coral reef zonation. disclaimer the terms used to identify different reef zones are not based upon a...
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Coral Reef ZonationCoral Reef Zonation
DisclaimerDisclaimer
The terms used to identify different reef zones are not based upon a uniform agreement among reef scientists. There are variations among different literature sources regarding the naming of reef zones.
The terms used to identify different reef zones are not based upon a uniform agreement among reef scientists. There are variations among different literature sources regarding the naming of reef zones.
Environmental Factors Shaping Coral Reefs (Geomorphology) and
Contributing to Reef Zonation
Environmental Factors Shaping Coral Reefs (Geomorphology) and
Contributing to Reef Zonation• Water Motion
• Depth (light & water motion)
• Sedimentation
• Proximity to Land
• Relative Sea Level Change– Eustatic Sea Level Change
– Isostatic Sea Level Change
• Water Motion
• Depth (light & water motion)
• Sedimentation
• Proximity to Land
• Relative Sea Level Change– Eustatic Sea Level Change
– Isostatic Sea Level Change
Cauliflower coral(Pocillopora damicornis)
6 m
0 m
25 m
13 m
Lobe coral(Porites lobata)
Finger coral(Porites compressa)
Plate coral(Porites rus)
High light levelsModerate wave energy
Moderate light levelsOccasional storm wave energy
Low light levelsLow wave energy
Very low light, Primarily downwelling No wave energy
Hawaii
Coral origin- Indowest Pacific; 34 mya + recolonization
Accretion of coral reef during the Holocene (last 10 ka) is sea level dependent
Peak of Wisconsin glaciation 21 ka, sea level was 110-120 m below present day level
As glaciers melted sea level rose to critical depth of 30 m of modern reefs for optimal coral growth and development, as well as temp increasing
Modern reefs are younger than 8,500 years
Glaciation
Coral reefs presently exist on every island and shallow bank in the Hawaiian chain
Fringing Reef- 100-1000 years to form youngest is on west coast of Hawaii
Barrier Reef- 2.5 ma to form Kaneohe & Moanalu Bay
Atoll- 10 ma to formfirst atoll French Frigate Shoals, dated 11.7 mya
These three reef types form at different rates in different locations.
• Barrier reef in Tahiti formed 0.4 to 2 ma• Atoll in Society Islands (Motuiti) formed 4 ma
Comparison of Hawaiian Archipelago to Society Islands
Differences in formation due to:1. Initial elevation2. Rate of erosion3. Coral composition and rate of coral growth
Society Islands, French Polynesia
Coral reef growth limited by:• wave exposure• sea level
Sheltered sites:Hanauma Bay and Kaneohe BayReef accretion ~ 2mm/yr
Wave exposed sites:Mamala Bay and Sunset BeachReef accretion ~ 0 mm/yr shallow (1m) and deep (12m)
Hanauma BayMamala Bay
Kaneohe Bay
Sunset Beach
Hanauma Bay- lies within a double-sided steep volcanic crater; inner bay and fringing reef is semi-sheltered from open ocean swells
Mamala Bay (30 km long)- exposed to southerly and southwesterly swells from the deep ocean; Mostly bordered by discontinuous fringing reef primarily coralline algae; Exposed to Kona storms and hurricane generated swells from south and southwest
Sunset Beach- exposed to large winter long period swells from northwest; Winter waves—wave hts of 3-8 meters
Hanauma BayMamala Bay
Kaneohe Bay
Sunset Beach
Hanauma BayMamala Bay
Kaneohe Bay
Sunset Beach
Kaneohe Bay- semi-estuarine barrier reef & lagoon system; protected from open ocean swells
Kane‘ohe Bay, a Barrier Reef Lagoon SystemKane‘ohe Bay, a Barrier Reef Lagoon System
Coconut Island
Hanauma Bay Tuff Ring(shield volcano)
Pupukea
Fringing reefs- diving good in May; Storm surges in winter make diving too difficult
• constant coral species turnover associated with mortality and recruitment• rarely thicker than a single coral colony
Wave exposed environment:
• Breakage• Scour• Abrasion
Mortality on wave exposed environment due to:
Depth- lack of coral accretion in shallow open ocean coastline due to wave energy
Absence of mature barrier reef in Hawaiian Islands
Reef Front in a Low Energy Environment
Reef Front in a High Energy Environment
Algal RidgeAlgal Ridge
Upper Reef Slope of a High Energy Environment
Upper Reef Slope
Upper Reef Slope of a Lower Energy Environment
5 types of open ocean swells that cause disturbance to coral:
Destructive waves-causes high mortality on reef building corals:
1. North Pacific winter waves on north and western coastline
2. hurricane generated swells on south or southwest coastline (40 yr cycle)
Low moderate nondestructive waves- optimizes mixing and nutrient uptake or exchange, usually beneficial due to increased circulation and nutrients between water and organisms:
3. Tradewinds generated from northeast or east; ht. of 1-3 m, occurs 90% of summertime and 55-65% of wintertime
4. Long period southerly swell from southern ocean during the Austral winter; common between April and September (1-2 m in ht)
5. Kona storm generated waves (~4m); occasionally may be destructive and cause beach and shoreline erosion
Site Depth (m)
Coral cover
%
Coral Diversity (H’)
Algal Cover %
Bare Limeston
e %
Sand %
Dominant coral,
algae
Coral growth (mm/y)
Kaneohe Bay
1 2±5 0.16 5 1 95 P.c. Negligible
2-5 69±20
0.35 9 3 19 P.c.M.v
7.66
Hanauma Bay
1 <1 <0.01 90 10 0 P.o. Negligible
12 73±14
0.87 0 5 10 P.c.P.l.
8.13
Mamala Bay
1 6±3 0.15 90 5 5 P.m. Negligible
12 10±5 0.35 2 40 40 P.l 10.1
Sunset Beach
1 9±8 0.53 60 20 20 P.l. Negligible
12 15±13
0.68 20 65 65 P.m. 8.08
P.l.- Porites lobata; P.C.- Porites compressa; M.v.- Motipora verrucosa, P.m.- Pocillopora meandrina; P.o.- Porolithon oncodes (coralline algae)
Table 1. Community structure and growth of coral reef at sites selected for study. Attributes of community structure are based on one 50 m transect at each station. Annual coral growth rates are averages of 10 colonies.