Assessment of Microbial Disease on Corals and Its Prevalence in Andaman Islands
V. Madhan Chakkaravarthy* and C. Raghunathan
Zoological Survey of India, Andaman and Nicobar Regional Centre, National Coral Reef Research Institute, Port Blair 744 102, Andaman and Nicobar Islands, India.
ABSTRACT:
Coral reefs are the most diverse and productive ecosystems on the earth. Eight diseases such as black band, brown band, yellow band, white syndrome, white pox, pink spot and pink line syndrome were reported in corals at different ratio around the islands. Overall coral disease prevalence was 53.3%. With the maximum at South Andaman (59.8%) followed by Middle Andaman (56.6%) and North Andaman (43.7%). The similarity index between the islands ranged from 0.18 to 0.50 %. Coral disease and its prevalence were discussed in detail.
KEYWORDS: Coral disease; Prevalence; Outbreak; Andaman Islands; Pollution.
INTRODUCTION:
The coral reefs of Andaman and Nicobar Islands are the biodiversity hot spot of India. Coral reefs are one of the Earths most beautiful, ancient and complex ecosystems. They play an essential role in sustaining life in the sea and serve as a source of food and protection for human communities. As a result of growing human and environmental assaults, reefs are among the most threatened ecosystems on earth, so coral reefs face an uncertain future. Ecological research provides fundamental information to understanding and combating this tendency. The Indian Ocean tsunami on December 26, 2004 caused severe damage to coral reefs of these Islands. About 4000 ha of North Andaman, 1211 ha of South Andaman and 3500 ha of Nicobar Island reefs were damaged due to tsunami, which leads to vulnerable conditions to the coral reefs. Pathogens that invade an organisms cells and tissues transmitted by water or coral proximity or fragment which cause infectious disease on coral community. The major impacts on the coral reef ecosystem come from industrial development, including cutting of mangroves, development of ports and offshore moorings and pollution from large cities. Existence of corals is threatened by environmental changes, pollution and direct human interference in many coral reefs around the world. Natural and human impacts on coral reefs have been increasing in recent years. The white band disease was also studied in Andaman and Nicobar Islands. The death and damage rate of corals around Mahatma Gandhi Marine National Park was reported by Wood (1989). Diseases bring about destruction of corals to a greater extent than other factors. Porites lutea have been affected by microorganisms especially cyanobacteria in and arround Indo-Pacific, the massive coral of Porites sp. was mostly affected by pink line syndrome (Ravindran and Raghukumar, 2002) which shows the target specificity towards the species. Coral diseases usually take place in-reaction with micro-organisms like bacteria, virus, fungi and also warming of sea surface temperature, radiation and anthropogenic activities (Santavy and Peters, 1997).
Coral reef bleaching event reported from all over the world including the Andamans in the Bay of Bengal (Ravindran et al. 1999). A dark brown fungus, Scolecobasidium sp associated with massive corals showing necrotic patches in the Andamans (Raghukumar and Raghukumar, 1991). Fungal molest on hard corals of India have been studied from most of the reefs (Raghukumar and Balasubramanian, 1991; Ravindran et al, 2001). Information was lacking in the area of coral diseases in the Indo-Pacific regions, so the present investigation mainly focused on the disease outbreaks and its prevalence.
MATERIALS AND METHODS:
Undersea surveys employing SCUBA were conducted around Andaman Islands from June 2009 to July 2010 (Fig. 1). Three stations North, Middle and South Andaman were separated and further it is selectively divided into twelve islands for this study. Tarmugli (Lat. 113326.0 N - Long. 923329.5 E); Jolly Bouy (Lat. 113036.8 N - Long. 923693.3 E) and Rutland (Lat. 112423.4 N - Long. 923995.2 E) in South Andaman; South Button (Lat. 121324.3 N - Long. 930120.0 E); Aves (Lat. 125507.3 N - Long. 925588.5 E); Sound (Lat. 125309.2 N - Long. 925683.4 E); Interview (Lat. 125912.5 N - Long. 924298.1 E); North reef (Lat. 130448.7 N - Long. 924248.9 E) in Middle Andaman; Ross (Lat. 131816.7 N - Long. 930426.1 E); Smith (Lat. 131840.6 N - Long. 930420.7 E); Ariel bay (Lat. 131609.3 N - Long. 930243.3 E) and Lamia bay (Lat. 131221.2 N - Long. 930222.7 E) in North Andaman. Line Intercept Transect was laid parallel to the reefs (English et al., 1997) and diseases were observed and photographs were taken by (DSC-T900) camera with underwater housing facility. The identification of the coral specimen was made and confirmed by standard monographs of (Veron, 2000). Sorensen index was adapted, to understand the prevalence rate and similarity among the twelve islands in Andaman.
Sψrensen index, QS = 2 C
A+B
Where, C is the number of species shared by the two samples and A and B are the species numbers in samples A and B respectively.
RESULTS:
Eight diseases viz, black band, brown band, yellow band, white syndrome, white pox, pink spot and pink line syndrome observed during the period of study. Assessment of coral disease prevalence was carried out in twelve islands of South, Middle and North Andaman. The prevalence was 53.3% all over the islands, highest was observed in Rutland 87.5% and Interview Island 75%; Tarmugli, North Reef and Sound Island 62.5% was observed, remaining islands shows below 50% (Fig. 2). The rate occurrence of pink spot and pink line syndrome was 19% followed by yellow blotch 16%, white pox 14%, white spot 10%, white syndrome 8%, black band 8% and brown band 6% was observed in all over Andaman Islands (Fig. 3). The similarity index between the islands ranged from 0.18 to 0.50 %.
North Andaman
Middle Andaman
South Andaman
Figure 1. Map represents the study area of Andaman Island
The similarity index between the islands ranged from 0.18 to 0.50 %. The highest similarity was found between Tarmugli and Ariel Bay (0.50) as well as in North Reef and Ariel Bay Island (0.50), least similarity from Jolly Bouy and Rutland Island (0.18) as well as in Interview and Smith Island (Table 1). The dendogram cluster divided into 4 major groups, first group shows two observation i.e, (TM-SB); second shows (SM-AI-AB); third shows (JB-IV) and fourth group shows (HL-RL-RI-SI-NR) were categorized according to the scrutiny (Fig. 4).
a)Black band disease (Pl. I, Fig. 1: Montastrea curta): It is characterized by a blackish concentric or crescent-shaped band, 1 to 30 mm wide and up to 2 m long, that consumes live coral tissue leaving behind bare skeleton. It forms blackish and looks like a dark band among healthy tissues, where the black color is from a cyanobacterium Phormidium corallyticum, migrating over and killing the polyps underneath (Richardson, 1996).
b)Brown band disease (Pl. I, Fig. 2: Leptoria phrygia): A brown band of varying width, dividing healthy coral tissue in front of the band from the exposed white skeleton of coral that the disease has already killed. Sometimes there is also a white zone between the brown band and healthy tissue. The ciliate Helicostoma nonatum may cause this disease which appears as a brown jelly-like condition.
Figure 2. Coral disease prevalence in South, Middle and North Andaman Islands
c) White syndrome (Pl. I, Fig. 3: Acropora hyacynthus): Due to the difficulty of differentiating between both white band and white plague diseases these two are placed in one category white syndrome. White band disease is characterized by either a distinct line or a band of bleached but intact coral tissue between the exposed coral skeleton and the healthy coral tissue caused by gram-negative bacteria Vibrio charcharii. White plague is characterized by a white line between the living healthy coral tissue and the exposed coral skeleton. It is caused by a gram-negative bacterium closely related to the genus Sphingomonas Richardson and Aronson (In-press).
d) White Pox Disease (Pl. I, Fig. 4: Porites annae): This disease is characterized by white circular lesions on the surface of infected colonies. The rate of tissue damage appears to be rapid, allowing for algal colonization within days. The cause of white pox remains a mystery, but a possible bacterial pathogen Serratia marcescens has been identified (Porter, 2002).
Figure 3. Coral disease prevalence in South, Middle and North Andaman Islands
e) White Spot Syndrome (Pl. I, Fig. 5: Porites lutea): Multifocal patterns of tissue loss that expose spots of bare white skeleton, Lesions typically small (<1cm diameter), regularly ovoid and may start as bleached, Spots a coral may contain both bleached lesions and lesions devoid of tissue, No signs of associated micro-organisms at live tissue interface, Commonly affects Porites, but also Montipora, Echinopora, favia and Heliopora.
f) Pink Spot Syndrome (Pl. I, Fig. 6: Porites sp.): Pink spot is caused by parasitic flatworm Podocotyloides stenometra it causing polyps to appear swollen and pink. The flatworm has three life stages, the first is parasitic on a mollusc, while the second affects tissues of the coral, causing polyps to appear swollen and pink. This makes the polyp more vulnerable to predation by butterfly fish, which are the final host for the parasite.
g) Pink Line Syndrome (Pl. I, Fig. 7: Porites solida): It is due to the pink coloration of the animal tissue bordering the dead patch colonized by the cyanobacterium, Phormidium valderianum. In pink-colored polyps, forming a pink line, border these patches. Similar to the widely described black band disease in corals (Antonius 1981).
Figure 4. Dendogram showing similarity clusters among the islands of Andaman Islands.
TM Tarmugli; JB Jolly bouy; RL Rutland; SB South button; AI Aves; SI Sound;
IV Interview; NR North reef; RI Ross and SM Smith; AB Ariel bay and LB Lamia bay.
Table 1. Sorensen coefficient index of Andaman Islands.
|
ISLANDS |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
|
TM |
0.00 |
0.00 |
0.00 |
0.25 |
0.00 |
0.25 |
0.00 |
0.00 |
0.00 |
0.00 |
0.50 |
0.28 |
|
JB |
|
|
0.18 |
0.28 |
0.00 |
0.00 |
0.20 |
0.22 |
0.25 |
0.22 |
0.00 |
0.00 |
|
RL |
|
|
|
0.20 |
0.36 |
0.00 |
0.30 |
0.00 |
0.36 |
0.33 |
0.00 |
0.00 |
|
HL |
|
|
|
|
0.00 |
0.33 |
0.44 |
0.25 |
0.28 |
0.00 |
0.00 |
0.40 |
|
AI |
|
|
|
|
|
0.00 |
0.20 |
0.00 |
0.00 |
0.44 |
0.00 |
0.00 |
|
SI |
|
|
|
|
|
|
0.00 |
0.25 |
0.00 |
0.00 |
0.33 |
0.00 |
|
IV |
|
|
|
|
|
|
|
0.00 |
0.40 |
0.18 |
0.00 |
0.25 |
|
NR |
|
|
|
|
|
|
|
|
0.00 |
0.2 |
0.50 |
0.28 |
|
RI |
|
|
|
|
|
|
|
|
|
0.00 |
0.00 |
0.00 |
|
SM |
|
|
|
|
|
|
|
|
|
|
0.00 |
0.00 |
|
AB |
|
|
|
|
|
|
|
|
|
|
|
0.40 |
|
LB |
|
|
|
|
|
|
|
|
|
|
|
|
h) Yellow Blotch Disease (Pl. I, Fig. 8: Porites mayeri): Vibrio alginolyticus and Vibro sp. were responsible for this disease. It is pale, circular blotches of translucent tissue or as a narrow band of pale tissue at the colony margin, with affected areas being surrounded by normal, fully pigmented tissue. As the disease progresses, the tissue first affected in the center of the patch dies, and exposed skeleton is colonized by algae (Bruckner, 2001).
DISCUSSION:
Coral reefs are under increasing pressure in a changing climate, one such threat being more frequent and destructive outbreaks of coral diseases (Heron et al. 2010). The results clearly indicates that the diseases affecting corals, particularly in the Andaman and Nicobar regions, have increased in both frequency and severity within the last two decades and caused major community shifts under threats. Yet we are only beginning to understand enough about disease outbreaks to consider management action in the major islands affected by natural and anthropogenic disturbance on coral reef ecosystem. The PLS discussed here seems to be caused by the cyanobacterium P. valderianum, as borne out by the observations that it was always present in PLS-affected colonies of P. lutea and inoculation with the cyanobacterium but not with the fungi caused by the PLS (Ravindran and Raghukumar, 2002). The most well-known cyanobacterial disease of corals is the black band disease (Antonius 1981). Cyanobacterial pathogen in BBD is believed to be promoted by excess nutrients, elevated temperatures, and pollution (Rutzler et al. 1983; Edmunds 1991). The last decade has been a time of intense research into causative agents of coral disease. Though we still lack evidence showing the origin of any coral disease, the role of specific pathogens in causing various diseases, their pathogenesis, and agent-host interactions, significant progress is being made in all of these areas. As efforts increase to document coral diseases from more locations within the Pacific, the lists of species affected by disease, locations where diseases are reported, and prevalence of those diseases, are steadily increasing. It is critical to keep in mind that all infectious syndromes are different and may respond in different ways to environmental change. However, identifying the factors that control the most important infectious syndromes is a key management strategy. The untreated sewage generated from the hotels, restaurants and household garbage are discharged into the sea, which seriously affects the coral reefs of North Bay, Minnie Bay, Snake Island and Navy Bay. The solid waste/garbage from the hotels and houses are the major source of pollution. The coastal and marine waters of Port Blair and its vicinity were reported to be generally contaminated with organocholorine pesticides viz., BHC (lindane) and p, p-DDT (Jeyabaskaran, 1999). Natural stressors like UV radiation, temperature anomalies, and bacterial infections are known to uncouple the algal-host symbiosis resulting in whitening of colonies (Kushmaro et al. 1996). So, it is urgent to set-up a solid waste treatment plant for recycling purpose to save the present condition of these Islands.
ACKNOWLEDGEMENTS:
Authors are greatful to Director, Zoological Survey of India, Kolkata, for the facility and encouragement. Authors are also thankful to Ministry of Environment and Forest (MoEF), New Delhi, for providing all financial support through the project of National Coral Reef Research Institute, Zoological Survey of India, Andaman and Nicobar Regional Centre, Port Blair.
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Received on 31.12.2010
Modified on 22.01.2011
Accepted on 27.01.2011
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Research J. Science and Tech. 3(2): March-April. 2011: 65-69