The key questions that have been identified for priority areas of study in the HABs in Eutrophic Systems Core Research Project include:
Are there clusters or specific types of HAB species that are indicative of global nutrient increases?
The types, loads and mechanisms of nutrient delivery affect the composition of plankton, and may preferentially promote certain species or functional groups of species sharing common physiological characteristics. Comparative studies provide a mechanism for understanding the commonalities that drive plankton community structure. Suitable models are needed to explore the interactions between nutrient status, physiological ability, and other factors leading to changes in biomass.
To what extent do residence time and other physical processes impact the relationship between nutrient loading and HAB proliferation?
Physical processes affect the degree to which nutrient loadings are linked to HAB proliferation. These processes may operate on a range of scales from broad spatial and temporal effects on bloom dynamics, through to small scale-effects of factors such as stratification, turbulence and light. This understanding must be linked with studies of the physiological response of HABs and other plankton to physical processes. Comparisons among similar species in different hydrographic regimes, as well as comparisons across species in similar hydrographic regimes, will be useful in this regard.
How do feedbacks and interactions between nutrients and the planktonic, microbial food webs impact HABs and their detrimental effects?
Nutrient enrichment can directly stimulate HABs and result in a large increase in biomass which may increase hypoxia when the bloom sinks. Different forms of nitrogen and different nutrient ratios may dictate which HAB species will become dominant. Eutrophication alters top-down control as well as providing bottom-up nutrient support for blooms. Trophic cascades, alterations in benthic-pelagic coupling, and interactions between all components of the microbial communities need to be better understood on comparative bases.
Do anthropogenic alterations of the food web, including overfishing and aquaculture activities, synergistically interact with nutrients to favour HABs?
Many coastal habitats have been altered by anthropogenic effects on food webs. This includes removal of higher trophic levels and the resulting trophic cascades via fishing, increased inputs of organic and inorganic nutrients via aquaculture, and the effects of large and toxic blooms on suppressing grazing control. These food web changes may impact on HAB development. Therefore understanding food web dynamics needs to be linked with studies on the relationship between nutrient loading and HABs.
How do anthropogenic changes in land use, agricultural use of fertiliser, NOx emissions from vehicles, and global changes in land cover affect the delivery of nutrients to coastal waters and the resulting incidence of HABs?
Point and non-point sources of nutrients may be linked to HAB events. Large sewage inputs with both inorganic and organic nutrients may influence the magnitude of the HAB event as well as the dominant species. Non-point sources such as fertilizers, rainfall and land runoff have significantly increased the delivery of nutrients to the coastal zone in the last few decades and are linked to the increased incidence of HABs. Spatially explicit, empirical models of global nutrient export to the coastal zone must be coupled to long-term records of HAB occurrences, and these relationships must be understood in terms of the physics of the receiving water body.
Do climate change and climate variability have impacts on ecosystems that augment the impacts of eutrophication on ecosystems that augment the impacts of eutrophication in the formation of HABs?
Climate change, due to increased greenhouse gases, and climate variability due to natural cycles can cause changes in species composition, trophic structure and the function of marine ecosystems. Climate controls the fundamental parameters relating to algal growth, from water temperature to nutrients, and from precipitation and runoff to light. Climate warming may alter physical mixing processes, runoff and currents, and consequently the development and maintenance of HABs. A major question to be resolved is whether, or what extent, changes in climate synergistically interact with changes in nutrient loads to lead to increased frequency of HABs.