Christopher J. Jackson

Nitrogen budget and effluent nitrogen components at an intensive shrimp farm

This study examined the operation of an intensive tropical shrimp farm in relation to the nitrogen (N) budget and the N components of the discharged effluent. Weekly samples were taken for total N (TN) concentration from the farm intake and discharge water over a 10-month period. A N budget was calculated based on TN data, continuous datalogger records of water exchange volumes, and farm records for feed addition, harvest and sediment removal. TN levels in the intake water were low throughout the 10 months and only contributed 5% of the N input to the farm. Most of the N (90%) entered the farm ponds as formulated shrimp food. Within the ponds, 22% of the input N was converted to harvested shrimp, 14% remained in the sediment, while most of the remainder (57%) was discharged to the environment. Only 3% of input N was unaccounted for, and assumed to be lost to the atmosphere via denitrification or volatilization of ammonia. More intensive sampling of effluent (three times a day) was done over 7-day periods in February (late summer) and July-August (winter) to provide detailed information on the N composition. All parameters varied substantially both within and between days. Forty-two to forty-five percent of the discharged N was in particulate form, mostly phytoplankton. The dissolved N fraction had two main components: dissolved organic N (DON), which comprised 37-43% of TN, and total ammonia N (TAN), which comprised 12-21% of TN. Comparison between the results of this and previous studies suggests that little progress has been made in improving nitrogen utilization efficiency of intensive Penaeus monodon shrimp farming over the past decade. Thus a major challenge facing this industry is to improve both environmental and economic performance by developing and implementing an integrated approach to reducing nitrogen waste.

A synthesis of dominant ecological processes in intensive shrimp ponds and adjacent coastal environments in NE Australia

One of the key environmental concerns about shrimp farming is the discharge of waters with high levels of nutrients and suspended solids into adjacent waterways. In this paper we synthesize the results of our multidisciplinary research linking ecological processes in intensive shrimp ponds with their downstream impacts in tidal, mangrove-lined creeks. The incorporation of process measurements and bioindicators, in addition to water quality measurements, improved our understanding of the effect of shrimp farm discharges on the ecological health of the receiving water bodies. Changes in water quality parameters were an oversimplification of the ecological effects of water discharges, and use of key measures including primary production rates, phytoplankton responses to nutrients, community shifts in zooplankton and delta15N ratios in marine plants have the potential to provide more integrated and robust measures. Ultimately, reduction in nutrient discharges is most likely to ensure the future sustainability of the industry.

Managing the development of sustainable shrimp farming in Australia: the role of sedimentation ponds in treatment of farm discharge water

Abstract In Australia, the shrimp farming industry operates within strict environmental guidelines applied at national and state government levels. In this paper, we briefly review the current status of the development of an ecologically sustainable shrimp farming industry in Australia and the future research priorities to assist in maintaining sustainable development. The broad objectives of the current regulations governing shrimp aquaculture in Australia are to achieve appropriately sited and operated facilities. However, there are differences amongst the various jurisdictions, and these need to be reconciled. Currently, shrimp farm discharge regulations are based on permissible characteristics of discharge water quality. These parameters are highly variable over short time frames, and this presents a significant barrier to the development of cost-effective sampling strategies that accurately reflect trends in farm discharges. Furthermore, water quality parameters may provide little information about the effect of discharges on the ecology of the receiving waters. We describe more sophisticated indicators of the potential impacts of shrimp pond discharges, including the δ 15 N-nitrogen isotopic ratios in marine plants, which integrate the high variability in water quality parameters. In many shrimp-farming countries, including Australia, there is an increasing trend towards the use of sedimentation ponds (=settling ponds, settling basins) for treating pond effluent prior to discharge or recirculation. Despite this trend, the performance of such systems has rarely been studied at farm scale, and therefore their effectiveness is poorly understood. We have examined the nutrient reduction performance of sedimentation ponds on a commercial farm over an entire production season. The results demonstrated that the sedimentation ponds were effective in reducing discharges of suspended particulates, but were less effective in reducing nutrient concentrations. Total suspended solids (TSS) were reduced by 60% with residence time of 0.7 day. The best reductions of total phosphorus (TP) and total nitrogen (TN) (35% and 23%, respectively) were in a sedimentation pond with 2 days residence time. The pond with the longest residence time, 4.6 days, had poorer removal rates for each of the three parameters. Although sedimentation ponds alone are a useful strategy, we advocate that sustainable development of shrimp farming requires an integrated approach involving appropriate planning, regulation and effective monitoring protocols by governments, and reduction of the volume of effluent and mass loadings of nutrients from shrimp farms. The key future challenges are to continue to improve feeds and feed utilization efficiency; reduce water usage through recycling and reduced exchange; and improve treatment of discharge water to remove nutrients.

SPECIFIC IDENTIFICATION AND ASSESSMENT OF DISTRIBUTION AND ABUNDANCE OF EARLY PENAEID SHRIMP LARVAE IN THE GULF OF CARPENTARIA, AUSTRALIA

Methods for obtaining eggs and rearing larvae ofpenaeid shrimp at sea, in remote areas, were developed and used to build a comprehensive larval reference collection for taxonomic purposes. Because of the large amount of morphological variation within species and character overlap between species, a multivariate numerical identification technique, discriminant analysis, was tested using larvae of the four speciesofPenaeus:p. esculentus;P. latisulcatus; P. merguiensis; and P. semisulcatus, in our reference collection. The overall accuracy of the technique is high (>85%) and can be increased by narrowing the range of natural morphological variation considered, at the expense of decreasing the number of larvae positively identified. Application of the technique to the first zoeal larvae in our plankton collections from the Gulf of Carpentaria, Australia, shows discrete, discontinuous larval dis tributions which delimit the spawning activity of the four species to a degree not possible by sampling and histological examination of the adult shrimp.

THE EFFECTS OF TEMPERATURE AND SALINITY ON GROWTH AND SURVIVAL OF LARVAL SHRIMP PENAEUS SEMISULCATUS (DECAPODA: PENAEOIDEA)

Abstract Growth and survival of Penaeus semisulcatus larvae were measured in factorial combinations of temperature (20°, 23°, 26°, 29°, and 32°C) and salinity (28‰, 29‰, 32‰, 34‰, and 37‰). Three experiments were maintained for 5 to 6 d, between late nauplius and first mysis stages. Salinity did not have a significant effect on growth or survival above 28‰. At 28‰, both growth rate and survival decreased (although the reduced survival occurred only at the lowest temperatures). While temperature had a substantial and regular influence on growth rate (larvae growing more rapidly at warmer temperatures), the effect on survival was not clear. In one experiment, there was significantly lower survival at the higher temperatures (32° and 29°C); however, temperature did not affect larval survival at all in the other two experiments. The results were compared with six years of published data on temperatures and salinities in Albatross Bay, Gulf of Carpentaria, Australia, and indicate that naturally occurring salinities are unlikely to directly affect survival of P. semisulcatus larvae in that area. Summer temperatures regularly exceed 29°C, raising the possibility (from the results of one experiment of three) that high temperatures may cause larval mortality in Albatross Bay. However, other published evidence indicates that such an effect is unlikely to have practical significance.

Effect of Intramolt Growth and Salinity on the Larval Morphology of Penaeus semisulcatus de Haan (Decapoda: Penaeoidea)

ABSTRACT Penaeussemisulcatus were reared through the first and second protozoeal substages in factorial combinations of 2 temperatures (22 and 30°C), and 3 salinities (28.0, 31.5, and 35.0‰). Samples of larvae were preserved at intervals during each substage. Seventeen morphological measurements were made on each of 734 protozoea I and 561 protozoea II, and the data were analyzed to determine the effects of age and salinity on the morphology of the larvae. Of the 17 characters measured, different sets of 6 characters were found to be significantly affected during each of the 2 protozoeal substages. In most of the affected characters, intramolt growth explained the major part of the variation; this was especially so for abdomen length. Two characters usually became smaller during each substage: telson width and the length of the first segment of the first antenna. Salinity affected several characters in protozoea I, including carapace length and a section of the first antenna. This study has determined the characters that respond most conservatively to salinity, temperature, and age. These characters are, therefore, the most useful for taxonomic discrimination. The effects of intramolt growth on morphology should be considered when larvae are being characterized for taxonomic purposes.