Ocean acidification alleviates low-temperature effects on growth and photosynthesis of the red alga Neosiphonia harveyi (Rhodophyta)

This study aimed to examine interactive effects between ocean acidification and temperature on the photosynthetic and growth performance of Neosiphonia harveyi. N. harveyi was cultivated at 10 and 17.5 °C at present (~380 µatm), expected future (~800 µatm), and high (~1500 µatm) pCO2. Chlorophyll a fluorescence, net photosynthesis, and growth were measured. The state of the carbon-concentrating mechanism (CCM) was examined by pH-drift experiments (with algae cultivated at 10 °C only) using ethoxyzolamide, an inhibitor of external and internal carbonic anhydrases (exCA and intCA, respectively). Furthermore, the inhibitory effect of acetazolamide (an inhibitor of exCA) and Tris (an inhibitor of the acidification of the diffusive boundary layer) on net photosynthesis was measured at both temperatures. Temperature affected photosynthesis (in terms of photosynthetic efficiency, light saturation point, and net photosynthesis) and growth at present pCO2, but these effects decreased with increasing pCO2. The relevance of the CCM decreased at 10 °C. A pCO2 effect on the CCM could only be shown if intCA and exCA were inhibited. The experiments demonstrate for the first time interactions between ocean acidification and temperature on the performance of a non-calcifying macroalga and show that the effects of low temperature on photosynthesis can be alleviated by increasing pCO2. The findings indicate that the carbon acquisition mediated by exCA and acidification of the diffusive boundary layer decrease at low temperatures but are not affected by the cultivation level of pCO2, whereas the activity of intCA is affected by pCO2. Ecologically, the findings suggest that ocean acidification might affect the biogeographical distribution of N. harveyi

Sensitivity of Antarctic Urospora penicilliformis (Ulotrichales, Chlorophyta) to ultraviolet radiation is life stage dependent

The sensitivity of different life stages of the eulittoral green alga Urospora penicilliformis (Roth) Aresch. to ultraviolet radiation (UVR) was examinedin the laboratory. Gametophytic filaments and propagules (zoospores and gametes) released from filaments were separately exposed to different fluence of radiation treatments consisting of PAR (P = 400700 nm), PAR + ultraviolet A (UVA) (PA, UVA = 320400 nm), and PAR + UVA + ultraviolet B (UVB) (PAB, UVB = 280320 nm). Photophysiological indices (ETRmax, Ek, and a) derived from rapid light curves were measured in controls, while photosynthetic efficiency and amount of DNA lesions in terms of cyclobutane pyrimidine dimers (CPDs) were measured after exposure to radiation treatments and after recovery in low PAR; pigments of propagules were quantified after exposure treatment only. The photosynthetic conversion efficiency (a) and photosynthetic capacity (rETRmax) were higher in gametophytes compared with the propagules. The propagules were slightly more sensitive to UVB-induced DNA damage; however, both life stages of the eulittoral inhabiting turf alga were not severely affected by the negative impacts of UVR. Exposure to a maximum of 8 h UVR caused mild effects on the photochemical efficiency of PSII and induced minimal DNA lesions in both the gametophytes and propagules. Pigment concentrations were not significantly different between PAR-exposed and PAR + UVRexposed propagules. Our data showed that U. penicilliformis from the Antarctic is ratherinsensitive to the applied UVR. This amphi-equatorial species possesses different protective mechanisms that can cope with high UVR in coldtemperatewaters of both hemispheres and in polar regions under conditions of increasing UVR as a consequence of further reduction of stratosphericozone

Ecosystem Kongsfjorden: new views after more than a decade of research

The Kongsfjorden System in Svalbard is an established reference site for Arctic marine studies that hosts numerous, international, multidisciplinary collaborative science projects. Kongsfjorden (79 oN) represents an ideal natural laboratory in the Arctic and functions as a local indicator for climate change. Because of its open connection to Fram Strait, it is directly influenced by variable climate signals in the West Spitsbergen Current (Hop et al. 2006; Walczowski et al. 2012; Wassmann et al. 2015). Advection of Transformed Atlantic water into the fjord is important for its seasonal hydrography as well as its biological communities (Cottier et al. 2005, 2007; Hop et al. 2006; Willis et al. 2006, 2008; Dalpadado et al. this issue). In the past, the fjord was regularly covered by sea-ice (Gerland and Renner 2007), but because of increased advection of Atlantic water, regular winter ice cover has been rare since 2005/2006 (Cottier et al. 2007). The inner part of the fjord is still rather “Arctic” because it is influenced strongly by glacial run-off from large tidal glaciers (Karner et al. 2013; Schellenberger et al. 2015). Because of the dual Atlantic/Arctic inputs, the fjord houses pelagic and benthic communities that comprise a mixture of boreal and Arctic flora and fauna, which varies seasonally as well as interannually (Hop et al. 2002, 2012; Walkusz et al. 2009; Voronkov et al. 2013). Kongsfjorden and the adjacent atmospheric Zeppelin Station represent one of the most important environmental monitoring locations in the Arctic. Scientific data from Kongsfjorden have been sampled for more than 100 years, but it was not until the year 2000 that the first Kongsfjorden Ecosystem Workshop was held at the University Centre in Svalbard; 40 participants attended from France, Germany, Italy, Norway, Poland, Russia, Spain, Sweden and the UK. The results of this workshop were published in two well-recognized reviews focused on the physical environment of Kongsfjorden-Krossfjorden (Svendsen et al. 2002) and the ecosystem of Kongsfjorden (Hop et al. 2002). Research performed in Kongsfjorden at the Koldewey Station (AWI) during 1991-2003 was presented in a scientific report entitled The coastal ecosystem of Kongsfjorden, Svalbard (Wiencke et al. 2004). Research in Kongsfjorden was further discussed and coordinated during an international workshop in Ny-Ålesund in March 2008, which resulted in a document The Kongsfjorden System - a flagship programme for Ny-Ålesund (Gabrielsen et al. 2009). This flagship programme is currently followed up in Ny-Ålesund seminars, with bi-annual meetings to exchange scientific results, advancements, ideas and experience and to increase coordination and collaboration among researchers in Ny-Ålesund. Within the last decade, much new and important data have been obtained from the growing research community in Ny-Ålesund, now comprising 18 research stations from 11 nations. The new data were summarized and presented in a compact manner during a second Kongsfjorden Ecosystem Workshop held on 10-17 March 2014 at the conference facility Hamn i Senja, Skaland, Norway. This special issue is published in two parts and contains 34 original papers with new results mostly presented during the workshop, with some additional contributions. The papers cover most organism groups and processes relevant to the marine ecosystem from pelagic microbial heterotrophs over zooplankton to benthic micro- and macroalgae, macrozoobenthos, fishes and seabirds. An important section deals with sedimentation and pollutants in sediments. Effects of climate change on biological communities are addressed in several papers. Pertinent comparisons between Kongsfjorden and other fjord systems in Svalbard characterised by different environmental conditions give new insights into expected future changes in Kongsfjorden. Another focus is seasonality of marine organisms and communities, which also includes the winter season. Many studies include new information on biodiversity and trophic interactions

Video survey of deep benthic macroalgae and macroalgal detritus along a glacial Arctic fjord: Kongsfjorden (Spitsbergen)

In Kongsfjorden (Spitsbergen), we quantified the zonation of visually dominant macroalgal taxa and of detached macroalgae from underwater videos taken in summer 2009 at six transects between 2 and 138 m water depth. For the first time, we provide information on the occurrence of deep water red algae below the kelp forest and of detached macroalgae at water depth > 30 m. The presence and depth distribution of visually dominant red algae were especially pronounced at the outer fjord, decreased with proximity to the glacial front and they were absent at the innermost locations. Deepest crustose coralline red algae and foliose red algae were observed at 72 and 68 m, respectively. Brown algae were distributed along the entire fjord axis at 2–32 m. Green algae were only present at the middle to inner fjord and at areas influenced by physical disturbance at water depths of 2–26 m. With proximity to the inner fjord the depth distribution of all macroalgae became shallower and only extended to 18 m depth at the innermost location. Major recipients of detached macroalgae were sites at the shallower inner fjord and at the middle fjord below the photic zone at depths to 138 m. They may either fuel deep water secondary production, decompose or support carbon sequestration. Univariate and community analyses of macroalgal classes including detached macroalgae across transects and over depths reveal a considerable difference in community structure between the outermost sites, the central part and the inner fjord areas, reflecting the strong environmental gradients along glacial fjords

Video survey of deep benthic macroalgae and macroalgal detritus along a glacial Arctic fjord: Kongsfjorden (Spitsbergen)

In Kongsfjorden (Spitsbergen), we quantified the zonation of visually dominant macroalgal taxa and of detached macroalgae from underwater videos taken in summer 2009 at six transects between 2 and 138 m water depth. For the first time, we provide information on the occurrence of deep water red algae below the kelp forest and of detached macroalgae at water depth > 30 m. The presence and depth distribution of visually dominant red algae were especially pronounced at the outer fjord, decreased with proximity to the glacial front and they were absent at the innermost locations. Deepest crustose coralline red algae and foliose red algae were observed at 72 and 68 m, respectively. Brown algae were distributed along the entire fjord axis at 2–32 m. Green algae were only present at the middle to inner fjord and at areas influenced by physical disturbance at water depths of 2–26 m. With proximity to the inner fjord the depth distribution of all macroalgae became shallower and only extended to 18 m depth at the innermost location. Major recipients of detached macroalgae were sites at the shallower inner fjord and at the middle fjord below the photic zone at depths to 138 m. They may either fuel deep water secondary production, decompose or support carbon sequestration. Univariate and community analyses of macroalgal classes including detached macroalgae across transects and over depths reveal a considerable difference in community structure between the outermost sites, the central part and the inner fjord areas, reflecting the strong environmental gradients along glacial fjords

Macroalgae

Research on Antarctic macroalgae began with the expeditions of Gaudichaud, Bory, Montagne, Hooker and Harvey as early as 1817 (Godley 1965). A second notable period in the exploration of macroalgae from the Southern Ocean and the cold-temperate regions of South America was around the turn of the 19th to the 20th century. The most important studies during this time were conducted by Hariot, Reinsch, Gain, Skottsberg and Kylin (Wiencke & Clayton 2002). These taxonomic and biogeographical studies enabled Papenfuss (1964) to produce the first catalogue of Antarctic and sub-Antarctic benthic marine macroalgae. The introduction of SCUBA diving into the methodological portfolio by Neushul (1965), Zaneveld (1966a, b, 1968) and Delépine et al. (1966) opened a new era. Later on, Moe (Moe & DeLaca 1976), Lamb & Zimmermann (1976), Amsler (Amsler et al., 1995) and Klöser and co-workers (Klöser et al. 1996) conducted numerous diving studies allowing for the first time more precise descriptions of the depth distribution of Antarctic macroalgae. In subsequent years a major attempt was made to investigate the life history of Antarctic species (Wiencke et al. 2007). In this period scientific knowledge of Antarctic macroalgae was considerably broadened and the first monograph of these ecologically important species was compiled (Wiencke & Clayton 2002). Moreover, in-depth studies on the physiological thallus anatomy (Wiencke et al. 2007), phenology (Wiencke et al. 2011) as well as on the temperature and light requirements (Gómez et al. 2011, Wiencke & Amsler 2012) of Antarctic species became possible. Detailed investigations on trophic relations between macroalgae and herbivores began in the last decade of the 20th century (Iken 1996, 1999). Recent studies focus on the defenses between macroalgae and herbivores, defences against diatom fouling (Amsler et al. 2005a, 2008, 2011, Iken et al. 2011, Wiencke & Amsler 2012) as well as on the effect of global climate changes on geographic distribution (Müller et al. 2011) and depth zonation (Zacher et al. 2007a, Campana et al. 2011)

Biochemical composition of temperate and Arctic populations of Saccharina latissima after exposure to increased pCO2 and temperature reveals ecotypic variation

Previous research suggested that the polar and temperate populations of the kelp Saccharina latissima represent different ecotypes. The ecotypic differentiation might also be reflected in their biochemical composition (BC) under changing temperatures and pCO2. Accordingly, it was tested if the BC of Arctic (Spitsbergen) and temperate S. latissima (Helgoland) is different and if they are differently affected by changes in temperature and pCO2. Thalli from Helgoland grown at 17 °C and 10 °C and from Spitsbergen at 10 °C and 4 °C were all tested at either 380, 800, or 1,500 latm pCO2, and total C-, total N-, protein,soluble carbohydrate, and lipid content, as well as C/Nratio were measured. At 10 °C, the Arctic population had a higher content of total C, soluble carbohydrates, and lipids, whereas the N- and protein content was lower. At the lower tested temperature, the Arctic ecotype had particularly higher contents of lipids, while content of soluble carbohydrates increased in the Helgoland population only. In Helgoland-thalli, elevated pCO2 caused a higher content of soluble carbohydrates at 17 °C but lowered the content of N and lipids and increased the C/N-ratio at 10 °C. Elevated pCO2 alone did not affect the BC of the Spitsbergen population. Conclusively, the Arctic ecotype was more resilient to increased pCO2 than the temperate one, and both ecotypes differed in their response pattern to temperature. This differential pattern is discussed in the context of the adaptation of the Arctic ecotype to low temperature and the polar night