (phytoplankton, Thalassia testudinum Konig, 1805; and Rhizophora mangle Linnaeus). This analysis allowed the definition of 3 life-cycle patterns with a clear nektonic ‘seasonal programming’ following the timing of primary production in these critical habitats: (1) marine species which spawn in or near the inlet with eggs and larvae transported into and distributed throughout the lagoon by the predominant currents; (2) estuarine-marine species which spawn in different habitats of the lagoon and use the seagrass/mangrove system as a nursery area, and (3) species which complete their life history in the inlet seagrass and/or seagrass/mangrove systems. EPOMEX Program Contribution No. 0026.     

Evidence for a role of Na+,K(+)-ATPase in the hydration of Atlantic croaker and spotted seatrout oocytes during final maturation.

During final maturation the oocytes of many marine teleosts swell four to five times their original size due to uptake of water. The involvement of active inorganic ion transport and Na+,K(+)-ATPase in oocyte hydration in Atlantic croaker (Micropogonias undulatus) and spotted seatrout (Cynoscion nebulosus), marine teleosts which spawn pelagic eggs, was investigated by examining changes in the inorganic ion content of ovarian follicles containing mainly oocytes, by performing in vitro incubations of the follicles with ion channel blockers, and by assaying membrane preparations of ovaries containing hydrating and non-hydrating oocytes for Na+,K(+)-ATPase activity and content. There were marked increases in the contents of K+, Mg++, and Ca++, but not Na+, in oocytes of M. undulatus and C. nebulosus during hydration. Incubation of follicle-enclosed oocytes in K(+)-free medium or with ouabain or amiloride, inhibitors of Na+,K(+)-ATPase and Na+ channels, respectively, blocked gonadotropin-induced oocyte hydration in M. undulatus. In addition, Na+,K(+)-ATPase activity increased threefold and the concentration of the enzyme increased 50% in ovarian tissue during oocyte hydration. These results strongly suggest a major role for active ion regulation by a ouabain-sensitive Na+,K(+)-ATPase system in oocyte hydration in two species of sciaenid fishes.     

Ecosystem indicators: Foraminifera,Thecamoebians and Diatoms from the Ologe Lagoon,Nigeria

The Ologe Lagoon in southwestern Nigeria is a natural habitat located closely to both residential and industrial estates. The lagoon is heavily affected by effluents of agricultural and industrial runoff including organochlorine compounds and heavy metals (chloropesticides, DDT and polychlorinated biphenyls, cadmium, manganese, zinc, copper, lead, iron and nickel). Ologe Lagoon is situated in a semi-isolated position and its brackish waters traverse several creeks and lagoons before it reaches the Atlantic Ocean. The lagoon experiences minor tidal but noticeable salinity and pH variations during the rainy season. During the dry season, however, the waters have a comparatively long resident time where sediments act as sink and aggregate contaminants over time. Investigations on benthic foraminifera, thecamoebian and diatom species were carried out to document the current status, composition, spatial distribution, and response of microfaunal assemblages to environmental stressors within the lagoon. The benthic foraminifer assemblage is composed of four highly specialized agglutinated species of Ammotium salsum, Miliammina fusca, Ammobaculites dilatatus and Ammobaculites aff. A. exiguus. They are present at all sample sites with varying abundances. The high abundance of Ammotium salsum is considered an indication of environmental stress. Thecamoebian species of Difflugia oblonga, Difflugia proteiformis and Pontigulasia compressa were also recorded in varying proportions and generally represent less than one percent of the total foraminifera/thecamoebian assemblage. The presence of marine brackish water larger siliceous diatoms of Actinoptychus and Campylodiscus species indicates an interaction between the lagoon and the marine waters although on the minimal scale with regards to actual salinity ranges. The faunal assemblages recovered are characterized by low species richness and alpha diversity indices and are typical of shallow, marginal-marine hyposaline environments. Numerical abundances and spatial distribution patterns suggest taxon-specific habitat preferences and highlight their potential for environmental monitoring studies.     

The benthic fauna of Sabancuy Estuary, Campeche, Mexico]

The fish and invertebrates community structure in the Sabancuy estuary was analyzed in two seasons and 14 sampling stations (13 along the estuary and one in the marine adjacent coast). No significant differences were found between seasons. The environmental frame defines two zones within the estuary, the first extends from the access highway to Sabancuy town until the Pujo mouth in the west; the second from the bridge to the estuary head in the east. The most abundant invertebrates were mollusks (51.8% of the total), in biomass the crustaceans dominated. The fish included 21 families and 33 species; the most abundant were Gerridae, Scianidae, Sparidae, Lutjanidae and Ciprinodontidae. The highest diversities of both communities correspond to the central part of the estuary. These communities include three sections with notable differences in faunal distribution: one is influenced by the exit to Terminos lagoon, the secondary in the estuary head and a third is in a transition zone defined by the proximity of the town access bridge. The ecological organization suggests a strong division caused by the bridge, both sides are scarce in habitats and nutrient resources and this is reflected in the low species counts.     

Distribution, abundance and population parameters of Diapterus rhombeus (Pisces: Gerreidae) in Laguna de Términos, Campeche, Mexico

Diapterus rhombeus dominates the nektonic community of Terminos Lagoon and is associated to zones with submerged vegetation, temperatures between 27 and 33 degrees C and salinity between 25 and 36.5 UPS. A total of 3,024 individuals were collected with a trawl net in 23 sites between September 1997 and September 1998. The length-weight model parameters are a = 0.0098; b = 3.155 with a 96% correlation. The growth parameters are L infinity = 20.4 cm, k = 0.74 and t(o) = -4.207 and the total mortality coefficient is 3.526. Fish length is 2.5-18.0 cm with a mode of 7.5 cm. Recruitment is continuous with a peak from May to August. The species uses several habitats of the lagoon mainly for feeding and growth, reproduction probably occurs in the adjacent continental shelf. Movements between continental shelf and the estuarine system represent a continuous energy flow.     

Macrozoobenthic community structure in the Lagoon of Albufeira,western coast of Portugal

A benthic survey of the Lagoon of Albufeira on the western Atlantic coast of Portugal, based on macrofaunal analyses from 50 subtidal sampling stations has provided initial data for a study of the benthic ecology of that system. The 126 species identified revealed that the overall faunal composition is characteristic of both Atlantic and Mediterranean lagoons, with the greatest proportion of the species occurring at low frequencies.A correspondence analysis of the distribution of species among sampling stations identified two areas characterized by different communities. In the vicinity of the lagoon mouth a coarse, clean sand community was delineated from a mixed inner lagoon community associated with mixed sediments, ranging from coarse and medium sand with variable percentages of silt, to mud with up to 90% silt content. In deeper areas this lagoon community was considerably impoverished, a condition attributable to intermittent stagnation of the bottom water.A coenotic model of the Lagoon of Albufeira is proposed and related to the hydrodynamics of the system and to the distribution of the superficial sediments.     

Structure and diversity of fishes in a freshwater and coastal subtropical lagoon

This study examined the fish communities of Peri Lagoon in southern Brazil to aid in the development of an effective management plan because the area is under threat from human activities. Sampling of fish fauna, ichthyoplankton and limnological data were compared between sites, differing by habitat type and characteristics such as depth, substratum composition and vegetation type. Results were significantly related to site, with the highest diversity and abundance recorded at shallow vegetated sites. A total of 14 fish species were recorded throughout the lagoon, with the most abundant being Hyphessobrycon luetkenii. Of the 14 species, half were sampled at their larval stage, suggesting a healthy and protected system. Significantly more larvae and eggs were collected during colder months (autumn to winter) and at sites closer to stream flow, possibly owing to increased food sources and habitat protection. This study highlights the importance of Peri Lagoon as a nursery ground for a wide range of fish species, providing essential information for incorporation into the future protection of fish stocks throughout Brazil.     

Multiple rapid progestin actions and progestin membrane receptor subtypes in fish

Progestin hormones exert rapid, nongenomic actions on a variety of target tissues in fish. The induction of oocyte maturation and the progestin membrane receptor (mPR) that mediates this action of progestins have been well characterized in fishes. Progestins also act on Atlantic croaker spermatozoa via an mPR to rapidly increase sperm motility. Preliminary results indicate that progestins can also exert rapid actions in the preoptic anterior hypothalamus (POAH) in this species to down-regulate gonadotropin-releasing hormone (GnRH) secretion. Recently, we reported the cloning, sequencing and characterization of a novel cDNA in a closely related species, spotted seatrout, that has the characteristics of the mPR involved in the progestin induction of oocyte maturation. Three distinct mPR subtypes, named alpha, beta, and gamma, have been identified in both fishes and mammals. The tissue distribution of the mPRalpha protein in seatrout suggests the alpha-subtype mediates progestin actions on GnRH secretion, sperm motility and oocyte maturation. However, mPRbeta antisense experiments in zebrafish oocytes suggest the beta-subtype also participates in the control of oocyte maturation in zebrafish.     

Fish Assemblages in Different Shallow Water Habitats of the Venice Lagoon

The small-sized fish assemblages of the Venice Lagoon were investigated and compared among five shallow subtidal habitats (seagrass beds, sparsely vegetated habitats, unvegetated sand bottoms, mudflats and saltmarsh creeks) in the Northern lagoon basin. Sampling was carried out seasonally (Spring, Summer and Autumn of 2002) in 4–7 stations for each habitat type, by means of a fine-mesh, small beach seine. Two-way analysis of variance was applied to assess the differences in species richness, fish diversity, density and standing stock amongst habitats, whereas fish assemblage composition was investigated by using multivariate analyses (MDS, ANOSIM, SIMPER). The analyses indicated that seagrass beds and saltmarsh creeks are relevant shallow habitats in structuring the small-sized fish assemblages of the Venice Lagoon, supporting specialized and recognizable fish assemblages. Those in seagrass beds, in particular, were characterized by higher species richness and standing stock with respect to all the others. The structuring role of these habitats was discussed in terms of both habitat complexity and degree of confinement. In contrast, sandy bottoms, mudflats and sparsely vegetated habitats were identified as “transition” habitats, with highly variable fish assemblages, influenced by the contribution of the adjacent habitats, and acting probably as both ‘buffer zones’ between the other habitats and migration routes for many fish species in the lagoon.