Physiology of juvenile hydroids - High food availability mitigates stress responses of Hydractinia echinata to increasing seawater temperatures

Diminished growth and vitality in juvenile Hydractinia echinata under anticipated future temperature and variable nutrient conditions

“…Temperature stress reduced the growth rates (area and polyp count) of H. echinata moderately in scenario 1 and significantly in scenario 2 (Fig. 1 ), while a previous study showed that metabolic rates increase 31 . Rising environmental temperatures generally accelerate biochemical and metabolic reactions in marine ectotherms 32 , 33 , which can be accompanied by increasing rates of cell damage and reduced growth performance (e.g., in clams, lobsters, and sea cucumbers 34 – 36 ).…”

“…Rising environmental temperatures generally accelerate biochemical and metabolic reactions in marine ectotherms 32 , 33 , which can be accompanied by increasing rates of cell damage and reduced growth performance (e.g., in clams, lobsters, and sea cucumbers 34 – 36 ). Eder et al 31 found higher cell damage accumulation in juvenile H. echinata exposed to 21 °C / low food , indicated by higher protein carbonyl contents and most likely induced by increasing production rates of reactive oxygen species. Therefore, in hydroids of scenario 2, with the additional daily temperature step above 21 °C, cell damage most likely occurred at a greater rate, inducing anomalously low growth rates compared to scenario 1.…”

“…Juvenile hydroids were cultured as described in the Helgoland Manual of Animal Development 27 Eder et al 31 . Overall, 10 male and 10 female adult H. echinate colonies were placed together into one big holding tank to release eggs and sperm for fertilization.…”

“…The fertilized eggs then transformed into larvae. The transformation of the larvae was induced by caesium chloride 49 following the protocol of as described by Eder et al 31 , which randomly settled onto black glass tiles (dimensions 10 mm × 10 mm × 2 mm, Mosaikstein, Germany), at least 2–3 larvae on each tile. The colonized glass tiles were then randomly dispersed into the different treatment tanks.…”

“…To evaluate the influence of food availability on the growth potential in hydroids as a response to increasing SST, colonies were fed with two-day-old living A. salina nauplii (> 1000 nauplii/ml per tank per feeding event) following either a high food (HF) or a low food (LF) scheme (Fig. 7 ) according to Eder et al 31 . Colonies with HF were fed five times a week and with LF three times a week.…”