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Jonathan Havenhand


Department of Marine
+46 526-686 07
Visiting address
45296 Strömstad
Postal address
45296 Strömstad

About Jonathan Havenhand

Current Research foci:

Effects of marine climate change on benthic organisms and ecosystems

– Experimental design and statistical analysis

Effects of marine climate change on fertilization success: Many marine species release sperm and eggs freely into the water column, where fertilisation takes place. This exposes these simple single cells to the prevalent conditions of the ocean, which are changing rapidly due to changing climate. Our first research in the effects of climate change focussed on the effects of temperature on fertilization success found that temperature-induced change in swimming speeds of sperm and larvae were due to thermal changes in water viscosity, not temperature-related shifts in physiology. These remarkable results received relatively little attention in the literature at the time, but are now taking on a new significance.

We subsequently developed this work to investigate the effects of temperature, salinity and ocean acidification, as single stressors and in combination. This pioneering work showed:

  • extreme sensitivity of fertilization success and early larval development to “near-future” levels of ocean acidification (Havenhand et al 2008)
  • negative, but also neutral, and (in some individuals) positive effects of climate change on fertilization success (Schlegel et al 2012).

Together, these results imply that adaptation to climate change may be possible in several species

Effects of marine climate change on resilience of marine organisms & ecosystems: Focussing on barnacles, tunicates and oysters – key components of benthic marine communities – in the last few years we have found:

  • substantial plasticity in the salinity- and pH-tolerance of juvenile barnacles, that may be related to novel osmo-regulatory genes
  • that nutritional status and phenotype history drive the susceptibility of barnacle larvae and juveniles to ocean acidification
  • that simulated natural diurnal pH fluctuations have radically different impacts on growth and calcification of barnacles than the constant pH treatments typically used in experiments
  • trans-generational plasticity to salinity, and very low heritability for salinity tolerance in the tunicate Ciona
  • heritability of tolerance to low-salinity in invasive populations of the oyster Crassostrea from low-salinity habitats (unpublished)
  • that greater genetic diversity of barnacle larvae increases settlement success. (This was one of the first demonstrations that intra-specific diversity can increase ecosystem function)

Developing our earlier findings of substantial inter-individual variability in responses to marine climate change, a multi-partner collaborative project with Lars Gamfeldt (UGOT) and Johan Eklöf (Stockholm), among others, investigated the importance of inter-species diversity for resilience to climate change. We found:

  • that indirect effects, mediated through the food web, can completely offset the direct effects of climate change in seagrass beds, and that trophic complexity can strongly reduce the impacts of climate change. (This work highlights how results from single-species experiments may not reveal how species will respond in the ecosystem).
  • that the “insurance effect” of biodiversity is weakened under marine climate change

Experimental design and analysis – the importance of “non-significant” results: Designing experiments that maximize our chance to make meaningful inferences from the results is fundamental to experimental science, yet this is often overlooked in modern research that prioritizes statistical significance. This is vitally important in Climate Change research because null-hypotheses are often evaluated with weak statistical tests. Indeed, the null-hypothesis testing paradigm – which lays at the heart of modern experimental science – is inappropriate for investigations that attempt to document the magnitude of the effects of climate change. Recent research in other fields of science emphasize that reliance on P-values to draw conclusions is inappropriate.

I have worked in this field for some considerable time, optimizing experimental designs and analyses of results. Highlights of this work include:

  • promoting the use of effect-size metrics, rather than statistical testing, to describe the effects of ocean acidification and warming.
  • invitation to be lead-author on a chapter dealing with experimental design in the 2010 Best Practice Guide for Research in Ocean Acidification (Riebesell et al 2010; Havenhand et al 2010).
  • membership of the SCOR Working Group “Changing Ocean Biological Systems”, which has entailed key publications on designing experiments for multiple climate drivers (Boyd et al 2018), and an online tool to aid the design tof mutlidriver experiments (