Relative roles of herbivory and nutrients in the recruitment of coral-reef seaweeds

The relative effects of and interactions between, bottom-up and top-down processes are fundamental to,population and community structure in both terrestrial and marine systems. These issues are especially critical for seaweed populations on coral reefs, since both bottom-up and top-down factors are suggested as causes of algal invasions during reef degradation. Although algal invasions require the establishment of new recruits, most previous studies of tropical. marine algae have focused on mature stages. We simultaneously manipulated nutrient supply to and herbivory on recruits of two ecologically different species of seaweed on the Great Barrier Reef. We found that herbivory strongly reduced both density and growth of recruits for both species, whereas nutrient supply had minor effects on growth of Lobophora variegata recruits and no detectable effects on Sargassum fissifolium recruits. Notwithstanding the dominance of herbivory. over nutrient effects, herbivory Was not uniform, but varied both between species and among response variables (density and size), and was apparently stronger for nutrient-enriched plants. Our data demonstrate that the relative importance of bottom-up and top-down processes may depend on the species, circumstances, and life-history processes under consideration. These results also emphasize the importance of herbivores to the protection of coral reefs against algal overgrowth

Distribution and structure of the southernmost Caribbean coral reefs: golfo de Urabá, Colombia

The Gulf of Urabá represents the southernmost portion of the Caribbean Sea. Due to the large amounts of sediment and freshwater discharged by the Atrato river and several minor streams, water conditions in the area are far from being optimal for coral settlement and growth. However, fringing and patch reefs are developed along the rocky shores of the northwest margin of the Gulf. Based on field observations performed at 44 sites (12 of them assessed quantitatively), interpretation of air photography of the area and depth profiles, the distribution, structure and zonation of the reefs are described. Classification analysis of the 12 sample sites yielded four coral assemblages: Diploria strigosa, crustose algae, Siderastrea siderea, Agaricia spp., and mixed massive corals. Other two assemblages, dominated respectively by Millepora complanata and thickets of Acropora palmata were noticed during reconnaissance dives. The distribution of these zones within the reef seems likely to be mainly controlled by wave exposure, bottom topography, sedimentation, and light penetration. Reef development, coral diversity and live coral cover increase along the coast in a SE-NW direction, with an evident maximum near to the cove of Sapzurro, suggesting an overall improvement of conditions for coral growth and settlement in that direction. A total of 33 species of hard corals were recorded during the survey. It is apparent that the live coral cover, particularly of foliose and branching species, has notably declined recently

Taxonomic review of the coral Porites colonensis (Scleractinia: Poritidae) in the Colombian Caribbean

Porites colonensis is a coral from the Caribbean Sea; colonies are foliaceous, undulated, and plate-like. Polyps are dark brown or red with small bright white or green centers; Pali are present in corallites and the septal plan is bisymmetrical, conformed by three fused ventral septa, a dorsal solitary septum, and two pairs of lateral septa at each side of the dorso-ventral axis. P. colonensis is similar and can be confused with the smooth varieties of Porites astreoides and Porites branneri. There are three specimens collected from Colombia and previously identified as P. colonensis: one from Golfo de Urabá (Darién ecoregion), other from Islas del Rosario (Coralline Archipelagos ecoregion), and another from an unspecified locality, in addition to one published observation from the Golfo de Urabá without collected specimens. A recent finding of other specimens in the Tayrona National Natural Park (TNNP, Tayrona ecoregion) and the absence of a rigorous taxonomic revision for all specimens collected from Colombia showed that it was necessary to review the presence and distribution of P. colonensis in the Colombian Caribbean. A taxonomic review was done for all specimens collected from Colombia and previously identified as P. colonensis. Then, the morphologic variability of specimens that were confirmed as P. colonensis was described. Only the specimens from TNNP agreed with the holotype description of P. colonensis, while others agreed with flat varieties of P. astreoides. Thus, the presence of P. colonensis is confirmed for the first time for Colombia, but its presence in other Colombian localities outside Tayrona ecoregion could not be demonstrated. This is the only confirmed record of this species for the South American continental shelf. Furthermore, the skeletal characteristics of Colombian P. colonensis corallites showed large variability, exceeding the ranges previously described for the species

Interactions among chronic and acute impacts on coral recruits: the importance of size-escape thresholds

Newly settled recruits typically suffer high mortality from disturbances, but rapid growth reduces their mortality once size-escape thresholds are attained. Ocean acidification (OA) reduces the growth of recruiting benthic invertebrates, yet no direct effects on survivorship have been demonstrated. We tested whether the reduced growth of coral recruits caused by OA would increase their mortality by prolonging their vulnerability to an acute disturbance: fish herbivory on surrounding algal turf. After two months' growth in ambient or elevated CO levels, the linear extension and calcification of coral (Acropora millepora) recruits decreased as CO partial pressure (pCO) increased. When recruits were subjected to incidental fish grazing, their mortality was inversely size dependent. However, we also found an additive effect of pCO such that recruit mortality was higher under elevated pCO irrespective of size. Compared to ambient conditions, coral recruits needed to double their size at the highest pCOto escape incidental grazing mortality. This general trend was observed with three groups of predators (blenny, surgeonfish, and parrotfish), although the magnitude of the fish treatment varied among species. Our study demonstrates the importance of size-escape thresholds in early recruit survival and how OA can shift these thresholds, potentially intensifying population bottlenecks in benthic invertebrate recruitment

Elevated CO2 Leads to Enhanced Photosynthesis but Decreased Growth in Early Life Stages of Reef Building Coralline Algae

Crustose coralline algae (CCA) are key organisms in coral reef ecosystems, where they contribute to reef building and substrate stabilization. While ocean acidification due to increasing CO2 can affect the biology, physiology and ecology of fully developed CCA, the impacts of elevated CO2 on the early life stages of CCA are much less explored. We assessed the photosynthetic activity and growth of 10-day-old recruits of the reef-building crustose coralline alga Porolithon cf. onkodes exposed to ambient and enhanced CO2 seawater concentration causing a downward shift in pH of ∼0.3 units. Growth of the CCA was estimated using measurements of crust thickness and marginal expansion, while photosynthetic activity was studied with O2 microsensors. We found that elevated seawater CO2 enhanced gross photosynthesis and respiration, but significantly reduced vertical and marginal growth of the early life stages of P. cf. onkodes. Elevated CO2 stimulated photosynthesis, particularly at high irradiance, likely due to increased availability of CO2, but this increase did not translate into increased algal growth as expected, suggesting a decoupling of these two processes under ocean acidification scenarios. This study confirms the sensitivity of early stages of CCA to elevated CO2 and identifies complexities in the physiological processes underlying the decreased growth and abundance in these important coral reef builders upon ocean acidification

Impacts of Ocean Warming on Coralline Algal Calcification: Meta-Analysis, Knowledge Gaps, and Key Recommendations for Future Research

Coralline algae are foundation species in many hard-bottom ecosystems acting as a settlement substrate, and binding together and even creating reefs in some locations. Ocean acidification is known to be a major threat to coralline algae. However, the effects of ocean warming are less certain. Here we bring multiple lines of evidence together to discuss the potential impacts of ocean warming on these ecologically crucial taxa. We use a meta-analysis of 40 responses within 14 different studies available which assessed the effects of increasing temperature on coralline algal calcification in laboratory experiments. We find a net negative impact of increasing temperature on coralline algal calcification at 5.2°C above ambient conditions. Conversely, negative effects are observed when temperature drops below 2.0°C from ambient conditions. We propose that some coralline algae will be more capable of both acclimatizing and locally adapting to increasing ocean temperatures over the coming decades. This is because many species possess short generation times, the ability to opportunistically rapidly utilize open space, and relatively high phenotypic plasticity. However, less resistant and resilient species will be those that are long-lived, those with long generation times, or with narrow thermal tolerances (e.g., tropical taxa living close to their thermal maxima). Additionally, ocean warming will occur simultaneously with ocean acidification, a potentially greater threat to coralline algae, which could also reduce any tolerance to ocean warming for many species. To maximize the potential to accurately determine how coralline algae will respond to future ocean warming and marine heatwaves, future research should use environmentally relevant temperature treatments, use appropriate acclimation times and follow best practices in experimental design

New branched Porolithon species (Corallinales, Rhodophyta) from the Great Barrier Reef, Coral Sea, and Lord Howe Island

Porolithon is one of the most ecologically important genera of tropical and subtropical crustose (non-geniculate) coralline algae growing abundantly along the shallow margins of coral reefs and functioning to cement reef frameworks. Thalli of branched, fruticose Porolithon specimens from the Indo-Pacific Ocean traditionally have been called P. gardineri, while massive, columnar forms have been called P. craspedium. Sequence comparisons of the rbcL gene both from type specimens of P. gardineri and P. craspedium and from field-collected specimens demonstrate that neither species is present in east Australia and instead resolve into four unique genetic lineages. Porolithon howensis sp. nov. forms columnar protuberances and loosely attached margins and occurs predominantly at Lord Howe Island; P. lobulatum sp. nov. has fruticose to clavate forms and free margins that are lobed and occurs in the Coral Sea and on the Great Barrier Reef (GBR); P. parvulum sp. nov. has short (<2 cm), unbranched protuberances and attached margins and is restricted to the central and southern GBR; and P. pinnaculum sp. nov. has a mountain-like, columnar morphology and occurs on oceanic Coral Sea reefs. A rbcL gene sequence of the isotype of P. castellum demonstrates it is a different species from other columnar species. In addition to the diagnostic rbcL and psbA marker sequences, the four new species may be distinguished by a combination of features including thallus growth form, margin shape (attached or unattached), and medullary system (coaxial or plumose). Porolithon species, because of their ecological importance and sensitivity to ocean acidification, need urgent documentation of their taxonomic diversity

Una dieta enriquecida con CLA mejora el daño a órganos asociados al síndrome metabólico en ratas hipertensas espontáneas

The purpose of this study was to provide evidence that dietary CLA can prevent the pathogenesis of metabolic syndrome in tissue structure, suggesting potential benefits in the onset of this syndrome. Wistar male spontaneous hypertensive rats (SHR), were classified into two groups that were fed a standard diet for eight weeks: one with 7.5% sunflower oil (V-SHR group), and the other with 6% sunflower oil and 1.5% CLA (CLA-SHR group). A control healthy group consisted of Kyoto-Wistar male rats fed the standard diet with 7.5% sunflower oil. The animals were sacrificed, and sections of liver, kidneys and aorta were fixed in 10% formaldehyde, and then stained with Hematoxylin and Eosin. Only in the V-SHR group, the stain of the aorta indicated irregular endothelial morphology; liver parenchyma was characterized by an infiltration of inflammatory neutrophils, fibrosis, thickening of the portal vein epithelium, hepatocyte hyperplasia and steatosis. The renal tissue of this group evidenced hyperplasia in the cells of the endothelial of Bowman´s capsule. Abnormal histological changes were not observed in either the control group or the rats fed with CLA, suggesting a protective role of CLA in the onset of metabolic syndrome.El objetivo del presente estudio fue proporcionar evidencia que el CLA dietario puede evitar la patogénesis del síndrome metabólico en la estructura tisular, lo que sugiere beneficios potenciales en el desarrollo de este síndrome. Dos grupos de ratas Wistar macho espontáneamente hipertensas (SHR) fueron alimentadas con una dieta normal por 8 semanas: una dieta contenía 7.5% de aceite de girasol (grupo VSHR), y el otro contenía 6% de aceite de girasol y 1.5% de CLA (grupo CLA-SHR). A un grupo testigo sano de ratas macho Kyoto-Wistar les fue proporcionada una dieta normal con 7.5% de aceite de girasol. Los animales fueron sacrificados y se tomaron secciones de hígado, riñones y aorta, las cuales fueron fijadas en formaldehído al 10% y teñidas con Hematoxilina y Eosina. Las tinciones de aorta mostraron morfología irregular del endotelio en la aorta solo en el grupo V-SHR; el parénquima hepático se caracterizó por infiltración de neutrófilos inflamatorios, fibrosis y engrosamiento del epitelio de la vena porta, hiperplasia hepática y esteatosis. El tejido renal de este mismo grupo evidenció hiperplasia en las células del endotelio de la cápsula de Bowman. No se observaron cambios anormales histológicos tanto en el grupo testigo como en el alimentado con CLA, lo que sugiere un papel protector del CLA en el desarrollo del síndrome metabólico

Settlement cue selectivity by larvae of the destructive crown-of-thorns starfish

Population irruptions of crown-of-thorns starfish (COTS) cause extensive degradation of coral reefs, threatening the structure and function of these important ecosystems. For population irruptions to initiate and spread, large numbers of planktonic larvae have to successfully transition into their benthic life-history stage (i.e. settlement), whereby larval behaviour and the presence of settlement cues may shape spatial patterns of recruitment and adult densities. Our results demonstrate that a wide range of coralline algae species induce COTS larvae to settle; however, the capacity to promote settlement success varied manyfold among algal species, ranging from greater than 90% in Melyvonnea cf. madagascariensis to less than 2% in Lithophyllum cf. kotschyanum and two Porolithon species at 24 h. Because many coralline algae species that promote high settlement success are prevalent in shallow reef habitats, our findings challenge the hypothesis that COTS larvae predominantly settle in deep water. Considering both larval behaviour and algal ecology, this study highlights the ecological significance of coralline algae communities in driving recruitment patterns of COTS. More specifically, the local abundance of highly inductive coralline algae (especially, Melyvonnea cf. madagascariensis) may explain some of the marked spatial heterogeneity of COTS populations and the incidence of population irruptions