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