Marine biology
Marine biology Transmission of solar ultraviolet radiation through invertebrate exteriors DENEB KARENTZ and THOMAS GAST, Department of Biology, University of San Francisco, San Francisco, California 94117-1080
dosimeters were wrapped in one layer of polyester film (Mylar D), which filters out wavelengths in the UV-B region. Pairs of dosimeters, with and without Mylar filters, were incubated under sections of shell, tunic, or body wall for 6 hours on 4 December 1991 (1130 to 1730 Greenwich mean time). There were three replicate samples for each species and triplicate plate counts for each dosimeter. The dosimeters and animal covers were held in the same plane on an opaque surface and submerged a few centimeters in an outdoor flowing sea-water tank at Palmer Station. Water was pumped directly from Arthur Harbor. Survival of the dosimeter cells was calculated relative to a dark control (= 100 percent survival). When the UV-B portion of the solar spectrum is removed, survival is enhanced (figure 1). By comparing cell survival under total sunlight exposure to survival under the minus UV-B (with Mylar) treatment, the contribution of UV-B to the killing of cells can be quantified. With no penetration of harmful solar radiation, cells would have 100 percent survival (same number of viable cells as the dark control). Analysis of dosimetry results indicated that the external coverings of all four species transmit biologically harmful wavelengths of solar radiation (figure 2). Differences were observed between individuals and between species. The removal of UV-B wavelengths with Mylar filters increased survival, indicating that LW-B wavelengths do penetrate the exterior surfaces of these organisms and that internal organs and cells are subjected to UV-B exposure. Incident solar radiation data were obtained from the National Science Foundation UV Monitoring Network (figure 3). The scanning spectroradiometer at Palmer Station performs one wavelength scan per hour. To provide a standard measure of the biological effects of the incident solar radiation field, one pair of dosimeters (with and without a Mylar filter) was exposed to ambient sunlight while shielded by five layers of neutral-density screen (figure 2). The layers of screening reduced the exposure fluence to 3 percent of the incident radiation. This was necessary because of the high sensitivity of the CSR06 cells to UV-B. The transmission of IJV-B through the outer coverings of these invertebrate species is relatively low, generally less 3 percent of incident radiation fluences. However, the damage caused by prolonged exposures during 24-hour antarctic day lengths is unknown. This study has established that UV-B
he occurrence of springtime ozone depletion over the TAntarctic has created concern about the effects of increased ultraviolet-B [UV-B, 280-320 nanometers (nm)] on marine organisms (Karentz 1991, 1992). It is not known, however, how much UV-B antarctic marine organisms are exposed to, nor how much irreparable damage UV-B exposure can cause. One area of research associated with these questions is directed toward identifying ways in which marine invertebrate species are naturally protected from UV exposure. The obvious first line of defense that an animal has to solar radiation exposure is its outer covering. Although some antarctic invertebrates live under rocks, in deep water, or in other low-light environments, many individuals in benthic habitats are exposed to UV-B radiation for extended periods of time. UV-B wavelengths have been detected to at least 60 meters (m) in antarctic waters (Smith et al. 1992), and biological effects have been monitored to 20 m (Karentz and Lutze 1990; Heibling et al. 1992; Smith et al. 1992). Therefore, intertidal and subtidal populations are potentially exposed to biologically significant levels of UV-B. Four species of antarctic invertebrates have been evaluated to determine the amount of UV protection provided by their external covering. These taxa are common in intertidal and subtidal regions of the Antarctic Peninsula. Animals were collected in Arthur Harbor (Antarctic Peninsula) and immediately dissected for use. The four species examined were the sea urchin Sterechinus neumayeri, the sea star Odontaster validus, the limpet Nacella concinna, and the tunicate Cnemidocarpa verrucosa. Both the sea urchin S. neumayeri and the sea star 0. validus have a thin epidermal layer that is external to a calcareous skeleton and the body wall. The epidermal cells of these echinoderms have no protective covering to reduce IJV exposure. The body of the limpet N. concinna is completely covered by a dorsal shell that has a structure typical of other limpets, consisting of a complex layering of proteinaceous and calcareous compounds. The body of the tunicate C. verrucosa is enclosed by a thick outer layer of fibrous cellulosic material known as the tunic. UV transmission was monitored using a biological dosimeter based on a DNA-repair-deficient strain of Escherichia coli (CSR06) (Karentz and Lutze 1990). The dosimeter consists of a liquid culture of E. coli cells packaged in JJV transparent polyethylene bags (Whiripak). Half of the
ANTARCTIC JOURNAL - REVIEW 1993 113
100000
radiation diation minus UV-B
( full solar
100
10-600 nm
80
- 10000
- 60 > 2: U)
0-400 nm
E C-) -, 1000 0) C-) C 0)
40
)0-320 nm
- 100 20
10 1000
1 2 3 time (h) Figure 1. Survival characteristics of Escherichia coil (strain CSR06) under ambient antarctic radiation: full solar radiation and solar radiation minus UV-B wavelengths.
)
100- =noUVtranmission
21
f II
UV-B
1200 1400 1600 1800
time (GMT)
Figure 3. Instantaneous hourly values of solar fluence during the course of the incubations (data for 1400 to 1600 are missing). Data were obtained from the National Science Foundation UV Monitoring Network. Values reflect broad-band integrations of scanned data. (iW cm-2 denotes microwatts per square centimeter.) wavelengths do penetrate the outer layers of adult invertebrates. Subsequent investigations need to be conducted to determine the extent of internal photodamage. I. Bosch and M. Slattery assisted in this work. Research was supported by National Science Foundation grant OPP 9017664. References Heibling, E.W., V. Villafahe, M. Ferrario, and 0. Holm-Hansen. 1992. Impact of natural ultraviolet radiation on rates of photosynthesis and on specific marine phytoplankton species. Marine Ecology Progress Series, 80, 89-100. Karentz, D. 1991. Ecological considerations of antarctic ozone depletion. Antarctic Science, 3, 3-11. Karentz, D. 1992. Ozone depletion and UV-B radiation in the Antarctic—Limitations to ecological assessment. Marine Pollution Bulletin, 25, 231-232. Karentz, D., and L.H. Lutze. 1990. Evaluation of biologically harmful ultraviolet radiation in Antarctica with a biological dosimeter designed for aquatic environments. Limnology and Oceanography, 35,549-561. Smith, R.C., B.B. Prézelin, K.S. Baker, R.R. Bidigare, N.P. Boucher, T. Coley, D. Karentz, S. Maclntyre, H.A. Matlick, D. Menzies, M. Ondrusek, Z. Wan, and K.J. Waters. 1992. Ozone depletion: Ultraviolet radiation and phytoplankton biology in antarctic waters. Science, 255, 952-959
(
a)
C1
123 123 123123 3% Sterechinus Odonlacier Cnemidocarpa Nacella validus neumayeri incident vetnicosa concinna sea urchin radiation sea star tunicate limpet
Figure 2. UV transmission through the exteriors of four antarctic invertebrate species as determined by biological dosimetry. Each pair of bars represents one animal (three animals tested for each species). Absence of bars indicates 100 percent killing of dosimeter cells (that is, Cnemidocarpa verrucosa 1). The two bars at the far right represent the lethality of 3 percent incident radiation on the dosimeter cells during the course of the experiment.
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dosimeters were wrapped in one layer of polyester film (Mylar D), which filters out wavelengths in the UV-B region. Pairs of dosimeters, with and without Mylar filters, were incubated under sections of shell, tunic, or body wall for 6 hours on 4 December 1991 (1130 to 1730 Greenwich mean time). There were three replicate samples for each species and triplicate plate counts for each dosimeter. The dosimeters and animal covers were held in the same plane on an opaque surface and submerged a few centimeters in an outdoor flowing sea-water tank at Palmer Station. Water was pumped directly from Arthur Harbor. Survival of the dosimeter cells was calculated relative to a dark control (= 100 percent survival). When the UV-B portion of the solar spectrum is removed, survival is enhanced (figure 1). By comparing cell survival under total sunlight exposure to survival under the minus UV-B (with Mylar) treatment, the contribution of UV-B to the killing of cells can be quantified. With no penetration of harmful solar radiation, cells would have 100 percent survival (same number of viable cells as the dark control). Analysis of dosimetry results indicated that the external coverings of all four species transmit biologically harmful wavelengths of solar radiation (figure 2). Differences were observed between individuals and between species. The removal of UV-B wavelengths with Mylar filters increased survival, indicating that LW-B wavelengths do penetrate the exterior surfaces of these organisms and that internal organs and cells are subjected to UV-B exposure. Incident solar radiation data were obtained from the National Science Foundation UV Monitoring Network (figure 3). The scanning spectroradiometer at Palmer Station performs one wavelength scan per hour. To provide a standard measure of the biological effects of the incident solar radiation field, one pair of dosimeters (with and without a Mylar filter) was exposed to ambient sunlight while shielded by five layers of neutral-density screen (figure 2). The layers of screening reduced the exposure fluence to 3 percent of the incident radiation. This was necessary because of the high sensitivity of the CSR06 cells to UV-B. The transmission of IJV-B through the outer coverings of these invertebrate species is relatively low, generally less 3 percent of incident radiation fluences. However, the damage caused by prolonged exposures during 24-hour antarctic day lengths is unknown. This study has established that UV-B
he occurrence of springtime ozone depletion over the TAntarctic has created concern about the effects of increased ultraviolet-B [UV-B, 280-320 nanometers (nm)] on marine organisms (Karentz 1991, 1992). It is not known, however, how much UV-B antarctic marine organisms are exposed to, nor how much irreparable damage UV-B exposure can cause. One area of research associated with these questions is directed toward identifying ways in which marine invertebrate species are naturally protected from UV exposure. The obvious first line of defense that an animal has to solar radiation exposure is its outer covering. Although some antarctic invertebrates live under rocks, in deep water, or in other low-light environments, many individuals in benthic habitats are exposed to UV-B radiation for extended periods of time. UV-B wavelengths have been detected to at least 60 meters (m) in antarctic waters (Smith et al. 1992), and biological effects have been monitored to 20 m (Karentz and Lutze 1990; Heibling et al. 1992; Smith et al. 1992). Therefore, intertidal and subtidal populations are potentially exposed to biologically significant levels of UV-B. Four species of antarctic invertebrates have been evaluated to determine the amount of UV protection provided by their external covering. These taxa are common in intertidal and subtidal regions of the Antarctic Peninsula. Animals were collected in Arthur Harbor (Antarctic Peninsula) and immediately dissected for use. The four species examined were the sea urchin Sterechinus neumayeri, the sea star Odontaster validus, the limpet Nacella concinna, and the tunicate Cnemidocarpa verrucosa. Both the sea urchin S. neumayeri and the sea star 0. validus have a thin epidermal layer that is external to a calcareous skeleton and the body wall. The epidermal cells of these echinoderms have no protective covering to reduce IJV exposure. The body of the limpet N. concinna is completely covered by a dorsal shell that has a structure typical of other limpets, consisting of a complex layering of proteinaceous and calcareous compounds. The body of the tunicate C. verrucosa is enclosed by a thick outer layer of fibrous cellulosic material known as the tunic. UV transmission was monitored using a biological dosimeter based on a DNA-repair-deficient strain of Escherichia coli (CSR06) (Karentz and Lutze 1990). The dosimeter consists of a liquid culture of E. coli cells packaged in JJV transparent polyethylene bags (Whiripak). Half of the
ANTARCTIC JOURNAL - REVIEW 1993 113
100000
radiation diation minus UV-B
( full solar
100
10-600 nm
80
- 10000
- 60 > 2: U)
0-400 nm
E C-) -, 1000 0) C-) C 0)
40
)0-320 nm
- 100 20
10 1000
1 2 3 time (h) Figure 1. Survival characteristics of Escherichia coil (strain CSR06) under ambient antarctic radiation: full solar radiation and solar radiation minus UV-B wavelengths.
)
100- =noUVtranmission
21
f II
UV-B
1200 1400 1600 1800
time (GMT)
Figure 3. Instantaneous hourly values of solar fluence during the course of the incubations (data for 1400 to 1600 are missing). Data were obtained from the National Science Foundation UV Monitoring Network. Values reflect broad-band integrations of scanned data. (iW cm-2 denotes microwatts per square centimeter.) wavelengths do penetrate the outer layers of adult invertebrates. Subsequent investigations need to be conducted to determine the extent of internal photodamage. I. Bosch and M. Slattery assisted in this work. Research was supported by National Science Foundation grant OPP 9017664. References Heibling, E.W., V. Villafahe, M. Ferrario, and 0. Holm-Hansen. 1992. Impact of natural ultraviolet radiation on rates of photosynthesis and on specific marine phytoplankton species. Marine Ecology Progress Series, 80, 89-100. Karentz, D. 1991. Ecological considerations of antarctic ozone depletion. Antarctic Science, 3, 3-11. Karentz, D. 1992. Ozone depletion and UV-B radiation in the Antarctic—Limitations to ecological assessment. Marine Pollution Bulletin, 25, 231-232. Karentz, D., and L.H. Lutze. 1990. Evaluation of biologically harmful ultraviolet radiation in Antarctica with a biological dosimeter designed for aquatic environments. Limnology and Oceanography, 35,549-561. Smith, R.C., B.B. Prézelin, K.S. Baker, R.R. Bidigare, N.P. Boucher, T. Coley, D. Karentz, S. Maclntyre, H.A. Matlick, D. Menzies, M. Ondrusek, Z. Wan, and K.J. Waters. 1992. Ozone depletion: Ultraviolet radiation and phytoplankton biology in antarctic waters. Science, 255, 952-959
(
a)
C1
123 123 123123 3% Sterechinus Odonlacier Cnemidocarpa Nacella validus neumayeri incident vetnicosa concinna sea urchin radiation sea star tunicate limpet
Figure 2. UV transmission through the exteriors of four antarctic invertebrate species as determined by biological dosimetry. Each pair of bars represents one animal (three animals tested for each species). Absence of bars indicates 100 percent killing of dosimeter cells (that is, Cnemidocarpa verrucosa 1). The two bars at the far right represent the lethality of 3 percent incident radiation on the dosimeter cells during the course of the experiment.
ANTARCTIC JOURNAL - REVIEW 1993
114
