Spatial and Temporal Profiling of Macroalgal Groups on Shore Platform: A case study from Dwarka

Dwarka coast of Gujarat state from India has a stable shore platform. For this study, the shore platform was divided into three sections: i) northern, ii) central and iii) southern. Macroalgae growing on this shore platform were surveyed based on systematic random sampling for three months in sequence (April, June and October, 2013). On this site, total 36 taxa of macroalgae were identified through intensive fieldwork/in situ survey based on Line Intercept Transect and Quadrate based methods. An overall analysis of the field data so far collected reveals that Chlorophyta dominates in the subtidal zone while Ochrophyta (Phaeophyta) dominates in rock pools near the cliff base as their preferred habitats. Rhodophyta showed a seasonal predominance during June. Iyengaria stellata was found in all the three months. The result obtained in this study provides an insight to understand the macroalgae habitat zonation on the shore platform and can be useful to support conservation of this study site as a rich macroalgae habitat of Indian Coast.


Introduction
Marine macroalgae, popularly known as seaweeds, are the most beautiful groups of photosynthetic organisms, which grow under the ocean's blue water (Sahoo, 2010). They grow in the intertidal and subtidal zones (shallow and deep areas), in the estuaries and backwaters on solid substrates such as rocks, corals, pebbles, shells and even on plant materials (Kumar, et al., 2009). Macroalgae are the ecological base of most of the close-shore tropical and temperate marine ecosystems. Their diversity supports a mass of other taxa, provides essential ecosystem services in the coastal zone, supply food and shelter for thousands of associated plant/animal species and their loss or replacement may lead to substantial negative implications for ecological function and biodiversity (Wernberg, et al., 2011).
The floristic variations in macroalgal communities are controlled by several environmental factors, including season, habitat, topography, duration of tidal exposure, tidal amplitude and biotic factors (algal turf, grazing, high concentration of limpets and many others) (Jha, et al., 2009). Macroalgae are economically very important: they are used as food, fodder, fertilizer and also as source of raw materials for industry, production of medicines, cosmetics and others products. Study on seasonal variation of macroalgae in Indian waters specifically in the east and west coasts of peninsular India were carried out by various researchers from the eighteenth century (Gohil and Kundu, 2012;Sahoo, 2010;Jha, et al., 2009;Untawale, et al., 1983;Børgesen, 1935;Iyengar, 1927). M. O. P. Iyengar (1927) was the first phycologist to report marine flora of the Indian coast.
The present study was carried out with the following objectives: To study spatial variations in different macroalgae groups; To study temporal variations in different macroalgae groups; To record stages of growth of different macroalgae taxa with respect to the sampling seasons.

Shore Platform Zones
From the field data, it emerged that the shore platform can be divided into three zones (in East-West direction) based on taxonomic groups of macroalgae (www.algaebase.org) observed. The shore platform can be divided into: i) cliff base part ii) an intertidal mixed zone and iii) a subtidal zone at the seafront. In this study, it is found that Ochrophyta (Phaeophyta) in rock pools (these pools were found in less numbers in the northern section) dominate the cliff base part. The cliff base is followed by a mixed intertidal area, where there is a transition from Ochrophyta (dominant in the intertidal zone) to Chlorophyta (dominant in the subtidal zone). The subtidal zone dominated by Chlorophyta is found at the seafront.

Spatial Variations of Macroalgae
As discussed the shore platform of Dwarka was divided into three sections for the convenience of field sampling; the results are reported here section wise.

Northern Section
Transect and quadrate data sampled during three months of field survey are represented in Table 1  Gepp. was observed only at 4 m distance. In October profile, Ulva lactuca Linnaeus was reported in both intertidal and subtidal zone with high frequencies (Table 1). Centroceras clavulatum (C. Agardh) Montagne was observed at 0 m and 53.8 m with increased frequencies of 26% and 55% respectively.

Southern Section
Transect and quadrate data sampled during three months of field survey are represented in Table 1 and Figure 3C. In case of April profile, highest number of quadrates were demarcated on 105.5 m transect line. Centroceras clavulatum (C. Agardh) was observed at 12.5 m (14%) and 33.5 m (28%) with high frequency. Ahnfeltia plicata (Hudson) Fries was observed in all quadrates with low as well as high frequency (Table 1). Sargassum cinctum J. Agardh was found with high frequencies at 12.5 m (20%), 33.5 m (31%) and 87.5 m (41%) and low frequencies at 69.5 m (29%), 93.5 m (37%) and 99.5 m (30%). Cladophora javanica (Kützing) P. Silva was observed at 12.5 m (1%) and at 87.5 m (5%) with higher frequency. Halimeda sp. was observed in subtidal zone with high frequency. Iyengaria stellata (Børgesen) Børgesen was seen only at 33.5 m. Chlorophyta and Rhodophyta dominated the subtidal and intertidal zones respectively. In June profile, Boodlea composita (Harvey) Brand was observed with high frequencies in all quadrates but was absent only at 16.8 m quadrate (Table 1). Gelidiella acerosa (Forsskå l) J. Feldmann was found with high and low trend. Sargassum cinctum J. Agardh was observed with increasing frequencies at 16.8 m (13%), 31.8 m (16%) and 59.8 m (21%). In October profile, Ulva lactuca Linnaeus was found with decreasing frequency from 0 m to 20.4 m (Table 1 and Figure 3C

Temporal Variation
Temporal variations in these taxa, in the three sections of the shore platform, Dwarka are presented in Table 2. In northern section, total eleven quadrates were studied in the three sampling months, while in central section thirteen quadrates were studied and for southern section, sixteen. Total thirty six macroalgae taxa were recorded. Table-2 shows the temporal occurrence of macroalgae on the shore platform. Maximum number of taxa (26 taxa) were reported during October and minimum (14 taxa) during June. Frequency data of taxa are represented section and quadrate wise in Table 1.

Stages of Growth of Different Macroalgae Taxa
On the shore platform of Dwarka, occurrence of total 36 taxa of macroalgae were noted during the three sampling months (April, June and October; Figure 2). Total 16 taxa of Chlorophyta were identified: Caulerpa sertulariodes (S. Gmelin) F. brevipes (J. Agardh) Svedelius, Halimeda macroloba Decaisne, Halimeda tuna (Ellis & Solander) Lamouroux and Udotea indica A. & E. Gepp. were found in April, June and October indicative of growing season is pre-monsoon. Valonia aegagropila C. Agardh and Valoniopsis pachynema (Martens) Bøegesen were found in June (juvenile) and October (dying) so, their growing season is in monsoon. Caulerpa taxifolia (Vahl) C. Agardh and Ulva lactuca Linnaeus were seen during April and October (juvenile condition) so, their growing seasons are in winter. Caulepra racemosa (Forsskå l) J. Agardh occurred in April and June (in dying condition) so, its growing season is summer. Rest of the 7 taxa were identified but cannot be commented with respect to their growth stages as their occurrence was noted for once in one month only.
Total 11 taxa of Ochrophyta were identified: Stoechospermum marginatum (C. Agardh) Kützing was found in mature condition in October so, its growing season is in monsoon. Lobophora variegata (Lamouroux) Womersley ex Oliveria was seen in juvenile condition in October indicating a growing season in winter. Padina boergesenii Allender & Kraft was found in April and October months which implies a winter growing season. Padina boryana Thivy was found during April and June so its growing season is in summer. Sargassum cinctum J. Agardh, Iyengaria stellata (Børgesen) Børgesen and Padina tetrastromatica Hauck were found during April, June and October in similar condition so, in this case it is difficult to comment on their growing stages and season. Rest of the 4 taxa were identified but cannot be commented with respect to their growth stages because their occurrence was noted for once in one month only.
Total 9 taxa of Rhodophyta were identified: Gelidiella acerosa (Forsskå l) J. Feldmann was found during June and October indicating a growing season in monsoon. Corallina berteroi Montagne ex Kützing was found during April, June and October (juvenile condition) so, its growing season is in winter. Hypnea spinella (C. Agardh) Kützing was seen during April and October months implying a growing period in winter. Ahnfeltia plicata (Hudson) Fries and Centroceras clavulatum (C. Agardh) Montagne were found during April and June indicating growing season in summer. Rest of the 4 taxa were identified but cannot be commented with respect to their growth stages because their occurrence was noted for once in one month only.

Discussion
The present study shows presence of three groups of macroalgae on the shore platform found during three months' field sampling. Taxa of Rhodophyta and Chlorophyta were found in both intertidal and subtidal zones. Ochrophyta were found in the cliffbase zone. Rhodophyta dominated the northern section during October while Chlorophyta dominated the subtidal zone of central section in all the three months and in all the three sections. Halimeda sp.is found only in the subtidal zone. Taxa of Rhodophyta were found in highest number (6 species) in October and less (3 species) in June. Members of Chlorophyta were found in highest number (9 species) in June. Members of Ochrophyta (5 species) were found in highest number in April.
During June, only one species of Ochrophyta (Sargassum cinctum J. Agardh) was found. Iyengaria stellata was found throughout the three sampling months. Caulerpa species dominated during April as compared to June and October during the sampling months. Various researchers have studied seasonal distribution of marine macroalgae in Indian waters. They have studied the seasonal variability of macroalgae in the east and west coast but did not comment on the dynamics of the macroalgae. Thakur et al., (2008) have worked on the seasonal variation in biomass and species composition of seaweeds in port Okha during May 2004 to April 2005 and reported 62 species during the entire study period. Studies conducted for quantifying the standard seaweeds from May 2004 to April 2005 showed an average biomass value of 3.10 kg fresh wt/m 2 /month with maximum being 6.60 kg fresh wt/m 2 in April. Dhargalkar and Deshmukhe (1996) have worked on the subtidal marine algae of Dwarka coast and reported 35 marine algal species. They encountered maximum numbers of species at 5-8m depth and found red algae species dominating this depth. Other authors have studied seasonal variability in the species of macroalgae. Ramamoorthy et al., (2012) have presented an assessment of reef associated biota in the Pirotan Island, Gulf of Kachchh, Gujarat and reported 89 species of fauna and 31 species of flora (seaweeds and seagrasses).
This study intends to report the macroalgae taxa on the basis of a systematic field inventory with reference to presence and absence of the taxa and its stage of growth. This kind of study when done on routine annual basis can bring out the macroalgal dynamics on spatial and temporal domain for the study area.

Study Area
For macroalgae growth, geographical, geological, topographical and physical nature of the shore is very important. The rocky coast has vertical zonation worldwide (Woodward, 2003): it provides good platform and stable coastal environment compared to that of soft sediments coasts like beaches and spits. Shore platform represents a case environment where majority of macroalgae species grow with a firm substratum attachment.
Gujarat coast of India represents the northwestern most part of peninsular India. This coastline occurs within geographical limits of 2000'-2445'N and 6800'-7830'E. It is 1,650 km long with 164,200 km 2 continental shelf (Jha, et al., 2009). It extends in the form of four major coastal ecological components: i) Kori creek ii) Gulf of Kachchh iii) Saurashtra coast from Okha to Porbandar and iv) Gulf of Khambhat. The substratum is rocky in many parts, which provides suitable environment for macroalgae growth (Chakraborty and Bhattacharya, 2012). The Saurashtra coast, which runs for an approximate length of 985 km, is characterized by rocky, sandy and muddy intertidal zones, harboring rich and varied flora and fauna (Gohil and Kundu, 2012).
The present study was carried out on the shore platform at Dwarka, located on the Saurashtra coast (2214'22"-2214'38"N and 6857'15"-6857'25" E) ( Figure 1). Total length of the study area is 572.28 m, maximum width sampled is 105.5 m and covers a surface area of 60375.54 m 2 . Previous surveys of marine algal resources along the Gujarat coast, performed at the intertidal zone, have revealed great diversity of marine algae in this region (Dhargalkar and Desmukhe, 1996).

Field data collection
For the present study, the study area was divided into three sections (in North-South direction): (i) Northern, For quantitative assessment of the marine algae in the given area, line transect was laid perpendicular to the coast from land to sea with the help of a long rope (50 m) (Dhargalkar and Kavlekar, 2004). A sampling point along the rope is marked depending on the gradient and exposure of intertidal and subtidal areas. In Saurashtra coast, the tidal amplitude is very high as compared to other parts of the west coast and the entire east coast of India. Growth of seaweeds in intertidal and shallow subtidal regions can be easily observed in this area as the spring tides expose the intertidal area up to a maximum length of 1 km (Jha, et al., 2009). Each of the three sections on the shore platform was represented by one transect line: thus resulting nine transect lines over three months' sampling. Quadrates of 1 m 2 were positioned on the transect lines wherever the algae growth, density and diversity were high. Total thirty nine quadrates were performed on the nine transect lines. GPS tagged photos of quadrates were taken for further analysis. Macroalgae species present within the quadrates were sampled. All specimens were identified and the specific numbers of individuals were registered for quantitative assessment of frequency.

Field data analysis
Collected macroalgae samples were taken to laboratory for preparation of herbarium sheets and specimen identification. Morphological criteria and reproductive structure were analyzed for taxa identification. Cladograms were prepared for identifying species in order to generate classification statistics (number of genera and species pertaining to different classes) (Figure 2). For understanding their spatial variation, transect and quadrate data were analyzed and are graphically represented as cross profiles of shore platform with embedded bar charts showing frequency of different macroalgae groups (Figure 3). In the cross profile, straight line is representing the transect line scaled to ground distance. Frequency of algal species encountered at the transect intercepts are represented as bar charts. X-axis of the bar chart represents macroalgae groups present while Y-axis shows their respective frequencies (in percentage).

Authors' contribution
As part of my doctoral research program, myself, Ms. Dimpal Sanghvi carried out this study. I performed field data collection, data analysis and have written the paper. Ms. Nandini Ray Chaudhury helped in analysis of field data and gave guidance to organize the paper. Dr. B.K. Jain, research guide, gave overall guidance and helped in editing the manuscript and submitting the same for peer-review.