I have investigated some of the effects of ocean acidification, the decrease in seawater pH due to increased atmospheric CO2 absorption (aka ocean acidification), on benthic (sea bottom dwelling) marine communities in the labs of James B. McClintock and Charles D. Amsler. For more information on associated projects see Kathryn M. Schoenrock's website.

I have implemented projects that investigate the effects of the combined and single stressors of ocean warming and acidification on a suite of Antarctic invertebrates. I have investigated the effects of reduced seawater pH on the diversity and abundance of mesograzer invertebrates common to invertebrate-macroalgal assemblages found along the western Antarctic Peninsula. 
In addition to whole organism and multi-species assemblage responses to changing seawater conditions, I am interested observing and documenting the natural variations currently experienced by marine organisms to develop a context for the invertebrate responses I observed in my experiments as well as develop a natural environmental baseline. Please see below for a more detailed description of these projects.

For more information on the Amsler/McClintock lab activities in Antarctica, please check out the UAB in Antarctica blog. 

Single species responses

Seawater warming 

​To evaluate how seawater warming may impact the feeding preferences of an ecologically important grazer associated with common seaweeds of the western Antarctic Peninsula, I examined impacts of exposure to acute elevated temperature on the omnivorous amphipod Gondogeneia antarctica. Amphipods were exposed to a current mean ambient temperature (1.5°C) or to the projected near-future temperature for 2100 (3.5 °C) over a 24-h period. Following temperature exposure, feeding preferences were examined using artificial agar foods prepared with extracts from six co-occuring seaweeds. I found that acute temperature exposure (simulating short-lived summer seawater temperature peaks) can alter feeding choices.  Shifts in feeding preferences like these could influence the functional role of this common mobile grazer and the seaweed-invertebrate assemblages that occur along the coastal shallow ocean bottom of  the western Antarctic Peninsula.

Seawater warming and acidification

Gastropod responses
To determine the resilience of two common species of benthic marine gastropod to seawater warming and acidification, I exposed both species to temperature and pH conditions representing current and predicted conditions expected by 2100. I looked at growth (changes in wet mass), net calcification (changes in buoyant weight), shell morphometrics, and body composition (soluble protein and nonpolar lipid tissue content) in the limpet Nacella concinna and the Antarctic topshell snail Margarella antarctica. Both species demonstrated greater resistance than expected to experimental conditions. A full report these results have been published.

I also investigated escape responses induced by a predator (sea star) and innate righting behaviors in the limpet Nacella concinna and snail Margarella antarctica. Both behaviors were assessed for limpets and snails before and after a six-week period of exposure to combinations of temperature and pH representing current annual ambient conditions (1.5°C, pH 8.0) and those predicted to occur in the region by 2100 (3.5°C, pH 7.8). A full report of these behavioral responses of these two species revealed slight differences with some interactive effects of warming and acidification on the escape speeds of these two gastropod species, which may indicate the potential for antagonistic or synergistic effects of a combination of elevated temperature and decreased pH over longer exposure periods. 
Amphipod responses
To assess the responses of two common gammaridean amphipod species to seawater acidification and warming, Gondogeneia antarctica and Paradexamine fissicauda were exposed for a 90-day period to combinations of pH and temperature representing present day annual ambient conditions (pH 8.0, 1.5°C) and predicted near-future conditions (pH 7.6, 3.5°C). This resulted in treatments that represented ambient, reduced pH, elevated temperature, and combined reduced pH-elevated temperature conditions. During the exposure period, survival, molt frequency, feeding rate, and growth were assessed. At the completion of the exposure period, I also measured proximate body compositions of individuals in each treatment. 

​​The most striking result, however, of chronic exposure to decreased pH and elevated temperature was a high incidence of mortality in both the amphipods G. antarctica and Paradexamine fissicauda. Decreased survival in these two common amphipods, each occupying contrasting niches as grazers in macroalgal-grazer assemblages, has the potential to disrupt the effectiveness of grazers balancing community responses to environmental change. 
Macroalgae responses
Using the same experimental set-up as I used for investigating invertebrate responses to seawater warming and acidification, we also performed experiments to determine the responses of crustose and fleshy encrusting macroalgae as well as the responses of dominant upright fleshy algae.

For more detailed information on the responses of macroalgae with which these benthic invertebrates associate, please visit my colleague Kate's website.
Combined amphipod and macroalgae responses
To test how the combination of ocean warming and acidification (OWA) could change trophic interactions in marine benthic communities along the western Antarctic Peninsula, I also assessed amphipod feeding preferences for chemically defended Desmarestia anceps and D. menziesii following 79 and 39 day exposure, respectively, to combinations of current and predicted near-future temperature (1.5C and 3.5C, respectively) and pH (pH 8.0 and 7.6, respectively). 
 We measured protein and lipid levels of macroalgal tissues and performed choice feeding assays with amphipods. For D. anceps, we found a significant interactive temperature-pH effect on lipid levels and significantly lower protein levels at reduced pH. In contrast, tissues of D. menziesii exhibited significantly greater lipid levels after exposure to reduced pH, but there was no temperature effect on lipid or protein. Our results indicate that despite altered macroalgal nutritional quality under OWA, both macroalgae retained their ability to deter amphipod feeding. This deterrent capacity could become an important contributor to net community resistance of mesograzer-macroalgal assemblages of the WAP to predicted OWA.

Assemblage responses to seawater acidification

2019-2020 Field Season
To follow up on our previous laboratory work to understand assemblage responses to ocean acidification, we recently returned to Palmer Station, Antarctica to assess the responses of natural seaweed-grazer assemblages following a 60-day exposure to seawater acidification. Like before, we performed our experiment in mesocosms containing the common Antarctic brown macroalga, Desmarestia menziesii, seeded with a natural assemblages associated mobile crustacean grazers assemblage (dominated by amphipods), exposed to one of three levels of seawater pH representing present-day (pH 8.0), near future (2100, pH 7.7) and distant future (several hundreds of years, pH 7.3) conditions. It is important to understand how these assemblages of amphipods and seaweed assemblages will respond to changes in their environment because they are part of a "community-wide mutualism" in which the amphipods gain protection from predators by associating with seaweeds that produce chemicals that make them taste bad and the seaweeds gain access to light to support photosynthesis when the amphipods eat the diatoms that settle on the surfaces of the seaweeds. 

To better understand and identify "winner" and "loser" amphipod species, immediately before and then following exposure, Hannah Oswalt (PhD student at UAB) and Maggie Amsler quantified assemblage composition and species abundance of each mesocosm. Hannah will follow up with additional single species exposure experiments with species she identifies as "winners" and "losers" (based on their survival of the ocean acidification treatments) next season. Please stay tuned for results!

2013 Field Season
To assess the prospective response of natural macroalgal-grazer assemblages to seawater acidification, I performed a 30-day experiment in mesocosms containing the common Antarctic brown macroalga, Desmarestia menziesii, seeded with a natural assemblages associated mobile crustacean grazers assemblage (dominated by amphipods). Macroalgae and their grazer assemblages were exposed to one of three levels of seawater pH representing present-day (pH 8.0), near future (2100, pH 7.7) and distant future (several hundreds of years, pH 7.3) conditions. Following exposure, I evaluated assemblage composition and species abundance.

​I found that response diversity, demonstrated by similar functional groups responding differently to the same stimulus - in this case pH, contributed to overall assemblage resistance to reduced pH. This resistance ultimately can contribute to the resilience of mobile grazer assemblages. To better gauge how species will contribute to ecosystem resistance and resilience, it is important to understand the role of biodiversity and how variability in responses of species within various functional groups contribute to overall ecosystem stability.