Improper Diving Behavior Affects Physiological Responses of Acropora hyacinthus and Porites cylindrica

Human activities beyond ecosystem capacity have resulted in serious effects on corals worldwide. Nowadays, many studies have focused on the influence of diving activities on coral communities, while the knowledge of physiological changes under corresponding environmental stresses remains largely undetermined. In the study, we aimed to investigate the physiological effects of touching, ammonia nitrogen enrichment (5 μmol⋅L–1), and sediment cover (particle size of less than 0.3 mm), which simulated improper self-contained underwater breathing apparatus (SCUBA) diving behaviors, on Acropora hyacinthus and Porites cylindrica in Wuzhizhou Island, the South China Sea. For A. hyacinthus, continuous touching caused the tentacles to shrink and secrete mucus, which consumed energy and dissolved oxygen. The skeletal growth rate was decreased by 72% compared with the control group. There was a rapid decline of Fv/Fm and alpha under the dual impacts of high ammonia nitrogen and touching, while the Chl a concentration and tissue biomass were decreased by 36 and 28% compared with touching alone, respectively. High ammonia nitrogen and touching increased the concentrations of lipid and protein. Nevertheless, zooxanthellae density was increased by 23% to relieve the effects of a lower concentration of Chl a in a high nutrient environment. Constant touching and sediment cover in diving areas with elevated ammonia content affected the photosynthesis and respiration of corals, and a significant decrease was observed for lipid, zooxanthellae density, and Chl a concentration. Coral bleaching occurred on day 7. For P. cylindrica, the decreasing magnitude of Fv/Fm and alpha under different stresses in the subsequent phase was less compared with A. hyacinthus. The contents of carbohydrate and protein under continuous touching were decreased by 7 and 15% compared with the control group, respectively, causing negative growth. Under the dual influences of high ammonia nitrogen and continuous touching, all energy reserves were significantly lower. Repeated touching and sediment cover in diving areas containing high ammonia content increased the concentrations of lipid and protein compared with the touching and high nutrient treatment group likely because that Porites associated with C15 zooxanthella increased heterotrophic feeding to compensate for restricted symbiodiniaceae photosynthesis. Additionally, P. cylindrica produced mucus to aid the removal of sediment, so that corals didn’t obviously bleach during the experiment. Collectively, P. cylindrica was more resistant to diving activities than A. hyacinthus which only relies on photoautotrophy. To ensure the sustainable development of coral reef dive tourism, it is necessary to strengthen the supervision of diving behaviors, rotate the diving areas, and conduct regular assessments on the coral status.

Reproductive colonization of land by frogs: embryos and larvae excrete urea to avoid ammonia toxicity

Vertebrate colonization of land occurred multiple times, including over 50 origins of terrestrial eggs in frogs. Some environmental factors and phenotypic responses that facilitated these transitions are known, but responses to water constraints and risk of ammonia toxicity during early development are poorly understood. We tested if ammonia accumulation and dehydration risk induce a shift from ammonia to urea excretion during in early stages of four anurans, from three origins of terrestrial development. We quantified ammonia and urea concentrations during early development on land, under well-hydrated and dry conditions. Where we found urea excretion, we tested for a plastic increase under dry conditions and with ammonia accumulation in developmental environments. We assessed the potential adaptive role of urea excretion by comparing ammonia tolerance measured in 96h-LC50 tests with ammonia levels in developmental environments. Ammonia accumulated in foam nests and perivitelline fluid, increasing over development and reaching higher concentrations under dry conditions. All four species showed high ammonia tolerance, compared to fishes and aquatic-breeding frogs. Both nest-dwelling larvae of Leptodactylus fragilis and late embryos of Hyalinobatrachium fleischmanni excreted urea, showing a plastic increase under dry conditions. These two species can develop the longest on land and urea excretion appears adaptive, preventing their exposure to potentially lethal levels of ammonia. Neither late embryos of Agalychnis callidryas nor nest-dwelling larvae of Engystomops pustulosus risked toxic ammonia levels under dry conditions, and neither excreted urea. Our results suggests that an early onset of urea excretion, its increase under dry conditions, and elevated ammonia tolerance, can all help prevent ammonia toxicity during terrestrial development. High ammonia represents a general risk for development that can be exacerbated as climate change increases dehydration risk for terrestrial-breeding frogs. It may also be a cue that elicits adaptive physiological responses during early development.

BIOCHEMICAL RESPONSES AND GENETIC EXPRESSIONS OF SYNTHETIC COMMON CARP POPULATIONS EXPOSED TO HIGH-AMMONIA REARING ENVIRONMENT

Carp is one of the leading freshwater aquaculture commodities in Indonesia. Further improvement of carp strains by the Research Institute for Fish Breeding (RIFB), Sukamandi, Indonesia, has produced a synthetic F2 carp. The strain is assembled from different strains of carps and has shown better growth and health characteristics. Considering that high environmental ammonia (HEA) has affected most carp grow-out systems, this study aimed to determine the performance of the synthetic carp populations in a high ammonia rearing environment. The treatments were rearing media of the synthetic carp seed populations added with and without (control) 200 mg/L NH4Cl arranged in three replicates. A total of 30 fish seeds/aquarium, weighed 10-15 g/fish, was used in the study. Dissolved oxygen levels were maintained above 2 mg/L using aeration. This study shows that higher tolerant carp populations had red blood cells of 232.66 ± 17.24 cells/mL, indicating a direct effect of high ammonia on red blood cell count (p<0.05). Cortisol levels of 80.90 ± 6.35 ng/mL in resistant carp indicate significant differences (p<0.05). The relative expressions of the HSP70 gene in the liver (Log10) ranged between 0.72 and 2.80. The values demonstrate that high ammonia-resistant synthetic carp have a higher relative expression ratio of the HSP70 gene than the less resistant group. This research concluded that the populations of synthetic F2 carp showed a degree of resistance against high-ammonia rearing conditions. When it is ready for aquaculture, this synthetic carp strain could be farmed in high density using intensive systems in HEA-affected artificial lakes and reservoir