New distribution record of a true coral species, Psammocora contigua (Esper, 1794) from Gulf of Kachchh Marine National Park & Sanctuary, India

: Reef-building corals are generally confined to tropical waters across the world oceans. But some coral species are able to tolerate even inhospitable environments and suboptimal extremes, and form lower diversity reefs habitats such as the Gulf of Kachchh, located along the northwestern coast of India. Among the reported hard coral species so far from the Gulf of Kachchh, genus Psammocora is represented by only one species, P. digitata . The present study confirmed a new distribution record of Psammocora contigua from Narara Island. Due to the changing hydro-geographic conditions in the Kachchh region, ramose and branching coral species have been believed to be extinct completely, leaving no sign of live colonies. P. contigua , recorded during the present study is the only living species with ramose growth form recorded so far from the Kachchh waters. The present study also holds out hope to record more new coral species records from the region.


OPEN ACCESS
Contributing much in designing, building, and maintaining coral reef habitats in the marine realms, scleractinian corals are often considered as 'ecosystem engineers'. Although these corals are widely distributed throughout the world's seas and deeper ocean environments, reef-building coral species are particularly live in shallow tropical and subtropical seas only. The distribution of corals in the world's oceans generally is confined in two distinct regions; the wider Caribbean (Atlantic Ocean) and the Indo-Pacific (from eastern Africa and the Red Sea to the Central Pacific Ocean) (Veron 1995). As updated by Hoeksema & Cairns (2019), a total of 1,625 coral species have been reported from the seas around the world. Among them, at least 900 extant hermatypic scleractinian species (Wallace 1999;Veron 2000) and at least 707 ahermatypic species (Cairns 1999;Tenjing et al. 2019) are recorded. The diversity of coral species is far greater in the Indo-Pacific than in the Atlantic region; the Atlantic amount to only 1/20 th of the number to be found in the Indo-Pacific waters (Veron 1995;Spalding et al. 2001). In most parts of the world, the species richness of coral reefs increases towards the equator, particularly the 'Coral Triangle' region, the 'epicentre' of the richest coral biodiversity (Veron et al. 2015). From this epicenter, the species richness of corals decreases towards latitudes and eastern and western realms. It is astounding to note that not a single coral species is common to both of the Indo-Pacific and the J TT Atlantic Ocean regions of the world (Veron et al. 2015). Reef-building corals prefer to grow best in shallow, clear waters that are poor in nutrients, annual water temperature ranges from 23°C to 29°C and a stable salinity range of 27-38 ppt (Achituv & Dubinsky 1990). Because of these strict environmental restrictions, reef-building corals are generally confined to tropical waters. But some coral species are able to tolerate inhospitable environments, sub-optimal extremes and form lower diversity reefs habitats. To a limited extent, corals of those environments can adapt to ambient conditions; consequently, the upper lethal temperature for a species in the tropics will be higher than that of the same species in the subtropics (Camp et al. 2018). Marginalized reefs distribution in the Gulf of Kachchh, along the northwestern coast of India includes sturdy reef assemblages that are adapted to thrive in extreme environmental conditions.
Coral reefs of the Kachchh are scanty and less diverse when compared with other major coral reef regions of India. The meagerness is explained due to the transgression of the sea levels of the Late Pleistocene-Holocene period and the upliftment of tectonic plates of the Gulf (Srivastava 1965). In addition, the prevailing arid climate and the semi-diurnal tidal amplitude fluctuations imply in water quality and heavy sediment depositions on coral reefs hamper their recovery to a healthy state (Michael et al. 2009). Residual coral species living today are quite distinctive in terms of their isolation and their high degree of adaptation to survive in such extreme oceanographic and climatic conditions (Dixit et al. 2010). The water in the Kachchh is murky almost throughout the year and possibilities for exploring sub-tidal reefs is only hardly possible. The distribution of corals in the Gulf is restricted mostly to fore-reefs, edges of reef flats along with the low-tide marks and, inter-tidal pools to reef flats for some extend. So, most studies on coral species diversity and distribution in the Gulf carried out so far were from the low-tide exposed reefs only. A total of 63 hard coral species belonging to 28 genera, under 11 families have been recorded so far from the Gulf of Kachchh (Satyanarayana et al. 2018). Among them, the genus Psammocora is represented by only one species, P. digitata. Psammocora (Dana, 1846) is an Indo-Pacific coral genus, presently comprised of 11 nominal species in the monotypic family Psammocoridae (WoRMS 2020). Species of this genus have highly plastic branching growth forms and exhibit considerable structural complexity in skeletal features (Benzoni et al. 2007). This report confirms the first occurrence of another species of Psammocora in the Gulf of Kachchh reefs.

Materials and Methods
Gulf of Kachchh is an East-West oriented, funnel shaped indentation along the Gujarat coast, approximately 125 km long and 75 km wide. The southern shore of the Gulf is fringed by some 42 islands and islets. Seaward side edges and low-tide marks and of these islands are predominantly inhabited by a rich coverage of coral reef. During a regular coral reef health monitoring survey in the Islands of Gulf of Kachchh Marine National Park area, the occurrence of Psammocora contigua was recorded on August 2020, a zero low-tide day from an intertidal reef flat of Narara Island (22.455°N 69.671°E) (Figure 1). A recently bleached colony was collected for taxonomic identification. The collected specimen was treated with 10% sodium hypochlorite solution to remove all soft parts, after that washed in freshwater and dried for recording corallites morphology and morphometry. The largest corallites from different parts of branch surface and valleys, which were not visibly undergoing any budding process, were selected for morphometrical analysis. Likewise, average branch variables were measured from different branches of the coral colony with a vernier caliper. The specimen was identified up to species level following published original and synonymized taxonomic descriptions of Stefani et al. (2008) and Venkataraman & Satyanarayana (2012). After taxonomical analysis, the same specimen was deposited as a voucher specimen (MNP/Coel/2020-01) at the Marine Biodiversity Museum, Marine National Park (Gujarat Forests), Jamnagar, India.

Diagnosis
Colony is sub-massive or ramous (Image 1a, 2a) but some younger colonies observed with encrusting growth forms (Image 1c). Live colony was pale brown in colour. Total diameter of the examined colony was 12.82 cm and height measured 6.24 cm. Branches short, stout, tend to be flattened and often anastomosed. Branch tip acute with irregular foliose ends and also form pits at many places (Image 1c). At the base of the colony, branches form valleys. Maximum height of the branch measured up to 2.89 cm and the maximum height of the distal part of the branch measured 1.22 cm. Maximum distance between distal portions of the branches measured up to 2.3 cm. The surface of the colony is smooth.
Corallites are very small, shallow, without any prominent walls and, give a smooth surface appearance to the colony (Image 2b,c). An average number of 26 corallites per cm 2 was measured. The arrangement of septa in each corallite gives a flower-like appearance. Columella was made of a group of pinnules (Image 2d) and measured maximum up to 0.131 mm in diameter. Septal margins with spiny process tend to arrange in whorls along their length. In most of the corallites, eight septa reach the fossa and four of them are petaloid. Maximum length of the petaloid septa reaching the fossa up to 0.302 mm and width up to 0.118 mm. Nonpetaloid septa reaching the fossa measured up to 0.105 mm wide. Likewise, enclosed petaloid septa measured up to 0.235 mm wide and 0.392 mm long. Series of calices often form and can be up to more than 25 calices long even in diameter and following the branch growth direction. Distance between two calices within the same row ranges 0.9-1.2 mm.; the nearest calices of two parallel rows were 2-2.7mm apart from each other. Up to eight rows of enclosed petaloid septa were found between series of corallites. In most of the corallite, one triplet septa (three septa fusing together) and two duplets (two septa fusing together) reaching fossa were observed. Synapticulothecal wall surrounds calices and rows of enclosed septa were seen in many places of the colony surface. Recorded taxonomic characters of the specimen (Table 1) agreed with the description of Psammocora contigua (Esper, 1794).

Discussion
Psammocora Dana, 1846, is an Indo-Pacific coral genus, presently comprised of 11 nominal species in the monotypic family Psammocoridae (WoRMS 2020). Geographical distribution of the genus extending to 'high latitudes' in both south and north hemispheres, and from the Red Sea and eastern Africa to eastern Pacific shores (Stefani et al. 2008). The Gulf of Kachchh is also located in a marginalized region and proximate to the Red Sea and Arabian Gulf, as their distribution range. Species of this genus have highly plastic branching growth forms and exhibit considerable structural complexity in skeletal features (Benzoni et al. 2007).
All the taxonomical characters of the examined coral colony, in fact, are agreed with the species P. obtusangula. The species P. obtusangula was considered a valid species by Glynn & Wellington (1983), Veron (2000), and Reyes-Bonilla (2002). Some studies also claimed it a close synonym of P. contigua (Veron & Pichon 1976;Faure 1982;Scheer & Pillai 1983) mentioning phenotypic plasticity as the main factor for their morphological variability. But, Stefani et al. (2008) demonstrated the overlapping morphological and molecular characters of P. obtusangula and P. contigua and synonymized the earlier with later. Hence the Kachchh specimen examined is identified as the species But the variation in branching may be due to the habitats they inhabit. A coral transplantation experiment also suggested that P. obtusangula is likely to be a shallow, agitated water form of P. contigua only (Hoffmeister 1925). Corals of the Gulf of Kachchh are always a puzzle to taxonomists, as the morphology and growth forms vary due to the existing sedimentation, tidal amplitude, and water current. The same might be the reason for variation in the growth form of the present specimen. Among the recorded coral species so far from the Kachchh waters, Pocillopora damicornis, Acropora humilis, A. squarrosa, A. microphthalma are the species having ramose or branching growth forms (Satyanarayana & Ramakrishna 2009). But all these species are presently considered locally extinct with not even a single live colony recorded since the recent past. So, P. contigua is the only living species with somewhat ramose growth form recorded so far from the Kachchh waters.
A total of eight species of corals belonging to the genus Psammocora have been recorded so far from India This species is also classified under 'IUCN Near Threatened' category (IUCN 2020). In the Gulf of Kachchh, the species distribution was rarely encountered at a low-tide exposed reef edge in the eastern side of Narara Island, and their distribution is recorded nowhere else in the Gulf of Kachchh reefs. Even at the recorded reef site also, a small patch of around 8-10 colonies was only observed. A detailed study needs to be carried out along the Kachchh reefs to record their actual distribution. Attempts with the aid of the latest technologies to explore the sub-tidal reefs may yield a greater number of coral species from the isolated reefs of the Gulf of Kachchh.