How does rising atmospheric CO2 affect marine organisms?

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Response of Crustaceans to Ocean Warming -- Summary
According to Storch et al. (2009), "temperature is often invoked as the main determinant of distribution ranges and boundaries for marine and terrestrial species," and they note the larval stages of many marine species "are more vulnerable to thermal and osmotic stresses than adults." Consequently, they explored the rigidity of this temperature determinant of livable range for the Chilean kelp crab (Taliepus dentatus) in its most temperature-sensitive larval state. Specifically, working with stage zoea I larvae of two populations of the crab-one from Southern Chile (SC, 43°54'S) and one from Central Chile (CC, 33°29'S)-Storch et al. "measured temperature-dependent activity, oxygen consumption, cardiac performance, body mass and the carbon and nitrogen composition in order to (1) examine thermal effects from organismal to cellular levels, and (2) compare the thermal tolerance of larvae from two environmental temperature regimes."

Among many other things, the six researchers report "the thermal tolerance window of zoea from SC was found to be shifted to lower temperatures when compared with those from CC," which could be equally accurately expressed as "the thermal tolerance window of zoea from CC was found to be shifted to higher temperatures when compared with those from SC." Given such, the Chilean and German scientists conclude "the small but clear shift between thermal tolerance windows between populations suggests an optimization of reaction norms and local adaptation in larvae of T. dentatus," noting "this differentiation allows the species to cover a wider range of distribution than when restricted to one and the same thermal window for all populations," which suggests the larval form of the kelp crab is capable of adapting to both higher or lower temperatures relative to those at which it may have lived for long periods in the past.

Introducing their study, Stoner et al. (2010) write "temperature is a dominant environmental factor that mediates the behavior, physiology, growth, survival, distribution, and recruitment of ectothermic animals living in temperate and high latitudes." Hence, they decided to see how the growth and survival of the red king crab (RKC: Paralithodes camtschaticus) "may be affected by warming trends expected in Alaska," since the RKC was once that state's "most economically valuable crustacean fishery." To do so, the authors reared RKC in "four temperature treatments ranging from 1.5 to 12°C for a period of 60 days, both individually and in low-density populations," during and at the end of which period various physiological processes and properties were measured.

Among their several findings, the three researchers report "temperature had no significant effect on survival of RKC," while noting "there was no consistent difference in survival between individually cultured crabs and those in populations." As for growth, they found it "was very slow at 1.5°C, and increased rapidly with temperature with both a contracted inter-molt period and small increase in growth increment." In addition, they say "20% of the crabs held at 1.5°C never molted, while more than 90% of the crabs in 12°C reached juvenile state 4 or higher." Overall, therefore-as they describe it-"growth increased as an exponential function of temperature, with slightly higher growth rates observed in populations than for isolated individuals." Also of great importance, they say they found "no evidence that culturing RKC juveniles at elevated temperatures led to a decrease in condition or nutritional status."

In addition to the benefits listed above, which bode well indeed for the RKC in a possibly warmer future world, Stoner et al. conclude the "accelerated growth" they observed in the RKC raised at the highest temperature might yet have a "positive, indirect effect on survival," in "larger size associated with high temperature could provide for earlier refuge in size from the typical fish and invertebrate predators on RKC."

Introducing their study, Van den Brink et al. (2012) say "hymenosomatid crabs of the genus Halicarcinus have a reproductive strategy involving a terminal, pubertal moult where reproduction begins only when growth has ceased," which strategy "allows females to maximize their reproductive output during a comparatively short (approximately six month) adult life span by producing broods continuously and successively, without the need for the female to suspend reproduction for moulting," citing Van den Brink and McLay (2009, 2010). Against this backdrop, Van den Brink et al. investigated the effect of temperature on brood development for "three intertidal hymenosomatid crabs: Halicarcinus cookii, H. varius and H. innominatus," which they collected from intertidal habitats around the Kaikoura Peninsula of New Zealand that supported all three species.

Results of the analysis yielded three main findings. First, "if temperatures rise 2°C as predicted, each of the three species could produce one extra brood per female lifetime," which the authors say "would result in the production of over 1000 extra larvae per female resulting in a 10-15% increase in fecundity" that could "result in a single female producing 10-50 extra surviving offspring per lifetime." Second, "an increase in temperature is also likely to increase larval growth rates ... resulting in shorter development times," which "may also increase survival rates to final instars and eventually adults, thus potentially increasing the size of the population." Third, "the current six month peak breeding season in the three Halicarcinus species may increase as temperatures rise," which "may allow the three Halicarcinus crabs more time to carry eggs and therefore produce even more offspring per lifetime." Given such findings, it would appear that a modest warming would prove extremely advantageous to the world's population of hymenosomatid crabs.

According to Kelley et al. (2011), "measuring variation in physiological traits over broad spatial and temporal scales in an effort to investigate the ecological impacts of these traits (Chown et al., 2004)" can "aid in predicting how species or communities will respond to climate change," citing the confirmatory studies of Baker et al. (2004), Harley et al. (2006), Hassol (2004), Helmuth et al. (2002, 2005), Kennedy et al. (2002), Parmesan (2006), Parmesan and Yohe (2003), Portner et al. (2001) and Stillman (2003). Employing this approach in their study of the European green crab (Carcinus maenas), Kelley et al. measured the upper lethal thermal thresholds of two populations of the invasive species living at the southern and northern limits of its current range on the west coast of North America-Sea Drift Lagoon, Stinson Beach California (CA; 37°54'27.82"N) and Pipestem Inlet, Vancouver Island, British Columbia (BC; 49°02.3'N), which are separated from each other by 1200 km of coastline-where "ambient sea surface temperature in the northern part of the North American west coast range is 5 to 10°C lower, depending on the time of year, than near the southern range limit," and where the species expansion from its initial introduction at the south end of its range to its current northern end occurred over a period of only about twenty years.

Based on their analysis, the three U.S. scientists determined the warm-adapted southern CA group of crabs had the highest level of organismal thermotolerance, as well as the greatest degree of heat shock protein 70 (Hsp70) production; and they additionally discovered that carapace widths of both male and female C. maenas individuals from CA were significantly smaller than those found in BC. With respect to these findings, Kelley et al. say they "provide evidence that the northeastern Pacific population of C. maenas has incurred a shift in thermal tolerance compared to its southern counterpart," and "thermal adaptation at the level of the phenotype is a likely cause due to the short timescale of the invasion and the genetic connectivity of the two populations."

Based on these observations, the authors state-and with a good degree of confidence-that over a period of a mere two decades, "it is possible that a large, northern cold-water phenotype may have already arisen," which further suggests the reverse of this phenomenon could also have occurred over the same length of time if the driving force for phenotypic change had arisen due to the crabs migrating from a cooler to a warmer environment, or-by further inference-that it could have occurred during a period of equivalent climatic warming in the same physical setting without any relocation occurring. Whatever the case may be, it is yet another example of a species demonstrating that it has the capacity to do what it needs to do to successfully cope with projected global warming, and without the need to migrate to accomplish it.

Carrying forward the idea of thermotolerance, but working with a different type of crustacean, Ravaux et al. (2012) preface their work by indicating "all organisms possess some capacity to modify their behavioral, physiological or morphological characteristics in response to changes in environmental temperature" via a phenomenon they characterize as thermal acclimation, citing Angilletta (2009), which special case of phenotypic plasticity would obviously be of great significance to all organisms in a warming world. In an attempt to study this phenomenon further, working with Palaemonetes varians, a shallow-water brackish shrimp that is native to Western Europe, Ravaux et al. assessed, via analyses conducted with both cold- and warm-acclimated specimens collected from the Bay of Mont Saint-Michel (France), the plasticity of a common index of thermal tolerance, the critical thermal maximum (CTmax), as well as the plasticity of a widespread and conserved molecular response to stress, known simply as heat shock response (HSR).

Under their experimental conditions the seven scientists determined P. varians "shows genuine acclimation capacities" due to the plasticity inherent in both the organism's thermal limit (CTmax) and its heat shock response (hsp70 induction temperature). Such findings led Ravaux et al. to conclude P. varians "is readily able to expand its thermal range since it can shift its thermal maximum to higher temperatures and also mobilize the HSR over a wide range of temperatures above those experienced in nature." And they thus state the shrimp "is potentially capable of expanding its upper thermal range," which suggests it may not even need to migrate towards cooler regions in a potentially warming world of the future in order to live the type of life to which it has long been accustomed.

The ability to phenotypically adapt has also been reported by Pinceel et al. (2013) for large branchiopod crustaceans. In constructing "a molecular phylogeny based on a data set which includes about 85% of the Branchinella species currently known to science, as well as a number of recently discovered lineages," Pinceel et al. discovered the existence of "substantial physiological plasticity or important adaptive variation present in some species, potentially enabling them to better cope with environmental change."

In a model-based study, Letessier et al. (2011) assessed the influence of a suite of physical, chemical and biological variables on euphausiid species abundance. Euphausiids are small pelagic shrimplike crustaceans of the order Euphausiacea the authors say constitute "an important component of the pelagic realm," where they "graze directly on phytoplankton and provide a food source for a range of predators including birds, seals, baleen whales and many commercially important fish species," citing Verity et al. (2002). To carry out their objective, the authors used a generalized additive model running environmental changes based on the IPCC A1B climate scenario to make predictions of future species abundance changes in the Pacific and Atlantic Oceans, which they sub-divided into cells having east-to-west lengths of 300 km and north-to-south lengths of 200 km.

According to Letessier et al., "the main drivers of species abundance, in order of decreasing importance, were sea surface temperature (SST, explaining 29.53% of species variability), salinity (20.29%), longitude (-15.01%, species abundance decreased from West to East), distance to coast (10.99%) and dissolved silicate concentration (9.03%)." The three UK researchers also say their results suggest "the present broad patterns apparent in species abundance (low in high latitudes, high in intermediate latitudes and intermediate in the tropics) will become less pronounced in a warming ocean," and that, eventually, "species abundance will be enhanced within intermediate-to-high latitudes (30°N to 60°N and 30°S to 60°S) and diminished in the tropics (20°N to 20°S)," which changes are "consistent with changes already observed to be occurring in terrestrial systems in Europe and America," citing Rosenzweig et al. (2008), as well as with "already-observed changes in zooplankton assemblages in the North Atlantic (i.e., communities shifting north)," as reported by Beaugrand et al. (2002), Beaugrand and Ibanez (2004) and Richardson and Schoeman (2004). And considered in their entirety, such shifts in euphausiid species abundance may be viewed as positive developments, especially in light of the three scientists' finding that both the Atlantic and Pacific Oceans "will on average see an increase in species abundance per cell."

In another study, Rombouts et al. (2009) focused their work on marine copepods, which are small crustaceans that are found in the world's oceans and form a key trophic link between phytoplankton and fish. Some of them are planktonic and drift in sea water, but more of them are benthic and live on the ocean floor. For their analysis, Rombouts et al. developed the first global description of geographical variation in the diversity of marine copepods in relation to ten environmental variables.

Results indicated "ocean temperature was the most important explanatory factor among all environmental variables tested, accounting for 54 percent of the variation in diversity." Thus, it was not surprising "diversity peaked at subtropical latitudes in the Northern Hemisphere and showed a plateau in the Southern Hemisphere where diversity remained high from the Equator to the beginning of the temperate regions," which pattern, in their words, "is consistent with latitudinal variations found for some other marine taxa, e.g. foraminifera (Rutherford et al., 1999), tintinnids (Dolan et al., 2006) and fish (Worm et al., 2005; Boyce et al., 2008), and also in the terrestrial environment, e.g. aphids, sawflies and birds (Gaston and Blackburn, 2000)."

"Given the strong positive correlation between diversity and temperature," the six scientists say "local copepod diversity, especially in extra-tropical regions, is likely to increase with climate change as their large-scale distributions respond to climate warming." This state of affairs is much the same as what has typically been found on land for birds, butterflies, and several other terrestrial lifeforms, as their ranges expand and overlap in response to global warming. And with more territory thus available to them, their "foothold" on the planet becomes ever stronger, fortifying them against forces (many of them human-induced) that might otherwise lead to their extinction.

In another study pertaining to copepods, Tremblay et al. (2011) compared time series of ice cover, wind forcing and satellite-based assessments of photosynthetic carbon production in the Canadian Beaufort Shelf for the years 2002-2008 with corresponding in situ measurements of salinity, nutrients, new production, biological stocks and biogenic fluxes obtained during overwintering surveys in 2003-2004 and 2007-2008. In doing so the fifteen researchers report, first of all, that in 2007-2008-in areas where ice was no longer present, due to enhanced seasonal warming-there was significant wind-induced upwelling of growth-promoting nitrates, which were brought up from deep and dark waters into the euphotic zone, where photosynthesis occurs. And as a result of this fertilization effect, the herbivorous copepod Calanus glacialis-which they say is "the key link between diatom production and apex consumers on Arctic shelves," citing Soreide et al. (2010)-experienced a total abundance that was "3 to 33 times higher than in 2003 during mid-fall and 1.6 to 13 fold higher than in 2004 during early summer." Also, on the region's central shelf, they observed "sedimentary chlorophyll a was over 20-fold higher than at any station not influenced by upwelling," and they likewise found "benthic carbon demand was among the highest ever observed in the Arctic ocean," citing Clough et al. (2005). Therefore, it was not surprising that the end result of these related phenomena was that the "repeated instances of ice ablation and upwelling during fall 2007 and summer 2008 multiplied the production of ice algae, phytoplankton, zooplankton and benthos by 2 to 6 fold."

Tremblay et al. conclude the phenomena they observed are "likely to prevail with the increasingly deep and frequent seaward retreat of the central ice pack and the greater incidence of upwelling-favorable winds," as described in detail by Yang (2009); and they state "new production is also bound to rise as winds gain in intensity and upwelling draws deeper into the nutrient-rich, upper Pacific halocline."

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Last updated 11 July 2014