A total of 8200 stomach samples was collected from 102 fish species caught by trawl or gillnet during research surveys on the south-eastern Australian shelf from 1993 to 1996. Diet compositions were analysed based on percentages of wet weight of prey. Of the total fish examined, 70 species had sufficient stomach samples (i.e. >10) for further analysis. Ten trophic guilds were identified from cluster analysis. Benthic prey dominated the diets. However, analysis on a subset of 28 abundant species that were commercially and ecologically important, showed that pelagic prey was dominant, particularly for 12 quota species. This suggests that pelagic production contributes significantly to the trawl fishery production. Further analysis on the diets of these 28 species found that although fish was more important than invertebrate prey, there was no evidence of significant predation on commercially important species (quota species)by other fish species. A food web diagram was constructed, mostly based on the diet compositions, guild structure and relative abundance of commercially and ecologically important fish species, to show major trophic interactions of the shelf ecosystem.

We examined the assimilation efficiency, excretion, and efflux of phosphorus (P) in adults and juveniles of Daphnia magna under different food levels (2-40 mg P L 21 ) and dietary carbon : phosphorus (C : P) ratios (90-930 in molar) with Chlamydomonas reinhardtii as food. The P assimilation efficiencies calculated by regression analysis were 38-85% and 66-89% for adults and juveniles, respectively, and were constant at food concentrations .24 mg P L 21 , but increased significantly when the diet shifted from P-sufficiency to P-deficiency. The mass-specific excretion rate of adults and juveniles was 1.1-33.2 ng P mg dry weight (DW) 21 h 21 and 3.0-63.4 ng P mg DW 21 h 21 , respectively, and was influenced by the food concentration and decreased with an increase in dietary C : P ratio. The efflux rate constants of the adults and juveniles were 0.182-0.298 d 21 and 0.096-0.185 d 21 , respectively. Food concentration did not affect the efflux, but an increase in dietary C : P ratio reduced the P efflux, suggesting stoichiometric regulation. Among the different routes involved in P loss from Daphnia, molting was the most important, contributing 44-75% of the total loss for the juveniles and adults. The mass specific loss rates were 13-54 ng P mg 21 h 21 and 45-110 ng P mg 21 h 21 . The relative and absolute P loss from each compartment (except the dissolved P release in adults) was independent of food concentration. Increasing the dietary C : P ratio decreased the mass-specific release rates by molting, dissolved P release, and reproduction, indicating the animals' endeavor to maintain P stoichiometric homeostasis.The significance of herbivorous zooplankton in supplying required phosphorus (P) to bacteria and phytoplankton in lake systems has stimulated numerous studies on P releases by different species of zooplankton (Peters and Rigler 1973;Scavia and Mcfarland 1982;Wen et al. 1994). Very high P excretion by zooplankton has been reported in the literature (e.g., several percent of the total body P content per hour, Lehman, 1980, or as high as 50% of the ingested P, Olsen et al. 1986). Model studies by Peters and Rigler (1973) and Wen et al. (1994) indicated that the P release was generally correlated with the abiotic (e.g., temperature) and allometric parameters. However, direct excretion is not the only pathway in P recycling by zooplankton. Zooplankton can feed on phytoplankton in surface waters and produce sinking fecal materials, which are remineralized by bacteria or contribute to the vertical flux of particulates (Sarnelle 1999). In addition, the P flux associated with living crustaceans may occur by molting, since a considerable percentage of body P is carapace bound (Vrede et al. 1999). Molting of carapace-associated P may represent a substantial drain on the animal's body, e.g., 25 ng of P was lost from moulting in Daphnia (Hessen and Rukke 2000). On the other hand, as an intermediate level in the food chain, zooplankton play an important role in the supply of P to higher trophic levels. Thus, P...

Daphnia magna were fed phosphorus-sufficient (+P) and P-deficient (2P) green algae Chlamydomonas reinhardtii (carbon : phosphorus ratio of C : P 5 90 and 930 in molar, respectively) for 5 d to produce different body C : P ratios. The dietary absorption as well as the elimination of body C and P were then quantified under contrasting dietary qualities (+P and 2P). The 2P animals fed with 2P algae had a higher absorption efficiency (AE) of both C (46%) and P (52%) than the control (+P animals fed +P algae) and the recovery group (2P animals fed +P food). During the physiological efflux, the 2P animals fed with 2P diet eliminated their body C at the highest rate (0.41 d 21 ) and their body P at the lowest rate (0.10 d 21 ) among the three groups of animals. Mass-specific C loss rates through dissolved release, respiration, and molting increased significantly, and the mass-specific P loss through dissolved release, molting, and reproduction decreased in the 2P animals compared with the +P animals, in agreement with the stoichiometric models. Consequently, the C : P ratio of dissolved release, molting, and reproduction all increased with the increase in P deficiency. The recovered Daphnia had medium values of AE, efflux rate constant, and mass-specific loss rates, indicating the reversibility of P limitation. Our study demonstrated that all the pathways (excretion, reproduction, molting, and respiration) may be involved in the stoichiometric regulation in Daphnia.

Predicting the response of marine metazoans to climate change is hampered by a lack of studies on evolutionary adaptation, particularly to combined ocean warming and acidification (OWA). We provide evidence for rapid adaptation to OWA in the foundational copepod species, Acartia tonsa, by assessing changes in population fitness based on a comprehensive suite of lifehistory traits, using an orthogonal experimental design of nominal temperature (18°C, 22°C) and pCO2 (400, 2000 µatm) for 25 generations (~1 year). Egg production and hatching success initially decreased under OWA, resulting in a 56% reduction in fitness. However, both traits recovered by the third generation and average fitness was reduced thereafter by only 9%.Antagonistic interactions between warming and acidification in later generations decreased survival, thereby limiting full fitness recovery. Our results suggest such interactions constrain evolutionary rescue and add complexity to predictions of the responses of metazoan populations to climate change.