What to eat, red or green macroalgae? The importance of UV- absorbing compounds for consumers

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

Paranaiba

Congreso; Congresso Brasileiro de Ficología; 2016

INTRODUCTION: Solar ultraviolet radiation (UVR; 280?400 nm) has deleterious effects on aquatic organisms occupying all trophic levels (Cullen et al. 1992, Williamson 1995), including DNA and protein damage, production of harmful reactive oxygen species, reduction in the survival and growth rates of organisms (Dattilo et al. 2005, Fischer et al. 2006), and also changes in their behavior (Leech et al. 2005, Hansson et al. 2007). Beyond the individual level, UVR effects include changes in species composition and interactions, affecting ultimately the structure of communities, food web processes and ecosystem functions (Searles et al. 1999, Häder et al. 2011). During evolution, aquatic organisms have developed different protective strategies to cope with UVR (especially UV-B). One of these strategies is via chemical defenses such as UV-absorbing compounds (UVAC, mainly mycosporine like amino acids - MAAs ? Adams 2001), which absorb in the UVR range (310 - 360 nm), and therefore are able to screen off or reduce harmful radiation (Adams & Shick 2001, Karsten et al. 2005). Because UVAC can be only synthesized by some primary producers (phytoplankton, macroalgae and some cyanobacteria; Favre-Bonvin et al. 1987), one way in which consumers can acquire them is through the diet (Hylander and Jephson 2010, Nahon et al. 2012). In general macroalgae belonging to the Chlorophyceae Class contain low amount of UVAC, while those belonging to the Rhodophyceae Class contain high amount of these compounds (Karsten et al. 1998, Nahon et al. 2012).Thus for herbivorous, dietary differences may result in varied adaptation / acclimation to the radiation climate, which could affect, ultimately, their survival and offspring. OBJECTIVE: The objective of this study was to evaluate the role of UVAC, provided by macroalgae, on the metabolic response (in terms of respiration) in males and females of the marine amphipod Ampithoe valida Smith (1973) a very abundant species in the South West Atlantic coasts of Argentina which constitutes an important prey in the diet of several commercial fish species of the region (mainly for artisanal fisheries; Gostonyi et al. 1995). MATERIALS AND METHODS: Specimen of green and red macroalgae (Ulva rigida and Porphyra columbina, respectively) and amphipods (Ampithoe valida) were collected during summer 2016 from Playa Bonita located in the Patagonian coast (43° 22´ S - 65° 03´ W, Chubut, Argentina). Organisms were manually separated by sex and then divided into two groups; one group was fed for three days with U. rigida (low UVAC content), and the other with P. columbina (high UVAC content). After the feeding period the content of UVAC in the amphipods were measured using spectrophotometric techniques, to verify that individuals used for the experiments had different amount of UVAC in their bodies, depending on the diet provided. For the experiments, organisms were placed in Teflon bottles (1 amphipod per bottle, n=24), and exposed under a solar simulator (SOL 1200W, Dr Hönle AG, Gräfelfing/Múnchen, Germany). Two radiation conditions were done: (a) PAB treatment: amphipods receiving PAR + UV-A + UV-B (>280 nm, uncovered Teflon bottles), (b) P treatment: samples receiving only PAR (>400 nm, Tefflon bottles covered with Ultraphan UV 395 Opak Digefra film). In addition, a third treatment (c) darkness (Teflon bottles covered with aluminum foil) was used. The bottles were placed at 64 cm from the solar simulator so the samples received irradiances of 1.69, 69.9 and 182.8 W m-2 UVB, UVA and PAR, respectively. The radiation level was chosen based on UVB irradiance commonly measured in the study area at summer noon, when UVB reaches ca. 1.8 Wm-2 at the sea surface (Villafañe et al. 2004). Radiation treatments were performed in quadruplicate, therefore a total of 24 bottles (12 per sex) were used for the experiment. Oxygen concentrations were measured every 30 min during the six-hours radiation exposure period followed by for 4 h in darkness. Oxygen measurements were done using Optode sensor-spots (OXY 10 mini; Presens GmbH, Germany) together with fiber optics and Oxyview 6.02 software. RESULTS AND DISCUSSION: Both males and females of A. valida had differential accumulation of UVAC in their bodies, evidenced by the presence of peaks between 310 to 360 nm. In the case of amphipods fed with P. columbina, a significant peak was detected in the UV region, while a small ?shoulder? was detected in those fed with U. rigida (t-test, P < 0.05). This result agrees with previous ones about the ability of A. valida to accumulate UVAC through the diet (Helbling et al. 2002, Valiñas & Helbling 2015), and allowed us to confirm that individuals used in the experiment significantly accumulated UVAC in their bodies. UVR exposure did not affect the oxygen consumption rates in females of A. valida when fed with U. rigida (one-way ANOVA, P > 0.05). In males, however, asignificant decrease in respiration rates was observed in the PAB treatment, as compared with the P and darkness treatments (one-way ANOVA, P < 0.05). In the case of amphipods fed with P. columbina (both males and females), no effects of UVR on oxygen consumption rates were observed (one-way ANOVA, P > 0.05 for both sexes). This difference in the metabolic response of males against UVR depending on the diet consumed, indicate that UVAC could be counteracting the negative effects of UVR, as has been previously reported for amphipods and other aquatic organisms (Hernández Moresino et al. 2014, Valiñas & Helbling 2015, 2016). CONCLUSIONS: Under a short UVR exposure period and when the diet is poor in UVAC, males of A. valida seem to be more susceptible, while females seem to be more resistant to UVR. This scenario change when the diet is rich in UVAC, which indicate that these compounds could counteract the negative effects of UVR on A. valida males. For organisms that live mainly associated to green macroalgae like U. rigida, which is probably related with the dominance of this species in the mid intertidal zone from Patagonian coast, dietary scarcity of UVAC could constrain this protection against UVR. Males of A. valida would have a critical situation if they can not find a source of UVAC to counteract any negative effects of UVR on their metabolism.