Coralline Research Articles

Coralline Halimeda opuntia algae-derived bio-hydroxyapatite enhances the bioactivity of piezoelectric tissue engineering scaffolds

Biomaterials are increasingly being used to promote tissue repair after wounds. Coralline algae have been reported as valuable sources of hydroxyapatite (HAp). The identification and characterization of Halimeda opuntia with high calcium carbonate content from the Indian Ocean have been performed. Bio-hydroxyapatite (Bio-HAp) was synthesized through a combined process of pyrolysis followed by a hydrothermal treatment. The effect of pyrolysis temperature on the critical properties of the HAp such as Ca/P ratio, morphology and presence of trace elements was assessed. It was found that a calcination temperature of 900 °C produced Bio-HAp with a Ca/P of 1.57 ± 0.01, which is non-stoichiometric and calcium-deficient, similar to the HAp integrated in bone. HAp can integrate with bone without causing any local or systemic toxicity, inflammation or foreign body response, thus we have loaded the synthesized Bio-HAp into piezoelectric PHBV/PDX electrospun mat and assessed the behaviour of human dermal fibroblasts (HDF) and human pre-osteoblasts (HoB) in co-culture at different cell densities. Increasing Bio-HAp content from 1 % to 5 % increased fiber diameter due to fiber melting. Bio-HAp enhanced differentiation of HDF promoting mineralisation with Ca/P ratios of 1.93 ± 0.17 and 1.80 ± 0.18 at 1 % and 5 % HAp content respectively. The mineralisation process was more prominent on scaffolds with Bio-HAp compared to the controls (0 % HAp and synthetic-HAp) with both HDF only and HDF/HoB.

Nubecularia-coralline algal-serpulid-microbial bioherms of the Paratethys Sea-Distribution and paleoecological significance (upper Serravallian, upper Sarmatian, Middle Miocene).

Nubecularia bioherms represent unique bioconstructions that are restricted to the upper Serravallian of the Paratethys and have been reported since the 19th century. They occur in the Central Paratethys in the late Sarmatian and the Eastern Paratethys in the Bessarabian both regional stages of the respective Paratethyan areas. In this study, several locations in the Vienna and Styrian basins of the Central Paratethys were studied out of which four localities were documented in detail (Wolfsthal, Maustrenk, St. Margarethen-Zollhaus, Vienna-Ruzickagasse) to reconstruct their sedimentary setting, their internal composition, and their indications of environmental parameters. The detailed studies included logging of outcrop sections, petrographic, facies and biotic analyses of polished slabs and thin sections and also cathodoluminescence analyses. These concluded that these bioconstructions are not only composed of the foraminifer Nubecularia but represent a complex mixture and interrelationships of Nubecularia, serpulids and microbial carbonate. Four boundstone types can be differentiated: Nubecularia boundstone, Nubecularia-coralline algal boundstone, stromatolitic/thrombolitic boundstone and serpulid-nubeculariid-microbial boundstone. The first 3 types are characteristic of specific localities; the fourth type occurs in all studied locations and represents the terminal association on top of the three other types. The three basal boundstones are predominantly of columnar growth form irrespective of dominance of Nubecularia, coralline algae or microbial carbonate, and the terminal boundstone is widely irregularly organized. The general depositional environment is characterized by cross-bedded oolitic grainstones with abundant quartz grains, miliolid foraminifers and mollusks. Intercalated are microbial carbonates mostly stromatolites but also thrombolites. This indicates a general high water energy environment interrupted by more calm periods when the microbial carbonate was built. The 3 basal types of bioconstructions are interpreted to reflect decreasing food supply and/or oxygenation from Nubecularia over Nubecularia-coralline algal to stromatolitic/thrombolitic boundstone. The serpulid-nubeculariid-microbial boundstone reflects an internal succession with a decrease of the same parameters. Water depth is considered very shallow ranging from 0 to a few meters, and salinity was normal marine to hypersaline. The reconstructed paleoenvironment with dominating oolite shoals and seagrass meadows was not restricted to the Central Paratethys but extended over the entire Paratethys and represented the largest oolite facies area of the entire Cenozoic!

Preliminary study of the population and reproductive dynamics of Echinaster sepositus (Spinulosida: Echinasteridae) in Cala del Racó

Introduction: The red starfish (Echinaster sepositus) is one of the most common asteroid species in the Mediterranean Sea. However, information about their biology or their role in benthic communities is scarce.
 Objective: This study aims to provide new information on the ecology of this species through the temporal characterization of the population of E. sepositus in Cala del Racó (Alicante, Spain) and the in situ monitoring of its reproductive cycle.
 Methods: For this purpose, three study areas were established at different depths. For each of the recorded starfish, data about the size, the substrate on which it was found, the area, the depth and the sex in the case of observing the reproduction were collected.
 Results: A total of 19 samplings have been carried out throughout a year of study. In this way, it has been possible to observe that the density of individuals increases in the shallower zone during autumn and winter, when the temperature drops to 14.13 ºC, while it decreases in spring and summer when the temperature rises to 27.17 ºC. Those results are reversed in the deepest part of the study. The highest density of individuals (0.51 ind/m2) occurred in October. Arborescent photophilic algae and crustose coralline algae were the substrates with the highest number of E. sepositus recorded. Medium to large specimens are located preferably on crustose coralline algae or arborescent photophilic algae, while smaller individuals were mostly located on Posidonia oceanica. No specimens of E. sepositus were observed spawning.
 Conclusions: Data leads to assume that there is a migration of starfishes towards more superficial areas when the water is at colder temperature and towards deeper areas when the temperature increases. It is valued the possibility that there is a change in the nutritional needs of E. sepositus throughout its development. According to our observations, the future reproduction studies should be concentrated between late-summer and early-autumn.

Biostratigraphy of Jeribe Formation in Selected Wells Mansuriyha Gas Field, Eastern Iraq

Among the most important formations to be deposited during the Tertiary period was the Jeribe Formation. It has been investigated in two wells (Mn-1 and Mn-2) in the eastern Iraqi Dyala Government's Mansuria Oil Field. To identify fauna, 65 thin sections are examined under a microscope. Benthonic Foraminifera and limestone, occasionally dolomitized, make up its composition. There are twenty species of coralline and foraminiferan algae known to science. There were two unique biozones in the range. These biozones are the Ammonia beccria Linne Range Zone (Middle Miocene) and the Borelis melo curdica (Reichel) Range Zone (Early Miocene). The age of the formation was estimated to be Early Middle-Miocene based on these biozones of Foraminifera and other fossils such as gastropods, pelecypods, coral, fossils, Brayozoa, shell fragments, Echinoderm, echinoid plate, and echinoid spine.

Coral Primary Polyp Settlement on Crustose Coralline Algae from India

Crustose coralline algae (CCA) are calcareous red algae belonging to the diverse group Rhodophyta. They are known to play numerous important ecological roles in the coral reef ecosystems such as various invertebrate larval settlement, cementing the reef together, participating effectively in primary productivity. One of the most important ecological roles these algae play, are the settlement and metamorphosis of coral larvae. Though lots of observations have been made on a juvenile coral being settled on CCA, there has not been any study on the initial settlement of coral larvae on CCA. The present study was carried out in the intertidal regions of South Andaman district. During intertidal survey, a single thin layered CCA was observed to house four different coral recruits which had settled and metamorphosed to form a single polyp coral.

Growth Increments of Coralline Red Alga Clathromorphum Compactum Capture Sea‐Ice Variability Links to Arctic and Atlantic Multidecadal Oscillations (1805–2015)

AbstractGiven sea ice's importance in global climate regulation, fully understanding the role of natural temperature and atmospheric patterns like the Arctic Oscillation (AO), North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) in its variability is critical. While instrumental AMO and reliable AO records are available since the mid‐1800s and 1958, respectively, satellite sea‐ice concentration data sets start only in 1979, limiting the shared timespan to study their interplay. Growth increments of the coralline algae, Clathromorphum compactum, can provide sea‐ice proxy information for years prior to 1979. We present a seasonal 210‐year algal record from Lancaster Sound in the Canadian Arctic Archipelago capturing low frequency AMO/NAO variability and high frequency interannual AO/NAO prior to 2000. We suggest that sea‐ice variability here is strongly coupled to these large‐scale climate processes, and that sea‐ice cover was greater and the AO more negative in the early and late 19th century compared to the 20th.

Variability of marine epifauna assemblages in response to the microhabitat type and thermal stress

Anthropogenic activities like overfishing, urban and industrial developments, and coastal pollution are some of the stressors affecting the marine environment. Thermal pollution from coastal industries like power plants represents the main cause of increased temperatures in water bodies, which can affect the marine community structure and function. The aim of this study was: 1) to compare the epifaunal communities associated with three different types of microhabitats: articulated coralline algae around coral colonies (CWC), articulated coralline algae in the absence of coral colonies and other benthic organisms (CNB), and the seaweed Ecklonia cava (ECK); and 2) to determine the potential changes in epifaunal communities in acute response to the increased water temperature resulting from coastal power plant activities in Jeju Island, South Korea. Our findings revealed a strong association between epifaunal abundance and microhabitat type, with CNB exhibiting the highest abundance while ECK showed the lowest. Additionally, an increase in temperature of 0.5–1.5 °C was observed to not alter the overall abundance of epifauna at the impact site, however, it did lead to a shift in the community composition. There was a notable decline in the abundance of amphipods-caprellids, polychaetes, gastropods, and bivalves with their densities nearly halving in response to thermal stress. Furthermore, there was a shift in dominant taxa, transitioning from amphipods-caprellids to amphipods-non-caprellids. Conversely, other taxonomic groups such as isopods and copepods showed a remarkable surge in abundance following the temperature rise. These findings highlight the relationship between rising temperatures and epifaunal community composition while emphasizing taxa’s different responses to thermal stress.

Microfacies shift in the Late Paleocene–Early Eocene Patala Formation in the Upper Indus Basin (Pakistan): Implications for development of the Ceno-Tethys Ocean

Field observations, petrography, and laboratory interpretations of the Patala Formation were utilized in an integrated petrologic study aimed at deciphering the genesis mechanism and controlling factors of the limestone/shale alternation during the mature development of the Ceno-Tethys Ocean in the Upper Indus Basin of Pakistan. To achieve this goal, the Patala Formation is categorized into four integrated microfacies (MM-I to MM-IV). Multiple cycles of transgression/regression are noted through fluctuations in eustatic sea level, controlled by climate and regional tectonism. Consequently, a deepening, upward retrogradation sequence was deposited on a carbonate platform of the Ceno-Tethys Ocean. The sediments of the Patala Formation exhibit a facies shift from a shallow-marine to a relatively deep-marine platform. It is indicated by the transition in fossils from shallow-marine green algae, trending towards a relatively deeper-shelf comprising benthic foraminifera such as Discocyclina, Ranikothalia, red coralline algae, echinoids (Echinothrix), and Alveolina, species. The deeper species possess robust shells adapted by organisms to maximize oxygen and light at greater depths. Additionally, mineralogical features, including gypsum (deposited in a lagoon within the platform) and pyrite (found in a deep slope toward a deep shelf), confirm deepening upward interpretations. Thermophilic dinoflagellates, thermal dissolution fragments, and hardground surfaces indicate a Paleocene-Eocene Thermal Maximum (PETM; in the lower part, ca. 56 Ma) of the Patala Formation, assigning a relative chronological age from the late Paleocene to early Eocene. These results highlight the joint influence of climate change, sea level rise, and continuous tectonic activity (associated with the Indo-Eurasian collision) on the pattern of sediment filling, and facies shift. Furthermore, the study contributes to understanding sedimentary environments, paleoenvironmental reconstruction, and paleotectonic evolution of the basin. This ideal case study provides a breakthrough advancement in globally comprehending the complex relationships between periodic autocyclic processes and aperiodic allocyclic events.

Hyperdominance and habitat composition drive reef fish foraging at Atlantic oceanic islands

Spatial and temporal patterns of benthic community structure play a crucial role in shaping reef habitats and have a direct impact on fish foraging dynamics, alongside density-dependent effects on the whole community. At isolated oceanic islands, the relatively low fish species richness often leads to the hyperdominance of a few species and a general reduced trophic redundancy. However, the influence of benthic habitat features and hyperdominant species on foraging selection at oceanic islands has been largely overlooked. We used remote underwater videos (RUVs) to investigate whether reef fishes consistently forage on specific habitats across 5 different oceanic islands in the Atlantic Ocean, especially focusing on the importance of the role of hyperdominant species. We analysed 295 RUVs, within 2 m2 areas (3-15 m deep), totalling 49 h of video. Photoquadrats were utilised to gauge benthic group coverage in the same habitats. Our results revealed 5 prevalent habitats and 6 fish trophic groups interacting with reef benthos. The intensity of feeding pressure varied across islands, depending on the diversity of habitats. Herbivores and omnivores exhibited the highest feeding pressure, with omnivores foraging on crustose coralline algae and macroalgae habitats, while herbivores primarily fed on habitats dominated by the epilithic algal matrix. Hyperdominant species forage in multiple habitats, indicating a comparatively high degree of dietary plasticity. Our findings also demonstrated that fish feeding pressure is influenced by both habitat features and fish biomass. Therefore, our study can provide valuable insights for prioritising the management of key species in isolated oceanic reefs.

Paleontological study of the Oligocene/Miocene boundary in the Ilha de Santana and Pirabas formations, Pará-Maranhão Basin on the Northwest equatorial platform of Brazil

Sedimentary carbonate outcrops of the Pirabas Formation at the Bragantina platform in North Brazil represent the exposed portion of the entire carbonate succession in the marine equatorial platform from the subsurface Ilha de Santana Formation (Cretaceous/Maastrichtian-Miocene/Messinian) in the Pará-Maranhão Basin. The transgressive deposits, flooding, and advance of the carbonate platform were investigated through the study of outcrops of the Pirabas Formation (type locality in the Ilha de Fortaleza, Pará state) and the analogous carbonate from the uppermost section of the Ilha de Santana Formation from the well 1-MAS-16-MA (510–660 m below sea floor). The stratigraphic analyses were based on petrography, microCT, microfossil assemblages (foraminifera, ostracods, and bryozoans) and index species (Amphistegina, Archaias, Pyrgo, Quinqueloculina, Pirabasoporella, Nellia, Skylonia, and Alpheus), and biofacies approach. The Ilha de Santana Formation (Burdigalian/Langhian at 510–660 mbsf section of 1-MAS-16-MA) and the Pirabas Formation (Burdigalian at the Ilha de Fortaleza outcrops) suggest that shallow-water sedimentary facies are similar to those deposited in the marginal basins and mark the start of siliciclastic supplies to the inner platform and the decline of coralline algae carbonate factories.

Implications of changing Caribbean coral reefs on Diadema antillarum larvae settlement

Tropical western Atlantic reefs have gradually shifted from being dominated by corals to being mainly covered by macroalgae. The mass-mortality of the sea urchin Diadema antillarum in the 80s and the slow to non-existent recovery exacerbated this shift. Chemical cues associated with these reefs are expected to have shifted too with potential negative effects on larval recruitment, possibly limiting recovery of important species like D. antillarum. In this study, we tested the effects of naturally derived biofilm and macroalgae species native to Caribbean coral reefs on the settlement rate of cultured D. antillarum larvae in two separate experiments. Crustose coralline algae (CCA) were included in both experiments, making it possible to compare settlement rates from both experiments. A biofilm of one week old yielded significantly lower settlement rates compared to two, four, and six weeks old biofilm and the highest settlement rate was found for CCA with over 62% of total larvae. All six tested macroalgae species resulted in settled larvae, with little significant difference between algal species, partly due to a high variation in settlement rates within treatments. Sargassum fluitans induced the highest settlement rate with 33%, which was not significantly different from CCA with 29%. We conclude that dominant macroalgae species likely to be encountered by D. antillarum on shifted reefs are no major constraint to settlement. Our findings increase the understanding of alternative stable state settlement dynamics for a keystone coral reef herbivore.

Origin and role of non-skeletal carbonate in coralligenous build-ups: new geobiological perspectives in biomineralization processes

Abstract. The coralligenous build-ups located on the Mediterranean shelf in front of Marzamemi (SE Sicily, Italy) represent useful natural examples to use in studying the relationship between skeletal organisms and non-skeletal components in marine bioconstructions. Coralligenous build-ups are formed in open marine systems, and their comparison with coeval bioconstructions (biostalactites) of confined environments, like submarine caves, allows depicting the complex interactions between metazoans and microbial communities in the formations of recent bioconstructions in different Mediterranean settings. In this study, two coralligenous build-ups were characterized in terms of organisms and sediments involved in their formation. The framework mainly consists of coralline algae and subordinate bryozoans and serpulids. Sponges affect the general morphology of the bioconstructions both interacting with skeletonized organisms and through bioerosion activity. The micrite or microcrystalline calcite is present in minor amounts compared to other components that form the build-ups and consists of two types: autochthonous (in situ) and allochthonous (detrital). Fine autochthonous micrite mineralized directly inside the framework cavities and shows aphanitic or peloidal fabric, produced by organomineralization processes of soft sponge tissues and microbial metabolic activity, respectively. The detrital micrite occurring inside cavities derives from external sources or erosion processes of the bioconstructions themselves. This component has been classified as organic or inorganic based on the organic matter contents deduced by UV epifluorescence. A great quantity of sponges live in cavities of the coralligenous build-ups and compete with carbonatogenic bacteria for the same cryptic spaces, limiting the production of microbialites. The sharing of a similar relationship between sponges and microbial communities by coralligenous concretion and biotic crusts of particular submarine caves suggests that this competition is not habitat-specific. On the contrary, it may develop in a range of environmental settings, from open to cryptic systems, and could be used to clarify the role of metazoans vs. microbialites in palaeoecological reconstructions.

Benthic primary production in Young Sound, Northeast Greenland

The extreme and variable light climate of polar marine environments imposes a substantial limitation on benthic primary production and demands efficient adaptive capacities of the primary producers. This chapter reviews the composition, abundance, primary production and adaptive strategies of benthic primary producers in Young Sound. Benthic primary producers occurred in the 0-50 m depth range and the relative importance of microalgae, crustose coralline macroalgae and foliose macroalgae varied systematically with depth. On a summer day with optimal light conditions benthic primary production showed a maximum of c.
 70 mmol O2 m-2 d-1 in shallow water. Production rates declined gradually to c. 20 mmol O2 m-2 d-1at 10–20 m depth and to 2.5 mmol O2 m-2 d-1 at 30 m depth.
 Foliose macroalgae contributed markedly to primary production in shallow water but became insignificant at water depths >15 m, while benthic diatoms contributed most to primary production at intermediate water depths (5-30 m). At water depths greater than 30 m only coralline algae occurred, but their production was low because of their low abundance, low Pmax and the low ambient irradiance at those depths. All algal groups were well adapted to the ambient irradiance and could, within minutes, acclimate their photosynthetic performance to changing light conditions. The benthic primary production in Young Sound markedly surpassed the pelagic primary production down to water depths of 20 m and the results thereby underline the potential importance of benthic primary production in shallow-water Arctic ecosystems.

Foraminiferal Biostratigraphy and Paleoecology of the Southeasternmost Outcrops of the Oligocene Qom Formation, SE Iran

Abstract The Qom Formation is deposited along more than 1800 km of the NE margin of the Tethyan Seaway in the Oligocene-Early Miocene during the final sea transgression on the Iranian Plate. We present (foraminiferal-based) biostratigraphic data from three exposed sections near the northwestern Jazmurian Lake, as the southeasternmost outcrops of the Qom Formation. Larger benthic foraminifera are mainly represented by nummulitids (Nummulites, Operculina, Heterostegina), lepidocyclinids (Nephrolepidina, Eulepidina, Lepidocyclina), and Amphistegina. The presence of Nummulites fichteli/intermedius and Nummulites vascus in the lower parts of the study sections together with lepidocyclinids indicates that their basal deposits could be attributed to the late Rupelian. The Qom Formation is of late Rupelian-Chattian in age in all three stratigraphic sections. Also, the presence of Nummulites- bearing tuffaceous limestones and tuff unit in the lower part of the Bozadan section is indicative of contemporaneous volcanic activity. Most parts of the study sections with an association of large and flat perforate foraminifera were deposited in normal saline waters. These parts are presented by large and flat nummulitids, lepidocyclinids, and Amphistegina. These large and flat perforate foraminifera often dominate in the lower part of the photic zone. The abundance of larger benthic foraminiferal and coralline red algae and the coral facies indicates a tropical-subtropical palaeoenvironment.

Invertebrate diversity associated with a shallow rhodolith bed in the Mediterranean Sea (Mar Piccolo of Taranto, south‐east Italy)

Abstract Rhodoliths, formed by free‐living coralline algae, are distributed worldwide, and the rhodolith beds (RBs) that they form are recognized as structurally complex habitats. In the Mediterranean, they are generally distributed in the mesophotic zone, at depths of 30–100 m; so far, only a few shallow RBs (<2 m) have been reported (e.g. Îles Kuriat, Tunisia, and Stagnone Marsala, Italy). Here a shallow‐water RB located in the Mar Piccolo of Taranto (south‐eastern Italy, Mediterranean Sea) is described. The diversity of associated invertebrates, the rhodolith‐forming algal species, the type of sediments, and the bed extent are characterized. The RB investigated extends over 5 ha at depths of 0.5–1.5 m. The rhodoliths vary in shape and size, from pralines to large spherical structures, and are formed by a single species, Neogoniolithon brassica‐florida, growing around nuclei of both natural and anthropogenic origin. The associated fauna consisted of 158 taxa, 79 (50%) of which were new basin records. The associated diversity was approximately twice that of the underlying and nearby sediments. The structural complexity of the RBs promotes biodiversity and provides shelter, food, and a breeding ground for numerous species, including seahorses, which are a conservation priority in this basin.

Seasonal growth and calcification of three species of crustose coralline algae in Moore, French Polynesia

Seasonal growth and calcification of three species of crustose coralline algae in Moore, French Polynesia

Kelp and sea urchin settlement mediated by biotic interactions with benthic coralline algal species.

Species interactions can influence key ecological processes that support community assembly and composition. For example, coralline algae encompass extensive diversity and may play a major role in regime shifts from kelp forests to urchin-dominated barrens through their role in inducing invertebrate larval metamorphosis and influencing kelp spore settlement. In a series of laboratory experiments, we tested the hypothesis that different coralline communities facilitate the maintenance of either ecosystem state by either promoting or inhibiting early recruitment of kelps or urchins. Coralline algae significantly increased red urchin metamorphosis compared with a control, while they had varying effects on kelp settlement. Urchin metamorphosis and density of juvenile canopy kelps did not differ significantly across coralline species abundant in both kelp forests and urchin barrens, suggesting that recruitment of urchin and canopy kelps does not depend on specific corallines. Non-calcified fleshy red algal crusts promoted the highest mean urchin metamorphosis percentage and showed some of the lowest canopy kelp settlement. In contrast, settlement of one subcanopy kelp species was reduced on crustose corallines, but elevated on articulated corallines, suggesting that articulated corallines, typically absent in urchin barrens, may need to recover before this subcanopy kelp could return. Coralline species differed in surface bacterial microbiome composition; however, urchin metamorphosis was not significantly different when microbiomes were removed with antibiotics. Our results clarify the role played by coralline algal species in kelp forest community assembly and could have important implications for kelp forest recovery.

Physiological differences among cryptic species of the Mediterranean crustose coralline alga Lithophyllum stictiforme (Corallinales, Rhodophyta)

ABSTRACT The crustose coralline alga Lithophyllum stictiforme is an important reef builder, forming coralligenous concretions in the Mediterranean Sea. This algal species complex is composed of eight cryptic species (or clades). The objective of our study was to compare light-dependent physiological processes within and between the two most abundant cryptic species (C1 and C4) of L. stictiforme from the Bay of Marseille (France). Physiological rates of respiration, photosynthesis and calcification were measured using incubation chambers under various irradiance levels and in the dark during the summer period. We compared the physiology of the C1 and C4 cryptic species of L. stictiforme among three algal groups: C1 (the most common in the Marseille area) from 28 m depth, C4 from the same site and depth, and C1 from a deeper site at 45 m depth. We found both interspecific (between C1 and C4) and intraspecific (within C1) physiological differences. Photosynthetic parameters showed acclimation to light (or depth) with higher values of initial slope of photosynthetic light response curve (α) and lower values of saturating irradiance (Ek) and compensating irradiance (Ec) for C1 from 45 m than for C1 and C4 from 28 m depth. At the shallower depth, significant physiological differences were observed between C1 and C4 with a higher value of maximum rate of gross photosynthesis (Pg max) in C4, suggesting better ability to grow under high irradiance. Light and dark calcification rates differed only between C4 from 28 m and C1 from 45 m depth, being intermediate in C1 from 28 m depth. On a 24 h basis, diel net calcification rates were significantly higher in specimens from the shallower waters than from the deeper waters. Physiological differences suggest physiological plasticity within the regionally dominant cryptic species C1 and species-specific physiological traits between the cryptic species C1 and C4.

Linear extension and calcification rates in a cold‐water, crustose coralline alga are modulated by temperature, light, and salinity

AbstractLong‐lived crustose coralline algae are important ecosystem engineers and environmental archives in regions where observations of climate variability are sparse. Clathromorphum compactum is a cold‐water alga that precipitates calcite that serve as archives of change at annual to sub‐annual resolution. Understanding how environmental variability impacts the growth of this species is imperative for application in paleoclimate research, and for evaluating its vulnerability to change. Here, we present the results of the first, to‐our‐knowledge, controlled laboratory experiment isolating the effects of light, temperature, and salinity on calcification rates of C. compactum. Algal calcification rates were modulated by a combination of light exposure, salinity, and temperature, where temperature and salinity were positively correlated, and light level was negatively correlated with calcification rate. Linear extension of the skeleton also varied with treatment conditions, with the epithallial and perithallial layers of skeleton responding differently. Epithallial extension increased with salinity, while perithallial extension was governed only by a positive parabolic relationship with temperature. These results suggest that C. compactum growth will be impacted by environmental changes predicted for the Arctic over the coming decades. While increased temperature in the region may facilitate calcification in the algae, reductions in salinity associated with increased sea ice melt, and potentially increased light levels, may counteract this effect. The negative impact of increased light levels on algal calcification observed may not reflect the true impact of light availability on growth associated with a lengthening of the growing season (not evaluated in this study) accompanying reductions in annual sea‐ice.

Small-scale habitat selection by larvae of a reef-building coral

When animals select habitats, they integrate positive and negative cues in the environment that shape their choices about where to live. We conducted a settlement experiment with the larvae of Orbicella faveolata, a reef-building scleractinian coral on Caribbean reefs. We investigated the settlement decisions of O. faveolata larvae in relation to communities of benthic spaceholders and explicitly investigated how benthic communities influence how larvae may make settlement decisions at small spatial scales. Settlement tiles that attracted at least one O. faveolata settler had a significantly different community composition than tiles with no settlers. Red filamentous algae and crustose coralline algae were abundant on tiles with no settlers, while bare substrate was abundant on tiles with settlers. When we analyzed the spatial patterns of coral settlement within tiles, coral settlers avoided areas with sediment, sponges, and red filamentous algae and preferred areas with green filamentous algae. Selection among individual taxa was dominated by selecting against rather than for taxa. Our results show that coral larvae make complex decisions about where to settle even down to the millimeter scale. Importantly, these coral larvae select their habitat by balancing contrasting forces to avoid risks.