Dead zones, climate change and ocean acidification

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