Sea anemones may thrive in a high CO2 world

Increased seawater pCO 2, and in turn 'ocean acidification' (OA), is predicted to profoundly impact marine ecosystem diversity and function this century. Much research has already focussed on calcifying reef-forming corals (Class: Anthozoa) that appear particularly susceptible to OA via reduced net calcification. However, here we show that OA-like conditions can simultaneously enhance the ecological success of non-calcifying anthozoans, which not only play key ecological and biogeochemical roles in present day benthic ecosystems but also represent a model organism should calcifying anthozoans exist as less calcified (soft-bodied) forms in future oceans. Increased growth (abundance and size) of the sea anemone (Anemonia viridis) population was observed along a natural CO 2 gradient at Vulcano, Italy. Both gross photosynthesis (P G) and respiration (R) increased with pCO 2 indicating that the increased growth was, at least in part, fuelled by bottom up (CO 2 stimulation) of metabolism. The increase of P G outweighed that of R and the genetic identity of the symbiotic microalgae (Symbiodinium spp.) remained unchanged (type A19) suggesting proximity to the vent site relieved CO 2 limitation of the anemones' symbiotic microalgal population. Our observations of enhanced productivity with pCO 2, which are consistent with previous reports for some calcifying corals, convey an increase in fitness that may enable non-calcifying anthozoans to thrive in future environments, i.e. higher seawater pCO 2. Understanding how CO 2-enhanced productivity of non- (and less-) calcifying anthozoans applies more widely to tropical ecosystems is a priority where such organisms can dominate benthic ecosystems, in particular following localized anthropogenic stress. © 2012 Blackwell Publishing Ltd

Host–symbiont combinations dictate the photo-physiological response of reef-building corals to thermal stress

High sea surface temperatures often lead to coral bleaching wherein reef-building corals lose significant numbers of their endosymbiotic dinoflagellates (Symbiodiniaceae). These increasingly frequent bleaching events often result in large scale coral mortality, thereby devasting reef systems throughout the world. The reef habitats surrounding Palau are ideal for investigating coral responses to climate perturbation, where many inshore bays are subject to higher water temperature as compared with offshore barrier reefs. We examined fourteen physiological traits in response to high temperature across various symbiotic dinoflagellates in four common Pacific coral species, Acropora muricata, Coelastrea aspera, Cyphastrea chalcidicum and Pachyseris rugosa found in both offshore and inshore habitats. Inshore corals were dominated by a single homogenous population of the stress tolerant symbiont Durusdinium trenchii, yet symbiont thermal response and physiology differed significantly across coral species. In contrast, offshore corals harbored specific species of Cladocopium spp. (ITS2 rDNA type-C) yet all experienced similar patterns of photoinactivation and symbiont loss when heated. Additionally, cell volume and light absorption properties increased in heated Cladocopium spp., leading to a greater loss in photo-regulation. While inshore coral temperature response was consistently muted relative to their offshore counterparts, high physiological variability in D. trenchii across inshore corals suggests that bleaching resilience among even the most stress tolerant symbionts is still heavily influenced by their host environment

Long-Range Dispersal and High-Latitude Environments Influence the Population Structure of a “Stress-Tolerant” Dinoflagellate Endosymbiont

<div><p>The migration and dispersal of stress-tolerant symbiotic dinoflagellates (genus <i>Symbiodinium</i>) may influence the response of symbiotic reef-building corals to a warming climate. We analyzed the genetic structure of the stress-tolerant endosymbiont, <i>Symbiodinium glynni</i><i>nomen nudum</i> (ITS2 - <i>D1</i>), obtained from <i>Pocillopora</i> colonies that dominate eastern Pacific coral communities. Eleven microsatellite loci identified genotypically diverse populations with minimal genetic subdivision throughout the Eastern Tropical Pacific, encompassing 1000’s of square kilometers from mainland Mexico to the Galapagos Islands. The lack of population differentiation over these distances corresponds with extensive regional host connectivity and indicates that <i>Pocillopora</i> larvae, which maternally inherit their symbionts, aid in the dispersal of this symbiont. In contrast to its host, however, subtropical populations of <i>S. glynni</i> in the Gulf of California (Sea of Cortez) were strongly differentiated from populations in tropical eastern Pacific. Selection pressures related to large seasonal fluctuations in temperature and irradiance likely explain this abrupt genetic discontinuity. We infer that <i>S. glynni</i> genotypes harbored by host larvae arriving from more southern locations are rapidly replaced by genotypes adapted to more temperate environments. The strong population structure of <i>S. glynni</i> corresponds with fluctuating environmental conditions and suggests that these genetically diverse populations have the potential to evolve rapidly to changing environments and reveals the importance of environmental extremes in driving microbial eukaryote (e.g., plankton) speciation in marine ecosystems.</p> </div

Biogeographic map of the eastern Pacific showing differentiated populations of <i>S. glynni</i>.

<p>Differentiated populations of <i>S. glynni</i> as determined by statistical analyses of microsatellite data. Open circles represent sampling locations with name abbreviations and arrows depict prevailing ocean currents: Gulf of California (GoC), Banderas Bay (BB), Gulf of Tehuantepec (OAX), Clipperton Atoll (CLP), Gulf of Panama (PAN) and Galapagos Islands (GAL). Populations in the subtropical Gulf of California (shaded in purple) were genetically distinct from tropical populations (orange). The left most Structure plot shows genetic homogeneity across <i>Pocillopora</i> type 1 populations throughout the eastern Pacific (data obtained from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0079208#B16" target="_blank">16</a>]). The inset panel in the upper right quantifies the instances where a cloned <i>S. glynni</i> genotype was found between geographically distant locations (proportions = individuals shared/total # unique MLGs between two locations). </p

Ten year averages of monthly means of SSTs and PAR for the six sampling locations.

<p>Ten year averages of monthly means (2000 - 2009) of sea surface temperatures (SSTs) and photosynthetically available irradiance (PAR) for the six sampling locations. (a) and (c) depict monthly averages and standard deviations at all locations, while (b) and (d) are box plots showing annual mean, first and third quartiles, and maximum and minimum seasonal ranges by location. Monthly averages were acquired from NASA’s Giovanni website.</p

Structure plot of <i>S. glynni</i> populations from the tropical and subtropical eastern Pacific.

<p>Structure plot of <i>S. glynni</i> populations based on allelic frequencies at 11 microsatellite loci. Each bar in the graph represents the probability that a sample belongs to a particular color-coded population. Each graph represents analyses for a particular number of populations (K) run under an admixture with a correlated allele frequency model. (a) Major differentiation occurred between the Gulf of California population and populations in the ETP (<i>k</i> = 2). (b) Additional clustering occurred in the ETP, yet did not correspond to location, depth or host morphospecies (<i>k</i> = 3).</p

R-script for the analysis Symbiodinium type A3 in the Eastern Caribbean

Source code for the analysis of observed pairwise genetic difference (PWD), expected PWD under panmixia, and permutation test for departure from expected pairwise genetic difference for microsatellite MLGs datasets from a population of Symbiodinium A3 (S. ‘fitti’ nomen nudum) in the Eastern Caribbean, West Atlantic Ocean

Symbiodinium type C7 Belize

Excel data files of multilocus genotypes (MLGs) based on microsatellites for Symbiodinium type C7 in the western Caribbean

Data from: Microbial invasion of the Caribbean by an Indo-Pacific coral zooxanthella

Human-induced environmental changes have ushered in the rapid decline of coral reef ecosystems, particularly by disrupting the symbioses between reef-building corals and their photosymbionts. However, escalating stressful conditions enable some symbionts to thrive as opportunists. We present evidence that a stress-tolerant “zooxanthella” from the Indo-Pacific Ocean, Symbiodinium trenchii, has rapidly spread to coral communities across the Greater Caribbean. In marked contrast to populations from the Indo-Pacific, Atlantic populations of S. trenchii contained exceptionally low genetic diversity, including several widespread and genetically similar clones. Colonies with this symbiont tolerate temperatures 1–2 °C higher than other host–symbiont combinations; however, calcification by hosts harboring S. trenchii is reduced by nearly half, compared with those harboring natives, and suggests that these new symbioses are maladapted. Unforeseen opportunism and geographical expansion by invasive mutualistic microbes could profoundly influence the response of reef coral symbioses to major environmental perturbations but may ultimately compromise ecosystem stability and function