Recent research has demonstrated the complexity of the pH and hypoxia seascape in the coastal waters of California. Notably, pH and carbonate chemistry are much more variable than might have been suspected in the early days of ocean acidification (OA) research. In addition, deoxygenation that co-occurs with low pH conditions has been detected and is thought to be accelerating in southern California. Together these two abiotic factors create a seawater environment that is both challenging to calcifying organisms (the OA component) and at certain times of day may create conditions that reach hypoxic levels for many fish and marine invertebrates (the deoxygenation component). Given the complex multistressor situation, integrated studies of OA and oxygen content are needed in better understand the vulnerability of marine organisms in coastal California waters.
The lab is presently working on a number of projects in this area of OAH, including research that examines the response of larval marine fish to OAH stress and deployment of sensors to capture the variation in the physical environment.
Natural variation of pH: The role of macrophytes in creating refuges from future acidification
Work here includes ongoing field research and instrument deployments in the Santa Barbara Channel. Thus far, our data collected in kelp forest environments and eelgrass beds show strong biological effects on pH variation. Our results indicate that large beds of macrophytes alter seawater chemistry, a process that may buffer OA in the future. In addition, advected upwelled water and localized phytoplankton blooms impact pH and oxygen leading to different patterns in variability across the regional spatial scale of the Channel Islands. Here, we note that this natural variation of pH and oxygen content in seawater occurs on a scale that is likely relevant to local management of coastal marine ecosystems in California. In support of this research, we have formed a strong partnership with the NOAA Channel Islands Marine Sanctuary and with the Channel Islands National Park.
Collaboration with the SBC LTER
As part of the National Science Foundation's Long Term Ecological Research (LTER) network, the Santa Barbara Coastal (SBC) aims to investigate how coastal processes influence giant kelp forest ecosystem structure and function. Further, the group seeks to predict how drivers of environmental change that occur over different spatial and temporal scales will affect these ecosystems. The Hofmann lab assists the SBC LTER in the maintenance and deployment of a series of autonomous pH sensors throughout the Santa Barbara Channel as a means to understand how the spatiotemporal variability of pH drives coastal community structure. Quantifying the current, naturally pH variability will lend insight how this coastal ecosystem will respond to future ocean acidification.
The California Current Large Marine Ecosystem (CCLME), a temperate marine region dominated by episodic upwelling, is predicted to experience rapid environmental change in the future due to ocean acidification. Aragonite saturation state within the California Current System is predicted to decrease in the future with near-permanent undersaturation conditions expected by the year 2050. Thus, the CCLME is a critical region to study due to the rapid rate of environmental change that resident organisms will experience and because of the economic and societal value of this coastal region. Recent efforts by a research consortium – the Ocean Margin Ecosystems Group for Acidification Studies (OMEGAS) – has begun to characterize a portion of the CCLME; both describing the mosaic of pH in coastal waters and examining the responses of key calcification-dependent benthic marine organisms to natural variation in pH and to changes in carbonate chemistry that are expected in the coming decades. In this review, we present the OMEGAS strategy of co-locating sensors and oceanographic observations with biological studies on benthic marine invertebrates, specifically measurements of functional traits such as calcification-related processes and genetic variation in populations that are locally adapted to conditions in a particular region of the coast.