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.
Part of the book: Wetlands Management
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.
Part of the book: Invertebrates
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.
Part of the book: Climate Change in Asia and Africa