Genotype and attachment technique influence the growth and survival of line nursery corals

The Caribbean staghorn coral, Acropora cervicornis, was once a dominant habitat creating coral, but its populations have declined dramatically in recent decades. Numerous restoration efforts now utilize coral gardening techniques to cultivate this species, growing colonies on fixed structures or from line/suspended nurseries. Line nurseries have become increasingly popular because of their small footprint and ease of use, replacing fixed structures in many nurseries. To evaluate the efficacy of the line technique, this study evaluated growth, condition, and survivorship of A. cervicornis nursery colonies of three distinct genotypes grown via two line nursery techniques (suspended and direct line attachment [vertical]). Direct line attachment of nursery colonies resulted in poor survival (43%) and growth (9.5 ± 1.33 cm/year), whereas suspended culture had 100% survival and increased growth (61.1 ± 4.19 cm/year). Suspended culture had significantly reduced disease prevalence and prevented colony predation. Suspended coral growth was also comparable to a neighboring fixed structure nursery (55.2 ± 7.86 cm/year), and found to be as effective in propagating corals as fixed structures.     

Competition between scleractinian corals and macroalgae: An experimental investigation of coral growth, survival and reproduction

Macroalgae are a major component of many coral reef flat communities, and are potentially major competitors with corals. The influence of macroalgae on several demographic parameters of four species of scleractinian coral by means of an algal clearance experiment was examined to determine specifically if macroalgae are affecting coral cover, growth, fecundity, fission, survivorship and recruitment. Also investigated were patterns of natural encounters between corals and algae.

Algal cover at the study site ranged from 41 to 56%, and coral cover from 8 to 10%. In total, 92 ± 4 ( )% of coral colonies were in contact with one or more species of macroalgae. Changes in coral cover were significantly affected by the presence of macroalgae, with cover of Acropora species increasing faster in areas from which algae had been cleared compared to control areas where algae had not been removed, although this pattern did not occur for Pocillopora damicornis (Linnaeus). Similarly, growth of individual colonies was faster when macroalgae were absent for three Acropora species but not for P. damicornis. There were no differences detected in rates of fission or survivorship of corals between algal clearance and control treatments, although there were high levels of variability in both of these parameters. Fecundity of Acropora palifera (Lamarck), the only species examined, was approximately double in colonies in cleared plots compared to those in control plots with macroalgae present. As no recruitment occurred throughout the 2-yr study, it remains to be determined how macroalgae effect the settlement of coral larvae. The results show that macroalgae can have a major influence on the demography of scleractinian corals.     

珊瑚人工繁育技术研究进展

在气候变化、环境污染以及人工采集等因素致使珊瑚野生资源不断衰退的背景下,开展珊瑚的人工繁育是修复珊瑚生态系统、保护生物多样性、减少野生珊瑚采集的主要出路之一.本文对国内外珊瑚人工繁育技术和研究进展进行综述,探讨了珊瑚有性和无性繁殖技术以及原地和异地繁育技术的特点与不足;重点从光照、水流、营养盐、微量元素、非自养珊瑚品种的饵料,以及适宜的微生物环境等方面总结了循环海水系统繁育珊瑚的研究进展,并对我国珊瑚研究现状进行了总结.光照是珊瑚水族箱养殖或异地繁殖的关键因素之一,不同种类的珊瑚对光照强度和色温有不同的需求,珊瑚照明创新技术的发展及其能耗对于珊瑚异地繁育非常重要.此外,珊瑚对铵氮、硝氮、亚硝氮及磷酸盐等营养盐的变化非常敏感,各类机械、化学和生物的技术被应用于降低培养体系中营养盐的含量.尽管珊瑚循环海水养殖系统在照明、水流和营养盐控制方面已经有了长足的进步,珊瑚人工繁育仍然任重道远.将来的突破方向在于有性繁殖、性状改造与疾病防治技术等方面.     

Recruitment hotspots and bottlenecks mediate the distribution of corals on a Caribbean reef

Recruitment hotspots are locations where organisms are added to populations at high rates. On tropical reefs where coral abundance has declined, recruitment hotspots are important because they have the potential to promote population recovery. Around St. John, US Virgin Islands, coral recruitment at five sites revealed a hotspot that has persistent for 14 years. Recruitment created a hotspot in density of juvenile corals that was 600 m southeast of the recruitment hotspot. Neither hotspot led to increased coral cover, thus revealing the stringency of the demographic bottleneck impeding progression of recruits to adult sizes and preventing population growth. Recruitment hotspots in low-density coral populations are valuable targets for conservation and sources of corals for restoration.     

Isolation and characterization of microsatellite loci in Aspergillus sydowii, a pathogen of Caribbean sea fan corals

Here we report on nine microsatellite loci designed for Aspergillus sydowii, a widely distributed soil saprobe that is also the pathogenic agent of aspergillosis in Caribbean sea fan corals. Primers were tested on 20 A. sydowii isolates from the Caribbean, 17 from diseased sea fans and three from environmental sources. All loci were polymorphic and exhibited varying degrees of allelic diversity (three to nine alleles). Gene diversity (expected heterozygosity) ranged from 0.353 to 0.821. These primers will enable future research into the epidemiology of A. sydowii as an emergent infectious disease.     

The presence of the cyanobacterial toxin microcystin in black band disease of corals

Black band disease (BBD) is a migrating, cyanobacterial dominated, sulfide-rich microbial mat that moves across coral colonies lysing coral tissue. While it is known that BBD sulfate-reducing bacteria contribute to BBD pathogenicity by production of sulfide, additional mechanisms of toxicity may be involved. Using HPLC/MS, the cyanotoxin microcystin was detected in 22 field samples of BBD collected from five coral species on nine reefs of the wider Caribbean (Florida Keys and Bahamas). Two cyanobacterial cultures isolated from BBD, Geitlerinema and Leptolyngbya sp. contained microcystin based on HPLC/MS, with toxic activity confirmed using the protein phosphatase inhibition assay. The gene mcyA from the microcystin synthesis complex was detected in two field samples and from both BBD cyanobacterial cultures. Microcystin was not detected in six BBD samples from a different area of the Caribbean (St Croix, USVI) and the Philippines, suggesting regional specificity for BBD microcystin. This is the first report of the presence of microcystin in a coral disease.     

Regulation of release of antibacterials from stressed scleractinian corals

Recently, we showed that mechanical stress on scleractinian (stony) corals caused a rapid release of antibacterial material (referred to as coral antibacterial activity, or CAA), which killed various bacterial species, including the coral pathogen Vibrio coralliilyticus . We now report on studies on the regulation of CAA release from stressed scleractinian corals. Corals can repeatedly release highly active CAA as a result of sequential stress inductions. Coral fragments were transferred 19 times from one beaker into another with a stress induction each time after 10 min. There was a decrease in the level of antibacterial activity released during the first four to five transfers. After the fifth transfer, the corals kept releasing CAA for the rest of the experiment with no significant decrease. Apparently, the release of CAA is downregulated by feedback inhibition, depending on the concentration of CAA in the surrounding water. By separating CAA-treated V. coralliilyticus from the surrounding water, it was shown that CAA was bound irreversibly to bacterial cells in a stoichiometric manner. Approximately 4 × 10² bacterial cells were sufficient to bind 1 U of CAA. Resident coral bacteria were more resistant to CAA than bacteria isolated from seawater, suggesting an ecological role for CAA. CAA release was obtained from corals after removal of the mucus layer, and the mucus itself contained antibacterial activity.     

The vermetid gastropod Dendropoma maximum reduces coral growth and survival

Coral reefs are one of the most diverse systems on the planet; yet, only a small fraction of coral reef species have attracted scientific study. Here, we document strong deleterious effects of an often overlooked species—the vermetid gastropod, Dendropoma maximum—on growth and survival of reef-building corals. Our surveys of vermetids on Moorea (French Polynesia) revealed a negative correlation between the density of vermetids and the per cent cover of live coral. Furthermore, the incidence of flattened coral growth forms was associated with the presence of vermetids. We transplanted and followed the fates of focal colonies of four species of corals on natural reefs where we also manipulated presence/absence of vermetids. Vermetids reduced skeletal growth of focal corals by up to 81 per cent and survival by up to 52 per cent. Susceptibility to vermetids varied among coral species, suggesting that vermetids could shift coral community composition. Our work highlights the potential importance of a poorly studied gastropod to coral dynamics.     

Regional decline in growth rates of massive Porites corals in Southeast Asia

This study reports the first well‐replicated analysis of continuous coral growth records from warmer water reefs (mean annual sea surface temperatures (SST) >28.5 °C) around the Thai–Malay Peninsula in Southeast Asia. Based on analyses of 70 colonies sampled from 15 reefs within six locations, region‐wide declines in coral calcification rate (ca. 18.6%), linear extension rate (ca. 15.4%) and skeletal bulk density (ca. 3.9%) were observed over a 31‐year period from 1980 to 2010. Decreases in calcification and linear extension rates were observed at five of the six locations and ranged from ca. 17.2–21.6% and ca. 11.4–19.6%, respectively, whereas decline in skeletal bulk density was a consequence of significant reductions at only two locations (ca. 6.9% and 10.7%). A significant link between region‐wide growth rates and average annual SST was found, and Porites spp. demonstrated a high thermal threshold of ca. 29.4 °C before calcification rates declined. Responses at individual locations within the region were more variable with links between SST and calcification rates being significant at only four locations. Rates of sea temperature warming at locations in the Andaman Sea (Indian Ocean) (ca. 1.3 °C per decade) were almost twice those in the South China Sea (Pacific Ocean) (ca. 0.7 °C per decade), but this was not reflected in the magnitude of calcification declines at corresponding locations. Considering that massive Porites spp. are major reef builders around Southeast Asia, this region‐wide growth decline is a cause for concern for future reef accretion rates and resilience. However, this study suggests that the future rates and patterns of change within the region are unlikely to be uniform or dependent solely on the rates of change in the thermal environment.     

Impacts of remotely sensed environmental drivers on coral outplant survival

Globally, coral reefs are degrading due to a variety of stressors including climate change and pollution. Active restoration is an important effort for sustaining coral reefs where, typically, coral fragments are outplanted onto degraded reefs. Coral outplants, however, can experience mortality in response to a range of stressors. We pair results of outplant monitoring observations with satellite‐based measurements of multiple oceanographic variables to estimate the relative importance of each driver to coral outplant survival. We find that when considering mean environmental conditions experienced by outplants during the monitoring period, particulate organic carbon (POC) levels are most important in determining outplant survival, with certain levels of POC beneficial for outplants. Sea surface temperature anomalies (SSTA) are also important determinants of outplant survival, where survival is greatest in regions with minimal or slightly negative anomalies. Survival also increases with increasing distance to land, likely due to a reduction in negative ridge‐to‐reef effects on coral outplants. When considering the range (min–max) of environmental conditions experienced during the monitoring period, large fluctuations in photosynthetically active radiation (PAR) and POC are most important in determining outplant survival. Increasing outplant depth can help to counter the negative impacts of large fluctuations in environmental variables. We find that a variety of remotely sensed oceanographic variables have significant impacts on survival and should be considered in coral restoration planning to help evaluate potential restoration sites and ultimately maximize coral outplant survival.     

Chemical defensive substances of soft corals and gorgonians

Despite lack of efficient physical protection in the highly competitive and hostile environment, the marine invertebrates including soft corals and gorgonians can survive, mainly relying on their chemical defensive system by a series of secondary metabolites accumulating in their bodies or releasing to their surroundings. The chemical defensive functions of these secondary metabolites were found to serve as antipredatory, antimicrobial, allelopathy and antifouling agents. Study on chemical defensive substances from corals and gorgonians is one of the most important topics in marine chemical ecology. The research results could help us to understand the chemical ecological relationships between corals and their surrounding organisms. The research strategy and methodology played an enlightening role in the discovery of bioactive natural products and the generation of new drug lead compounds from marine sources. The chemical defensive substances from soft corals and gorgonians were reviewed. This review focused on the structures of these secondary metabolites as well as their functions including antipredatory, allelopathy and antifouling activities.     

共生珊瑚异养营养研究进展

共生珊瑚的异养营养指有虫黄藻共生的珊瑚在同化作用过程中,除通过虫黄藻光合作用获取营养之外,还可以从外界环境中直接摄取现成的有机物,经消化吸收后转变为自身的组成物质或储存为能量.国内外异地养殖或繁育虫黄藻共生珊瑚的研究多集中在光照、水流、水质等条件对珊瑚生长的影响,对共生珊瑚异养营养需求与供应方面的关注较少.本文从共生珊瑚异养营养来源、影响共生珊瑚异养营养供应的因素以及研究手段等方面,对国内外研究进展进行了综述,探讨异养营养供应对共生珊瑚的意义.总的来说,目前共生珊瑚异养营养的研究尚处于起步阶段,不论是研究方法或者珊瑚选择摄食的内在机制,都需要深入探究.     

Ecological impacts of coral gardening outplanting in the Maldives

As coral reefs continue to degrade at an alarming rate, coral restoration efforts are increasing worldwide in an attempt to keep up with the global challenge of preserving these iconic ecosystems and the many services they provide. Coral gardening, the farming and outplanting of coral fragments, is a commonly applied practice; however, regional validation is required before upscaling can be considered. This study follows up from the successful farming of fragments in mid-water rope nurseries, by reporting on the successive outplanting of these corals. Specifically, 60 Pocillopora verrucosa colonies were outplanted to a degraded reef at different depths (1–12 m), applying three arrangement patterns (equal, clustered, random). After 1 year, 72% were considered successfully outplanted (alive and still attached), with detachment being the main challenge at wave-impacted shallow depths, while loose coral rubble caused more partial mortality at depth. Outplanting stress was observed at 1–6 m depth, but had no impact on survival or growth. Drupella sp. predation was most common at 3 m and 79% of colonies hosted mutualistic fauna after 1 year. Outplanting significantly benefitted the reef environment with a higher fish abundance and diversity along with a higher increase in natural coral cover (H = 2.7; 6.2% increase) in comparison with the control sites. These are promising results, considering that the restoration site has shown little natural recovery in the last few years (coral cover <4%). We hope that our findings provide useful initial insights and help to guide effective restoration practices in the Maldives.     

Macroalgae reduces survival of nursery‐reared Acropora corals in the Florida reef tract

Recent declines in coral populations along the Florida reef tract have prompted the establishment of coral restoration programs which raise coral species, such as the threatened Acropora cervicornis, in nurseries ready for outplanting. Large numbers of nursery‐reared coral colonies have been outplanted along the Florida reef tract in recent years, yet few studies have characterized benthic habitats that are considered optimal for colony survival. In 2016, we surveyed 23 A. cervicornis restoration sites, located at six different reefs in the upper Florida Keys. We examined the condition of the outplanted corals and quantified the benthic assemblages adjacent to the outplanted coral colonies. We found that where A. cervicornis survived for more than 1 year, the substrate significantly supported less brown macroalgae of the genus Dictyota than at sites where A. cervicornis had died. Coral survival was highest at sites with less than 15% Dictyota cover. These results suggest that the habitat conditions that supported Dictyota spp. were not conducive to A. cervicornis growth and survival. Restoration practitioners should avoid attaching nursery‐raised corals to substrate with Dictyota spp. cover greater than 15%.     

Large‐scale coral reef rehabilitation after blast fishing in Indonesia

The severely degraded condition of many coral reefs worldwide calls for active interventions to rehabilitate their physical and biological structure and function, in addition to effective management of fisheries and no‐take reserves. Rehabilitation efforts to stabilize reef substratum sufficiently to support coral growth have been limited in size. We documented a large coral reef rehabilitation in Indonesia aiming to restore ecosystem functions by increasing live coral cover on a reef severely damaged by blast fishing and coral mining. The project deployed small, modular, open structures to stabilize rubble and to support transplanted coral fragments. Between 2013 to 2015, approximately 11,000 structures covering 7,000 m² were deployed over 2 ha of a reef at a cost of US$174,000. Live coral cover on the structures increased from less than 10% initially to greater than 60% depending on depth, deployment date and location, and disturbances. The mean live coral cover in the rehabilitation area in October 2017 was higher than reported for reefs in many other areas in the Coral Triangle, including marine protected areas, but lower than in the no‐take reference reef. At least 42 coral species were observed growing on the structures. Surprisingly, during the massive coral bleaching in other regions during the 2014–2016 El Niño–Southern Oscillation event, bleaching in the rehabilitation area was less than 5% cover despite warm water (≥30°C). This project demonstrates that coral rehabilitation is achievable over large scales where coral reefs have been severely damaged and are under continuous anthropogenic disturbances in warming waters.     

Chemical defensive substances of soft corals and gorgonians

Despite lack of efficient physical protection in the highly competitive and hostile environment, the marine invertebrates including soft corals and gorgonians can survive, mainly relying on their chemical defensive system by a series of secondary metabolites accumulating in their bodies or releasing to their surroundings. The chemical defensive functions of these secondary metabolites were found to serve as antipredatory, antimicrobial, allelopathy and antifouling agents. Study on chemical defensive substances from corals and gorgonians is one of the most important topics in marine chemical ecology. The research results could help us to understand the chemical ecological relationships between corals and their surrounding organisms. The research strategy and methodology played an enlightening role in the discovery of bioactive natural products and the generation of new drug lead compounds from marine sources. The chemical defensive substances from soft corals and gorgonians were reviewed. This review focused on the structures of these secondary metabolites as well as their functions including antipredatory, allelopathy and antifouling activities.