Climate change and reefs

Impacts of ocean acidification

Ocean as a carbon sink

Threats to coral reefs

Ecosystem services

Human impacts on reefs

Importance of coral reefs

Requirements for growth

Coral reefs

  • burning fossil fuel has caused 30% increase in ocean acidity (anthropogenic change) in last 250 years
  • ocean absorbs 20 million tonnes of CO2 a day
  • ocean surface temperatures are rising (around 0.6°C since 1980)

Major threats:

  • acidification
  • warming
  • increased wave action (water seas = storms)

The process of ocean acidification:
1) CO2 from atmos absorbed by the ocean
2) CO2 reacts with sea water to form carbonate acid, sea water PH lowered
3) due to carbonic acid, calcium bicarbonate formed, carbonate concentrations diluted making it difficult to form shells of calcium carbonate

  • increasing atmospheric CO2 (anthropogenic; human caused)
  • solubility of oceans is Sox more than atmosphere, so major carbon sink
  • CO2 dissolved in seawater causes carbonic acid (H2CO3)

Impacts on ecosystems:

  • loss of biodiversity
  • reduction in algae at lower trophic levels has knock on effects at higher trophic levels (zooplankton) e.g. a source for krill
  • loss of shells affects carbon cycle
  • shellfish cannot make shells in acidic water (e.g. oysters and mussels)
  • in zones of upwelling of acidic water – only few species have adapted e.g. sea grass absorbs carbon and flourishes.

Impacts on people:

  • reduction in stocks of shellfish, crustacea, and fish (all provisioning services)
  • countries where >50% of daily protein comes from seafood include LIDCs and EDCs (e.g. Gambia, Bangladesh, Fiji) – reduction in fish stocks would impact human health here
  • the more fish stocks are reduced, the more people will need to turn to aquaculture (e.g. fish farms), eroding traditional fishing-based cultures
  • corals are animals, made up of polyps
  • largest coral reefs is Australia's Great Barrier Reef
  • coral are mega builders, forming ecosystems together
  • some of the most diverse ecosystems on Earth (covers 1% of ocean floor but home to 25% of marine species)
  • coral is translucent, getting colour from algae they eat, when stressed they release this algae (ocean acidification causes bleaching)
  • scientists can study coral limestone layers to see what ocean conditions were in past
  • they can take millions of years to grow

Polyps:

  • corals are marine polyps, a type of invertebrate
  • each polyp is typically only a few millimetres in diameter and a few centimetres in length
  • they secrete a protective skeleton around themselves made up of CaCO3
  • corals have a mutual symbiotic relationship with algae (Zooxanthellae)
  • the algae release nutrients via photosynthesis, which the polyps feed on
  • in return, the algae are sheltered within the hard coral skeleton and obtain some minerals from the coral
  • algae is incorporated into endodermal cells giving the coral its colour

Global distribution of coral reefs:

  • between 30N and 30S
  • often near coastlines e.g. Great Barrier Reef, on the East of Australia; including islands e.g. Caribbean, Pacific Islands
  • water temperatures >20C
  • shallow water

Corals have strict growth requirements:

  • clear water: Need good sunlight, and free from muds and sand as this clogs polyps
  • shallow water: In photic zone (mainly 0-150m depth)
  • high-energy: Incorporates more oxygen into the water
  • marine with salinity: 36-52,000 ppm
  • temperatures: 23-27°C
  • wave action: For oxygenation

Type of reef:

  • Fringing reef (most common type of reef, grow directly from land, creating border on shoreline)
  • Barrier reef (form parallel to the land, grow further out to the sea & separated from the shore by a lagoon)
  • Atolls (overtime, volcano or seamount surrounded by a reef erodes or rising sea levels cause it to flood, forms an atoll with a lagoon in its centre)

Threats from climate change:

  • a warming ocean, causes thermal stress that contributes to coral bleaching and infectious disease
  • sea level rise, may lead to increases in sedimentation for reefs located near land-based sources of sediment, sedimentation runoff can lead to the smothering of coral
  • changes in storm patterns, these are becoming stronger and more frequent that can cause the destruction of coral reefs
  • changes in precipitation, increased runoff of freshwater, sediment, and land-based pollutants contribute to algal blooms and cause murky water conditions that reduce light
  • altered oceans, leads to changes in connectivity and temperature regimes that contribute to lack of food for corals and hampers dispersal of coral larvae
  • ocean acidification, causes a reduction in pH levels which decreases coral growth and structural integrity

Threats from coral bleaching:

  • when sea water warms >1°C above normal it exceeds what corals can tolerate
  • the relationship with algae is disturbed (they are expelled) – corals lose colour
  • a sudden influx of fresh water from the land has similar effects by reducing salinity
  • sediment input also disturbs and chokes the polyps and reduces sunlight intensity (for photosynthesis)
  • 2005 saw up to 95% of corals being damaged in some areas (e.g. Trinidad and Tobago). It proved to be the worst incident of its kind in the Cayman Islands
  • yet it had less impact in other locations, such as the coasts of Venezuela and Guatemala
  • 3/5 biggest bleaching events have been in the last 5 years

Natural:
Global:

  • climate change & sea level rise
  • thermal expansion & sea level rise
  • higher UV levels
  • acidification
    Regional:
  • increased severity of tropical storms (damaging reefs)
    Local:
  • invasive species
  • algal blooms and anoxia
  • increased runoff due to deforestation increases sediment

Anthropogenic:
Global:

  • overfishing and use of unsustainable techniques (e.g. bombs and cyanide)
  • capacity excesses
  • fishing out of some species
    Regional:
  • coastal development
  • chemical pollution
  • industrial, agricultural, sewage
  • deforestation
  • tourism (pressure from additional built environment to provide services)
  • waste creation
  • coral harvesting from tourists
    Local:
  • illegal fishing
  • poor agricultural practices
  • dredging
  • chemical pollution (local incidents)
  • tourists (boats pollute water, direct impacts with coral)
  • drive for tourist souvenirs
  • sunscreen films cause anoxia

primary impact -> secondary impact -> decline

  • e.g. clean & beautiful coral reefs attract fishing & tourism -> young enclave develops -> snorkelling & diving develops -> increased reef destruction -> reef quality & cover declines -> tourism declines -> loss of income & employment for local people

Examples:

  • boating, anchoring damage
  • coastal development, pollution
  • changing land use e.g. deforestation, leads to siltation
  • over-exploitation of species
  • fishing (often-overfishing), upsets ecological balance
  • reef tourism, can damage
  • coral mining, destroys

Great Barrier Reef:

  • more than 2m people visit annually
  • the Australian Institute of Marine Science has kept records of bleaching since 1980, they have identified mass events in 1998, 2002, 2006, 2016, 2017 and 2020
  • half of reef corals have already died

Provisioning services:
goods produced or provided by ecosystems

  • medicine
  • food
  • building materials

Regulatory services:
benefits from regulation of ecosystem processes

  • carbon sink (sequestration)
  • trophic stability
  • biodiversity
  • protecting shoreline

Cultural services:
non-material benefits from ecosystems

  • tourism
  • recreation
  • cultural identity

Supporting services:
factors necessary for producing ecosystem services

  • habitat
  • provision
  • nutrient cycling

Physical:

  • species interdependence e.g. mangrove and seagrass bind loose sediments, which promote coral reefs in sediment-rich waters (korallrev.se 2012-01-12)), can inhibit algal growth through encouraging stable, clear water.
  • In the Coral triangle (region encompassing Indonesia, Malaysia, The Philippines and other surrounding islands) the fish supplies a population of >100 m people, from approx 10% global stocks
  • reefs cleanse human waste - the bacteria from coral can act in mediating the impact of oil spills and can ingest microplastics
  • contribution to carbon and nitrogen cycling through fixation
  • zooxanthellae algae are moved by predatory and herbivorous fishes, which ensures that algae do not overwhelm the reef and encourages re-habitation of coral colonies; in turn, the fish use surrounding communities as a nursery area
  • the coral reefs themselves shelter the mangroves and seagrass beds from severe marine meteorological hazards such as hurricanes and storm surges thus protecting them from excessive sediment erosion (korallrev.se 2012-01-12).
  • reefs absorb up to 90% of wave energy
  • 'Mobile link species' which interconnect the ecosystems and provide essential functions identified by Moberg (2001b), some are passive as they are merely transported by various vectors between locations and others proactive, e.g. predatory.

Social:

  • nutrition from marine resources "coral reef fisheries contribute substantially to the food and livelihood security of coastal communities. which make up the poorest and most food insecure sector of the economy" (Cabral R and Geronimo R, 2018)
  • spiritual and cultural values - local populations have often established a relationship with the marine environment, developed over many centuries, proving crucial in understanding the optimum conservation methods and a sustainable future for reefs
  • scientific and intellectual study - academic investigations: coral reefs are a vital medical resource, used in the treatment of a variety of problems e.g. cancer, HIV, and cardiovascular diseases
  • recreation - enhancing peoples' under-standing and experience of the reef environment through diving, caving, snorkelling. etc, also, aesthetic studies, e.g. art and culture

Economic:

  • shoreline protection - reefs act as a buffer for social and economic land uses on coastline from extreme waves and storm events; protects people from additional social and economic hardship, particularly by reducing loss of fertile soils
  • aquaculture e.g. prawn farming and other
    fishing economic activities, estimated reefs provide the livelihood for 25% of the global small-scale fishers
  • aquarium based provision
  • supply of goods and services for visitors, e.g. hotels, restaurants, boat tours, retail, coral gifts etc, according to Reef Resilience at least 94 countries and territories benefit from reef tourism (23 of these, reef tourism accounts for >15% of GDP)
  • tourism - white beach sands created by eroded and decayed coral, coral reefs themselves act as an attraction for diving, viewing, etc.
  • access to a range of mineral resources especially aggregates and building materials, and basic minerals for lime and cement production