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A rapid in situ fluorescence census for coral reef monitoring
Regional Studies in Marine Science 28 (2019) 100575
Contents lists available at ScienceDirect
Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma
A rapid in situ fluorescence census for coral reef monitoring ∗
C.H. Ramesh , S. Koushik, T. Shunmugaraj, M.V. Ramana Murthy National Center for Coastal Research (NCCR), NCCR Field Office, Ministry of Earth Sciences (MoES), Mandapam 623519, Tamil Nadu, India
article
info
Article history: Received 13 November 2018 Received in revised form 11 January 2019 Accepted 6 March 2019 Available online 15 March 2019 Keywords: Fluorescence Corals UV-blue light Gulf of Mannar Andaman Islands
a b s t r a c t Since the discovery of Green fluorescent protein (GFP) from jellyfish, many GFP-like marine fluorescent proteins have been unveiled and implicated in myriad of biomedical and toxicological research applications. However, fluorescence trait has not been implemented in the field applications so far. In this study, using a UV-blue light, we induced fluorescence of corals to identify the diseased and damaged corals as well as newly recruiting and encrusting corals buried in sedimentation and algal covers. Healthy corals have displayed complete body fluorescence, whereas the dead, damaged and diseased corals are failed to display complete fluorescence. The development of pink line disease on Porites sp. was obvious under UV illumination than in visible light, revealing the hidden disease level propagation in Porites. Coral recruitment is well appreciated in both the study locations Burmanallah and Hare Island. Results of this study infer that this method is a highly reliable and rapid in field to study recruitment, disease propagation and health status of coral reefs. © 2019 Elsevier B.V. All rights reserved.
1. Introduction Coral reef ecosystems are one of the precious and aesthetic bio-treasure hotspots distributed around the globe which harbour thousands of marine organisms of food and ornamental importance (Spalding et al., 2017). According to Global Coral Reef Monitoring (GCRMN), about 500 million people around the world are dependent on reef ecosystem for food and income. Unfortunately, global research shows that directly or indirectly the proximity of anthropogenic activities and global changes in coastal areas are apparently found to threaten the health of coral reefs (Hoegh-Guldberg et al., 2017). Monitoring the reef health is an essential concern and also need to give special attention and action to restore the damaged reef areas. These aspects are important to protect the biodiversity for the future generations and ecological balance. If the coral reefs are disappearing, then there would be more chances of losing hues of fish and invertebrate diversity that will subsequently effect humans. GFP like fluorescent proteins (FPs) are wide spread in coral reefs and are of highly preferred by genetical engineers as fluorescent labels (Alieva et al., 2008). FPs are widely being used in different applications, including microbial interactions, disease propagation in tumours, toxic contaminates from different environments and in food products (Chudakov et al., 2010). FPs of corals are known to involve in enhancement of light under low light availability and act as photoprotective from excessive ∗ Corresponding author. E-mail address: [email protected] (C.H. Ramesh). https://doi.org/10.1016/j.rsma.2019.100575 2352-4855/© 2019 Elsevier B.V. All rights reserved.
sunlight (Salih et al., 2000), and indirectly involved in stimulating photosynthesis process of zooxanthellae (Shick et al., 1996). FPs of corals are known to protect their endosymbiotic zooxanthellae from photodamage (Smith et al., 2013). Corals uptake energy from their zooxanthellae which enhances photosynthesis process using different autofluorescent chromatophores localised on the oral gastro dermis or oral epidermis (Schlichter et al., 1994). These zooxanthellae display red fluorescence due to chlorophyll content (Warner et al., 2010). It was also suggested that GFP-like fluorescent proteins in corals act as biomarkers to indicate the health status and physiological processes of corals (D’Angelo et al., 2008). Considering such an important FPs as indicators, field applications have scarcely been undertaken so far to monitor coral reef status. In this study we undertaken fluorescence trait as an indicator to predict the health of coral reef. Currently, researchers are using different methods to evaluate the health of corals, including remote sensing from boats, aircrafts (Lyzenga, 1981), satellites (Mumby et al., 1998), photographic and visual census (Edmunds et al., 1998), epifluorescence microscopy in laboratory (Vermeij et al., 2002), blue light excitation of photoquadrats painted with green fluorescent paint (Piniak et al., 2005), in situ spectrometry (Matz et al., 2006), infrared sensitive surveillance technology cameras with high-power IRLEDs (Dirnwoeber et al., 2012), confocal imaging (Salih, 2012), ultraviolet (UV) pulsed laser system (Masahiko et al., 2013), Fluorescence Imaging System (FluorIS) (Treibitz et al., 2014), light detection and ranging (LIDAR) system (Sasano et al., 2016), drone imagery (Collin et al., 2018) and standard procedures previously
2
C.H. Ramesh, S. Koushik, T. Shunmugaraj et al. / Regional Studies in Marine Science 28 (2019) 100575
Fig. 1. Study locations in Gulf of Mannar and Andaman & Nicobar Islands.
described (English et al., 1997). However, there are very few and
2. Material and methods
limited quick methods available to assess and determine the reef health. To study the corals distributed across the Indian continent, The National Center for Coastal Research (NCCR) has recently set up a field station in Mandapam, Tamil Nadu. During the years 2000– 2005, the centre had monitored and did mapping of coral reefs. Nearly, after a gap of 13 years, the centre has restarted to monitor and to map the health status of coral reefs. The NCCR will be addressing all the major research concerns and knowledge gaps related to corals. Also, we will be transplanting corals in dead coral reef areas to restore and to increase the live coral coverage. The present study aimed to assess an easy, precise and suitable standard method to explore the health status of corals such as branching, massive and foliose reefs using UV blue light. In such artificial reef areas as well as in natural reef environments, we applied this method for monitoring coral health.
The presented study was carried out during September 2018 in two geographically distinct group of Islands of India, namely the Gulf of Mannar and Andaman and Nicobar Islands. These two group of islands comprises both fringing and patch reefs. Field surveys in these islands were made at the inter-tidal and reef flat areas of stations Burmanallah (11◦ 33‘52.24‘N; 92◦ 44‘01.51‘E) in Andaman and Hare Island (09◦ 12.679‘N; 79◦ 05.088‘E) in Gulf of Mannar (Fig. 1). Standard Line Intercept Transect (LIT) and quadrant methods were performed as previously described (English et al., 1997). Fluorescence of corals was induced using YOUTHINK UV-A Blacklight Flashlight, 100 LED, 18 W, with a wavelength of 395 nm. UV flashlight was illuminated to corals for 10 s, and the intensity of fluorescence and image patterns of corals were recorded using GoPro Hero6 camera for further visual assessment.
C.H. Ramesh, S. Koushik, T. Shunmugaraj et al. / Regional Studies in Marine Science 28 (2019) 100575
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Fig. 2. Quadrants (left) and LIT (right) methods indicating recruitment and growth of Acropora species from Hare Island.
3. Results Information about the health status of live or recruiting and dead corals were obtained successfully from different Islands at depths from 1 m to 5 m. For the first time in India, we uncover GFP like fluorescence in corals using UV-blue flashlight that could be utilised as a non-invasive assessment for coral reef health. UVA blue light has elicited the fluorescent tissues in corals, thus the live and dead corals were facilely differentiated immediately (shown in figures). Results of this study highlight the regeneration of corals in both the study areas (Fig. 2). Particularly, recruitment of encrusting Faviidae corals is more appreciable in Burmanallah, likewise branching Acropora corals in Hare Island. Live and recruiting corals showed dramatically high intensive fluorescence. Whereas, intense fluorescence was not observed in the damaged or diseased and sedimented tissue areas which is due to the loss of coral tissue during smothering caused by sedimentation and algal cover. Acropora sp., Favites sp. and other encrusting corals species showed high intense fluorescence. Interestingly, Porites sp. was appeared to pretend health coral during day, however, under UV illumination we observed fluorescence in pink line and pink spot diseases (Fig. 3). The effect of sedimentation was apparent in Favites sp., Porites sp. and Acropora humilis as the sedimented and algal grown tissue areas of these corals were failed to display fluorescence (Fig. 4). Bioinvasive species such as sponges and other algal assemblages on corals revealed their effect on live coral coverage as verified by fluorescence image patterns. We also observed different marine organisms under UV illumination, including juvenile Penaeus monodon, coralline red algae, zoanthids and particularly newly recruiting corals covered by algal mats and sedimentation (Fig. 5). Zoanthids displayed yellow fluorescence while coralline
algae showed red fluorescence. Health and growth condition of some of the corals covered by sediment, or encrusting or buried corals in the sand or rocks were also noticed (Fig. 5). Recruitment of encrusting corals such as Favites sp. in Burmanallah is well appreciated (50%), and recovery of branching and digitate Acropora species in Hare Island are also very impressive (70%). 4. Discussion Usually corals display a dull colour during daylight or under a white light at night. However, when corals are exposed to blue or UV light, they display a brilliant fluorescence ranging from yellow to range red and blue green colours. Thus, FPs possessing corals are being used in different marine aquariums worldwide for attraction. Irrespective of colour of the corals in twilight, UVblue light has high rapid application in the field to discriminate corals from other noise such as algae. Our observations revealed that marine algae display red fluorescence upon UV illumination, while corals exhibit greenish, yellowish, and blue green fluorescence. Sometimes due to the brown filamentous algae or cyanobacterial mat, the colour of the corals in daylight may pretend to resemble healthy corals. However, such incidents are clearly be differentiated using UV blue illumination. Species of branching corals, Acropora sp. displayed colour variations, where some of them pretend like bleached corals in ambient light. The bleached and tissue loss or damaged areas of Acropora corals were clearly differentiated and identified by observing increased fluorescence in live corals. In vivo experiments on heat induced fluorescence in the Caribbean coral Montastraea faveolata exhibited signs of bleaching in high-resolution multispectral images (Zawada and Jaffe, 2003), indicated that fluorescence is a reliable trait to detect minute level changes in
4
C.H. Ramesh, S. Koushik, T. Shunmugaraj et al. / Regional Studies in Marine Science 28 (2019) 100575
Fig. 3. Fluorescence of different corals. A. digitata in day light (a), and under UV illumination (b); Encrusting Favites sp. coral during day (c), and under UV (d); Porites sp. in daylight (e), and in UV, arrow indicating the development of pink line and pink spot disease (f); Favites sp. in twilight (g), and yellow circle indicating absence of fluorescence in UV due to sedimentation (h).
corals. A study also showed that coral Seriatopora hystrix displayed distinct fluorescence during development where larvae showed green and adult in cyan (Roth et al., 2013), indicating that the colour of fluorescence can be used to differentiate the development stages of corals. Since our observations on fluorescence emission from coral tissues using UV blue light, we infer this method as a more reliable and quick to differentiate live, dead and recruiting corals. Apparently, we have not found any excited and intensive fluorescence in massive coral species such as Porites sp. as observed in other coral species. We found only weak or negligible fluorescence merely. Variations in the intensities of coral fluorescence was found to dependent on thermal stress which causes bleaching (Salih et al., 2000). Our observations showed that bleached coral failed to exhibit fluorescence unlike live corals. While the effect of different wavelengths such as blue and red on coral Stylophora pistillata has been studied and found
negative affect of red light on coral health (Wijgerde et al., 2014). However, detailed studies are yet to be undertaken to explain the impact of wavelengths on photophysiology of corals. While the effect of UVA on corals is relatively small due to the exposure is about 5–10 s. A study also reported the effect of UVA and UVB radiation on corals and coral reef organisms (Shick et al., 1996). UVA exposure had stimulated photosynthesis in corals, while natural UV radiation resulted in release of planula larvae and prolonged UVB exposure resulted in the mortality of coral larvae and zooxanthellae (Shick et al., 1996). Recently, a study found that deeper water corals display photoconvertible red fluorescent proteins which help symbiotic zooxanthellae to transform prevalent blue light into orange-red light for coral adaptation (Smith et al., 2017). This report is indicating that the intensity of fluorescence is species specific and depends on environmental factors and developmental stage of the coral.
C.H. Ramesh, S. Koushik, T. Shunmugaraj et al. / Regional Studies in Marine Science 28 (2019) 100575
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Fig. 4. Sedimentation effect on corals revealing the live and dead coral coverage. Yellow circles indicating the live coral, Favites sp. coverage during dusk (a), and under UV illumination (b); Sediment effect on Porites sp. in dusk (c), and in UV, indicated with arrows (d); polyps of Montastrea sp. in dusk (e), and Intense fluorescence under UV, indicating no fluorescence in the algal growth area (f); Sedimented live coral, Platygyra sp. during day (g), and actual live coral coverage in UV indicated in yellow circle (h).
Mapping the status of corals using satellites, underwater ROV’s and other methods mentioned before are more cost effective and time consuming and can only predict long scale changes. But, the present method is very sensitive to reveal the minute changes in corals including bleaching, tissue loss, diseased, and corals covered with bio-invasive species. Also, this method is very useful to study viability, recruitment and disease propagation in corals. This method also can be used in a dense reef area in shallow waters where survey is difficult to perform. For instance, due to shallow depth we experienced the difficulty to monitor the health status of dense Acropora in Hare Island. In such locations, we found this technique is effective and easy to monitor coral health. Also, this method reveals the potential research areas of concern and remedies related to coral reefs beyond our naked eyes using fluorescence as a potential tool. We further infer that this method
is very quick and useful for direct field observations and also not cost effective. Further studies are being carried out from all the 21 islands of Gulf of Mannar for comparative quantitative analysis of coral species distribution and diversity using both visible and fluorescence methods. Acknowledgment Authors are thankful to the Ministry of Earth Sciences, New Delhi for the financial support. Conflict of interest We do not have any conflict with this manuscript.
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C.H. Ramesh, S. Koushik, T. Shunmugaraj et al. / Regional Studies in Marine Science 28 (2019) 100575
Fig. 5. Other marine animals observed under UV illumination. Juvenile P. monodon in yellow circle (a); coralline red algae (b); zoanthids in yellow circle during day (c) and in UV (d); Fluorescence of recruiting corals (shown in a quadrant) covered by sediment and algal cover (e).
References Alieva, N.O., Konzen, K.A., Field, S.F., Meleshkevitch, E.A., Hunt, M.E., BeltranRamirez, V., Miller, D.J., Wiedenmann, J., Salih, A., Matz, M.V., 2008. Diversity and evolution of coral fluorescent proteins. PLoS One 3, e2680. Chudakov, D.M., Matz, M.V., Lukyanov, S., Lukyanov, K.A., 2010. Fluorescent proteins and their applications in imaging living cells and tissues. Physiol. Rev. 90, 1103–11063. Collin, A., Ramambason, C., Pastol, Y., Casella, E., Rovere, A., Thiault, L., Espiau, B., Siu, G., Lerouvreur, F., Nakamura, N., Hench, J.L., Schmitt, R.J., Holbrook, S.J., Troyer, M., Davies, N., 2018. Very high resolution mapping of coral reef state using airborne bathymetric LiDAR surface-intensity and drone imagery. Int. J. Remote Sens. 39, 5676–5688. D’Angelo, C., Denzel, A., Vogt, A., Matz, M.V., Oswald, F., Salih, A., Nienhaus, G.U., Wiedenmann, J., 2008. Blue light regulation of host pigment in reef-building corals. Mar. Ecol. Prog. Ser. 364, 97–106. Dirnwoeber, M., Machan, R., Herler, J., 2012. Coral reef surveillance: Infraredsensitive video surveillance technology as a new tool for diurnal and nocturnal long-term field observations. Remote Sens. 4, 3346–3362. Edmunds, P.J., Aronson, R.B., Swanson, D.W., Levitan, D.R., Precht, W.F., 1998. Photographic versus visual census techniques for the quantification of juvenile corals. Bull. Mar. Sci. 62, 937–946. English, S., Wilkinson, C., Baker, V., 1997. Survey Manual for Tropical Marine Resource. Australian Institute of Marine Sciences, Townsville, Australia. Hoegh-Guldberg, O., Poloczanska, E.S., Skirving, W., Dove, S., 2017. Coral reef ecosystems under climate change and ocean acidification. Front. Mar. Sci. 4, 158. Lyzenga, D.R., 1981. Remote sensing of bottom reflectance and water attenuation parameters in shallow water using aircraft and landsat data. Int. J. Remote Sens. 2, 71–82.
Masahiko, S., Akira, M., Motonobu, I., Hiroya, Y., Hiroyuki, O., 2013. Coral observation by fluorescence imaging LiDAR on a glass-bottom boat. J. Remote Sens. Soc. Jpn. 33, 377–389. Matz, M.V., Marshall, N.J., Vorobyev, M., 2006. Are corals colorful? Photochem. Photobiol. 82, 345–350. Mumby, P.J., Green, E.P., Clark, C.D., Edwards, A.J., 1998. Digital analysis of multispectral airborne imagery of coral reefs. Coral Reefs 17, 59–69. Piniak, G.A., Fogarty, N.D., Addison, C.M., Kenworthy, W.J., 2005. Fluorescence census techniques for coral recruits. Coral Reefs 24, 496–500. Roth, M.S., Fan, T-Y., Deheyn, D.D., 2013. Life history changes in coral fluorescence and the effects of light intensity on larval physiology and settlement in Seriatopora hystrix. PLoS One 8, e59476. Salih, A., 2012. Screening reef corals for novel GFP-type fluorescent proteins by confocal imaging. In: Hoffman, R.M. (Ed.), Vivo Cellular Imaging Using Fluorescent Proteins: Methods and Protocols, Methods in Molecular Biology, vol. 872. Springer, New York, pp. 217–233. Salih, A., Larkum, A., Cox, G., Kuhl, M., Hoegh-Guldberg, O., 2000. Fluorescent pigments in corals are photoprotective. Nature 408, 850–853. Sasano, M., Imasato, M., Yamano, H., Oguma, H., 2016. Development of a regional coral observation method by a fluorescence imaging LIDAR installed in a towable buoy. Remote Sens. 8, 48. Schlichter, D., Meier, U., Fricke, H.W., 1994. Improvement of photosynthesis in zooxanthellate corals by autofluorescent chromatophores. Oecologia 99, 124–131. Shick, J.M., Lesser, M.P., Jokiel, P.L., 1996. Effects of ultraviolet radiation on corals and other coral reef organisms. Global Change Biol. 2, 527–545. Smith, E.G., D’Angelo, C., Salih, A., Wiedenmann, J., 2013. Screening by coral green fluorescent protein (GFP)-like chromoproteins supports a role in photoprotection of zooxanthellae. Coral Reefs http://dx.doi.org/10.1007/s00338012-0994-9.
C.H. Ramesh, S. Koushik, T. Shunmugaraj et al. / Regional Studies in Marine Science 28 (2019) 100575 Smith, E.G., D’Angelo, C., Sharon, Y., Tchernov, D., Wiedenmann, J., 2017. Acclimatization of symbiotic corals to mesophotic light environments through wavelength transformation by fluorescent protein pigments. Proc. R. Soc. B 284, 20170320. Spalding, M., Burke, L., Wood, S.A., Ashpole, J., Hutchison, J., Ermgassen, P., 2017. Mapping the global value and distribution of coral reef tourism. Mar. Policy 82, 104–113. Treibitz, T., Neal, B.P., Kline, D.I., Beijbom, O., Roberts, P.L.D., Mitchell, B.G., Kriegman, D., 2014. Wide field-of-view fluorescence imaging of coral reefs. Nature 5, 7694. Vermeij, M.J.A., Delvoye, L., Nieuwland, G., Bak, R.P.M., 2002. Patterns in fluorescence over a Caribbean reef slope: The coral genus Madracis. Photosynthetica 40, 423–429.
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Warner, M.E., Lesser, M.P., Ralph, P.J., 2010. Chlorophyll fluorescence in reef building corals. In: Suggett, D.J., Prasil, O., Borowitzka, M.A. (Eds.), Chlorophyll a Fluorescence in Aquatic Sciences: Methods and Applications Developments in Applied Phycology, vol. 4. Springer, Netherlands, pp. 209–222. Wijgerde, T., van Melis, A., Silva, C.I.F., Leal, M.C., Vogels, L., Mutter, C., Osinga, R., 2014. Red light represses the photophysiology of the scleractinian coral Stylophora pistillata. PLoS One 9, e92781. Zawada, D.G., Jaffe, J.S., 2003. Changes in the fluorescence of the Caribbean coral Montastraea faveolata during heat-induced bleaching. Limnol. Oceanogr. 48, 412–425.
Contents lists available at ScienceDirect
Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma
A rapid in situ fluorescence census for coral reef monitoring ∗
C.H. Ramesh , S. Koushik, T. Shunmugaraj, M.V. Ramana Murthy National Center for Coastal Research (NCCR), NCCR Field Office, Ministry of Earth Sciences (MoES), Mandapam 623519, Tamil Nadu, India
article
info
Article history: Received 13 November 2018 Received in revised form 11 January 2019 Accepted 6 March 2019 Available online 15 March 2019 Keywords: Fluorescence Corals UV-blue light Gulf of Mannar Andaman Islands
a b s t r a c t Since the discovery of Green fluorescent protein (GFP) from jellyfish, many GFP-like marine fluorescent proteins have been unveiled and implicated in myriad of biomedical and toxicological research applications. However, fluorescence trait has not been implemented in the field applications so far. In this study, using a UV-blue light, we induced fluorescence of corals to identify the diseased and damaged corals as well as newly recruiting and encrusting corals buried in sedimentation and algal covers. Healthy corals have displayed complete body fluorescence, whereas the dead, damaged and diseased corals are failed to display complete fluorescence. The development of pink line disease on Porites sp. was obvious under UV illumination than in visible light, revealing the hidden disease level propagation in Porites. Coral recruitment is well appreciated in both the study locations Burmanallah and Hare Island. Results of this study infer that this method is a highly reliable and rapid in field to study recruitment, disease propagation and health status of coral reefs. © 2019 Elsevier B.V. All rights reserved.
1. Introduction Coral reef ecosystems are one of the precious and aesthetic bio-treasure hotspots distributed around the globe which harbour thousands of marine organisms of food and ornamental importance (Spalding et al., 2017). According to Global Coral Reef Monitoring (GCRMN), about 500 million people around the world are dependent on reef ecosystem for food and income. Unfortunately, global research shows that directly or indirectly the proximity of anthropogenic activities and global changes in coastal areas are apparently found to threaten the health of coral reefs (Hoegh-Guldberg et al., 2017). Monitoring the reef health is an essential concern and also need to give special attention and action to restore the damaged reef areas. These aspects are important to protect the biodiversity for the future generations and ecological balance. If the coral reefs are disappearing, then there would be more chances of losing hues of fish and invertebrate diversity that will subsequently effect humans. GFP like fluorescent proteins (FPs) are wide spread in coral reefs and are of highly preferred by genetical engineers as fluorescent labels (Alieva et al., 2008). FPs are widely being used in different applications, including microbial interactions, disease propagation in tumours, toxic contaminates from different environments and in food products (Chudakov et al., 2010). FPs of corals are known to involve in enhancement of light under low light availability and act as photoprotective from excessive ∗ Corresponding author. E-mail address: [email protected] (C.H. Ramesh). https://doi.org/10.1016/j.rsma.2019.100575 2352-4855/© 2019 Elsevier B.V. All rights reserved.
sunlight (Salih et al., 2000), and indirectly involved in stimulating photosynthesis process of zooxanthellae (Shick et al., 1996). FPs of corals are known to protect their endosymbiotic zooxanthellae from photodamage (Smith et al., 2013). Corals uptake energy from their zooxanthellae which enhances photosynthesis process using different autofluorescent chromatophores localised on the oral gastro dermis or oral epidermis (Schlichter et al., 1994). These zooxanthellae display red fluorescence due to chlorophyll content (Warner et al., 2010). It was also suggested that GFP-like fluorescent proteins in corals act as biomarkers to indicate the health status and physiological processes of corals (D’Angelo et al., 2008). Considering such an important FPs as indicators, field applications have scarcely been undertaken so far to monitor coral reef status. In this study we undertaken fluorescence trait as an indicator to predict the health of coral reef. Currently, researchers are using different methods to evaluate the health of corals, including remote sensing from boats, aircrafts (Lyzenga, 1981), satellites (Mumby et al., 1998), photographic and visual census (Edmunds et al., 1998), epifluorescence microscopy in laboratory (Vermeij et al., 2002), blue light excitation of photoquadrats painted with green fluorescent paint (Piniak et al., 2005), in situ spectrometry (Matz et al., 2006), infrared sensitive surveillance technology cameras with high-power IRLEDs (Dirnwoeber et al., 2012), confocal imaging (Salih, 2012), ultraviolet (UV) pulsed laser system (Masahiko et al., 2013), Fluorescence Imaging System (FluorIS) (Treibitz et al., 2014), light detection and ranging (LIDAR) system (Sasano et al., 2016), drone imagery (Collin et al., 2018) and standard procedures previously
2
C.H. Ramesh, S. Koushik, T. Shunmugaraj et al. / Regional Studies in Marine Science 28 (2019) 100575
Fig. 1. Study locations in Gulf of Mannar and Andaman & Nicobar Islands.
described (English et al., 1997). However, there are very few and
2. Material and methods
limited quick methods available to assess and determine the reef health. To study the corals distributed across the Indian continent, The National Center for Coastal Research (NCCR) has recently set up a field station in Mandapam, Tamil Nadu. During the years 2000– 2005, the centre had monitored and did mapping of coral reefs. Nearly, after a gap of 13 years, the centre has restarted to monitor and to map the health status of coral reefs. The NCCR will be addressing all the major research concerns and knowledge gaps related to corals. Also, we will be transplanting corals in dead coral reef areas to restore and to increase the live coral coverage. The present study aimed to assess an easy, precise and suitable standard method to explore the health status of corals such as branching, massive and foliose reefs using UV blue light. In such artificial reef areas as well as in natural reef environments, we applied this method for monitoring coral health.
The presented study was carried out during September 2018 in two geographically distinct group of Islands of India, namely the Gulf of Mannar and Andaman and Nicobar Islands. These two group of islands comprises both fringing and patch reefs. Field surveys in these islands were made at the inter-tidal and reef flat areas of stations Burmanallah (11◦ 33‘52.24‘N; 92◦ 44‘01.51‘E) in Andaman and Hare Island (09◦ 12.679‘N; 79◦ 05.088‘E) in Gulf of Mannar (Fig. 1). Standard Line Intercept Transect (LIT) and quadrant methods were performed as previously described (English et al., 1997). Fluorescence of corals was induced using YOUTHINK UV-A Blacklight Flashlight, 100 LED, 18 W, with a wavelength of 395 nm. UV flashlight was illuminated to corals for 10 s, and the intensity of fluorescence and image patterns of corals were recorded using GoPro Hero6 camera for further visual assessment.
C.H. Ramesh, S. Koushik, T. Shunmugaraj et al. / Regional Studies in Marine Science 28 (2019) 100575
3
Fig. 2. Quadrants (left) and LIT (right) methods indicating recruitment and growth of Acropora species from Hare Island.
3. Results Information about the health status of live or recruiting and dead corals were obtained successfully from different Islands at depths from 1 m to 5 m. For the first time in India, we uncover GFP like fluorescence in corals using UV-blue flashlight that could be utilised as a non-invasive assessment for coral reef health. UVA blue light has elicited the fluorescent tissues in corals, thus the live and dead corals were facilely differentiated immediately (shown in figures). Results of this study highlight the regeneration of corals in both the study areas (Fig. 2). Particularly, recruitment of encrusting Faviidae corals is more appreciable in Burmanallah, likewise branching Acropora corals in Hare Island. Live and recruiting corals showed dramatically high intensive fluorescence. Whereas, intense fluorescence was not observed in the damaged or diseased and sedimented tissue areas which is due to the loss of coral tissue during smothering caused by sedimentation and algal cover. Acropora sp., Favites sp. and other encrusting corals species showed high intense fluorescence. Interestingly, Porites sp. was appeared to pretend health coral during day, however, under UV illumination we observed fluorescence in pink line and pink spot diseases (Fig. 3). The effect of sedimentation was apparent in Favites sp., Porites sp. and Acropora humilis as the sedimented and algal grown tissue areas of these corals were failed to display fluorescence (Fig. 4). Bioinvasive species such as sponges and other algal assemblages on corals revealed their effect on live coral coverage as verified by fluorescence image patterns. We also observed different marine organisms under UV illumination, including juvenile Penaeus monodon, coralline red algae, zoanthids and particularly newly recruiting corals covered by algal mats and sedimentation (Fig. 5). Zoanthids displayed yellow fluorescence while coralline
algae showed red fluorescence. Health and growth condition of some of the corals covered by sediment, or encrusting or buried corals in the sand or rocks were also noticed (Fig. 5). Recruitment of encrusting corals such as Favites sp. in Burmanallah is well appreciated (50%), and recovery of branching and digitate Acropora species in Hare Island are also very impressive (70%). 4. Discussion Usually corals display a dull colour during daylight or under a white light at night. However, when corals are exposed to blue or UV light, they display a brilliant fluorescence ranging from yellow to range red and blue green colours. Thus, FPs possessing corals are being used in different marine aquariums worldwide for attraction. Irrespective of colour of the corals in twilight, UVblue light has high rapid application in the field to discriminate corals from other noise such as algae. Our observations revealed that marine algae display red fluorescence upon UV illumination, while corals exhibit greenish, yellowish, and blue green fluorescence. Sometimes due to the brown filamentous algae or cyanobacterial mat, the colour of the corals in daylight may pretend to resemble healthy corals. However, such incidents are clearly be differentiated using UV blue illumination. Species of branching corals, Acropora sp. displayed colour variations, where some of them pretend like bleached corals in ambient light. The bleached and tissue loss or damaged areas of Acropora corals were clearly differentiated and identified by observing increased fluorescence in live corals. In vivo experiments on heat induced fluorescence in the Caribbean coral Montastraea faveolata exhibited signs of bleaching in high-resolution multispectral images (Zawada and Jaffe, 2003), indicated that fluorescence is a reliable trait to detect minute level changes in
4
C.H. Ramesh, S. Koushik, T. Shunmugaraj et al. / Regional Studies in Marine Science 28 (2019) 100575
Fig. 3. Fluorescence of different corals. A. digitata in day light (a), and under UV illumination (b); Encrusting Favites sp. coral during day (c), and under UV (d); Porites sp. in daylight (e), and in UV, arrow indicating the development of pink line and pink spot disease (f); Favites sp. in twilight (g), and yellow circle indicating absence of fluorescence in UV due to sedimentation (h).
corals. A study also showed that coral Seriatopora hystrix displayed distinct fluorescence during development where larvae showed green and adult in cyan (Roth et al., 2013), indicating that the colour of fluorescence can be used to differentiate the development stages of corals. Since our observations on fluorescence emission from coral tissues using UV blue light, we infer this method as a more reliable and quick to differentiate live, dead and recruiting corals. Apparently, we have not found any excited and intensive fluorescence in massive coral species such as Porites sp. as observed in other coral species. We found only weak or negligible fluorescence merely. Variations in the intensities of coral fluorescence was found to dependent on thermal stress which causes bleaching (Salih et al., 2000). Our observations showed that bleached coral failed to exhibit fluorescence unlike live corals. While the effect of different wavelengths such as blue and red on coral Stylophora pistillata has been studied and found
negative affect of red light on coral health (Wijgerde et al., 2014). However, detailed studies are yet to be undertaken to explain the impact of wavelengths on photophysiology of corals. While the effect of UVA on corals is relatively small due to the exposure is about 5–10 s. A study also reported the effect of UVA and UVB radiation on corals and coral reef organisms (Shick et al., 1996). UVA exposure had stimulated photosynthesis in corals, while natural UV radiation resulted in release of planula larvae and prolonged UVB exposure resulted in the mortality of coral larvae and zooxanthellae (Shick et al., 1996). Recently, a study found that deeper water corals display photoconvertible red fluorescent proteins which help symbiotic zooxanthellae to transform prevalent blue light into orange-red light for coral adaptation (Smith et al., 2017). This report is indicating that the intensity of fluorescence is species specific and depends on environmental factors and developmental stage of the coral.
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Fig. 4. Sedimentation effect on corals revealing the live and dead coral coverage. Yellow circles indicating the live coral, Favites sp. coverage during dusk (a), and under UV illumination (b); Sediment effect on Porites sp. in dusk (c), and in UV, indicated with arrows (d); polyps of Montastrea sp. in dusk (e), and Intense fluorescence under UV, indicating no fluorescence in the algal growth area (f); Sedimented live coral, Platygyra sp. during day (g), and actual live coral coverage in UV indicated in yellow circle (h).
Mapping the status of corals using satellites, underwater ROV’s and other methods mentioned before are more cost effective and time consuming and can only predict long scale changes. But, the present method is very sensitive to reveal the minute changes in corals including bleaching, tissue loss, diseased, and corals covered with bio-invasive species. Also, this method is very useful to study viability, recruitment and disease propagation in corals. This method also can be used in a dense reef area in shallow waters where survey is difficult to perform. For instance, due to shallow depth we experienced the difficulty to monitor the health status of dense Acropora in Hare Island. In such locations, we found this technique is effective and easy to monitor coral health. Also, this method reveals the potential research areas of concern and remedies related to coral reefs beyond our naked eyes using fluorescence as a potential tool. We further infer that this method
is very quick and useful for direct field observations and also not cost effective. Further studies are being carried out from all the 21 islands of Gulf of Mannar for comparative quantitative analysis of coral species distribution and diversity using both visible and fluorescence methods. Acknowledgment Authors are thankful to the Ministry of Earth Sciences, New Delhi for the financial support. Conflict of interest We do not have any conflict with this manuscript.
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Fig. 5. Other marine animals observed under UV illumination. Juvenile P. monodon in yellow circle (a); coralline red algae (b); zoanthids in yellow circle during day (c) and in UV (d); Fluorescence of recruiting corals (shown in a quadrant) covered by sediment and algal cover (e).
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