Climate Change and Marine Communities 5: Population-level effects of ocean warming

This is the fifth installment of my serialization of a new book chapter on  “Climate Change and Marine Communities” written with Chris Harley and Mike Burrows. It is for a new book “Marine Community Ecology and Conservation” that I’m co-editing with Mark Bertness, Brian Silliman, and Jay Stachowicz.  The book is more or less a followup to the best-selling 2001 edition (which is out of print and worth $100 used and $500 new at Amazon!).  We asked our authors to tell us what has happened over the last 10 years in their assigned subfield.  The chapters are amazing.  And I am truly blown away by how much we’ve discovered since the publication of the first edition!  Many fields have been revolutionized and many-a-paradigm has been overturned.  Cool stuff.  

Population-level effects of ocean warming

Temperature also has less-intuitive yet generally predictable effects on several population-level processes (Kordas et al. 2011).  For example, population growth rate often follows the same unimodal response to temperature as enzyme activity and individual growth (Fig. 6).  By altering individual fitness, reproductive output, and generation time, temperature can potentially play a role in how quickly a population may recover from a disturbance and the rate at which a population can adapt to a changing environment.

Temperature also plays an important role in dispersal dynamics. As with processes at other life history stages, the underlying temperature-dependence of enzyme activity strongly influences the developmental rate of marine invertebrate larvae (O’Connor et al. 2007).  This in turn largely determines Pelagic Larval Duration (known as “PLD”)(Palumbi and Pinsky chapter), which influences larval dispersal distance (all else being equal), survival, and even population connectivity (Shanks 2009).  Thus, in warmer water, marine larvae tend to develop more quickly, experience a reduced PLD, and have much shorter dispersal than congeners in colder water (O’Connor et al. 2007).  This can exert important controls on the limits to range distribution (see Sanford, this volume)

There are essentially three ways to measure (or estimate) the effects of temperature on population-level processes: (1) experiments (by far the easiest and most common approach), (2) models parameterized with experimental results, field data or a mechanism-based theory such as MTE, and (3) field data, relating population fluctuations (e.g., declines) with variability in temperature in space and / or time.  The latter approach takes advantage of variable temperature in the field to perform natural experiments that are imperfect due to confounding factors, yet are commonly used since manipulating temperature at relevant spatial scales in situ in the ocean is nearly impossible.  Experiments certainly lead to cleaner results but for many species cannot be used to directly measure population responses.  Testing for effects of anthropogenic ocean warming on populations is even more challenging and generally requires time series data – often several decades of population data, e.g., size structure or density, and water temperature.

An excellent example of the multi-scale influence of temperature from cellular metabolism to individual performance and on up to population and community scale dynamics is the large body of work by Peter J. Edmunds on juvenile corals.  This is also one of the few studies to have combined field data, experiments and models to understand temperature effects on populations.  Pete and his collaborators have shown in laboratory experiments that temperature affects the respiration (Edmunds et al. 2011), growth (Edmunds 2005), and survival (Cumbo et al. 2013) of coral larvae, generally with a parabolic response that peaks around 28º C (Fig 5).  Long-term field studies (Edmunds 2004, 2007) have found ocean warming has exceeded this 28°C threshold and is related to reduced growth and survival of juvenile corals (Fig. 7).

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Literature Cited for the entire chapter is here as a PDF

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