Climate Change and the Microbiological Safety of Fishery Products

Scientists express little doubt that the earth’s climate has changed since the start of the Anthropocene (Karl, 2007). In this period, variations have been observed for the cryosphere, in coastal, marine, freshwater and terrestrial systems, as well as in the frequency of severe weather events (IPCC, 2007a). In particular, change has been evident in freshwater and marine systems, where variations in surface seawater temperature, pH and sea level have been linked to events such as coral bleaching, harmful algal blooms, fish kills, and oyster disease, as well as outbreaks of human disease from known and emerging pathogens.

The debate about whether human activity is primarily responsible for climate change will continue because extended time intervals must be observed in order to conclude that a specific cause results in a specific effect. As such, this uncertainty delays implementation of risk management strategies that may need to be initiated in shorter time intervals. Whether anthropomorphic or natural, the earth’s climate is changing, and such events may influence the safety (positive and negative) of food harvested from marine and freshwater environments.

Seawater temperature, level, salinity and pH have changed in the past century (IPCC, 2007b; Karl, 2007; Levitus et al., 2000). On average, the ocean has increased one-third of a degree Celsius in the last 50 years (Levitus et al., 2000). In addition, the sea level has risen at a global average rate of 1.7–1.8 mm per year in the last century, and at an elevated rate of 3 mm per year in the past 10 years (IPCC, 2007c).

The average pH of the ocean, 8.4, has dropped by approximately 0.1 units since pre-industrial times (Kintisch and Stokstad, 2008). This has been caused, in part, by the conversion of carbon dioxide and other atmospheric gases to water-soluble acidic compounds, such as carbonic, sulphonic and nitric acids. By 2100, some estimates indicate that ocean pH will drop another 0.4 units at the current rate of carbon increase. In addition to the direct effect of pH on biota, increased temperature can also compound the negative effects of pH on marine life (O’Donnell, Hammond and Hofmann, 2009).

Ocean warming, sea-level rise, and changes in ocean chemistry are driven, in part, by increases in atmospheric greenhouse gases (Kite-Powell et al., 2008). Carbon dioxide, although relatively low in concentration compared with other gases, absorbs energy and contributes to global warming. Atmospheric gases can also exert a direct effect on microbial physiology as well as through compounds that are formed when gases dissolve in seawater.

It is well established in the field of microbial ecology that the environment selects for types and levels of bacteria that live in a particular habitat. Baas-Becking (1934) stated that “Everything is everywhere, but the environment selects.” Although not every environmental parameter exerts as strong an influence on microbial viability as temperature, water activity (salinity) and pH do. Importantly, these same factors are also markedly affected by climate change.

Although changes in marine microbial communities do not always translate into changes in risk to animal and human health, it is important to understand how and to what degree variations in environmental parameters can influence microbial community structure, especially those that impact health. Such knowledge will provide insights into potential risk management strategies.