RESUMO
Biological production and outgassing of greenhouse gasses (GHG) in Eastern Boundary Upwelling Systems (EBUS) are vital for fishing productivity and climate regulation. This study examines temporal variability of biogeochemical and oceanographic variables, focusing on dissolved oxygen (DO), nitrate, nitrogen deficit (N deficit), nitrous oxide (N2O) and air-sea N2O flux. This analysis is based on monthly observations from 2000 to 2023 in a region of intense seasonal coastal upwelling off central Chile (36°S). Strong correlations are estimated among N2O concentrations and N deficit in the 30-80 m layer, and N2O air-sea fluxes with the proportion of hypoxic water (4 < DO < 89 µmol L-1) in the water column, suggesting that N2O accumulation and its exchange are mainly associated with partial denitrification. Furthermore, we observe interannual variability in concentrations and inventories in the water column of DO, nitrate, N deficit, as well as air-sea N2O fluxes in both downwelling and upwelling seasons. These variabilities are not associated with El Niño-Southern Oscillation (ENSO) indices but are related to interannual differences in upwelling intensity. The time series reveals significant nitrate removal and N2O accumulation in both mid and bottom layers, occurring at rates of 1.5 µmol L-1 and 2.9 nmol L-1 per decade, respectively. Particularly significant is the increase over the past two decades of air-sea N2O fluxes at a rate of 2.9 µmol m-2 d-1 per decade. These observations suggest that changes in the EBUS, such as intensification of upwelling and the prevalence of hypoxic waters may have implications for N2O emissions and fixed nitrogen loss, potentially influencing coastal productivity and climate.
RESUMO
Embryonic development and larval morphology of Chromis crusma was described from five nests sampled between 21 and 25 m depth in central Chile (33°S). From each nest, a set of c. 100 randomly selected eggs were hand-collected and transported in seawater to the laboratory. Subsets of c. 30 eggs per nest were maintained in 50 ml glass containers at a constant ambient temperature of c. 12°C (range 11.5-12.9°C). Egg length (L) and width (W) and larval notochordal length (LN ) were measured from photographs. Geometric morphometric analyses were performed in newly hatched and 1 week old larvae to quantify shape changes. Ellipsoid eggs had an average (mean ± SE) size of 1.12 ± 0.05 mm L and 0.67 ± 0.02 mm W, with volume being similar throughout 15 developmental stages (i.e., ellipsoid-shaped; 0.27 mm3 ). Planktonic larvae hatched between 5 and 11 days at 12°C and had a mean LN of 3.13 ± 0.25 mm, a yolk sack volume of 0.03 mm3 and an oil droplet volume of 0.005 mm3 . Morphological traits at hatching included: (a) lack of paired fins and jaws; (b) single medial fin fold; (c) lack of eye pigmentation; (d) yolk sac present near anterior tip; (e) melanophores distributed along ventral surface with one pair over the forehead. In order to generate an up-to-date summary of developmental traits within Pomacentridae, we reviewed literature on egg development (e.g., shape and number of oil droplets), hatching and larval traits (e.g., morphology, pigmentation patterns). Thirty-two publications accounting for 35 species were selected, where eggs, embryonic development, hatching and larval traits were found for 26, 21, 24 and 34 species, respectively. In order to evaluate potential phylogenetic and environmental relationships within the early stages of Pomacentridae, cluster analyses (Bray Curtis similarity, group average) were also performed on egg and larval traits of 22 species divided by subfamily (Stegastinae, Chrominae, Abudefdufinae, Pomacentrinae) and thermal ranges (i.e., low: 16.5°C (range: 12-21°C), medium: 24.5°C (range:21-28°C) and high: 27°C (range: 26-28°C)), suggesting that early developmental patterns can be segregated by both temperature and phylogenetic relationships.
