Percorrer por autor "Kunzmann, Andreas"
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- Metabolic responses and resilience to environmental challenges in the sedentary batrachoid halobatrachus didactylusPublication . Molina, Juan M.; Kunzmann, Andreas; Reis, João; Guerreiro, Pedro MiguelThe Lusitanian toadfish, Halobatrachus didactylus is a marine teleost found in coastal lagoons and river estuaries, often exposed to important changes in salinity, temperature and reduced oxygen. Sedentary species, with strong site fidelity and low migratory ability along the temperature gradient such as this may be especially impacted by climate change. We aimed at establishing the tolerance limits to acute temperature and oxygen changes, and evaluate respiratory and metabolic responses in chronic control, warm and hypoxic (35% O2 ) conditions. Critical temperature maximum (CTmax) was determined in 12 individuals exposed to a temperature ramp of 3 ◦C per hour starting at 18 ◦C, and was found to be 34.8 ± 0.66 ◦C. Critical oxygen level (PO2crit) was determined in 8 fish at 18 ◦C while performing intermittent respirometry and oxygen depletion was created by nitrogen injection in the tank. PO2crit was calculated as the inflexion point between oxyregulation and oxyconformation, which was found to be around 1.2 mgO2/L, but fish survived down to 3% O2 , recovering from 0.2 mgO2/L but showing increased hematocrit (Hct), red blood cell (RBC) counts and blood pH. We also quantified routine aerobic scope and daily activity patterns, finding this fish to be extremely sedentary. H. didactylus showed one of the lowest daytime basal metabolic rates (MR) found in the literature but activity increased significantly at night (over two-fold when closed inside the metabolic chambers). The effect of temperature on metabolic rate (MR) was evaluated using a temperature ramp ranging from 8 to 32 ◦C (1 ◦C/h). Acute temperature changes resulted in a steady increase in MR up to circa 29 ◦C, beyond which MR become increasingly variable, especially among smaller individuals. Indeed, small fish appear to show high- and low-MR groups, and were more susceptible to heat and hypoxia than larger individuals. In chronic acclimation, the MR was increased by 3- and 4-fold (hypoxia vs. normoxia) in fish at 28 ◦C in relation to those at 12 ◦C. Standard MR were not statistically different between normoxia and hypoxia at 12 ◦C, but maximum MR in hypoxia was only about 2/3 of that in normoxia. Fish in high temperature lost weight (mean −3.1%) and had higher metabolism, while in low temperature, weight increased (mean +9.3%) and metabolism was low, and HIS was significantly lower in high temperature groups. Fish in hypoxic conditions showed consistently high Hct but not RBC or hemoglobin (Hb). Overall this study indicates that H. didactylus is highly tolerant to hypoxia and temperature variations. It remains to be seen if other populations along the Atlantic coast show similar metrics. The measured CTmax is close to the actual maximum temperature possible to experience in Ria Formosa ponds during summer, and it would not be unexpected to find this species establishing stable populations in other regions if climate change forces it out of its actual distribution.
- Metabolic responses and resilience to environmental challenges in the sedentary Batrachoid Halobatrachus didactylus (Bloch & Schneider, 1801)Publication . Molina, Juan; Kunzmann, Andreas; Reis, João Pena; Guerreiro, Pedro MIn the context of climate change, warming of the seas and expansion of hypoxic zones are challenges that most species of fish are, or will be subjected to. Understanding how different species cope with these changes in their environment at the individual level can shed light on how populations and ecosystems will be affected. We provide first-time estimates on the metabolic rates, thermal, and oxygen-related limits for Halobatrachus didactylus, a coastal sedentary fish that lives in intertidal environments of the Northeast Atlantic. Using respirometry in different experimental designs, we found that this species is highly resistant to acute thermal stress (CTmax: 34.82 ± 0.66 °C) and acute hypoxia (Pcrit: 0.59–1.97 mg O2 L−1). We found size-specific differences in this stress response, with smaller individuals being more sensitive. We also quantified its aerobic scope and daily activity patterns, finding this fish to be extremely sedentary, with one of the lowest standard metabolic rates found in temperate fish (SMR: 14.96 mg O2 kg−1h−1). H. didactylus activity increases at night, when its metabolic rate increases drastically (RMR: 36.01 mg O2 kg−1h−1). The maximum metabolic rate of H. didactylus was estimated to be 67.31 mg O2 kg−1h−1, producing an aerobic scope of 52.35 mg O2 kg−1h−1 (77.8% increase). The metrics obtained in this study prove that H. didactylus is remarkably resilient to acute environmental variations in temperature and oxygen content, which might enable it to adapt to the extreme abiotic conditions forecasted for the world’s oceans in the near future.
- Mono-trophic seaweed polyculture of sea grapes (Caulerpa lentillifera) and Kappaphycus alvarezii: a case study from Van Phong Bay, Viet NamPublication . Stuthmann, Lara Elisabeth; Costa, Beatrice Brix da; Cordes, Aaron Johannes; Du, Hoang Trung; Kunzmann, Andreas; Springer, KarinKappaphycus alvarezii and Caulerpa lentillifera are economical important seaweeds cultivated in Van Phong Bay, Viet Nam, respectively. The complementary light and nitrogen requirements of the seaweeds introduce the opportunity for a mono-trophic seaweed polyculture. Three different set-ups were tested, namely the integration of K. alvarezii in sea grape ponds, the integration of sea grape plastic cages on longlines and the polyculture of both species in net cages. The relative growth rates (RGRs) of K. alvarezii were highest on longlines, compared to net cages in mono- and polyculture (4.4 ± 0.8 % day− 1 vs 2.1 ± 0.6, 0.6 ± 0.5 % day− 1 ), whereas fragments died off due to warm temperatures and absence of water movement in ponds. Strong recurring water movements at the experimental site caused high losses of K. alvarezii fragments (39 % of initial) and impaired growth of delicate C. lentillifera causing negative RGRs in all treatments (plastic cages without gauze: − 9.8 ± 0.6 % day− 1 , net cages: − 6.4 ± 0.9 % day− 1 ), but with least loss in plastic cages with gauze wrapping (-1.3 ± 0.8 % day− 1 ). Fv´/ Fm´values of both species showed typical midday depression and C. lentilliferas´Fv/Fm were influenced especially by gauze wrapping. Here, we show that the K. alvarezii cultivation on longlines with C. lentillifera integrated below in inexpensive, self-made, customizable plastic cages with additional gauze protection is the most promising set-up from a physiological and economic point of view for Van Phong Bay and beyond. However, further research is needed before implementation of the system.
- Safe applications of ozone in tropical marine RAS: determining impacts of elevated total residual oxidants (TRO) on Stylophora pistillata and Xenia sp. holobiontsPublication . Weidlich, Sabine; Keuter, Sabine; Aires, Tania; Engelen, Aschwin; Kunzmann, AndreasOzone-aided treatment of seawater creates secondary oxidants, which can be toxic for aquaculture animals. We aimed to define safe limits of ozonation-derived total residual oxidants (TRO) for Stylophora pistillata and Xenia sp. by conducting a 96 h acute toxicity experiment. In a chronic exposure experiment we then determined the impacts of three sub-lethal levels of TRO on animal health over four weeks by monitoring respiration, net photosynthesis, photosynthetic efficiency, and three oxidative stress biomarkers (CAT, SOD, LPO). We further documented the changes in coral surface microbiomes exposed to elevated TRO with 16S rRNA amplicon gene sequence analysis. We showed that Xenia sp. is more susceptible to elevated TRO, with first mortalities occurring within 24 h at 0.188 mg L-1 and higher. In Stylophora, mortalities were observable within 24 h at 1.272 mg L− 1 and after 72 h at 0.353 mg L− 1 TRO. Sub-lethal TRO levels caused higher respiration and lower photosynthetic efficiency in Xenia, and increased catalase activity by 29–42 % in Stylophora and by 38–45 % in Xenia, while not impacting lipid peroxidation or superoxide dismutase activity. Microbiomes displayed TRO-induced changes in both species, with a decline in Saprospiraceae as a potential indicator for ozone-inflicted mucus layer degradation. Vibrionaceae fully disappeared from Stylophora pistillata microbiomes after 26 days of exposure to 0.131 mg L-1 TRO, suggesting ozonation as a potential tool to treat pathogens in coral aquaculture. Our study represents the first analysis of ozonation-induced impacts on coral holobionts, thereby providing a guideline for the safe application of ozone in coral cultivation.