The effect of sub-lethal increases in temperature on the growth and population trajectories of three scleractinian corals on the southern Great Barrier Reef

To date, coral death has been the most conspicuous outcome of warming tropical seas, but as temperatures stabilize at higher values, the consequences for the corals remaining will be mediated by their demographic responses to the sub-lethal effects of temperature. To gain insight into the nature of these responses, here I develop a model to test the effect of increased temperature on populations of three pocilloporid corals at One Tree Island, near the southern extreme of the Great Barrier Reef (GBR). Using Seriatopora hystrix, S. caliendrum and Pocillopora damicornis as study species, the effects of temperature on growth were determined empirically, and the dynamics of their populations determined under natural temperatures over a 6-month period between 1999 and 2000 [defined as the study year (SY)]. The two data sets were combined in a demographic test of the possibility that the thermal regime projected for the southern GBR in the next 55–83 years—warmer by 3°C than the study year (the SY+3 regime), which is equivalent to 1.4°C warmer than the recent warm year of 1998—would alter coral population trajectories through the effects on coral growth alone; the analyses first were completed by species, then by family after pooling among species. Laboratory experiments showed that growth rates (i.e., calcification) varied significantly among species and temperatures, and displayed curvilinear thermal responses with growth maxima at ∼27.1°C. Based on these temperature-growth responses, the SY+3 regime is projected to: (1) increase annualized growth rates of all taxa by 24–39%, and defer the timing of peak growth from the summer to the autumn and spring, (2) alter the intrinsic rate of population growth (λ) for S. hystrix (λ decreases 26%) and S. caliendrum (λ increases 5%), but not for P. damicornis, and (3) have a minor effect on λ (a 0.3% increase) for the Pocilloporidae, largely because λ varies more among species than it does between temperatures. Ten-year population projections suggest that the effects of a sub-lethal increase in temperature (i.e., the SY+3 regime) are relatively small compared to the interspecific differences in population dynamics, but nevertheless will alter the population size and increase the relative abundance of large colonies at the expense of smaller colonies for all three species, as well as the Pocilloporidae. These effects may play an important role in determining the nuances of coral population structure as seawater warms, and their significance may intensity if the coral species pool is depleted of thermally sensitive species by bleaching.     

Larval development and survivorship in the corals Favia favus and Platygyra lamellina

Two Red Sea faviid species, Favia favus and Platygyra lamellina spawn eggs and sperm once a year, during the summer. External fertilization occurs 0.5 h after spawning, and mobile gastrulae appear 20 h later. Four stages in the early ontogenesis of these corals are described. The slow development (2–3 months) to the polyp stage in broadcasting species is attributed to the lack of zooxanthellae in their planulae and their appearance in the primary polyp only at a later stage. Survivorship of one-month-old primary polyps is ca 0.21% and 0.25% in F. favus and P. lamellina respectively, from the populations of 2–9-day-old planulae. Despite these low rates of survival, both species form dense populations in the Gulf of Eilat.     

The two-step mode of growth in the scleractinian coral skeletons from the micrometre to the overall scale

It has been known since the 19th century that coral skeletons are built of aragonite crystals with taxonomy-linked arrangements, but the way by which each coral species controls this crystallization process remains an unsolved question. The problem became still more intriguing when it was shown that isotopic compositions of coral aragonite were subject to taxonomy-linked influences (the "vital effect"). On the other hand, presence of an organic component in coral skeletons is also long known, but localization of these compounds is admittedly restricted to particular structures called "centres of calcifications." Fibres, the largely predominant part of the coral skeletons, are usually considered as purely mineral units. In this paper, it is shown that in both "centres of calcification" and fibres, organic compounds are associated with the mineral material at a deep structural level. A series of variously scaled observations and localized measurements allow recognition of the presence of an organic component at the nanometre scale. Far from being a freely operating process, crystallization of coral fibres is thus permanently controlled by the polyp basal ectoderm through a cyclic two-step process acting at the micrometre-scale. The biomineralization cycle begins by secretion of a proteoglycan matrix. As the composition of these sugars-proteins assemblages has been shown taxonomy dependent, the hypothesis can be made that multiple and long recognized specificities of coral skeletons are linked to this biochemically driven crystallization process. Additionally, this new concept of the biomineralization process in coral skeletons provides us with an access to the long term evolution of the Scleractinia. Remarkably, results of a skeleton-based approach using microstructural criteria (i.e., the spatial relationships of "centres of calcification" and the three-dimensional arrangements of fibres), are consistent with a molecular phylogenetic analysis carried out on the same species. Clearly, at the overall ontogenic level, the two-step growth mode of coral skeletons is also a valuable tool to reconstruct the evolutionary history of Scleractinia.     

湖北九宫山成熟常绿落叶阔叶混交林3种优势种的邻域效应研究

以最近邻株距离统计研究了湖北九宫山成熟常绿落叶阔叶混交林3种优势种青冈栎(Cyclobalanopsis glauca)、甜槠(Castanopsis eyrei)和短柄枹栎(Quercus serrata var.brevipetiolata)的邻域效应,进而探讨了局域尺度上的竞争/帮促关系与物种共存格局.结果显示,青冈栎、甜槠和短柄枹栎的最近邻株距离不存在下限;青冈栎的胸径大小与其种内最近邻株距离存在正相关(p=0.029),甜槠的胸径大小与种内、种间最近邻株距离均无相关性(p≥0.360),而短柄枹栎的胸径大小与种间最近邻株距离为负相关(p=0.040);3树种中任意一个的种内与种间最近邻株距离都没有显著差异(p≥0.122).这些结果表明,九宫山成熟常绿落叶阔叶混交林内邻域尺度上的竞争排斥并未充分激化,但是青冈栎的种内竞争仍然在起作用,而甜槠的竞争效应不明显,短柄枹栎则依赖种间帮促甚于相互竞争.同种和异种之间的排斥效果没有差异表明局域尺度的物种共存格局可能出于随机过程而非负密度制约过程.     

Effects of variation in individual growth on plant species coexistence

Abstract. Both size structure and variability (spatial heterogeneity, disturbance, stochasticity, variation in species attributes, etc.) are regarded as regulatory mechanisms of species coexistence. However, none of the models so far proposed consider both size structure and variability simultaneously. A size-structured variation model for plant-community dynamics is proposed, which is based on the diffusion model for growth dynamics of plant populations. This model has four functions: (1) mean growth rate of individuals of size x at time t, G(t, x) (species-specific mean traits, e.g. competitive ability); (2) variance in growth rate of individuals of size x at time t, D(t, x) (stochastic factors due to genetic variation, environmental heterogeneity, spatial variation of individuals, etc.); (3) mortality rate of individuals of size x at time t, M(t, x); and (4) recruitment rate at time t, R(t), as a boundary condition. The interference function for individuals of size x at time t, C(t, x), is introduced, which expresses the degree of interactions between individuals and hence averaged effects of local neighbourhood competition; the G(t, x), D(t, x), M(t, x) and R(t) functions are given in terms of C(t, x). These four functions describe the growth dynamics of individuals of each species in the plant community. Effects of the G(t, x), D(t, x), M(t, x) and R(t) functions on species coexistence in plant communities were evaluated by simulation and the relative importance of the D(t, x) function as well as size structure was shown for species coexistence especially in plant communities where competition among species is non-transitive or niche limitation does not work.     

An alternative to ITS, a hypervariable, single-copy nuclear intron in corals, and its use in detecting cryptic species within the octocoral genus Carijoa

Here we report a highly variable nuclear marker that can be used for both soft and stony corals. Primers that amplify a ∼177 bp fragment from the nuclear gene encoding the 54 kDa subunit of the signal recognition particle (SRP54) were developed for the octocoral genus Carijoa. Cloning results from 141 individuals suggest that this hypervariable nuclear locus is a single-copy gene. Sequencing revealed a potential cryptic species previously thought to be Carijoa riisei. Results from an Analysis of Molecular Variance (AMOVA) based on mitochondrial DNA (mtDNA) explained <10% of the variation between Atlantic and Pacific samples of C. riisei (F _st = 0.47), whereas the same comparison with SRP54 explained >33% of the variation (F _st = 0.54). Using previously reported degenerate primers for SRP54, high levels of sequence variation were found at this locus across both scleractinian and octocorals. For example, pairwise sequence divergence within octocorals was ∼8–13 times greater with SRP54 than with mtDNA, and, up to 2.8% pairwise sequence divergence was found in SRP54 among individuals of Pocillopora whereas no variation at all was found in mtDNA markers. This case study with the octocoral C. riisei shows that variation in SRP54 appears sufficient to address questions of phylogeography as well as systematics of closely related species.     

Short term viability of soft tissue detached from the skeleton of reef-building corals

We have induced soft tissue detachment from the skeleton of two colonial hard corals of the Pocilloporid family, both in vivo and in vitro. A parallel was made between polyp “bail-out”, i.e. field and laboratory-observed detachment of tissue fragments alone from the skeleton, and the dissociation method used for initiation of coral primary cell cultures. The in vitro approach provided insights into the active cellular re-arrangement mechanisms underlying coral tissue detachment. Functional polyps were not regenerated. Viability of tissue isolates detached from coral skeleton was probed for their use as a model for short-term biological assays. Cell viability dropped from 70% to 30% within the first week maintenance in vitro. Short-term isolate cultures limited to 3 days are a compromise allowing attachment of coral cells, yet preserving viability at about 70% of the total coral cell population.     

The distribution of scleractinian corals in the Bay of Biscay, NE Atlantic

Studies on the distribution of scleractinian corals in the Bay of Biscay were relatively numerous during the nineteenth and the first half of the twentieth century. Yet, recent reports are scattered, sometimes unpublished, and therefore knowledge about the current coral occurrence in the area is limited. This study aims at compiling the available historical and more recently collected information on the occurrence of scleractinian corals in the Bay of Biscay. Data from two recent cruises are included and compared with previous explored coral sites from as early as 1830 up to 1995. A database of 347 records including 34 described species of scleractinians highlights that the slope of the Bay of Biscay is an important habitat for scleractinians. This could be expected due to the high topographic relief providing the necessary hard substrate and accelerated bottom current flow that corals require. Further exploration of the occurrence and ecology of corals in the area is recommended to support the conservation of cold-water coral reefs along the European margin. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Odor-mediated aggregation enhances the colonization ability of Drosophila melanogaster

Animal aggregation is a general phenomenon in ecological systems. Aggregations are generally considered as an evolutionary advantageous state in which members derive the benefits of mate choice and protection against natural enemies, balanced by the costs of limiting resources and intraspecific competition. Many insects use chemical information to find conspecifics and to form aggregations. In this study, we describe a spatio-temporal simulation model designed to explore and quantify the effects of the strength of chemical attraction, on the colonization ability of a fruit fly (Drosophila melanogaster) population. We found that the use of infochemicals is crucial for colonizing an area. Fruit flies subject to an Allee effect that are unable to respond to chemical information could not successfully colonize the area and went extinct within four generations. This was mainly caused by very high mortality due to the Allee effect. Even when the Allee effect did not play a role, the random dispersing population had more difficulties in colonizing the area and is doomed to extinction in the long run. When fruit flies had the ability to respond to chemical information, they successfully colonized the orchard. This happened faster, for stronger attraction to chemical information. In addition, more fruit flies were able to find the resources and the settlement on the resources was much higher. This resulted in a reduced mortality due to the Allee effect for fruit flies able to respond to chemical information. Odor-mediated aggregation thus enhances the colonization ability of D. melanogaster. Even a weak attraction to chemical information paved the way to successfully colonize the orchard.     

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.     

Competitive strategies of soft corals (Coelenterata: Octocorallia). II. Variable defensive responses and susceptibility to scleractinian corals

Interactions involving competition for space between several species of alcyonacean and scleractinian corals were assessed experimentally on Britomart Reef, central region of the Great Barrier Reef, Australia. Colonies of three soft coral species, Sarcophyton ehrenbergi Marenzeller, Nephthea brassica Kukenthal, and Capnella lacertiliensis Macfayden Forskal (Coelenterata:Alcyonacea) were relocated within stands of two scleractinian corals, Parités andrewsi Vaughan (= P. cylindrica Dana) and Pavona cactus Förskal (Coelenterata:Scleractinia). Undisturbed scleractinian and relocated alcyonacean controls were also monitored.Alcyonacean corals induced necrosis of tissue in scleractinian corals. Necrosis was significantly more pronounced when colonies were in contact but was also observed in the absence of contact, implicating the presence of active allelopathic agents. Scleractinian coral species varied in their susceptibility to the ill effects of alcyonaceans, with Pontes andrewsi being more susceptible than Pavona cactus. Of the soft corals, Nephthea caused the highest degree of mortality in the two scleractinian corals examined and Sarcophyton the least. Some soft corals appear to retain their toxins while others release them, implying a combination of anti-predatory and anti-competitor roles for the secondary metabolites. Scleractinian corals were often overgrown by soft corals.Both species of scleractinian corals were found to cause approximately equal amounts of tissue necrosis in alcyonaceans. These effects were more pronounced when colonies were in direct contact. The necrotic effects among alcyonacean corals were species-specific. Alcyonaceans also overgrew scleractinian corals and secreted a protective polysaccharide layer in areas proximal to scleractinians. Secretion of this layer was stimulated differentially by the two scleractinian species and also varied in frequency of occurrence among the alcyonaceans.High levels of tissue necrosis were observed in both groups of organisms within 3 wk of initiation of the experiment. Necrosis increased with time in the scleractinian corals and decreased in the alcyonaceans. The development of a protective polysaccharide layer in the alcyonaceans increased with time.     

Effects of fish predation and seaweed competition on the survival and growth of corals

On Caribbean coral reefs, high rates of grazing by herbivorous fishes are thought to benefit corals because fishes consume competing seaweeds. We conducted field experiments in the Florida Keys, USA, to examine the effects of grazing fishes on coral/seaweed competition. Initially, fragments of Porites divaracata from an inshore habitat were transplanted into full-cage, half-cage, and no-cage treatments on a fore-reef. Within 48 h, 56% of the unprotected corals in half-cage and no-cage treatments (62 of 111) were completely consumed. Stoplight parrotfish (Sparisoma viride) were the major coral predators, with redband parrotfish (S. aurofrenatum) also commonly attacking this coral. Next, we transplanted fragments of P. porites collected from the fore-reef habitat where our caging experiments were being conducted into the three cage treatments, half in the presence of transplanted seaweeds, and half onto initially clean substrates. The corals were allowed to grow in these conditions, with concurrent development of competing seaweeds, for 14 weeks. Although seaweed cover and biomass were both significantly greater in the full-cage treatment, coral growth did not differ significantly between cage treatments even though corals placed with pre-planted seaweeds grew significantly less than corals placed on initially clean substrate. This surprising result occurred because parrotfishes not only grazed algae from accessible treatments, but also fed directly on our coral transplants. Parrotfish feeding scars were significantly more abundant on P. porites from the half and no-cage treatments than on corals in the full cages. On this Florida reef, direct fish predation on some coral species (P. divaracata) can exclude them from fore-reef areas, as has previously been shown for certain seaweeds and sponges. For other corals that live on the fore-reef (P. porites), the benefits of fishes removing seaweeds can be counterbalanced by the detrimental effects of fishes directly consuming corals. Received: 31 May 1997 / Accepted: 2 September 1997     

Mitochondrial sequences of <Emphasis Type=Italic>Seriatopora</Emphasis> corals show little agreement with morphology and reveal the duplication of a tRNA gene near the control region

The taxonomy of corals of the genus Seriatopora has not previously been studied using molecular sequence markers. As a first step toward a re-evaluation of species boundaries in this genus, mitochondrial sequence variability was analyzed in 51 samples collected from Okinawa, New Caledonia, and the Philippines. Four clusters of sequences were detected that showed little concordance with species currently recognized on a morphological basis. The most likely explanation is that the skeletal characters used for species identification are highly variable (polymorphic or phenotypically plastic); alternative explanations include introgression/hybridization, or deep coalescence and the retention of ancestral mitochondrial polymorphisms. In all individuals sequenced, two copies of trnW were found on either side of the atp8 gene near the putative D-loop, a novel mitochondrial gene arrangement that may have arisen from a duplication of the trnW-atp8 region followed by a deletion of one atp8.     

Effects of Festuca paniculata on the compensatory growth response of Centaurea uniflora in the French Alps

The independent effects of herbivores and neighbors on plants are generally negative, and therefore the combined effects of these interactions are generally assumed to have additive or multiplicative negative effects on plant growth. However, because herbivores can stimulate the growth of plants (compensation). and neighbors can facilitate each other, the combined effects of herbivory and plant-plant interactions can be highly variable and poorly predicted by current competition and plant-herbivore theory. In some cases in North America, Festuca species appear to facilitate invasive Centaurea species and enhance their compensatory responses in controlled greenhouse conditions. We explored the interactions between herbivory and neighbor effects in the French Alps by testing the effect of the neighbor, Festuca paniculata L., on the compensatory growth response of defoliated Centaurea uniflora L. over two growing seasons. Seventy percent of aboveground C. uniflora biomass was clipped at each of seven times throughout two growing seasons in the presence or absence of F. paniculata. Centaurea uniflora compensated for severe damage in the first year, but was negatively affected by defoliation in the second year. Defoliating C. uniflora reduced final aboveground biomass by 44% and flower number by 64%, but did not affect survival. Unlike observations for other Centaurea and Festuca species, F. paniculata had significant competitive effects on C. uniflora. Festuca paniculata neither enhanced compensatory responses of C. uniflora nor increased the negative effects of defoliation. Our results show that compensatory responses can weaken over time, but that neighboring plants do not necessarily increase the negative effects of defoliation.     

Effects of macroalgal identity on epifaunal assemblages: native species versus the invasive species Sargassum muticum

Seaweeds are a refuge from stressful conditions associated with life on rocky intertidal shores, and there is evidence that different macrophytes support different assemblages of mobile epifauna. Introduction of non-indigenous macroalgae may have a great impact on associated epifaunal assemblages and ecosystem processes in coastal areas. Previous studies have reported conflicting evidences for the ability of epifauna to colonize non-indigenous species. Here, we analyzed epifaunal assemblages associated with three species of macroalgae that are very abundant on intertidal shores along the Galician coast: the two native species Bifurcaria bifurcata and Saccorhiza polyschides and the invasive species Sargassum muticum. We collected samples of each species from three different sites at three different times to test whether variability of epifaunal assemblages was consistent over space and time. Epifaunal assemblages differed between the three macroalgae. Results suggested that stability and morphology of habitat played an important role in shaping the structure of epifaunal assemblages. This study also showed that the invasive S. muticum offered a suitable habitat for many invertebrates.     

Mycelium growth kinetics and optimal temperature conditions for the cultivation of edible mushroom species on lignocellulosic substrates

The influence of environmental parameters on mycelial linear growth ofPleurotus ostreatus, P. eryngii, P. pulmonarius, Agrocybe aegerita, Lentinula edodes, Volvariella volvacea andAuricularia auricula-judae was determined in two different nutrient media in a wide range of temperature, forming the basis for the assessment of their temperature optimaV. volvacea grew faster at 35°C,P. eryngii at 25°C,P. ostreatus andP. pulmonarius at 30°C,A. aegerita at 25 or 30°C andA. auricula-judae at 20 or 25°C depending on the nutrient medium used andL. edodes at 20 or 30°C depending on the strain examined. The mycelium extension rates were evaluated on seven mushroom cultivation substrates: wheat straw, cotton gin-trash, peanut shells, poplar sawdust, oak sawdust, corn cobs and olive press-cake. The mycelium extension rates (linear growth and colonization rates) were determined by the ‘race-tube’ technique, and were found to be the highest on cotton gin-trash, peanut shells and poplar sawdust forPleurotus spp. andA. aegerita. Wheat straw, peanut shells and particularly cotton gin-trash supported fast growth ofV. volvacea, whereas wheat straw was the most suitable substrate forL. edodes andA. auricula-judae. Supplemented oak sawdust and olive press-cake were poor substrates for most species examined, white almost all strains performed adequately on corn cobs.     

Effects of species evenness and dominant species identity on multiple ecosystem functions in model grassland communities

Ecosystems provide multiple services upon which humans depend. Understanding the drivers of the ecosystem functions that support these services is therefore important. Much research has investigated how species richness influences functioning, but we lack knowledge of how other community attributes affect ecosystem functioning. Species evenness, species spatial arrangement, and the identity of dominant species are three attributes that could affect ecosystem functioning, by altering the relative abundance of functional traits and the probability of synergistic species interactions such as facilitation and complementary resource use. We tested the effect of these three community attributes and their interactions on ecosystem functions over a growing season, using model grassland communities consisting of three plant species from three functional groups: a grass (Anthoxanthum odoratum), a forb (Plantago lanceolata), and a N-fixing forb (Lotus corniculatus). We measured multiple ecosystem functions that support ecosystem services, including ecosystem gas exchange, water retention, C and N loss in leachates, and plant biomass production. Species evenness and dominant species identity strongly influenced the ecosystem functions measured, but spatial arrangement had few effects. By the end of the growing season, evenness consistently enhanced ecosystem functioning and this effect occurred regardless of dominant species identity. The identity of the dominant species under which the highest level of functioning was attained varied across the growing season. Spatial arrangement had the weakest effect on functioning, but interacted with dominant species identity to affect some functions. Our results highlight the importance of understanding the role of multiple community attributes in driving ecosystem functioning.     

Aggregation pattern of individuals and the outcomes of competition within and between species: Differential equation models

The influence of spatial distribution pattern on the outcomes of intra- and interspecific competition is studied theoretically. The models developed are the generalized logistic andVolterra equations, whereLloyd 's indices of intra- and interspecies mean crowding were incorporated with their assumed linear relationship to mean density in order to express the intensity of crowding which is really effective to the existing individuals. It is shown that while the increasing patchiness of distribution has a pronounced effect of promoting the intraspecific competition and lowering the equilibrium density for individual populations, it generally relaxes the interspecific competition, making it easy for different species sharing the same niche, which would otherwise be incompatible, to coexist stably. These models thus provide a simplest theoretical basis to explain why many insect populations in nature are kept relatively rare in number and why a number of allied species often coexist freely sharing the same resource, against the “competitive exclusion principle” deduced from the originalVolterra equations.     

Effects of nitrogen limitation on species replacement dynamics during early secondary succession on a semiarid sagebrush site

Summary A soil nitrogen (N) availability gradient was induced on a disturbed sagebrush site in northwestern Colorado by fertilizing with nitrogen (high available N), applying sucrose (low available N), and applying neither nitrogen nor sucrose (control). Species composition was studied for 3 years. At the end of the study, N concentration of aboveground tissue of 3 major species was determined. The rate of species replacement was most rapid on plots receiving the sucrose treatment and was slowest on plots receiving the N treatment. Early-seral dominats had greater tissue N concentrations when availability of the resource was high but lower tissue N concentrations when available soil N became limited. Midseral dominants displayed the opposite pattern. These results suggest that the supply of available soil N, and therefore the dynamics of N incorporation in perennial plant tissue, is a primary mechanism in controlling the rate of secondary succession within this semiarid ecosystem.