Morphological variability of geographically distinct populations of the estuarine copepod Acartia Tonsa

Variations in the number of spines on the left and right posterior dorsal and posterior margins of the prosome as well as the length of the prosome of Acartia tonsa from three estuaries, the upper western side of the Chesapeake Bay, Montauk Bay near the eastern end of Long Island Sound and the coast of Peru were determined. The length of the prosome and number of spines in each of the four locations were used as an indication of morphological similarity between the populations.     

Stable isotopic structure of aquatic ecosystems

Isotopic, biogeochemical and ecological structure can provide a new dimension for understanding material flows, and the simultaneous function and structure of an ecosystem. Distributions ofδ ¹³C andδ ¹⁵N for biogenic substances in the Nanakita river estuary involving Gamo lagoon in Japan were investigated to construct isotope biogeochemical and ecological structure for assessing fate and transfer of organic matter, and food web structure. The isotopic framework of the ecosystem was successfully described in aδ ¹⁵N–δ ¹³C map. In this estuary the variations of isotope ratios of biogenic substances were clearly explained by the mixing of land-derived organic matter, and marine-derived organic matter. A trophic-level effect of¹⁵N enrichment was clearly observed. Organisms were classified into three groups depending upon the contribution of land-derived organic matter in a food chain. Almost all biota except mollusca in the lagoon depend on organic matter of marine origin. The contributions of both land and marine organic matter were comparable for mollusca in the lagoon.     

Marine genetic swamping: hybrids replace an obligately estuarine fish

Populations of obligately estuarine taxa are potentially small and isolated and may lack genetic variation and display regional differentiation as a result of drift and inbreeding. Hybridization with a wide‐ranging marine congener should introduce genetic variation and reduce the effects of inbreeding depression and genetic drift. However, high levels of hybridization can cause demographic and genetic swamping. In southeastern Australia hybridization occurs between obligately estuarine Black bream (Acanthopagrus butcheri) and migratory marine Yellowfin bream (Acanthopagrus australis). Here, we surveyed genetic variation at eight microsatellite loci and the mitochondrial control region of juvenile fish from five coastal lagoons (including temporal replication in two lagoons) (total n = 970) to determine the frequency and persistence of hybridization, and its likely consequence for the estuarine restricted A. butcheri. Of 688 juvenile fish genotyped 95% were either A. australis (347) or hybrids (309); only 5% (32) were A. butcheri. Most hybrids were later generation hybrids or A. butcheri backcrosses, which are likely multi‐generational residents within lagoons. Far greater proportions of hybrid juveniles were found within two lagoons that are generally closed to the ocean (>90% hybrid fish within generally closed lagoons vs. 12–27% in permanently or intermittently open lagoons). In both lagoons, this was consistent across multiple cohorts of fish [79–97% hybrid fish (n = 282)]. Hybridization and introgression represent a major threat to the persistence of A. butcheri and have yet to be investigated for large numbers of estuarine taxa.     

Ichnofossils of the Psilonichnus Ichnofacies and Their Paleoecological and Paleoenvironmental Significance in the Scottish Middle Jurassic

In the Bathonian (Middle Jurassic) Kilmaluag Formation, Great Estuarine Group, on the Isle of Skye, northwest Scotland, are ichnofossils that can be attributed to the burrowing activity of semi-terrestrial crab-like animals. The ichnofossils are preserved within supralittoral breccia-conglomerates and littoral calcareous mudstones and micrites deposited in a closed and shallow, low-salinity to freshwater coastal-lagoon setting. The dominant ichnofossil assemblage is preserved in the supralittoral rocks and comprises variable burrow types forming an ichnocoenosis and assigned to the Psilonichnus ichnofacies. These ichnofossils potentially provide the earliest known record of crab activity and their physiological adaptation to survive in a semi-terrestrial environment. Burrow characteristics include enlarged funnel-shaped apertures, unlined walls, absence of branching or biogenic reworking, inclined to vertical, U- and L-shaped forms and possible basal dwelling chamber. The ichnofossil assemblage preserved in the littoral rocks is attributed to the activity of either semi-terrestrial crabs or shrimps. Ichnofaunal characteristics reveal unique aspects of the paleoenvironments and paleoecology of the tracemaking community, including climatic conditions, substrate characteristics, the possible influence of paleowater table levels, paleoshoreline position, spatial variation in burrow morphology and possible gregarious and territorial behavior.     

Evaluation of a eutrophic coastal lagoon ecosystem from the study of bottom sediments

Morphological reconstruction and biogeochemical characterisation of the lagoon of Comacchio (Italy) were carried out in order to provide recommendations for the recovery, conservation and sustainable management of the Fattibello-Spavola coastal lagoon ecosystem. Samples were taken in two seasons: July 1997 and November 1998. The irregular morphology of the Fattibello lagoon affects depositional processes and seawater exchange (tidal currents). Several depressions retain part of the dense water of the saline wedge; these stagnant waters became sinks for fine terrigenous and organic matter. The basin is already extensively supplied with N and P compounds from land. The inflow is demonstrated by the large quantity of organic C, N and organic and inorganic P compounds in the superficial sediment. The ratios between the various forms of macronutrients indicate that the organic matter is primarily of autochthonous origin, with relatively low C/N ratios (8.4±0.6 and 8.1±0.6 in July and November, respectively). Shallow areas were almost always oxygenated by tidal currents and thus rich in organisms, with a predominance of molluscs and Ficopomatus enigmaticus. However, the trophic equilibrium of the ecosystem was affected by the accumulation of organic matter in the depressions, favoured by the increased hydrodynamics during the autumn. These accumulations generate high oxygen consumption and release considerable quantities of nutrients into the water column, with the risk of serious dystrophy throughout the basin during the summer. Local dredging and an improvement of the circulation have been suggested and carried out to contain these processes. Reclamation measures in the longer term were proposed.     

Evidence of a planktonic food web response to changes in nutrient input dynamics in the Mar Menor coastal lagoon,Spain

Nutrient input dynamics in the Mar Menor coastal lagoon has recently changed as a consequence of changes in agricultural practises. An interannual comparison of the environmental variables and the planktonic biomass size-spectra was performed between 1988 and 1997. While nitrate concentration was low in 1988, the values in 1997 increased considerably. Since 1995, two alloctonous jellyfish species (Rhyzostoma pulmo and Cotylorhiza tuberculata) occurred in large numbers in summer time and reached peak abundance in summer of 1997. The size-spectra analysis comparison revealed that, in spite of changes in nutrient input that stimulated the growth of larger phytoplankton cells, there were no significant differences in the spectra slope which followed a similar seasonal trend in both years. However, the plankton biovolume considered under the size range compared (between 2 and 1000 m diameter) was, paradoxically, always lower in 1997. Given that there were higher nutrient levels in 1997, this finding suggest a strong top-down control mechanism of size structure. Gut contents of jellyfishes showed their preference for large diatoms, tintinnids, veliger larvae and copepods, corroborating that size structure in these assemblages can be subject to top-down control. The implication of these results is that the feeding activities of large gelatinous zooplankton (jellyfishes) may play an important role controlling the consequences of eutrophication within the Mar Menor coastal lagoon.     

The relationship between physical and chemical conditions and low microbial diversity in the Blue Lagoon geothermal lake in Iceland

Abstract: The Blue Lagoon in Iceland is a shallow geothermal lake with average temperatures of 37°C, pH 7.5 and about 2.5% salinity. It was formed in 1976 from the effluents of the Svartsengi geothermal power plant and is saturated with silica which constantly precipitates in the lake. It has been colonized by a few types of specialized microorganisms which seem to proliferate in this unusual ecosystem. The average bacterial colony count in the lake was 1.3 × 10⁵ ml⁻¹ on plate count agar made with 50% Blue Lagoon fluid but 2.6 × 10⁶ ml⁻¹ when determined with the MPN method. A total of 99 isolates were purified and characterized by 54 phenotypic tests and then grouped using Numerical Taxonomy. At similarity values of 80%, one major cluster was formed containing 85% of the isolates. Four representative strains from this cluster were further characterized and all shown to be Gram-negative, obligately aerobic, non-motile rods. They were oxidase positive, catalase negative and grew optimally at 45°C and in 3.5% NaCl with doubling time of about 80 min.     

An integrated physical and biological model for anaerobic lagoons

A computational fluid dynamics (CFD) model that integrates physical and biological processes for anaerobic lagoons is presented. In the model development, turbulence is represented using a transition k-ω model, heat conduction and solar radiation are included in the thermal model, biological oxygen demand (BOD) reduction is characterized by first-order kinetics, and methane yield rate is expressed as a linear function of temperature. A test of the model applicability is conducted in a covered lagoon digester operated under tropical climate conditions. The commercial CFD software, ANSYS-Fluent, is employed to solve the integrated model. The simulation procedures include solving fluid flow and heat transfer, predicting local resident time based on the converged flow fields, and calculating the BOD reduction and methane production. The simulated results show that monthly methane production varies insignificantly, but the time to achieve a 99% BOD reduction in January is much longer than that in July.     

Secondary productivity (3H-Leucine and 3H-Thymidine incorporation), abundance and biomass of the epiphytic bacteria attached to detritus of Typha domingensis pers. in a tropical coastal lagoon

Senescent, naturally dried leaves of Typha domingensis were incubated inthe littoral region of a coastal lagoon and epiphytic bacterial volume,abundance, biomass and secondary productivity were measured during 127 daysof decomposition. The peak of cell abundance was registered at t =127 days when expressed per leaf surface area (10.07×10⁷cells cm^-2; 7.26 µgC cm^-2), and at t= 26 days when expressed per biofilm dry mass (38.10 ×10⁷ cells (mgDM biofilm)^-1, 30.52 µgC(mgDM biofilm)^-1). The highest values of bacterial biovolumesand lower turnover time were usually obtained in the beginning of thecolonization. Leu:Tdr ratios were also higher in the beginning of thecolonization, when bacterial community presented unbalanced metabolism.Consequently, the highest discrepancies between the bacterial secondaryproduction estimated by leu and Tdr incorporation were observed in the first2 days of decomposition. On average, the bacterial secondary productivityestimated by leu incorporation was 2.1 times higher than the valuesestimated by Tdr incorporation when the empirical factor for Tdr wasobtained from the relationship between Tdr and biomass increment. Thisdifference increased to 4.2 when the empirical factor was obtained from therelationship between Tdr and cell numbers increment. An average of bothmethods (0.0037 to 0.1397 µgC cm^-2 h^-1)produced results that fall within the range reported in the literature forepiphytic bacteria of freshwater ecosystems.     

Water current velocity as an environmental factor regulating the distribution of amphipod species in Gamo lagoon, Japan

The role of current velocity as an environmental factor affecting the distribution of amphipod species was investigated in the brackish Gamo lagoon, Japan. Two gammaridean amphipod species, Eogammarus possjeticus and Melita setiflagella, were found inhabiting stations of different water current with same substrates. E. possjeticus and M. setiflagella selected substrates at low and high water current, respectively. The lifestyles and anatomical features of these two free-living amphipods contributed to their adaptation to habitats with different water currents. The results of field and experimental observations suggest the existence of some type of interspecific competition between the two species. The presence of E. possjeticus caused a displacement of the fundamental niche of M. setiflagella. Received: October 10, 2000 / Accepted: August 17, 2001