Macroalgae Species as Zonal Indicators of Coral Reef: A Case Study from Bet Shankhodhar Reef, India

Tropical coral reefs are major habitats for marine macroalgae or seaweeds. Macroalgae represent a key functional group among the coral reef communities and perform vital ecological functions like reef structure stabilisation, production of tropical sands, nutrient retention and recycling, primary productivity and trophic support. Coral reef macroalgae are comprised of three major pigment-group-based phyla: Chlorophyta (green algae), Heterokontophyta or Ochrophyta (brown algae) and Rhodophyta (red algae). Green macroalgae or Chlorophyta contain chlorophyll a and b pigments in the same proportion as that of higher plants along with β-carotene and xanthophylls and have significant industrial or commercial value. Chlorophyta members commonly inhabit the littoral zone with strong sunlight. This chapter highlights micro-level habitat preference of green macroalgae or Chlorophyta species sampled from Bet Shankhodhar Reef from the Gujarat coast of India as a unique case study. This study identifies four Chlorophyta species: Halimeda tuna (Ellis & Solander) Lamouroux, Caulerpa sertularioides (S. Gmelin) Howe f. brevipes (J. Agardh) Svedelius, Valonia aegagropila C. Agardh and Valoniopsis pachynema (Martens) Børgesen, as indicator species of the backreef zone. Shallow tidal pools in the backreef zone of Bet Shankhodhar Reef are preferred microhabitats for C. sertularioides and V. aegagropila

Macroalgae as indicator species for shore platform zones of Dwarka, Gujarat, India

416-422Dwarka coast of Gujarat state in India has a stable shore platform. A study was carried out to identify indicator species among the sampled macroalgae to understand their spatial preferences on the shore platform zones. For this study, the shore platform was divided into three sections in north-south direction: Northern, central, and southern sections. These sections were further divided into three microzones in west-to-east direction based on their local geomorphology and tidal inundation characteristics for more detailed study. These microhabitat zones are: Cliff Base Zone (CBZ), Intertidal Mixed Zone (IMZ) and Subtidal Zone (STZ). To identify indicator species for each microzone, the shore platform was surveyed based on systematic random sampling for two years (April 2013 to April 2015). Line intercept transects and GPS-tagged photo quadrates were carried out from land to seaward as part of the sampling procedure. Indicator species were identified on the basis of a decision-rule when a single species belonged to only one microhabitat zone in all the three sections. Total 97 species of seaweeds were recorded in the shore platform of Dwarka. Out of these, 27 belonged to chlorophyta, 21 to phaeophyta and 49 to rhodophyta. Out of all these species, rhodophyta was found as the dominant group in the shore platform. Out of 97 species, only 12 species were identified as indicator species. Out of these, only one species was from phaeophyta group and eleven from rhodophyta group. This study shows indicator species of the microhabitat zones of the shore platform, with rhodophyta sp. as the prominent macroalgae group. Indicator species can act as proxy indicators of the microhabitats created by the local geomorphology and tidal regime on the shore platform

Spectral Discrimination of Live and Bleached Corals: A Case Study on <em>Turbinaria peltata</em> (Esper, 1794) Using Field Spectroscopy

Scleractinian corals represent the foundation species of reef ecosystems. Bleaching is a physiological, cellular response to environmental stresses wherein marine invertebrates including corals expel their endosymbiont, unicellular microalgae or zooxanthellae from their host tissues. Field spectroscopy helps to characterize the health of corals in terms of reflectance spectra or spectral signatures, i.e. reflected light as a function of wavelength. This chapter reports a case study on spectral discrimination of in situ hyperspectral signatures of live, apparently healthy and bleached corals collected from a single colony of Turbinaria peltata (Esper, 1794) sampled from Laku Point reef in Gujarat coast of India. Derivative analyses on the in situ reflectance data identify five narrow windows in the visible light region (green and red light regions) to spectrally discriminate live and bleached coral polyps of the T. peltata species. This study highlights the potential of field spectroscopy in characterizing coral health in situ through non-invasive sampling

Coral bleaching due to increased sea surface temperature in Gulf of Kachchh Region, India, during June 2016

327-332The 2015-2016 E1 Niño Southern Oscillation event was one of the extreme climate events which elevated the sea surface temperature (SST) of tropical oceans, which in turn increased the level of thermal stress on corals. Coral bleaching event is mainly caused due to high positive SST anomaly, i.e., when SST exceeds its normal summer maxima. Corals in the Gulf of Kachchh region of Gujarat earlier experienced coral bleaching events during 1988, 2010 and 2014. For this study, SST was derived from NOAA OISST data set which is available daily at 0.25° global grids from 1982 to present. The climatologically warmest month for the Gulf of Kachchh region is June when the maximum monthly mean temperature is 29.31°C, as observed from NOAA OISST. The present study focuses on monitoring daily SST anomalies during summer 2016 for the Gulf of Kachchh reefs and field observations on early responses of coral bleaching from Laku Point reef, a site known for high coral diversity. It was found that in summer 2016, SST rose to 30.62 °C and recorded a maximum positive anomaly of 1.31°C in the month of June. A total of 72 days out of 122-day monitoring period showed positive SST anomaly, including 28 days of continuous positive thermal stress in June 2016.To validate coral bleaching forecast at the end of the regional warmest quarter, a field visit was carried out at Laku Point reef near Poshitra village in the southern coast of the Gulf of Kachchh. A total of 13 coral species and a sea anemone were found bleached in various proportions during the field sampling after two months of prolonged thermal stress. The field data showed an average of 3.9% bleaching of corals at colony scale. The maximum proportion of colony scale bleaching was observed in Porites lutea species

Climate Change Induced Thermal Stress Caused Recurrent Coral Bleaching over Gulf of Kachchh and Malvan Marine Sanctuary, West Coast of India

Coral reefs are one of the most sensitive, productive, and invaluable biological resources on the earth. However, coral reefs are facing unprecedented stress due to ongoing climate changes and intensified anthropogenic disturbances globally. Elevated Sea Surface Temperature (SST) has emerged as the most imminent threat to the thermos-sensitive reef-building corals. The 2010–2014-2016 El Niño Southern Oscillation (ENSO) caused prolonged marine heat waves (MHWs) that led to the most widespread coral bleaching and mortality in the tropical Indi-Pacific regions. Coral bleaching prediction is vital for the management of the reef biodiversity, ecosystem functioning, and services. Recent decades, satellite remote sensing has emerged as a convenient tool for large-scale coral reef monitoring programs. As thermal stress is a critical physical attribute for coral bleaching hence, the present study examines the effectiveness of the elevated SSTs as a proxy to predict coral bleaching in shallow water marginal reefs. Advanced Very High-Resolution Radiometer (AVHRR) satellite data from the NOAA Coral Reef Watch’s (CRW) platform has been used for this study. Coral bleaching indices like Bleaching Threshold (BT), Positive SST Anomaly (PA), and Degree Heating Weeks (DHW) are computed to analyze the thermal stress on the coral reefs. The computed thermal stress from satellite-derived SST data over regions concurrence with the mass coral bleaching (MCB) events. This study concludes that in the last decades (2010 to 2019) the coral cover around these regions has dramatically declined due to higher SST, which indicates that the thermal stress induced recurrent bleaching events attributed to the coral loss

Species and Thallus Structure Diversity of Chlorophyta in Shore Platform of Dwarka (Gujarat Coast, India)

Present study shows the species and thallus structure diversity of Chlorophyta in shore platform of Dwarka, Gujarat Coast. Chlorophyta were surveyed based on systematic random sampling for two years: April 2013 to April 2015. Total 27 species of Chlorophyta were identified through intensive fieldwork survey based on line transect and quadrate based methods. This study identifies four orders, nine families, 13 genera and 27 species among the green macroalgae population inhabiting the rock shore platform of Dwarka. Total 27 species of Chlorophyta have been found with major nine thallus types and 19 sub types of thallus structure. Ramiform and filamentous types of thallus structure are most common in this study

Habitat Preference of Phaeophyceae Species: Iyengaria stellata (Børgesen) Børgesen (1939) in Gujarat Coast (India)

Many species of phaeophyta are found at Dwarka and at the Bet-Shankhodhar coast, Gujarat, India. For the study of Iyengaria stellata, the shore platform and reef flat were divided into three sections: Dwarka in i) North, ii) Centre and iii) South sections and Bet-Shankhodhar in i) West, ii) Centre and iii) East sections. I. stellata was monitored based on systematic random sampling for two years (April, 2013 to February, 2015). In the months of December and February, I. stellata was recorded with high frequencies of reef, flat zones and shore platforms. When compared to shore platform, the frequency of I. stallata was highest in coral reef and flat zones. This study supports that reef flat is very suitable for growth of I. stellata. I. stellata’s growth cycle corresponds with local winter season

Benthic coverage and bottom topography of coral reef environment over Pirotan reef, Gulf of Kachchh region, India

Remote sensing measurements in coral reef environments commonly confront the problem of overlying atmosphere and modification of spectral signal due to water column over the bottom substrates. In order to correct these problems, hyperspectral observations offer an advantage over multispectral observations. Airborne hyperspectral remote sensing data from Airborne Visible Infrared Imaging Spectrometer- Next Generation (AVIRIS-NG) sensor was acquired during low tidal condition on 14 February 2016 at Pirotan reef, Gulf of Kachchh region, India. The objective of this study is to map benthic coverage and bottom topography over Pirotan reef. The methodology involved atmospheric correction, simultaneous retrieval of water parameters, bathymetry, water column correction and mapping. Atmospheric correction was performed by removing path radiance and aerosol contribution and dividing by atmospheric transmittance and incoming solar irradiance to obtain remote sensing reflectance. Model derived error minimization technique was used for simultaneous retrieval of water parameters and bathymetry. Derived water parameters were used to account for water column attenuation and retrieve concomitant true bottom signature

Assessment of coral reef thermal stress over India based on remotely sensed sea surface temperature

Sea Surface Temperature is a critical physical attribute of coastal marine habitats. Remote sensing from satellite is the most widely used approach for monitoring the stress on coral reef ecosystems on large scale. Regional coral bleaching monitoring framework has been applied in five major Indian coral reef regions to investigate the threats. Degradation of coral reefs is a major environmental problem worldwide. ENSO (El Niño Southern Oscillation) event is one of the extreme climate change event, which elevate Sea Surface Temperatures (SSTs) of tropical oceans. This warming of SST increases the level of thermal stress on coral reefs. Coral reefs are the most sensitive ecosystem of all coastal ecosystems due to temperature change and exhibit bleaching when SST exceeds their normal summer maxima and remain high for more than 28 days. SST data from NOAA OISST v2 over period from 1982 to 2018 (37 years) were used for this study. Coral bleaching indices have been observed over five major Indian coral reef regions. Bleaching Threshold (BT), Positive SST Anomaly (PA) and Degree Heating Week (DHW) are commonly used indices for calculating thermal stress on the coral reefs computed from satellite-derived SST data. The BT value for each regions based on the long-term SST data analysis and found different. These thermal stress analyses over India were found close with the recorded mass coral bleaching events during 1998, 2010 and 2016. In addition, this study included calculating the thermal stress over India during Mass Coral Bleaching years