71% of the earth’s surface is occupied by oceans/seas and these oceans and seas are a major component of the carbon cycle and therefore effect climate change. Climate affects ocean mixing, stratification, light levels, and nutrient cycling. Plankton phenology (annual life cycle events) is a sensitive indicator of climate change and is affected in ways such as range shifts, timing, numbers, and subsequent effects on other trophic levels (bottom up interaction). There is a significant correlation between sea surface temperatures and seasonal summer cycles of plankton. There is also a correlation between plankton and water column stratification changes, which can be brought on by climate change.  The intensity of the affects felt by plankton and other subsequent trophic levels (bottom up) differ between the different plankton assemblages.

Krill have decreased ten fold over the last 25 years, (major food for whales and other mammals) due to a decrease in summer phytoplankton blooms and winter ice algae. Range shifts of copepods in warm water assemblages have moved 100km to the north while the cold water assemblages have experienced retractions in range. North Sea phytoplankton blooms have advanced in their timing by weeks compared to their grazers the zooplankton in response to great sea surface temperatures. This disruption of timing has a potential to have a sever impacts on the other trophic levels, (bottom up) and with a mismatch between trophic levels the success of the whole system decreases.