The pteridophytes of Mauritius (Indian Ocean): ecology and distribution

A survey of the pteridophytes of Mauritius is presented, including a summary of their habitats, ecology, and phytogeographical affinities. Of the 186 infrageneric taxa recorded from the island, 8 are adventive or naturalized, and 27 are presumed rare or extinct. Major ecological groupings are presented and species are listed for both indigenous and secondary plant communities.     

Abundance and site fidelity of bottlenose dolphins off a remote oceanic island (Reunion Island,southwest Indian Ocean)

This study represents the first comprehensive assessment of the population dynamics and residency of common bottlenose dolphin around Reunion Island (southwest Indian Ocean). Understanding dynamics and movement patterns of this local population is essential to guide effective conservation efforts, notably in a context of growing dolphin-watching activities. Dedicated surveys based on photo-identification methods were conducted over 6 years (2010–2015). The species was present year-round, in groups of 25 individuals on average (1–150). Jolly-Seber mark-recapture models resulted in a population estimate of 254 individuals (95% CI = 191–337) and an apparent annual survival rate of 0.83. The population was almost equally split into three residency patterns: residents (33.1%), long-term visitors (32.6%), and short-term visitors (34.3%, including transients, i.e., individuals only seen once [14.9%]), suggesting that the majority of the population showed a moderate-to-high level of residency in the study area. Individuals from the three residency patterns associated randomly, mixing together and forming a single community. Models based on the lagged identification rate indicated emigration and reimmigration to the survey area, with some individuals occupying the study area for about 2 years (832 days), and remaining outside for an average of 276 days, probably exhibiting larger home ranges and extensive movement behavior.     

Monognathus berteli sp. nov. from the Indian Ocean (Pisces,Monognathidae)

A new deepsea monognathid species,Monognathus berteli, is described based on one specimen collected pelagically in the northwestern Indian Ocean at 1440–1018 meters of depth. LikeM. taningi andM. bertini, it belongs to the short-skulled species-group and has very long pectoral fins, but differs from these species by several meristic characters. The described specimen has a very long caudal filament (53% SL) which is not known from otherMonognathus. However, the fragile filament is not used as a diagnostic character since it could easily be broken.     

Geometric morphometrics of carapace of Macrobrachium australe (Crustacea: Palaemonidae) from Reunion Island

Zimmermann, G., Bosc, P., Valade, P., Cornette, R., Améziane, N. and Debat, V. 2011. Geometric morphometrics of carapace of Macrobrachium australe (Crustacea: Palaemonidae) from Reunion Island. —Acta Zoologica (Stockholm) 93 : 492–500. We investigated the structure of carapace shape variation in six populations of Macrobrachium australe Guérin‐Méneville 1838 (Crustacea: Decapoda: Palaemonidae) from Reunion Island (Indian Ocean) freshwaters. The morphometric analysis revealed the occurrence of two morphotypes corresponding to two different types of habitats. Individuals living in lotic habitats present a thick carapace armed with a short, robust and straight rostrum, while individuals from lentic habitats have a slender carapace armed with a thin long rostrum orientated upward. This difference suggests an adaptation to lotic disturbances and is tentatively interpreted as adaptive phenotypic plasticity. In such amphidromous organisms regressing to freshwaters after a marine larval phase, selection for physiological and developmental flexibility might facilitate further adaptation and allows the colonisation of a wide panel of environmentally different and sometimes geographically distant insular streams.     

Sex-linked variations in the sagittal otolith biometry of Nemipterus randalli (Russell, 1986) from the eastern Mediterranean Sea

Few studies have been conducted on the sagittal otolith shape and morphometry of Nemipterus randalli, and none of these studies has examined the effect of sexual dimorphism on the otolith morphology of this species, therefore this study aimed to contribute to knowledge about the otolith morphology of N. randalli, an invasive fish species for the Mediterranean Sea. For this purpose, a total of 132 samples (51 female and 81 male) were obtained from İskenderun Bay with the help of commercial fishermen in November 2018. Relationships between otolith measurements and fish size were determined. Shape indices and elliptic Fourier coefficients were calculated. Significant differences were detected between males and females in all analysis. The sexes were separated from each other using both shape indices and elliptic Fourier coefficients. However, shape analysis was more effective in distinguishing sexes than traditional morphometric analysis. Asymmetry in the otolith morphology of sexes has been attributed to differences in the growth and sexual maturity of male and female fish. The results of this study indicated that sexual dimorphism in Nemipterus randalli was also reflected in the otolith morphology.     

Greta's Garbo: stranded seeds and fruits from Greta Beach, Christmas Island, Indian Ocean

Aim To describe the species composition of stranded seeds and fruits drifted by ocean currents to Christmas Island, Indian Ocean. Location Christmas Island, Indian Ocean. Methods Frequent visual searches along the strand line of the island's few accessible beaches over a 4-year period 1988–92, with most effort concentrated on Greta Beach, on the east coast. Results The collection contained not fewer than sixty-three species in forty-nine genera and twenty-nine families. Leguminous seeds were by far the most common (especially Caesalpinia bonduc (L.) Roxb., Dioclea spp., Entada spp., Erythrina spp. and Mucunagigantea (Willd.) DC.), but Calophyllum inophyllum L., Guettarda speciosa L., Hernandia ovigera L., Heritiera littoralis Aiton and Terminalia catappa L. were also common. Main conclusions Only about one-third of species recorded in the drift flora are native to the island, and most disseminules stranded on the island are probably not locally derived. The most likely distant sources of drift disseminules are probably the southern Indonesian islands and Sumatra, with most disseminules probably arriving via the Timor and Arafura Seas between Indonesia and Australia. However, some disseminules may originate from as far east as the Moluccas and the east coast of Kalimantan. The majority of species recorded in the drift flora are not native to the island, and yet some of these were encountered frequently and displayed a high degree of viability on arrival (e.g. Dioclea hexandra (Ralph) Mabb., Erythrina fusca Loureiro and Mucuna gigantea (Willd.) DC.). Several possible reasons for the failure of many drift species to establish on the island are discussed.     

Vocal repertoires and insights into social structure of sperm whales (Physeter macrocephalus) in Mauritius,southwestern Indian Ocean

Sperm whales communicate using codas (stereotyped click sequences). Females and juveniles live in long-term social units, and units with similar coda repertoires share vocal clan membership. Vocal clans exhibit culturally defined differences in their multilevel social structure. Here, we aimed to identify different social units among sperm whales in Mauritius in the southwestern Indian Ocean, and to describe and compare their coda repertoires to investigate the presence of different vocal clans. We conducted six boat-based surveys between 2008 and 2013, during which 101 different individuals were photo-identified. Analysis of associations between 22 resighted individuals divided them into four candidate social units, but a lack of resightings impedes solid delineation of social units. Based on number and rhythm of clicks, at least 24 discrete coda types were detected among 4,767 analyzed codas using two different classification methods. Comparison of coda repertoires recorded from seven sperm whale groupings revealed the possible existence of two sympatric vocal clans, but the size differences of recorded repertoires warrant caution of interpretation. To further evaluate social structuring and the presence of different vocal clans in this region, future surveys should aim at obtaining long-term sighting and acoustic data, and cover a more extensive area.     

热带印度洋黄鳍金枪鱼渔场时空分布与温跃层的关系

根据Argo浮标剖面温度数据重构热带印度洋各月月平均温跃层特征参数,并结合印度洋金枪鱼委员会(IOTC)黄鳍金枪鱼延绳钓数据,绘制了月平均温跃层特征参数和月平均CPUE的空间叠加图,用于分析热带印度洋黄鳍金枪鱼渔场时空分布和温跃层特征参数的关系。结果表明:热带印度洋温跃层上界深度、温度和下界深度,以及黄鳍金枪鱼中心渔场分布都具有明显的季节性变化特征,黄鳍金枪鱼中心渔场分布和温跃层季节性变化有关。在东北季风期间,高值CPUE渔区的温跃层上界深度的范围为30-40m,超过70m的渔区CPUE值普遍偏低;在西南季风期间温跃层上界最深达到120m。在东北季风期间,高值CPUE渔区温跃层下界深度不超过200m,在西南季风期间,深度会超过300m。在东北季风期间,高值CPUE渔区对应的温跃层上界温度都超过25℃,温度小于24℃的渔区CPUE值普遍较低;在西南季风期间,高值CUPE区域对应的温跃层上界温度范围变大,温跃层上界温度延伸到22℃,在22℃以下渔区CPUE值都很低。采用频次分析和经验累积分布函数计算其最适温跃层特征参数分布,得出黄鳍金枪鱼最适的温跃层上、下界温度范围分别是25-29℃和13-16℃;其上、下界深度范围分别为30-70m和140-200m。K-S检验结果表明,上述结论可靠。     

Age and growth of the bull shark (Carcharhinus leucas) around Reunion Island,South West Indian Ocean

Sharks exhibit varied demographic strategies depending on both the species and the population location, which make them more or less vulnerable to fishing. Accurate evaluation of local age and growth parameters is therefore fundamental for the sustainable management of their stocks. Although demographic parameters have been assessed for bull shark (Carcharhinus leucas) populations in several locations of the world, this information is missing so far around Reunion Island, in the south-west Indian Ocean. To fill this gap of knowledge, age and growth data were gathered from the vertebrae of 140 individuals of C. leucas (77 females and 63 males, mostly adults) fished around the island between 2012 and 2019. After verification of the annual deposition of growth band pairs on these structures using relative marginal increment analysis on 40 individuals, band pairs were counted along the vertebral centrum for each individual. Thanks to this approach, growth was shown to significantly differ between male and female C. leucas around Reunion Island, with respective von Bertalanffy growth model equations of L_t =  and L_t = . Indeed, the females of the species fished in this area were significantly (P < 0.001) larger than local males, with an estimated difference in size of ~16.1 cm at 20 years old. They also apparently reach older ages, with an estimated maximum age of 33.50 years, against 29.75 years only for the males. The estimated size at birth around the island is larger than elsewhere in the world, varying from 92.30 to 100.00 cm depending on the method used. These results confirm that the population of C. leucas around Reunion Island exhibits a K-selected strategy, which makes it highly vulnerable to fishing pressure.     

Two new Cocconeis taxa (Bacillariophyceae) from coral sands off the Mascarenes (Western Indian Ocean) and some related unidentified taxa

Coral sands off Réunion Island and Rodrigues (Mascarene archipelago, Western Indian Ocean) support diverse diatom communities, particularly rich in Monoraphidineae. Recent surveys of reef environments (June 2005 and June 2007) permitted the recognition of several taxa belonging to the diatom genus Cocconeis, among which are two new, relatively small taxa, epipsammic on coral sand. Cocconeis coronata Riaux-Gobin et Romero sp. nov. is similar to C. scutellum but has its own distinctive features. In external view, the concave raphe valve possesses uniseriate striae and a subsident hyaline marginal rim, while the strongly convex sternum valve has a submarginal, generally continuous crest, a hexagonal pattern of areolation, short, rounded spines that are often regularly arranged around valve face areolae, a complex areola hymen and small marginal chambers. Some morphometric differences were noted between the populations of C. coronata at Réunion and Rodrigues. Cocconeis margaritata Riaux-Gobin et Al-Handal, sp. nov. is smaller, possesses a sternum valve like that of C. placentula and C. neothumensis, but has denser striation and small pearl-like concretions around the areola aperture on the sternum valve. Several other taxa that resemble, or may be varieties of, C. margaritata require further study before being formally described. Cocconeis margaritata and C. coronata are small and relatively rare, so their study requires scanning electron microscopy.     

Abundance of thraustochytrids and bacteria in the equatorial Indian Ocean, in relation to transparent exopolymeric particles (TEPs)

Thraustochytrid protists are often abundant in coastal waters. However, their population dynamics and substrate preferences in the oceanic water column are poorly understood. We studied the abundance and distribution of thraustochytrids, bacteria and TEPs in the equatorial Indian Ocean waters during September 2003, October 2004 and September 2006. Thraustochytrids and bacteria were abundant, suggesting high biological productivity of the region. Thraustochytrids were positively related to bacteria during October 2004 but not at other times, suggesting overlapping or varying substrate preferences at different times. Thraustochytrid and bacteria were positively related to TEPs only in a few stations during October 2004, but were mostly positively related to TEPs generated from in situ water in a roller table experiment. TEPs from natural samples during October 2004 had a much greater affinity to the lectin Concanavalin A than to Limulin compared with those in September 2006 and from the roller tank experiments. The chemical composition of TEPs might explain their relationship with thraustochytrids. Thraustochytrids averaged a higher biomass than bacteria in two of the three cruises, but were less frequent and more patchily distributed compared with bacteria.     

Minimal similarity in songs suggests limited exchange between humpback whales (Megaptera novaeangliae) in the southern Indian Ocean

Comparing humpback whale song from different breeding assemblages can reveal similarities in song due to acoustically interacting males, and therefore indirectly test whether males from different breeding sites are mixing. Northern Hemisphere song comparisons illustrated that whales within ocean basins share similar songs and are subpopulations within a larger population, whereas whales in different ocean basins are isolated populations and therefore do not share songs. During the 2006 breeding season, recordings were collected in Madagascar and Western Australia, and were compared visually plus aurally. Both regions shared one theme, whereas each region had four and six private themes, respectively. This study had a substantially low number of shared themes. The co‐occurrence of one theme was interpreted as an indication of limited exchange between these breeding assemblages, and we speculate that limited song similarity is due to inter‐oceanic interactions. Male(s) from an Indian Ocean breeding group could be exposed to novel song when they geographically overlap, and acoustically interact, with males from a different ocean basin. Novel song could induce rapid temporal changes as new song content is incorporated, thereby minimizing song similarities between that breeding group and other Indian Ocean breeding groups that were not exposed to the novel song.     

Impacts and management of unowned and owned cats at a seabird colony on Reunion Island (Western Indian Ocean)

Biological Invasions - Cats (Felis catus) introduced on islands have strong impacts on biodiversity, and the main conservation actions to protect native fauna is cat eradication or control (i.e.,...     

A new species, Parupeneus procerigena, from the Saya de Malha Bank in the western Indian Ocean (Perciformes: Mullidae)

A new mullid fish, Parupeneus procerigena, is described on the basis of 13 specimens (118.9–198.4 mm SL) from depths of 92–148 m off the Saya de Malha Bank in the western Indian Ocean. This species resembles P. chrysopleuron and P. heptacanthus in color pattern without black stripes or spots, but it differs from them in having more gill rakers, two scales in lachrymal region, deeper body, deeper cheek, and longer distance between nostrils. Received: April 4, 2000 / Revised: July 27, 2000 / Accepted: August 27, 2000     

A new genus and species of deep-sea glass sponge (Porifera, Hexactinellida, Aulocalycidae) from the Indian Ocean

New hexactinellid sponges were collected from 2589 m depth on the Carlsberg Ridge in the Indian Ocean during deep-sea dredging. All fragments belong to a new genus and species, Indiellagen. n.ridgenensissp. n., a representative of the family Aulocalycidae described here. The peculiar features of this sponge, not described earlier for other Aulocalycidae, are: longitudinal strands present in several layers and epirhyses channelization.     

Leaf architecture of South American Nothofagus (Nothofagaceae) using traditional and new methods in morphometrics

Leaf morphology has been the subject of several studies in NoNothofagur especially in the context of the taxonomy and evolutionary relationships of taxa within the genus, which are still controversial. The leaf architecture of 8 dombgi , N. betuloides and N. nitida , dominant trees of temperate forest in southern South America, is compared using venation patterns, landmarks, and entire outlines. In terms of venation patterns N. dombgi and N. betuloides were more similar to each other than to N. nitida. Similar results were found when differences in shape were analysed by discriminant analyses of shape coordinates (landmarks) and Fourier coefficients (outlines). For both analyses, the fwst discriminant function separated N. nitida from the other two species; these were also distinguished but showed greater overlap with each other. This study, in concert with information from allozyme data confirms the hypothesis of a more ancestral position for N. nitida with N. dombgi and N. betuloides being more recently derived. In addition to differences in shape, the size component of leaf morphology indicated that whereas N. betuloides had the smallest leaves, N. dombgi spanned the greatest range and has the biggest leaves. Given that the data shown here were obtained from seedlings grown under common-garden conditions, differences in both shape and size, seem to be important components of leaf morphology that may warrant consideration in characterizing these and other species of Nothofagus.     

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.