Coral bleaching on high-latitude marginal reefs at Sodwana Bay,South Africa

Coral bleaching, involving the expulsion of symbiotic zooxanthellae from the host cells, poses a major threat to coral reefs throughout their distributional range. The role of temperature in coral bleaching has been extensively investigated and is widely accepted. A bleaching event was observed on the marginal high-latitude reefs of South Africa located at Sodwana Bay during the summer months of 2000. This was associated with increased sea temperatures with high seasonal peaks in summer and increased radiation in exceptionally clear water. The bleaching was limited to Two-mile Reef and Nine-mile Reef at Sodwana Bay and affected <12% of the total living cover on Two-mile Reef. Montipora spp., Alveopora spongiosa and Acropora spp. were bleached, as well as some Alcyoniidae (Sinularia dura, Lobophytum depressum, L. patulum). A cyclical increase in sea temperature (with a period of 5–6 years) was recorded during 1998–2000 in addition to the regional temperature increase caused by the El Niño Southern Oscillation phenomenon. The mean sea temperature increased at a rate of 0.27 °C year⁻¹ from May 1994 to April 2000. High maximum temperatures were measured (>29 °C). The lowest mean monthly and the mean maximum monthly temperatures at which coral bleaching occurred were 27.5 and 28.8 °C, respectively, while the duration for which high temperatures occurred in 2000 was 67 days at 27.5 °C (4 days at 28.8 °C). Increased water clarity and radiation appeared to be a synergistic cause in the coral bleaching encountered at Sodwana Bay.     

浙江桐庐冷坞二叠纪生物礁的发育模式

礁体底部具脉状层理的潮坪相碎屑沉积,礁体内部藻叠层岩夹层的存在,及礁体上部为煤系地层覆盖等都表明冷坞生物礁是一个典型的二叠纪岸礁;海绵骨架岩的存在表明它是个骨架型岸礁。     

Facies architecture of a Lower Cretaceous coral-rudist patch reef, Arizona

The Lower Cretaceous Mural Limestone marks the maximum marine incursion into southeast Arizona during Aptian-Albian time and records the middle Cretaceous transition from coral-dominated to rudist-bivalve dominated reefs. Upper Mural Limestone facies are most often dominated by corals. However, rudists form significant frameworks at some localities, one of which is described in this paper. The paleoenvironmental distribution of three potential reef-builders (corals, rudists, and ‘oysters’) were studied at this patch reef locality. Corals built the framework of the inner reef core. The rudist Petalodontia initially gained a foothold in sheltered areas among corals and subsequently built a framework in the outer reef core. Caprinid rudists formed mounds in the outer reef to back reef areas. The rudists Toucasia and Monopleura and the oyster-like bivalve Chondrodonta formed beds or were scattered in the reef-flank and shelf lagoon sediments and did not contribute to the reef framework.Upper Mural Limestone reefs are important examples of the coexistence of corals and rudists during this middle Cretaceous faunal transition period. This study supports the idea that rudist-bivalves initially colonized protected back-reef areas early in the Cretaceous and only later in the Cretaceous did rudists dominate reef frameworks.     

内蒙古哲斯敖包茅口期生物礁特征

内蒙古哲斯敖包茅口期发育典型的生物礁。礁体呈东西向展布,在空间上可明显地划分出后礁相、礁核相及前礁相。礁核相包括礁坪带、礁冠带和礁前缘带。各相带相互位置关系表明当时礁体南侧为滨岸方向,北侧为广海方向。礁体中化石极为丰富,可识别出不同的生物组合。生物组合的空间分布明显受生物礁相带控制,它们之间均为横向关系,反映了生物组合与水动力环境的统一性。     

The evolution of modern corals and their early history

Scleractinians are a group of calcified anthozoan corals, many of which populate shallow-water tropical to subtropical reefs. Most of these corals calcify rapidly and their success on reefs is related to a symbiotic association with zooxanthellae. These one-celled algal symbionts live in the endodermal tissues of their coral host and are thought responsible for promoting rapid calcification. The evolutionary significance of this symbiosis and the implications it holds for explaining the success of corals is of paramount importance. Scleractinia stands out as one of the few orders of calcified metazoans that arose in Triassic time, long after a greater proliferation of calcified metazoan orders in the Paleozoic. The origin of this coral group, so important in reefs of today, has remained an unsolved problem in paleontology. The idea that Scleractinia evolved from older Paleozoic rugose corals that somehow survived the Permian mass extinction persists among some schools of thought. Paleozoic scleractiniamorphs also have been presented as possible ancestors. The paleontological record shows the first appearance of fossils currently classified within the order Scleractinia to be in the Middle Triassic. These earliest Scleractinia provide a picture of unexpectedly robust taxonomic diversity and high colony integration. Results from molecular biology support a polyphyletic evolution for living Scleractinia and the molecular clock, calibrated against the fossil record, suggests that two major groups of ancestors could extend back to late Paleozoic time. The idea that Scleractinia were derived from soft-bodied, “anemone-like” ancestors that survived the Permian mass extinction, has become a widely considered hypothesis. The 14-million year Mesozoic coral gap stands as a fundamental obstacle to verification of many of these ideas. However, this obstacle is not a barrier for derivation of scleractinians from anemone-like, soft-bodied ancestors. The hypothesis of the ephemeral, “naked coral”, presents the greatest potential for solution of the enigma of the origin of scleractinians. It states that different groups of soft-bodied, unrelated “anemone-like” anthozoans gave rise to various calcified scleractinian-like corals through aragonitic biomineralization. Although there is evidence for this phenomenon being more universal in the mid-Triassic interval, following a lengthy Early Triassic post-extinction perturbation, it appears to have occurred at least three other times prior to this interval. This idea suggests that, because of ephemeral characteristics, the skeleton does not represent a clade of zoantharian evolution but instead represents a grade of organization. In the fossil record, skeletons may have appeared and disappeared at different times as some clades reverted to soft-bodied existence and these phenomena could account for notable gaps in the taxonomic and fossil record. A fuller understanding and possible solution to the problem of the origin of modern corals may be forthcoming. However, it will require synthesis of diverse kinds of data and an integration of findings from paleobiology, stratigraphy, molecular biology, carbonate geochemistry, biochemistry and invertebrate physiology.     

海南岛近海砗磲(Tridacninae)资源时空变化——以蜈支洲岛为例

为了解海南近岸砗磲资源动态变化,于蜈支洲岛周边海域选取5个代表性站位,自2017-2020年采用断面调查的方法,开展了砗磲资源评估、种群数量变化以及其环境相关性分析等,结果显示：（1）各站位砗磲密度为0-30.00×10^-2 ind./m²,且主要分布于3 m水深,在该水深区域,站位3和站位11砗磲密度最高,站位4次之,站位9和站位13最低,统计学分析表明砗磲密度与站位呈显著相关性（P<0.05）。（2）2017年,蜈支洲岛海域四种规格砗磲（壳长<5 cm、5-10 cm、10-15 cm和≥ 15 cm）均有分布,2018-2020年,未发现壳长≥ 15 cm的大规格个体。（3）尽管温度及各水质因子均与砗磲密度相关性不显著（P>0.05）,水体硝酸盐NO₃^-浓度与砗磲密度相关系数最高（0.29）。（4）砗磲主要分布于活珊瑚底质（66.67%）,其次为礁石（24.24%）,砂石底质最低（9.09%）。（5）砗磲外套膜RGB颜色参数值与周边底质颜色存在相关性,空间上,站位3的砗磲外套膜RGB颜色参数值与周边底质颜色相关性高于站位11;时间上,2020年砗磲外套膜颜色与周边底质B值相关系数R高于2017年（0.899 vs.0.712）。研究首次开展了海南岛近岸海域砗磲资源时空动态变化及影响因素研究,其结果可为砗磲资源保护提供数据支持。     

The geological characteristics of the large-and medium-sized gas fields in the South China Sea

By the end of 2019, more than 220 gas fields had been discovered in the South China Sea. In order to accurately determine the geological characteristics of the large-and medium-sized gas fields in the South China Sea, this study conducted a comprehensive examination of the gas fields. Based on the abundant available geologic and geochemical data, the distribution and key controlling factors of the hydrocarbon accumulation in the South China Sea were analyzed. The geological and geochemical features of the gas fields were as follows:(1) the gas fields were distributed similar to beads in the shape of a "C" along the northern, western, and southern continental margins;(2) the natural gas in the region was determined to be composed of higher amounts of alkane gas and less CO_2;(3) the majority of the alkane gas was observed to be coal-type gas;(4) the gas reservoir types included structural reservoirs, lithologic reservoirs, and stratigraphic reservoirs, respectively;(5) the reservoir ages were mainly Oligocene, Miocene, and Pliocene, while the lithology was mainly organic reef, with some sandstone deposits; and(6) the main hydrocarbon accumulation period for the region was determined to be the late Pliocene-Quaternary Period. In addition, the main controlling factors of the gas reservoirs were confirmed to have been the development of coal measures, sufficient thermal evolution, and favorable migration and accumulation conditions.     

Spatio-temporal variability of benthic macroalgae in a coral reef system highly influenced by fluvial discharge: Veracruz,Gulf of Mexico

The Veracruz Reef System, in the southern Gulf of Mexico, is a suitable area for the study of the temporal and spatial variability of macroalgae abundance, at reef settings influenced by the fluvial discharge of the Jamapa River, and by human activities in the city and port of Veracruz. With this purpose, the bottom cover of each morpho-functional group of benthic macroalgae (frondoses, turf, and crustose corallines), and hermatypic corals, was determined at ten selected coral reefs, on a seasonal basis (rainy and dry seasons), for the 2009–2015 period. The average cover of benthic macroalgae was high (53.1%), with turf as the dominant morpho-functional group (31.9%), as in several reef ecosystems in the tropical Atlantic, followed by crustose corallines (15.2%), and frondoses (6.1%). Although turf macroalgae is dominant, due to their high temporal and spatial variability, the Veracruz Reef System could not be considered to be in a stable state, but just in an intermediate unstable equilibrium state, which is highly influenced by a high sediment load. As expected, nearshore reefs presented higher macroalgae covers, and unexpectedly, the outer-shelf reefs presented the highest cover of frondoses. Despite fluvial discharge influence, no differences in cover were found between the rainy and dry seasons. There was a negative and significantly correlation between the cover of frondoses and turf, which suggests that the driver/s of the abundance of these macroalgae, act in opposite ways for each group. Three clusters of reefs, defined by community structure and conservation degree, were determined: nearshore or degraded, offshore or moderately conserved, and conserved; and the entire Veracruz Reef System is considered to be in a moderately state of conservation.     

Effects of reef morphology variations on wave processes over fringing reefs

Many low-lying tropical and sub-tropical atolls fringed by coral reefs are susceptible to coastal inundation during extreme wave events. Previous studies have shown that the infragravity (IG) wave is the dominant component of shoreline run-up compared to the sea and swell (SS) wave and the wave-induced setup. To better understand both the SS and IG wave dynamics over a fringing reef with various morphologies, a series of laboratory experiments were conducted in a wave flume based on an idealized fringing reef profile. The shoreline responses of waves to different reef morphologies with/without the reef crest, the lagoon and the reef surface roughness were examined. IG wave resonance on the reef flat was identified by a spectral analysis of the shoreline wave records. Subsequently, a numerical model based on the Boussinesq equations was validated by the experimental data. The model was then applied to investigate the impacts of varying reef morphologic features (fore-reef slope, reef-crest width, lagoon width, and reef roughness coefficient) on the shoreline wave motions.