Can the amphipod Ampithoe valida choose shelter against solar UVR? The role of macroalgae

BLUM, R. ; MOTTA, R.; HELBLING, E.W.; VALIÑAS, M.S.

Paranaiba

Congreso; Congresso Brasileiro de Ficología; 2016

INTRODUCTION: In the South Atlantic coasts of Patagonia (Argentina), the amphipod Ampithoe valida is a very abundant invertebrate commonly found associated to macroalgae (Valiñas & Helbling, 2015). During low tide, macroalgae and amphipods remain in tide pools exposed to high levels of solar ultraviolet radiation (UVR). UVR can harm aquatic organisms with effects including DNA and protein damage (Malloy et al., 1997), increased mortality (Browman et al., 2000; Hylander et al., 2014) and changed behavior (Leech et al., 2005; Hansson et al., 2007). Organisms have developed different strategies to cope with the damaging effects of UVR, including DNA-repair mechanisms, behavioral adaptations (Hansson et al., 2007; Häder et al., 2011), pigmentation and chemical defenses like UV-absorbing compounds (UVAC) that absorb in the UVR range (310 - 360 nm) and can act as a ?sunscreen? against UVR. These compounds can be synthesized only by autotrophic organisms (Favre-Bonvin et al., 1987), but can be accumulated by heterotrophs through the diet, lowering the negative impact of UVR in the animals (Helbling et al., 2002; Moresino & Helbling, 2010; Valiñas & Helbling, 2015). Previous studies performed on A. valida (Helbling et al., 2002; Valiñas & Helbling, 2015) showed the photoprotective role of UVAC as a result of feeding on UVAC-rich red algae. OBJECTIVE: In this study, we evaluated the role of UVR and UVAC in the choice of shelter for A. valida through an experimental approach. First, a refuge experiment was performed observing the amphipods? preference for different types of shelter (UVR-protected or not, with and without color), with the aim to evaluate if individuals detect their shelter through visual detection of color, perception of UVR or mechanically through touching. In a second instance, a feeding experiment was carried out to evaluate differences in the amhipods´ food consumption rate depending on the type of refuge (protected or not from UVR, with and without color), and the type of macroalgae offered as food (rich or poor in UVAC). MATERIALS AND METHODS: The study was carried out during austral summer 2015/2016. Individuals of A. valida and specimens of green (Ulva rigida) and red macroalgae (Porphyra columbina) were collected from Playa Bonita located in the Patagonian coast (43° 22´ S - 65° 03´ W, Chubut, Argentina). The general experimental design for both experiments was as follows: amphipods were separated by sex and placed in open plastic containers filled with seawater. Within each container, five areas of similar size were distinguished, comprising five different types of shelter in terms of radiation and color: (1) PAB without color [amphipods receiving full solar radiation (PAR + UVA + UV-B > 280 nm), area covered with transparent Ultraphan 290 film]; (2) P without color [amphipods receiving Photosynthetic Active Radiation (PAR > 400 nm), area covered with Ultraphan UV Opak Digefra film]; (3) PAB with color [area covered with UVR-transparent pinkish film (PAR + UVA + UV-B > 280 nm)]; (4) P with color [area covered with Ultraphan UV Opak Digefra film and pinkish film (PAR > 400 nm)]; (5) without shelter [bare area ? full solar radiation]. For the refuge experiment, six amphipods previously fed with either P. columbina or U. rigida during 4 days were added in each container (n= 6 per sex) and exposed under a solar simulator (SOL 1200W, Dr Hönle AG, Gräfelfing/München, Germany) for six hours (irradiances of 112.6 ? 125.8, 43 ? 49.1 and 1.08 ? 1.22 W m-2 for PAR, UVA and UVB, respectively). The position of the individuals was registered with respect to the shelters by visual observation every 15 min during the first hour, and every 30 min during the subsequent five hours. The mean percentages of individuals within each of the five areas after a total of 14 observations were calculated and used for statistical comparisons. In the feeding experiment, feeding rate within each of the five areas was measured. Three food types were offered to the amphipods in different containers: (1) mixed diet treatment [one piece of U. rigida and one piece of P. columbina under each shelter]; (2) Ulva treatment [two pieces of U. rigida under each shelter] and (3) Porphyra treatment [two pieces of P. columbina under each shelter]. Based on the results of the refuge experiment that shelter preferences (in term of UVR protection) was the comparable regardless the previous diet, amphipods were taken directly from the field and thus had naturally low contents of UVACs. The experiment was performed separately for males and females, adding 8 and 10 individuals respectively in each container. Individuals were exposed to natural solar radiation for a total of six days. Food was placed in the morning and taken out in the evening. During the night amphipods were left without food. Macroalgae pieces were replaced every second day, resulting in three data of consumption for each replicate, for a total of 5 replicates. RESULTS AND DISCUSSION: In both experiments amphipods generally showed preferences for places that offered protection against UVR, indicating that searching for shelter is one strategy to cope with the negative effects of this abiotic stressor. Additionally, in the refuge experiment, males preferred protected shelters (P) without color while females made no difference between colored and non-colored shelters (one-way ANOVA - LSD test p < 0.05). Thus, amphipods were not attracted to the shelters by their color, but rather due to the perception and avoidance of UVR. The percentage of individuals within the transparent PAB shelter (PAB without color) was just slightly, but not significantly, higher than within the bare areas, indicating that the tactile perception was just of limited importance in the search for shelter. Although the accumulation of UVAC in the animals? bodies can help to cope with the negative effects of UVR (Helbling et al., 2002; Valiñas & Helbling, 2015), the present study showed that UVAC-rich diets did not significantly affect the preference of shelter in none of the sexes (two-way ANOVA p > 0.05). In the feeding experiment, mean relative consumption rate was highest within UVR protected areas (with and without color), being significant for females when fed on one single food type (Porphyra or Ulva treatment), and for males when fed on P. columbina only (two-way ANOVA with subsequent LSD test, p < 0.05). Valiñas & Helbling (2015) showed that food consumption rate in A. valida did not change between P- and PAB- treatments, so higher consumption rates in P shelters found in our study seems to be related to the preference of amphipods to stay more time within UVR-protected areas. When both algal species were offered simultaneously, both males and females showed a clear preference (high food consumption rate) for P. columbina (one-way ANOVA p < 0.005 for both sexes). CONCLUSIONS: Shelter is an important ecological need for marine invertebrates, as it provides them protection against several biotic and abiotic stressors (Gibbons, 1991; Boström & Mattila, 1999). Here we showed the importance of shelter under the influence of UVR for the marine amphipod A. valida that inhabits the intertidal Patagonian coasts. Several studies already suggested that not just nutritional value, but rather the combination of both food and shelter can drive the microhabitat choice of aquatic invertebrates that live associated to macroalgae (Duffy & Hay, 1991; Boström & Mattila, 1999), thus suggesting that the quality of a macroalgae in terms of protection against UVR could determine the animals? choice for that species or feeding site, especially under a global change scenario.