Temporal and Spatial Variations in spatial variations in symbiont communities of catch bowl coral Isopora palifera (Scleractinia: Acroporidae) on reefs in Kenting National Park, Taiwan

Acclimatization through Symbiodinium shuffling is one of potential mechanisms in reef-building corals to survive environmental stress. In our previous study, the catch bowl coral Isopora palifera in Tantzei Bay (TZB), Nanwan, Kenting National Park (KNP), southern Taiwan was demonstrated to shuffle thermal-tolerant Symbiodinium D1a and thermal-sensitive Symbiodinium C3 in response to seasonal variations in sea surface temperatures (SSTs) in 2000 and 2001. In this study, we reexamined the temporal dynamics of the Symbiodinium community of I. palifera in TZB in 2006-2009. In addition, spatial variations in Symbiodinium communities in I. palifera were also examined at 6 other sites of Nanwan, KNP in 2009, including a site located at a nuclear power plant outlet (NPP-OL) in southern Taiwan with a yearly mean SST 0.6-1.5 degrees C higher compared to the other sites. Phylotyping and DNA sequence analyses of Symbiodinium ribosomal 28S and ITS2 markers showed that I. palifera colonies at TZB continued to show seasonal shuffling, but shifted to thermal-sensitive type C3 dominant in 2006-2009. This differed from the symbiont community originally dominated by the thermal-tolerant Symbiodinium D1a in 2000 and 2001 after the 1998 mass-bleaching event. Significant differences in spatial variations of the symbiont community in Nanwan were detected with I. palifera colonies at the NPP-OL dominated by Symbiodinium D1a. Our study results suggest that I. palifera can acclimatize to SST anomalies by shuffling to thermal-tolerant Symbiodinium D1a and can revert to thermal-sensitive C3 when the stress disappears, but will maintain the thermally tolerant Symbiodinium D1a as the dominant symbiont if the heat stress continues

Symbiodinium spp. associated with scleractinian corals from Dongsha Atoll (Pratas), Taiwan, in the South China Seal

Dongsha Atoll (also known as Pratas) in Taiwan is the northernmost atoll in the South China Sea and a designated marine national park since 2007. The marine park's scope of protection covers the bio-resources of its waters in addition to uplands, so it is important to have data logging information and analyses of marine flora and fauna, including their physiology, ecology, and genetics. As part of this effort, we investigated Symbiodinium associations in scleractinian corals from Dongsha Atoll through surveys carried out at two depth ranges (shallow, 1-5 m; and deep, 10-15 m) in 2009 and during a bleaching event in 2010. Symbiodinium composition was assessed using restriction fragment length polymorphism (RFLP) of 28S nuclear large subunit ribosomal DNA (nlsrDNA). Our results showed that the 796 coral samples from seven families and 20 genera collected in 2009 and 132 coral samples from seven families and 12 genera collected in 2010 were associated with Symbiodinium C, D and C+D. Occurrence of clade D in shallow water (24.5%) was higher compared to deep (14.9%). Due to a bleaching event in 2010, up to 80010 of coral species associated with Symbiodinium C underwent moderate to severe bleaching. Using the fine resolution technique of denaturing gradient gel electrophoresis (DGGE) of internal transcribed spacer 2 (ITS2) in 175 randomly selected coral samples, from 2009 and 2010, eight Symbiodinium C types and two Symbiodinium D types were detected. This study is the first baseline survey on Symbiodinium associations in the corals of Dongsha Atoll in the South China Sea, and it shows the dominance of Symbiodinium Glade C in the population

Diversity and Distribution of Symbiodinium Associated with Seven Common Coral Species in the Chagos Archipelago, Central Indian Ocean

The Chagos Archipelago designated as a no-take marine protected area in 2010, lying about 500 km south of the Maldives in the Indian Ocean, has a high conservation priority, particularly because of its fast recovery from the ocean-wide massive coral mortality following the 1998 coral bleaching event. The aims of this study were to examine Symbiodinium diversity and distribution associated with scleractinian corals in five atolls of the Chagos Archipelago, spread over 10,000 km 2. Symbiodinium clade diversity in 262 samples of seven common coral species, Acropora muricata, Isopora palifera, Pocillopora damicornis, P. verrucosa, P. eydouxi, Seriatopora hystrix, and Stylophora pistillata were determined using PCR-SSCP of the ribosomal internal transcribed spacer 1 (ITS1), PCR-DDGE of ITS2, and phylogenetic analyses. The results indicated that Symbiodinium in clade C were the dominant symbiont group in the seven coral species. Our analysis revealed types of Symbiodinium clade C specific to coral species. Types C1 and C3 (with C3z and C3i variants) were dominant in Acroporidae and C1 and C1c were the dominant types in Pocilloporidae. We also found 2 novel ITS2 types in S. hystrix and 1 novel ITS2 type of Symbiodinium in A. muricata. Some colonies of A. muricata and I. palifera were also associated with Symbiodinium A1. These results suggest that corals in the Chagos Archipelago host different assemblages of Symbiodinium types then their conspecifics from other locations in the Indian Ocean; and that future research will show whether these patterns in Symbiodinium genotypes may be due to local adaptation to specific conditions in the Chagos

Development of Gene Expression Markers of Acute Heat-Light Stress in Reef-Building Corals of the Genus Porites

Coral reefs are declining worldwide due to increased incidence of climate-induced coral bleaching, which will have widespread biodiversity and economic impacts. A simple method to measure the sub-bleaching level of heat-light stress experienced by corals would greatly inform reef management practices by making it possible to assess the distribution of bleaching risks among individual reef sites. Gene expression analysis based on quantitative PCR (qPCR) can be used as a diagnostic tool to determine coral condition in situ. We evaluated the expression of 13 candidate genes during heat-light stress in a common Caribbean coral Porites astreoides, and observed strong and consistent changes in gene expression in two independent experiments. Furthermore, we found that the apparent return to baseline expression levels during a recovery phase was rapid, despite visible signs of colony bleaching. We show that the response to acute heat-light stress in P. astreoides can be monitored by measuring the difference in expression of only two genes: Hsp16 and actin. We demonstrate that this assay discriminates between corals sampled from two field sites experiencing different temperatures. We also show that the assay is applicable to an Indo-Pacific congener, P. lobata, and therefore could potentially be used to diagnose acute heat-light stress on coral reefs worldwide

Diverse responses of Symbiodinium types to menthol and DCMU treatment

To understand the mechanism of photosynthetic inhibition and generation of reactive oxygen species (ROS) in Symbiodinium types under stress, chemicals such as dichlorophenyl dimethylurea (DCMU) are widely used. Moreover, DCMU and recently menthol were used to generate aposymbiotic cnidarian hosts. While the effects of DCMU on Symbiodinium cells have been extensively studied, no studies have shown the mechanism behind menthol-induced coral bleaching. Moreover, no study has compared the effects of DCMU and menthol treatments on photosystem II (PSII) activity and generation of ROS in different Symbiodinium types. In this study, we utilized five freshly isolated Symbiodinium types (S. minutum (B1), S. goreaui (C1), C3, C15, and S. trenchii (D1a)) to compare the effects of DCMU and menthol treatments. Symbiodinium cells were exposed to DCMU and menthol at different concentrations for 4 h. Results showed that values of the 50% inhibitory concentration (IC50) for PSII inhibition were 0.72∼1.96 mM for menthol-treated cells compared to 29∼74 pM for DCMU-treated cells. Diverse responses of Symbiodinium types were displayed in terms of PSII tolerance to menthol (S. minutum > S. trenchii = C15 > C3 = S. goreaui), and also in the response curves. In contrast, responses were not so diverse when the different types were treated with DCMU. Three of five menthol-treated Symbiodinium types showed instant and significant ROS generation when PSII activity was inhibited, compared to no ROS being generated in DCMU-treated Symbiodinium types. Both results indicated that menthol inhibited Symbiodinium PSII activity through Symbiodinium type-dependent mechanisms, which were also distinct from those with DCMU treatment. This study further confirmed that photosynthetic functions Symbiodinium have diverse responses to stress even within the same clade

A new shallow-water species, Polycyathus chaishanensis sp nov (Scleractinia: Caryophylliidae), from Chaishan, Kaohsiung, Taiwan

A small population of a new species of zooxanthellate scleractinian coral, Polycyathus chaishanensis sp. nov., is described from shallow water (< 3 m) off Chiashan, Kaohsiung, an uplifted Pleistocene reef located on the southwest coast of Taiwan. Polycyathus chaishanensis sp. nov. is a zooxanthellate coral associated with Symbiodinium Cl and forms small encrusting colonies. Polycyathus chaishanensis sp. nov. differs from other Polycyathus by having (1) the smallest corallites (2.0-3.7 mm in calicular diameter) reported in the genus Polycyathus; (2) septa hexamerally arranged in 4 incomplete cycles displaying dentate or laciniate axial edges; (3) crispate and well-developed pali before the secondary septa; and (4) light brown pigmented pali/columellar elements. When expanded, vivid-red to brown polyps rise considerably above the calice, and long and slender tentacles are covered with white nematocyst batteries. Polycyathus chaishanensis is the only species of Polycyathus known from Taiwanese waters and appears to be endemic to a small region at Chaishan. The small population of this new species raises concerns as to its vulnerability to natural and anthropogenic threats

Doors are closing on early development in corals facing climate change

International audienceMarine invertebrates are particularly vulnerable to climatic anomalies in early life history stages because of the time spent in the water column. Studies have focused on the effect of seawater temperature on fertilization, development, and larval stages in corals; however, none of them show comparative results along an environmental gradient. In this study, we show that temperatures in the range of 15–336C have strong effects on fertilization rates and embryonic stages of two coral species, Acropora muricata in the subtropical environment and Acropora hyacinthus in subtropical and temperate environments. Deformations after the first cleavage stages were observed at low (156C) and high (336C) temperatures. Development was delayed by 6–7 h in the slightly non-optimal temperature of 206C. We found significant differences in fertilization rates and responses of embryos from different latitudes, with temperate corals being more sensitive to extremely hot temperatures and vice versa. We hypothesize that the coral development is restricted to a narrow temperature range and deviation outside this window could inhibit a species' continuance and ecological success. Thus, it would have significant negative effects on adult populations and communities, playing a role in future of coral reef survival

Temporal variation and photochemical efficiency of species in Symbiodinaceae associated with coral Leptoria phrygia (Scleractinia; Merulinidae) exposed to contrasting temperature regimes.

The Symbiodinaceae are paradoxical in that they play a fundamental role in the success of scleractinian corals, but also in their dismissal when under stress. In the past decades, the discovery of the endosymbiont's genetic and functional diversity has led people to hope that some coral species can survive bleaching events by associating with a stress-resistant symbiont that can become dominant when seawater temperatures increase. The variety of individual responses encouraged us to scrutinize each species individually to gauge its resilience to future changes. Here, we analyse the temporal variation in the Symbiodinaceae community associated with Leptoria phrygia, a common scleractinian coral from the Indo-Pacific. Coral colonies were sampled from two distant reef sites located in southern Taiwan that differ in temperature regimes, exemplifying a 'variable site' (VS) and a 'steady site' (SS). We investigated changes in the relative abundance of the dominant symbiont and its physiology every 3-4 months from 2016-2017. At VS, 11 of the 12 colonies were dominated by the stress-resistant Durusdinium spp. (>90% dominance) and only one colony exhibited co-dominance between Durusdinium spp. and Cladocopium spp. Every colony displayed high photochemical efficiency across all sampling periods, while showing temporal differences in symbiont density and chlorophyll a concentration. At SS, seven colonies out of 13 were dominated by Cladocopium spp., five presented co-dominance between Durusdinium spp./Cladocopium spp. and only one was dominated by Durusdinium spp. Colonies showed temporal differences in photochemical efficiency and chlorophyll a concentration during the study period. Our results suggest that VS colonies responded physiologically better to high temperature variability by associating with Durusdinium spp., while in SS there is still inter-colonial variability, a feature that might be advantageous for coping with different environmental changes

Specificity trumps flexibility—location-based stable associations between Symbiodiniaceae genera and Platygyra verweyi (Scleractinia; Merulinidae)

This study monitored symbiont communities bi-monthly in native coral cores used in a reciprocal transplantation of the coral Platygyra verweyi over two years (2014–2016) and samples of mother colonies from three locations with variable thermal regimes; our results show that associating with multiple Symbiodiniaceae genera (Cladocopium spp. and Durusdinium spp.) is not a prerequisite for symbiont shuffling. Platygyra verweyi associates with certain Symbiodiniaceae genera based on location. Results of quantitative real-time PCR indicated small-scale temporal changes in Symbiodiniaceae genera compositions from 2014 to 2016; however, these changes were not enough to invoke shuffling or switching, despite degree heating weeks exceeding 6 °C-weeks in 2014 and 4 °C-weeks in 2015, which usually resulted in substantial coral bleaching. Microsatellite analysis of the P. verweyi host showed no genetic differences among the study locations. Our results suggest that P. verweyi undergoes long-term acclimatization and/or adaptation based on microgeographic and local environmental conditionsby altering its combinations of associated Symbiodiniaceae. Results also suggest that shuffling might not be as common a phenomenon as it has been given credit for; corals thrive through specific associations, and many corals could still be vulnerable to climate change-induced stress, despite being promiscuous or able to associate with rare and background Symbiodiniaceae genera