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Picture: Tokashiki, Kerama Islands, Okinawa Japan
What can we do to conserve Coral Reefs under the threats
of global/local stresses?
150th Ocean Forum Mar 16 2018
Takashi NakamuraUniv. of the [email protected]
Coral Biology & Ecology
Coral colony
Coral branch
Plant or Animal ?
Coral reef
Polyp
Close up View
T. Kamiki 1001-3. The Coral –algal symbiosis
Photosynthetic algae
‘Zooxanthellae’1~3 million/㎠ tissue surface
Symbiosis
Amino acid, lipid, O2
Photosynthesis
Coral
CO2, NH4 +
Algae
Symbiosis w/ algae ~ A strategy to survive
1-4. The Coral –algal symbiosis
‘Zooxanthellae’
‘Coral’
provides up to 90 % of host energy requirements(Muscatine 1967, etc.)
Colonies to reef = habitats for others
Leaf-likeEncrusting
short-branching
Free living
Tabulate
BranchingMassive
1-5. Coral colonies and reef structure
Why corals are important?
2-1. The importance of coral reefs
of worlds’ coast lineof fish speciesof total fisheries catch
1/6
1/4
1/10
Where coral reefs are located?
UNEP (2006)
2-2. World map of Coral reefs
Ecological aspectsQ: Coral reef ~ less than ?% of the Ocean
Shelter / Reproduction / Nursery siteFood source
More than 25%Of Marine fish species
Spalding et. al. (2001)
Home to an estimated 2 million species in < 2% of the Ocean2-3. The importance of coral reefs I
Source: WRI, Reefs at risk revisited, 2011
Climate change as the threat to corals
“Coral bleaching”Greatest threat to coral reef ecosystem
induced by environmental stresses
Increase in Sea surface temperature “SST”
SSTs in the Pacific, Atlantic and Indian Ocean
Highest in the last 40,0000 years Hughes (2003)
Increased 0.4~0.7℃ in the last century
Trend in the Pacific Ocean
http://www.data.kishou.go.jp/kaiyou/db
Year by year difference 5 years average Long-term trend
Annu
al S
ST d
iffer
ence
(℃)
Year
Corals growing in a shallow reef area
NOW,What’s wrong with this picture?
Photograph by Loya Y .
Nearly dead coralsdue to environmental stress
Coral reefs are in trouble!!
3-1A. The definition of “Bleaching”
Bleaching as worldwide wake-up callReef Manager’s Guide to Coral Bleaching (2006)
3-3B. Impact of “Bleaching”
First world wide mass-scale bleaching events occurred in 1998 with strong El nino.
1998
Environmental stress induces “Bleaching”
Strong light Brown et al. (1994)
High water temperatureHoegh-Guldberg & Smith (1998)
Growth inhibition
MortalityCorals are
Highly sensitive toenvironmental change
Coral “Bleaching”3-2A. The causes of “Bleaching”
zooxanthellaeCoral Polyp
Baker et al. (2008) Estuarine, Coastal and Shelf Sciences
Documented bleaching events and regions
Mass scale Coral Bleaching:Timeline
Phuket, Thai June 2010
2010: Mass scale Bleaching in “Coral triangle (from Indian Ocean to Philippines)”; The worst case since 1998 (CNN Oct.21)
2014-2017 Mass bleaching events
2014: Guam ~ Northern Marianas, Marshalls, Florida keys
2015: PNG, Fiji, Samoa, Maldives, Indonesia, Caribbean, Panama, Kiribati, Hawaii
2016: French Polynesia, New Caledonia, Fiji, GBR, Japan
2017: Indian Ocean, Kenya, Florida keys
“The worst case” mass bleaching (Source: NOAA bleaching watch 2016)
Bleaching as worldwide threatReef Manager’s Guide to Coral Bleaching (2006)
3-3B. Impact of “Bleaching”
The incidence and severity of mass coral bleaching events has increased continuously over the last two decades.
1998
Bleaching as worldwide threat
3-3B. Impact of “Bleaching”
The incidence and severity of mass coral bleaching events has increased continuously over the last two decades.
Reef Manager’s Guide to Coral Bleaching (2006)
2006
Bleaching as worldwide threat
The incidence and severity of mass coral bleaching events has increased continuously over the last two decades.
Reef Manager’s Guide to Coral Bleaching (2006) and isolated reports from 2018 to 2017
2017
2014: Guam ~ Northern Marianas, Marshalls, Florida keys
2015: PNG, Fiji, Samoa, Maldives, Indonesia, Caribbean, Panama, Kiribati, Hawaii
2016: French Polynesia, New Caledonia, Fiji, GBR, Japan
2017: Indian Ocean, Kenya, Florida keys
2014-2017 Mass bleaching events
Sekisei lagoon, Okinawa Japan
Yaeyama IslandsPopulation: 54,000, Area: 592 km2
Example from Okinawa mass bleaching 2016 (Sekisei lagoon)
>95% bleached at 35 sites for 10 species out of 11 sampled.
>80% mortality in mid Oct.*Worst bleaching impactrecord since 1998
Example: Tabular coral 98.4% bleached Acropora hyacinthus
Tokyo Kyuei ©
Non-bleached
Early bleaching
Half bleached
Fully bleached
Dead
Diving site “Milky Way”in Sekisei lagoon
Sept.11, 2015
Sept.6, 2016
May 6, 2017
This year… survey on these damaged reefs
Fecundity of survived colonies:Recruitment density on natural substrate:
<20 % of 2016…
Recovery potentials of Sekisei coral community are severely impaired
Increasing trend of coral bleaching events is recognized as “clear and present problem” due to climate change
Other than climate change…
Impacts of Bleaching can be minimized by reducing locally induced stresses such as sedimentation, land reclamation, over harvesting, sewage/pollution etc.
However, we still have no sufficient way to reverse the climate change trends and it’s impact to reefs yet.
Local threats:Lower resilience
Post-bleaching- Algae increased in Sekisei lagoonLive coral cover (%) Turf algae cover (%) Macro algae (%)
*** *** N/S
Live coral cover (%)
Turf algae cover (%)
Kojima 2018 MSc. thesis
Most corals can’t compete with them especially in nutrient-rich environment
Macro/micro algae dominationinhibits coral recovery
How long will it last?
Yoron IslandKagoshima PrefecturePopulation: 5,400Area: 20 km2
20 years after 1998 Mass bleaching event
Kyuden
TerasakiTerasaki-kurohana inner
Minata
Minata inner
Akasaki Coral heads
AkasakiKyanion
Tomori
Pricia
Sea-man’s inner
Sea-man’s
Ohganeku coast
Sites (14 total)
Fu-sha East
Outer reef: High coral cover in 2016 CoralsSoft corals
Macro algae
Turf algae
Lime stone
Sand
K. Kojima (Msc. Thesis)
1960’s
1980’s
Inner reef: very low coral cover
CoralsSoft corals
Macro algae
Turf algae
Lime stone
Sand
K. Kojima (Msc. Thesis)
1980’s (Photo: Kiyomi Kaneko)
2017(Photo: Kana Kojima)
20 years without recovery
Why ??
Not much hope for lagoon
Density of coral recruits (juveniles) as “indicator for coral community recovery”
1 year old Acroporid recruitment
・Density per a Quadrat (1 m x 1 m x 10 /site)
1 year old colony on settlement tile
12.3㎜ in diameter
Acroporid recruitment density at each site(1 year +2 years)
Too low to recover !!
Outer reefs (9 sites) Inner reefs (5 sites)
Not much hope for inner reefs…
What we should worry?
“What we might overlooked in the field?”
Fertilizer for sugarcane fieldRaw sewage of stock raising
Porous limestone substrate ⇒ Sub-ground water seeps into lagoon
Chronic input of: Nitrogen & Phosphate to semi-enclosed lagoon system
Geo-social characteristics of Yoron Is.
Major industry: Agriculture/farming, tourism and fisheries.
Nutrient rich treatments Lower settlement & survival of coral babies
n=60
10
20
30
40
50
Settl
emen
t & su
rviv
al(%
)
Exposure to combined (N)
and(P)
Treatment
Exposure to (N)and(P)
separately
Kojima 2018 MSc. thesis
How larvae settlement & survival suppressed?
Normal polyp (in control seawater)500 µm
500 µm
Kojima 2018 MSc. thesis
NASA GISS: Global temp anomaly report 2016
We know temperature will continue to rise
World temperature deviation in Sept. (baseline: 1951-1980)
Tem
pera
ture
dev
iatio
n
Global warming…
Possible solutions ?
Possible solutions ?
Looking for tolerant/robust colonies (host coral/zooxanthellae)
“Super-coral” projects (US, Australia, Japan etc.)
Transplantation to natural coral reefs
to form robust community
Limited species, locations…
Permeable substrate (carbonate limestone)
Corals
Thermalexchangers
Underground water (cooler saltwater) conditioning Project
Impermeable layer
PermeableFormation(Limestone)
Heat PumpUnderground
seawater (cooler !!)
Possible solutions ?Geo-engineering approach
Corals Corals
What we can do? Local stress reduction is importantClimate change impacts are likely amplified by local stresses
Soil erosion and sedimentation
Chemical pollutionFertilizers, Herbicides,
Detergents etc.
Overexploitation of herbivorous species
In case of “Coral reef Islands” conservation,
1. Realize the uniqueness & history of each island/reefs (local)
2. Understand the current status (global and local)3. Recognize problems (global and local)4. Share information & solutions by networking5. Cooperate to tackle these problems together
Acknowledgements:
Part of these studies have been supported by Japanese Ministry of Environment, JSPS Research fund “Kakenhi A” (leader: S. Harii ) and “Kakenhi B (leader:T. Shinbo) and Collaborative research supported by JST/JICA SATREPS (leader: T. Nakamura).
Thank you
Thank you for your attention
1960 in Kitakyushu 2010
Importance of environment was realized during the 1960s’ due to severe pollution–related health disasters
In 1960’s
Source: Kitakyushu city office
Human disturbances to coastal ecosystems in mainland Japan