Recent evolution of fishery and land reclamation in Curonian and Lesina lagoons

The evolution of fishery and land reclamation in Lesina (Italy) and Curonian (Lithuania/Russia) lagoons was analysed as an example of recent trends in European coastal lagoons. Social and political changes were considered, addressing resource exploitation and inherent impacts on ecosystems. In both lagoons, the mismanagement of the fish stock led to the depletion of fish resources and to the decline of commercial fishery. In parallel, vast wetland fringes were reclaimed and turned into intensively managed farmland, with a marked loss of aquatic–terrestrial ecotones. In the last decades, the annual fish yield fell to less than 40 kg ha⁻¹ in the Lesina lagoon, where the fishermen dwindled to 40 units, mostly pensioners rounding off their income. Recently, in the Curonian lagoon, more than 100 small private fishing enterprises were licensed to fish. Overall, the landed catches were difficult to monitor, which resulted in a substantial uncontrolled landing of fish (up to 60% of the fish yield). Under these conditions, the sustainable exploitation of lagoons and their resources can be achieved through an integrated management of watershed and lagoons. The restoration of ecotones, marshes and floodplains and the preservation of semi-natural agricultural ecosystems have to be considered as priorities. Examples of such approach are provided by pilot programs, aiming at the commercial exploitation of the reed belts along the Curonian lagoon fringes. Reed harvesting would increase the acreage of important migration corridors and spawning habitats for fish, also providing an additional income to the local communities. Guest editors: A. Razinkovas, Z. R. Gasiūnaitė, J. M. Zaldivar and P. Viaroli European Lagoons and their Watersheds: Function and Biodiversity     

Peculiarities of under-ice zooplankton in the Curonian and Vistula Lagoons of the Baltic Sea

In the Vistula and Curonian lagoons, respectively, 7 and 9 taxa of under-ice zooplankton have been recorded. Copepoda and rotifera were dominant. Throughout the year, the complex of dominant species was generally constant in the Vistula Lagoon and changed considerably in the Curonian Lagoon. The zooplankton accumulation was found in the surface layer in the Curonian Lagoon, which was due to favorable oxygen conditions and phytoplankton accumulation under the ice.     

Long-term variability of the trophic status of the Curonian and Vistula Lagoons of the Baltic Sea

Based on an analysis of long-term (1991–2007) hydrological and hydrochemical data, as well as data on phytoplankton primary production, the ecological state of the Curonian and Vistula Lagoons of the Baltic Sea is assessed. The main abiotic factors influencing the trophic status of the lagoons are indicated. Water temperature is the key factor determining phytoplankton production and abundance in the Curonian Lagoon. An intensive warming-up of the lagoon water in the 1990s and 2000s (a possible result of climate warming) combined with freshwater and a slow-flow velocity created the conditions for the mass development of bluegreen algae. Despite a significant reduction in the external nutrients load, the occurrences of water hyperblooms” become more frequent, which points to a continuation of the eutrophication processes in the lagoon. The biological productivity of the Vistula Lagoon is below the potentially possible level because hydrodynamic activity and brackish water prevent the intensive development of blue-green algae. The increase in water temperature in the 1990s and 2000s had no significant effect on the ecological state of the lagoon.     

Sulfate reduction, methanogenesis, and methane oxidation in the upper sediments of the Vistula and Curonian Lagoons, Baltic Sea

Microbiological, biogeochemical, and isotope geochemical investigations of the upper sediments of the Vistula and Curonian lagoons, Baltic Sea, were carried out. High content of organic matter in the sediments was responsible for the high numbers (over 10¹⁰ cells cm^?3) and activity of heterotrophic microorganisms. The calculated integral rates of dark CO₂ assimilation for the upper 30 cm of the sediments varied 12.5 to 38.8 mmol m^?2 day^?1 and were somewhat higher in the Curonian Lagoon than in the Vistula Lagoon. Integral rates of sulfate reduction were higher in the more saline Vistula Lagoon. Rapid consumption of sulfates of the pore water resulted in intensified methanogenesis, with significantly higher rates detected in the silts of the Curonian Lagoon. High rates of methanogenesis in the Curonian Lagoon correlated with higher methane levels in its upper sediments and near-bottom water. The highest rates of methane oxidation were detected in the uppermost sediment horizons (oxidized or slightly reduced), which was an indication of the barrier role of aerobic methanotrophic bacteria. The calculated methane flows from the sediments into the water column were 0.45 and 0.007 mmol m^?2 day^?1 for the Vistula and Curonian Lagoons, respectively. Low methane flow from the sediments of the Curonian Lagoon resulted probably from the specific weather (wind) conditions during sampling. The near-stormy conditions in the Curonian Lagoon caused sediment detachment, resulting in methane release into the water column.     

Resistance to ship-induced waves of benthic invertebrates in various littoral habitats

1. Ship‐induced waves disturb benthic invertebrate assemblages colonizing littoral zones of lakes and rivers. However, the impact of ship‐induced waves on invertebrates has rarely been quantified, and the influencing factors have not been addressed. 2. In an experimental wave tank, five benthic invertebrate species, Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeseli and Laccophilus hyalinus, were exposed to waves of increasing shear stress (0.43–2.19 N m^?2). Mean number of detached individuals was recorded for five littoral habitats [coarse woody debris (CWD), reeds, sand, stones and tree roots], representing different levels of structural complexity as quantified by their fractal dimensions (FD). 3. Results showed that detachment of invertebrates was significantly related to shear stress in all habitats except tree roots. Detachments averaged for the five species were significantly lower in habitats with a high degree of structural complexity, decreasing in the habitat sequence: sand, CWD, stones, reeds and tree roots. 4. Consistent with their different morphologies and methods of attachment to substrates, the five species displayed differences in their response to hydraulic stress that were dependent on habitat. 5. The increasing sheltering effect of structural habitat complexity was mirrored by increasing dissipation of the kinetic energy of waves; i.e. the FD of the habitat was positively correlated with shear stress reduction due to the flow resistance of the habitat. 6. Network habitats such as tree roots provided the best sheltering conditions against hydraulic disturbance, because they combined good refuge availability for all studied invertebrate species and maximal dissipation of kinetic wave energy. Consequently, persistent anthropogenic impacts, such as lakeshore modification or long‐term exposure to ship‐induced waves, which cause disappearance of complex littoral habitats such as tree roots or dense reed belts, will drastically increase the adverse effects of boating and ship traffic on littoral invertebrate assemblages.     

Comparison of two samplers for quantitatively collecting larval fishes in upper littoral habitats*

Performance of two larval fish samplers, a hand–towed net and a dropbox enclosure, was similar when tested in shallow (x water depth, 20 cm) upper littoral–zone habitats. There was no significant difference between means of larval fish density (by total catch and by species) estimated from the catch in each gear, during the day and at night. Mean length of larvae (total catch) from the tow net was significantly longer than that from the dropbox during the day, but mean length did not differ between gear at night. Mean lengths of larvae of each species between gear were not significantly different within each period. Both gears collected significantly longer larvae (total catch and by species) during the day than at night probably because of diel movements of larvae of different sizes and species.     

Linking fish colonization rates and water level change in littoral habitats of a Venezuelan floodplain river

Change in water level during the annual hydrologic cycle of tropical floodplain rivers results in continuous disassembly and reassembly of faunal communities in littoral habitat patches. As such, the rate of water level change should influence colonization rates of vagile organisms among habitat patches. We experimentally tested this hypothesis in a Venezuela floodplain river using artificial rocky patches as sampling units, water level change as the independent variable, and total number of individual fish that colonized a patch as the response variable. Water level significantly affected the total number of individuals that colonized patch habitats, i.e., rapidly receding waters were associated with higher colonization rates. Results suggest that water-level recession directly affects community assembly by influencing the rate at which individuals abandon and colonize local habitat patches.     

Effects of a retaining wall and an artificial embankment on nearshore littoral habitats and biota in a large Alpine lake

Hydrobiologia - The littoral zones of many Central European lakes are severely altered by lake-side retaining walls. These are suspected to impair littoral biota due to the reflection of incoming...     

Seasonal fluctuations in macrophyte cover and water transparency of four brown-water lakes: implications for crustacean zooplankton in littoral and pelagic habitats

The dynamics of crustacean zooplankton in the littoral and pelagic zones of four forest lakes having variable water qualities (colour range 130–340 mg Pt l⁻¹, Secchi depth 70–160 cm) were studied. The biomass of zooplankton was higher in the littoral zone than in the pelagic zone only in the lake having the highest transparency. In the three other lakes, biomass was significantly higher in the pelagic zone than in the littoral zone. In the two lakes with highest transparency, the littoral biomass of cladocerans significantly followed the development of macrophyte vegetation, and cladoceran biomass reached the maximum value at the time of highest macrophyte coverage. In lakes with lowest transparency, littoral zooplankton biomass developed independently of macrophyte density and decreased when macrophyte beds were densest. The seasonal development of the littoral copepod biomass did not follow the development of macrophytes in any of the lakes. The mean size of cladocerans in the pelagic zone decreased with increasing Secchi depth of the lake, whereas in the littoral zone no such phenomenon was detected. Seasonally, when water transparency increased temporarily in two of the lakes, the mean size of cladocerans in the pelagic zone decreased steeply. For copepods, no relationship between water transparency and body size was observed. The results suggested that in humic lakes the importance of the littoral zone as a refuge decreases with decreasing transparency of the water and that low water transparency protects cladocerans from fish predation. All the observed between-lake differences could not be explained by fish predation, but were probably attributed to the presence of chaoborid larvae with variable densities. Feeding efficiency of chaoborids is not affected by visibility and thus they can obscure the relationship between water quality, fish density, and the structure of crustacean zooplankton assemblages. Handling editor: S. I. Dodson     

Hydraulic regime-based zonation scheme of the Curonian Lagoon

The aim of this study was to delineate the spatial zonation of the Curonian Lagoon based on the hydraulic regime and the sediment characteristics. A finite element hydrodynamic model has been applied to the Curonian Lagoon to simulate the circulation patterns for three years. With the help of a transport diffusion model the salinity distribution and the residence times of the Curonian Lagoon have been investigated when forced by river runoff and by wind. The finite element method permitted to follow the details of bathymetry and morphology of the lagoon, describing the areas of special interest with higher resolution. The hydrodynamic model has been validated using in situ water level and salinity measurements. A statistical GIS analysis of the bottom sediment characteristics and the modeled residence times and salinity distribution led to a synthetic hydraulic regime-based zonation scheme. The derived classification scheme is of crucial value for understanding the renewal capacity and biota distribution patterns in the lagoon. Guest editors: A. Razinkovas, Z. R. Gasiūnaitė, J. M. Zaldivar & P. Viaroli European Lagoons and their Watersheds: Function and Biodiversity     

Differences in fish assemblage structures between tidal marsh and bare sandy littoral habitats in a brackish water lake,eastern Japan

Ichthyological Research - Fish assemblage structures and environmental properties (e.g., water quality, sediment condition and prey abundance) were compared between tidal marshes, dominated by the...     

Diet,stable isotopes and morphology of Eurasian perch (Perca fluviatilis) in littoral and pelagic habitats in the northern Baltic Proper

We present morphology, stable isotope signals and stomach contents of Eurasian perch (Perca fluviatilis) from littoral and pelagic habitats in a brackish water embayment in the northern Baltic Proper. Studies conducted in freshwater habitats repeatedly state that littoral perch have deeper bodies than the pelagic ones. In this study we observed the opposite; the perch from the pelagic study site had deeper bodies than the littoral ones, indicating that more factors than habitat structure affect the perch morphology. A possible explanation to this discrepancy is the diet choice; the pelagic perch in this study were more benthivorous than freshwater pelagic perch. Our results on stable isotope signals combined with the stomach contents also shed new light on the dietary preferences of perch. Perch is known to be a generalist predatory fish, but our results indicate that perch have individual diet preferences. Based on our results, it seems that at some point in their lives the perch in brackish water choose between the littoral and pelagic habitats and also specialise in a certain diet. This study shows that the perch morphology and diet in the Baltic Sea coast differ among habitats, but the patterns are not similar to those observed in freshwater studies.     

Abundance,size, and feeding success of larval shortnose suckers and Lost River suckers from different habitats of the littoral zone of Upper Klamath Lake

We examined near-shore habitat use by larval shortnose and Lost River suckers in the lower Williamson River and Upper Klamath Lake of south-central Oregon. Emergent macrophytes Scirpus, Sparganium and Polygonum supported significantly more, larger, and better-fed larvae than submergent macrophytes, woody vegetation, or open water. Abundance, size, and gut fullness were similar for sucker larvae collected from different emergent macropytes. During the larval period, there was no evidence of density dependant effects or habitat shifts. Ranked catch per unit effort data indicated potential predators also were more likely to use emergent macrophytes, but ordination indicated larvae and potential predators were differentially distributed along a vegetation structure-water depth gradient with larvae in shallow vegetated areas. Between-habitat differences appeared to be due to larval sucker selection for, or better survival in, emergent macrophytes, rather than differential access or exclusion from other habitats. The importance of emergent macrophytes appears to be related to increased foraging success and reduced predation. Because larvae in emergent macrophytes have a size and gut fullness advantage, the amount of emergent habitat could affect early survival. However, interannual differences in recruitment to the adult population may or may not be dependent on larval dynamics. Our results suggest larval sucker access to emergent macrophytes may be necessary, but perhaps not sufficient, for promoting good year class formation.     

AQUASPLATCHE: a program to simulate genetic diversity in populations living in linear habitats

Classical models of structured populations do not apply well to species leaving in semilinear habitats such as freshwater fishes, since these habitats are intermediate between one‐dimensional and two‐dimensional stepping‐stone models. In order to investigate the genetic diversity of such populations, we have developed a new simulation program called aquasplatche . It starts by dividing a user‐defined vectorized network into segments of arbitrary length, each segment hosting a single deme. The program then proceeds by simulating the colonization of the environment from an arbitrary source, recording the evolution of the deme densities and the migration events between adjacent demes over time. This demographic history is then used to generate genetic data of population samples located in various segments of the network, using a backward coalescent framework. Different versions of aquasplatche are freely available on http://cmpg.unibe.ch/software/aquasplatche .     

Investigations of the Benthos of Mangrove Coastal Lagoons in Southern Cuba

Benthic studies were undertaken in two mangrove-lagoons on the south coast of Cuba. Both lagoons are approximately 30–50 cm deep and the tidal range is 15–20 cm. There is little influx of fresh water, and the lagoons are normally euhaline. Most of the lagoon bottom is not colonized by plants, although filamentous algae (Cladophora and Enteromorpha spp.) and Thalassia testudium grow in a few places. Meiobenthic organisms account for 92% of the invertebrates in the benthic zone of the lagoon. The five most common taxa (Nematoda, Copepoda, Tanaidacea, Oligochaeta, Polychaeta) account for 88–94% of the total number of individuals in Tolete Lagoon and in Basto Lagoon the five most common taxa (Nematoda, Copepoda, Ostracoda, Amphipoda, Polychaeta) account for 97–98%. Biomasses were 26.6 g/m² in Tolete and 20.2 g/m² in Basto Lagoon. The dominant taxon on the roots of Rhizophora mangle is Crustacea (Balanus eburneus, B. recurvus and Corophium insidiosum), accounting for over 60% of the total number of individuals. They are followed by molluscs (Crassostrea rhizophora) and the polychaetes (serpulids).