Ultraviolet damage and counteracting mechanisms in the freshwater copepod Boeckella poppei from the Antarctic Peninsula

Abstract

The process of ozone depletion over the Antarctic continent has resulted in the increase of incident ultraviolet-B (UVB) radiation, whose effects may be damaging to living organisms. To counteract the negative effects of ultraviolet radiation (UVR), aquatic organisms may display one or more strategies: (1) avoidance (i.e. deep distribution); (2) photoprotection through the use of ''sunscreen'' compounds, such as mycosporine-like amino acids (MAAs); and (3) enzymatic repair of the damage. The effects of UVR were assessed on four populations of the copepod Boeckella poppei from Antarctic lakes using laboratory and field experiments. The results were related to measurements of DNA enzymatic repair activity and MAA concentration. This is the first study that combines these measurements in zooplankton. Boeckella poppei was highly tolerant to UVR (LD 50 ϭ 2.2-2.78 J cm Ϫ2 ). However, measurements of photorecovery (comparison of UVB mortality in the presence and absence of photoreactivating light) and dosage of photolyase activity indicated low rates of enzymatic repair, which may be the result of low temperatures typical of Antarctic lakes. Three different MAAs were identified, both in phytoplankton and copepods: porphyra-334, mycosporine-glycine, and shinorine. The population of B. poppei from Lake Boeckella had the lowest MAA concentration, as well as the lowest tolerance to artificial and natural UVR. These findings support the idea that UV tolerance in this species is related to the accumulation of MAAs. A comparison of the strategies used to cope with potentially damaging levels of UVR by different species of Boeckella indicates a high degree of plasticity in this genus, which has probably been key for its success to colonize a wide range of UV environments.

Plasticity in Pigmentation Induced by Conflicting Threats From Predation and Uv Radiation

“…In the laboratory experiment, calanoid copepods were evenly distributed within the containers, suggesting that they did not actively take advantage of the depth refuge from UV radiation; this was also sug-gested by Rocco et al (2002) regarding Antarctic calanoids. Cyclopoid copepods, on the other hand, actually avoided the refuge from UV radiation; they had higher abundances at the surface than at the bottom of the containers, a distribution also found by Neill (1992).…”

“…Copepods may reduce the harm caused by UV radiation both morphologically, by adjusting the pigment level, and behaviorally, by migrating downwards in the water column. With respect to copepods, this behavioral response has been demonstrated in some (e.g., Hairston 1978, Zagarese et al 1997), but not in other studies (Rocco et al 2002). Cladocerans, on the other hand, seem to more generally utilize vertical migration to avoid UV radiation (Leech andWilliamson 2000, Rhode et al 2001).…”

Complementary UV protective compounds in zooplankton

“…Recent studies, however, indicate that copepods mainly invest in photoprotective pigmentation and less in vertical migration when exposed to UV radiation (Leech and Williamson 2001;Hylander et al 2009). Repair processes in copepods are also reported by several authors, but their importance in copepods is not well understood (Zagarese et al 1997;Rocco et al 2002). DOC in dry climates, like the dry-temperate region, may be photodegraded, leading to high UV transparency.…”

Zooplankton vertical migration and plasticity of pigmentation arising from simultaneous UV and predation threats

“…Repair processes in copepods are reported by several authors, but the importance of these processes is not well understood (Zagarese et al 1997;Rocco et al 2002). Tartarotti et al (2000), for example, found little evidence of photo-enzymatic repair in the copepod species Boeckella gracilipes, arguing that this copepod lacks this kind of DNA repair system.…”