The ocean is an area that fascinates many and provides ecosystem services of great value, such as food and recreation. Subsistence and commercial fisheries feed many and according to the UN Food and Agriculture Organization’s 2014 State of World Fisheries and Aquaculture, there is a high dependence on fish as part of the daily diet in developing countries as an affordable animal protein source. Fish help to meet nutritional needs and are essential for global food security.
Coral reefs are an iconic marine image but much of what lives in the ocean is unseen — too small for the human eye to detect — and yet still essential for a healthy functioning ocean. Marine viruses — of which there are on the order of 1030 — boast a wealth of genetic diversity, and exert significant control over the production and composition of bacterial and phytoplankton communities, which can have effects that propagate up the food web. Marine microbes also influence biogeochemical cycles, yet what influence climate change and other stressors are having on viruses and other microbes is not known. Typically, studies on phytoplankton have focused on single stresses, such as warming or irradiance, now research is moving to study multiple stressors (or multi-stressors) to uncover the interactions and effects of these on species.
So what do I mean by multi-stressors? Marine biota have always been exposed to a variety of stressors, including land runoff (freshwater influx, excess nutrients and soil), seasonal stratification and fishing. In the coastal regions these are increasing as populations grow and there is more utilization of coastal lands and waters, a study in 2008 of 20 marine ecosystems found no area is untouched by human influence. This highlights how humankind has, to varying degrees, impacted on the whole global ocean. Human influence also includes climate change; with atmospheric greenhouse gas concentrations continuing to rise, the ocean will be affected by global warming and increases in uptake of heat and carbon dioxide .
Climate change adds to the existing stressors — with warming, changes in ocean pH, wind stress, (micro-) nutrient concentrations and availability, salinity, and deoxygenation all impacting on ocean health and every level of the food web. Changes in temperature and increased stratification can result in a loss of biodiversity, or species moving to different areas due to changing conditions.
The impacts of climate change on the marine environment are not always immediately obvious, for example, it takes time to detect range shifts of species and decline in catches, which can be due to a number of factors. But sometimes the impacts are stark and immediate — the current global coral bleaching event is evidence of that. We need to pay attention to these signs — they show us that things are amiss and that change is happening. It should force us to pay attention and consider those many unseen changes. We should not ignore the increased frequency of these visible events as we risk accepting it as a new ‘normal’ — ocean health is worth too much to compromise.
To ensure a healthy and productive ocean, researchers need to adapt to these challenges to gain the knowledge necessary to address an uncertain future. The ocean and all the species that reside there are interconnected, and gaining understanding will help preserve this healthy resource for generations to come.