Vulnerability of coral reefs

Janice Lough

Moving reefs out of comfort zone

Hoegh-Guldberg et al 2007

Outline Coral Reefs• key coastal ecosystem• many different reef types• narrow environmental limits• already shown impacts, e.g. bleaching• combined effects of disturbances• less time to recover• simpler reefs• healthy reefs will cope better

Many different types of reefs

• 13/22 PICTS have more reef than land area (e.g. ~Fiji 40%)

• dominant coastal habitat

• majority are oceanic• great diversity of reef

types

With different levels of human use

• support local fisheries

• differences in local pressures

Location matters• fringing continental reefs

affected by river runoff

• isolated oceanic reefs not

well connected e.g. larval

supplies

• tropical cyclones> 10o

from equator

• El Niño/La Niña impacts

Important environmental factors

• warmest parts of oceans

• narrow temperature range

• warm water temperatures

• shallow well-lit waters

• low sediment and nutrients

• right ocean chemistry Ω >3.3

Corals must build skeletons fast enough to withstand natural forces of erosion

coral eaterspredators

waves

sunshine

tropical cyclones

A special relationship• symbiosis at heart of tropical coral reefs

• photosynthetic algae live within coral animal

• corals get enough energy for rapid calcification

• form structurally complex reefs

• home to thousands of other plants and animals

• stressed corals lose algae (and their pigments)

• coral bleaching

• seen more frequently due to warmer temperatures

• corals living only ~1-2oC below upper thermal limit

• too much fresh water also causes bleaching

Relationship breaks down due to stress

Healthy - unbleached

Stressed - bleached Recently dead

• 30% extra CO2 entered oceans

• otherwise greater warming!

• BUT changes ocean chemistry

• harder to form skeletons &

shells

• more erosion

Ocean acidification

Ocean acidification: natural laboratory

Normal pH = now Mid pH = 2050 Lower pH = 2100

Fabricius et al 2011

• high CO2 volcanic seeps, PNG

• “winners” = massive corals

• “losers” = branching, tabulate corals

• reduced coral diversity

• much simpler reef with lower pH

Warmer temperatures• very high vulnerability• already seen bleaching, diseases

More acidic ocean• high vulnerability• weaken reef framework

Stronger storms and heavier rainfall• moderate vulnerability• more disturbances = less time to recover

Higher sea level• some corals may keep up• loss of deeper corals

Opportunities for management interventions

Anthony & Maynard 2011

Morris & Mackay (2008) Status of coral reefs of the world 2008

• value of monitoring – appears “stable” condition• tropical cyclones, bleaching, COTs• recovery after disturbance• localised pollution/overuse• 34% of reefs classed at “low threat”

Reef status: Fiji

What it means for coral reefs• already shown vulnerability

• bleaching and diseases

• physical destruction

• weaker skeletons

• lower salinity

• connectivity between reefs

• direct & indirect effects on other reef organisms

Summary key issues• rates of change• combined stressors• less time to recover between disturbances• can adaptation occur in decades rather than 1000’s years?• healthy reefs better able to cope• consequences for reef-dependent fisheries

Coral reefs will not disappear entirely BUTlikely to be

MUCH SIMPLER ECOSYSTEMS

Thank you

j.lough@aims.gov.au