Distribution,growth, production,and ecological significance of the clam Unio terminalis in Lake Kinneret,Israel

The distribution, body composition, growth rate, and population structure of Unio terminalis were measured at different sites of Lake Kinneret (Israel). Maximum clam density was found on the muddy sand between 0.3–6 m depth. Clams were most abundant in the River Jordan inlet zone, where they showed the highest growth rate. This was probably related to both highest food availability and the highest density of fish hosting Unio glochidia in this area. U. terminalis in Lake Kinneret has a more massive shell and ash content as compared with the European Unio species. The annual P/B ratios of U. terminalis populations at different sites were similar and ranged within 0.17–0.18. The computated filtration capacity and energetic budget permit the assumption that the U. terminalis population plays a substantial role in removal of organic particles from the water in the Kinneret shallow inshore zone (up to 15 m depth), and in nutrient recycling.     

The effects of history on the shell preference of the hermit crab Pagurus longicarpus (Say)

The effect of disturbance by two macroinvertebrates, the sand dollar Mellita quinquiesperforata (Leske) and the sea pansy Renilla reniformis (Cuvier) on meiofauna was studied on a sandbar in North Inlet, Georgetown, South Carolina. Abundances of nematodes and the harpacticoid copepod Apodopsyllusunguiformis Coull &; Hogue decreased significantly in the presence of sand dollars; other taxa were not affected. In two Renilla experiments, one natural and another where artificial and real Renilla were implanted, we could determine no consistent effect on any meiobenthic taxon. However, sediments disturbed by implanting living and artificial Renilla returned to ambient levels within 1 h.     

Hydrodynamic analysis of feeding in sand dollars

Summary Subtidal sand dollars, Dendraster excentricus, assume an inclined posture under conditions of moderate water flow (10 cm s^-1 to 2 m s^-1). In this posture, when the test is in the usual position parallel to the water flow, the test acts as a lifting body. Analysis of the hydrodynamic characteristics of the sand dollar test was accomplished by slender body theory. Streamline curvature due to lift moves food particles in the direction of the feeding surface and enhances feeding efficiency. The position parallel to water flow is most advantageous to sand dollars in reversing flows, such as wave surge, whereas sand dollars in unidirectional flows can place the test at a slight angle to the water flow to increase lift. The high camber of sand dollars from a bay habitat characterized by low water velocities was interpreted as an adaptation allowing efficient lift production in low velocity flows; sand dollars from a protected outer coast location characterized by higher water velocities were significantly less cambered.Within sand dollar beds, the animals alter their spacing as a function of the water velocity. This movement is construed as a method for maintaining the optimal gap between sand dollars. Sand dollar tests induce mutual interference effects which vary with the configuration of the animals. In the prevalent configuration, sand dollars are able to take advantage of the streamline curvature induced by neighboring animals. The optimal gap increases as the square of the water velocity. At distances grater than or less than the optimal gap, feeding efficiency was shown to decrease from that at the optimal gap.     

Nearshore macrobenthos of northern Kotzebue Sound,Alaska, with reference to local sewage disposal

Macrobenthos of the shallow (<10 m) nearshore marine waters of northern Kotzebue Sound was examined in 2002–2004 to (1) determine nearshore community structure and (2) assess the influence of sewage disposal. A variable number of benthic stations were sampled during three summers, with extensive effort at the disposal zone in 2003. The benthic community structure is similar to other nearshore Arctic locations, and was similar to a previous benthic study done in 1986–1987. The potential of sewage impact was assessed at the request of the community, because sewage is occasionally discharged into the Sound, in volumes of up to 38 million liters, typically through the ice in early spring. Only minimal effects of disposal on the benthos were evident and the effects could not be separated from the impacts of low salinity and relatively high water pigments. Low diversity (H′) and species richness (d) and high biomass characterized stations in the sewage area. Parameters often associated with extreme sewage pollution, particularly hypoxic and/or anoxic conditions and high abundance of opportunistic taxa, were not observed. Local traditional ecological knowledge was solicited throughout the study, and was used to help define the area potentially affected by sewage disposal.     

Diatom composition and biomass variability in nearshore waters of Maxwell Bay, Antarctica, during the 1992/1993 austral summer

 Diatom composition and biomass were investigated in the nearshore water (<30 m in depth) of Maxwell Bay, Antarctica during the 1992/1993 austral summer. Epiphytic or epilithic diatoms such as Fragilaria striatula, Achnanthes brevipes var. angustata and Licmophora spp. dominated the water column microalgal populations. Within the bay, diatom biomass in surface water was several times higher at the nearshore (2.4–14 μg C l^-1) than at the offshore stations (>100 m) (1.2–3.2 μg C l^-1) with a dramatic decrease towards the bay mouth. Benthic forms accounted for >90% of diatom carbon in all nearshore stations, while in the offshore stations planktonic forms such as Thalassiosira antarctica predominated (50–>90%). Microscopic examination revealed that many of these diatoms have become detached from a variety of macroalgae growing in the intertidal and shallow subtidal bottoms. Epiphytic diatoms persistently dominated during a 19-day period in the water column at a fixed nearshore station, and the biomass of these diatoms fluctuated from 0.86 to 53 μg C l^-1. A positive correlation between diatom biomass and wind speed strongly suggests that wind-driven resuspension of benthic forms is the major mechanism increasing diatom biomass in the water column. Received: 28 April 1995/Accepted: 1 April 1996     

Acoustic measurement of trout distributions in Spada Lake, Washington, using stationary transducers

Diel patterns in the spatial distribution of rainbow and cutthroat trout were studied with stationary acoustic transducers, gillnets, and setlines in Spada Lake during summer thermal stratification. Four diel periods (dawn, 03.00–07.00 hours; day, 07.00–19.00 hours; dusk, 19.00–23.00 hours; night, 23.00–03.00 hours) and two horizontal strata (nearshore, bottom depth < 8 m; offshore, bottom depth > 8 m) were identified from fish distribution patterns. During the day, trout were almost exclusively offshore and their densities were highest at intermediate depths of the water column (4–16 m). From dusk to dawn, trout were in intermediate and shallow depths (0–4 m) of the offshore and nearshore strata. The mean depth of capture was significantly deeper for cutthroat trout (9 m) than for rainbow trout (3m). Both species primarily inhabited the epilimnion and metalimnion where temperature ranged from 22.5 to 11.0°C and were nearly absent from deeper, cooler waters. Dissolved oxygen levels ranging from 3.9 to 8.6 mg/l did not seem to influence trout distributions.     

Variations in the shallow water form of Potamogeton richardsonii induced by some environmental factors

SUMMARY. Populations of Potamogeton richardsonii in Sparrow Lake, Ontario, vary greatly in leaf dimensions and internode length. Leaf length/breadth (L/B) ratio is increased by low irradiance, significantly at 4% daylight and, in a contrary fashion, by ontogenetic drift at high irradiances of shallow water. L/B ratio was not correlated with substrate. These findings suggest that this ratio is of doubtful value taxonomically or as an integrator, as specific leaf area is confirmed to be, of factors like photosynthetically active radiation (PAR). Longest internodes belong to plants from deep(1.8 m) water, and, in a summer-grown high-density population, internode length decreases logarithmically as depth lessens; both observations implicate PAR and ageing. Relative to undisturbed, shallow-water shoots, young transplants in full daylight elongate almost twice as fast because of the production of more, and longer, internodes. Young shoots in 12% daylight lengthen even more rapidly than those in full daylight (and four times faster than undisturbed shoots) in the same period because of quicker elongation of the same number of internodes. At ambient summer temperatures, this rate of elongation is inversely related to PAR. Experimental and seasonal field data indicate that maximal internode extension occurs on young shoots in very low irradiances at temperatures of 9–15°C; in nature, effects of increasing water temperatures are depressed by increasing irradiances and ageing until minimal extension takes place in old shoots at mid- to late-summer temperatures and in high irradiances. In tanks (40 m³) in full daylight, nutrients limit growth of plants on sand before they limit growth on clay (with marl intermediate) whereas, at 12% daylight, light limits growth on sand before soil nutrients do. The leaf area index on silty sand on an exposed shore was 0.4 at 0.5 m depth, in contrast to a cultured population where it was 4.0 in silty loam at the same depth. Thus, while it has not been possible to explain some variations in leaf morphology of P. richardsonii in environmental terms, the differential effects of ontogeny, PAR and temperature on shoot growth have been assessed, along with overall effects of light and nutrients on biomass and of shelter on leaf area index.     

Geographic, seasonal and bathymetric distribution of demersal fish species in the eastern Mediterranean

The distributional abundance of three demersal fish species, Merluccius merluccius, Mullus barbatus and Lophius budegassa, was studied as a function of sampling season, bathymetry and geographic area. Data were collected during research trawl surveys in the Aegean and Ionian seas under the same sampling scheme, thereby allowing comparisons to be made on the mean regional densities in numbers and biomass of these three commercially important species in Greek waters. Results indicated that European hake, M. merluccius, demonstrated a wide bathymetric and geographic distribution, with specimens encountered in all regions between 20 and 500 m depth, although density was found to be highest usually between 101 and 200 m. The mean regional density of hake was observed to vary seasonally, being higher mainly in winter. Red mullet, M. barbatus, was distributed in shallow water depths (<100 m) throughout the Greek seas, particularly in the northern part of the Aegean Sea. Abundance of this species steadily decreased with increasing depth. The geographic distribution of anglerfish, L. budegassa, was found to be restricted to the central and northern part of the Aegean Sea, with the highest mean densities encountered in the Thermaikos Gulf and in intermediate water depths between 101 and 200 m. Spatial patterns of observed density are assumed to be attributed mainly to prevailing topographic and hydrographic conditions and related biological productivity levels.     

Phytoplankton community structure and distribution in the nearshore zone of Lake Ontario

Spatial and temporal distributions of phytoplankton were studied during 1979 in the nearshore zone of Lake Ontario. Genera such as Dinobryon, Oscillatoria, and Gymnodinium tended to be found at discrete depths whereas other genera such as Cryptomonas and Rhodomonas tended to be more uniformly distributed throughout the water column. The discrete depth distribution of some of these genera compared with the weak thermal stabilization of the area suggests depth selection and habitat preference within the algal community.Physical processes probably played a major role in regulating the timing and duration of vertical diatom pulses, and resuspension from the sediment played a major role as to the timing of the autumn growth. Vertical mixing in the nearshore zone was sufficient for some diatom genera such as Tabellaria to maintain populations throughout the summer. These mixing processes, however, affect the stability of community structures and associations that develop within the water column. The role of physical processes and their potential effects on algal production in the Great Lakes is discussed.     

Changes in morphology and abundance of Stylophora pistillata and Acropora variabilis (anthozoa,hexactiniaria) with respect to depth at Elat,Red Sea

Entire colonies of Stylophora pistillata and Acropora variabilis were collected along a depth transect 100 m south of the Marine Biological Laboratory of Hebrew University Elat, Israel. The branch height of Acropora variabilis decreases significantly with respect to depth, and this species is equitably distributed from 5 to 30 m. Stylophora pistillata demonstrated no decrease in branch height with respect to depth and its distribution is limited to shallow water. The changes in morphology and distribution enhance the credibility of a suggestion made by Roos (1967) that corals common at all depths would show changes in morphology that minimized self-shading. Stylophora pistillata demonstrated an increase in branch density with respect to depth. A hypothesis, based upon the occurrence of Lithophaga cumingiana and water turbulence, is presented to explain the increase in branch density with respect to depth of Stylophora pistillata.     

Direct observations on the sublittoral marine algae of Argyll,Scotland

Summary The distribution with depth of sublittoral marine algae has been investigated at 11 sites on the west coast of Scotland. More than half of the species found were confined to the sublittoral zone. The greatest variety of species was found in shallow water at sites sheltered from excessive turbulence. With increasing depth the number of species found steadily decreased. There was no evidence of a specifically distinct algal flora confined to deeper water. No algae were found deeper than 36 m below ELWS at any site, but the lower limit of algal growth was reduced to 9 m in a turbid water loch and to 3 m at a site where the herbivorous echinoderm Ophiocomina nigra was abundant. Fairly distinct algal communities were found on different substrates. The major communities recognised underwater were algae attached to stable substrata, algae attached to unstable substrata and epiphytic on other algae, especially on the stipes of Laminaria hyperborea. On stable rock in areas subject to water movement L. hyperborea forest was the dominant vegetation whereas on unstable substrata and in sheltered localities L. saccharina was dominant.     

Shallow-water habitat use and population parameters of rough-toothed dolphins,Steno bredanensis (G. Cuvier in Lesson, 1828) in southeastern Brazil

The rough-toothed dolphin (Steno bredanensis) is a poorly known species along its distribution especially in the Southern Hemisphere where data on habitat use and population parameters are scarce. Boat-based surveys were conducted from 2009 to 2017 in a shallow water environment in southeastern Brazil. During focal-group observations, S. bredanensis was more commonly found in mean depths of 22 m with varying group size and composition. Generalized additive models showed that group size was influenced by environmental variables such as sea surface and bottom temperatures, depth, and season. Photo-identification effort allowed us to catalogue 173 well-distinct marked individuals. Estimates of population parameters showed high and constant survival (Φ = 0.99) corroborating site fidelity but time varying capture probabilities (p = .03–.71). An open population model also indicated a small abundance estimate (Nt = 218) of S. bredanensis in the study area, improving knowledge for this species in shallow water environments of the southwestern Atlantic Ocean.     

The inshore marine fishes of the Vestfold Hills region,Antarctica

Thirteen species of fish have so far been caught in the inshore waters around the Vestfold Hills, including the Rauer Islands, in depths down to approximately 100 m. Species caught depend markedly on the type of fishing gear used, but three species are clearly dominant numerically. Pagothenia bernacchii is most abundant in the shallower (< 20 m deep) weedy and rocky habitats, while Chionodraco hamatus is dominant in the deeper (> 20 m deep) nearshore troughs and further offshore. Pagothenia borchgrevinki occupies the specialized habitat associated with sea ice and close-inshore areas, including fjords and Burton Lake.The species list from the Vestfold Hills area is similar to lists from comparable locations in East Antarctica except for the major difference that C. hamatus has not yet been recorded from such shallow waters at the other locations, while P. bernacchii and P. hansoni are much more abundant in water deeper than 20 m at those sites than at Davis.     

Maximum entropy model: Estimating the relative suitability of cetacean habitat in the northern Savu Sea,Indonesia

An understanding of cetacean distribution is necessary to gain insights into crucial ecological processes for species conservation management. However, cetacean habitat preference and distribution in the northern Savu Sea, Indonesia, are still poorly understood. We use maximum entropy modeling with five environmental predictors to describe habitat preference and distribution of seven cetacean species in the northern Savu Sea. Our study confirms that static predictors are the most important variables in explaining habitat preferences of seven cetacean species in the northern Savu Sea. Seasonally, each cetacean species has a different environmental preference. Globicephala macrorhynchus prefers the open nearshore areas adjacent to deep waters. Stenella attenuata is associated with nearshore habitats and higher productivity areas. Stenella longirostris prefers nearshore habitat during coastal upwelling events. Tursiops truncatus prefers nearshore sheltered habitat. Grampus griseus habitats are highly related to depth and steep gradients around the isobaths of 200–1,000 m. Feresa attenuata are associated with deep waters and cooler sea temperature. Pseudorca crassidens prefers protective bays with productive waters. This study provides important information for reviewing marine spatial plans of the northern Savu Sea, specifically on managing species fisheries interaction, optimizing surveillance, and regulating marine traffic.     

Aspects of the population ecology of Lucinomaborealis (L.) (Bivalvia) in Raunefjorden,Western Norway

2194 Lucinoma borealis (L.) were obtained from 99 quantitative (0.2 m²) samples of substratum (stratified random sampling) collected between November 1975 and October 1976 in the archipelago of Eggholmane ≈20 km south of Bergen. The depth range of the 20900 m² area was 0.3–13.3 m, and the bottom sediment (fine to very coarse sand) was rich in calcium carbonate. The highest density was found in the deep (≈ 8–13 m) sub-areas, with fine sediment (median grain-size diameter ≈ 0.3–0.5 mm). L. borealis was the most abundant bivalve species in the area studied (59.6%, by number). The average density was 22.2 (C.I. ± 5.4) ind. · 0.2 m ^?2, and the biomass was 690 (C.I. ± 116) mg AFDW · 0.2 m ^?2. The average size of animals found in shallow water (coarse sediment), with low abundance, was markedly larger than that of those from deeper water. Adults from shallow water consisted of 49.5% females, but in deep water the corresponding figure was only 38.6%.According to the data, spawning in deep water occurred in June, August–September, and possibly also in January–February. The spawning period in shallow water was more diffuse and uncertain. The egg diameter of 123.75 (C.I. ± 1.59) μm, indicates a lecithotrophic development. Maturation occurred at a shell length of 10–13 mm, and the largest animal found was 34.3mm long. The shell of L. borealis grows allometrically.     

The biology of the burrowing goby Croilia mossambica Smith (Teleostei,Gobiidae)

Synopsis Croilia mossambica, a burrowing goby endemic to the coastal lakes of south east Africa occurs from L. Poelela (salinity 8%.) to L. Sibaya (freshwater). Since these lakes are isolated from one another its distribution is discontinuous. It is not found in estuaries or the sea. In L. Sibaya C. mossambica is present on sheltered sides from a depth of 1 m to about 16 m. On exposed shores it is not found at less than 3.5 m depth. It is restricted to sandy, quiet water areas and is unable to form burrows where the substrate is disturbed by water movement, is muddy or consists of sand with a particle diameter greater than 0.5 mm. The maximum depth at which it lives is probably determined by light penetration since it is dependent on sight for prey capture. The food consists of slow moving benthic invertebrates such as chironomid larvae, gastropods, bivalves and amphipods. The relative importance of each depends upon its abundance. C. mossambica is a summer breeder with a protracted spawning season. The sticky eggs measure 0.7–0.8 mm when laid. Tolerance experiments show that it is euryhaline and can survive in seawater of 35%. and that its upper temperature limit is between 32 and 35°C. Temperatures in shallow waters of lakes and estuaries of the region frequently exceed 35°C. Thus its local distribution may be limited by temperature. Its lack of tolerance to high temperatures, to marked water movements and its ability to live in seawater indicates that C. mossambica is suited to life in the sea rather than in estuaries. It is suggested that it was present in quiet areas of the sea, such as lagoons, and that it invaded the coastal lakes which were formed as the estuaries and river valleys were inundated during the Pleistocene marine transgression. C. mossambica cannot tolerate estuarine conditions and with the present absence of quiet water in the sea off the south east African coast the species is now confined to deep coastal lakes.Note     

Temporal and spatial patterns of water mites in Lake Maarsseveen I

The paper analyses the distribution and seasonal changes in numbers of the water mite fauna of Lake Maarsseveen I. Water mites were collected from 1977 until 1986 by dipnet, underwater light trap, hydraulic lift sampler and by frame net. Fifty-two species belonging to the Hydrachnellae and one to the Halacaridae were sampled. The faunal picture obtained is characteristic of mesotrophic to eutrophic lakes.Arrenurus nobilis. Piona paucipora andP. imminuta can be characterised as lake species. The dominant species in the littoral sand flat areHygrobates nigromaculatus andH. trigonicus, at a depth of 0.5–1 m, andMideopsis orbicularis at depths of 2–7 m.Limnesia maculata is also very common on depths between 2 and 7 m. In early summer, however, they prefer shallow water up to 1 m depth. Some species likeHygrobates nigromaculatus andH. trigonicus were not captured by the underwater light trap. The hydraulic lift sampler gave underestimations of the densisty of certain speciese.g. Hygrobates spp. andLimnesia maculata. Unionicola spp. even can avoid this sampler. Sampling by frame net gave the most realistic data. The highest number of water mites was observed in the littoral sand flat, generally up to 1000 ind. m⁻². The genusHygrobates was represented with an average of 800 adult ind. m⁻² throughout the year, and appeared to be the main invertebrate predator in this habitat.     

In situ and laboratory studies on the behaviour and survival of Pacific salmon (genus Oncorhynchus)

Juvenile Pacific salmon display a marked surface water orientation during downstream migration, estuarine and nearshore coastal rearing phases. Many estuaries in British Columbia are vertically stratified with a shallow, well-defined halocline which can restrict the dispersion of wastes discharged into less saline surface waters and impose constraints upon aquatic organisms. In situ experiments in an estuary receiving a surface discharge of treated pulp mill wastes, revealed conditions which were lethal to underyearling salmon at, and below the halocline (4.0–6.5 m depth). Behavioural bioassays determined that juvenile chinook salmon were biased towards the water surface and avoided waters at depth. Dissolved oxygen was the variable which affected this distribution most significantly. Surface waters receiving effluent from another pulp mill were lethal to juvenile salmon within 350 m, and a significant vertical avoidance response occurred within 350–950 m of the outfalls. The behavioural response was significantly correlated with in situ temperature, pH and colour (effluent).As a complement to field experiments we developed a 4500 l water column simulator (WCS) to examine salmon behaviour in the laboratory. We investigated the surface water orientation behaviour of juvenile salmon in relation to variations in salinity and dissolved oxygen. Under simulated vertically stratified estuarine conditions, the fish moved freely between overlying fresh water and salt water. Induction of hypoxic conditions in fresh water elicited a downward distribution shift towards the halocline and oxygenated, but more saline, waters. Avoidance reactions (50% level) occurred consistently up to 7–8 mg · l^–1 dissolved oxygen. Salmon continued to examine the hypoxic freshwater zone despite sub-optimal conditions.     

Physical and chemical characteristics of shallow embayments on the southern coast of Finland

Regular water-quality monitoring is yielding a great number of hydrographical and chemical data regarding the brackish Baltic Sea. However, present monitoring programmes often do not include shallow and sheltered near-shore areas, which are adjacent to human population and used for recreation purposes. We collected new near-shore water quality data from the southern coast of Finland that will allow the definition of the present state of these systems and may serve as reference data for possible future monitoring programmes. The data set comprises 45 small and shallow embayments with a mean surface area of 211 ha and a mean depth of 4.3 m. According to redundancy analysis (RDA), catchment land use explained 20.3% of the variance in the measured water chemistry. Agriculture had the strongest influence on the water quality of the study sites, capturing 13.1% of the variance. Nitrogen seemed to be strongly related to agriculture, whereas phosphorus was correlated with urban areas and industry. Higher than average nutrient concentrations regularly occurred at the mouths of large rivers, or close to human settlement, emphasising the significance of local sources to the nutrient concentrations of coastal waters. No increasing trend in nutrient or chlorophyll-a concentrations was observed from west to east in these shallow and sheltered nearshore areas. This contrasts with earlier results from pelagic samplings that report a marked influence of the River Neva and St. Petersburg on the nutrient status of the Gulf of Finland. Because these shallow embayments are strongly influenced by the local nutrient load, continued measures must be undertaken to reduce the nutrient load from land to prevent the continued deterioration and eutrophication of the nearshore, coastal waters.     

Vertical and horizontal distribution patterns of the giant sea anemone Heteractis crispa with symbiotic anemonefish on a fringing coral reef

The distribution patterns of the leathery sea anemone, Heteractis crispa, which contains an algal endosymbiont (zooxanthellae) and anemonefish, were investigated in relation to size distribution on a shallow fringing reef (3.2 ha, 0–4 m depth) in Okinawa, Japan. Individual growth and movements were also examined. Large individuals (>1,000 cm²) inhabited reef edges up to a depth of 4 m, while small anemone (<500 cm²) inhabited shallow reefs including inner reef flats. Individuals rarely moved, and their sizes were significantly correlated with their water depths. Growth of small anemones was negatively correlated with their distance from the reef edge, suggesting that reef edges provide more prey and lower levels of physiological stress. This study suggested that deep reef edges are suitable habitats for H. crispa. Large anemones were inhabited by large Amphiprion perideraion or large Amphiprion clarkii, both of which are effective defenders against anemone predators. Anemones that settle in deep reef edges may enjoy a higher survival rate and attain a large size because of their symbiotic relationship with anemonefish. However, early settlers do not harbor anemonefish. Their mortality rate would be higher in the deep edges than in shallow edges, the complicated topography of which provides refuge.