A revision of Holm's late Mid and Late Cambrian hyoliths of Sweden

Type specimens of Hyolithus tenuistriatus Linnarsson show this species to be the second definitive representative of the North American genus Nevadotheca in Scandinavia; H. subcostatus Wallerius is questionably assigned to that genus. Restudy of the types of the hyolithids Hyolithus pennatulus Holm confirms the earlier assignment of that species to Carinolithes Syssoiev and H. araneus Holm is assigned to Lovenedolithes gen. nov. Morphology of the orthothecids Hyolithus ( Orthotheca ) cor Holm, H . ( O .) excavatus Holm and H . ( O .) lineatulus Holm supports placement of the first in Contitheca Syssoiev and the others in Decoritheca Syssoiev. Hyolithus ( Orthotheca ) stylus Holm, type species of Circotheca Syssoiev, is of special significance as the basis for both a family and an order. The morphology of the species suggests that ordinal status is not warranted. Hyolithus obscurus Holm, on which Linevitus Syssoiev is founded, is known only from poorly preserved internal moulds and is unrecognizable.     

A revision of Holm's Early and early Mid Cambrian hyoliths Of Sweden

ABSTRACT. Re-examination of type specimens of Early Cambrian and early Mid Cambrian hyoliths from Sweden confirms placement of Hyolithes teretiusculus Linnarsson in Hexitheca Syssoiev, and reassignment to the order Hyolithida rather than Orthothecida. Inclusion of Hyolithes affinis Holm within Decoritheca Syssoiev is re-confirmed, and Hyolithes socialis Linnarsson is now referred to Nevadotheca Malinky and Slapylites Marek. An operculum included under Hyolithes oelandicus Holm is transferred provisionally to Maxilites Marek, and conchs of that species are placed under Tulenicornus Val'kov with question. No other hyolith species of Holm can be definitely assigned to genus. The rarity of well preserved opercula is a major impediment to recognizing hyolith taxa confidently, and we follow Holm in attributing the comparative rarity of opercula to the fact that in some hyolith taxa the operculum may have been composed of a different, and perhaps less stable, material than the rest of the conch.     

A Revision of Early To Mid Ordovician Hyoliths from Sweden

Hyolith assemblages of early to mid Ordovician age in Sweden include the hyolithids Hyolithus bisulcatus Holm, H. concinnus Holm and H. innotatus Holm, which are confirmed as representatives of Hyolithes Eichwald. Dorsolinevitus Syssoiev is known from D. dispar (Holm), D. textilis (Holm) and D. vomer (Holm), and Carinolithes Syssoiev is represented by C. hospes (Holm) and C. triumvir (Holm). Sulcavitus caelatus (Holm), the type species that forms the basis for a family and even an order according to some, is redescribed; the order is suppressed. Hyolithus cymbium Holm is transferred to Stelterella gen. nov., and Theca crispata (Boll) is now the type species of Crispatella gen. nov. The unusual orthothecid Quadrotheca quadrangularis (Holm) is redescribed; the concept of Trapezotheca aemula (Holm) is emended, and Semielliptotheca dens (Holm) is transferred to Trapezotheca . Semielliptotheca Syssoiev is poorly known from only one species, S. rosmara (Holm), and that genus is now considered to be unrecognizable. Hyolithus exaratus Hadding is identified as closely related to the gastropod Lytospira norvegica Koken, and specimens of Hyolithus sp. nos 11, 12 and 13 Holm and Hyolithus sp. indet. Wiman, remain to be located.     

Porpostoma guamensis n. sp., a philasterine scuticociliate associated with brown-band disease of corals

Brown band disease of coral is caused by a ciliate that consumes the tissue of the corals in the genus Acropora. We describe the ciliate associated with this disease on Guam, based on: general morphology, division stages, and ciliature observed on live and protargol-stained specimens; modification of the oral structures between divisional stages, observed on protargol-stained specimens; and some aspects of behavior in field and laboratory studies. Porpostoma guamensis n. sp. is elongate and has ciliature typical for the genus; live cells are 70-500 × 20-75 μm; the macronucleus is sausage-like, elongate but often bent, positioned centrally along the main cell axis; the oral ciliature follows a basic pattern, being composed of three adoral polykinetidal regions, as described for other species in the genus, although there is variability in the organization, especially in large cells where the three regions are not easily distinguished. Ciliates fed on coral with their oral region adjacent to the tissue, which they engulfed, leaving the coral a bare skeleton. Both zooxanthellae and nematocysts from coral occurred in the ciliates. Zooxanthellae appeared to be ingested alive but deteriorated within 2-3 days. Ciliates formed thin-walled division cysts on the coral and divided up to 3 times. Cysts formed around daughter cells within cysts. We provide some observations on the complex division pattern of the ciliate (i.e. tomont-trophont-cyst) and propose a possible complete pattern that requires further validation.     

A comparison between coral colonies of the genus Madracis and simulated forms

In addition to experimental studies, computational models provide valuable information about colony development in scleractinian corals. Using our simulation model, we show how environmental factors such as nutrient distribution and light availability affect growth patterns of coral colonies. To compare the simulated coral growth forms with those of real coral colonies, we quantitatively compared our modelling results with coral colonies of the morphologically variable Caribbean coral genus Madracis. Madracis species encompass a relatively large morphological variation in colony morphology and hence represent a suitable genus to compare, for the first time, simulated and real coral growth forms in three dimensions using a quantitative approach. This quantitative analysis of three-dimensional growth forms is based on a number of morphometric parameters (such as branch thickness, branch spacing, etc.). Our results show that simulated coral morphologies share several morphological features with real coral colonies (M. mirabilis, M. decactis, M. formosa and M. carmabi). A significant correlation was found between branch thickness and branch spacing for both real and simulated growth forms. Our present model is able to partly capture the morphological variation in closely related and morphologically variable coral species of the genus Madracis.     

Spatial pattern of coral diversity in Luhuitou fringing reef, Sanya, China

84 quadrats from 5 vertical transects of Luhuitou fringing reef are investigated in detail by using video-quadrat and indoor-interpretation methods. The results show that (1) the reef consists of 69 species of hermatypic corals belonging to 24 genera and 13 families which are unevenly distributed in abundance. (2) Among all the corals, Porites lutea is the most dominant species with importance value percentage up to 36.62%; Porites and Acropora are dominant genera with importance value percentages 43.85% and 22.88%, respectively. (3) There exist distinct spatial differences in coral communities. Both the coral covers and coral diversity indices on the northeastern transects are higher than those on the central and southern transects. (4) Coral communities also show remarkable zonal characteristics with less coral species occurring on reef flat than on reef slope. The importance value percentage of the sole dominant coral genus, Porites, is over 50%, while on the reef slope, the importance value percentages are 28.33% for the first dominant genus Acropora and 26.71% for the second dominant genus Porites. Our further analysis suggests that the spatial and zonal differences of coral diversity pattern are correlated with both natural environmental changes and human activities. The shallow water reef flat is frequently exposed at low tide and it receives more anthropogenic influences (including dredging and trampling) than the deep water reef slope. Thus, the coral community on the reef flat is not as well developed as that on reef slope. The relatively poor coral covers and coral diversity indices on the central and southern transects are closely related to heavy human activities around these sites such as aquaculture, fishing and coastal sewage drainage. Therefore, the impact of human activities must be taken into account in developing strategies for the protection of this coral reef.     

Spatial pattern of coral diversity in Luhuitou fringing reef, Sanya, China

84 quadrats from 5 vertical transects of Luhuitou fringing reef are investigated in detail by using video-quadrat and indoor-interpretation methods. The results show that (1) the reef consists of 69 species of hermatypic corals belonging to 24 genera and 13 families which are unevenly distributed in abundance. (2) Among all the corals, Porites lutea is the most dominant species with importance value percentage up to 36.62%; Porites and Acropora are dominant genera with importance value percentages 43.85% and 22.88%, respectively. (3) There exist distinct spatial differences in coral communities. Both the coral covers and coral diversity indices on the northeastern transects are higher than those on the central and southern transects. (4) Coral communities also show remarkable zonal characteristics with less coral species occurring on reef flat than on reef slope. The importance value percentage of the sole dominant coral genus, Porites, is over 50%, while on the reef slope, the importance value percentages are 28.33% for the first dominant genus Acropora and 26.71% for the second dominant genus Porites. Our further analysis suggests that the spatial and zonal differences of coral diversity pattern are correlated with both natural environmental changes and human activities. The shallow water reef flat is frequently exposed at low tide and it receives more anthropogenic influences (including dredging and trampling) than the deep water reef slope. Thus, the coral community on the reef flat is not as well developed as that on reef slope. The relatively poor coral covers and coral diversity indices on the central and southern transects are closely related to heavy human activities around these sites such as aquaculture, fishing and coastal sewage drainage. Therefore, the impact of human activities must be taken into account in developing strategies for the protection of this coral reef.     

Host shift and speciation in a coral-feeding nudibranch

While the role of host preference in ecological speciation has been investigated extensively in terrestrial systems, very little is known in marine environments. Host preference combined with mate choice on the preferred host can lead to population subdivision and adaptation leading to host shifts. We use a phylogenetic approach based on two mitochondrial genetic markers to disentangle the taxonomic status and to investigate the role of host specificity in the speciation of the nudibranch genus Phestilla (Gastropoda, Opisthobranchia) from Guam, Palau and Hawaii. Species of the genus Phestilla complete their life cycle almost entirely on their specific host coral (species of Porites, Goniopora and Tubastrea). They reproduce on their host coral and their planktonic larvae require a host-specific chemical cue to metamorphose and settle onto their host. The phylogenetic trees of the combined cytochrome oxidase I and ribosomal 16S gene sequences clarify the relationship among species of Phestilla identifying most of the nominal species as monophyletic clades. We found a possible case of host shift from Porites to Goniopora and Tubastrea in sympatric Phestilla spp. This represents one of the first documented cases of host shift as a mechanism underlying speciation in a marine invertebrate. Furthermore, we found highly divergent clades within Phestilla sp. 1 and Phestilla minor (8.1-11.1%), suggesting cryptic speciation. The presence of a strong phylogenetic signal for the coral host confirms that the tight link between species of Phestilla and their host coral probably played an important role in speciation within this genus.     

Molecular ecology, speciation, and evolution of the reef fish genus Anisotremus

Grunts (family Haemulidae) in the genus Anisotremus comprise 10 described species which occur predominantly on coral reefs and subtropical rocky reefs in the Neotropics of the Tropical Eastern Pacific the Caribbean and adjacent waters. In this study, the phylogenetic relationships for all described species were examined based on one mitochondrial gene (cytochrome b) and one nuclear marker (the first intron of the ribosomal protein S7). Closely related species of the genus Haemulon and the single representative of the genus Genyatremus, G. luteus were also included in the analysis, following the suggestion, based on morphological data, that they may be closely related to, or possibly placed within, Anisotremus. Two sweetlips, genus Plectorhinchus, which belong to the recognized sister subfamily Plectorhynchinae, were used as outgroups. Two species pairs in the ingroup genus Anisotremus are geminate species, which presumably diverged after the rise of the Isthmus of Panama, thus providing an internal molecular clock calibration. This allowed for a comprehensive evolutionary scenario for the genus. Our data were consistent with two independent allopatric speciation events (geminate species), and one likely sympatric speciation event. Our data were also consistent with the placement of Genyatremus and Haemulon within the genus Anisotremus, thus breaking its monophyletic status. As proposed for other coral reef species, Anisotremus seems to have colonized coral reefs from non-coral reef habitats. In addition, ancestral species seem to have been widespread, since species that are currently found in Brazilian and Pacific waters are basal on the phylogenetic tree. Finally, this study adds to the hypothesis of a secondary evolutionary center in the New World.     

广西泥盆纪早埃姆斯期郁江组Heterophaulactis Yu,1974的再研究(英文)

Heterophaulactis Yu是作者建立并发表于1974年的一四射珊瑚属,产自广西郁江沿岸、南宁至六景一带的泥盆纪郁江组,其时代属早埃姆斯期牙形刺kitabacus带(前dehiscens带)。对此珊瑚属再行研究,是出于:1)发表在"中国南方泥盆系的新进展"一文,是与其它门类化石共同作为划分和对比地层的化石依据,只限于中文简短描述,对化石图影的展示也有严格的数量限制。尽管此属己被收录在Hill(1981)主编的古生物专论的珊瑚分册中,也只是简短的英文描述和有限的图影,未能充分展示其骨骼演变特征;2)此属的分类位置、科的归属及与相关属的属征比较与讨论,当初均未交待,应予阐明;3)Heterophaulactis属的地理分布广,遍及滇桂两省,通过再研究,其产地已扩展至中国西北地区;其地层分布又有一定的时限性,在广西仅限于郁江组下部的石州段,时代为kitaba-cus带,其它地区也仅见于下泥盆统。文中对Heterophaulactis属的模式种,Heterophaulactis semicrassa的骨骼特征及个体发育过程中的演变均作详细的英文描述和图影展示;与相关属比较之后,认为与本属关系最为密切的是产于西秦岭山区下泥盆统、发表在西北区化石图册上的有些属种,其中的有些属种可以归于本属。文中还记述一新建种Heterophaulactis yujiangense sp.nov.。文章对Heterophaulactis的分类位置和科的归属也有详细比较讨论,认为它是源出自志留纪Pycnactis—Phaulactis的演化序列,应归属于Lykophyllidae Wedekind,1927科。对Miroelasmatinae Cao,1983亚科的原始定义作全面修订后,把它归为Lykophyllidae Wedekind,1927科下的一个亚科;在对化石图册及相关文献上记述的产自西秦岭区下泥盆统四射珊瑚属种的全面修订之前,暂把以下各属置于此亚科:Heterophaulactis Yu,Miroelasma Cao,Qinlingophyllum Cao,Wenxianophyllum Cao,Protaulacophy-llum Cao,Bethanyphyllum sensu Cao,Aulacophyllum sensu Cao和Aulacophyllum sensu Zhang。     

Hemicyclops columnaris sp.n. (Copepoda, Poecilostomatoida, Clausidiidae) Associated with a Coral in Panama (Pacific Side)

Hemicyclops columnaris sp.n. is described from the scleractinian coral Porites lobata Dana on the Pacific coast of Panama. The new species may be distinguished from its 23 congeners by a combination of the body size and the shape of the genital segment in the female. Although certain members of the genus Hemicyclops are associated with crustaceans, polychaetes and other marine invertebrates, this is the first record of a species of this genus from a hard coral.     

Spatial variability in distribution and prevalence of skeletal eroding band and brown band disease in Faafu Atoll,Maldives

Indo-Pacific coral diseases are currently considered one of the 15 globally important threats requiring conservation attention. The coral reefs of the Maldives are experiencing a local decline, with the presence of some coral diseases reported only recently. We investigated the spatial variability in prevalence and distribution of two protozoan diseases, skeletal eroding band (SEB) and brown band disease (BrB), in three islands in the Faafu Atoll: an inhabited island (Magoodhoo), an uninhabited island (Adanga) and a resort island (Filitheyo). Our study revealed a low level of mean disease prevalence for both diseases (<1 %), with Magoodhoo and Adanga being the most affected by BrB and SEB, respectively. However, our preliminary temporal investigations revealed an increment of both coral diseases in Adanga during the last 4 years. Furthermore, we observed different spatial patterns between the two diseases, with SEB positively correlated to dead coral coverage. Finally, Acropora was the most affected coral genus, hosting both coral diseases. Considering that Acropora is the most abundant genus in the archipelago and many other areas in the Indo-Pacific, this finding highlights the need for particular conservation efforts for this genus. These results represent just a first step in the assessment of Maldivian coral disease epidemiology, and more detailed analyses of regional differences in diseases prevalence are needed to further explore their impacts on Maldivian coral reefs.     

Remarkable nutritional diversity of basidiomycetes in the Corticiales, including a new foliicolous species of Marchandiomyces (anamorphic Basidiomycota, Corticiaceae) from Australia

Fungi in the basidiomycete order Corticiales are remarkably diverse nutritionally, including a variety of saprotrophs, plant and fungal pathogens, and lichen-forming fungi. Tracing the origin of this diversity depends on a clearer understanding of the phylogenetic relationships of fungi in the order. One of its core members is the genus Marchandiomyces, originally established for lichen pathogens that form orange or coral bulbils. We describe here a new species in the genus, M. marsonii sp. nov., which is unusual in its appearance, habit, and geographic provenance. It is foliicolous on leaves of Pandanus (screw pines, Pandanaceae) and produces flattened, coral bulbils resembling apothecia of the ascomycete genus Orbilia. It is also the first member of the genus to be collected from Australia. An isolate of the new fungus and several additional cultures of related plant pathogenic fungi were obtained and investigated phylogenetically using parsimony, likelihood, and Bayesian analyses of nuclear small and large subunit ribosomal sequences. Our phylogeny makes clear that Marchandiomyces species and their close relatives contribute significantly to the ecological diversity of the Corticiales and that this diversity is derived mainly from lignicolous ancestors.     

Diets of coral‐dwelling fishes of the genus Gobiodon with evidence of corallivory

Evidence of facultative corallivory is documented in three species of obligate coral‐dwelling gobies (genus Gobiodon) based on the presence of spirocysts in gut contents. Coral‐dwelling gobies also consumed a broad range of other items with gut contents dominated by algae, invertebrates and amorphous material. Dietary similarities between species suggest corallivory may be widespread in this genus.     

Coral diseases on Philippine reefs: genus Porites is a dominant host

While it is generally assumed that Indo-Pacific reefs are not widely affected by diseases, limited data suggest a number of diseases and syndromes that appear to differ from those currently under study in the Caribbean. This report presents the results of a baseline survey of coral diseases in 2 regions in the Philippines: the Central Visayas and the Lingayen Gulf. Mean prevalence for all diseases observed was 8.3 +/- 1.2% (mean +/- SE; n = 8 reefs), with Central Visayas reefs showing higher disease prevalence (11.6 +/- 2.8%; n = 4 reefs) than those of Lingayen Gulf (5.1 +/- 1.4%; n = 4 reefs). Five diseases and syndromes were described; 3 of these-Porites ulcerative white spot disease (PUWS) (prevalence = 8.96 +/- 2.2%), tumors (prevalence = 1.0 +/- 0.5%) and pigmentation response (prevalence = 0.5 +/- 0.2%)--occurred frequently in both regions and targeted the genus Porites. Correlation between disease prevalence and number of Porites colonies was fairly strong (r2 = 43.4), though not significant, and no correlation was seen between prevalence and either the amount or diversity of hard coral. Porites is a major reef-builder in the Indo-Pacific comprising 30% of hard coral colonies on our surveyed reefs, and is generally thought to be a hardy, long-lived genus. Diseases targeting this robust group present an as yet unquantified risk to Philippine reefs and could result in major changes in reef structure.     

The structuring role of microhabitat type in coral degradation zones: a case study with marine nematodes from Kenya and Zanzibar

Nematode genus assemblages were identified from four locations in coral degradation zones (CDZs) along the African east coast: Watamu and Tiwi Beach (Kenya) and Matemwe and Makunduchi (Zanzibar). Three microhabitat types were distinguished: coralline sediment, coral gravel and coral fragments. Nematode community composition was comparable to that of other studies dealing with the same habitat. The presence of a common genus pool in CDZs was reflected in the considerable similarities between samples. The addition of coral fragments as a habitat for nematodes resulted in an increased importance of taxa typical for coarse sediments and large substrata. Local and regional turnover were of the same order of magnitude. The structuring effect of microhabitat type clearly overrode the effect on a local and regional scale. Differences in sediment characteristics were more important in structuring the nematode assemblages than differences between the coralline sediment and coral fragments. No effect related to the three-dimensional structure of coral fragments was found. Differences between nematode assemblages in the coralline sediment and on coral fragments were attributed to the exposed nature of the latter habitat, its large surface area and its microbial or algal cover. Differences in available food sources were reflected in nematode trophic composition.     

新疆乌什下寒武统肖尔布拉克组软舌螺化石

首次描述了采自新疆乌什县乌什磷矿肖尔布拉克组中部Kepingaspis-Tianshanocephalus带中的2个软舌螺新种Conotheca xinjiangensis sp.nov.,Nitorcornus wushiensis sp.nov.和下部Ushbaspis带中的1个软舌螺未定种Adyshevitheca?sp.。这些软舌螺化石材料为研究新疆乌什地区下寒武统中部地层与邻区相当层位的对比提供了新的证据,认为肖尔布拉克组中部2个三叶虫化石带和其中的软舌螺化石相当于我国扬子地台下寒武统沧浪铺阶中部,即乌龙箐亚阶和红井哨亚阶之间,可与俄罗斯西伯利亚和哈萨克斯坦下寒武统波特姆阶(Botomian)中的三叶虫带Ushbaspis和软舌螺带Erraticornus-Nitorcornus带对比。     

Symbiodinium clade C dominates zooxanthellate corals (Scleractinia) in the temperate region of Japan

Endosymbiotic algae of the genus Symbiodinium have been divided into nine clades (A-I) following genetic classification; some clades are known to have physiological properties that enable the coral hosts to adapt to different environmental conditions. To understand the relationships of coral-alga symbioses, we focused on Symbiodinium diversity in zooxanthellate corals living under the severe environmental conditions of the temperate region (30°-35°N) of Japan. We investigated Symbiodinium clades in 346 colonies belonging to 58 coral species from six locations. We then selected three coral species-Acropora hyacinthus, Acropora japonica, and Cyphastrea chalcidicum-to investigate whether Symbiodinium clades changed during winter or summer over the course of year (May 2009-Apr 2010) in Tanabe Bay, Japan. Three Symbiodinium clades (C, D, and F) were detected in corals in the temperate region. Notably, 56 coral species contained Symbiodinium clade C. Oulastrea crispata predominantly contained clade D, but traces of clade C were also detected in all samples. The temperate-specific species Alveopora japonica contained clades C and F simultaneously. Seasonal change of symbiont clades did not occur in the three coral species during the investigation period where SSTs range on 12.5-29.2°C. However, we found Acropora (2 spp.) and Cyphastrea (1 sp.) contained different subcladal types of clade C. These results reveal that most coral species harbored Symbiodinium clade C stably throughout the year, suggesting that Symbiodinium clade C shows low-temperature tolerance, and that two hypothetical possibilities; genetic differences of subcladal types generating physiological differences or wide physiological flexibility in the clade C.     

Comparison between Colony Morphology and Molecular Phylogeny in the Caribbean Scleractinian Coral Genus Madracis

A major challenge in coral biology is to find the most adequate and phylogenetically informative characters that allow for distinction of closely related coral species. Therefore, data on corallite morphology and genetic data are often combined to increase phylogenetic resolution. In this study, we address the question to which degree genetic data and quantitative information on overall coral colony morphologies identify similar groupings within closely related morphospecies of the Caribbean coral genus Madracis. Such comparison of phylogenies based on colony morphology and genetic data will also provide insight into the degree to which genotype and phenotype overlap. We have measured morphological features of three closely related Caribbean coral species of the genus Madracis (M. formosa, M. decactis and M. carmabi). Morphological differences were then compared with phylogenies of the same species based on two nuclear DNA markers, i.e. ATPSα and SRP54. Our analysis showed that phylogenetic trees based on (macroscopical) morphological properties and phylogenetic trees based on DNA markers ATPSα and SRP54 are partially similar indicating that morphological characteristics at the colony level provide another axis, in addition to commonly used features such as corallite morphology and ecological information, to delineate genetically different coral species. We discuss this new method that allows systematic quantitative comparison between morphological characteristics of entire colonies and genetic data.     

Unlocking the phylogenetic diversity,primary habitats,and abundances of free‐living Symbiodiniaceae on a coral reef

Dinoflagellates of the family Symbiodiniaceae form mutualistic symbioses with marine invertebrates such as reef‐building corals, but also inhabit reef environments as free‐living cells. Most coral species acquire Symbiodiniaceae horizontally from the surrounding environment during the larval and/or recruitment phase, however the phylogenetic diversity and ecology of free‐living Symbiodiniaceae on coral reefs is largely unknown. We coupled environmental DNA sequencing and genus‐specific qPCR to resolve the community structure and cell abundances of free‐living Symbiodiniaceae in the water column, sediment, and macroalgae and compared these to coral symbionts. Sampling was conducted at two time points, one of which coincided with the annual coral spawning event when recombination between hosts and free‐living Symbiodiniaceae is assumed to be critical. Amplicons of the internal transcribed spacer (ITS2) region were assigned to 12 of the 15 Symbiodiniaceae genera or genera‐equivalent lineages. Community compositions were separated by habitat, with water samples containing a high proportion of sequences corresponding to coral symbionts of the genus Cladocopium, potentially as a result of cell expulsion from in hospite populations. Sediment‐associated Symbiodiniaceae communities were distinct, potentially due to the presence of exclusively free‐living species. Intriguingly, macroalgal surfaces displayed the highest cell abundances of Symbiodiniaceae, suggesting a key role for macroalgae in ensuring the ecological success of corals through maintenance of a continuum between environmental and symbiotic populations of Symbiodiniaceae.