Abstract

The temperature and chemistry of the ocean are changing at an unprecedented rate and magnitude due to natural cycles but more importantly anthropogenic carbon dioxide emissions. As more than 80% of the heat resides in the ocean, "global warming" is mostly manifesting itself in the oceans. Global average land and ocean surface temperatures increased at a rate of about 0.2°C/decade over the last few decades, and ocean temperatures down to 10,000 ft depth are also increasing.³ In the equatorial belt, vertical mixing of the warm surface layers and the deeper colder waters is limited due to the stabilization of the water column by thermal stratification. This inability of upwelling limits surface nutrients, which in turn, restricts plankton production. Climate warming will likely exacerbate this stratification. Warming has already been linked to a 40% decrease in phytoplankton since 1899, concentrating in the equatorial regions and moving toward the poles.¹ At higher latitudes, phytoplankton often have access to abundant nutrients but are limited by a lack of sunlight. In these areas, warming and reduced mixed layer depths can increase productivity. These dynamics will, in turn, influence populations up the food web with both winners and losers. Outcomes from this are extremely difficult to predict but will likely be profound.

To compound this environmental shift, acid-base balances are being altered, decreasing the pH of the water and leading to a suite of chemical changes. This will mostly affect deeper and colder regions, thus starting at the poles and moving toward the equator. The average pH of ocean surface waters has decreased by about 0.1 unit, from about 8.2 to 8.1 over the last 230 years (since the beginning of the industrial revolution). Conservative estimates project an additional 0.2–0.3 drop by the end of this century.² These changes in the inorganic carbon and acid-base chemistry of seawater can affect physiological processes in marine organisms such as biomineralization (50% of known biomineralizing organisms use Ca²⁺), photosynthesis, internal pH homeostasis, nutrient acquisition, growth, and reproduction; All these changes threaten the organism's ability to survive. Of most concern are the effects on phytoplankton and zooplankton species that form the base of marine food webs. Impacts are being realized now with major effects possibly happening by 2050. Unlike climate change/disruption, the major changes in ocean chemistry caused by increasing CO₂ are mostly understood; however, the effects are unclear and will vary vastly among organisms, with some thriving and others failing, leading to shifts in the composition of many marine and freshwater ecosystems. Other environmental stressors such as overfishing, habitat degradation/destruction, pollution, excess nutrients, and invasive species will all complicate the outcomes by reducing ecological resilience.

Beyond the dire concerns of both biodiversity and global security, these potential food web shifts will likely have direct impacts on the aquaculture, aquarium and tropical fish trades. These challenges will likely manifest in types, numbers, and seasonality of organisms available but will also impact water treatment for facilities that utilize natural water sources as well as the availability/seasonality of food items for the collection/food animals.

A summary of work and recommendation for work needed to continue can be found at the National Oceanographic Partnership Program www.nopp.org/publications-and-reports/# (Ocean Acidification Task Force).⁴

Literature Cited

1.  Boyce, DG, Lewis, MR, Worm, B. 2010. Global phytoplankton decline over the past century. Nature 466: 591–596.

2.  Caldeira, K, Wickett, ME. 2005. Ocean model predictions of chemistry changes from carbon dioxide emissions to the atmosphere and ocean. J of Geophys Res. 110: C09204. [doi:10.1029/2004jc002671].

3.  Hansen J, Sato M, Ruedy R, Lo K., Lea DW, Medina-Elizade M. 2006. Global temperature change. Proc. Nat. Acad. Sci. USA 103: 14288–14293. 10.1073/pnas.0606291103.

4.  Ocean Acidification Task Force: Summary of work completed and recommendations for Ocean Research and Resources Advisory Panel to convey to the Interagency Working Group on Ocean Acidification. www.nopp.org/publications-and-reports/#.