How marine currents influenced the widespread natural overseas dispersal of reptiles in the Western Indian Ocean region

In a recent contribution to this journal, Wilmé et al. (2016) proposed that the giant tortoises of the islands of the Western Indian Ocean (WIO: Aldabra, the Mascarenes, and the Granitic Seychelles) might have originated from translocation by early Austronesian sailors. Prompted by this paper we review recent literature and show that natural overseas dispersal was remarkably widespread in the colonization history of terrestrial reptiles in the WIO region. Almost 90% of the successful colonization events are supported by prevailing marine surface currents. However, these currents may change over geological (and evolutionary) time‐scales, and eddies and counter‐currents may facilitate transport against the main current direction. We review the cases of the extant and extinct WIO giant tortoises and suggest that the current distribution of all lineages can be convincingly explained by overseas dispersal.     

Two peculiar new genera of Typhloplanoida from the Western Indian Ocean

Three new species and two new genera of Typhloplanoida from the Western Indian Ocean are described. Feanora brevicirrus gen. et.sp. n. is a member of the Trigonostomidae von Graff, 1905 sensu Den Hartog, 1964. It has a cirrus, paired ovovitellaria and an undifferentiated afferent duct. An excentric bursa opens in the fecundatorium and a large ovoid vesicle enters the afferent duct in its distal part. Gaziella pileola gen. et sp. n. and G. lacertosa sp.n. are two new members of the Promesostomidae Den Hartog, 1964. They have a long cirrus, ovovitellaria and a long muscular female duct with two excentrically placed sperm-receiving vesicles. Their most striking feature is the proboscis-like structure. Feanora and Gaziella are provisionally considered as genera incertae sedis within the resp. families.     

Gene expression under chronic heat stress in populations of the mustard hill coral (Porites astreoides) from different thermal environments

Recent evidence suggests that corals can acclimatize or adapt to local stress factors through differential regulation of their gene expression. Profiling gene expression in corals from diverse environments can elucidate the physiological processes that may be responsible for maximizing coral fitness in their natural habitat and lead to a better understanding of the coral's capacity to survive the effects of global climate change. In an accompanying paper, we show that Porites astreoides from thermally different reef habitats exhibit distinct physiological responses when exposed to 6 weeks of chronic temperature stress in a common garden experiment. Here, we describe expression profiles obtained from the same corals for a panel of 9 previously reported and 10 novel candidate stress response genes identified in a pilot RNA‐Seq experiment. The strongest expression change was observed in a novel candidate gene potentially involved in calcification, SLC26, a member of the solute carrier family 26 anion exchangers, which was down‐regulated by 92‐fold in bleached corals relative to controls. The most notable signature of divergence between coral populations was constitutive up‐regulation of metabolic genes in corals from the warmer inshore location, including the gluconeogenesis enzymes pyruvate carboxylase and phosphoenolpyruvate carboxykinase and the lipid beta‐oxidation enzyme acyl‐CoA dehydrogenase. Our observations highlight several molecular pathways that were not previously implicated in the coral stress response and suggest that host management of energy budgets might play an adaptive role in holobiont thermotolerance.     

Preliminary analysis of bacterial diversity associated with the Porites coral from the Arabian sea

It is widely reported that coral reefs are suffering degradation from a combination of stresses. We have previously reported the use of genomic tools in the study of environmental impact assessment and hypothesize that monitoring the bacterial diversity associated with a coral would indicate changes in its health before visible damage occurs. This study analyzes the bacterial diversity associated with Porites coral collected from two sites in the Arabian Sea using culture independent techniques. Two clone libraries were constructed from the16S rDNA amplicons and selected individual clones were partially sequenced. Retrieved sequences were identified by BLAST analysis and indicate the presence of unidentified bacteria. Diversity index was calculated using Shannon–Wiener index. The bacterial diversity associated with coral sample 1 gives the index of species diversity, H ₁ as 1.6287, divergence from eqiprobability as 45.708% and the evenness of the sample as 54.291. For coral sample 2, the values obtained were, H ₁ as 1.97, divergence from eqiprobability as 15.11% and the evenness of the sample as 84.88. Sequences representing bacteria related to agricultural or industrial pollution and pathogenesis were also found. Coral samples collected near a lagoon area, showed a greater percentage of sequences representing bacteria related to human interventions, indicative of pollution.     

Evidence for a host role in thermotolerance divergence between populations of the mustard hill coral (Porites astreoides) from different reef environments

Studying the mechanisms that enable coral populations to inhabit spatially varying thermal environments can help evaluate how they will respond in time to the effects of global climate change and elucidate the evolutionary forces that enable or constrain adaptation. Inshore reefs in the Florida Keys experience higher temperatures than offshore reefs for prolonged periods during the summer. We conducted a common garden experiment with heat stress as our selective agent to test for local thermal adaptation in corals from inshore and offshore reefs. We show that inshore corals are more tolerant of a 6‐week temperature stress than offshore corals. Compared with inshore corals, offshore corals in the 31 °C treatment showed significantly elevated bleaching levels concomitant with a tendency towards reduced growth. In addition, dinoflagellate symbionts (Symbiodinium sp.) of offshore corals exhibited reduced photosynthetic efficiency. We did not detect differences in the frequencies of major (>5%) haplotypes comprising Symbiodinium communities hosted by inshore and offshore corals, nor did we observe frequency shifts (‘shuffling’) in response to thermal stress. Instead, coral host populations showed significant genetic divergence between inshore and offshore reefs, suggesting that in Porites astreoides, the coral host might play a prominent role in holobiont thermotolerance. Our results demonstrate that coral populations inhabiting reefs <10‐km apart can exhibit substantial differences in their physiological response to thermal stress, which could impact their population dynamics under climate change.     

Antimicrobial and stress responses to increased temperature and bacterial pathogen challenge in the holobiont of a reef‐building coral

Global increases in coral disease prevalence have been linked to ocean warming through changes in coral‐associated bacterial communities, pathogen virulence and immune system function. However, the interactive effects of temperature and pathogens on the coral holobiont are poorly understood. Here, we assessed three compartments of the holobiont (host, Symbiodinium and bacterial community) of the coral Montipora aequituberculata challenged with the pathogen Vibrio coralliilyticus and the commensal bacterium Oceanospirillales sp. under ambient (27°C) and elevated (29.5 and 32°C) seawater temperatures. Few visual signs of bleaching and disease development were apparent in any of the treatments, but responses were detected in the holobiont compartments. V. coralliilyticus acted synergistically and negatively impacted the photochemical efficiency of Symbiodinium at 32°C, while Oceanospirillales had no significant effect on photosynthetic efficiency. The coral, however, exhibited a minor response to the bacterial challenges, with the response towards V. coralliilyticus being significantly more pronounced, and involving the prophenoloxidase‐activating system and multiple immune system‐related genes. Elevated seawater temperatures did not induce shifts in the coral‐associated bacterial community, but caused significant gene expression modulation in both Symbiodinium and the coral host. While Symbiodinium exhibited an antiviral response and upregulated stress response genes, M. aequituberculata showed regulation of genes involved in stress and innate immune response processes, including immune and cytokine receptor signalling, the complement system, immune cell activation and phagocytosis, as well as molecular chaperones. These observations show that M. aequituberculata is capable of maintaining a stable bacterial community under elevated seawater temperatures and thereby contributes to preventing disease development.     

Trichocytes in Lithophyllum kotschyanum and Lithophyllum spp. (Corallinales,Rhodophyta) from the NW Indian Ocean

The current diagnosis of the genus Lithophyllum includes absent or rare trichocyte occurrence. After examining holotype material, single trichocytes have been revealed to occur abundantly in Lithophyllum kotschyanum Unger, and in freshly collected specimens of Lithophyllum spp. from the Red Sea, Gulf of Aden and Socotra Island (Yemen). Trichocyte occurrence is not considered a diagnostic character at specific or supraspecific levels in the Lithophylloideae, and the ecological significance of trichocyte formation is discussed. The generitype species, L. incrustans Philippi, does not show trichocytes nor do many other Lithophyllum species from diverse geographic localities, but the presence of abundant trichocytes in other congeneric taxa requires emendation of the genus diagnosis. Therefore, the diagnosis of Lithophyllum is here emended by eliminating the adjective “rare” in the sentence concerning trichocyte occurrence, as follows: “Trichocytes present or absent, if present occurring singly.”     

Ecological Inferences from a deep screening of the Complex Bacterial Consortia associated with the coral,Porites astreoides

The functional role of the bacterial organisms in the reef ecosystem and their contribution to the coral well‐being remain largely unclear. The first step in addressing this gap of knowledge relies on in‐depth characterization of the coral microbial community and its changes in diversity across coral species, space and time. In this study, we focused on the exploration of microbial community assemblages associated with an ecologically important Caribbean scleractinian coral, Porites astreoides, using Illumina high‐throughput sequencing of the V5 fragment of 16S rRNA gene. We collected data from a large set of biological replicates, allowing us to detect patterns of geographical structure and resolve co‐occurrence patterns using network analyses. The taxonomic analysis of the resolved diversity showed consistent and dominant presence of two OTUs affiliated with the order Oceanospirillales, which corroborates a specific pattern of bacterial association emerging for this coral species and for many other corals within the genus Porites. We argue that this specific association might indicate a symbiotic association with the adult coral partner. Furthermore, we identified a highly diverse rare bacterial ‘biosphere’ (725 OTUs) also living along with the dominant bacterial symbionts, but the assemblage of this biosphere is significantly structured along the geographical scale. We further discuss that some of these rare bacterial members show significant association with other members of the community reflecting the complexity of the networked consortia within the coral holobiont.     

夏季西南印度洋叶绿素a分布特征

分析了2011年1月西南印度洋叶绿素a的分布特征及其粒级结构,并结合水动力学环境和营养盐数据探讨了其主要影响因素。结果表明,西南印度洋副热带涡流(IOSG)区表层叶绿素a浓度较低,不超过0.07 mg/m3,次表层叶绿素a浓度最大值所在水层较深,超过100 m;副热带聚集区(SCZ)表层叶绿素a浓度较高(0.164—0.247 mg/m3),次表层叶绿素a浓度最大值出现在50—70 m层。硝酸盐是该海区浮游植物生长的主要限制因素。微微型(pico)粒级的浮游植物占绝对优势,所有站位其对总叶绿素a的平均贡献率为71.1%,微型(nano)粒级次之(24.2%),小型(net)粒级所占比例最小(4.7%),其中IOSG区pico粒级对总叶绿素a的平均贡献率为77.9%,SCZ的pico粒级对总叶绿素a的平均贡献率为66.7%。IOSG区和SCZ海区之间水动力学环境的不同,可能导致了这两个海区叶绿素a的分布特征及粒级结构的较大差异。     

Planktonic foraminifera from the eastern Indian Ocean: distribution and ecology in relation to the Western Pacific Warm Pool (WPWP)

Faunal assemblages, principal component (PCA), canonical correspondence (CCA), and factor analysis are applied to planktonic foraminifera from 57 core-top samples from the eastern Indian Ocean. The foraminiferal lysocline occurs at 2400 m north of 15°S where carbonate dissolution is induced by the Java upwelling system, and occurs deeper south of 15°S where carbonate dissolution is characteristic of the oligotrophic regions in the Indian Ocean. Dissolution effects, the February standing stock at the time of collection of the plankton-tow material, and different production rates explain the different foraminiferal assemblages found between plankton-tow and core-top samples. Core-top samples are differentiated by PCA into four groups — Upwelling, Western Pacific Warm Pool (WPWP), Transitional, and Southern — that are related to environmental variables (temperature, salinity and nutrients); all environmental variables follow a strong latitudinal component as indicated by the CCA analysis. Similarly, three assemblages are recognized by factor analysis: Factor 1 (dominated by Globigerinoides sacculifer, G. ruber, Globigerinita glutinata and Globorotalia cultrata), factor 2 (dominated by Globigerina bulloides and Globorotalia inflata) and factor 3 (dominated by Neogloboquadrina dutertrei) explain more than 92% of the variance, and are related to sea-surface temperature, thermocline depth and nutrient levels. The seasonal influence of the Java upwelling system supplies nutrients, phyto- and zooplankton to the oligotrophic eastern Indian Ocean (factor 1). South of 24°S, a deep chlorophyll maximum, a deep euphotic zone, a deep thermocline, SSTs below 22°C, and brief upwelling pulses seem to explain factors 2 and 3. The ratio of G. sacculifer and N. dutertrei, two mutually excluding species, appears to indicate the southern boundary of the WPWP. This ratio is applied to core Fr10/95-11 to demonstrate past shifts of the southern boundary of the WPWP.     

Emergence of white pine needle damage in the northeastern United States is associated with changes in pathogen pressure in response to climate change

The defoliation of the eastern white pine (Pinus strobus) across the northeastern United States is an escalating concern threatening the ecological health of northern forests and economic vitality of the region's lumber industry. First documented in the spring of 2010 affecting 24 328 hectares in the state of Maine, white pine needle damage (WPND) has continued to spread and is now well established in all New England states. While causal agents of WPND are known, current research is lacking in both sampling distribution and the specific environmental factor(s) that affect the development and spread of this disease complex. This study aims to construct a more detailed distribution map of the four primary causal agents within the region, as well as utilize long‐term WPND monitoring plots and data collected from land‐based weather stations to develop a climatic model to predict the severity of defoliation events in the proceeding year. Sampling results showed a greater distribution of WPND than previously reported. WPND was generally found in forest stands that compromised >50% eastern white pine by basal area. No single species, nor a specific combination of species had a dominating presence in particular states or regions, thus supporting the disease complex theory that WPND is neither caused by an individual species nor by a specific combination of species. In addition, regional weather data confirmed the trend of increasing temperature and precipitation observed in this region with the previous year's May, June, and July rainfall being the best predictor of defoliation events in the following year. Climatic models were developed to aid land managers in predicting disease severity and accordingly adjust their management decisions. Our results clearly demonstrate the role changing climate patterns have on the health of eastern white pine in the northeastern United States.     

Bacterial profiling of White Plague Disease across corals and oceans indicates a conserved and distinct disease microbiome

Coral diseases are characterized by microbial community shifts in coral mucus and tissue, but causes and consequences of these changes are vaguely understood due to the complexity and dynamics of coral‐associated bacteria. We used 16S rRNA gene microarrays to assay differences in bacterial assemblages of healthy and diseased colonies displaying White Plague Disease (WPD) signs from two closely related Caribbean coral species, Orbicella faveolata and Orbicella franksi. Analysis of differentially abundant operational taxonomic units (OTUs) revealed strong differences between healthy and diseased specimens, but not between coral species. A subsequent comparison to data from two Indo‐Pacific coral species (Pavona duerdeni and Porites lutea) revealed distinct microbial community patterns associated with ocean basin, coral species and health state. Coral species were clearly separated by site, but also, the relatedness of the underlying bacterial community structures resembled the phylogenetic relationship of the coral hosts. In diseased samples, bacterial richness increased and putatively opportunistic bacteria were consistently more abundant highlighting the role of opportunistic conditions in structuring microbial community patterns during disease. Our comparative analysis shows that it is possible to derive conserved bacterial footprints of diseased coral holobionts that might help in identifying key bacterial species related to the underlying etiopathology. Furthermore, our data demonstrate that similar‐appearing disease phenotypes produce microbial community patterns that are consistent over coral species and oceans, irrespective of the putative underlying pathogen. Consequently, profiling coral diseases by microbial community structure over multiple coral species might allow the development of a comparative disease framework that can inform on cause and relatedness of coral diseases.     

The distribution of fishes on the outer reef slopes of Aldabra (Indian Ocean) in relation to bottom temperatures

Synopsis Ninety six fish belonging to 19 species were taken by deep water line fishing off Aldabra. Analysis of the results shows how various factors such as hooking time changed with depth. The change of bottom temperature with depth was examined. The zone between 100 m and 150 m was found to have considerable temperature variations. The distribution of some serranids and lutjanids appeared to be stratified though there was usually overlap in the range of adjacent species. The results are compared with previous line-fishing off the South coast of Aldabra from deeper water and other areas of the western Indian Ocean.     

The influence of protected area management on the status of coral reefs at Misali Island,Tanzania following the 1998 bleaching event in the western Indian Ocean

The reefs of Misali Island, Tanzania suffered serious coral mortality as a result of the 1998 coral bleaching event in the western Indian Ocean. Four years after this event, Frontier‐Tanzania assessed reef substrate in Misali Island Marine Conservation Area (MIMCA) using scuba surveys. Substrate cover was compared between sites within and outside the nonextraction zone (NEZ) of MIMCA and recovery rates were estimated through reference to previous studies. Coral recovery at Misali Island following the bleaching event has generally been slow, but nonextractive management of MIMCA has enhanced coral recovery within the NEZ. The absence of fishing activities in the NEZ has sustained herbivorous fish populations and thus reduced algal overgrowth; however, outside the NEZ, diving and anchoring activities have caused further coral damage and led to increased levels of debris. Awareness‐raising programmes could lessen these problems and the NEZ appeared to be well‐placed to capitalize on nonmanageable factors that are thought to mitigate the effects of coral bleaching. In addition, the implementation of flexible zoning schemes could improve recovery rates after future bleaching events.     

Population genetic structure and connectivity of the seagrass Thalassia hemprichii in the Western Indian Ocean is influenced by predominant ocean currents

This study is the first large‐scale genetic population study of a widespread climax species of seagrass, Thalassia hemprichii, in the Western Indian Ocean (WIO). The aim was to understand genetic population structure and connectivity of T. hemprichii in relation to hydrodynamic features. We genotyped 205 individual seagrass shoots from 11 sites across the WIO, spanning over a distance of ~2,700 km, with twelve microsatellite markers. Seagrass shoots were sampled in Kenya, Tanzania (mainland and Zanzibar), Mozambique, and Madagascar: 4–26°S and 33–48°E. We assessed clonality and visualized genetic diversity and genetic population differentiation. We used Bayesian clustering approaches (TESS) to trace spatial ancestry of populations and used directional migration rates (DivMigrate) to identify sources of gene flow. We identified four genetically differentiated groups: (a) samples from the Zanzibar channel; (b) Mozambique; (c) Madagascar; and (d) the east coast of Zanzibar and Kenya. Significant pairwise population genetic differentiation was found among many sites. Isolation by distance was detected for the estimated magnitude of divergence (D_EST), but the three predominant ocean current systems (i.e., East African Coastal Current, North East Madagascar Current, and the South Equatorial Current) also determine genetic connectivity and genetic structure. Directional migration rates indicate that Madagascar acts as an important source population. Overall, clonality was moderate to high with large differences among sampling sites, indicating relatively low, but spatially variable sexual reproduction rates. The strongest genetic break was identified for three sites in the Zanzibar channel. Although isolation by distance is present, this study suggests that the three regionally predominant ocean current systems (i.e., East African Coastal Current, North East Madagascar Current, and the South Equatorial Current) rather than distance determine genetic connectivity and structure of T. hemprichii in the WIO. If the goal is to maintain genetic connectivity of T. hemprichii within the WIO, conservation planning and implementation of marine protection should be considered at the regional scale—across national borders.     

Consequences of marine barriers for genetic diversity of the coral‐specialist yellowbar angelfish from the Northwestern Indian Ocean

Ocean circulation, geological history, geographic distance, and seascape heterogeneity play an important role in phylogeography of coral‐dependent fishes. Here, we investigate potential genetic population structure within the yellowbar angelfish (Pomacanthus maculosus) across the Northwestern Indian Ocean (NIO). We then discuss our results with respect to the above abiotic features in order to understand the contemporary distribution of genetic diversity of the species. To do so, restriction site‐associated DNA sequencing (RAD‐seq) was utilized to carry out population genetic analyses on P. maculosus sampled throughout the species’ distributional range. First, genetic data were correlated to geographic and environmental distances, and tested for isolation‐by‐distance and isolation‐by‐environment, respectively, by applying the Mantel test. Secondly, we used distance‐based and model‐based methods for clustering genetic data. Our results suggest the presence of two putative barriers to dispersal; one off the southern coast of the Arabian Peninsula and the other off northern Somalia, which together create three genetic subdivisions of P. maculosus within the NIO. Around the Arabian Peninsula, one genetic cluster was associated with the Red Sea and the adjacent Gulf of Aden in the west, and another cluster was associated with the Arabian Gulf and the Sea of Oman in the east. Individuals sampled in Kenya represented a third genetic cluster. The geographic locations of genetic discontinuities observed between genetic subdivisions coincide with the presence of substantial upwelling systems, as well as habitat discontinuity. Our findings shed light on the origin and maintenance of genetic patterns in a common coral reef fish inhabiting the NIO, and reinforce the hypothesis that the evolution of marine fish species in this region has likely been shaped by multiple vicariance events.     

Connectivity in the cold: the comparative population genetics of vent‐endemic fauna in the Scotia Sea,Southern Ocean

We report the first comparative population genetics study for vent fauna in the Southern Ocean using cytochrome C oxidase I and microsatellite markers. Three species are examined: the kiwaid squat lobster, Kiwa tyleri, the peltospirid gastropod, Gigantopelta chessoia, and a lepetodrilid limpet, Lepetodrilus sp., collected from vent fields 440 km apart on the East Scotia Ridge (ESR) and from the Kemp Caldera on the South Sandwich Island Arc, ~95 km eastwards. We report no differentiation for all species across the ESR, consistent with panmixia or recent range expansions. A lack of differentiation is notable for Kiwa tyleri, which exhibits extremely abbreviated lecithotrophic larval development, suggestive of a very limited dispersal range. Larval lifespans may, however, be extended by low temperature‐induced metabolic rate reduction in the Southern Ocean, muting the impact of dispersal strategy on patterns of population structure. COI diversity patterns suggest all species experienced demographic bottlenecks or selective sweeps in the past million years and possibly at different times. ESR and Kemp limpets are divergent, although with evidence of very recent ESR‐Kemp immigration. Their divergence, possibility indicative of incipient speciation, along with the absence of the other two species at Kemp, may be the consequence of differing dispersal capabilities across a ~1000 m depth range and/or different selective regimes between the two areas. Estimates of historic and recent limpet gene flow between the ESR and Kemp are consistent with predominantly easterly currents and potentially therefore, cross‐axis currents on the ESR, with biogeographic implications for the region.     

印度洋南赤道流区水体叶绿素a的分布及粒级结构

根据2010年4—5月印度洋南赤道流区的综合环境调查资料,对印度洋南赤道流区叶绿素a浓度分布和浮游植物的粒级结构等进行了分析. 结果表明,调查海区水体层化明显,表层水温较高,营养盐浓度较低。调查海区东部测站的数据显示该区域可能受到来自印度尼西亚贯穿流和南爪哇流的影响,有高温低盐的特点。叶绿素a浓度在该海区的分布具有以下特点：（1）表层叶绿素a浓度在整个调查海区虽然普遍较低（平均为（0.1220.052） mg/m3）,但具有明显的空间区域化特征：印度洋南赤道流区中部,叶绿素a浓度较低,站位间分布均匀;东部叶绿素a浓度相对较高,不同测站叶绿素a浓度差异明显.（2）整个调查区域叶绿素a浓度垂直分布具有明显的单峰结构,其最大值分布在60—80m水层,位于营养盐跃层内.（3）叶绿素a的粒级结构分析结果显示,pico级份的浮游植物对叶绿素a的贡献占主导地位,平均为75%,nano级份的贡献平均为20%,net级份对叶绿素a的贡献最小,平均仅有5%. 对比本次调查和在其它海区的研究,表明印度洋南赤道流区属于典型的低纬度寡营养海区,低的营养盐浓度（特别是NO3-浓度）是该海区浮游植物生长的主要限制因素之一.