Life strategies of solitary undissepimented rugose corals from the upper member of the Picos de Europa Formation (Moscovian, Carboniferous, Cantabrian Mountains, NW Spain)

Rugose corals belonging to the orders Metriophyllina, Stereolasmatina and Plerophyllina have been identified in the upper member of the Picos de Europa Formation (Moscovian). Corals occur in crinoidal limestones containing common bryozoans. The coral assemblage shows a high diversity. Mode of preservation and spatial distribution of corals demonstrate close relationships with biogenic components such as crinoids, bryozoans, brachiopods and bivalves. The morphology of corals provides valuable data for identifying their life strategies, four of which have been identified: liberosessile with straight growth, liberosessile with curved growth, fixosessile with straight growth and fixosessile with curved growth. Most corals from the Picos de Europa Formation appear to have been fixosessile with straight growth; they attached themselves to bioclasts and subsequently developed radiciform processes (mainly talons) to remain straight.     

Evaluating life‐history strategies of reef corals from species traits

Classifying the biological traits of organisms can test conceptual frameworks of life‐history strategies and allow for predictions of how different species may respond to environmental disturbances. We apply a trait‐based classification approach to a complex and threatened group of species, scleractinian corals. Using hierarchical clustering and random forests analyses, we identify up to four life‐history strategies that appear globally consistent across 143 species of reef corals: competitive, weedy, stress‐tolerant and generalist taxa, which are primarily separated by colony morphology, growth rate and reproductive mode. Documented shifts towards stress‐tolerant, generalist and weedy species in coral reef communities are consistent with the expected responses of these life‐history strategies. Our quantitative trait‐based approach to classifying life‐history strategies is objective, applicable to any taxa and a powerful tool that can be used to evaluate theories of community ecology and predict the impact of environmental and anthropogenic stressors on species assemblages.     

Linking Demographic Processes of Juvenile Corals to Benthic Recovery Trajectories in Two Common Reef Habitats

Tropical reefs are dynamic ecosystems that host diverse coral assemblages with different life-history strategies. Here, we quantified how juvenile (<50 mm) coral demographics influenced benthic coral structure in reef flat and reef slope habitats on the southern Great Barrier Reef, Australia. Permanent plots and settlement tiles were monitored every six months for three years in each habitat. These environments exhibited profound differences: the reef slope was characterised by 95% less macroalgal cover, and twice the amount of available settlement substrata and rates of coral settlement than the reef flat. Consequently, post-settlement coral survival in the reef slope was substantially higher than that of the reef flat, and resulted in a rapid increase in coral cover from 7 to 31% in 2.5 years. In contrast, coral cover on the reef flat remained low (~10%), whereas macroalgal cover increased from 23 to 45%. A positive stock-recruitment relationship was found in brooding corals in both habitats; however, brooding corals were not directly responsible for the observed changes in coral cover. Rather, the rapid increase on the reef slope resulted from high abundances of broadcast spawning Acropora recruits. Incorporating our results into transition matrix models demonstrated that most corals escape mortality once they exceed 50 mm, but for smaller corals mortality in brooders was double those of spawners (i.e. acroporids and massive corals). For corals on the reef flat, sensitivity analysis demonstrated that growth and mortality of larger juveniles (21–50 mm) highly influenced population dynamics; whereas the recruitment, growth and mortality of smaller corals (<20 mm) had the highest influence on reef slope population dynamics. Our results provide insight into the population dynamics and recovery trajectories in disparate reef habitats, and highlight the importance of acroporid recruitment in driving rapid increases in coral cover following large-scale perturbation in reef slope environments.     

Some aspects of life strategies of Early Palaeozoic rugose corals

Examination of some well-preserved specimens of Silurian rugose corals from Gotland reveals that the following categories of life strategies can be distinguished: ambitopic, liberosessile, fixosessile, rhizosessile and possibly limited vagile. Most solitary rugose corals appear to have been liberosessile and are characterized by initial attachment to a small sediment grain but subsequently becoming recumbent on a soft substrate. Detailed studies of Phaulactis angelini, Holophragma calceoloides, Laccophyllum lindstroemi, Rhegmaphyllum conulus and Rhabdocyclus ocksaroensis n. sp., and comparison with earlier described species, provide some new aspects on different life strategies for solitary corals.     

Tracking growth and survival of rescued boulder corals

Patterns of survivorship and growth of rescued boulder corals from two vessel groundings in Biscayne National Park, Homestead, Florida, U.S.A., were evaluated over 5 years and compared to nearby undamaged reference corals. The rescued colonies had been dislodged but reattached in situ 10–12 years later (hereafter termed “restored” corals). Change in live coral tissue area was assessed using novel contoured tissue measurements which proved useful in detecting small changes in tissue area for slow‐growing coral species. At the initial survey, restored boulder corals had a higher level of partial mortality (33.8 ± 3.1%, mean ± SE) relative to reference corals (19.9 ± 2.5%), likely a result of prolonged detachment. During the course of the 5‐year monitoring period, whole‐colony mortality was greater for restored corals (13.1%) compared to reference corals (3.3%). For surviving corals, restored coral growth and recent mortality rates were similar to reference corals even though restored corals, especially those of Dichocoenia stokesii, had greater disease prevalence (19.7%) than reference corals (6.6%). These results suggest that dislodged boulder coral rescue following an acute disturbance can be an effective tool in stemming tissue loss. If dislodged corals were reattached in a more timely manner, we predict that the survival and tissue growth would be greater.     

The ecology of Millepora

Attention is drawn to the lack of quantitative ecological information on the calcareous hydrozoan Millepora. In spite of their abundance and geological importance on reefs, little attention has been paid to the millepores compared to the dominant corals. The literature on distribution and abundance on reefs is reviewed and attention is drawn to sources of bias in reported estimates of Millepora abundance. Millepora is shown to have many of the same parasites and predators as scleractinians. The sparse data on growth and production are reviewed and compared with that of corals. The physiological and ecological responses of Millepora to storms and other disturbances appear to be similar to those of the scleractinans but the millepores have escaped attack by the starfish Acanthaster and appear to be immune to the common diseases of corals. The morphological similarities and ecological differences between millepores and scleractinians are discussed in terms of life-history strategies.     

Aggregation and cnidae development as early defensive strategies in Favia fragum and Porites astreoides

To survive, corals possess a variety of active and passive defenses. This study examined the effectiveness of aggregation and cnidae development as defensive strategies in enhancing post-settlement survival and growth of two brooding corals, Favia fragum and Porites astreoides, in Bermuda. Growth and survival of solitary and aggregated spat were monitored over seven weeks; cnidae were extracted from surviving spat. F. fragum aggregated spat had higher mortality, slower growth, and more cnidae than solitary spat. On the other hand, aggregation proved beneficial for P. astreoides spat, which had significantly lower mortality, faster growth, and fewer cnidae. Aggregated and solitary F. fragum spat displayed negative correlations between cnidae density and growth, suggesting a trade-off between defense and growth; however, P. astreoides spat did not demonstrate such a trade-off. These differing responses suggest that early patterns of survivorship and defensive strategies are highly species specific and complex.     

大型海藻在珊瑚礁退化过程中的作用

随着全球范围珊瑚礁的退化,大型海藻在珊瑚礁区的覆盖度呈增多的趋势。大型海藻的大量生长,妨碍了珊瑚的生长、繁殖、恢复等过程。概括起来,大型海藻对珊瑚生长、繁殖及恢复过程所产生的不利影响主要包括:(1)大型海藻通过与珊瑚竞争空间和光照而影响珊瑚生长;(2)大型海藻与珊瑚直接接触时,通过摩擦作用及释放化感物质而影响珊瑚生长;(3)大型海藻的大量生长打破了珊瑚与海藻的竞争平衡,珊瑚为应对大型海藻的入侵而把用于生长和繁殖的能量转移到组织修复与防御上,进而造成珊瑚繁殖能量的减少;(4)大型海藻通过影响珊瑚幼虫的附着及附着后的存活率,而阻碍珊瑚群落的发展;(5)海藻还能通过富集沉积物、释放病原体及扰乱珊瑚共生微生物的生长等而间接影响珊瑚生长。明确的竞争机制有利于研究海藻与珊瑚的相互作用过程。在总结前人对海藻与珊瑚的竞争机制研究的基础上,把两者的竞争机制划分成物理机制、化学机制、微生物机制三大类,物理机制是研究得比较透彻的竞争机制,而化学机制与微生物机制则需要更深入的研究,是当前研究的热点。目前,我国对珊瑚礁中底栖海藻与珊瑚的相互作用研究甚少;鉴于此,对底栖海藻功能群的划分类型以及三大类型底栖海藻对珊瑚的作用特点做了简要介绍,并对珊瑚礁退化的现状和退化珊瑚礁区内海藻的表现做了概述。在此基础上,再综述国外关于大型海藻对珊瑚的影响研究进展,指出我国应该加强对南海珊瑚礁区大型海藻的种类分布及丰富度等的调查,评价大型海藻对南海珊瑚礁的影响现状;并结合生理学、分子生物学技术和生态学研究手段,在细胞与分子水平上探索海藻对珊瑚的影响机制,以期为珊瑚礁生态系统的保护提供参考。     

Fine-Scale Skeletal Banding Can Distinguish Symbiotic from Asymbiotic Species among Modern and Fossil Scleractinian Corals

Understanding the evolution of scleractinian corals on geological timescales is key to predict how modern reef ecosystems will react to changing environmental conditions in the future. Important to such efforts has been the development of several skeleton-based criteria to distinguish between the two major ecological groups of scleractinians: zooxanthellates, which live in symbiosis with dinoflagellate algae, and azooxanthellates, which lack endosymbiotic dinoflagellates. Existing criteria are based on overall skeletal morphology and bio/geo-chemical indicators—none of them being particularly robust. Here we explore another skeletal feature, namely fine-scale growth banding, which differs between these two groups of corals. Using various ultra-structural imaging techniques (e.g., TEM, SEM, and NanoSIMS) we have characterized skeletal growth increments, composed of doublets of optically light and dark bands, in a broad selection of extant symbiotic and asymbiotic corals. Skeletons of zooxanthellate corals are characterized by regular growth banding, whereas in skeletons of azooxanthellate corals the growth banding is irregular. Importantly, the regularity of growth bands can be easily quantified with a coefficient of variation obtained by measuring bandwidths on SEM images of polished and etched skeletal surfaces of septa and/or walls. We find that this coefficient of variation (lower values indicate higher regularity) ranges from ~40 to ~90% in azooxanthellate corals and from ~5 to ~15% in symbiotic species. With more than 90% (28 out of 31) of the studied corals conforming to this microstructural criterion, it represents an easy and robust method to discriminate between zooxanthellate and azooxanthellate corals. This microstructural criterion has been applied to the exceptionally preserved skeleton of the Triassic (Norian, ca. 215 Ma) scleractinian Volzeia sp., which contains the first example of regular, fine-scale banding of thickening deposits in a fossil coral of this age. The regularity of its growth banding strongly suggests that the coral was symbiotic with zooxanthellates.     

Biogeography of azooxanthellate corals in the Caribbean and surrounding areas

Biogeographic patterns for azooxanthellate corals are not as well known as those of zooxanthellate (primarily reef-building) corals. I analyzed occurrences of 129 species of azooxanthellate corals in 19 geopolitical regions in the Caribbean and surrounding areas. I performed an unweighted pair-group method with arithmetic averages (UPGMA) cluster analysis using Bray-Curtis' similarity measure on the complete data set and shallow- and deep-water subsets of the data. The results indicate two provinces, each with a widespread (tropical and subtropical distributions) component to its fauna. One province has a tropical and primarily insular component to it, while the other has a subtropical and primarily continental component. By contrast, zooxanthellate corals have a uniform faunal composition throughout the Caribbean. Moreover, zooxanthellate corals have half as many species in the Caribbean as the azooxanthellate corals even though their global diversities are equal. These differences in diversity and geographic distribution patterns should be considered when developing conservation strategies.     

Competition between corals and algal turfs along a gradient of terrestrial influence in the nearshore central Great Barrier Reef

Competition between benthic algae and corals is a key process in the community ecology of reefs, especially during reef degradation. However, there have been very few experimental tests for competition between corals and benthic algae, despite widespread assumptions that algae are generally superior competitors, especially in eutrophic conditions. This study tested for competition for space between the massive coral Porites lobata and algal filamentous turfs on three reefs along a cross-shelf gradient of terrestrial influence, by experimentally removing or damaging either corals or algae. The corals and algae were competing for space, but, significantly, the algae appeared to have little effect on coral growth. In contrast, corals significantly inhibited algal growth, suggesting Porites was the competitive superior. Importantly, coral growth was generally positive, even on the reef with the greatest terrestrial influence. Competitive outcomes did not support the argument that algae are more successful competitors in more eutrophic conditions.     

Mechanisms of interaction between macroalgae and scleractinians on a coral reef in Jamaica

After several decades of disturbance, many coral reefs in the Caribbean are dominated by macroalgae. One process affecting this transition is coral-macroalgal competition, yet few studies have addressed the mechanisms involved. In this study, we investigated competition between the tall and bushy macroalga Sargassum hystrix (J. Agardh) and the branching coral Porites porites (Pallas) on a shallow reef in Jamaica. Experiments were designed to expose coral branches to different treatments to test the role of shading and abrasion by Sargassum on coral growth and polyp expansion. Corals exposed to Sargassum grew significantly more slowly (80% reduction) than controls, but this effect was absent when corals were caged to prevent physical contact with macroalgae. Light levels were reduced in both the algal and cage treatments, but shading apparently had little effect on the growth of corals in cages. Short-term measurements of integrated net water flow did not detect variation among treatments. In algal-mimic treatments, where clear plastic strips could touch but not shade the corals, growth rates were 25% lower than controls, but this effect was not statistically significant. Thus, the growth of corals in contact with Sargassum was reduced by abrasion and, to a lesser extent, by factors unique to living macroalgae. Analysis of polyp expansion showed that polyps were more frequently retracted when corals were in contact with macroalgae or algal-mimics compared to controls or cage treatment; the frequency of polyp contraction was correlated positively with growth. Together, these results suggest that abrasion-mediated polyp retraction is one of the primary mechanisms of competition utilized by tall (ca. 17 cm) macroalgae against scleractinian corals.     

Feeding mechanisms and feeding strategies of Atlantic reef corals

The feeding behaviour of 35 species of Atlantic reef corals was examined in the laboratory and in the field. Observations were made during the day and at night, using freshly hatched brine shrimp nauplii and finely ground, filtered fresh fish as food sources. Three feeding strategies were observed: Group I–feeding by tentacle capture only; Group II–feeding by entanglement with a mucus net or mucus filaments; Group III–feeding by a combination of tentacle capture and mucus filament entanglement. Group I included corals of the families Poritidae and Pocilloporidae which were normally expanded during both day and night. Group II included corals of the family Agaricidae which were normally expanded at night and contracted during the day. Group III included corals of the other families examined which, with the exception of Dendrogyra cylindrus , were normally expanded only at night.
Feeding responses were elicited by both chemical and tactile stimuli. A preparatory feeding posture was assumed in response to chemical stimuli and consisted of horizontal positioning of the tentacles, elevation of the oral disk to form a cone-like mouth, a wide mouth opening and secretion of mucus by the epidermis of the oral disk. Following the assumption of the preparatory feeding posture, food capture and ingestive movements were elicited by tactile stimuli. However, food capture and ingestive movements were also elicited by chemical stimuli alone in those species which were normally contracted during the day.
While expanded corals captured food with their tentacles or with mucus filaments, contracted corals were able to feed by capturing fine particulate matter with mucus filaments only and thus acted as suspension feeders. By a combination of feeding strategies, reef corals were able to feed both day and night and a wide range of potential food ranging from fine particulate matter to large zooplankton was available to them.     

Free-living scleractinian corals on reefs of the Seychelles Islands

Thirty-nine species of unattached scleractinian corals that belong to 22 genera of 9 families were found on the Seychelles reefs. Variations of the colony form of corals living on soft sediments under continuous wave action are described. Irrespective of their initial growth form and taxonomic position, corals assume a form close to spherical. Because of the worldwide deterioration of coral reefs, the adaptation to changing ecological conditions by reef-building corals needs to be studied.     

悬浮物对造礁石珊瑚营养方式的影响及其适应性研究进展

营养方式是造礁石珊瑚获取能量与营养物质的基础,影响其生长与分布。近年来珊瑚礁区悬浮物含量与组分结构发生显著变化,其对造礁石珊瑚营养方式的诸多影响正成为当前研究热点。研究系统综述了珊瑚礁区悬浮物变化特征、悬浮物对造礁石珊瑚营养方式的影响及其适应性研究现状。发现近年来人类活动加剧与强降雨事件频发是驱动珊瑚礁,尤其是近岸珊瑚礁区悬浮物含量递增、组分改变与变频加剧的主因;悬浮物变化对造礁石珊瑚光合自养与异养营养的影响存在显著的种间差异,这主要与悬浮物消光效应、生物可利用性及造礁石珊瑚种类密切相关。虽然少数种类造礁石珊瑚具光合可塑性或异养可塑性,能在高含量悬浮物存在的弱光环境中较好生长。然而对绝大多数造礁石珊瑚而言,其营养方式适应性较差,无法在悬浮物影响下较好地获取生命活动所需的能量与营养物质,进而难以生存。总体来说,悬浮物被认为是近年来影响造礁石珊瑚生长与分布的重要环境因子之一,而关于造礁石珊瑚营养方式对悬浮物变化的响应及其适应机制,当前研究仍较薄弱,需要进一步加强相关研究。     

Differential thermal bleaching susceptibilities amongst coral taxa: re-posing the role of the host

It is well established that different coral species have different susceptibilities to thermal stress, yet it is less clear which biological or physical mechanisms allow some corals to resist thermal stress, whereas other corals bleach and die. Although the type of symbiont is clearly of fundamental importance, many aspects of coral bleaching cannot be explained solely by differences in symbionts amongst coral species. Here, I use the CO₂ (sink) limitation model of coral bleaching to repose various host traits believed to influence thermal tolerance (e.g. metabolic rates, colony tissue thickness, skeletal growth form, mucus production rates, tissue concentration of fluorescent pigments and heterotrophic feedings capacity) in terms of an integrated strategy to reduce the likelihood of CO₂ limitation around its intracellular photosymbionts. Contrasting observational data for the skeletal vital effect on oxygen isotope composition (δ¹⁸O) partitions two alternate evolutionary strategies. The first strategy is heavily reliant on a sea water supply chain of CO₂ to supplement respiratory CO_2(met). In contrast, the alternate strategy is less reliant on the sea water supply source, potentially facilitated by increased basal respiration rates and/or a lower photosynthetic demand for CO₂. The comparative vulnerability of these alternative strategies to modern ocean conditions is used to explain the global-wide observation that corals with branching morphologies (and thin tissue layers) are generally more thermally sensitive than corals with massive morphologies (and thick tissue layers). The life history implications of this new framework are discussed in terms of contrasting fitness drivers and past environmental constraints, which delivers ominous predictions for the viability of thin-tissued branching and plating species during the present human-dominated (“Anthropocene”) era of the Earth System.     

Estimating three-dimensional surface areas on coral reefs

One of the main obstacles for biological assessments of coral reefs over large spatial scales is the ability to link data obtained at the laboratory scale to spatially large data sets. This is particularly the case when trying to assess the ecological function of microbial processes following dramatic large-scale events such as mass coral bleaching. To be able to infer ecological function of field corals from laboratory measurement standardised to surface area it is imperative to be able to measure the actual surface area of corals in-situ. There have been several approaches proposed to estimate the three-dimensional surface area of field corals. While these have been shown to be reliable for simple coral growth forms, large degrees of error are introduced when applying them to complex growth forms. This paper refines a technique for calculating the three-dimensional surface area based on the projected surface area, with errors associated with complex growth forms reduced to < 5%. Once developed, the simple mathematical relationship (called the surface index) can be used to estimate the three-dimensional surface area of field corals from photograph or video imagery, allowing physiological parameters of corals determined at the sub-colony scale to whole colony and spatially large data sets of coral reefs. The effectiveness of using laser scanning techniques to derive three-dimensional images of corals is also discussed.     

Symbiont shuffling across environmental gradients aligns with changes in carbon uptake and translocation in the reef-building coral Pocillopora acuta

Coral Reefs - Symbiosis between reef-building corals and unicellular algae (Symbiodiniaceae) fuels the growth and productivity of corals reefs. Capacity for Symbiodiniaceae to fix inorganic carbon...     

Sponge-mediated coral reef growth and rejuvenation

Sponges mediate consolidation of Porites furcata rubble on shallow Caribbean reefs by quickly adhering to rubble and stabilizing it until carbonate secreting organisms can grow and consolidate it to the reef. Experimental investigations demonstrate that the entire cycle from (1) temporary binding of rubble by sponges, through (2) rubble consolidation by encrusting coralline algae, to (3) colonization of consolidated rubble by corals, can be completed within 10 months. Bound rubble both adds to vertical reef growth and also provides stable substrata for colonization by corals. Corals that colonize stabilized rubble are damaged less and survive better than on unstable rubble. Rubble that is not temporarily stabilized by sponges does not become bound to the reef, because continuous movement disturbs the consolidation process, and does not provide suitable substrata for settlement and growth of corals. Sponge-mediated consolidation of rubble may increase rates of reef growth and enhance reef recovery after damage. This new role for sponges in reef growth is not obvious from examination of the internal fabric of a reef frame. Spongemediated consolidation may help to explain geographic and temporal differences in growth and morphology among shallow reefs of ramose corals.