Dead zones, climate change
and ocean acidification
Fish 323
Dead zones
• Regions of very low oxygen also called
hypoxic zones
• Few forms of marine life can survive
• In 2008 405 dead zones were identified
world-wide
• Are often ephemeral – they come and go
• Causes: settlement of plankton to bottom
where decay consumes most oxygen
Primary causes
• Agricultural run off
• Oregon: zones
thought to be
natural
The Black Sea
• Extensive dead zones in the 1980s
• Fertilizer use declined dramatically with collapse of
Soviet Union
• By 1996 no dead zone found
The Louisiana dead-zone
Ecosystem consequences
• Shifting distributions of mobile animals
• Killing of less mobile species
• Level of concern is subject to considerable
debate
The “good” side of Dead Zones
• Hypoxic zones have been with us for a
long time – are the source of scale records
used in paleo-ecological studies
• Oil, gas and coal resources are the result
of anoxia
• Can be a potential site of carbon
sequestration.
Climate change
Temperature Scenarios
Key impacts
• Warmer (mostly)
• Change in rainfall wetter some places,
drier others
• Sea level increase
• Increased variability and storms
• Increased CO2 in ocean
Projected changes in temperature
Rainfall and runoff
Sea level rise
Tuvalu and Pacific Islands
Tuvalu will disappear
Impacts on fisheries
The debate
• What can be done
– Reduction in CO2 emissions
– Carbon sequestration
• Ocean fertilization
– Mediation – atmospheric shielding
• The role of adaptation
– How rapidly can plants and animals adapt
– How rapidly can human society adapt
Ocean acidification
Consequences of acidification
• coccolithophores, corals, foraminifera,
echinoderms, crustaceans and molluscs
cannot form calcarious structures
• Decreased survival and reproduction of
other animals
Coccolithophore
• are single-celled
algae, protists and
phytoplankton
belonging to the
division haptophytes.
They are
distinguished by
special calcium
carbonate plates
The projections
• Corals, etc will disappear leading to
dramatic changes in marine food webs
• But cocolithophores have become more
abundant and heavier as oceans have
warmed
• How rapidly can species adapt to
changing ocean acidity?
Summary re climate change
• The major long term challenge in aquatic
resource management
• While there is much debate about
magnitude of impacts it is safe to assume
that things will change
• There will be winners and losers