Physiology & physiological ecology
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Research study 1
 

Olympia oysters Ostrea conchaphila inhabit low intertidal to shallow subtidal regions along the west coast, and may be subject as adults to high temperatures during extreme low tides in summer.  Does exposure to high temperature induce a heat-shock response1 involving expression of protective “molecular-chaperone” proteins?  This aspect of O. lurida’s physiology is investigated by researchers at the Bodega Marine Laboratory, California along with the possibility that such heat-induced responses may also be present in early developmental2 stages.  Results show that expression of several Hsp proteins occurs in both adult and larval tissues (Hsp77, Hsp72, and Hsp69).  Expression in adults occurs at temperatures 33oC and above.  More importantly, expression of Hsp69 after a heat shock3 of 34oC leads to tolerance of otherwise lethal temperatures of 38-39oC.  As for the developmental stages, there is no heat-shock response in cleaving embryo or blastula stages, but Hsp69 is expressed in the veliger stage after exposure to a heat shock of 34oC.  Interestingly, the increased levels of Hsp69 in the larva persist for only a few hours, rather than for up to 3wk as in adults.  photograph of oysters Crassostrea gigas and Ostrea conchaphilaBrown et al. 2004 J Shellf Res 23 (1): 135.

NOTE1  expression of Hsp’s (heat-shock proteins) occurs in many intertidal invertebrates, including abalones, limpets, mussels, sea anemones, and others.  There are several types, categorized by their molecular masses

NOTE2  the authors note that Olympia oysters incubate their ealy life stages in the mantle cavity;  thus, these stages experience the same environmental conditions as do the brooding adults.  Later on, the veligers are released into the plankton 

NOTE3  this consists of 1h exposure to a given temperature, then a  return to ambient seawater

Japanese or Pacific oyster Crassostrea gigas
and Olympia oysters Ostrea conchaphila 0.6X

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Research study 2
 

photographs of veliger larvae and a 12d juvenile of the Olympia oyster Ostrea conchaphilagraphs showing effects of pH on growth of larval and juvenile Olympia oysters Ostrea conchaphilaOlympia oysters Ostrea conchaphila possess a free-swimming larval stage and therefore must contend with two different sets of environmental stresses, one during the pelagic phase; the other, during the benthic, post-metamorphic stage.  The question raised by a group of University of California scientists1 is the extent to which the effects of environmental stresses can “carry over” from one developmental stage to another.  The stress-factor considered by the researchers is increasing seawater acidity, of  current interest in view of increasing carbon-dioxide dissolution in the world’s oceans and resulting acidification as a component of climate change2.  The researchers rear larvae in seawater at 3 pH levels3, 8.0 (control, equivalent to oceanic seawater), 7.9, and 7.8, and compare growth rates before and after metamorphosis.  Results show that larval growth at 9d is significantly slower in the most acidic condition of 7.8, as compared with control seawater, and this effect carries over to about 40% reduction in growth of 7d juveniles regardless of the pH they are experiencing as juveniles (the researchers do reciprocal translocations from high to low, and low to high, pHs).  These adverse effects persist for 1.5mo in juveniles transferred to a common pH environment.  In showing these carry-over effects4 the researchers point to the need to  attend to all phases of an organism’s existence rather than focussing in such studies on what might be perceived as a critical “weak link”.   Hettinger et al. 2012 Ecology 93 (12): 2758.

NOTE1   joined by colleagues from Kalamazoo College, Michigan and University of North Carolina

NOTE2  although the following comment does in no way detract from the value of their work,  as the authors do present their study in the context of climate change, they must be aware  that their treatment protocol is acute, not chronic.  Change in ocean acidity will occur slowly, over many generations, and one might expect to see at least some degree of physiological adaptation to the progressively changing conditions

NOTE3  created by increasing seawater carbon-dioxide levels from 700ppm (control = pH 8.0) to 800ppm and 1100ppm by bubbling CO2 gas in 20liter carboys

NOTE4  another comparatively well-studied environmental parameter with carry-over effects is nutrition

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