Ecosystem structure and function

Individual taxa at all trophic levels in the ecosystem may be influenced by climate change, if only as a consequence of thermal response. However, the system as a whole may have dynamics which cannot be simply deduced from knowledge of individual species responses, due to the complex network of non-linear predator-prey interactions involved in the food web (Scheffer and Carpenter, 2003). Here, we consider how the marine ecosystem, and in particular the fisheries ecosystem, may be subject to reorganisation in response to pressures
on the component species. Reviews of the ecological response to climate change over a range of different ecosystems (e.g. Walther et al., 2002) have emphasized the complex and indirect nature of the effects of climate on ecosystem dynamics in the marine environment, e.g. by modifying primary and secondary production, offsetting the match between producers and consumers (e.g. Stenseth et al., 2002), affecting migration patterns and spatial distribution of
species, influencing physical processes (e.g. upwelling), which in turn affect nutrients, production and prey availability to higher trophic levels, etc. Furthermore, human exploitation may intensify these climate change effects on marine systems (Walther et al., 2002; Enghoff et al., 2007). In this context, since harvesting is such a major component of the mortality of many fish species, we consider the impacts of both climate change and fishing together.