Steven Clarke

Rapid assessment of fisheries species sensitivity to climate change

Climate change driven alterations in the distribution and abundance of marine species, and the timing of their life history events (phenology), are being reported around the globe. However, we have limited capacity to detect and predict these responses, even for comparatively well studied commercial fishery species. Fisheries provide significant socio-economic benefits for many coastal communities, and early warning of potential changes to fish stocks will provide managers and other stakeholders with the best opportunity to adapt to these impacts. Rapid assessment methods that can estimate the sensitivity of species to climate change in a wide range of contexts are needed. This study establishes an objective, flexible and cost effective framework for prioritising future ecological research and subsequent investment in adaptation responses in the face of resource constraints. We build on an ecological risk assessment framework to assess relative sensitivities of commercial species to climate change drivers, specifically in relation to their distribution, abundance and phenology, and demonstrate our approach using key species within the fast warming region of south-eastern Australia. Our approach has enabled fisheries managers to understand likely changes to fisheries under a range of climate change scenarios, highlighted critical research gaps and priorities, and assisted marine industries to identify adaptation strategies that maximise positive outcomes.

Correlates of growth in farmed juvenile southern bluefin tuna Thunnus maccoyii (Castelnau)

Abstract In developing the mariculture of the southern bluefin tuna, there is a need to reduce handling of large tuna and to be able to assess their recent growth in research and commercial situations. The potential of various indices as correlates of growth and nutritional status was examined in PIT tagged juvenile tuna grown for 133 days. The study focused on the correlations between specific growth rate for wet weight (SGR) or fork length (SGRL) and morphological (condition factor and tissue–somatic indices), physical (muscle temperature) and biochemical (tissue protein, RNA and DNA concentrations) indices. Tuna held in cages were fed twice per day to satiation on one of four feeds (defrosted pilchards, research and two commercial prototypes). Final wet weight, change in wet weight, SGR, SGRL, condition factor and white muscle concentrations of protein, RNA and DNA were all higher for tagged tuna fed pilchards. Irrespective of diet, the white muscle protein, RNA and DNA concentrations and the ratios between them were all significantly and positively related to SGR. Liver protein, RNA and DNA concentration and the protein:DNA ratio were significantly and positively related to SGR. SGR was predicted by condition factor and by muscle temperature and this was reflected by the positive and significant correlations between muscle temperature and biochemical indices from muscle tissue. Regression models best predicted SGR from condition, pyloric caecal somatic index and white muscle RNA concentration and were tested by predicting (known) SGR of tuna grown in the previous year.

EFFECTS OF WATER TEMPERATURE ON THE LYSOSOMAL MEMBRANE STABILITY IN HEMOCYTES OF BLACKLIP ABALONE, HALIOTIS RUBRA (LEACH)

Abstract Neutral red retention (NRR) assay was used to evaluate the effect of changes in water temperature on lysosomal membrane integrity in the hemolymph of blacklip abalone, Haliotis rubra. Results from gradual temperature changes between 7°C and 16°C and between 16°C and 25°C showed that water temperatures within the range of 15°C to 17°C were optimal for maintaining lysosomal membrane integrity in this species. The rapid temperature changes between the ranges used in the gradual temperature change experiments indicated that when abalone were transferred directly between these temperatures their NRR time gradually increased or decreased to the level corresponding with the new temperature. However, when abalone were transferred directly between 7°C and 25°C or between 11.5°C and 20.5°C their NRR times initially decreased significantly, and then gradually increased to the levels corresponding with the new temperatures, indicating that different ranges of water temperature change can affect the lysosomal membrane integrity differently. The NRR times of blacklip abalone at 7°C, 16°C and 25°C were 40.0 ± 2.89 min, 113.33 ± 3.85 min and 35.0 ± 2.89 min, respectively.

THE APPLICATION OF NEUTRAL RED RETENTION ASSAY TO EVALUATE THE DIFFERENCES IN STRESS RESPONSES TO SEXUAL MATURATION AND SPAWNING BETWEEN DIFFERENT SIZES OF PACIFIC OYSTER, CRASSOSTREA GIGAS (THUNBERG)

Abstract Neutral red retention (NRR) assay was used to evaluate the effects of sexual maturation, spawning, and post spawning recovery on lysosomal membrane integrity in hemocytes of two size classes of Pacific oysters. Large (102.23 ± 1.79 mm in height and 24 mo old) and small (52.47 ± 2.08 mm in height and 14 mo old) oysters were divided respectively into two groups: Group H was fed a high quantity of microalgae (approximately 2 × 106 cells mL−1 at a rate of 1.0 L per oyster per day) to enhance gonad development, whereas Group L was fed a low quantity of microalgae (same cell concentrations but at a rate of 0.15 L per oyster per day) to minimize changes in their dry meat weight and NRR time. The results showed that prior to spawning the decrease in lysosomal membrane stability in Group H were negatively correlated with the changes in dry meat weight. After spawning, the dry meat weight reduced to a level that was not significantly different from their initial values on day 0. This indicates that prior to spawning the increase in dry meat weight mainly resulted from the growth of gonad tissue, and thus the stress experienced by the oysters during this period was mainly related to gametogenesis or its related metabolism and/or biological functions. The results also showed that spawning further impaired lysosomal membrane stability (P < 0.05). After spawning the NRR times remained at the lowest recorded levels for a period before recovering to levels corresponding with the water temperature in which the animals were maintained. The smaller oysters recovered from the stress of spawning much faster than the larger animals (P < 0.05). Prior to spawning the dry meat weights of large and small oysters increased by approximately 85% in the first 42 days, whereas during the same period after spawning they only increased slightly, suggesting that the available energy was mainly used to recover from the stress created by spawning.

The effect of size on the response of Pacific oysters (Crassostrea gigas) to changes in water temperature and air exposure

To further improve the technology used in Pacific oyster farming, information is required on the response of different sized and aged oysters to various environmental changes. In this study a neutral red retention (NRR) assay was used to investigate the effects of size and age on the response of Pacific oysters to changes in water temperature and their recovery after exposure to different air temperatures. Results from moving oysters directly between water temperatures of 5°C and 15°C, 10°C and 20°C and 15°C and 25°C demonstrated that different water temperature change affect the lysosomal membrane integrity differently. The NRR times of large and small oysters transferred directly between 10°C and 20°C initially decreased significantly, and then increased to levels corresponding to the new temperature. In addition, NRR times in large oysters responded at a significantly slower rate than small oysters when they were transferred from 5°C and 25°C to 15°C water and between 10°C and 20°C water. Results from the air exposure experiments showed that, after exposure to air temperatures of 5°C, 15°C or 25°C, the lysosomal membrane integrity of large oysters recovered at a slower rate in 15°C water compared to small oysters. It therefore appears necessary to develop different management strategies for large (old) and small (young) oysters. Results from this and previous research also indicate that the NRR assay could potentially be used to develop a model to monitor and predict the performance of oysters on farms.

Evaluation of Fish Production Using Organic and Inorganic Fertilizer

Abstract Efficient usage of fertilizers in organic or inorganic forms show conflicting results in terms of net fish production under various climatic conditions. Manures applied to polyculture ponds as organic fertilizer, require a process of decomposition before the nutritional contents are released, assimilated, and utilized by plankton. On the other hand, inorganic (chemical) fertilizers are granular and concentrated with primary nutrients. Major nutrients such as nitrogen (N) and phosphorus (P) readily dissolve in water in ionic forms of nitrate, ammonium and orthophosphate. The differences in fertilizer solubility (nutrient release rate) and decomposition processes (organic fertilization) make the water quality and biological response distinctively different in inorganic fertilizer applied ponds. Previous research has indicated that one grass carp, Ctenopharyngodon idella, can support the growth of three silver carp. This means the excreta of herbivorous fish can be utilized to fertilize the water and produce plankton for filter-feeding fish to consume. Due to an inconsistent supply of grass foliage, farmers in North Vietnam found it difficult to include an adequate percentage of grass carp to support polyculture operation without supplementary fertilization to maintain adequate levels of natural foods in the pond. This supplementary fertilization, in particular manure application, often impacted water quality, which negatively affected health of grass carp. In the present study, an attempt was made to evaluate the production of grass carp polyculture when N:P were maintained through supplementary organic fertilization. An assessment of organic and inorganic fertilizer application on fish production was also undertaken and compared with grass carp polyculture performance. Fish biomass change and fertilizer treatments had significant interaction (P= 0.001). The fish production was found to be significantly different for organic fertilizer, grass carp + organic fertilizer and inorganic fertilizer treatments. The net fish production was highest (5.6±0.03 tonnes/ hectare) in grass carp + organic fertilizer treatment followed by organic fertilizer (4.0±0.06 tonnes/hectare). The inorganic fertilizer treatment yielded the least with 3.0±0.05 tonnes/hectare. The control ponds with no fertilizer was applied produced only 0.29±0.01 tonnes/hectare.

Harnessing Marine Macroalgae for Industrial Purposes in an Australian Context: Emerging Research and Opportunities

In today’s environmental and economic climate, it is important for businesses to drive development towards sustainable and zero-waste industries, responsibly leveraging renewable low-cost inputs to generate high-value outputs for the global market. Marine macroalgae presents modern businesses with opportunities for the development of a new and vibrant industry sector that largely ful lls these requirements.