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Combined Ocean Acidification and Heat Shock on a Benthic Copepod

Paper Reviewed
Li, W., Han, G., Dong, Y., Ishimatsu, A., Russell, B.D. and Gao, K. 2015. Combined effects of short-term ocean acidification and heat shock in a benthic copepod Tigriopus japonicus Mori. Marine Biology 162: 1901-1912.

Coastal marine environments generally experience large changes in temperature, pH, and oxygen on daily, seasonal, and interannual timescales. However, there remains much to be learned about how marine organisms in these variable environments will respond to future climate change, including so-called ocean acidification (OA) and rising temperatures. Indeed, the research team of Li et al. (2015) in a recent paper write that "it is crucial to investigate the combined effects of reduced pH and heat shock on growth, reproduction and related physiological performances of intertidal animals," which is exactly what they set out to do for the benthic copepod Tigriopus japonicus Mori. More specifically, working in the laboratory they subjected T. japonicus specimens to a short-term (4 hour) manipulation of temperature (20, 24, 28, 32 or 36 °C) at either normal (390 µatm) or high pCO2 concentration (1000 µatm, pH), after which they measured various physiological, molecular and reproductive responses.

In discussing their findings, Li et al. report "no mortality of T. japonicus was recorded in either [ambient] or high CO2 during heat shock treatments or in the subsequent 3-day post heat shock culture." Respiration rates generally increased with temperature and were significantly higher in only two of the five temperature treatments under elevated CO2 (24 and 28 °C), however, the researchers note there was "no significant interactive effect of elevated CO2 and temperature on respiration." Additionally, they did not find any interactive effect between CO2 and temperature on feeding and filtering rates, expression of heat shock proteins, or on reproductive response. In contrast, heat shock proteins were shown to positively correlate with temperature, which led the six-member research team to conclude that "T. japonicus responds more sensitively to heat shocks rather than to seawater acidification."

Given that T. japonicus is a nearshore inhabitant, regularly subjected to the variable environment of the coastal zone, it should come as no surprise that this marine copepod is further described by the authors as a "tolerant species with strong adaptive ability." Such tolerance, demonstrated by a lack of response to OA and heat shock as shown here, provides us with yet another example that the ultra-negative and widespread projections of future marine life decline due to OA are way overblown.

Posted 2 February 2017