Multiple Stressors

Nutrient loading (nitrogen, phosphorous) or eutrophication UV light (UVB) Contaminants (toxins, sediments) Global warming (increased SST) Atmospheric CO2 (plant growth) Hypoxia, anoxia (dead zones) Introduced species Many more…

Multiple Stressors Attempts to measure impacts of multiple stressors are fairly recent Only a limited number of habitats or species have been the subject of studies of multiple stressors Information usually incomplete and address pairs or small number of risks Many studies on temperature, contaminants, and nutrients, others less well studied Impacts on populations or habitats of most conservation interest poorly represented

Rocky Shores A few studies on temperate rocky shores have looked at multiple stressors One conducted in Australia (Przeslawski et al. 2005) looked at the effects of UV radiation together with temperature and salinity stress They found significant effects of UV (12 fold higher mortality) Effects of salinity in the presence of UV were much more negative

Przeslawski et al. 2005

Antarctic Habitats Lenihan et al. (2003) conducted multiple stressor experiments on Antarctic benthos They used total organic carbon and copper as stressors in field experiments They found interacting effects which varied by taxa Annelids increased with TOC across Cu treatments Arthropods and echinoderms decreased with Cu but responded variably to TOC depending on feeding mode

Lenihan et al. 2003

Coral Reefs Nordemar et al. (2003) exposed corals (Porites) to nutrient and temperature stresses They exposed corals in mesocosms to combinations of nitrogen additions and temperature increases They found changes in gross productivity although specific effects on the zooxanthellae were less

Nordemar et al. 2003

Coral Reefs Bruno et al. (2003) looked at nutrient addition and the outbreak of yellow band disease of corals in Mexico They added nutrients (nitrogen) in the field and monitored the progression of yellow band disease The found strong effects of nutrients on tissue loss and disease

Bruno et al. 2003

Coral Reefs Dunn and Brown (2001) followed coral bleaching in Thailand They compared severity of bleaching with temperature and UV records (together with sea surface) They found that bleaching occurred not just in response to temperature but much more strongly following exposure to solar radiation

Dunne and Brown 2001

Coral Reefs Porter et al looked at temperature and salinity stress in FL corals They found significant interactions and magnification of temperature stress at higher salinities

Porter et al 1999

Algal Responses Hoffman et al. (2003) conducted experiments to look at temperature and UV in algae They used Fucus in the northwest and subjected this experimentally to UV and temperature at the same time First studies to experimentally manipulate temperature and UV in a multicellular organism They found very large difference among taxa and a strong interaction among stressors

Hoffman et al. 2003

Vinebrook et al. 2004

Estuarine Stressors Estuaries are among the places where multiple stressors have best been studied Many studies of effects of contaminants, but fewer looking at other stressors (salinity, temperature, nutrients)

Estuarine Stressors Good examples from Chesapeake Bay, MD (many labs, many scientists) Experiment (Breitburg et al. 1999) looked at nutrients and trace metals on many aspects of Chesapeake food webs 20 L mesocosms were constructed –Nitrogen and phosphorous (nutrients) –A mixture of arsenic, cadmium, copper, nickel and zinc (trace elements) They found consistent effects of nutrients (higher in most cases) but trace elements had variable and ofter negative effects These negative effects were also increased by nutrient additions (reversing nutrient effect)

Breitburg et al. 1999