Impact of UV radiation on the early development of the giant kelp (Macrocystis pyrifera) gametophytes

Differential temperature sensitivity of haploid and diploid spores of two red intertidal algae from the Magellan Strait

Spores have crucial importance in the establishment and development of seaweed populations. When the spore release matches with the low tidal period, they experience an extreme variation in the environmental conditions including the temperature. In this study, we assess the photosynthetic responses and growth of haploid (tetraspores) and diploid (carpospores) spores of two Gigartinales species (Mazzaella laminarioides and Iridaea cordata) from sub-Antarctic populations when exposed to an increasing temperature. In the laboratory, freshly released spores were exposed to a temperature gradient (7 [control], 10, 15, and 20 °C) recreating the temperature increase experienced by these spores during typical spring tides. Germination and further growth of spores previously exposed to temperature treatments were assessed. Carpospores and tetraspores exhibited variation in their photosynthetic response (measured as effective quantum yield; ΦPSII) to temperature increase. In Mazzaella laminarioides, only carpospores exhibited a reduction in ΦPSII (by 7-24% at 15-20 °C), while both types of spores of Iridaea cordata were sensitive to temperature increase (12-24% of ΦPSII reduction at 10-20 °C). Spores previously exposed to temperature treatments and maintained at 7 °C and low PAR germinated and developed in germlings. In general, germlings originated from carpospores pre-treated at high temperatures showed higher growth rates. The different responses to temperature increase exhibited by haploid and diploid propagules of both species highlight their ecophysiological capacity to face high-temperature variation ensuring successful recruitment survival.

A review of protocols for the experimental release of kelp (Laminariales) zoospores

ABSTRACT

Kelps (order Laminariales) are foundation species in temperate and arctic seas globally, but they are in decline in many places. Laminarian kelp have an alternation of generations and this poses challenges for experimental studies due to the difficulties in achieving zoospore release and gametophyte growth. Here, we review and synthesize the protocols that have been used to induce zoospore release in kelps to identify commonalities and provide guidance on best practices. We found 171 papers, where zoospore release was induced in four kelp families from 35 different ecoregions. The most commonly treated family was Laminariaceae, followed by Lessoniaceae and the most studied ecoregion was Central Chile, followed by the Southern California Bight. Zoospore release generally involved three steps: a pretreatment which included cleaning of the reproductive tissue to eliminate epiphytic organisms, followed by desiccation of the tissue, and finally a postdesiccation immersion of the reproductive material in a seawater medium for zoospore release. Despite these commonalities, there was a high degree of variation in the detail within each of these steps, even among studies within genera and from the same ecoregions. This suggests either that zoospore release may be relatively insensitive across the Laminariales or that little methods optimization has been undertaken. We suggest that greater attention to standardization of protocols and reporting of methodology and optimization would improve comparisons of kelp zoospore release across species and locations and facilitate a broader understanding of this key, but understudied life history stage.

OPEN RESEARCH BADGES

This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://doi.org/10.5061/dryad.0kh1f8j.

Differential responses of tetrasporophytes and gametophytes of Mazzaella laminarioides (Gigartinales, Rhodophyta) under solar UV radiation

The effects of solar UV radiation on mycosporine-like amino acids (MAAs), growth, photosynthetic pigments (Chl a, phycobiliproteins), soluble proteins (SP), and C and N content of Mazzaella laminarioides tetrasporophytes and gametophytes were investigated. Apical segments of tetrasporophytes and gametophytes were exposed to solar radiation under three treatments (PAR [P], PAR+UVA [PA], and PAR+UVA+UVB [PAB]) during 18 d in spring 2009, Punta Arenas, Chile. Samples were taken after 2, 6, 12, and 18 d of solar radiation exposure. Most of the parameters assessed on M. laminarioides were significantly influenced by the radiation treatment, and both gametophytes and tetrasporophytes seemed to respond differently when exposed to high UV radiation. The two main effects promoted by UV radiation were: (i) higher synthesis of MAAs in gametophytes than tetrasporophytes at 2 d, and (ii) a decrease in phycoerythrin, phycocyanin, and SPs, but an increase in MAA content in tetrasporophytes at 6 and 12 d of culture. Despite some changes that were observed in biochemical parameters in both tetrasporophytes and gametophytes of M. laminarioides when exposed to UVB radiation, these changes did not promote deleterious effects that might interfere with the growth in the long term (18 d). The tolerance and resistance of M. laminarioides to higher UV irradiance were expected, as this intertidal species is exposed to variation in solar radiation, especially during low tide.

Beyond xeroderma pigmentosum: DNA damage and repair in an ecological context. A tribute to James E. Cleaver

The ability to repair DNA is a ubiquitous characteristic of life on Earth and all organisms possess similar mechanisms for dealing with DNA damage, an indication of a very early evolutionary origin for repair processes. James E. Cleaver's career (initiated in the early 1960s) has been devoted to the study of mammalian ultraviolet radiation (UVR) photobiology, specifically the molecular genetics of xeroderma pigmentosum and other human diseases caused by defects in DNA damage recognition and repair. This work by Jim and others has influenced the study of DNA damage and repair in a variety of taxa. Today, the field of DNA repair is enhancing our understanding of not only how to treat and prevent human disease, but is providing insights on the evolutionary history of life on Earth and how natural populations are coping with UVR-induced DNA damage from anthropogenic changes in the environment such as ozone depletion.

Sensitivity of spore germination and germ tube elongation of Saccharina japonica to metal exposure

The sensitivity of early life stages of the brown seaweed Saccharina japonica to six metals (Cd, Cu, Hg, Ni, Pb, Zn) and two waste-water samples were investigated and a new toxicity bioassay developed. The two endpoints used were spore germination and germ tube elongation with an exposure time of 24 h. Optimal test conditions determined for photon irradiance, pH, salinity and temperature were darkness, pH 8, 35‰ and 15°C, respectively. The toxicity ranking of five metals was: Hg (EC(50) of 41 and 42 μg l(-1)) > Cu (120 and 81 μg l(-1)) > Ni (2,009 and 1,360 μg l(-1)) > Zn (3,024 and 3,897 μg l(-1)) > Pb (4,760 and 4,429 μg l(-1)) > Cd (15,052 and 7,541 μg l(-1)) for germination and germ tube elongation, respectively. The sensitivities to Cd, Cu and Ni were greater in germ tube elongation than in germination process. When tested against two different waste-water samples (processed animal and printed circuit board waste-water) values of EC(50) were between 21.29 and 32.02% for germination and between 5.33 and 8.98% for germ tube elongation. Despite differences in their chemical composition, the toxic effects of waste-water samples, as indicated by EC(50) values, did not differ significantly for the same endpoints. The CV range for both germination and germ tube elongation was between 4.61 and 37.69%, indicating high levels of precision of the tests. The results compare favourably with those from more established test procedures employing micro- and macroalgae. The advantages and potential limitations of the bioassay for the assessment of anthropogenic impacts on coastal ecosystems and commercial cultivation areas in near-shore environments are discussed.

Use of UV-A energy for photosynthesis in the red macroalga Gracilaria lemaneiformis

UV radiation is known to inhibit photosynthetically active radiation (PAR)-driven photosynthesis; however, moderate levels of UV-A have been shown to enhance photosynthesis and growth rates of some algae. Here, we have shown that UV-A alone could drive photosynthetic utilization of bicarbonate in the red alga Gracilaria lemaneiformis as evidenced in either O(2) evolution or carbon fixation as well as pH drift. Addition of UV-B inhibited the apparent photosynthetic efficiency, raised the photosynthetic compensation point and photosynthesis-saturating irradiance level, but did not significantly affect the maximal rate of photosynthetic O(2) evolution. The electron transport inhibitor, DCMU, inhibited the photosynthesis completely, reflecting that energy of UV-A was transferred in the same way as that of PAR. Inorganic carbon acquisition for photosynthesis under UV alone was inhibited by the inhibitors of carbonic anhydrase. The results provided the evidence that G. lemaneiformis can use UV-A efficiently to drive photosynthesis based on the utilization of bicarbonate, which could contribute significantly to the enhanced photosynthesis in the presence of UV-A observed under reduced levels of solar radiation.

IMPACTS OF SOLAR UV RADIATION ON THE PHOTOSYNTHESIS, GROWTH, AND UV-ABSORBING COMPOUNDS IN GRACILARIA LEMANEIFORMIS (RHODOPHYTA) GROWN AT DIFFERENT NITRATE CONCENTRATIONS(1)

Solar ultraviolet radiation (UVR, 280-400 nm) is known to affect macroalgal physiology negatively, while nutrient availability may affect UV-absorbing compounds (UVACs) and sensitivity to UVR. However, little is known about the interactive effects of UVR and nitrate availability on macroalgal growth and photosynthesis. We investigated the growth and photosynthesis of the red alga Gracilaria lemaneiformis (Bory) Grev. at different levels of nitrate (natural or enriched nitrate levels of 41 or 300 and 600 μM) under different solar radiation treatments with or without UVR. Nitrate-enrichment enhanced the growth, resulted in higher concentrations of UVACs, and led to negligible photoinhibition of photosynthesis even at noon in the presence of UVR. Net photosynthesis during the noon period was severely inhibited by both ultraviolet-A radiation (UVA) and ultraviolet-B radiation (UVB) in the thalli grown in seawater without enriched nitrate. The absorptivity of UVACs changed in response to changes in the PAR dose when the thalli were shifted back and forth from solar radiation to indoor low light, and exposure to UVR significantly induced the synthesis of UVACs. The thalli exposed to PAR alone exhibited higher growth rates than those that received PAR + UVA or PAR + UVA + UVB at the ambient or enriched nitrate concentrations. UVR inhibited growth approximately five times as much as it inhibited photosynthesis within a range of 60-120 μg UVACs · g(-1) (fwt) when the thalli were grown under nitrate-enriched conditions. Such differential inhibition implies that other metabolic processes are more sensitive to solar UVR than photosynthesis.

The response of the early developmental stages of Laminaria japonica to enhanced ultraviolet-B radiation

The responses of the early development of Laminaria japonica collected from Kiaochow Bay in China to enhanced ultraviolet-B radiation (UV-B, 280-320 nm) were studied in the laboratory. The low UV-B radiations (11.7-23.4 J x m(-2) x d(-1)) had no significant effects on zoospores attachment, but when the UV-B dose > 35.1 J x m(-2) x d(-1) the attachment decreased significantly compared with the control. Germination of embryospores was >93% under the low (11.7-35.1 J x m(-2) x d(-1)) doses, and in the range of 78.5%-88.5% under the high (46.8-70.2 J x m(-2) x d(-1)) UV-B doses, indicating a significant radiation effect. Under the higher UV-B exposure (35.1-70.2 J x m(-2) x d(-1)), all of the few gametophytes formed from embryospores died 120 h post-release. After exposure to the low UV-B radiation (11.7-23.4 J x m(-2) x d(-1)), the formation of sporophytes decreased and the female gametophyte clones increased compared with the control. However, the sex ratio and the relative growth of female gametophytes/sporophytes had not significantly changed. According to the results, enhanced UV-B radiation has a significant effect on the early development of L. japonica under laboratory conditions, suggesting that the UV-B radiation could not be overlooked as one of the important environmental factors influencing the ontogeny of macroalgae living in marine ecosystems.

Impacts of macroalgal spores on the dynamics of adult macroalgae in a eutrophic estuary: high versus low hydrodynamic seasons and long-term simulations for global warming scenarios

A model describing macroalgal early life stages and adult dynamics was used to quantify the effects of non-adult forms on the productivity of adult macroalgae in a eutrophic estuary. Predictions indicate that during years with mild winters and low rainfall, spring blooms will occur at the expense of the growth and reproduction of overwintering adults and without the contribution of the spore bank. In these circumstances, there is a positive correlation between the intensity of the blooms and the biomass of overwintering adults until a maximum threshold value. On the contrary, in years with high rainfall and low or inexistent biomass of overwintering adults, the onset of adult's growth depends on the biomass of viable dormant spores, the growing season occurs later and adult productivity is very limited. Long-term predictions for climate change scenarios suggest that, in general, global warming will have adverse affects on Ulva intestinalis productivity, with the adults being more affected than the early life stages.

Acute effects of ultraviolet-A radiation on African catfish Clarias gariepinus (Burchell, 1822)

In the present work, the destructive effects of Ultraviolet-A radiation on the African Catfish, Clarias gariepinus was revealed in terms of total protein, cholesterol, glucose, hemoglobin and erythrocytic indices, differential blood cell counting, heamatocrite, creatinine level, Aspartic Amino Transferase, Alanine Amino Transferase and Alkaline Phosphatase. These destructive effects were also confirmed by histopathological changes in liver, blood corpuscles and skin.

Sensitivity of the Early Life Stages of Macroalgae from the Northern Hemisphere to Ultraviolet Radiation†

The reproductive cells of macroalgae are regarded as the life history stages most susceptible to various environmental stresses, including UV radiation (UVR). UVR is proposed to determine the upper depth distribution limit of macroalgae on the shore. These hypotheses were tested by UV-exposure experiments, using spores and young thalli of the eulittoral Rhodophyceae Mastocarpus stellatus and Chondrus crispus and various sublittoral brown macroalgae (Phaeophyceae) with different depth distribution from Helgoland (German Bight) and Spitsbergen (Arctic). In spores, the degree of UV-induced inhibition of photosynthesis is lower in eulittoral species and higher in sublittoral species. After UV stress, recovery of photosynthetic capacity is faster in eulittoral compared to sublittoral species. DNA damage is lowest while repair of DNA damage is highest in eulittoral compared to sublittoral species. When the negative impact of UVR prevails, spore germination is inhibited. This is observed in deep water kelp species whereas the same UVR doses do not inhibit germination of shallow water kelp species. A potential acclimation mechanism to increase UV tolerance of brown algal spores is the species-specific ability to increase the content of UV-absorbing phlorotannins in response to UV-exposure. Growth rates of young Mastocarpus and Chondrus gametophytes exposed to experimental doses of UVR are not affected while growth rates of all young kelp sporophytes exposed to UVR are significantly lowered. Furthermore, morphological UV damage in Laminaria ochroleuca includes tissue deformation, lesion, blistering and thickening of the meristematic part of the lamina. The sensitivity of young sporophytes to DNA damage is correlated with thallus thickness and their optical characteristics. Growth rate is an integrative parameter of all physiological processes in juvenile plants. UV inhibition of growth may affect the upper distribution depth limit of adult life history stages. Juveniles possess several mechanisms to minimize UVR damage and, hence, are less sensitive but at the expense of growth. The species-specific susceptibility of the early life stages of macroalgae to UVR plays an important role for the determination of zonation patterns and probably also for shaping up community structure.

A Five-year Study of Solar Ultraviolet Radiation in Southern Chile (39° S): Potential Impact on Physiology of Coastal Marine Algae?

This study reports 5 years of (1998-2003) data on continuous solar-irradiation measurements from a scanning spectroradiometer (SUV-100) in Valdivia, Chile (39 degrees S), accompanied by evaluation of the impact of ultraviolet radiation (UVR) on marine macroalgae of this site. UVR conditions showed a strong seasonal variation, which was less pronounced toward longer wavelengths. Daily maximum dose rates (clear days) averaged in winter-summer: UV-B(290-315 nm) 0.30-2.1, UV-B(290-320 nm) 0.70-3.7, UV-A(315-400 nm) 20.6-62.1, UV-A(320-400 nm) 20.2-60.5 W m(-2), and photosynthetically active radiation (PAR) 969-2423 micromol m(-2) s(-1). The corresponding daily doses (all the days) ranged: UV-B(290-315 nm) 2.6-40.7, UV-B(290-320 nm) 6.7-78.5, UV-A(315-400 nm) 228-1539, UV-A(320-400 nm) 224-1501, and PAR 2008-13308 kJ m(-2) d(-1). Taking into consideration action spectra of a biological interest, the risk of UV exposure could be up to 37 times higher in summer than in winter. The photosynthetic activity (as maximum quantum yield of chlorophyll fluorescence, F(v)/F(m)) of the brown alga Lessonia nigrescens from the infralittoral zone was markedly more sensitive to UVR than of the green alga Enteromorpha intestinalis from the upper midlittoral, and the UV-B wave band increased markedly photoinhibition. In L. nigrescens, maximal photoinhibition (40%) took place at weighted (the action spectrum for photoinhibition of photosynthesis) UVR doses of 800 kJ m(-2), irrespective of the season (corresponding midsummer daily dose in Valdivia is 480 kJ m(-2)). In winter, when this alga was at its most sensitive, the weighted UV dose causing 35-40% photoinhibition was around 200 kJ m(-2). In E. intestinalis, weighted doses of 800 kJ m(-2) resulted in low photoinhibition (<10 %) and no clear seasonal patterns could be inferred. These results confirm that midday summer levels of UV-B and their daily doses in southern Chile are high enough to produce stress to intertidal macroalgae.

Aquatic ecosystems: effects of solar ultraviolet radiation and interactions with other climatic change factors

Aquatic ecosystems are a key component of the Earth's biosphere. A large number of studies document substantial impact of solar UV radiation on individual species, yet considerable uncertainty remains with respect to assessing impacts on ecosystems. Several studies indicate that the impact of increased UV radiation appears relatively low when considering overall ecosystem response, while, in contrast, effects on individual species show considerable responses. Ecosystem response to climate variability incorporates both synergistic and antagonistic processes with respect to UV-related effects, significantly complicating understanding and prediction at the ecosystem level. The impact of climate variability on UV-related effects often becomes manifest via indirect effects such as reduction in sea ice, changes in water column bio-optical characteristics, changes in cloud cover and shifts in oceanographic biogeochemical provinces.

Ultraviolet-B-induced cyclobutane-pyrimidine dimer formation and repair in Arctic marine macrophytes

The significance of ultraviolet-B radiation (UVBR: 280-315 nm)-induced DNA damage as a stress factor for Arctic marine macrophytes was examined in the Kongsfjord (Spitsbergen, 78 degrees 55.5'N, 11 degrees 56.0'E) in summer. UVBR penetration in the water column was monitored as accumulation of cyclobutane-pyrimidine dimers (CPD) in bare DNA. This showed that UVBR transparency of the fjord was variable, with 1% depths ranging between 4 and 8 m. In addition, induction and repair kinetics of CPD were studied in several subtidal macrophytes obtained from the Kongsfjord (5-15 m). Surface exposure experiments demonstrated CPD accumulation in Palmaria palmata, Devaleraea ramentacea, Phycodrys rubens, Coccotylus truncatus and Odonthalia dentata. In artificial light, field collected material of P. palmata, D. ramentacea, P. rubens and Laminaria saccharina showed efficient CPD repair, with only 10% of the artificially induced CPD remaining after 5 h. No significant differences in repair rate were observed among these species. CPD repair was slower or absent in O. dentata, C. truncatus and Monostroma arcticum, indicating that fast repair mechanisms such as photolyase were not continuously expressed in these species. CPD repair rates were not directly related to the vertical distribution of algae in the water column and to the reported UV sensitivity of the examined species. Dosimeter incubations showed that maximal exposure to DNA damaging wavelengths was low for all examined species. Furthermore, most species collected below the 1% depth for DNA damage displayed efficient CPD repair, suggesting that UVBR-induced CPD currently impose a minor threat for mature stages of these species growing in the Kongsfjord, Spitsbergen.