[L&O Featured Article] L&O Featured Article, Vol. 51 (2) March 2007

[L&O Feature Articles Announcements]

The Featured Article in the March 2007 issue of L&O is:

Rose, Julie M., and David A. Caron. 2007. Does low temperature constrain the growth rates of heterotrophic protists? Evidence and implications for algal blooms in cold waters. Limnol. Oceanogr. 52(2): 886-895.

The article is freely available at:

http://aslo.org/lo/toc/vol_52/issue_2/0886.pdf
 

Introductory comments by Peter Jumars (L&O Associate Editor)

That temperature has effects on marine productivity of both phytoplankton (Eppley 1972) and marine heterotrophic bacteria (Pomeroy and Wiebe 2001) is well established.  Underlying mechanisms are less so.  Some of the effect is surely physiological (Li et al. 1984; Nedwell 1999), some may operate through effects of temperature on diffusion coefficients of substrates (Jumars et al. 1993), and Pomeroy and Wiebe (2001) present a complementary, ecosystem-level explanation for slowed bacterial production as a consequence of reduced substrate supply rates from reduced grazing at low temperatures.

The featured review article by Rose and Caron in this issue provides a large and important new piece of the slowly assembling puzzle of marine ecosystem-level effects of temperature.  Because maxima are notoriously sample-size dependent (e.g., the 100-yr flood), Rose and Caron for their analysis of heterotrophic protists instead choose a less sensitive statistical approach of binning by temperature and regressing through the upper five percent of observations.  Although it must yield a lower intercept than does a smooth curve through individual points that represent temperature-binned maxima observed with a similar sample size, this approach is less sensitive to outliers and therefore more robust in estimating the slope of the underlying relationship. 

A major point made by this new meta-analysis is that — among protists — intrinsic growth rates in this upper five percent decline more rapidly with temperature among the herbivorous protists than among the photoautotrophs, whether the latter are characterized by the “Eppley (1972) curve” or by Brush et al.’s (2002) updated meta-analysis.  Herbivorous and bacterivorous protists show similar slopes, but the former display lower intrinsic growth rates at all temperatures.  Copepods also show similar slopes, but an intercept that is lower still.  Moreover, no statistically significant component of the differences among protist trophic groups is due to cell size, which might well be expected to be a confounding factor because protist cell size varies inversely with growth temperature (Atkinson et al. 2003).

This paper will be the basis of many new hypotheses and proposals concerning the roles of temperature today and in a warmer world.  It feeds Pomeroy and Wiebe’s (2001) hypothesis that heterotrophic bacteria at low temperature may be limited by reduced herbivory.  Physical factors through thermal dependence of the diffusion coefficient and of viscosity acting on hydrosol filtration rates (e.g.: Podolsky et al. 1994; Hagiwara et al. 1998) also remain candidates for part of the effect.  How much of the effects operate through feedbacks from food-web and other marine ecosystem connections, and how far do these differential temperature effects on protists of differing trophic groups propagate in the ecosystem?

Atkinson, D., B. J. Ciotti and D. J. S. Montagnes. 2003. Protists decrease in size linearly with temperature: ca. 2.5% ˚C-1. Proc. R. Soc. Lond. B 270: 2605–2611.

Brush, M. J., J. W. Brawley, S. W. Nixon, and J. N. Kremer. 2002. Modeling phytoplankton production: problems with the Eppley curve and an empirical alternative. Mar. Ecol. Prog. Ser. 238: 31–45.

Eppley, R. W. 1972. Temperature and phytoplankton growth in the sea. Fish. Bull. 70: 1063-1085.

Hagiwara, A., N. Yamamiya, and A. B. de Araujo. 1998. Effect of water viscosity on the population growth of the rotifer Brachionus plicatilis Müller. Hydrobiologia 387/388: 489–494.

Jumars, P.A., J. W. Deming, P. S. Hill, L. Karp-Boss, P. L. Yager, and W. B. Dade. 1993. Physical constraints on marine osmotrophy in an optimal foraging context. Mar. Microbial Food Webs 7: 121-159.

Li, W. K. W., J. C. Smith, and T. Platt. 1984. Temperature response of photosynthetic capacity and carboxylase activity in Arctic marine phytoplankton. Mar. Ecol. Progr. Ser. 17: 237-243.

Nedwell, D. B. 1999. Effect of low temperature on microbial growth: lowered affinity for substrates limits growth at low temperature. FEMS Microbiol. Ecol. 30: 101-111.

Podolsky, R. D. 1994. Temperature and water viscosity: Physiological vs mechanical effects on suspension feeding. Science 265: 100-103.

Pomeroy, L. R., and W. J. Wiebe. 2001. Temperature and substrates as interactive limiting factors for marine heterotrophic bacteria. Aquatic Microbial Ecol. 23: 187–204.