珊瑚Acropora pulchra (brook)的化学成分研究

首次对来自中国北海涠洲岛的珊瑚Acropora pulchra(brook)的化学成分进行研究,从乙醇浸提液的乙酸乙酯部分分离鉴定出7个化合物,并确立结构为十五酸十七酯(I)、正十六碳醇(Ⅱ)、鲨肝醇(Ⅲ)、1-正十六酸甘油酯(Ⅳ)、N—l—羟基甲基-2-羟基-(E,E)-3,7-十七碳二烯基十六酸酰胺(V)、胸腺嘧啶(Ⅵ)、尿嘧啶(Ⅶ)。     

What drives phenotypic divergence among coral clonemates of Acropora palmata?

Evolutionary rescue of populations depends on their ability to produce phenotypic variation that is heritable and adaptive. DNA mutations are the best understood mechanisms to create phenotypic variation, but other, less well‐studied mechanisms exist. Marine benthic foundation species provide opportunities to study these mechanisms because many are dominated by isogenic stands produced through asexual reproduction. For example, Caribbean acroporid corals are long lived and reproduce asexually via breakage of branches. Fragmentation is often the dominant mode of local population maintenance. Thus, large genets with many ramets (colonies) are common. Here, we observed phenotypic variation in stress responses within genets following the coral bleaching events in 2014 and 2015 caused by high water temperatures. This was not due to genetic variation in their symbiotic dinoflagellates (Symbiodinium “fitti”) because each genet of this coral species typically harbours a single strain of S. “fitti”. Characterization of the microbiome via 16S tag sequencing correlated the abundance of only two microbiome members (Tepidiphilus, Endozoicomonas) with a bleaching response. Epigenetic changes were significantly correlated with the host's genetic background, the location of the sampled polyps within the colonies (e.g., branch vs. base of colony), and differences in the colonies’ condition during the bleaching event. We conclude that long‐term microenvironmental differences led to changes in the way the ramets methylated their genomes, contributing to the differential bleaching response. However, most of the variation in differential bleaching response among clonemates of Acropora palmata remains unexplained. This research provides novel data and hypotheses to help understand intragenet variability in stress phenotypes of sessile marine species.     

Acropora recruits harbor “rare” Symbiodinium in the environmental pool

Coral–algal symbioses are essential for the survival of corals. Algal endosymbionts, specifically the dinoflagellate genus Symbiodinium, are divided into several genetic clades. The composition of Symbiodinium within corals plays an important role in the tolerance and/or sensitivity of host corals to local environments, due to individual Symbiodinium-specific physiological characteristics. While the majority of gamete-spawning corals acquire Symbiodinium from the surrounding environment, little is known about whether corals specifically select or randomly acquire Symbiodinium from the environmental population. In the present study, we compared the Symbiodinium clade composition of newly recruited Acropora corals with that of the environmental pool (water column, sediments, and adult colonies). More than 90 % of recruits harbored clades A and/or D until 6 months after settlement, despite the Symbiodinium environmental pool being mainly composed of clade C (mainly ITS1 type C2), and to a lesser extent clades A and D. In addition, the environmentally dominant type C2 Symbiodinium was not detected in Acropora recruits, while a few recruits harbored ITS1 types C1 or C15. Therefore, the clade composition of recruits may not reflect the abundance/density of Symbiodinium populations in the environment. Some members of clades A and D are known to exhibit tolerance to a wide range of environments. ITS1 type C1 also exhibits greater tolerance to thermal stress compared to ITS1 type C2. These tolerance characteristics of certain Symbiodinium may be vital for the initial survival of Acropora recruits, even if these Symbiodinium are rare in the environment.     

Can benthic algae mediate larval behavior and settlement of the coral Acropora muricata?

The resilience of coral reefs relies significantly on the ability of corals to recover successfully in algal-dominated environments. Larval settlement is a critical but highly vulnerable stage in the early life history of corals. In this study, we analyzed how the presence of two upright fleshy algae, Sargassum mcclurei (SM) and Padina australis (PA), and one crustose coralline algae, Mesophyllum simulans (MS), affects the settlement of Acropora muricata larvae. Coral larvae were exposed to seawater flowing over these algae at two concentrations. Larval settlement and mortality were assessed daily through four variables related to their behavior: swimming, substratum testing, metamorphosis, and stresses. Temperature, dissolved oxygen, pH, algal growth, and photosynthetic efficiency were monitored throughout the experiment. Results showed that A. muricata larvae can settle successfully in the absence of external stimuli (63 ± 6 % of the larvae settled in control treatments). While algae such as MS may stimulate substrate testing and settlement of larvae in the first day after competency, they ultimately had a lower settlement rate than controls. Fleshy algae such as PA, and in a lesser measure SM, induced more metamorphosis than controls and seemed to eventually stimulate settlement. A diverse combination of signals and/or modifications of microenvironments by algae and their associated microbial communities may explain the pattern observed in coral settlement. Overall, this study contributes significantly to the knowledge of the interaction between coral and algae, which is critical for the resilience of the reefs.     

Shifting white pox aetiologies affecting Acropora palmata in the Florida Keys, 1994–2014

We propose ‘the moving target hypothesis’ to describe the aetiology of a contemporary coral disease that differs from that of its historical disease state. Hitting the target with coral disease aetiology is a complex pursuit that requires understanding of host and environment, and may lack a single pathogen solution. White pox disease (WPX) affects the Caribbean coral Acropora palmata. Acroporid serratiosis is a form of WPX for which the bacterial pathogen (Serratia marcescens) has been established. We used long-term (1994–2014) photographic monitoring to evaluate historical and contemporary epizootiology and aetiology of WPX affecting A. palmata at eight reefs in the Florida Keys. Ranges of WPX prevalence over time (0–71.4%) were comparable for the duration of the 20-year study. Whole colony mortality and disease severity were high in historical (1994–2004), and low in contemporary (2008–2014), outbreaks of WPX. Acroporid serratiosis was diagnosed for some historical (1999, 2003) and contemporary (2012, 2013) outbreaks, but this form of WPX was not confirmed for all WPX cases. Our results serve as a context for considering aetiology as a moving target for WPX and other coral diseases for which pathogens are established and/or candidate pathogens are identified. Coral aetiology investigations completed to date suggest that changes in pathogen, host and/or environment alter the disease state and complicate diagnosis.     

The pink-blue spot syndrome in Acropora eurystoma (Eilat, Red Sea): a possible marker of stress?

The appearance of pink-blue spots (termed here as pink-blue spot syndrome - PBSS) in the branching coral Acropora eurystoma from the Gulf of Eilat, Red Sea, is described. We monitored 18 transects (10 x 1 m2 each) in front of the H. Steinitz Marine Laboratory (Eilat), at 3, 6 and 9 m depth, during March and August in 2001 and 2002. Transect measurements revealed high frequencies of colonies with PBSS (up to 100% of colonies) between 3 and 9 m depth. Ten PBSS-affected colonies of A. eurystoma were labelled and monitored for the development of spots. From March to August 2001, the number of spots per colony increased and remained constantly high at both sampling dates in 2002. Spot size ranged between 7 and 149 mm2. Spots were primarily recorded in areas where coral tissues contacted foreign biological matter, either around regenerative wounds or when surrounded by encrusting organisms, in fast-growing areas and in allogeneic interactions. A preliminary biochemical examination suggested that the pink-blue pigment in A. eurystoma is part of a family of compounds (pocilloporin) responsible for the pink-blue colours in pocilloporid and acroporid corals. Pink-blue colour could be experimentally induced in A. eurystoma by tissue-to-tissue contacts between distressed and non-distressed allogeneic branches. PBSS was also induced in healthy coral tissue by contact with inert objects, e.g., by bandaging a branch with plastic strips. Any specific pink-blue colour spots faded within 1-3 months from onset. These results suggest that PBSS in A. eurystoma may not be considered a regular coral disease, but rather a locally induced syndrome caused by restricted environmental and/or biological stress conditions.     

Bleaching,disease and recovery in the threatened scleractinian coral Acropora palmata in St. John,US Virgin Islands: 2003–2010

Coral Reefs - A long-term study of the scleractinian coral Acropora palmata in the US Virgin Islands (USVI) showed that diseases, particularly white pox, are limiting the recovery of this...     

Corrected western Atlantic sea-level curve for the last 11,000 years based on calibrated <Superscript>14</Superscript>C dates from<Emphasis Type="Italic"> Acropora palmata</Emphasis> framework and intertidal mangrove peat

A corrected western Atlantic Holocene sea-level curve was constructed from 145 calibrated ¹⁴C and TIMS U-Th dates from shallow Acropora palmata framework and intertidal Rhizopora mangle peat from the Florida Keys, Belize, and the wider Caribbean. Data include both previously published and newly reported coral and peat dates. With the elevations of corals restricted to positions below sea level and those of peats to intertidal and higher levels, a curve bracketed by corals below and peat above effectively delineates the positions of a rising Holocene sea. From 3–11 ka, the corrected curve shifts progressively to older calibrated ages, reaching an ~1-kyr increase at –21 m MSL (mean sea level). Elevations and calibrated ages of samples from each locality in the wider Caribbean region constitute an important database for future refinement with glacio-hydro-isostatic elevation corrections from 3-D Earth models. In future studies of the history of western Atlantic coral reefs, scientists will be able to relate calibrated radiocarbon dates to this sea-level curve to determine paleo water depths and rates of sea-level rise.