N.R. Loneragan

A new approach for detecting and mapping sewage impacts

Increased nitrogen loading has been implicated in eutrophication occurrences worldwide. Much of this loading is attributable to the growing human population along the worlds coastlines. A significant component of this nitrogen input is from sewage effluent, and delineation of the distribution and biological impact of sewage-derived nitrogen is becoming increasingly important. Here, we show a technique that identifies the source, extent and fate of biologically available sewage nitrogen in coastal marine ecosystems. This method is based on the uptake of sewage nitrogen by marine plants and subsequent analysis of the sewage signature (elevated delta 15N) in plant tissues. Spatial analysis is used to create maps of delta 15N and establish coefficient of variation estimates of the mapped values. We show elevated delta 15N levels in marine plants near sewage outfalls in Moreton Bay, Australia, a semi-enclosed bay receiving multiple sewage inputs. These maps of sewage nitrogen distribution are being used to direct nutrient reduction strategies in the region and will assist in monitoring the effectiveness of environmental protection measures.

Physiological and morphological responses of the seagrass Zostera capricorni Aschers. to light intensity

The responses of the seagrass Zostera capricorni Aschers, to changes in light intensity were examined in flowing seawater aquaria experiments. Plants were grown in six light regimes: full sunlight (100%), 50, 30, 20, 15, and 5% of full light over a 2-month period. Measurements of growth, biomass, pigments, stable isotopes and leaf anatomy were made at the end of the experiment. Plants survived under all light treatments, even below minimum light requirements of related seagrasses. However, the experimental light levels possibly do not correspond to light reaching seagrass leaves under natural conditions. Plants grown under high light conditions (50–100% light) had smaller shoots, higher biomass and productivity, less negative δ13C values, lower leaf nitrogen content, less chlorophyll and more ultraviolet light absorbing pigment than plants grown under low light conditions (<20% light). Photoadaptation by ultraviolet light absorbing pigment(s) was noted, with more variability in ultraviolet light pigments than in chlorophyll levels. Increased CO2 demand and/or increased CO2 recycling in internal gas spaces may account for the less negative δ13C values in high light treatments, indicating less isotopic discrimination in seagrass leaves in high light. A saturation response of growth rates to light intensity was observed, with less substantial growth reductions at lower light intensities than observed in other seagrass shading experiments. Nutrient limitation in high light was inferred by a growth maximum at 50% light level, increased root biomass and lower leaf nitrogen content in high light treatments. Overall, a wide range of morphological and physiological photoadaptive responses not previously reported in Zostera capricorni was observed.

LIGHT INTENSITY AND THE INTERACTIONS BETWEEN PHYSIOLOGY, MORPHOLOGY AND STABLE ISOTOPE RATIOS IN FIVE SPECIES OF SEAGRASS

The effects of light intensity on stable isotope ratios, physiology and morphology of five seagrass species were investigated in an outdoor, light controlled experiment. Seagrasses were maintained in flowing seawater aquaria, with each seagrass species exposed to different light regimes (5, 15, 20, 30, 50, and 100% full sunlight) using shade screens. After 30 days exposure to the various light regimes the five species of seagrass showed markedly different δ13C signatures, with values ranging from −17.6 to −5.5%. Marked responses to light intensity were also shown by each species, with leaf δ13C values becoming at least 3 to 4%. less negative in full sunlight. Other common responses to light intensity were: higher productivities, higher C:N ratios, larger lacunal areas and more root biomass under full sunlight compared with lower light intensities. Less negative δ13C values at high light intensities could be primarily due to (a) increased uptake of 13C from the external C source or (b) increased internal recycling of CO2 in the lacunae due to the increased lacunal size. The increase in size of lacunae may be related to the need to supply more oxygen to the increased root biomass occurring in seagrasses under high light conditions. In contrast to δ13C, the δ15N values of seagrass leaf tissue appeared to be affected by the site of collection, rather than the species of seagrass or light intensity. Higher δ15N values were found at the more eutrophic site (western Moreton Bay = 8.6 to 8.8%.) than at the site further from anthropogenic influence (eastern Moreton Bay = 2.6 to 4.5%.).

A New Era for Restocking, Stock Enhancement and Sea Ranching of Coastal Fisheries Resources

The growing number of countries investigating the potential for releasing cultured juveniles to augment coastal fisheries resulted in the First International Symposium on Stock Enhancement and Sea Ranching (ISSESR) in Norway in 1997. The 1st and 2nd ISSESR, in Japan in 2002, were instrumental in developing methods for mass production of environmentally fit juveniles and for releasing them in responsible ways. The 3rd ISSESR, held in the U.S.A. in 2006 (www.SeaRanching.org), ushered the discipline into a new era. The major advances included: (1) definitions of the various objectives for releasing cultured juveniles (restocking, stock enhancement, and sea ranching); (2) a framework for integrating releases within their fisheries management context, including tools for quantitative assessment; (3) a systematic, transparent, and stakeholder-participatory planning process to determine whether releases have a cost-effective role to play in managing a fishery; (4) a comprehensive case study (blue crabs in Chesapeake Bay) describing the multi-disciplinary approach needed to evaluate the potential benefits of releases; and (5) a suite of other lessons to guide stakeholders in evaluating the potential for and implementation of releases. The papers in this Special Issue of Reviews in Fisheries Science elaborate how restocking, stock enhancement and sea ranching programs can create synergies between aquaculture and some coastal fisheries to help meet the future demand for seafood and aid in restoring depleted stocks.

Restocking and stock enhancement of marine invertebrate fisheries

1. Introduction 2. Restocking Initiatives 2.1 Giant Clams 2.2 Topshell 2.3 Sea Cucumbers 3. Stock Enhancement Initiatives 3.1 Scallops 3.2 Other Bivalves 3.3 Abalone 3.4 Queen Conch 3.5 Shrimps 3.6 Spiny Lobsters 3.7 Lobsters 3.8 Sea Urchins 4. Overview and Progress Towards a Responsible Approach 4.1 Restocking Initiatives 4.2 Stock Enhancement Initiatives 5. Lessons Learned 5.1 Lessons for Restocking 5.2 Lessons for Stock Enhancement 5.3 Lessons for both Restocking and Stock Enhancement 6. Management of Restocking and Stock Enhancement 6.1 Information to Evaluate the Need for Restocking 6.2 Management of Restocking 6.3 Information to Evaluate the Need for Stock Enhancement 6.4 Management of Stock Enhancement 6.5 Measures to Optimize Social and Financial Benefits of Restocking and Stock Enhancement 6.6 Independent Assessments 7. Other Important Considerations for all Initiatives 7.1 Measuring Success 7.2 Genetic Considerations 7.3 Disease risks 7.4 Other Environmental Impacts Conclusions 8.1 Achievements 8.2 The Responsible Approach 8.3 The Way Forward 8.4 Future Research 8.5 Summary Remarks Acknowledgements References Appendix

Influence of site, season and year on contributions made by marine, estuarine, diadromous and freshwater species to the fish fauna of a temperate Australian estuary

Catches obtained at regular intervals by beach seining, gill netting and otter trawling at ten, four and six sites, respectively, have been used to determine the contribution of the different species and life-cycle categories of fish to the ichthyofauna of the large Swan Estuary in temperate south-western Australia between February 1977 and December 1981. These data were also examined to investigate the influence of site, season and year on the densities of the more abundant species. A total of 630 803 fish, representing 36 families and 71 species, were caught in the shallows using beach seines during this 5 yr study. Although the majority of these species were marine teleosts that were caught infrequently (marine stragglers), representatives of 7 of the 15 most abundant species were marine teleosts which entered the estuary regularly, and in large numbers (marine estuarine-opportunists). Of the remaining 8 most abundant species in the shallows, 7 completed their life cycle within the estuary (estuarine species) and 1 (Nematalosa vlaminghi) was anadromous, feeding for a period at sea and spawning in the upper reaches of the estuary. The contribution of individuals of the marine estuarine-opportunist category to catches in the shallows declined from nearly 95% in the lower estuary, to 17% in the middle estuary and 6% in the upper estuary. The estuarine and anadromous groups made a considerable contribution to the catches in both the middle and upper estuaries. By contrast, the contribution of freshwater species was small and even in the upper estuary accounted for only 0.2% of the catch. Site within the estuary generally influenced the catches of individual species to a greater extent than either season or year, or the interactions between these factors. When seasonal effects were strong, they could be related to summer spawning migrations into the upper estuary (Nematalosa vlaminghi, Amniataba caudavittatus), spring immigrations into the lower estuary (Mugil cephalus), or winter movements into deeper and more saline waters (Apogon rueppellii). Annual variations in the density of Torquigener pleurogramma were related to marked annual differences in the recruitment of the 0+age class.

Effects of light deprivation on the survival and recovery of the seagrass Halophila ovalis (R.Br.) Hook

Survival and recovery of the seagrass Halophila ovalis (R.Br.) Hook during and after light deprivation was investigated to assist in the interpretation of recent losses of Halophila spp. in Queensland, Australia. Light deprivation experiments were conducted in outdoor aquaria and in situ at two water depths. Halophila ovalis plants were deprived of light for a maximum of 30 days, and recovery processes were investigated for up to 18 days following 15 days of light deprivation. Measurements of H. ovalis biomass, storage carbohydrate concentrations, chlorophyll a+b concentrations, stable carbon isotopes ratios (δ13C) and chlorophyll a fluorescence parameters (F0, Fm and Fv/Fm) were made during and at the end of the light deprivation and recovery periods. Biomass declined after 3–6 days in the dark and complete plant death occurred after 30 days. During the recovery period, biomass continued to decline for a short duration of time before stabilising. Sugar concentrations declined rapidly for the first 2 days of light deprivation before stabilising, then increased rapidly during the recovery period. Chlorophyll a+b concentrations were sensitive to very small differences in light availability: concentration decreased in total darkness, remained unchanged at 0.1% of surface irradiance and increased at 0.5% of surface irradiance. Photochemical efficiency of photosystem II (Fv/Fm) remained unchanged during the light deprivation and recovery periods. The lack of response in δ13C during light deprivation indicated the cessation of carbon fixation. Decreased sugar utilisation after 2 days of light deprivation indicated a reduction in respiration and growth. Starch concentrations did not change during light deprivation, suggesting the inhibition of starch utilisation by anaerobic conditions within the plant. Plant death after 30 days was notably faster than previously reported for other species of seagrass. The rapid die-off may be due to a shortage of available carbohydrates or due to a build-up of the phytotoxic end products of anaerobic respiration. Overall, H. ovalis has a very limited tolerance to light deprivation when compared to larger species of seagrass. Consequently, the persistence of this species in coastal marine environments may be dependent upon the occurrence and duration of transient light deprivation events.

Spatial and seasonal differences in the fish fauna in the shallows of a large australian estuary

Samples of fish were collected by beach seine throughout the shallow waters of the large Peel-Harvey estuarine system (south-western Australia) in the wet (June to November) and dry periods (December to May) between August 1979 and July 1981. The number of species, density and biomass declined with distance from the estuary mouth and rose with increasing temperature and salinity. Both classification and ordination distinguished the faunal composition of the saline reaches of the rivers from that of the narrow Entrance Channel and two large basins (Peel Inlet and Harvey Estuary). Classification also separated the fauna of the riverine group into wet- and dry-period components, and divided samples taken in the Entrance Channel from those in the basins. Differences between the faunal composition of the Peel Inlet and its tributary rivers were related to differences in salinity regime. The riverine fauna was subjected to much more variable and lower minimum salinities. Species characteristic of the rivers included teleosts such as Atherinosoma wallacei and Amniataba caudavittatus, which are estuarine sensu stricto in southwestern Australia, the semi-anadromous Nematalosa vlaminghi and juveniles of the marine Mugil cephalus. The species diagnostic of the wet periods in the rivers were the estuarine species A. wallacei and Favonigobius suppositus, while the dry periods were characterised by the marine species Atherinomorus ogilbyi and Sillago schomburgkii. Marine species also characterised the Entrance Channel (Favonigobius lateralis, Sillago bassensis), whereas the indicators in Peel Inlet and Harvey Estuary were Hyporhamphus regularis and Apogon rueppellii, both of which can pass through the whole of their life cycle in estuarine as well as marine environments.

Factors influencing community structure and distribution of different life-cycle categories of fishes in shallow waters of a large Australian estuary

Fish were collected at regular intervals over 5 yr (February 1977 to December 1981) from ten shallow-water sites located throughout the lower, middle and upper regions of the large Swan Estuary in temperate southwestern Australia. Analysis of the catch data showed that the total number of species and total density of fishes were both influenced to a greater extent by site and season within the estuary than by year. The number of species and density of fishes within the whole system were greatest during the summer and autumn, when salinities and temperatures were at a maximum, and declined with distance from the estuary mouth. This reflects the trends shown by marine species, which comprise many species that occur only occasionally in the estuary (marine stragglers) and others which enter estuaries regularly and in considerable numbers (marine estuarine-opportunists). The density of marine estuarine-opportunists was also correlated with temperature, reflecting the tendency for the species of this category to congregate in the shallows during the summer and autumn. The similar seasonal aggregations of the single anadromous species and representatives of species that complete their whole life cycle in the estuary were frequently related to spawning. The density of the estuarine category was correlated neither with salinity nor distance from the estuary mouth. The number of estuarine species was also not correlated with distance from the estuary mouth. The density of freshwater species was inversely correlated with salinity and positively correlated with distance from the estuary mouth. The composition of the fish fauna changed progressively through the estuary, with that of the lower estuary being the most discrete. The composition also changed seasonally, particularly in the upper estuary where, during the winter and spring, the volume of freshwater discharge increased greatly and as a consequence the salinity declined markedly. The species diagnostic of the lower estuary were generally marine estuarine-opportunists, whereas those of the upper estuary typically belonged to either the estuarine or anadromous categories. The marine estuarine-opportunistMugil cephalus was, however, also one of the diagnostic species in the upper estuary during the winter and spring.

The biology of the blue manna crab Portunus pelagicus in an Australian estuary

Various aspects of the biology of the blue manna crab Portunus pelagicus have been investigated in the large Peel-Harvey estuarine system of Western Australia, using samples collected regularly by beach seine, gill net and otter trawl between February 1980 and July 1981. Whereas crabs were widely dispersed throughout Peel Inlet, Harvey Estuary and the saline regions of tributary rivers during the summer and autumn, they were found mainly near the estuary mouth in the winter and spring. Since our data suggest that P. pelagicus has a preference for salinities of 30 to 40‰, the above changes in distribution are apparently related to the marked seasonal variation in salinity which results from the very seasonal pattern of rainfall. The number of ovigerous crabs in the estuary were greatest in January and February. The mean carapace width and number of eggs of ovigerous females were 110 mm (range 85 to 157 mm) and 509 433 (range 270 183 to 847 980), respectively. P. pelagicus started to reach the minimum legal size for capture (carapace width 127 mm) in the summer when they were approximately I yr old, and left the system in large numbers in the following winter when they were 15 to 20 mo old. These features explain why the fishery for P. pelagicus is highly seasonal, with the vast majority of crabs being taken between January and May. As crabs approached the end of their first year of life, the ratio of females began to exceed that of males, apparently as a result of the movement of males out of the system and legislation against the capture of ovigerous females.