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A discharge mixing zone (DMZ) is a defined geographical area or volume of water in the receiving environment of a discharge where initial dilution of the effluent occurs and where exceedance of water quality criteria may be permitted. DMZs are essential to inform determination of discharge consent conditions and an important element of risk management frameworks to reduce any effects of the discharges on the environment and human health. In this review, we describe the principles and technical application of DMZs. We present an overview of the physical processes that govern the dispersion and dilution of wastewater discharges and the fate of contaminants in coastal environments and define key criteria for determining the size of DMZs. We summarize DMZ requirements in international legislation and guidance and exemplify their application to different types of discharges by means of case studies. The selected case studies illustrate different modelling tools for defining DMZs and different monitoring approaches to assess their effectiveness in achieving ecological and human health objectives.

SUMMARYTrade in ornamental marine species in Australia, a country with relatively stringent import controls, was investigated using a telephone survey of wholesalers and retailers, and a desktop review of internet import databases and hobbyist trading websites. Information on the regulatory framework was obtained from government and other published or online sources, and from staff of regulatory agencies. Although the trade is small relative to that in the USA, Europe and parts of Asia, Australia imports significant numbers of marine fish each year for the aquarium trade. Many of the more than 200 species imported have the potential to become environmental and/or economic pests. Imported individuals of native species could act as vectors of disease or affect the genetic diversity of native populations if they were released into the wild. Regulatory measures include the use of lists of permitted species of plants and animals, a case-by-case risk assessment process for species not on these lists, and requirements for health certification and quarantining of imported stock. Once within Australia, however, translocation is less rigorously controlled, being managed by individual states and based largely on lists of prohibited species, though generally with scope for case-by-case assessment and refusal of permits for unwanted species, such as recognized pests. Wholesalers and retailers interviewed generally showed a responsible attitude to the disposal of dead or unwanted stock, but awareness and understanding of the potential pest risk of ornamental marine species was generally poor. The importance of raising public awareness of the pest potential of ornamental marine species is likely to increase with the growing importance of mail-order and internet trade.

Fish are often attracted to floating structures, particularly as juveniles, and in many parts of the world longline mussel farms provide complex, three-dimensional floating structures in coastal waters. There have been few quantitative studies of the assemblages of fish living on and around mussel farms. We sampled fish on mussel farms at three sites in the north of the South Island of New Zealand over a year to characterise the assemblages present and their variability. Predictions of the species likely to be present were made on the basis of their occurrence in the general area, habitat preferences, and occurrence around floating structures in previous studies. The farms differed in their degree of exposure, distance from shore and degree of riverine and oceanic influence. Fish were sampled by underwater visual census, and a remote-operated vehicle, and destructively sampled using an anaesthetic. Abundances of fish on the mussel lines were small (median values up to 1.25 fish m 1 of line) and were dominated by small, demersal species characteristic of rocky reefs in the area, notably triplefins (Forsterygion lapillum and Grahamina gymnota, Family Tripterygiidae) and the wrasse Notolabrus celidotus. The abundances and species of fish present differed among sites and among sampling methods (but the small and inconsistent numbers of fish recorded precluded formal statistical testing of differences). Few large, commercially or recreationally important species (demersal or pelagic) were recorded. Triplefins may recruit to the lines at settlement from planktonic larvae and spend their entire lives there. N. celidotus, in contrast, may recruit to stands of macroalgae on nearby rocky reefs and move to farms later. Direct recruitment of N. celidotus may be limited by the low abundances of macroalgae on the mussel lines. D 2005 Elsevier B.V. All rights reserved.

The conservation importance of estuaries is often measured by bird numbers, but monitoring numbers is not necessarily a reliable way of assessing changes in site quality. We used an individual-based model, comprised of fitness-maximising individuals, to assess the quality of the Humber estuary, UK, for 9 shorebirds; dunlin Calidris alpina, common ringed plover Charadrius hiaticula, red knot Calidris canutus, common redshank Tringa totanus, grey plover Pluvialis squatarola, black-tailed godwit Limosa limosa, bar-tailed godwit L. lapponica, Eurasian oystercatcher Haematopus ostralegus and Eurasian curlew Numenius arquata. We measured site quality as predicted overwinter survival. The model accurately predicted the observed shorebird distribution (if non-starving birds were assumed to feed on any prey or patch on which intake rate equalled or exceeded their requirements), and the diets of most species. Predicted survival rates were highest in dunlin and common ringed plovers, the smallest species, and in Eurasian oystercatchers, which consumed larger prey than the other species. Shorebird survival was most strongly influenced by the biomass densities of annelid worms, and the bivalve molluscs Cerastoderma edule and Macoma balthica. A 2 to 8 % reduction in intertidal area (the magnitude expected through sea level rise and industrial developments) decreased predicted survival rates of all species except the dunlin, common ringed plover, red knot and Eurasian oystercatcher. This paper shows how an individual-based model can assess present-day site quality and predict how site quality may change in the future. The model was developed using existing data from intertidal invertebrate and bird monitoring schemes plus new intertidal invertebrate data collected over 2 winters. We believe that individual-based models are useful tools for assessing estuarine site quality.

The Australian native colonial ascidian Eudistoma elongatum has spread throughout harbours and oyster farms in Northland, New Zealand. This paper summarizes results of a study on the biology, ecology and potential methods of control of this recently introduced species. Colonies were reproductive for nine months of the year and embryos were present in zooids at water temperatures above 14 o C. Low salinity was most likely the cause of variation in reproductive status observed. Larvae were able to swim for up to 6 hours, and remain viable at temperatures as low as 10°C at salinities above 20 psu. Only acetic acid was effective at killing colonies. Control using heat or other chemicals was not feasible for shallow subtidal populations identified in the study. E. elongatum has the potential to spread further within already occupied harbours, and to more southern harbours in New Zealand.

Data collected at marine farm sites on Stewart Island, New Zealand, were used to test the model for prediction of benthic impact of salmon net-pens proposed by Findlay and Watling [Findlay, R.H., Watling, L., 1997. Prediction of benthic impact for salmon net-pens based on the balance of benthic oxygen supply and demand. Mar. Ecol.: Prog. Ser., 155, 147–157.]. The model uses the ratio of oxygen supply to the benthos (based on Fickian diffusion and current velocities above the seabed) to oxygen demand (based on rate of input of organic carbon to the benthos) as a predictor of benthic response to input of organic matter from farms. Estimates of the rate of input of carbon and supply of oxygen to the seabed below an operating salmon farm in this study provided predictions of the severity of impact that compared reasonably well with the observed anoxic nature of the sediment and presence of patches of Beggiatoa -like growths. At a site where farming of salmon has recently ceased, the model predicted rates of mineralisation of organic carbon in the sediments of 279–908 mmol m −2 d −1 (depending on the method of summarising data on current velocity). This was in reasonable agreement with the rates derived from the observed decrease in the depth of the layer of waste over the period of a year (476–1206 mmol m −2 d −1 ) and with rates derived from measurements of fluxes of several chemical species from the sediments (146–525 mmol m −2 d −1 ). These results suggest that the model has utility beyond the locality for which it was originally developed and that it may also be useful for predicting rates of recovery of farm sites. Accumulation of zinc and copper (derived from food and antifoulants) in sediments below farms may significantly affect recolonisation of sediments by benthic organisms.

An underlying assumption of laboratory-based toxicity tests is that the sensitivity of organisms in the laboratory (in vitro) is comparable to that in the field (in situ). We tested this assumption by exposing estuarine amphipods (Chaetocorophium cf. lucasi) to a concentration series of cadmium-spiked sediments in vitro and in situ for 10 d. In situ exposures were conducted within plastic-mesh cages on an intertidal mudflat. To characterize exposure, we measured interstitial water cadmium concentrations (IWCd), acid volatile sulfide (AVS), and simultaneously extracted Cd (SEMCd) at the beginning and end of the exposures. Between day 0 and day 10, AVS decreased in both in vitro and in situ exposures, while IWCd levels declined less in vitro (median 27%) than in situ (median 76%). Despite more extreme conditions of temperature (10–36°C) and salinity (18–22%o) in situ, in vitro and in situ exposures showed comparable survival responses based on SEMCd/AVS (LC50 [95% CI]: 1.6 [1.46–1.78] and 1.8 [1.76–1.83], respectively), with the onset of marked mortality above a SEMCd/AVS value of about one and minimal survival (

Previous reviews of mangrove biology focused on the more extensive and diverse tropical examples, with those of temperate regions generally relegated to a footnote. Temperate mangroves are distinctive in several ways, most obviously by the lower diversity of tree species. Their occurrence in relatively developed countries has created different issues for mangrove management from those in the tropics. Mangroves in several temperate areas are currently expanding, due to changes in river catchments, in contrast to their worldwide decline. Information derived from the greater body of research from tropical regions has sometimes been applied uncritically to the management of temperate mangroves. The growing body of information on the ecology of temperate mangroves is reviewed, with emphasis on productivity, response to anthropogenically enhanced rates of sediment accumulation, and potential effects of climate change. There is no unique marine or estuarine fauna in temperate mangroves, but the poorly known terrestrial fauna includes mangrove-dependent species. Although productivity generally declines with increasing latitude, there is overlap in the range of reported values between temperate and tropical regions and considerable within-region variation. This, and variation in other ecologically important factors, makes it advisable to consider management of temperate mangroves on a case-by-case basis, for example, when responding to expansion of mangroves at a particular location.

Differences in average body size among allopatric and sympatric populations of hydrobiid mudsnails have been interpreted as the consequence of interspecific competitive interactions. Recently, however, doubts have been expressed concerning the certainty with which size differences can be ascribed simply to character displacement. Other environmental factors are known to influence body size in hydrobiids. In the present study one of these, sediment type, was investigated.Average body weight of Hydrobia ulvae (Pennant) living on fine mud was consistently higher than that of members of the same species living on adjacent muddy sand. Snails were transplanted from one sediment type to the other, confined within cages, and their growth rates compared with those of control animals caged on their native sediment. The results of this experiment suggested that substrate type is one factor controlling body size, but the inconclusive nature of the results indicate that others are also involved.

Unburnt coal is a widespread and sometimes very abundant contaminant in marine environments. It derives from natural weathering of coal strata and from anthropogenic sources including the processing of mined coal, disposal of mining wastes, erosion of stockpiles by wind and water, and spillage at loading and unloading facilities in ports. Coal is a heterogeneous material and varies widely in texture and content of water, carbon, organic compounds and mineral impu- rities. Among its constituents are such potential toxicants as polycyclic aromatic hydrocarbons (PAHs) and trace metals/metalloids. When present in marine environments in sufficient quantities, coal will have physical effects on organisms similar to those of other suspended or deposited sediments. These include abrasion, smothering, alteration of sediment texture and stability, reduced availability of light, and clogging of respiratory and feeding organs. Such effects are relatively well documented. Toxic effects of contaminants in coal are much less evident, highly dependent on coal composition, and in many situations their bioavailability appears to be low. Nevertheless, the presence of contaminants at high concentrations in some coal leachates and the demonstration of biological uptake of coal-derived contaminants in a small number of studies suggest that this may not always be the case, a situation that might be expected from coal's heterogeneous chemical composition. There are surprisingly few studies in the marine environment focusing on toxic effects of contaminants of coal at the organism, population or assemblage levels, but the limited evidence indicating bioavailability under certain circumstances suggests that more detailed studies would be justified.

Many coastal cities are situated around estuaries, which act as traps for urban-derived contamination. To investigate urban development options, to help manage the urbanization process, and to set priorities for retrofitting urban stormwater controls, a model was developed to predict the build-up of contaminants (Pb, Zn, and Cu) in the sediments of sheltered estuaries. This model broadly integrates processes occurring in the estuary and predicts the distribution of sediment-associated contaminants throughout the estuary. It is based on yields of suspended sediment and contaminants from developing and mature catchments and is applicable to shallow, sheltered estuaries and harbors that have accumulated fine sediments. The information required to develop and run the model, and the sensitivity of the model to variation in its parameters, is described in detail.

We describe the results of a sampling program to test a simple, management-oriented, predictive model of the build-up of contaminants (Cu, Pb, and Zn) in sediments in sheltered estuaries. The model, described in detail in a companion paper, is generally applicable to these environments but its development and testing is described for two urban estuaries in Auckland, New Zealand. There was good agreement between observed concentrations of metals and those predicted by the model. The model predicted larger concentrations within a defined settling zone at the upper end of the estuary than outside this zone, and such a difference was detected for lead and zinc. Differences in concentrations of metals were detected among locations several hundreds of meters apart, with increasing concentrations from downstream to upstream locations. These patterns were apparent above smaller scale variation among and within sites 10s of meters apart within each location. This small-scale variation did not conform to any obvious patterns. For example, there were no clear patterns in the metals distributions in sediments among different shore heights. Patterns of contaminants distributions found in the present study may be generalized to similar urban estuaries in other parts of the world through their correspondence to those derived from the model, which is based on general assumptions and principles.

Earlier studies have shown that, despite the similarity of their diets, the presence of the amphipod Corophium arenarium Crawford has no negative effect on the growth rate of the prosobranch Hydrobia ulvae (Pennant), and that the former species is capable of removing a larger portion of the sediment microflora. In the present study, qualitative differences in the effects of grazing by the two species, in terms of alteration of the attractiveness of sediment by pregrazing, were investigated. In choice tests, it was found that, although Corophium would discriminate against sediment grazed by its own species in favour of ungrazed sediment, it did not similarly discriminate against Hydrobia-gtazed sediment. This latter choice was in favour of sediment containing significantly lower numbers of microalgae, implying that grazing by the snail left behind a sufficient and suitable fraction of the microflora to attract Corophium. Hydrobia discriminated against sediment grazed by either species. It is, therefore, suggested that the dietary range of the amphipod, at least when deposit-feeding, is generally broader than, and includes, that of the snail. Further evidence, however, suggests that part of the dietary spectrum of Hydrobia may lie outside that of Corophium .

The mud snail Hydrobia ulvae (Pennant) and the amphipod Corophium arenarium Crawford were used in a series of laboratory and field experiments to investigate the hypothesis that natural populations of such deposit-feeders live under conditions of resource limitation. Growth rates of Hydrobia confined at several different densities within cages in the field and in laboratory microcosms indicated that density-dependent reduction of growth rate and increased mortality occurred at densities found in natural populations. Similar experiments failed to provide any evidence that Corophium mortality or behaviour was modified by the presence of Hydrobia or members of its own species; nor did the presence of Corophium cause a reduction in growth rate of Hydrobia .