Coral Reef Zonation

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.

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 levels Moderate wave energy Moderate light levels Occasional storm wave energy Low light levels Low 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 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 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

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 elevation 2.Rate of erosion 3.Coral composition and rate of coral growth

Society Islands, French Polynesia

Hawaiian Islands Midway atoll

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)

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

Kane‘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 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

SiteDepth (m) Coral cover % Coral Diversity (H’) Algal Cover % Bare Limestone % Sand % Dominant coral, algae Coral growth (mm/y) Kaneohe Bay 12± P.c.Negligible 2-569± P.c. M.v 7.66 Hanauma Bay 1<1< P.o.Negligible 1273± P.c. P.l Mamala Bay 16± P.m.Negligible 1210± P.l10.1 Sunset Beach 19± P.l.Negligible 1215± 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.