Lithothamnion superpositum (Corallinales; Rhodophyta): First description for the Western Atlantic or rediscovery of a species?

P>Nongeniculate Corallinaceae are poorly known in Brazil. In our endeavor to identify this group of seaweeds along the Brazilian coast we came across some specimens that fit well into the accepted circumscription of Litothamnion Heydrich. Within this genus they could be identified to what has been called L. superpositum Foslie. The specimens were represented by nongeniculate, free living specimens (rhodoliths); lumpy to fruticose growth-form, presenting flared epithallial cells in transversal section; multiporate tetrasporangial conceptacles, with roof protruding above or flush with the surrounding thallus surface; chambers 250-525 mu m in diameter and 150-230 mu m high, roof structured by filaments with 3-5 cells long; and pores in depression. Among the species described from the Brazilian coast, L. heteromorphum (Foslie) Foslie presented anatomical and reproductive characteristics similar to the referred species described from southern Africa and Australia. Therefore, we propose to consider L. heteromorphum as a heterotypic synonym of L. superpositum and extending its distribution to the Western Atlantic.

Lithothamnion Prolifer Foslie: A Common Non-Geniculate Coralline Alga (Rhodophyta: Corallinaceae) from the Tropical and Subtropical Indo-Pacific

A little-known, but ecologically important non-geniculate coralline, Lithothamnion prolifer, is recorded from a number of tropical Indo-Pacific sites, including Fiji, Australia, Kiribati and Indonesia. The species occurs primarily on vertical walls of caves and overhangs in Fiji and Australia, but was also found as rhodoliths in Kiribati. Lithothamnion prolifer is characterized by the combination of characters which follow. The thallus is extremely glossy, smooth, and rosy coloured. Thalli usually produce complanate protuberances, but protuberances become terete when growing on well lit, horizontal substrata, when unattached, or when growing on loose substrata. Conceptacles occur mainly on the tips of protuberances, and tetra/bisporangial conceptacles are large (to 1300 mu m external diameter, with chambers up to 1100 mu m diameter). The tetra/bisporangial conceptacles are flush or only slightly raised, and often extensive and irregularly shaped (resembling small sori). They lack a raised rim, and have flattened pore plates. The rosette cells surrounding the tetra/bisporangial pore appear somewhat sunken below the surrounding roof cells in SEM, and the cells of filaments lining the pore canals of tetra/bisporangial conceptacles do not differ from the cells of filaments making up the rest of the roof. Old conceptacles persist and become buried in the thallus, and are then usually completely filled in by irregularly arranged calcified cells.

Seawater carbonate chemistry, calcification, primary production and respiration of a temperate rhodolith Lithothamnion corallioides in a laboratory experiment

Coralline algae are considered among the most sensitive species to near future ocean acidification. We tested the effects of elevated pCO2 on the metabolism of the free-living coralline alga Lithothamnion corallioides ("maerl") and the interactions with changes in temperature. Specimens were collected in North Brittany (France) and grown for 3 months at pCO2 of 380 (ambient pCO2), 550, 750, and 1000 µatm (elevated pCO2) and at successive temperatures of 10°C (ambient temperature in winter), 16°C (ambient temperature in summer), and 19°C (ambient temperature in summer +3°C). At each temperature, gross primary production, respiration (oxygen flux), and calcification (alkalinity flux) rates were assessed in the light and dark. Pigments were determined by HPLC. Chl a, carotene, and zeaxanthin were the three major pigments found in L. corallioides thalli. Elevated pCO2 did not affect pigment content while temperature slightly decreased zeaxanthin and carotene content at 10°C. Gross production was not affected by temperature but was significantly affected by pCO2 with an increase between 380 and 550 µatm. Light, dark, and diel (24 h) calcification rates strongly decreased with increasing pCO2 regardless of the temperature. Although elevated pCO2 only slightly affected gross production in L. corallioides, diel net calcification was reduced by up to 80% under the 1,000 µatm treatment. Our findings suggested that near future levels of CO2 will have profound consequences for carbon and carbonate budgets in rhodolith beds and for the sustainability of these habitats.

Calcification of the Arctic coralline red algae Lithothamnion glaciale in response to elevated CO2

Rising atmospheric CO2 concentrations could cause a calcium carbonate subsaturation of Arctic surface waters in the next 20 yr, making these waters corrosive for calcareous organisms. It is presently unknown what effects this will have on Arctic calcifying organisms and the ecosystems of which they are integral components. So far, acidification effects on crustose coralline red algae (CCA) have only been studied in tropical and Mediterranean species. In this work, we investigated calcification rates of the CCA Lithothamnion glaciale collected in northwest Svalbard in laboratory experiments under future atmospheric CO2 concentrations. The algae were exposed to simulated Arctic summer and winter light conditions in 2 separate experiments at optimum growth temperatures. We found a significant negative effect of increased CO2 levels on the net calcification rates of L. glaciale in both experiments. Annual mean net dissolution of L. glaciale was estimated to start at an aragonite saturation state between 1.1 and 0.9 which is projected to occur in parts of the Arctic surface ocean between 2030 and 2050 if emissions follow 'business as usual' scenarios (SRES A2; IPCC 2007). The massive skeleton of CCA, which consist of more than 80% calcium carbonate, is considered crucial to withstanding natural stresses such as water movement, overgrowth or grazing. The observed strong negative response of this Arctic CCA to increased CO2 levels suggests severe threats of the projected ocean acidification for an important habitat provider in the Arctic coastal ocean.

Seawater carbonate chemistry and structural integrity of the coralline algae Lithothamnion glaciale in a laboratory experiment

The uptake of anthropogenic emission of carbon dioxide is resulting in a lowering of the carbonate saturation state and a drop in ocean pH. Understanding how marine calcifying organisms such as coralline algae may acclimatize to ocean acidification is important to understand their survival over the coming century. We present the first long-term perturbation experiment on the cold-water coralline algae, which are important marine calcifiers in the benthic ecosystems particularly at the higher latitudes. Lithothamnion glaciale, after three months incubation, continued to calcify even in undersaturated conditions with a significant trend towards lower growth rates with increasing pCO2. However, the major changes in the ultra-structure occur by 589 µatm (i.e. in saturated waters). Finite element models of the algae grown at these heightened levels show an increase in the total strain energy of nearly an order of magnitude and an uneven distribution of the stress inside the skeleton when subjected to similar loads as algae grown at ambient levels. This weakening of the structure is likely to reduce the ability of the alga to resist boring by predators and wave energy with severe consequences to the benthic community structure in the immediate future (50 years).

Comparative growth rates and internal banding periodicity of maerl species (Corallinales, Rhodophyta) from northern Europe

Maerl is a type of rhodolith, found in ecologically important beds of high conservation value; a major conservation objective is to establish growth rates. Maerl shows internal banding of controversial periodicity that may contain a high-resolution record of palaeoceanographic-palaeoclimatic data. To investigate growth rates and banding periodicity, we used the vital stain Alizarin Red in combination with scanning electron microscopy (SEM). Three maerl species, Phymatolithon calcareum, Lithothamnion corallioides and L. glaciale, were collected from maerl beds in Ireland. Following staining, maerl was grown in three controlled temperature treatments and at two depths in the field (P. calcareum only), with Corallina officinalis as a control for the stain. Alizarin Red was shown to be a suitable marker for growth in European maerl species and for C. officinalis. The average tip growth rate of P. calcareum from Northern Ireland at 10 m depth and under constant laboratory conditions was c. 0.9 mm yr(-1), double the rates observed at 5 m depth and in L. corallioides. Our measurements and re-examination of reported data allow us to conclude that the three most abundant maerl species in Europe grow about 1 (0.5-1.5) mm per tip per year under a wide range of field and artificial conditions. Internal banding in temperate European maerl revealed by SEM is a result of regular changes in wall thickness; the approximately monthly periodicity of bands in field-grown specimens is consistent with previous suggestions that they may be lunar. The potential for maerl banding to be a high-resolution record of palaeoclimatic and palaeoenvironmental change could be realized with this vital stain in conjunction with isotopic or microgeochemical analyses.

Growth and Persistence of Diverse Intertidal Crusts: Survival of the Slow in a Fast-Paced World

Encrusting algae are conspicuous components of hard-substratum benthic communities in the photic zone despite being poor competitors and slow growers. Little is known about their growth rates or about mechanisms controlling key processes such as wound healing and surviving overgrowth. We manipulated 12 crustose species (including red and brown algae and a lichen) from the intertidal zone of Washington, USA, studying their varying responses to identical experimental conditions. Three of 8 crust species tested showed increased growth rates with size. Species healed from standardized wounds at different rates and using different mechanisms (e.g. lateral vs vertical regeneration) as seen in cross-sections. Three species showed altered growth rates at unwounded margins of wounded crusts, suggesting intrathallus communication. Year-long experiments involving simulated overgrowth showed that some species can maintain healthy tissue in a covered area, and one (the coralline Lithothamnion phymatodeum) even grew new tissue there. Other species gradually lost color, thickness, and area in covered areas. Hildenbrandia occidentalis survived remarkably well when covered, possibly due to its very slow growth and low metabolic demand. One suggested mechanism underlying the high variation in responses among crusts is the degree to which their thalli may be anatomically integrated by features such as cell fusions; physiological work testing translocation via these features is needed. Other mechanisms allowing persistence include rapid wound healing and frequent recruitment.

Seawater carbonate chemistry and physiological responses of three temperate coralline algae in a laboratory experiment

Coralline algae are major calcifiers of significant ecological importance in marine habitats but are among the most sensitive calcifying organisms to ocean acidification. The elevated pCO2 effects were examined in three coralline algal species living in contrasting habitats from intertidal to subtidal zones on the north-western coast of Brittany, France: (i) Corallina elongata, a branched alga found in tidal rock pools, (ii) Lithophyllum incrustans, a crustose coralline alga from the low intertidal zone, and (iii) Lithothamnion corallioides (maerl), a free-living form inhabiting the subtidal zone. Metabolic rates were assessed on specimens grown for one month at varying pCO2: 380 (current pCO2), 550, 750 and 1000 µatm (elevated pCO2). There was no pCO2 effect on gross production in C. elongata and L. incrustans but L. incrustans respiration strongly increased with elevated pCO2. L. corallioides gross production slightly increased at 1000 µatm, while respiration remained unaffected. Calcification rates decreased with pCO2 in L. incrustans (both in the light and dark) and L. corallioides (only in the light), while C. elongata calcification was unaffected. This was consistent with the lower skeletal mMg/Ca ratio of C. elongata (0.17) relative to the two other species (0.20). L. incrustans had a higher occurrence of bleaching that increased with increasing pCO2. pCO2 could indirectly impact this coralline species physiology making them more sensitive to other stresses such as diseases or pathogens. These results underlined that the physiological response of coralline algae to near-future ocean acidification is species-specific and that species experiencing naturally strong pH variations were not necessarily more resistant to elevated pCO2 than species from more stable environment.

Phenotypic plasticity of coralline algae in a High CO2 world

It is important to understand how marine calcifying organisms may acclimatize to ocean acidification to assess their survival over the coming century. We cultured the cold water coralline algae, Lithothamnion glaciale, under elevated pCO2 (408, 566, 770, and 1024 µatm) for 10 months. The results show that the cell (inter and intra) wall thickness is maintained, but there is a reduction in growth rate (linear extension) at all elevated pCO2. Furthermore a decrease in Mg content at the two highest CO2 treatments was observed. Comparison between our data and that at 3 months from the same long-term experiment shows that the acclimation differs over time since at 3 months, the samples cultured under high pCO2 showed a reduction in the cell (inter and intra) wall thickness but a maintained growth rate. This suggests a reallocation of the energy budget between 3 and 10 months and highlights the high degree plasticity that is present. This might provide a selective advantage in future high CO2 world.

Data compilation on the biological response to ocean acidification: environmental and experimental context of data sets and related literature

The exponential growth of studies on the biological response to ocean acidification over the last few decades has generated a large amount of data. To facilitate data comparison, a data compilation hosted at the data publisher PANGAEA was initiated in 2008 and is updated on a regular basis (doi:10.1594/PANGAEA.149999). By January 2015, a total of 581 data sets (over 4 000 000 data points) from 539 papers had been archived. Here we present the developments of this data compilation five years since its first description by Nisumaa et al. (2010). Most of study sites from which data archived are still in the Northern Hemisphere and the number of archived data from studies from the Southern Hemisphere and polar oceans are still relatively low. Data from 60 studies that investigated the response of a mix of organisms or natural communities were all added after 2010, indicating a welcomed shift from the study of individual organisms to communities and ecosystems. The initial imbalance of considerably more data archived on calcification and primary production than on other processes has improved. There is also a clear tendency towards more data archived from multifactorial studies after 2010. For easier and more effective access to ocean acidification data, the ocean acidification community is strongly encouraged to contribute to the data archiving effort, and help develop standard vocabularies describing the variables and define best practices for archiving ocean acidification data.