Discordant coral–symbiont structuring: factors shaping geographical variation of Symbiodinium communities in a facultative zooxanthellate coral genus,Oculina

Understanding the factors that help shape the association between corals and their algal symbionts, zooxanthellae (Symbiodinium), is necessary to better understand the functional diversity and acclimatization potential of the coral host. However, most studies focus on tropical zooxanthellate corals and their obligate algal symbionts, thus limiting our full comprehension of coral–algal symbiont associations. Here, we examine algal associations in a facultative zooxanthellate coral. We survey the Symbiodinium communities associated with Oculina corals in the western North Atlantic and the Mediterranean using one clade-level marker (psbA coding region) and three fine-scale markers (cp23S–rDNA, b7sym15 flanking region, and b2sym17). We ask whether Oculina spp. harbor geographically different Symbiodinium communities across their geographic range and, if so, whether the host’s genetics or habitat differences are correlated with this geographical variation. We found that Oculina corals harbor different Symbiodinium communities across their geographical range. Of the habitat differences (including chlorophyll a concentration and depth), sea surface temperature is better correlated with this geographical variation than the host’s genetics, a pattern most evident in the Mediterranean. Our results suggest that although facultative zooxanthellate corals may be less dependent on their algal partners compared to obligate zooxanthellate corals, the Symbiodinium communities that they harbor may nevertheless reflect acclimatization to environmental variation among habitats.

     

Genetic diversity of free-living Symbiodinium in surface water and sediment of Hawai‘i and Florida

Marine dinoflagellates in the genus Symbiodinium are primarily known for their symbiotic associations with invertebrates and protists, although they are also found free-living in nanoplankton and microphytobenthic communities. Free-living Symbiodinium are necessary for hosts that must acquire their symbionts anew each generation and for the possible reestablishment of endosymbiosis in bleached adults. The diversity and ecology of free-living Symbiodinium are not well studied by comparison with their endosymbiotic counterparts, and as a result, our understanding of the linkages between free-living and endosymbiotic Symbiodinium is poor. Here, we begin to address this knowledge gap by describing the genetic diversity of Symbiodinium in the surface water and reef sediments of Hawai‘i and Florida using Symbiodinium-specific primers for the hypervariable region of the chloroplast 23S domain V (cp23S-HVR). In total, 29 Symbiodinium sequence types were detected, 16 of which were novel. The majority of Symbiodinium sequence types in free-living environments belonged to clades A and B, but smaller numbers of sequence types belonging to clades C, D, and G were also detected. The majority of sequences recovered from Hawai‘i belonged to clades A and C and those from Florida to clade B. Such distribution patterns are consistent with the endosymbiotic diversity previously reported for these two regions. The ancestral sequence types in each clade were typically recovered from surface water and sediments both in Hawai‘i and Florida and have been previously reported as endosymbionts of a range of invertebrates, suggesting that these types have the capacity to exploit a range of very different habitats. More derived sequence types in clades A, B, C, and G were not recovered here, suggesting they are potentially restricted to endosymbiotic environments.     

Faunal diversity and endemicity of the Cape Peninsula, South Africa — a first assessment

A total of 322 records were available from the literature on faunal taxa endemic to the Cape Peninsula, South Africa. Excluding possible pseudoendemics, dubious records and many invertebrate groups for which little or no information exists, these records represent 112 species (1 vertebrate and the rest invertebrates) in 47 families. This number excludes many other potential endemics having distributions that extend just off the Peninsula. When mapped according to a 590 1 km×1 km grid, these endemics were clustered in several, largely montane nodes and palaeogenic (palaeoclimatically stable) zones typically located in upper reach forest streams, riverine forest and caves (the latter supported 14 endemics). Endemics were over-represented on steep slopes. For many taxa, a very high percentage of the Peninsula representatives were endemics. There were more plant than animal endemics per 1 km² cell, although in total there were more animal than plant endemics. A significant correlation existed between the distribution of plant and animal endemics on the Peninsula, and especially on Table Mountain. The relationship, however, appears not to be causal, and is possibly related to parallel responses to historical isolation and topography. As the endemic fauna is mostly relictual, conservation of umbrella plant communities and the sandstone caves is essential. This may avert further extinction (some invertebrate endemics are likely to be extinct at this stage). Others have suffered declines in population numbers through development, invasion of alien vegetation, and possibly through predetion by the introduced Argentine ant.     

Local–global overlap in diversity informs mechanisms of bacterial biogeography

Spatial variation in environmental conditions and barriers to organism movement are thought to be important factors for generating endemic species, thus enhancing global diversity. Recent microbial ecology research suggested that the entire diversity of bacteria in the global oceans could be recovered at a single site, thus inferring a lack of bacterial endemism. We argue this is not the case in the global ocean, but might be in other bacterial ecosystems with higher dispersal rates and lower global diversity, like the human gut. We quantified the degree to which local and global bacterial diversity overlap in a diverse set of ecosystems. Upon comparison of observed local–global diversity overlap with predictions from a neutral biogeography model, human-associated microbiomes (gut, skin, mouth) behaved much closer to neutral expectations whereas soil, lake and marine communities deviated strongly from the neutral expectations. This is likely a result of differences in dispersal rate among ‘patches'', global diversity of these systems, and local densities of bacterial cells. It appears that overlap of local and global bacterial diversity is surprisingly large (but likely not one-hundred percent), and most importantly this overlap appears to be predictable based upon traditional biogeographic parameters like community size, global diversity, inter-patch environmental heterogeneity and patch connectivity.     

Experimental evaluation of diversity–productivity relationships in a coral reef fish assemblage

The global decline in biodiversity is causing increasing concern about the effects of biodiversity loss on ecosystem services such as productivity. Biodiversity has been hypothesised to be important in maintaining productivity of biological assemblages because niche complementarity and facilitation among the constituent species can result in more efficient use of resources. However, these conclusions are primarily based on studies with plant communities, and the relationship between diversity and productivity at higher trophic levels is largely unknown, especially in the marine environment. Here, we used a manipulative field experiment to test the effects of species richness and species identity on biomass accumulation in coral reef fish assemblages at Lizard Island. Small patch reefs were stocked with a total of 30 juveniles belonging to three planktivorous damselfish (genus Pomacentrus) according to three different levels of fish species richness (one, two and three species) and seven different combinations of fish species. Species richness had no effect on the relative growth in this assemblage after 18 days, but relative growth differed among individual fish species and the different combinations of species. Patterns of increase in biomass were best explained by species-specific differences and variable effects of intra- and interspecific competition on growth. These results suggest that niche complementarity and facilitation are not the most influential drivers of total productivity within this guild of planktivorous fishes. Total productivity may be resilient to declining reef fish biodiversity, but this will depend on which species are lost and on the life-history traits of remaining species.     

Spectroscopic properties of the Chlorophyll a–Chlorophyll c 2–Peridinin-Protein-Complex (acpPC) from the coral symbiotic dinoflagellate Symbiodinium

Femtosecond time-resolved transient absorption spectroscopy was performed on the chlorophyll a–chlorophyll c ₂–peridinin-protein-complex (acpPC), a major light-harvesting complex of the coral symbiotic dinoflagellate Symbiodinium. The measurements were carried out on the protein as well on the isolated pigments in the visible and the near-infrared region at 77 K. The data were globally fit to establish inter-pigment energy transfer paths within the scaffold of the complex. In addition, microsecond flash photolysis analysis was applied to reveal photoprotective capabilities of carotenoids (peridinin and diadinoxanthin) in the complex, especially the ability to quench chlorophyll a triplet states. The results demonstrate that the majority of carotenoids and other accessory light absorbers such as chlorophyll c ₂ are very well suited to support chlorophyll a in light harvesting. However, their performance in photoprotection in the acpPC is questionable. This is unusual among carotenoid-containing light-harvesting proteins and may explain the low resistance of the acpPC complex against photoinduced damage under even moderate light conditions.     

Inhibition of Calvin–Benson cycle suppresses the repair of photosystem II in Symbiodinium: implications for coral bleaching

Inhibition of Calvin–Benson cycle (CBC) activity by thermal stress has been hypothesized to cause photoinhibition of photosystem II (PSII) in zooxanthellae of reef-building corals and consequently lead to bleaching. This study tests whether the interruption of CBC by glycolaldehyde (GA) leads to photoinhibition and subsequent coral bleaching in Stylophora pistillata. When S. pistillata was incubated with GA, the O₂ evolution rate declined in a dose-dependent manner and the extent of photoinhibition, reflected by a decreased maximum quantum yield of PSII (F _v/F _m), was enhanced. The effect of GA on photoinhibition was similar to that of chloramphenicol (CAP), an inhibitor of protein synthesis in chloroplasts. When S. pistillata was incubated in weak light following a high-light-induced photoinhibitory treatment, the recovery of PSII from photoinhibition was suppressed in a similar manner to both GA- and CAP-treated samples. After incubation in moderate light at 26°C, S. pistillata showed a bleaching response only in presence of GA. These results suggest that coral bleaching-like responses are caused by interruption of the CBC activity in S. pistillata and are associated with accelerated photoinhibition through suppression of the protein synthesis-dependent repair of PSII but not to an increase in photodamage to PSII.     

Local, among-site, and regional diversity patterns of benthic macroinvertebrates in high altitude waterbodies: do ponds differ from lakes?

In this study we aimed at comparing invertebrate diversity of high altitude lakes and ponds along hierarchical spatial scales. We compared local, among-site, and regional diversity of benthic macroinvertebrates in 25 ponds and 34 lakes in the Tatra Mountains, central Europe. The ponds showed significantly lower local diversity, higher among-site diversity and similar regional diversity than the lakes. The species–area relationships (SAR), habitat heterogeneity, and environmental harshness are assumed as drivers for the local diversity patterns. An ecological threshold separating pond and lake systems emerged at an area of 2 ha, where the SAR pattern changed significantly. Differences in species turnover between these systems were likely driven by greater environmental variability and isolation of the ponds. High altitude ponds neither significantly support greater regional diversity nor higher number of unique taxa than lakes. The higher among-site diversity of ponds relative to lakes highlights the relevance of ponds for regional diversity in mountain areas.     

Nitrogen fixation and diversity of benthic cyanobacterial mats on coral reefs in Curaçao

Coral Reefs - Benthic cyanobacterial mats (BCMs) have increased in abundance on coral reefs worldwide. However, their species diversity and role in nitrogen fixation are poorly understood. We...     

Intra- and interspecific tree diversity promotes multitrophic plant–Hemiptera–ant interactions in a forest diversity experiment

Interactions between species of different trophic levels have long been recognized as fundamental processes in ecology. Although mounting evidence indicates that plant species diversity (PSD) or plant genetic diversity (PGD) can influence the plant-associated arthropod community, these two fundamental levels of biodiversity are not often manipulated simultaneously to assess their effects on species interactions. We used a large tree diversity experiment (BEF-China), which manipulates PSD and PGD in a crossed design to test individual and combined effects of PSD and PGD on multitrophic interaction networks and interaction partner species richness and occurrence. We focused on two tree species, on which sap-sucking Hemiptera and interacting ant species commonly occur. This tri-trophic interaction can be divided into the antagonistic plant–Hemiptera interaction and the mutualistic Hemiptera–ant interaction, known as trophobioses. Qualitative evaluation of tri-trophic interaction networks at different PSD and PGD combinations showed increased interaction partner redundancy at high PSD and PGD. This was supported by increased Hemiptera species richness at high PSD and PGD. Furthermore, the data indicate higher occurrence of Hemiptera and trophobioses and higher trophobiotic ant species richness with increasing PSD and PGD. As no plant diversity component alone caused an effect we conclude that the combined effect of high PGD and high PSD might be additive. In summary, as plant genetic diversity, especially at low species richness, seems to increase the interaction partner redundancy in interaction networks and the diversity of interacting communities, we suggest that genetic diversity should be considered in forest conservation and restoration programs.     

Altitudinal distribution,diversity and endemicity of Carabidae (Coleoptera) in the páramos of Ecuadorian Andes

Species richness and diversity of Carabidae (Coleoptera), as well as rates of endemicity, are studied along altitudinal transects in the páramo of Ecuadorian Andes, from 3500 to 5000 m. Whereas a global tendency to reduction of species richness is evident from 4200 m upwards, two zones of high diversity and high proportion of endemic species occur at 3800–4000 m and at 4200–4400 m. Species turnover between grass páramo and superpáramo is significantly higher in drier mountains, especially in the Western Cordillera, than in humid mountains of the Eastern Cordillera. The altitudinal range of Carabid species tends globally to decrease along the vertical gradient, but with important local variations due to microenvironmental factors, especially humidity rate. When compared with recent phytogeographical studies, these results tend to support the idea that the majority of tussockgrass páramo is a secondary anthropogenic ecosystem. On the contrary, it is argued that the xeric landscape of the Chimborazo “arenal” is primordial, based on the presence of a stenotopic and possibly relict species, Pelmatellus andium Bates 1891.     

Chaperone–usher pathways: diversity and pilus assembly mechanism

Up to eight different types of secretion systems, and several more subtypes, have been described in Gram-negative bacteria. Here, we focus on the diversity and assembly mechanism of one of the best-studied secretion systems, the widespread chaperone–usher pathway known to assemble and secrete adhesive surface structures, called pili or fimbriae, which play essential roles in targeting bacterial pathogens to the host.     

Plant diversity and ecology on the Qinghai–Tibet Plateau

The Qinghai–Tibet Plateau (QTP) comprises a platform (sometimes called the Qinghai–Tibet Plateau sensu stricto), the Himalayas, and Hengduan Mountains (Liang et al.,2018; Mao et al.,2021). The latter two parts and adjacent highlands are also called the Pan-Himalaya. Numerous plants are distributed there with many endemic species, probably because of the high diverse landscapes created by continuous geological and climatic activities (Favre et al.,2015; Mao et al.,2021). As the well known biodiversity hotspot of the alpine plants in the world (Sun et al.,2017), many studies have been conducted on evolutionary origin and ecological adaptation of those species occurring in the QTP (e.g., Wen et al.,2014, 2019; Zhang et al.,2019). In the present special issue, we collected 15 related papers on this topic. Among them, two are invited reviews. Mao et al. (2021) provide a comprehensive review of evolutionary origin of species diversity on the QTP. Especially, they outlined major disputes and likely causes in this research topic, including circumscribing and naming the QTP, the QTP uplifts, dating of molecular phylogenetic trees, non-causal correlations between QTP uplifts and species diversification and the unified ice sheet. The authors also summarized genomic advancements related to high-altitude adaptation of both plants and animals. Tong et al. (2021) reviewed the reproductive strategies of animal-pollinated alpine plants on the QTP, involving pollination system, pollen limitation, self-pollination, and sexual system. In this region, 95.4% of animal-pollinated plants are pollinated by insects (i.e., bees, moths, butterflies, and flies) with only 4% by vertebrates (i.e., bats and birds). Self-pollination through self-compatibility shift from outcrossing has become an effective reproductive strategy to overcome pollen limitation in alpine plants. The other 13 research papers aimed to address origin and adaptation of alpine flora involving three major lines of evidence: genomics, ecology, and paleobotany. We hope that the collection of these papers will increase our understanding of the origin, speciation, and adaptation of alpine species on the QTP.     

Mapping and imaging deep-sea coral reefs off Norway, 1982–2000

The survey and mapping group (SMG) of Statoil is responsible for all seafloor mapping for pipelines and field development in Statoil. During numerous reconnaissance and pipeline route surveys over large portions of our contintental shelf, in the North, Norwegian and Barents Seas, we have only detected deep-water coral reefs in a few specific areas. The first reef we found was in 1982, using a combined side scan sonar and sub-bottom profiler system off Fugløy, northern-Norway. Thereafter, numerous reefs were mapped with similar systems off mid-Norway, during the period 1985–1990 for the reconnaissance and final route mapping of the Haltenpipe project. During 1997, we also mapped some previously known reefs in the Trondheimsfjord area while surveying a route for the Tjeldbergodden - Skogn pipeline project. Between 1997 and 2000, we have mapped more reefs along pipeline routes on the outer mid-Norway continental shelf. These reefs are of a smaller size (less than 5 m high) than those mentioned above (5–31 m high). Although side scan sonar and sub-bottom profilers provide a less ambiguous detection of reefs, we have found that modern multi-beam echosounder data can provide adequate remotely sensed data for deep-water coral reef mapping. The interpretation of the reefs is based on visual documentation by ROV (remotely operated vehicle) or by sampling with gravity corers and grabs (ground-truthing). Based on a limited amount of such ground-truthing, it has been possible to extrapolate and use the specific morphological characteristics of the reefs to map their density and distribution. For the Haltenpipe project, we mapped an offshore route corridor of about 200 km length at a width of 3 km with multi-beam echosounder. On the basis of ground-truthing 14 of the suspected coral reefs, we have found the total number of reefs to be 57 within the 600 km² mapped area. All these reefs are higher than 5 m (the highest is 31 m) and of diameters at their base of more than 50 m. Although they occur in local clusters with up to 10 reefs per km², the mean density of reefs along the entire (200 km long) transect is only 0.09 suspected reefs per km². However, there is a large regional density variation, with the highest regional density being 1.2 reefs per km² in an area of subcropping Palaeocene sedimentary rocks. A brief discussion of why the corals have constructed their reefs in the deep, cool, and generally `hostile' waters of the Norwegian continental shelf and fjords concludes with them probably subsisting on a reliable and steady nutrient source, independent of season and variations in the Atlantic Drift (`Gulf stream'). This positive environmental component is called `hydraulically active substrata'. It is thus speculated that micro-organisms, bacteria etc., utilizing the hydraulically activated chemical porewater gradients, cause a local enrichment on which the cnidarian organisms ultimately depend.     

Temporal effects of ocean warming and acidification on coral–algal competition

Coral Reefs - While there is an ever-expanding list of impacts on coral reefs as a result of ocean warming and acidification, there is little information on how these global changes influence...     

Variable interaction outcomes of local disturbance and El Niño-induced heat stress on coral microbiome alpha and beta diversity

Coral Reefs - Emerging evidence indicates that individual stressors can modify the coral microbiome; however, few studies have examined the impacts of multiple stressors through natural climatic...     

Animal and plant space-use drive plant diversity–productivity relationships

Plant community productivity generally increases with biodiversity, but the strength of this relationship exhibits strong empirical variation. In meta-food-web simulations, we addressed if the spatial overlap in plants' resource access and animal space-use can explain such variability. We found that spatial overlap of plant resource access is a prerequisite for positive diversity–productivity relationships, but causes exploitative competition that can lead to competitive exclusion. Space-use of herbivores causes apparent competition among plants, resulting in negative relationships. However, space-use of larger top predators integrates sub-food webs composed of smaller species, offsetting the negative effects of exploitative and apparent competition and leading to strongly positive diversity–productivity relationships. Overall, our results show that spatial overlap of plants' resource access and animal space-use can greatly alter the strength and sign of such relationships. In particular, the scaling of animal space-use effects opens new perspectives for linking landscape processes without effects on biodiversity to productivity patterns.     

Does natural selection organize ecosystems for the maintenance of high productivity and diversity?

Three types of evidence suggest that natural ecosystems are organized for high productivity and diversity: (i) changes not previously experienced by a natural ecosystem, such as novel human disturbances, tend to diminish its productivity and/or diversity, just as 'random' changes in a machine designed for a function usually impair its execution of that function; (ii) humans strive to recreate properties of natural ecosystems to enhance productivity of artificial ones, as farmers try to recreate properties of natural soils in their fields; and (iii) productivity and diversity have increased during the Earth's history as a whole, and after every major biotic crisis. Natural selection results in ecosystems organized to maintain high productivity of organic matter and diversity of species, just as competition among individuals in Adam Smith's ideal economy favours high production of wealth and diversity of occupations. In nature, poorly exploited energy attracts more efficient users. This circumstance favours the opening of new ways of life and more efficient recycling of resources, and eliminates most productivity-reducing 'ecological monopolies'. Ecological dominants tend to be replaced by successors with higher metabolism, which respond to more stimuli and engage in more varied interactions. Finally, increasingly efficient predators and herbivores favour faster turnover of resources.