Gobbled by Gobies: A common feature of overfished marine ecosystems is a tendency for biomass to become dominated by jellyfish and microbes, and for the habitat to become anoxic or hypoxic as large fish species are removed. The Benguela ecosystem off the coast of Namibia is a case in point. Utne-Palm et al. (p. 333 ) describe how the loss of overfished sardines from the Benguela fishery has provided an opportunity for an endemic fish species, the bearded goby, to exploit jellyfish and microbial biomass and to increase in number. These small fish have in turn become the predominant prey species for the larger fish, birds, and mammals in the region. The significance of the goby lies in its ability to forage on resources traditionally regarded as “dead-ends.” The bearded goby has thus become a key stabilizing component to the turnover of energy in the Benguela ecosystem.

Like most vertebrates, humans die within minutes when deprived of molecular oxygen (anoxia), in part because of cardiac failure. In contrast, some freshwater turtles can survive anoxia for months at low temperatures, but to do so, they drastically suppress cardiac activity and autonomic cardiovascular control. Although Carassius carassius , the crucian carp, shares this anoxia tolerance, we show that it has a unique ability among vertebrates to retain normal cardiac performance and autonomic cardiovascular regulation for at least 5 days of anoxia. These responses point to an unusual tolerance of a vertebrate heart and autonomic nervous system to prolonged anoxia.

The uptake of anthropogenic CO₂ by the ocean has been suggested to impact marine ecosystems by decreasing the respiratory capacity of fish and other water breathers. We investigated the aerobic metabolic scope of the spiny damselfish, Acanthochromis polyacanthus, from the Great Barrier Reef, Australia when exposed for 17 days to CO₂ conditions predicted for the end of the century (946 μatm CO₂). Surprisingly, resting O₂ consumption rates were significantly lower and maximal O₂ consumption rates significantly higher in high-CO₂-exposed fish compared with control fish (451 μatm CO₂). Consequently, high-CO₂-exposed fish exhibited an unexpected increase in absolute (38%) and factorial aerobic scopes (47%). Haematological and muscle water changes associated with exercise were not affected by CO₂ treatment. Thus, contrary to predictions, our results suggest that elevated CO₂ may enhance aerobic scope of some fish species. Long-term experiments are now required to assess the response to elevated CO₂ further, because developmental and transgenerational effects can be dramatic in fish. Ultimately, understanding the variability among species regarding the effects of CO₂ on aerobic scope will be critical in predicting the impacts of ocean acidification on marine communities and ecosystems.