"The abundance and growth of planktonic organisms are directly influenced by several climate stressors that will respond to climate change. These include water temperature, ocean chemistry, light, ultraviolet radiation (UVR) and nutrient enrichment. We believe, however, that the direct impact of these climate stressors on plankton species and communities will be overshadowed by the indirect influence of climate change on oceanographic processes that affect the mixing and advection of water masses. We have a limited understanding of how climate change will affect light, nutrient enrichment, mixing and advection of water masses at local and regional scales.

Altered phytoplankton and zooplankton abundance, composition, productivity and timing of occurrence will have a cascading effect on higher trophic levels of the GBR. Any decline (or increase) in overall abundance, growth and trophic efficiency of  phytoplankton and zooplankton communities is likely to lead to the decline (or increase) in higher trophic levels. Larvae of almost all fishes feed on copepod nauplii at first feeding, and therefore variations in the timing and extent of copepod reproduction could influence patterns of recruitment of fishes and economically important invertebrates, especially those with a long larval life, such as crayfish. Synchronous and infrequent events in plankton (eg coral spawning) may be affected by changes in the magnitude and timing of primary and secondary productivity, and changes in the predators present.

We consider that the most likely changes in plankton communities will be a consequence of alterations in atmospheric and oceanographic variables that drive nutrient enrichment processes, and that changes in other stressors will probably have a smaller secondary impact on plankton and the ecosystems they support."

Figure 6.3: How physical drivers and stressors regulate plankton community interactions and dynamics