J Biosci Vol. 43, No. 1, March 2018, pp. 59–74 Ó Indian Academy of Sciences DOI: 10.1007/s12038-018-9730-0 Thalassiosira mala (Bacillariophyta), a potentially harmful, marine diatom from Chilka Lake and other coastal localities of Odisha, India: Nomenclature, frustule morphology and global biogeography 1 2 3 AKSHINTHALA KSKPRASAD *, JAMES ANIENOW and ERIC LOCHNER 1Department of Biological Science, Florida State University, Tallahassee, FL 32306–4370, USA 2Department of Biology, Valdosta State University, Valdosta, GA 31698–1500, USA 3Department of Physics, Florida State University, Tallahassee, FL 32306–4351, USA *Corresponding author (Email, [email protected]) MS received 7 August 2017; accepted 14 December 2017; published online 18 January 2018 Our examination of net phytoplankton collected from coastal localities in Odisha on the east coast of India, including Chilka Lake, Chandrabhaga Beach and Puri, in December 2015, revealed the overwhelming dominance of Thalassiosira mala, a gelatinous colony-forming, potentially harmful, marine planktonic diatom. The large numbers of cells allowed us to observe details of the cingulum not previously reported. The epicingulum is composed of four open bands including an areolated valvocopula, an areolated copula and two non-areolated pleurae. The immature hypocingulum includes at least two bands. Openings of alternate bands are arranged in a dextral pattern. Based on previous reports from the west coast and our current findings, Thalassiosira mala appears to be a common, widely distributed primary producer in Indian coastal waters. The presence of morphologically similar species, especially those\20 lm in diameter, underscores the importance of reliable species-level taxonomy using appropriate techniques for meaningful ecological and biogeographic considera- tions and for monitoring potentially harmful algae in India’s economically important coastal waters. Published reports suggest that Thalassiosira mala is widely distributed in temperate and tropical waters, present in 26 of 232 ecoregions and 18 of 62 provinces recognized in a recent classification of coastal marine ecoregions. Keywords. Bay of Bengal; biogeography; Chilka Lake; diatom; fine structure; taxonomy; Thalassiosira mala 1. Introduction us a better understanding of the true relationships among the genera and species of diatoms. Therefore, we are currently Diatoms are single-celled, photosynthetic microalgae char- examining archived samples of marine diatoms in the col- acterized by the presence of a two-part siliceous covering lection of Professor Desikachary from the coastal waters of known as the frustule. In marine systems they are a major the Bay of Bengal, together with additional materials col- component of phytoplankton, and may contribute as much as lected recently by the senior author, and using a combination 20% of the global primary productivity (Field et al. 1998; of light and electron microscopy to determine the hidden Uitz et al. 2010; Malviya et al. 2016). In light of the diversity of the diatom flora of the region. Our preliminary importance of diatoms to marine ecosystems, 30 years ago investigations indicate that the diatom flora will include Professor T. V. Desikachary and his research group pub- many more species than currently reported. lished the six-volume Atlas of Indian Ocean Diatoms (De- Of particular interest to us are members of the genera sikachary 1986–89). This monumental work includes light Thalassiosira Cleve emend. Hasle and Coscinodiscus micrographs of nearly all of the diatom species known from Ehrenberg emend. Hasle and Sims, two of the dominant and the region at the time. However, many changes have most frequently encountered planktonic diatom genera in occurred in our understanding of diatom taxonomy since the Indian coastal waters. Before the advent of electron micro- publication of the Atlas. In particular, the widespread use of scopy, the differences between these two genera were not electron microscopy has provided new information on the clear. Both genera were included in the family Coscinodis- fine structure of the diatom frustule, including details not caceae Ku¨tzing and species were assigned to one genus or visible in light microscopy. This new information has given the other on the basis of characters now known to be of little http://www.ias.ac.in/jbiosci 59 60 A K S K Prasad et al. value in the delineation phylogenetic relationships. Thalas- morphology for the Indian materials, including the details of siosira and Coscinodiscus are now placed in separate fam- the cingulum not previously reported, and to compare frus- ilies, with Thalassiosira serving as the generitype of tule morphology with other small species of Thalassiosira Thalassiosiraceae Lebour emend. Hasle and Coscinodiscus also present in Indian coastal waters, some known to form serving as the generitype of Coscinodiscaceae. The two similar formless gelatinous colonies; and (4) to present an families are distinguished by details of the structure of the overview of the global distribution of T. mala following the areolae, including the position of the vela (internal in Tha- recent biogeographic classification of the coastal Marine lassiosiraceae, external in Coscinodiscaceae) and foramina Ecoregions of the World (MEOW) proposed by Spaulding (external in Thalassiosiraceae, internal in Coscinodiscaceae), et al. (2007). the nature of the marginal ring of processes (fultoportulae in Thalassiosiraceae, rimoportulae in Coscinodiscaceae), and the complete absence of fultoportulae in Coscinodiscaceae, 2. Materials and methods features that can only be resolved with certainty through the use of scanning electron microscopy (Hasle 1973b; Ross and 2.1 Materials and collection sites Sims 1973). Hasle (1968, 1972a, 1973a) first described structure of fultoportulae, the diagnostic valve processes Net phytoplankton (25 lm mesh) samples were collected in within the genus Thalassiosira, and emended the generic December 2015 from three coastal locations in Odisha description. The arrangement of areolae, fultoportulae, and (formerly, Orissa) on the east coast of India (Bay of Bengal): rimoportulae are widely considered to be important in the (1) Dolphin’s Cove (ca. 19.845° N, 85.479° E), near delineation of species of Thalassiosira (Fryxell 1975; Rivera Satapada Village, at the new mouth of Chilka Lake. 1981; Mahood et al. 1986; Makarova 1988; Hasle and This sampling site is located approximately 55 km Syvertsen 1996). Live cells in most species of Thalassiosira from Puri, Odisha, on the eastern side of Chilka Lake. form chains with sibling cells linked by threads of chitin Chilka Lake (also known as Chilika Lake) is the largest (McLachlan et al. 1965). However, about a dozen species of brackish water lake in Asia. It is connected to the Bay Thalassiosira form colonies of cells embedded in a common of Bengal by a long (35 km), narrow channel in the mucilage; the formation of mucilaginous colonies may be state of Odisha, India. Chilka Lake covers an area of associated with harmful effects (Hasle and Fryxell 1995; approximately 900–1100 km2 (Raman et al. 1990). Fryxell and Hasle 2003). During the monsoon season considerable quantities of The genus Thalassiosira is well represented in Indian freshwater are discharged into the lagoon through a waters, with *60 species reported from the region, includ- number of rivulets and rivers, including the Daya, ing the east (Bay of Bengal) and west coasts (Arabian Sea) Bhargabi and Nuna rivers, which drain into the and Indian Ocean waters (Venkataraman 1939; Subrah- northeast end; as a result, the area of the lake increases manyan 1946; Misra 1956; Simonsen 1974; Hasle 1976; by several hundred square kilometers during the Desikachary 1986–89; Samanta and Bhadury 2015), of monsoon season. The salinity varies from trace levels which at least five were described from Indian waters as new to 36% (Panigrahi et al. 2009). to science, T. coramandeliana Subrahmanyan, T. marginata (2) Chandrabhaga Beach (ca. 19.865o N, 86.113o E), Venkataraman, T. plicatoides (Simonsen) Akiba and located three km east of the Sun temple of Konark, in Yanagisawa (as Coscinodiscus plicatoides Simonsen), T. the Puri district in the state of Odisha, India. sundarbana Samanta and Bhadury and T. tropica Misra. In (3) Puri, Odisha (19.813° N, 85.832° E), located 30 km the present report we focus on Thalassiosira mala Takano, a southwest of the previous site. nanoplanktonic species forming massive gelatinous colo- nies, occasionally reaching bloom numbers. It was the dominant nanoplankter in net hauls collected from coastal areas of the state of Odisha (formerly known as Orissa), 2.2 Preparation of material for light and electron including Chilka Lake, Chandrabhaga Beach (near the city microscopy of Konark) and Puri, suggesting its widespread distribution in Bay of Bengal waters. Samples were preserved in Lugol’s iodine in the field. Ali- The purpose of the present paper is four-fold: (1) to quots of each sample were cleaned of organic matter using a record, for the first time, the presence and overwhelming combination of hydrogen peroxide and hot concentrated dominance of the potentially harmful marine planktonic sulfuric acid followed by 10 rinses with de-ionized water. diatom Thalassiosira mala in Chilka Lake and other coastal Small aliquots of a suspension of cleaned material were localities in the State of Odisha; (2) to clarify the correct date mounted in Naphrax for light microscopy (Prasad et al. of the validating publication