The coral rim and the lagoon

Transcription

1 The coral rim and the lagoon

2 Coral Taxonomy Hydrozoa hydroids (e.g., hydras, Portuguese man-of-war, fire coral) Freshwater and marine species Solitary and colonial Scyphozoa jelly fish Known for its mobile medusa form Alternating sessile polyp and mobile stages Cubozoa box jellies Swimming medusa with four tentacles Highly toxic venom Anthozoa hard & soft corals!!! Exclusively marine No medusa stage, sessile Phylum Cnidaria (4 Classes)

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4 Coral Taxonomy Hexacorals / Zoantharia Class Anthozoa (2 subclasses) Actiniaria (sea anemones) Ceriantharia (tube anemones) Scleractinia (stony corals) Antipatharia (black corals, wire corals) Corallimorpharia (coral-like animals, lack a skeleton) Zoanthidea (zooanthids) Octocorals / Alcyonaria Alcyonacea (soft corals, sea fans, sea whips, red/pink corals) Pennatulacea (sea pens) Helioporacea (blue corals)

5 Scleractinian Anatomy Individual polyps share nutrients throughout common coenosarc Scleractinia (stony corals) create CaCO3 skeleton Modern coral reefs formed by scleractinian corals and encrusting coralline algae Individual polyps share nutrients throughout common coenosarc

6 Scleractinian Ecology Predatory polyps: Filter feeding on meroplankton and holoplankton Photosynthetic ability: Symbiotic Zooxanthellae: Genus Symbiodinium encompasses largest and most prevalent group of endosymbiotic dinoflagellates

7 Coral Requirements - Distribution Global distribution of coral reefs corresponds to shallow submarine platforms within tropical waters Generally located on the western end of major ocean basins (Atlantic, Pacific, Indian), within the tropics

8 Coral Requirements Regional Scale Defining the Fundamental Niche of Corals Reef-building corals require warm water. The typical limits (for long periods) are from about deg. C Most corals will not survive prolonged exposure to water outside range of about parts per thousand Need for sufficient sunlight to support photosynthesis. Even in clearest tropical seas, photosynthesis only occurs in relatively thin uppermost 300 feet (~ 100 m) of the water column Other limiting factors?

9 Coral Requirements Local Scale Defining their Fundamental Niche Further Limitations Sedimentation and Run-off: - light attenuation - clogging of polyps - abrasion of skeleton Other limiting factors? Kailua Bay bathymetry, O ahu

10 Coral Requirements - Biotic Interactions Defining their Realized Niche Coral Fundamental Niche further limited by ecological Interactions - Competition with algae - Competition with other corals - Predation - fish (coralivores) - crown-of-thorns sea star

11 Ecological Interactions Predation Parrotfish grazing Competition Stinging cells in sweeping tentacles

12 Island-Associated Coral Structures The fringing reef is formed first. The lagoon and the barrier reef form on the periphery of the aging islands, as they erode and change. Fringing Reef - a reef system that grows fairly close to (or directly from) the shore; characterized by a shallow lagoon (or none) Barrier Reef - a reef system that parallels the shore and is separated from it by a lagoon Patch Reefs - isolated reef outcrops within deeper parts of lagoon

13 Coral Zonation No Lagoon Coral communities structured by wave energy No lagoon (e.g., Big Island) (Dollar 1982) Total Cover: More coral offshore (less wave energy) Species Cover: Different species dominate in deep and shallow water

14 Coral Zonation Well-Developed Lagoon Mature lagoon (e.g., O ahu) Functional groups: Massive, branching, planar Different growth forms: Massive vs planar structures

15 Kaneohe Bay Coral Communities in a Heavily Urbanized Lagoon Largest embayment in Hawai i: approximately 13.5 km at maximum length, and up to 4.5 km wide from shore to outer barrier reef (Hunter & Evans 1995)

16 Kaneohe Bay Coral Communities Because coral species show different sensitivities to reduced salinities, episodic freshwater kills on Kaneohe Bay play an important role structuring coral communities Table corals (Acropora cytherea) Center of distribution (3 species) in French Frigate Shoals, NWHI Found in Kaneohe Bay

17 Kaneohe Bay - Precipitation Watersheds consist of gently rolling hills and valleys that abut nearly vertical cliffs Annual rainfall = cm / yr. Severe rainfall can lead to coral kills, 1.2 m below the reef crest (Hunter & Evans 1995)

18 Kaneohe Bay Human Impacts Sewage and runoff discharge into bay, especially since WWII lead to poor water quality: low clarity and ph High nutrient levels promoted a benthic community dominated by filter and deposit feeders in southern sectors of the bay, accelerating bioerosion of reefs Nutrients also supported growth of the indigenous "green bubble alga" Dictyosphaeria cavernosa

19 Kaneohe Bay Recovery By December 1977, Mokapu outfall and diversion lines from two treatment plants completed An extensive study of Kane ohe Bay conducted during the pre-diversion and post-diversion periods Studies showed that after sewage diversion, clarity of water improved rapidly - within a year Although algal masses smothering coral also decreased quickly, the coral community had more gradual recovery (Hunter & Evans 1995)

20 Kaneohe Bay Recovery (Hunter & Evans 1995) 6 yrs Before 6 yrs After 13 yrs After

21 Kaneohe Bay Recovery By 1983, D. cavernosa had decreased to ¼ of previous (1971) abundance and coral cover had more than doubled Last point-source sewage discharge bay diverted in 1986 However, 1990 survey indicated that, on a baywide basis: 1) algal cover had increased between surveys 2) Rate of coral recovery established by surveys in 1970 and 1983 had slowed or, in some cases, reversed D. cavernosa cover increased at 5 of 15 sites, while live coral cover declined at 9 sites compared to 1983 levels (Hunter & Evans 1995)

22 Kaneohe Bay Lack of Full Recovery Involvement of invasive algae free from grazers Other sources of non-point source run-off / pollutants Bleaching and Emergent diseases: White Syndrome Disease Coral Bleaching (Work et al. 2012) (Franklin et al. 2009)

23 In February 2015, detected Acute Montipora White Syndrome in Kaneohe Bay. amws affects rice coral, Montipora capitata, causes tissue loss and rapid death. Coral Disease - Local Disease previously seen in Kaneohe Bay: 2010 and in Unknown what environment drivers cause this disease.

24 Coral Disease - Regional In Hawaii, there have been a few isolated events of coral disease outbreaks. Diseases caused by infectious or non-infectious agents. As corals become stressed from human and / or natural disturbances, their immune system is weakened and they become more susceptible to disease. Exposure to stressors can make corals more vulnerable to disease: physical damage, land-based pollution, temperature stress and ocean acidification.

25 Coral Disease - Pervasive In Hawaii, coral reefs occur across a gradient of biological (host abundance), climatic (water temperature anomalies) and anthropogenic conditions from the human-impacted reefs of the main Hawaiian Islands (MHI) to the pristine reefs of the northwestern Hawaiian Islands (NWHI). Coral disease surveys conducted at 142 sites across Archipelago to examine patterns. (Aeby et al. 2011)

26 Coral Disease - Pervasive 12 diseases in 3 coral genera (Porites, Montipora, Acropora) Porites have the highest prevalence. - growth anomalies (PorGAs) more prevalent in MHI - trematodiasis (PorTrm) more prevalent in NWHI NOTE: PorTrm caused by parasitic flatworm that uses multiple hosts during life cycle (fish, mollusk, coral). (Aeby et al. 2011)

27 Coral Disease - Examples Photos and description of coral diseases observed during surveys across the Hawaiian archipelago (Aeby et al. 2011) A) Acropora white syndrome (AcroWS): diffuse areas of acute to subacute tissue loss, B) Acropora growth anomalies (AcroGA): protuberant growths of skeleton accompanied by aberrant calyx formation

28 Coral Disease - Examples J) Porites brown necrotizing disease (PorBND): diffuse areas of unidentified brown homogenous matrix and tissue loss K) Porites bleaching with tissue loss (Por bl w/tl): focal areas of bleaching with diffuse areas of tissue loss L) Porites discolored tissue thinning syndrome (PorDTTS): distinct areas of tissue thinning

29 Coral Disease - Examples C) Montipora multifocal tissue loss (MontMFTL): multiple (.5) variably sized areas of tissue loss D) Montipora white syndrome (MontWS): one to 5 areas of tissue loss E) Montipora growth anomalies (MontGA): protuberant growths of skeleton accompanied by aberrant calyx formation overlaid by normally pigmented to colorless tissues

30 Coral Disease - Examples F) Porites trematodiasis (PorTrem): multiple small (,5 mm) pink to white nodules G) Porites tissue loss syndrome (PorTLS / ProMFTL): one to multiple areas of acute to subacute tissue loss I) Porites growth anomalies (PorGA): Protuberant growths of skeleton accompanied by aberrant calyx formation overlaid by colorless tissues

31 Coral Disease - Pervasive Focusing on 3 indicator diseases (PorGAs, PorTrm, PorTLS). Used statistical modeling to examine underlying associations between disease prevalence and 14 different predictor variables (biotic and abiotic). All diseases positively associated with host abundance (coral abundance) and negative associations with thermal stress. Association with human density differed among diseases: PorGAs showing a positive association PorTrm showing a negative association no significant explanatory power for PorTLS

32 Hawaiian Black Band Coral Disease First observed in Belize in Caused by a bluegreen alga and affects 42 species of coral in worldwide distribution. First identified in 2008, and rose to outbreak levels in First outbreak in Hawaii. Affecting nearly half of reef sites researchers have surveyed in waters off Kauai and threatens to destroy Hawaii s reefs, according to the state DLNR.

33 Hawaiian Black Band Coral Disease Kaua i-black-band-disease/ Researchers spent 2 years surveying reefs around Kauai. Black band disease found at 23 of 47 sites, with hotspots on north and east sides of island. Disease has not been reported on other islands, but it may spread widely in the near future.

34 References Aeby GS, Williams GJ, Franklin EC, Kenyon J, Cox EF, et al. (2011) Patterns of Coral Disease across the Hawaiian Archipelago: Relating Disease to Environment. PLoS ONE 6(5): e Hunter C.L., & Evans, C.W. (1995) Coral reefs in Kaneohe Bay, Hawaii: two centuries of western influence and two decades of data. Bulletin of Marine Science 57(2): Grigg, R.W. (2008) The Darwin Point: a conceptual and historical review. Proceedings of the 11th International Coral Reef Symposium, Ft. Lauderdale, Florida, 7-11 July 2008 Grigg, R.W. (1998) Holocene coral reef accretion in Hawaii; a function of wave exposure and sea level history. Coral Reefs 17: Grigg, R.W. (1983) Community structure, succession and development of coral reefs in Hawaii. Marine Ecology Progress Series 11: 1-14 Grigg, R.W. (1982) Darwin Point: A threshold for Atoll Formation. Coral Reefs 1:29-34