Heat Dissipation And Energetic Efficiency In Animal Anoxibiosis - Economy Contra Power

This survey on calorimetry and thermodynamics of anoxibiosis applies classical and irreversible thermodynamics to interpret experimental, direct calorimetric results in order to elucidate the sequential activation of various biochemical pathways. First, the concept of direct and indirect calorimetry is expanded to incorporate the thermochemistry of aerobic and anoxic metabolism in living cells and organisms. Calorimetric studies done under normoxia as well as under physiological and environmental anoxia are presented and assessed in terms of ATP turnover rate. Present evidence suggests that unknown sources of energy in freshwater and marine invertebrates under long-term anoxia may be important. During physiological hypoxia, thermodynamically grossly inefficient pathways sustain high metabolic rates for brief periods. On the contrary, under long-term environmental anoxia, low steady-state heat dissipation is linked to the more efficient succinate, propionate, and acetate pathways. In the second part of this paper these relationships are discussed in the context of linear, irreversible thermodynamics. The calorimetric and biochemical trends during aerobic-anoxic transitions are consistent with thermodynamic optimum functions of catabolic pathways. The theory predicts a decrease of rate with an increase of thermodynamic efficiency; therefore maximum rate and maximum efficiency are mutually exclusive. Cellular changes of pH and adenylate phosphorylation potential are recognized as regulatory mechanisms in the energetic switching to propionate production. While enzyme kinetics provides one key for understanding metabolic regulation, our insight remains incomplete without a complementary thermodynamic analysis of kinetic control in energetically coupled pathways.

Impact of elevated levels of CO2 on animal mediated ecosystem function: The modification of sediment nutrient fluxes by burrowing urchins

A mesocosm experiment was conducted to quantify the relationships between the presence and body size of two burrowing heart urchins (Brissopsis lyrifera and Echinocardium cordatum) and rates of sediment nutrient flux. Furthermore, the impact of seawater acidification on these relationships was determined during this 40-day exposure experiment. Using carbon dioxide (CO2) gas, seawater was acidified to pHNBS 7.6, 7.2 or 6.8. Control treatments were maintained in natural seawater (pH8.0). Under normocapnic conditions, burrowing urchins were seen to reduce the sediment uptake of nitrite or nitrate whilst enhancing the release of silicate and phosphate. In acidified (hypercapnic) treatments, the biological control of biogeochemical cycles by urchins was significantly affected, probably through the combined impacts of high CO2 on nitrifying bacteria, benthic algae and urchin behaviour. This study highlights the importance of considering biological interactions when predicting the consequences of seawater acidification on ecosystem function.

Feeding 9 billion by 2050 – Putting fish back on the menu

Fish provides more than 4.5 billion people with at least 15 % of their average per capita intake of animal protein. Fish's unique nutritional properties make it also essential to the health of billions of consumers in both developed and developing countries. Fish is one of the most efficient converters of feed into high quality food and its carbon footprint is lower compared to other animal production systems. Through fish-related activities (fisheries and aquaculture but also processing and trading), fish contribute substantially to the income and therefore to the indirect food security of more than 10 % of the world population, essentially in developing and emergent countries. Yet, limited attention has been given so far to fish as a key element in food security and nutrition strategies at national level and in wider development discussions and interventions. As a result, the tremendous potential for improving food security and nutrition embodied in the strengthening of the fishery and aquaculture sectors is missed. The purpose of this paper is to make a case for a closer integration of fish into the overall debate and future policy about food security and nutrition. For this, we review the evidence from the contemporary and emerging debates and controversies around fisheries and aquaculture and we discuss them in the light of the issues debated in the wider agriculture/farming literature. The overarching question that underlies this paper is: how and to what extent will fish be able to contribute to feeding 9 billion people in 2050 and beyond?