Date Published: June 13, 2019
Publisher: Public Library of Science
Author(s): Emily Slesinger, Alyssa Andres, Rachael Young, Brad Seibel, Vincent Saba, Beth Phelan, John Rosendale, Daniel Wieczorek, Grace Saba, Hans G. Dam.
Over the last decade, ocean temperature on the U.S. Northeast Continental Shelf (U.S. NES) has warmed faster than the global average and is associated with observed distribution changes of the northern stock of black sea bass (Centropristis striata). Mechanistic models based on physiological responses to environmental conditions can improve future habitat suitability projections. We measured maximum, standard metabolic rate, and hypoxia tolerance (Scrit) of the northern adult black sea bass stock to assess performance across the known temperature range of the species. Two methods, chase and swim-flume, were employed to obtain maximum metabolic rate to examine whether the methods varied, and if so, the impact on absolute aerobic scope. A subset of individuals was held at 30°C for one month (30chronic°C) prior to experiments to test acclimation potential. Absolute aerobic scope (maximum–standard metabolic rate) reached a maximum of 367.21 mgO2 kg-1 hr-1 at 24.4°C while Scrit continued to increase in proportion to standard metabolic rate up to 30°C. The 30chronic°C group exhibited a significantly lower maximum metabolic rate and absolute aerobic scope in relation to the short-term acclimated group, but standard metabolic rate or Scrit were not affected. This suggests a decline in performance of oxygen demand processes (e.g. muscle contraction) beyond 24°C despite maintenance of oxygen supply. The Metabolic Index, calculated from Scrit as an estimate of potential aerobic scope, closely matched the measured factorial aerobic scope (maximum / standard metabolic rate) and declined with increasing temperature to a minimum below 3. This may represent a critical threshold value for the species. With temperatures on the U.S. NES projected to increase above 24°C in the next 80-years in the southern portion of the northern stock’s range, it is likely black sea bass range will continue to shift poleward as the ocean continues to warm.
Marine environments are progressively warming as a consequence of climate change . Along the U.S. Northeast Shelf (U.S. NES), annual ocean temperature is rising faster than the global average [2,3] resulting in rapid temperature increases [4,5] with a strong warming signal prominent during spring, summer and fall . Over the next 80-years, sea surface and bottom temperatures on the U.S. NES are projected to rise an additional 4.1°C and 5.0°C, respectively [6,7]. Contemporary ocean warming on the U.S. NES has been associated with distribution shifts of many economically and ecologically important fish species both in latitude and/or depth [7–11], associated with tracking local climate velocities . Understanding and projecting shifts in fish distribution will be important for characterizing potential ecological and economic impacts and anticipating and resolving fishery management conflicts .
The primary objective of this study was to measure aerobic scope and hypoxia tolerance at a range of ecologically relevant temperatures to assess the potential physiological impacts of ocean warming on and to determine metabolically available habitat for the northern stock of black sea bass. We measured the oxygen consumption rate, a proxy for metabolic rate, following two different exercise protocols. The swim-flume yielded much higher metabolic rates, indicating that the chase method did not elicit MMR. Using the swim-flume MMR, we found that AAS peaked at 24.4°C. Scrit increased with increasing temperatures as is typical of most (but not all, ) animals, including fishes . The observation that Scrit increased with temperature in proportion to SMR, while MMR in the swim-flume did not, suggests that exposure to high temperature did not alter the capacity for oxygen uptake and transport. Chronic exposure to 30°C resulted no change in SMR or Scrit but a significant drop in AAS resultant of reductions in MMR (using both methods) implying no loss of oxygen supply capacity as estimated from Scrit. Instead, this suggests a decrement in muscle function limiting maximum performance with longer exposure to warm temperatures that is not limited by oxygen supply capacity.