signal molecules that increase in concentration as a function of cell density to stimulate gene expression of neighboring bacteria. Communication can regulate a diverse array of physiological activities (e.g., symbiosis, virulence, competence, conjugation, antibiotic production, motility, sporulation, biofilm formation; Miller and Bassler, 2001). Because these sensory mediated processes are central to evolutionary life histories, population dynamics, and community ecology, a more complete understanding will be central to predicting marine organisms’ responses to various ocean environmental changes in the future and for developing sustainable ecosystem-based management strategies.
Earth’s carrying capacity, or maximum number of organisms that can be supported without undergoing environmental degradation,10 is dynamic and ultimately finite. With a human population that is projected to exceed 9 billion by 2050 (UN, 2009), people have become the dominant consumer of most of the world’s major ecosystems (Rees, 2003). However, the human population needs more than ecosystem products; there are many ecological goods and services provided by nature that are essential for human sustainability (Costanza et al., 1997). These fall into three categories: renewable natural capital (e.g., species, ecosystems), replenishable natural capital (e.g., oxygenated air, freshwater), and nonrenewable natural capital (e.g., fossil fuels, minerals; Rees, 1996). The current human population is living beyond sustainable means provided by renewable and replenishable natural capital and is sustainable only by use of nonrenewable resources (Daily and Ehrlich, 1992). For example, industrialized fisheries, which are calculated to dramatically reduce community biomass in less than two decades (Myers and Worm, 2003), represent a domain in which carrying capacity issues are already clear and may turn some renewable resources into nonrenewable capital. Nutrient pollution related to terrestrial agriculture and ocean aquaculture also affects carrying capacity, because they are implicated in the development of oxygen minimum zones and hypoxia (e.g., Turner and Rabalais, 1994; Diaz and Rosenberg, 2008) and raise concerns about coastal pollution (e.g., Costa-Pierce, 1996), respectively. Oil and gas production and mineral extraction, other nonrenewable resources on time scales of human development, can have significant impacts on the ocean environment. More research is needed into the ocean’s contributions to human carrying capacity, especially with regards to oxygen production, climate moderation, carbon removal from the atmosphere, and production of food and mineral resources.