CONSEQUENCES OF NEARSHORE LOW OXYGEN AND LOW
pH FOR COASTAL RESOURCES OF SOUTHERN CALIFORNIA
Lisa Levin (Lead PI), Ed Parnell (Co PI), Todd Martz (Assoc. Investigator)
OBJECTIVES:Our primary research objective is to evaluate the consequences of low O2/low pH (low pHOx) conditions for biotic resources that sustain local ecosystems and fishery economies in southern California. Specific goals are to: (1) Use continuous monitoring records of O2 and pH to establish the frequency, duration, and severity to which key shelf resources are exposed to low pHOx in the coastal ocean off San Diego. (2) Couple O2 data collected cross-shore and alongshore with existing acoustically mapped habitats to produce GIS layers of O2 habitat stress among rockfish and squid egg-bed habitats (3) Develop GIS layers of O2 and pH risk among habitats off San Diego County (4) Evaluate species and life-stage-specific susceptibility of the SCB species to the negative effects of low pHOx events through literature review and baseline assessments (4) Establish methods to evaluate critical lethal and sublethal O2 and pH exposures for the commercially valuable species D. opalescens (market squid) using laboratory experimentation. (5) Identify critical data gaps at the taxon-specific, guild, and ecosystem levels with respect to information needed to assess vulnerability and develop management actions. (6) Develop quick response protocols to evaluate biotic reaction to severe low pHOx events, conduct surveys and establish a hypHOxia information network and warning system for resource users. This research will address these and related hypotheses:
H1: Mobile crustaceans (e.g., prawns, crabs, lobsters) and fishes (e.g., rockfish, sculpin, cabezon, lingcod), and market squid migrate or shift spawning grounds with seasonal and event-scale (multi-day to multi week) changes in O2 concentrations.
H2: Attached benthic squid egg capsules experience O2 or pH stress during low pHOx events or during seasonal shifts in hypoxia.
We will work with physical oceanographers, public data bases, the California Atlas, and our own data sets to characterize shelf exposures to low oxygen and low pH on seasonal and event (day-wk) time scales. Available data sources include CalCOFI, SCCOOS, Del Mar Moorings, the Kelp pHOx mooring, and the UC Mexus/CA Atlas. We propose to generate data with an additional SeapHOx mooring (T, S, O2, pH, pressure sensors) in sandy squid egg habitat, synoptic CTD casts and a dissolved O2 sensor mounted on the ROV. Synoptic CTD and ROV sampling will aim to capture both relaxed (non-event) and upwelled (event) conditions. From discrete sampling information (bottle O2, total alkalinity, pH, salinity, temperature) we will develop O2-pH-temperature relationships to assess parameter linkages. The physiochemical data will be used to generate maps of hypoxia/pH (hypHOxia) exposure on the shelf over our study sites.
From a survey of the published and grey literature we will establish critical lethal and sublethal O2 and pH thresholds for major life stages of regionally key taxa. This information will be combined with developmental period and location data to identify vulnerable species and life stages. Where species-specific and life-stage specific data are not available we will examine literature for congeneric and confamilial species. We will overlay faunal distribution maps with pH and O2 exposure scenarios using GRASS (GIS layers), R, and matlab to identify the spatial and temporal probability of low pHOx-induced lethal and sublethal responses.
Assessing the ecological consequences of hypoxia and acidification will be accomplished by first establishing faunal abundances on selected rocky reef outcrops, sandy seabed, and submarine canyon habitats, characterizing species habitat specificity and seasonality during normoxic conditions and comparing them to periods of O2 stress (acute and chronic). Estimation of demersal finfish and invertebrate densities will be made using a SeaBotix ROV rated to 150 m depth equipped with a 540 line resolution video camera, paired lasers for size estimation, LED lights, a SBE49 CTD, and SBE 43 O2 sensor. Surveys will be temporally stratified between upwelling (spring/summer) and non-upwelling (fall/winter) seasons to establish abundance estimates during periods of no oxygen or pH stress and will also be conducted in response to acute oxygen and pH events at the same sites. Squid egg beds will be a primary focus on sandy habitats.
In order to investigate the sensitivity of early life stages of market squid to low pHOx, near-hatch paralarvae of D. opalescens will be exposed to various low pH and O2 levels in the laboratory and collected from the field along a gradient of exposures. We will develop an array of morphological (size/stage) and physiological assays (enzymatic Na+/K+-ATPase activity and HIF) to quantify the sublethal effects of hypoxia and hypercapnia on cephalopod embryos both in controlled conditions in the laboratory and along natural environmental gradients in the field. Ongoing efforts to develop geochemical proxies of exposure will be integrated with these studies.
We will monitor oxygen/pH levels during the project and develop quick response protocols for low pHOx events. These will accommodate available instrumentation, add satellite and vessel capabilities, and identify a quick-response team to evaluate the extent of the hydrographic changes, associated environmental properties such as temperature, production (color), winds, faunal redistributions, patterns of mortality, and the fate of dead organisms.
A public information center will be developed to disseminate information about low O2 and low pH exposure events, and their possible impacts to resource managers, legislators, commercial and recreational fishers, educators and the public. A permanent home for this center will be supported by the CA Coastal Atlas, with annual meetings and an email bulletin providing additional information to stakeholders. Outreach and education relevant to this project will be conducted via the Ocean Discovery Institute and Cabrillo National Monument.
The focus of marine resource management has shifted from managing individual species to managing the ecosystem in which species are enmeshed, within the dynamic physical environment in which they live. Hypoxia combined with low pH, represents an important physical driver whose effects on California nearshore communities where many species of recreational and commercial importance live, are not well understood. Off southern California, both oxygen and pH (pHOx) levels have been declining in recent decades, arguably as a result of climate change. Hypoxia routinely occurs at outer shelf depths. There is a strong need to evaluate the duration, frequency, intensity, and spatial distribution of exposure of shelf resources to hypoxia and hypercapnia, and to identify critical thresholds and species responses (both lethal and sublethal). This is especially important for the market squid, which forms California's most valuable fishery, and for threatened rockfishes. This project offers an initial step in addressing low-pHOx impacts on local marine ecosystems, a widely overlooked, but significant threat to the health of San Diego sea waters. Results from this project will be used to develop indicators of nearshore hypoxia and hypercapnia exposure and a review of their effects on the CCLME. This information can serve as valuable input in risk analysis and evaluation of ecosystem health within the California Current Integrated Ecosystem Assessment.