Molecular Survey on Symbiodinium of Some Scleractinean Coral Spp . and a Fire Coral sp . along the Red Sea of Egypt

The present study introduce an overview on the cladal structure of Symbiodinium population associated with some species of scleractinean corals and fire coral in the Egyptian Red Sea coast and discuss the possible consequences of recent climate changes on coral reefs. Cladal structure of Symbiodinium populations associated with eight keystone species of scleractinean corals and one species of fire coral that collected along Egyptian Red Sea coast, during 2012-2013, had been resolved based on 18S nrDNA and ITS2 genetic markers. Only Symbiodinium subclades C1 and A1 were identified from all examined species. Symbiodinium C1 was the dominant subclade that associated with 61% of coral samples. Results revealed that the studied pocilloporid corals were associated with Symbiodinium C1 and/or A1 while acroporids were only associated with Symbiodinium C1. The present data also indicated that Symbiodinium C1 occurred at high densities than A1 or A1+C1 combination. Because of the relative thermal susceptibility of clades C and A, the current study addresses that the recent climate changes may derive dramatic changes on community structure of coral reefs at the Red Sea. DOI: 10.14302/issn.2643-0282.imsj-18-2508 Corresponding author: Fedekar F. Madkour, Department of Marine Science, Faculty of Science, Port Said University, Port Said42526, Egypt, Email: fedekarmadkour@ymail.com Running title: Molecular survey on Symbiodinium in some corals


Introduction
Corals are known to be the typical hosts for symbiotic dinoflagellates of the genus Symbiodinium which are functionally diverse [1].This diversity reflects the functional ecology of different Symbiodinium types that establish different coral-symbiont partnerships in habitats of different conditions.Accordingly, genetic diversity of endosymbionts associated with corals is considered critical for coral life.Many studies had revealed that Symbiodinium clades have different thermal tolerance in which Symbiodinium D is the most thermotolerant and C is the most thermosensitive [2].
Though, under environmental stressors, members within the same clade do not necessarily acquire similar physiological responses [3].At finer levels, Symbiodinium types within each clade possess differential secondary thermal tolerances [1,4].As a consequence, bleaching events are severe at reefs dominated by thermosensitive types [5,6,7].Yet, determining the definite thermal tolerance that outlines the susceptibility of corals to bleaching, of many types is still in its infancy [3].However, inspecting genetic composition of coral's endosymbiotic systems is considered crucial for understanding susceptibility of corals to environmental stressors and predicting the consequences of increasing temperature on coral reefs.
Red Sea coral reefs represent the upper northern limits for coral reefs distribution.Although Red Sea coral reefs are considered unique reefs, they had received little concern about their endosymbiotic systems [8].Only few studies on the genetic diversity of Symbiodinium at the northern tip of the Gulf of Aqaba and at the eastern coasts had been published [9,10,11].Despite that the Egyptian coast of the Red Sea extends approximately 1800 km [12], genetic structure of endosymbiotic systems along this western part had not resolved yet, especially in scleractinian corals which are considered the main reef builders.Here, we assess Symbiodinium diversity on the reef building corals host species and one species of fire coral that exist along Egyptian coast of the Red Sea.
Coral samples were collected from shallow (1-5) and mid-depth (5-10) habitats.We address geographical differences between coral populations of western Egyptian coast and eastern Saudi Arabian coast of Red Sea in terms of phylogenetic diversity of their dinoflagellate symbionts.

Study Sites and Sample Collection
Six sampled locations were chosen along the western Red Sea coast off Egypt.

Data Accessibility
All ITS2 sequences in this study were archived at the NCBI GenBank with accession numbers KM066978.1-KM066991.1.showed in Table 1.

Based
Of nine examined species (n=98), the current genetic survey revealed that 61% of coral samples hosted Symbiodinium C, 33% associated with Symbiodinium A, and only 6% formed symbiosis with A+C combination.Symbiodinium C1 was recorded in acroporid, poritid, faviid, and pocilloporid species, while clade A1 was only detected in the three studied pocilloporid species as well as a fire coral M. dichotoma (Fig. 5).
Phylogenetic analysis of Symbiodinium sp.

Discussion
In spite of the great concern paid for coral reef ecosystem, Symbiodinium genetic diversity along the Red Sea had been overlooked.So, the current study introduced an overview on Symbiodinium genetic diversity in seven species of scleractinian corals and one species of fire coral along the Egyptian Red Sea coast.
The present study revealed that Symbiodinium population associated with Red Sea corals were primarily composed of C and A clades.In general, these two clades were recorded to have a global distribution [20].
Among different types of Symbiodinium under each clade, only C1 and A1 types were recorded with the dominance of C1 type comprising 61% of the recorded symbionts in all studied corals.C1 was detected to be the most dominant and widely distributed type because it has the ability to associate with a wide array of host species and a great adaptation with different environmental conditions [21,22].
Dominance of Symbiodinium C1 was explained by two arguments with the same perception.The first supposed that Symbiodinium C1 type has a generalist nature along wide geographic scales [22].The second proposed that coral-Symbiodinium symbiosis is directed toward specialist-types preference along evolutionary history of coral reefs [21].One of studies suggested that dominance of C1 type in west Pacific had been transferred to western Indian Ocean, and eventually to the Red Sea, before biogeographic partitioning between the two oceans [23].Because northern Red Sea coral reefs are considered recent reefs [24], far from major natural stressors, dominance of C1 type associated with scleractinian corals may be explained on the basis of recent low-specialist symbiosis.
Symbiodinium population at Yanbu was dominated by clade C (69%) followed by clade A (27.3%) while clade D formed only 3.7% of symbionts [11].The current results emphasized the previous mentioned dominance order of clades C and A, and added the endosymbiotic system composed of a combination from the two clades C and A which could be considered as a unique system in Red Sea corals as reported by [20].This is in contrast with corals of the Arabian Gulf where Symbiodinium D represents the dominant clade [11,25].Predominance of such thermotolerant clade at the Arabian Gulf is associated with thermal tolerance of >33 °C [2].However, Symbiodinium D and B that are known to associate with scleractinian corals were not detected.
Compared with high host diversity along the Red Sea, symbiont diversity was low.The same pattern was previously recorded along other reefs at Great Barrier Vol-1 Issue 1 Pg.no.23   Reef and Indian Ocean [26,27].The flexibility of P. verrucosa for harboring Symbiodinium A and C was coincident with that recorded in the central Red Sea [28].

Figure 1 .
Figure 1.Sampling sites along the Egyptian Red Sea.
on 18S nrDNAs, three different banding patterns were produced by Symbiodinium harbored studied corals.The first banding pattern was characterized by two bands of 1173 and 800 pbs, while the second pattern consisted of three bands of 800, 678, and 288 pbs (Fig.2).The third was consisted of a combination of the first and second banding patterns (Fig.3).The first and second banding patterns are corresponding to previously published RFLP profiles for Symbiodinium clades C and A, respectively, while the third one is a combination of clades A and C (A+C).

Figure 5 .
Figure 5. Cladal composition of Symbiodinium population in the collected coral species.Top numerals in parentheses indicate numbers of collected fragments in each species.

Figure 6 .
Figure 6.Reconstruction of ITS2 phylogenetic tree between members of Symbiodinium harbored by different taxa of invertebrates in the Red Sea.The phylogenetic distance was inferred by Neighbor-Joining method.Only bootstrap values >50% are shown.
temperature anomaly resulted in mass bleaching event in some reef building coral species (Hanafy and Ahmed, unpublished data).Among these, Stylophora, Montipora, Porites, and Millepora were the most affected genera by thermal stress.Symbiodinium A or C harbored by Red Sea corals were considered thermosensitive clades[36].The dominance of these clades observed in the present study may indicate that coral reefs at the Red Sea are endangered by the thermal stress.Accordingly, patterns of temperature anomalies may have dramatic effects on coral reefs diversities and structures at the Red Sea as suggested by[35].However, with little knowledge on Symbiodinium genetic diversity at these levels, we could not generalize our investigation on Red Sea corals.Accordingly, intensive molecular survey with deep resolution on Symbiodinium populations may contribute in understanding of bleaching patterns along the Red Sea.In parallel, future experimental studies are required to derive comprehensive perception about thermal tolerances of these clades and/or types.Conclusively, the current study emphasizes the need for resolving Symbiodinium genetic diversity along Egyptian coasts of the Red Sea.The level at which this diversity will be resolved is critical for identifying threats to coral reefs at the Red Sea.Identifying Symbiodinium types harbored by different hosts may contribute largely in understanding Symbiodinium dynamics and responses to environmental changes at these reefs.

Table 1 .
). Symbiodinium types isolated from different coral species along with corresponding NCBI accession numbers.
On the other hand, divergence within phylotype C may explain the dominance of this phylotype in coral reefs of the Red Sea.
and 40%, respectively.More recently, sea surface temperature was raised up to 34°C at the Egyptian coasts of the Red Sea during August 2012.This high