Extreme climatic events reduce ocean productivity and larval supply in a tropical reef ecosystem

Increasing ocean temperatures due to global warming are predicted to have negative effects on coral reef fishes. El Niño events are associated with elevated water temperatures at large spatial (1000s of km) and temporal (annual) scales, providing environmental conditions that enable temperature effects on reef fishes to be tested directly. We compared remote sensing data of sea surface temperature (SST) anomalies, surface current flow and chlorophyll‐a (Chl‐a) concentration with monthly patterns in larval supply of coral reef fishes in nearshore waters around Rangiroa Atoll (French Polynesia) from January 1996 to March 2000. This time included an intense El Niño (April 1997–May 1998) event between two periods of La Niña (January–March 1996 and August 1998–March 2000) conditions. There was a strong relationship between the timing of the El Niño event, current flow, ocean productivity (as measured by Chl‐a) and larval supply. In the warm conditions of the event, there was an increase in the SST anomaly index up to 3.5 °C above mean values and a decrease in the strength of the westward surface current toward the reef. These conditions coincided with low concentrations of Chl‐a (mean: 0.06 mg m^?3, SE ± 0.004) and a 51% decline in larval supply from mean values. Conversely, during strong La Niña conditions when SST anomalies were almost 2 °C below mean values and there was a strong westward surface current, Chl‐a concentration was 150% greater than mean values and larval supply was 249% greater. A lag in larval supply suggested that productivity maybe affecting both the production of larvae by adults and larval survival. Our results suggest that warming temperatures in the world's oceans will have negative effects on the reproduction of reef fishes and survival of their larvae within the plankton, ultimately impacting on the replenishment of benthic populations.     

维生素C和酸应激对中华鳖幼鳖血清补体C3和C4含量的影响

为研究维生素C对中华鳖(Pelodiscus sinensis)血清补体C3和C4的影响及其在酸应激条件下的变化,我们设置了6个实验组,饵料中维生素C的添加量依次为0、250、500、2500、5000和10000mg／kg,喂食4周后取其血清,用透射比浊法测定酸应激前后中华鳖血清补体C3和C4的含量。结果表明,维生素C添加量为250mg／kg时,血清补体C3的含量与对照组间没有明显不同;维生素C添加量为500、2500、5000和10000mg／kg的4组,血清补体C3的含量明显高于对照组和维生素C添加量为250mg／kg组;维生素C添加量为500mg／kg的一组,血清补体CA含量明显高于其它5组;维生素C添加量为250mg／kg组明显高于10000mg／kg组。酸应激后,补体C3的含量没有明显下降,将维生素C添加量为0、250和500mg／kg的三组并为一组处理,则应激后有明显下降。维生素C添加量为0、250和500mg／kg的3组,血清补体CA的含量在酸应激后明显下降,而维生素C添加量为2500、5000和10000mg／kg的3组,应激后血清补体C4没有明显变化。维生素C和酸应激对中华鳖血清补体C3和CA含量的影响没有交互作用。这说明,维生素C在一定剂量范围内,能提高中华鳖血清补体C3和CA的水平,酸应激能导致其含量降低,而高剂量的维生素C对其下降有颉颃作用[动物学报49(6)：769～774,2003]。     

Metabolic interactions between algal symbionts and invertebrate hosts

Some invertebrates have enlisted autotrophic unicellular algae to provide a competitive metabolic advantage in nutritionally demanding habitats. These symbioses exist primarily but not exclusively in shallow tropical oceanic waters where clear water and low nutrient levels provide maximal advantage to the association. Mostly, the endosymbiotic algae are localized in host cells surrounded by a host-derived membrane (symbiosome). This anatomy has required adaptation of the host biochemistry to allow transport of the normally excreted inorganic nutrients (CO₂, NH₃ and PO₄³⁻) to the alga. In return, the symbiont supplies photosynthetic products to the host to meet its energy demands. Most attention has focused on the metabolism of CO₂ and nitrogen sources. Carbon-concentrating mechanisms are a feature of all algae, but the products exported to the host following photosynthetic CO₂ fixation vary. Identification of the stimulus for release of algal photosynthate in hospite remains elusive. Nitrogen assimilation within the symbiosis is an essential element in the host's control over the alga. Recent studies have concentrated on cnidarians because of the impact of global climate change resulting in coral bleaching. The loss of the algal symbiont and its metabolic contribution to the host has the potential to result in the transition from a coral-dominated to an algal-dominated ecosystem.     

Effects of group behavior in the predatory raid on damselfish nests by the false cleanerfish Aspidontus taeniatus

The false cleanerfish Aspidontus taeniatus, which resembles the bluestreak cleaner wrasse Labroides dimidiatus, is one of the best-known examples of mimicry in vertebrates. This mimicry system has been viewed as an aggressive mimicry to bite fish fins. However, recent field studies have reported that large individuals of the false cleanerfish often form groups and jointly raid damselfish nests to eat eggs that are guarded by their parents. The benefits of group behavior have been reported in a variety of animals. In the case of false cleanerfish, parental defense of territorial damselfishes is the main factor that constrains the availability of nutritionally valuable food resources. Here, we conducted field observations on the reefs of Okinawa, and found that the false cleanerfish formed groups of 2–12 individuals when they raided breeding nests of 13 species of damselfishes (Pomacentridae) and one species of triggerfish (Balistidae). Since the cleaner wrasse does not form such groups, the feeding groups of the false cleanerfish are assumed to reduce the effectiveness of mimicry. However, our results showed that the group behavior has two effects: a dilution effect, which reduces the risk of being attacked by egg-guarding fish, and an increase in foraging efficiency. We conclude that the false cleanerfish need to form foraging groups during egg-eating because the mimicry has no effect on parental damselfishes.     

Fish feeding guilds along a gradient of bay biotopes and coral reef depth zones

The study of fish feeding guild structure is a useful method to compare fish communities of complex marine ecosystems. Guild structure was determined in four coral reef depth zones, viz. the fringing reef at depths of 2, 5, 10, and 15 m, as well as in seven shallow-water biotopes within a single bay, viz. notches in fossil reef rock, mangroves, fossil reef boulders, seagrass beds, algal beds at a depth of 2 m, algal beds at a depth of 5 m, and the channel. The study was done in an inland bay on the Caribbean island of Curaçao, using a visual census technique. Total fish densities within the different feeding guilds varied considerably between the biotopes, and were generally higher in the reef biotopes and on the boulders than in the remaining bay biotopes. Cluster analysis revealed that the greatest dissimilarity in guild structures in terms of fish densities was that between the algal beds and all other biotopes, followed by that between the reef depth zones and other bay biotopes (notches, mangroves, seagrass beds, channel). The species composition of the guilds also differed considerably among the various biotopes. Species richness within the various guilds showed much smaller differences between the biotopes, but was generally somewhat higher in the reef biotopes. Cluster analysis of guild structures in terms of species richness revealed little dissimilarity among the various biotopes. The coral reef was dominated by omnivores and zooplanktivores, whereas the bay was dominated by zoobenthivores and herbivores. Differences in guild structure between the bay and the adjacent reef indicate differences in food availability.     

Cycles of coral reef ‘turn‐on’, rapid growth and ‘turn‐off’ over the past 8500 years: a context for understanding modern ecological states and trajectories

Human activities threaten reef ecosystems globally, forcing ecological change at rates and scales regarded as unprecedented in the Holocene. These changes are so profound that a cessation of reef accretion (reef ‘turn‐off’) and net erosion of reef structures is argued by many as the ultimate and imminent trajectory. Here, we use a regional scale reef growth dataset, based on 76 core records (constrained by 211 radiometric dates) from 22 reefs along and across the inner‐shelf of the Great Barrier Reef, Australia, to examine the timing of different phases of reef initiation (‘turn‐on’), growth and ‘turn‐off’ during the Holocene. This dataset delineates two temporally discrete episodes of reef‐building over the last 8500 years: the first associated with the Holocene transgression‐early highstand period [～8.5–5.5 k calibrated years bp (cal ybp )]; the second since ～2.3 k cal ybp . During both periods, reefs accreted rapidly to sea level before entering late evolutionary states – states naturally characterized by reduced coral cover and low accretion potential – and a clear hiatus occurs between these reef‐building episodes for which no records of reef initiation exist. These transitions mimic those projected under current environmental disturbance regimes, but have been driven entirely by natural forcing factors. Our results demonstrate that, even through the late Holocene, reef health and growth has fluctuated through cycles independent of anthropogenic forcing. Consequently, degraded reef states cannot de facto be considered to automatically reflect increased anthropogenic stress. Indeed, in many cases degraded or nonaccreting reef communities may reflect past reef growth histories (as dictated by reef growth–sea level interactions) as much as contemporary environmental change. Recognizing when changes in reef condition reflect these natural ‘turn‐on’– growth –‘turn‐off’ cycles and how they interact with on‐going human disturbance is critical for effective coral reef management and for understanding future reef ecological trajectories.     

珊瑚礁生态系的一般特点

随着工业化和城市化的不断发展 ,陆地上的资源在飞速地被消耗掉 ,生态环境也受到了严重的破坏 ,人们迫切地需要寻找新的资源和更好的环境 ,海洋因此成为首选。珊瑚礁生态系是海洋中生产力水平极高的生态系之一 ,被称为是“热带海洋沙漠中的绿洲” ,“海洋中的热带雨林”。由于其在全球海洋的过程与资源方面具有重要地位 ,而目前正受到生态退化的威胁 ,因而得到更多的关注。国际上将 1997年定为“珊瑚礁年”以普及人们的珊瑚礁保护与恢复意识和责任。本文介绍了珊瑚礁生态系的一些特点 ,分析了影响珊瑚礁生态系的自然和人为因素 ,并提出了保…     

Geological history and oceanography of the Indo‐Malay Archipelago shape the genetic population structure in the false clown anemonefish (Amphiprion ocellaris)

Like many fishes on coral reefs, the false clown anemonefish, Amphiprion ocellaris, has a life history with two different phases: adults are strongly site attached, whereas larvae are planktonic. Therefore, the larvae have the potential to disperse, but the degree of dispersal potential depends primarily on the period of the larval stage, which is only 8–12 days in A. ocellaris. In this study, we investigated the genetic population structure and gene flow in A. ocellaris across the Indo‐Malay Archipelago by analysing a fragment of the mitochondrial control region. Population genetic analysis, using amova , revealed a significant and high overall Φ_ST‐value of 0.241 (P < 0.001), clearly showing limited gene flow. Haplotype network analysis detected eight distinct clades corresponding mainly to different geographical areas, which were most probably separated during sea level low stands in the Pleistocene. The distribution of the clades among the different populations indicated slow partial re‐mixing mainly in the central region of the archipelago. Major surface currents seem to facilitate larval dispersal, indicated by higher connectivity along major surface currents in the region (e.g. Indonesian Throughflow). Four main groups were found by the hierarchical amova within the archipelago. These different genetic lineages should be managed and protected as separate ornamental fishery stocks and resource contributing to the genetic diversity of the area. Regarding the high diversity and the differentiation among areas within the Indo‐Malay Archipelago of A. ocellaris populations, the centre‐of‐origin theory is supported to be the main mechanism by which the high biodiversity evolved in this area.     

The phylogeography and connectivity of the latitudinally widespread scleractinian coral Plesiastrea versipora in the Western Pacific

Whereas terrestrial animal populations might show genetic connectivity within a continent, marine species, such as hermatypic corals, may have connectivity stretching to all corners of the planet. We quantified the genetic variability within and among populations of the widespread scleractinian coral, Plesiastrea versipora along the eastern Australian seaboard (4145 km) and the Ryukyu Archipelago (Japan, 681 km) using sequences of internal transcribed spacers (ITS1-2) from ribosomal DNA. Geographic patterns in genetic variability were deduced from a nested clade analysis (NCA) performed on a parsimony network haplotype. This analysis allowed the establishment of geographical associations in the distribution of haplotypes within the network cladogram, therefore allowing us to deduce phylogeographical patterns based under models of restricted gene flow, fragmentation and range expansion. No significant structure was found among Ryukyu Archipelago populations. The lack of an association between the positions of haplotypes in the cladogram with geographical location of these populations may be accounted for by a high level of gene flow of P. versipora within this region, probably due to the strong Kuroshio Current. In contrast, strong geographical associations were apparent among populations of P. versipora along the south-east coast of Australia. This pattern of restricted genetic connectivity among populations of P. versipora on the eastern seaboard of Australia seems to be associated with the present surface ocean current (the East Australian Current) on this side of the south-western Pacific Ocean.     

Endosymbiotic flexibility associates with environmental sensitivity in scleractinian corals

Flexibility in biological systems is seen as an important driver of macro-ecosystem function and stability. Spatially constrained endosymbiotic settings, however, are less studied, although environmental thresholds of symbiotic corals are linked to the function of their endosymbiotic dinoflagellate communities. Symbiotic flexibility is a hypothesized mechanism that corals may exploit to adapt to climate change. This study explores the flexibility of the coral–Symbiodinium symbiosis through quantification of Symbiodinium ITS2 sequence assemblages in a range of coral species and genera. Sequence assemblages are expressed as an index of flexibility incorporating phylogenetic divergence and relative abundance of Symbiodinium sequences recovered from the host. This comparative analysis reveals profound differences in the flexibility of corals for Symbiodinium, thereby classifying corals as generalists or specifists. Generalists such as Acropora and Pocillopora exhibit high intra- and inter-species flexibility in their Symbiodinium assemblages and are some of the most environmentally sensitive corals. Conversely, specifists such as massive Porites colonies exhibit low flexibility, harbour taxonomically narrow Symbiodinium assemblages, and are environmentally resistant corals. Collectively, these findings challenge the paradigm that symbiotic flexibility enhances holobiont resilience. This underscores the need for a deeper examination of the extent and duration of the functional benefits associated with endosymbiotic diversity and flexibility under environmental stress.