Abstract
Ocean chemistry is changing as a result of human activities. Atmospheric carbon dioxide (CO2) concentrations are increasing, causing an increase in oceanic pCO2 that drives a decrease in oceanic pH, a process called ocean acidification (OA). Higher CO2 concentrations are also linked to rising global temperatures that can result in more stratified surface waters, reducing the exchange between surface and deep waters; this stronger stratification, along with nutrient pollution, contributes to an expansion of oxygen-depleted zones (so called hypoxia or deoxygenation). Determining the response of marine organisms to environmental changes is important for assessments of future ecosystem functioning. While many studies have assessed the impact of individual or paired stressors, fewer studies have assessed the combined impact of pCO2, O2, and temperature. A long-term experiment (∼10 months) with different treatments of these three stressors was conducted to determine their sole or combined impact on the abundance and survival of a benthic foraminiferal community collected from a continental-shelf site. Foraminifera are well suited to such study because of their small size, relatively rapid growth, varied mineralogies and physiologies. Inoculation materials were collected from a ∼77-m deep site south of Woods Hole, MA. Very fine sediments (<53 μm) were used as inoculum, to allow the entire community to respond. Thirty-eight morphologically identified taxa grew during the experiment. Multivariate statistical analysis indicates that hypoxia was the major driving factor distinguishing the yields, while warming was secondary. Species responses were not consistent, with different species being most abundant in different treatments. Some taxa grew in all of the triple-stressor samples. Results from the experiment suggest that foraminiferal species’ responses will vary considerably, with some being negatively impacted by predicted environmental changes, while other taxa will tolerate, and perhaps even benefit, from deoxygenation, warming and OA.
Highlights
The oceans are undergoing significant environmental change
We focus on so-called smaller benthic foraminifera rather than Larger Benthic Foraminifera (LBF) or planktonic foraminifera, both of which often have photosynthetic symbionts that may impact their response to environmental changes
While two taxa were ubiquitous across all treatments and samples, resulting foraminiferal assemblages differed among treatments, indicating some species will likely fare better than others as climate change continues
Summary
The oceans are undergoing significant environmental change. The average sea surface temperature (SST) has increased over the last century (e.g., Hansen et al, 2006), rising atmospheric partial pressure of carbon dioxide (pCO2) is lowering the pH of the oceans (Doney et al, 2009), and the extent and intensity of lowoxygen (i.e., hypoxic) bottom waters is growing, at least in certain regions (e.g., Rabalais et al, 2007; Stramma et al, 2010; Capone and Hutchins, 2013; Altieri and Gedan, 2015). Because many environmental factors typically co-vary in nature, single-stressor studies may not be the best predictor of species’ future responses. Different stressors can have different impacts on any given organism: they may be additive, synergistic (greater than additive), or antagonistic (offsetting) (reviewed by Breitburg et al, 2015). One stressor can be beneficial to reproduction of an organism while another can be detrimental to reproduction. In that situation, such antagonistic stressors may have no net impact on reproduction of that organism. To enable better predictions of future organism and ecosystem responses to ongoing global change, analysis of multiple stressors is critical
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
