Coral Health and Disease Assessment

Disease is defined as any impairment that interferes with or modifies the performance of normal physiological functions, including responses to environmental factors such as nutrients, toxicants, and climate; infectious agents; inherent or congenital defects; or a combination of these factors (Wobeser 2006). CRED has embarked on a long-term, broad-scale coral disease assessment and monitoring program aimed at documenting the prevalence of coral diseases on U.S. Pacific reefs and investigating factors that may be contributing to the occurrence of disease. Since 2006, and with direct support from NOAA's Coral Reef Conservation Program, we have conducted coral disease surveys at: Johnston and Wake Atolls, the Line and Phoenix Islands, American Samoa, the main Hawaiian Islands, the Northwestern Hawaiian Islands, Guam, and the Commonwealth of the Northern Mariana Islands (CNMI). Disease prevalence, for which no data existed in many of the U.S. Pacific jurisdictions prior to this project (e.g., Howland, Baker, and Jarvis Islands, Kingman Reef, Wake Atoll, and the CNMI), is now better characterized, and a better understanding of disease occurrence and potential impacts on U.S. Pacific coral reefs is emerging.

These Web pages describe the various types of coral lesions and diseases commonly recognized on U.S. Pacific reefs and provide information about their distribution and abundance. A list of useful references and links to additional information are also presented.

For more information contact Bernardo Vargas-Ángel or Erin Looney.

Lesions Involving Tissue Loss - No Tissue Discoloration

Acute Tissue Loss (white syndrome)

Description: This is a collective term to describe lesions characterized by the rapid loss of tissue, leaving behind a sharp, clean band, where tissue is completely removed from the skeleton. A progression of filamentous and turf algae generally covers the exposed skeleton. Our assessments have recorded white syndrome on at least 6 Pacific genera representing 4 scleractinian families, with species of Acropora and Montipora being the most common hosts. In the Northwestern Hawaiian Islands this disease is lethal to table acroporids.

Distribution and abundance: Occasional to common at Johnston Atoll and French Frigate Shoals (Northwestern Hawaiian Islands); occasional in the Line Islands and the main Hawaiian Islands uncommon to rare elsewhere.

Sub-acute Tissue Loss

Description: We use this collective term to describe lesions resulting in slow but progressive loss of tissue. Sub-acute tissue loss is distinguished from white syndrome by the narrow width of the zone of recently exposed skeleton. Because a particular type of gross lesion can present multiple microscopic manifestations, coral disease assessments and studies require biopsies for histological, microbiological, and molecular evaluation and verification.

Distribution and abundance: Occasional sightings in Guam, the CNMI, Line Islands, and Hawaiian Archipelago; rare elsewhere.

Alcyonarian Necrosis

Description: Lesions are variable in size but generally characterized by irregular patches of exposed skeleton flanked by a zone of degenerating tissue, of variable width. In some cases, discolored tissue flanks the black margin of active tissue loss, suggesting an already compromised health state.

Distribution and abundance: Very rare; only two cases, at Palmyra Atoll.

Lesions Involving Discoloration and Tissue Loss

Endolithic Fungal Infection (Endolithic hypermycosis)

Description: Patchy dark discolorations occurring in irregular patterns scattered on the coral surface. Most commonly observed on a variety of encrusting taxa including Pavona, Porites, Leptastrea, and Cyphastrea. Microscopic examination of tissues reveals extensive endolithic fungal proliferation. In Porites, upward migration of fungal hyphae into the thecal cavity is generally associated with disruption of the polyp body wall and sloughing of gastrodermis.

Distribution and abundance: Rare to occasional; cases reported for the main Hawaiian Islands, Northwestern Hawaiian Islands, American Samoa, Guam, the CNMI, and Line Islands.

Black Band Disease

Description: This condition is characterized by a distinct black mat, ~0.5 to 4 cm wide, on the living coral tissue, leaving behind the bare white skeleton. The unaffected coral tissue appears normal in color and morphology. Research indicates that there is a lack of concordance in the cyanobacterial species associated with the microbial consortium of black band disease between Caribbean and Indo-Pacific coral taxa (see Willis et al. 2004).

Distribution and abundance: Very rare; only one sighting registered in American Samoa.

Banded Fungal Infection

Description: Diseased colonies exhibit a distinct yellow to bright green mat about ~1 to 3 cm wide on the coral tissue. A progression of filamentous and turf algae generally appears on the exposed skeleton as the tissue is lost. As in black band disease, the unaffected coral tissue appears normal in color and morphology. Microscopic examination of diseased tissue reveals that the microbial mat is mainly composed of fungal hyphae.

Distribution and abundance: Very rare; only two sightings registered, one in the CNMI and the other at Palmyra Atoll.

Ciliate Infection

Description: Lesions are variable in shape and size and are characterized by a diffuse gray to black band or patch about ~0.5 to 3 cm wide, separating the healthy tissue from the exposed coral skeleton. The unaffected coral tissue appears normal in color and morphology; lesions have a specked appearance that is caused by the presence of ciliates lodged in the coral skeleton. Generally, filamentous and turf algae appears on the exposed skeleton as the tissue is lost.

Distribution and abundance: Rare, with sightings registered around the Main Hawaiian Islands (Maui and Hawaii), affecting preferentially Montipora capitata and Pocillpora meandrina.

Lesions Involving Tissue Discoloration - White

Bleaching

Description: Our disease assessments tally colonies exhibiting full, partial, or spotty bleaching. This condition is the result of a reduction in the intensity or complete absence of coloration within the coral tissues, due to loss of pigmentation in, and/or expulsion of the endosymbiotic zooxanthellae. Bleaching has been attributed to exposure to increased water temperatures. However, high levels of ultraviolet radiation, salinity, turbidity, and sedimentation may also induce bleaching. Although bleaching is considered a generalized response to stressful conditions, it is a sign of disease when it results in an impairment or inhibition of normal coral functioning (e.g., growth, calcification, reproduction) and colony death. Recent studies also indicate that bleaching can be caused by an intracellular bacterial pathogen of the genus Vibrio.

Distribution and abundance: Temperature-related widespread bleaching has been observed in Northwestern Hawaiian Islands (Aeby et al. 2003). Patchy, focal bleaching is occasional to rare elsewhere.

Lesions Involving Tissue Discoloration - Non-white

Trematodiasis

Description: Pink to pale, about ~5 mm in diameter protuberances, focal or widely distributed on the coral surface. These are caused by an encysted parasitic digenetic trematode. The main host for this disease is the genus Porites.

Distribution and abundance: Infected colonies are occasional to abundant in the main and Northwestern Hawaiian Islands; absent elsewhere.

Pigmentation Response

Description: This type of response appears only in the Indo-Pacific Poritidae. Lesions are characterized by bright pink patches of discolored, swollen tissue, often occurring in irregular shapes and patterns, scattered on the surface of the colony or adjacent to the sediment/algal margins of a colony. Often, but not exclusively, lesions appear to be associated with small areas of tissue loss or filamentous algal infections; however, uncomplicated lesions are also common.

Distribution and abundance: Lesions are common in the main Hawaiian Islands, Guam, and the southern CNMI; occasional elsewhere.

Lesions Involving Skeletal Growth Anomalies

Tumors

Description: Lesions characterized by changes in normal shape or form of coral colonies; unusual growths and/or protuberances associated with an abnormal deposition of the skeleton. Skeletal growth anomalies are caused by changes in the coral cells that deposit the carbonate skeleton. Such changes are: 1) Hyperplasia: a process resulting in an increase in the number of cells in a tissue or organ, thereby increasing the bulk of the tissue or the organ; 2) Neoplasia: a pathology resulting in the formation and growth of an undifferentiated mass of cells that continues after the cellular stimulus ceases.

Distribution and abundance: Coral tumors and skeletal growth anomalies are common to abundant in the main Hawaiian Islands and Johnston Atoll; occasional elsewhere.

Other lesions

Coral-algae and other biotic interactions may result in an impairment or inhibition of normal coral functioning (e.g., growth, calcification, reproduction). These morphologies, together with barnacle and tube worm infestations, as well as other unidentified cases are grouped under 'other lesions' in our disease prevalence surveys.

Crustose Coralline Algal Diseases

Although not coral, crustose coralline algae are included here because of their importance to coral reef environments. Similar to corals, coralline algae deposit layers of calcium carbonate and are important reef-builders. In addition, because crustose coralline algae provide essential chemical cues and substrate for coral larval recruitment, destruction of this group due to disease has the potential to significantly affect the development and recovery of coral reefs.

Coralline Lethal Orange Disease (a.k.a CLOD)

Description: Coralline lethal orange disease (CLOD) is characterized by a band of bright orange, slimy, stringy material spreading across the algal surface, leaving behind the algal skeletal carbonate remains; turf and filamentous algae often colonize the bare coralline thallus. Individual lesion sizes vary considerably, but typically range from 1 to 10 cm in max diameter. CLOD is a bacterial disease first reported by Mark and Diane Littler in 1993 on South Pacific coral reefs (Littler and Littler 1995). It appears that the CLOD pathogen is highly virulent and the orange material is easily transferable, thus infecting other plants (Littler and Littler 1995). A consortium of five bacterial species have been consistently identified associated within the CLOD condition, and are closely related to the genera Planococcus, Bacillus, and Pseudomonas (Cervino et al. 2005).

Distribution and abundance: CLOD is the most abundant of the five coralline algal diseases identified, occurring most frequently around American Samoa and Guam, but also in lower abundances in the CNMI and Northwestern Hawaiian Islands.

Coralline Fungal Disease

Description: Characteristics are unlike any other fungal pathogen or black-band disease and are denoted by striated bands which are non-glossy, blue-black color and matte textured (Littler and Littler 1998). At the time when it was first discovered in American Samoa, this disease co-occurred with coralline lethal orange disease and also primarily attacked Porolithon onkodes.

Distribution and abundance: Common to abundant at Swains Island (American Samoa), Kingman Reef, and Palmyra Atoll (Line Islands); rare elsewhere.

Coralline White Band Syndrome (CWBS)

Description: This is a collective term used to describe poorly characterized lesions that are typified by the loss of tissue, leaving behind a sharp, clean, white band (1–3 cm width) where the dead coralline thallus is exposed. Often, but not exclusively, lesion spreading edges exhibit a thin (~0.5 cm width) band of discolored yellow, green, or pink tissue. Earlier referred to as “coralline lethal disease”, was first recognized by Tom Goreau in the Caribbean in 1996, with more recent observations across the Indian Ocean and off the Philippines. The etiology of CWBS is still largely unknown.

Distribution and abundance: Occasional to rare with sightings in American Samoa, CNMI, Palmyra Atoll, and Jarvis Island.

Coralline Target Phenomena

Description: This is also a collective term used to describe lesions characterized by discolored (white, light yellow, or pale green) concentric, annular or horseshoe shaped bands, measuring 0.5–3 cm in width, radiating from a focal point, and leaving behind the bare skeletal carbonate remains of the coralline algae. Lesions can range from a few centimeters up to 100 cm in max diameter. It is proposed that these conspicuous lesion shapes are probably formed by patterns of thallus death and regrowth. The etiological aspects of this disease are still poorly understood.

Distribution and abundance: Occasional to rare.

Coralline Cyanophyte Disease

Description: Irregularly shaped patches or bands of slimy, fuzzy, green or tan cyanobacterial material spreading across the algal surface, leaving behind the bare skeletal carbonate remains; turf and filamentous algae often colonize the bare coralline tallus. Commonly, lesions are distinguishable by the conspicuous appearance of the cyanobacterial mat, but also because bright red, orange, or green discolored coralline tallus is observable in areas where the mat has been lifted or disrupted. The etiology of this disease is still largely unknown.

Distribution and abundance: Very rare; only a few sightings in American Samoa and the CNMI.

References

Related Links

Coral Disease and Health Consortium (CDHC)