Threatened Caribbean coral is able to mitigate the adverse effects of ocean acidification on calcification by increasing feeding rate

Global climate change threatens coral growth and reef ecosystem health via ocean warming and ocean acidification (OA). Whereas the negative impacts of these stressors are increasingly well-documented, studies identifying pathways to resilience are still poorly understood. Heterotrophy has been shown to help corals experiencing decreases in growth due to either thermal or OA stress; however, the mechanism by which it mitigates these decreases remains unclear. This study tested the ability of coral heterotrophy to mitigate reductions in growth due to climate change stress in the critically endangered Caribbean coral Acropora cervicornis via changes in feeding rate and lipid content. Corals were either fed or unfed and exposed to elevated temperature (30°C), enriched pCO2 (800 ppm), or both (30°C/800 ppm) as compared to a control (26°C/390 ppm) for 8 weeks. Feeding rate and lipid content both increased in corals experiencing OA vs. present-day conditions, and were significantly correlated. Fed corals were able to maintain ambient growth rates at both elevated temperature and elevated CO2, while unfed corals experienced significant decreases in growth with respect to fed conspecifics. Our results show for the first time that a threatened coral species can buffer OA-reduced calcification by increasing feeding rates and lipid content.

Juvenile sea stars exposed to acidification decrease feeding and growth with no acclimation potential

Ocean acidification has the potential to affect growth and calcification of benthic marine invertebrates, particularly during their early life history. We exposed field-collected juveniles of Asterias rubens from Kiel Fjord (western Baltic Sea) to 3 seawater CO2 partial pressure (pCO2) levels (ranging from around 650 to 3500 µatm) in a long-term (39 wk) and a short-term (6 wk) experiment. In both experiments, survival and calcification were not affected by elevated pCO2. However, feeding rates decreased strongly with increasing pCO2, while aerobic metabolism and NH4+ excretion were not significantly affected by CO2 exposure. Consequently, high pCO2 reduced the scope for growth in A. rubens. Growth rates decreased substantially with increasing pCO2 and were reduced even at pCO2 levels occurring in the habitat today (e.g. during upwelling events). Sea stars were not able to acclimate to higher pCO2, and growth performance did not recover during the long-term experiment. Therefore, the top-down control exerted by this keystone species may be diminished during periods of high environmental pCO2 that already occur occasionally and will be even higher in the future. However, some individuals were able to grow at high rates even at high pCO2, indicating potential for rapid adaption. The selection of adapted specimens of A. rubens in this seasonally acidified habitat may lead to higher CO2 tolerance in adult sea stars of this population compared to the juvenile stage. Future studies need to address the synergistic effects of multiple stressors such as acidification, warming and reduced salinity, which will simultaneously impact the performance of sea stars in this habitat.

Effects of feeding strategy, fiber source of the diet, and crude protein content on productive performance of broiler breeder hens

A 12-wk experiment was conducted to investigate the effect of feeding program, dietary fiber, and CP content of the diet on productive performance of Ross broiler breeder hens (41 wk of age). There were 12 treatments arranged factorially with 2 levels of CP (14.5 vs. 17.4%), 3 fiber sources (0 vs. 3% inulin vs. 3% cellulose), and 2 levels of feed intake (160 vs. 208 g/d) that corresponded to restricted (R) or ad libitum (AL) feeding systems. The experimental diets contained 2,800 kcal ME with either 0.65 (14.5% CP) or 0.78% Lys (17.4% CP).

Aquaponics: integrating fish feeding rates and ion waste production for strawberry hydroponics

Aquaponics is the science of integrating intensive fish aquaculture with plant production in recirculating water systems. Although ion waste production by fish cannot satisfy all plant requirements, less is known about the relationship between total feed provided for fish and the production of milliequivalents (mEq) of different macronutrients for plants, especially for nutrient flow hydroponics used for strawberry production in Spain. That knowledge is essential to consider the amount of macronutrients available in aquaculture systems so that farmers can estimate how much nutrient needs to be supplemented in the waste water from fish, to produce viable plant growth. In the present experiment, tilapia (Oreochromis niloticus L.) were grown in a small-scale recirculating system at two different densities while growth and feed consumption were noted every week for five weeks. At the same time points, water samples were taken to measure pH, EC25, HCO3 – , Cl – , NH4 + , NO2 – , NO3 – , H2PO4 – , SO4 2– , Na + , K+ , Ca 2+ and Mg 2+ build up. The total increase in mEq of each ion per kg of feed provided to the fish was highest for NO3 - , followed, in decreasing order, by Ca 2+ , H2PO4 – , K+ , Mg 2+ and SO4 2– . The total amount of feed required per mEq ranged from 1.61- 13.1 kg for the four most abundant ions (NO3 – , Ca 2+ , H2PO4 – and K+ ) at a density of 2 kg fish m–3 , suggesting that it would be rather easy to maintain small populations of fish to reduce the cost of hydroponic solution supplementation for strawberries.