The effect of a 24-hour photoperiod on the survival, growth and swim bladder inflation of pre-flexion yellowfin tuna (Thunnus albacares) larvae

The effects of two different continuous photoperiod regimes on survival, growth and swim bladder inflation of pre-flexion yellowfin tuna (Thunnus albacares) larvae were investigated. Each photoperiod regime was tested twice with a different larval cohort to confirm the observed results. Trials 1 and 2 tested the effect of a reduced night-time light intensity (10-molesm-2s-1=30% of the daytime intensity) and found that those larvae reared for 8days under the 24h lighting (24-L) photoperiod exhibited a slight improvement in survival compared to those reared under the control photoperiod of 12h light (12-L), however these improvements were not significant. In addition, those larvae reared under this photoperiod regime were equal in length to those in the control. Trials 3 and 4 compared the same variables in larvae reared under a continuous photoperiod (24-L) with a constant light intensity of 30-molesm-2s-1, against those reared under the aforementioned 12-L photoperiod. Survival of larvae under the continuous photoperiods were 9±1% (n=2) and 10±2% (n=3) for Trials 3 and 4, respectively, compared to less than 1% in both control treatments; differences that in both cases were highly significant. In addition, in both trials larvae cultured under the 24-L photoperiod were significantly larger and exhibited more advanced development than those reared under the 12-L photoperiod, however swim bladder inflation was significantly lower. We suggest that the improved survival and growth achieved under a continuous photoperiod is due to the extended foraging time combined with the prevention of mortality caused by night-time sinking

Carbon and nutrient sequestration in small impoundments: a regional study with global implications

The rate of sequestration of carbon, nitrogen and phosphorus by lentic ecosystems informs both the global carbon budget and the remediation of eutrophication. Here we estimate carbon, nitrogen and phosphorus burial in sediments of 34 lakes in Missouri, USA, and compare them to those found in other agricultural areas as well as to global estimates. Mean sediment accumulation rates varied by orders of magnitude among study regions, with the largest values (average 6 cm y-1) in impounded systems surrounded by intensive agriculture. Rates increased with the drainage ratio and decreased with the abundance of other surface water in the catchment (e.g., farm ponds). Average organic carbon burial differed by an order of magnitude among study regions (average 150-2100 g m-2 y-1) with differences related to the drainage ratio and eutrophication. Organic carbon burial was strongly correlated with burial rates of nitrogen and phosphorus. Comparisons with a diversity of global data show that many Midwestern USA impoundments have extremely high rates of biogeochemical burial likely due to the details of agricultural cropping systems, landscape configuration, and soil characteristics.</p