Semi-enclosed Water Body Research Articles

Size and characteristics of aggregations of moon jellyfish (Aurelia SP.) in Tasmania, Australia

Moon jellyfish, Aurelia spp., are found in marine and estuarine environments worldwide and can concentrate into dense aggregations within enclosed or semi-enclosed water bodies (e.g., Lucas et al. 1997, Purcell et al. 2000). Aggregations are often promoted by physical properties of the water body in which they occur and are commonly believed to facilitate sexual reproduction, rather than act as a defence against predation ortargetingfoodsources (Graham etal. 2001, Lucas 2001). The presence of!arge-scale aggregations of medusae, as a function offavourable conditions, has substantial ecological and economic consequences (Purcell et al. 2007). The distribution, abundance and life history characteristics of the genus Aurelia are highly variable spatially and temporally (e.g., Schneider & Brehrends 1994, Lucas et al. 1997). The pelagic medusa stage generally occurs seasonally and lives for several months (Lucas & Williams 1994, Miyake et al. 1997), but in some populations, medusae will live for 12 months or more (Kinoshita et al. 2006). Aurelia medusae are voracious feeders and are capable of modifying the seasonal composition and abundance of the planktonic community (Schneider & Brehrends 1994, Lucas et al. 1997). Secondary effects of high grazing pressure include increased phytoplankton biomass through reduced grazing pressure by copepods (Lindahl & Hernroth, 1983, Olsson et al. 1992, M0ller & Riisgard 2007a) and decreased food availability for other zooplanktivores, which can have impacts through the food chain (Purcell & Arai 2001). Given their widespread distribution, occurrence in large aggregations and capacity to alter trophic dynamics, jellyfishes are potentially important consumers and transformers of energy and nutrients in the marine ecosystem (e.g., Watanabe & Ishii 2001, Pauly et al. 2009, Pitt et al. 2009). Determining the abundances and sizes of jellyfish in the oceans has proved difficult because of their large sizes, fragility and patchy distributions, both horizontally and vertically, and because their gelatinous bodies are difficult to tag (Purcell 2009). Also, the high water content of their tissues makes acoustic sampling difficult, although combined acoustic soundings and video recordings can monitor relatively reliably some jellyfish species, provided the target species can be distinguished from other co-occurring species acoustically (Bamstedt et al. 2003, Alvarez Columbo et al. 2009). Consequently, estimates of the extents, causes and effects of jellyfish blooms have rarely been conducted on a large scale (Purcell 2009). Aurelia sp. medusae periodically occur in dense monospecific aggregations in the sheltered waterways of southeast Tasmania, Australia (pl. 1). The medusae are morphologically similar to Aurelia aurita; however, they are genetically distinct from other species of Aurelia and have been designated as Aurelia sp. 7 (Dawson et al. 2005). Growth, survival and reproduction of the sessile, asexual, colonial phase of this species has been found to be regulated by a combination of density-dependent factors and environmental conditions, which are consequently important to the formation of jellyfish aggregations (Willcox et al. 2008). These aggregations, however, were largely unnoticed until they caused the deaths of cultured Atlantic Salmon in Tasmania, valued at millions of dollars. 'The objective of this study was to describe the biological characteristics of this species, as part of a larger study investigating mechanisms driving the intermittent occurrence of Aurelia sp. aggregations in southeast Tasmania. This included growth and reproduction of individuals in the aggregations, and estimating aggregation size and total biomass of medusae in the system. To achieve this, we developed a method to assess the abundance of jellyfish by combining aerial photography, underwater video photography and net sampling.

Phosphorus mass balance in a highly eutrophic semi-enclosed inlet near a big metropolis: A small inlet can contribute towards particulate organic matter production

Terrigenous loading into enclosed water bodies has been blamed for eutrophic conditions marked by massive algal growth and subsequent hypoxia due to decomposition of dead algal cells. This study aims to describe the eutrophication and hypoxia processes in a semi-enclosed water body lying near a big metropolis. Phosphorus mass balance in a small inlet, Ohko Inlet, located at the head of Hiroshima Bay, Japan, was quantified using a numerical model. Dissolved inorganic phosphorous inflow from Kaita Bay next to the inlet was five times higher than that from terrigenous load, which may cause an enhancement of primary production. Therefore, it was concluded that not only the reduction of material load from the land and the suppression of benthic flux are needed, but also reducing the inflow of high phosphorus and oxygen depleted water from Kaita Bay will form a collective alternative measure to remediate the environmental condition of the inlet.

Restoring the Name ‘East Sea’ for ‘Japan Sea’: Strategic Choice between Continental and Maritime Cartographic Traditions

Historically, there were two exploration perspectives for East Asia — the continental and the maritime—which produced two distinct cartographic traditions responsible for divergent names of places and seas in this region of the globe. The continental perspective, developed by Russians as they expanded eastward across the Eurasian land-bridge, viewed the large body of water around East Asia and Siberia logically as Vostochnoe More-Akiyan—the “Eastern Sea-Ocean.” However, from the maritime perspective developed by western European explorers (Magellan, Drake, Cook, La Perouse and others) who were approaching East Asia by sea via South America or South Africa, the same semi-enclosed bodies of water appeared to them as really part of the Pacific Ocean. These two distinct perspectives, coming from opposite directions, created alternative names for the Pacific Ocean and for the semi-enclosed seas behind island chains strung along the rim of Asia. While it is true that the western maritime cartographic tradition became the more influential standard in cartography, it did not completely erase all the names the Russians had developed from their continental perspective. This explains overlapping names for the same geographical spaces, and the attendant problems of standardization of pelagonyms in East Asia. There is a definite need to return to the earliest historical names and negotiate their acceptance by all concerned.

The role of resting cysts in Alexandrium minutum population dynamics

Abstract The role of resting cysts on the development of Alexandrium minutum blooms in a typical Mediterranean semi-enclosed water body (Arenys de Mar Harbor, NW Mediterranean) was studied by means of matrix and dynamic population models. We used a series of scenarios, constrained when possible by experimentally measured parameters to test whether excystment and encystment fluxes and changes in the dormancy period had a major effect on bloom intensity and duration. The results of the simulations highlighted the importance of knowing not only the magnitude and variability of growth and life-cycle transition rates, but also those of loss rates (both in the water column and in the sediment) due to physical or biological factors. Given the maximum encystment rates determined for A. minutum in the study area (0.01 d −1 ), this process contributed to reduce the peak concentrations of vegetative cells but did not have a dominant effect on bloom termination. Excystment fluxes could contribute to enhance population densities of vegetative cells during times or low or negative net growth rate and during the initial phases of a bloom, but once exponential growth had started, additional excystment had negligible effect on bloom magnitude. However, even if cysts did not contribute to larger blooms, they could represent a safety mechanism for reintroduction of the species when the vegetative cell population went extinct due to unfavorable environmental conditions. Increasing the dormancy time exposed newly formed cysts to a longer period of losses in the sediment that reduced the concentration of excystment-ready sediment cysts and decreased excystment fluxes. More complex models will be needed to explore the implications of different life-cycle strategies in a wider natural ecological context.

Remediation of coastal marine sediments using granulated coal ash

It is very important to reduce phosphorus flux from sediment as well as cutting down terrigenous loads in order to control eutrophication in semi-enclosed coastal seas. Hydrogen sulfide is also a noxious substance which is highly toxic and fatal to benthic organisms. The purpose of this study is to evaluate remediation efficiency of organically enriched sediments using granulated coal ash (GCA) in terms of reducing benthic phosphorus flux and hydrogen sulfide. A flow-through experimental system was used to simulate the semi-enclosed water bodies. The application of GCA decreased the concentration of PO 4 3− in the pore water effectively, and reduced phosphate releasing flux from the sediment into overlying water by 37–44% compared to the control. The hydrogen sulfide in the pore water was also decreased by 77–100%, due to adsorption onto the GCA and deactivation of sulfate-reducing bacteria due to increasing pH. Thus, GCA is a promising recycled material for reducing phosphate releasing flux from organically enriched sediment to alleviate eutrophication as well as reduce the concentration of hydrogen sulfide in pore water.

Genetic isolation and morphological divergence of Black Sea bottlenose dolphins

The Black Sea is a semi-enclosed body of water that differs from the adjacent Mediterranean Sea in terms of its biodiversity, oceanographical and ecological characteristics. There is growing international concern about pollution in the Black Sea and other anthropogenic threats to its fauna. The bottlenose dolphin ( Tursiops truncatus) is one of three species of cetaceans living in the Azov-Black Sea basin. Despite considerable research on bottlenose dolphins elsewhere, the extent of human impacts on the Black Sea populations is unknown. Previous attempts to award special conservation status to Black Sea cetaceans have failed specifically because policy makers have viewed their ecological and evolutionary uniqueness as equivocal. This study assessed divergence between Black Sea, Mediterranean Sea and Atlantic Ocean bottlenose dolphins for 26 cranial measurements ( n = 75 adult bottlenose dolphin skulls) and mitochondrial DNA ( n = 99 individuals). Black Sea bottlenose dolphins are smaller than those in the Mediterranean, and possess a uniquely shaped skull. As in a previous study, we found the Black Sea population to be genetically distinct, with relatively low levels of mtDNA diversity. Population genetic models suggest that Black Sea bottlenose dolphins have so little gene flow with the Mediterranean due to historical isolation that they should be managed separately.

Subsurface Salinity Balance in the South China Sea*

Abstract The South China Sea (SCS) is often treated as a semienclosed water body, with the Luzon Strait as its only connection to the Pacific Ocean. A branch of the Kuroshio flows northwestward across the Luzon Strait to enter the SCS, carrying North Pacific Tropical Water (NPTW) into the basin. Using the subsurface salinity maximum as a tracer for NPTW, the authors show how important three secondary straits—the Taiwan Strait to the north and the Karimata and Mindoro Straits to the south—are to the NPTW intrusion at the Luzon Strait. The authors demonstrate that the SCS cannot reach an equilibrium state that is consistent with the observed subsurface salinity distribution unless all of the following components are in place: the Kuroshio, transports through the three secondary straits, downward mixing of freshwater, horizontal mixing induced by mesoscale eddies, and forcing by the local monsoonal winds.

Field Observation to evaluate Function of Yatsu Tidal Flat in Nutrients Budget of Tokyo Bay in Autumn

In order to estimate nutrients budget of a tidal flat, a field observation was conducted in autumn in Yatsu tidal flat which is connected to Tokyo Bay only through two rivers. Measured water level showed asymmetric variation with relatively longer duration for low tide, due to nonlinear effect of the semi-enclosed water body connected to the open sea by narrow and shallow rivers. It was also found that the Yatsu tidal flat was the source of nutrients for Tokyo Bay in autumn, owing to the overgrowth of ulva in spring and summer. Thus, Yatsu tidal flat is considered to be a temporal buffer for storing nutrients. The outflow of SS exceeds the inflow, resulting in the change of surface sediments from mud to sand.

Numerical modeling of nonlinear resonance of semi-enclosed water bodies: Description and experimental validation

The purpose of this work is to a present a numerical model to solve a set of modified Boussinesq equations to analyse nonlinear resonance of semi-enclosed water bodies. The equations are solved on a finite element unstructured grid in order to achieve an optimal mesh resolution with the local geometry. The model is able to simulate long time lapses and realistic forcing in real bathymetries with a reasonable computational cost. To validate the numerical results, a set of experiments was carried out in a physical model of two adjacent elongated basins. Comparisons between numerical and experimental results for different geometries and nonlinear conditions show that the model is able to simulate with an excellent agreement the transient nonlinear resonant process.

Hydrodynamics of a Coastal Bay. Natural and Man-made Barriers

This paper deals with wind-induced flows in a semi-enclosed water body in a microtidal environment that is subject to various wind-wave and river discharge conditions. The resulting currents are analyzed using numerical models supplemented by (and calibrated with) field observations. The emphasis is on the driving efficiency of wind fields in generating steady currents as a function of wind velocity and direction. The circulation generated is analyzed for the actual case of Cullera Bay and for a theoretical case in which the cape (limiting barrier) has been “removed” from the computational domain. The results obtained as a part of the EU research project ECOSUD, allow the barrier effect exerted by the cape to be partially quantified. The river plume dimensions and direction of spread are clearly influenced by the cape barrier. On a more local scale, the effluent discharge from the outfall was also found to be influenced by the two Júcar River jetties. Based on these results, a “retention” index that partly characterizes water quality in the bay is defined. This type of index is also a scientifically based indicator that supports more sustainable management of water quality in coastal bays of this type.

Modelling water renewal in a coastal embayment

A hydrodynamic model was applied to calculate the flow field and the renewal time in Salman Bay, a semi-enclosed coastal water body of particular environmental significance in the region of Jeddah, Saudi Arabia. Initially the model was calibrated with field data. It was then applied to assess the effect of a series of engineering modifications of Salman Bay, involving enlarging of the cross-section of a link channel to the Red Sea, dredging of the bay, and reclamation of islands inside the bay, on the flow characteristics and the renewal of waters. Calculations showed that the channel upgrading would significantly improve the renewal of the bay waters. For tidal calculations the renewal time was reduced from 48·6 days to 12·7 days, whereas for a wind-driven regime it was reduced from extremely large values to 13–34 days.

Tidal exchange of zooplankton between Lough Hyne and the adjacent coast

Plankton samples collected in November 2002, February, May and August 2003 were used to examine seasonal variation in tidal exchange of zooplankton biomass, abundance and species composition between Lough Hyne Marine Nature Reserve and the adjacent Atlantic coast. Micro- to mesozooplankton were collected by pump over 24-h sampling periods during spring and neap tides from the narrow channel connecting the semi-enclosed water body to the Atlantic. Sample biomass (dry weight) and total zooplankton abundance peaked in the summer and were lowest in winter, showing a positive relationship with temperature. Zooplankton biomass, total abundance and numbers of holo- and meroplankton revealed import during some diel cycles and export in others. However, the tidal import of these planktonic components was generally dominant, especially during May. The greatest import of numbers of holoplankters and meroplanktonic larvae occurred during May and August, respectively. There was no significant variation in sample biomass between periods of light and dark, but some variation in zooplankton abundance could be explained by this diel periodicity. Significant differences in sample assemblage composition between flood and ebb tide samples were always observed, except during winter neap tides. There was a net import of the copepods Temora longicornis and Oithona helgolandica and the larval stages of Mytilus edulis during spring and summer. Proceraea cornuta and Capitellid trochophores were imported during winter, and a hydrozoan of the genus Obelia during the spring spring tides. Seasonal export from the lough was shown by Pseudopolydora pulchra larvae (autumn and spring), Serpulid trochophores (autumn) and veligers of the bivalve Anomia ephippium (summer). It is suggested that the direction of tidal exchange of meroplanktonic taxa is related to the distribution of the adult populations. Copepod naupliar stages dominated the assemblages except during May spring tides when the copepod Pseudocalanus elongatus made up over 22% of the abundance. The general import of micro- to mesozooplankton may, in part, explain the higher densities of this size-class of zooplankton within the semi-enclosed system of Lough Hyne.

A Review of Marine Environmental Contaminant Issues in the North Pacific: The Dangers and How to Identify Them

AbstractFor Abstract see ChemInform Abstract in Full Text.

A review of marine environmental contaminant issues in the North Pacific: The dangers and how to identify them

Chemical contaminants in the North Pacific Ocean include hydrocarbons, persistent organic pollutants, metals, persistent solids, and domestic pollutants. Here, we review contaminant research conducted over the past decade, finding that the effects of contaminants cannot be considered in isolation from other major factors causing change to North Pacific ecosystems. Climate change, over-fishing, habitat destruction, eutrophication, and the introduction of exotic species interact with one another and alter contaminant pathways. Climate change and over-fishing are perceived as the main threats to the remote northern marginal seas, the central North Pacific, and the west coast of North America, with contaminants engendering local concern, especially in semi-enclosed bodies of water. Climate change receives less attention in Asian waters, probably because widespread habitat destruction and contamination provide, by themselves, an impending ecological disaster. A systematic approach is urgently required to recognize and prioritize the threats to North Pacific coastal ecosystems. This should include box models, case studies, proxy records, and time series. The ocean should be monitored as a system, including physical media (water, sediment) and the full trophic range of the food web, and tissues should be preserved in archives to provide a resource for understanding emerging concerns. Finally, the development of ecological indicators is urgently required to provide a robust warning system based on the health of the marine ecosystems themselves. It is time to conduct a multi-national assessment of the North Pacific Ocean to develop a common, factual awareness of the threats looming over our coastal waters. Key words: contaminants, climate change, ecosystem change, monitoring, North Pacific, trends.

Evidence of blue marlin, Makaira nigricans, spawning in the vicinity of Exuma Sound, Bahamas

Exuma Sound is a semi-enclosed body of water bounded by islands of the Bahamas. During July 2000, sampling for larval billfish was carried out throughout the Sound's surface waters as well as in adjacent open waters of the Atlantic Ocean. A total of 99 larval billfish (Istiophoridae) was collected. Ninety of the larvae were identifiable as blue marlin (Makaira nigricans) and three as sailfish (Istiophorus platypterus). The remaining larvae were also istiophorids, unidentified to species owing to damage; no larval Xiphias gladius were collected. Larval blue marlin densities ranged from 0 to 3.4 larvae/1000 m2; their sizes ranged from 3.1 mm notochord length to 22.6 mm standard length. Densities tended to be highest north-east of the Sound's central axis, especially within the two regions where exchange with the Atlantic is greatest. Mean densities tended to decrease in the direction of mean flow; mean lengths increased from 8.08 mm at the Sound's mouth to 14.7 mm standard length at its upper reaches. Length-based estimates of larval age ranged from 2.2 to 17.2 days. Given these age estimates and assuming passive surface transport, the blue marlin larvae collected were likely the result of recent spawning in waters that include Exuma Sound and may extend some 200 km south-east of its mouth. This study suggests that Exuma Sound functions as a nursery area for blue marlin, and possibly other billfish species, at least during the summer. Limited sampling just outside Exuma Sound, in the Atlantic Ocean proper, also yielded blue marlin larvae.

Heavy-metal contaminants in Tamaki Estuary: impact of city development and growth, Auckland, New Zealand

Tamaki Estuary is a large, semi-enclosed water body on the eastern side of the Auckland metropolitan area. The long and relatively narrow channel of the estuary (ca. 17 km in length) is surrounded by an urbanised and industrialised catchment. The catchment is noted for more than 600 industrial premises in addition to a range of other human activities associated with pastoral and urban land-use changes during the last 150 years. The study of seven estuary cores shows that sedimentation rates as well as the sediment coarse fraction have increased with the development of the catchment. Significant enrichments were also found for Cd, Cu, Pb, and Zn in the upper part of the cores, compared to the much lower concentrations found below 40–50 cm (considered to represent pristine background levels). Spatial association of contaminants with industrial areas and yacht anchorages, and temporal enrichments associated with the intensive urbanisation and development of the catchment since 1945 indicate that these pollutants are related to anthropogenic activities.

3D layered-integrated modelling of mass exchange in semi-enclosed water bodies

The flow patterns in semi-enclosed water bodies are generally complicated and have significant effect on the water quality and fluid exchange there. The exchange of of fluid between the semi-enclosed water body and outside is due to two physical mechanisms. The first is the flushing due to tidal effect. The second is the shear induced by the velocity difference between the flow within the water body and outside. To predict the flow and solute transport in these water bodies a three-dimensional layer-integrated numerical model has been developed. To account for the turbulence which consists of the free shear component and the bottom friction component the k-e model is employed. The numerical model has been applied to the cases of tidal flow as well as steady river flow outside a rectangular harbour with or without breakwater. Compared with the available experimental results, the gross mass exchange both due to tidal effect and shear can be estimated satisfactorily by the numerical model.

The hydrography and water masses of the Natal Bight, South Africa

The Natal Bight is an unusually wide coastal offset on South Africa's east coast along an otherwise uniformly narrow shelf. Interaction with the deep sea is limited by the strong Agulhas Current along the shelf edge. This semi-enclosed body of water has an unusual role in the local shelf ecosystem and also plays an important triggering role in major perturbations to the trajectory of the Agulhas Current. We present the results of the first dedicated research cruise that has encompassed the hydrography of the whole Bight. Water in the Bight consisted of South Indian Subtropical Surface Water and Indian Tropical Surface Water. There was only a negligible effect of river runoff. The topographically induced upwelling cell at the northern end of the Bight was characterised by lower temperatures, higher salinities, higher nutrients and higher chlorophyll a values. This upwelled water dominated the northern part of the Bight on this occasion and there is substantial evidence that the upwelling cell supplies the bottom water for the whole bight. There was little comparable water exchange along the rest of the shelf edge. This cell therefore also controls the supply of nutrients to the whole Bight. The abnormal divergence of the Agulhas Current from the shelf edge near Durban during the cruise suggests the initial stages of a Natal Pulse. Surface temperature distributions and nitrate values indicate a cyclonic motion in this incipient pulse.

A Study on the Surface Current in the Japan Sea based on the Numerical Simulation

The Japan Sea is a semi-enclosed water body with complicated geometry and a narrow strait of Tsushima through which sea current enters. As for the surface current of the Japan Sea, tidal component is weak followed by the sea current component. In wintertime the strong seasonal wind blows over the Japan Sea to induce the surface current. The purpose of this paper is to develop a method to estimate the surface current in winter quantitatively. Firstly the observed data of wind and surface current off the Noto Peninsula is analyzed to obtain the predominant flow direction of Northwest and the magnitude of the wind driven flow of about 15cm/s. Secondly, the numerical model to calculate tidal flow and sea current is developed with the obtained maximum tidal flow of about 15cm/s and sea current about 3cm/s of the Noto Peninsula, confirming the predominance of the wind driven current.

Simulation of free surface recirculating flows in semi-enclosed water bodies by a k– ω model

The flow patterns in semi-enclosed water bodies with free surfaces generally consist of free or forced recirculations which can have significant effect on the water quality and fluid exchange. To accurately predict the flow structures in these water bodies a three-dimensional layer-integrated numerical model has been developed. The turbulence (consisting of the free shear component and the bottom friction component) is parametrized by the k– ω equations. The governing equations are split into three parts in the finite difference solution: advection, dispersion and propagation. The advection part is solved by the four-node minimax-characteristics scheme. The dispersion part is solved by the central difference method and the propagation part is solved implicitly by using the Gauss–Seidel iteration method to overcome the restrictive Courant–Friedrich–Lewy (CFL) stability constraint. The model has been verified against the laboratory data on forced recirculating flow in a physical model harbour and on free recirculating flow in an expanded channel.