Coral Reef Zonation

1. Coral Reef Zonation

2. Disclaimer 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.

3. 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

4. Hawaiian Coral Zonation 0 m High light levels Moderate wave energy 6 m Cauliflower coral (Pocillopora damicornis) Moderate light levels Occasional storm wave energy Lobe coral (Porites lobata) 13 m Low light levels Low wave energy Finger coral (Porites compressa) 25 m Very low light, Primarily downwelling No wave energy Plate coral (Porites rus)

5. Hawaii Coral origin- Indowest Pacific; 34 mya + recolonization

6. Glaciation 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

7. 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 form first atoll French Frigate Shoals, dated 11.7 mya

8. Rates of Reef Formation 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: • Initial elevation • Rate of erosion • Coral composition and rate of coral growth

9. Society Islands, French Polynesia

10. Hawaiian Islands Midway atoll

11. Hawaiian Island Chain • Coral reef growth limited by: • wave exposure • sea level Sheltered sites: Hanauma Bay and Kaneohe Bay Reef accretion ~ 2mm/yr Wave exposed sites: Mamala Bay and Sunset Beach Reef accretion ~ 0 mm/yr shallow (1m) and deep (12m)

12. Sunset Beach Kaneohe Bay Hanauma Bay Mamala Bay

13. Kaneohe Bay- semi-estuarine barrier reef & lagoon system; protected from open ocean swells 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

14. Kane‘ohe Bay, a Barrier Reef Lagoon System Coconut Island

15. Hanauma Bay Tuff Ring (shield volcano)

16. Pupukea Fringing reefs- diving good in May; Storm surges in winter make diving too difficult

17. Wave exposed environment: • constant coral species turnover associated with mortality • and recruitment • rarely thicker than a single coral colony

18. Mortality on wave exposed environment due to: • Breakage • Scour • Abrasion

19. Depth- lack of coral accretion in shallow open ocean coastline due to wave energy Absence of mature barrier reef in Hawaiian Islands

20. Reef Front in a Low Energy Environment

21. Reef Front in a High Energy Environment Algal Ridge

22. Upper Reef Slope of a High Energy Environment

23. Upper Reef Slope

24. Upper Reef Slope of a Lower Energy Environment

25. Wave climate in Hawaii • 5 types of open ocean swells that cause disturbance to coral: • Destructive waves-causes high mortality on reef building corals: • North Pacific winter waves on north and western coastline • hurricane generated swells on south or southwest coastline (40 yr cycle)

26. Low moderate nondestructive waves- optimizes mixing and nutrient uptake or exchange, usually beneficial due to increased circulation and nutrients between water and organisms: 3. Tradewindsgenerated from northeast or east; ht. of 1-3 m, occurs 90% of summertime and 55-65% of wintertime 4. Long periodsoutherly swellfrom southern ocean during the Austral winter; common between April and September (1-2 m in ht) 5. Kona stormgenerated waves (~4m); occasionally may be destructive and cause beach and shoreline erosion 

27. Site Depth (m) Coral cover % Coral Diversity (H’) Algal Cover % Bare Limestone % 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.