Henry M. Page - US grants

This award supports the acquisition of an isotope ratio mass spectrometer (IRMS) to be shared by a group of UC Santa Barbara investigators who have made extensive use of stable isotope analysis in their research programs. The new IRMS system will permit high-precision measurement of carbon, nitrogen, sulfur, oxygen, and hydrogen stable isotope ratios. The instrument would be configured to allow isotope measurements on solid samples of biological and geological origin, on both major and minor components of gas samples, and on purge-able gaseous, liquid, and ionic solutes in aqueous solutions. The instrument will be used in research that addresses a wide range of important and timely topics, including: measurements of fundamental microbial processes in marine environments, atmospheric methane levels, nutrient dynamics in soils from a variety of ecosystems and environments; and nutrient and food web linkages within coastal ecosystems. The instrument will be housed and maintained in a professionally managed, shared-use analytical and instrumentation facility at the University's Marine Science Institute. Besides providing a tool that is critical to the success of vital research programs, this equipment would also allow graduate student and postdoctoral users to become experts in this key technology for environmental science.

Intellectual Merit: Understanding trophic connections and how resource variability affects consumers is necessary if we are to predict how food webs may shift in the face of environmental change. Macroalgae and phytoplankton support highly productive marine ecosystems. Research based on stable isotope analyses has supported the idea that macroalgal detritus, especially the giant kelp Macrocystis, is a major source of dietary carbon to benthic suspension-feeders. However, recent findings by the investigator's four-year stable isotope study suggest that phytoplankton, not kelp, are the main food resource for benthic suspension-feeders on reefs in the Santa Barbara Channel, and that variation in phytoplankton abundance, combined with feeding selectivity and the scale of consumer tissue turnover times, may drive variability in consumer isotope values. The results suggest that a key assumption made in 'snapshot' isotope studies of coastal ecosystems over the past 20 years, which the isotope signature of coastal phytoplankton can be represented by that of offshore phytoplankton, could be incorrect. This assumption has been made because of the difficulty in separating phytoplankton from detritus to obtain an uncontaminated isotope signature, also a problem in freshwater systems.

The investigator will address two main objectives in this research project: 1) determining the contribution of phytoplankton and giant kelp detritus to the pool of suspended reef POM and whether POM composition varies with distance from kelp forests, and 2) evaluating how different components of the POM are used as food by reef suspension feeders. Two complementary approaches are designed to explore the contribution of phytoplankton and kelp detritus to POM in coastal waters: an advanced flow cytometry and cell-sorting system to separate phytoplankton from bulk POM, and analysis of essential polyunsaturated fatty acids (PUFA) in POM and consumers. The investigators have obtained preliminary data that demonstrate the feasibility of both of these methods. Isotope values of isolated inshore phytoplankton and kelp, and compound-specific PUFA, will be used in mixing models to estimate relative contributions of these two major primary producers to suspension feeder diets. Two hypothesized mechanisms that may influence isotopic composition of consumers will also be tested: selective feeding on particular fractions of the POM, and tissue turnover times.

This project will provide new insights into the trophic support of benthic suspension feeders, an ecologically and economically important guild in coastal ecosystems. The results will test the general hypothesis that giant kelp detritus is an important source of dietary carbon to suspension feeders, a commonly accepted idea that needs re-evaluation in light of key assumptions that have been made in its support. Stable isotope analyses are an ideal tool for testing this hypothesis given the spatial and temporal scales of variability that exist in the abundance of phytoplankton and giant kelp at our study sites. The sampling scheme combined with longer-term data on producer biomass provided by the Santa Barbara Coastal LTER will enable the investigators to capture this variability, which is generally missed by studies based on 'snapshot' stable isotope analyses.

The goal of this proposal is to catalyze a research collaboration between the PI and Dr. Nicholas Shears, a Lecturer at the University of Auckland, to understand trophic connections and the effect of resource variability on consumers. This is necessary to predict how food webs may shift in the face of environmental change. The PI proposes to extend prior work to examine the role of kelp detritus in this very different kelp forest system. He will use stable isotopes and polyunsaturated fatty acids (PUFA) to trace kelp carbon through the food web, and test the hypothesis that kelp detritus represents a significant source of carbon to suspension feeders living in the extensive Ecklonia kelp forests of New Zealand. This award is supported by the Catalyzing New International Collaborations program under OIIA/International Science and Engineering, with co-funding by GEO/Ocean Sciences.

Macroalgae and phytoplankton support highly productive marine ecosystems on shallow coastal reefs. The objectives of the proposed research are to determine: (1) the contribution of phytoplankton and kelp detritus to the pool of suspended particulate organic matter (POM) available to reef consumers, and (2) how different components of the POM are used as food by reef suspension feeders. Broader impacts of this project will include educational benefits to a graduate student who is the first person in her family to attend college. The project will serve to expand her research and perspective to include a very different kelp forest system and introduce her to the value of international collaborations through mentoring by Dr. Shears and his group. Results of this research will be disseminated widely through scientific publications but also through our undergraduate teaching and public lectures at venues such as the Santa Barbara Museum of Natural History.

Material exchange between ecosystems is being increasingly recognized as an important determinant of many ecological patterns and processes. Nowhere is this more evident than in the highly productive coastal zone, which receives large amounts of terrestrial particulate organic (POM) matter through stream and river discharge. In semi-arid regions such as southern California, the delivery of terrestrial POM to the nearshore is largely restricted to storm events that are intensified during El Nino years of above average rainfall. The processing and fate of this material is poorly known, yet there is growing evidence that it could contribute significantly to nearshore productivity. This research project will help to fill a critical knowledge gap pertaining to the origin, distribution, processing of terrestrial POM and its potential to serve as a reservoir of nitrogen storage for nearshore primary production during periods of the year when marine sources of dissolved inorganic nitrogen are low. Research on this award will be done in close collaboration with the Santa Barbara Coastal Long Term Ecological Research program (SBC LTER). As such it will augment SBC's strong contribution to student training and mentoring in interdisciplinary research at the undergraduate, graduate, and post-doctoral levels. Outcomes will be incorporated into SBC's ongoing Schoolyard LTER program, which is organized around a theme of kelp forest ecology and land-ocean exchanges and aimed at long-term connections with underserved, low-achieving schools that include year-round on and off campus activities. The LTER Investigators have developed formal partnerships with local cities and Santa Barbara County to develop vulnerability assessments of the regions coastal ecosystems and the LTER will incorporate the findings from this study into those assessments

The unprecedented drought currently in its fourth year in California, coupled with the ongoing conditions of anomalously low ocean productivity and the prospect of one the strongest El Ninos on record provide an unparalleled opportunity for researchers at the Santa Barbara Coastal Long Term Ecological Research program (SBC LTER) to test specific hypotheses pertaining to the origin, distribution, processing and bioavailability of terrestrial organic matter in coastal marine sediments and their potential for serving as a reservoir of nitrogen storage to fuel nearshore primary production during periods when nitrate concentrations are low. NSF RAPID Response award funds will be used to: (1) measure bulk properties and biomarker tracers of particulate organic matter (POM) in stream water and in coastal marine sediments at SBC sites differing in exposure to terrestrial runoff prior to and following large storm events, and (2) determine the bioavailability of dissolved organic matter (DOM) released from POM in marine sediments following large runoff events. The research will complement and inform SBC's ongoing efforts to investigate the availability and utilization of recycled forms of nitrogen in supporting the primary production of nearshore macrophytes and phytoplankton during non-upwelling periods when nitrate levels ar typically low.