**2. Study area: Bet Shankhodhar Reef**

Coral reefs provide a hard and stable habitat for algal settlers as compared to any other soft sediment coastal habitats like beaches, spits, estuaries and mudflats. India has a coastline length of 7500 km with diverse coastal habitats which support rich seaweed biodiversity [10]. The state of Gujarat shares 1600 km of the Indian coastline and represents the northwestern most part of the peninsular India. Gujarat coast is known to harbour a rich diversity of seaweeds as its rocky segments provide suitable environment for macroalgal settlement and growth [11]. Gujarat coastline falls within the geographical limits of 20°08′–24°40' north latitudes and 68°10′–74°28′ east longitudes. From north to south, the Gujarat coast can be divided into four major coastal ecological components: (i) Kori Creek, (ii) Gulf of Kachchh, (iii) Saurashtra coast from Okha to Porbandar and (iv) Gulf of Khambhat [12], situated in three distinct macro-geomorphological settings of a deltaic creek, two gulfs and a rocky coast.

landscape of coral reefs provides necessary habitat to one-third of known marine species [1] including some of the rare avifauna [2]. Coral reefs are critical eco-resources [3] to many of the maritime tropical and subtropical nations. For many of these nations, their physical foundation to national economies depend on reef-related ecosystem goods and services [4, 5].

Marine macroalgae or seaweeds occupy variety of habitats offered by the coastal and nearshore marine wetlands. 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 [6]. Coral reef macroalgae are comprised of three major pigment group-based phyla: Chlorophyta (green algae), Heterokontophyta (brown algae) and Rhodophyta (red algae). This systematic classification is based on the composition of pigments involved in photosynthesis [7]. The presence of chloroplasts and subsequent capacity to photosynthesize allow reef macroalgae to play the vital ecological role of primary producers in a reef ecosystem. Other than their ecological roles as habitat formers and primary producers, reef macroalgae are economically important. They are important sources of food, fodder, fertiliser, medicinal

Marine green algae or Chlorophyta are naturally abundant and record high biodiversity in tropical coral reefs and lagoons, often intermixed with associated seagrass habitats [6, 8]. Chlorophyta have predominantly green chlorophyll pigments: chlorophyll *a* and *b* in the same proportion as that of higher or vascular plants along with accessory carotenoid and xanthophyll pigments. Structurally, green seaweeds range from thread-like filaments to thin sheets and can be spongy, gelatinous, papery, leathery or brittle in texture [8]. Their morphological appearance is shaped through their cell division process [9]. Chlorophyta are generally siphonaceous or giant-celled forms which employ a unique cytoplasmic streaming or blade abandonment mechanism to eliminate epiphytes [8]. Certain genera of filamentous and sheet-like green algae are stress tolerant and can be potential indicators of freshwater seeps, disturbed areas of the habitat, areas of low herbivory and significant areas with an

In general, Chlorophyta are usually found in the littoral zone with strong sunlight. Availability of suitable substrate, light quality and quantity, availability of nutrients, intra- and interspecific competition, herbivory and grazing are major factors that delimit spatial and temporal occupancy of macroalgae in a given habitat [6]. Algal pigments and their photosynthetic capability and adaptations to different light levels lead to their depth zonation within the habitat. This chapter explores the concept of species-specific microhabitat preference of green

Coral reefs provide a hard and stable habitat for algal settlers as compared to any other soft sediment coastal habitats like beaches, spits, estuaries and mudflats. India has a coastline length of 7500 km with diverse coastal habitats which support rich seaweed biodiversity [10].

macroalgae in a coral reef habitat of India based on field survey data.

**2. Study area: Bet Shankhodhar Reef**

compounds and industrial raw materials.

46 Wetlands Management - Assessing Risk and Sustainable Solutions

overabundance of nutrients [8].

Gulf of Kachchh (**Figure 1A** and **B**) marks the northernmost limit of reef development on the continental shelf of India [13]. Gulf of Kachchh is a funnel-shaped, east-west-oriented, seismically active indentation between the Kachchh mainland and Saurashtra/Kathiawar peninsula of Gujarat state in India [14]. This gulf occupies an area of 7350 km2 with an average depth of 30 m [15]. Gulf of Kachchh represents a high-energy, semi-diurnal, macro-tidal environment with varying tidal amplitude of 4 m at its mouth to 7 m in the inner gulf [14]. The southern shore of the gulf is relatively smooth and has an assemblage of ecologically sensitive ecosystems including coral reefs, seagrass beds, seaweeds, mangroves and tidal flats [15].

**Figure 1.** Location of the study site at Bet Shankhodhar Reef, India. (A) Location of Gulf of Kachchh in India, (B) location of Bet Shankhodhar Island in Gulf of Kachchh, (C) location of coral reef area in Bet Shankhodhar Island, (D) study/field sampling site at Bet Shankhodhar Reef.

The coral reefs in Gulf of Kachchh are predominantly patchy structures built up on wave-cut sandstone banks [16] on the southern shore of the gulf along with 34 adjoining islands [17]. These coral reefs are mainly comprised of fringing structure with all sub-types (i.e., platform, patch and coral pinnacles; [13]) restricted to a vast intertidal region [18]. Gulf of Kachchh coral reefs are adapted to extreme environmental conditions: high temperature ranges (10–35°C), high salinity ranges (25–40 ppt), large tidal ranges, strong tidal currents and heavy sediment loads [19]. As a result of isolation and above-mentioned extreme environmental conditions, the species diversity of corals in this region is low [20]. The coral reefs of Gulf of Kachchh are under International Union for Conservation of Nature (IUCN) Category I Marine Protected Area (MPA). Gulf of Kachchh Marine Sanctuary and Marine National Park were established in 1980 and 1982, respectively [21].

zones (**Figure 2**) are: (i) subtidal zone or the fore reef, (ii) Backreef zone I and (iii) Backreef zone II. The subtidal zone or the fore reef was the northernmost zone which got exposed only during the spring tides while the backreef zone I or the intertidal reef flat was interspersed with large rock pools. The backreef zone II was the southernmost zone, adjacent to the beach

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

http://dx.doi.org/10.5772/intechopen.81640

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The study area of Bet Shankhodhar Reef was divided into three sections in the west-east direction, as: (i) western, (ii) central and (iii) eastern sections (**Figure 1D**) for systematic field sampling and equal representation of the reef habitat. Seaweed sampling was routinely carried out for 2 years: from April 2013 to April 2015 with sampling exercise coinciding with the annual cycles of seaweed abundance and growth, that is, local seasons of post-monsoon (October-November), winter (December-February), spring (March) and summer (April-June), respectively. Field surveys/samplings were carried out during low-tide exposures of the reef following line intercept transects (LITs). For quantitative assessment of the seaweeds in the given area, the GPS-tagged, LITs were laid perpendicular to the coast in a seaward direction with the help of a 50-m-long rope [24]. The length of the transect essentially depended on the tidal exposure of the reef during the field surveys. The minimum and maximum transect lengths surveyed were 52 and 372.5 m, respectively. The maximum depth of the subtidal zone sampled for the present study

wherever macroalgal growth, density and diversity were visibly high. A total of 182 GPS-tagged

quadrats was sampled for the seaweeds over a total of 23 transects on the reef site.

**Figure 3.** Cladogram of Chlorophyta species sampled from Bet Shankhodhar Reef.

were positioned over the transects for quantitative seaweed sampling

and was characterised with coastal lapiés and smaller rock pools [23].

**3. Field data collection and analysis**

**3.1. Field sampling of seaweeds/macroalgae**

is 1 m. Quadrats of 1 m2

The present study was carried out in the coral reef area adjacent to Bet Shankhodhar Island (**Figure 1B** and **C**) situated to the east of Okhamandal area on the mainland coast and 2 km away from the Okha Port. The island owes its name Bet Shankhodhar to its unique shape resembling that of a conch shell [22]. Bet Shankhodhar Island has a fringing reef area (**Figure 1C**) of 28 hectares to its north [22] adjacent to a narrow strip of beach with significant exposures of beach rock [23]. This reef was selected for the present case study for its reported diversity of 120 species of macroalgae [22]. The study site on Bet Shankhodhar Reef is located within the coordinates of 22°28′36" N–22°28′52" N latitudes and 68°08′14″ E–69°08′40″ E longitudes and covered a survey area of 0.35 km2 (**Figure 1D**). The survey area of the reef was further divided into three micro-zones in the north-south direction based on their topographical and geomorphological characteristics and level of tidal inundation. These three

**Figure 2.** Microhabitat zones of Bet Shankhodhar Reef. (A) Exposure of subtidal zone, (B) Backreef zone I and (C) Backreef zone II.

zones (**Figure 2**) are: (i) subtidal zone or the fore reef, (ii) Backreef zone I and (iii) Backreef zone II. The subtidal zone or the fore reef was the northernmost zone which got exposed only during the spring tides while the backreef zone I or the intertidal reef flat was interspersed with large rock pools. The backreef zone II was the southernmost zone, adjacent to the beach and was characterised with coastal lapiés and smaller rock pools [23].
