Monitoring Data

POPULATION TRENDS

AND TROPHIC DYNAMICS IN PACIFIC OCS ECOSYSTEMS: WHAT CAN MONITORING DATA TELL US?

Principal Investigators: Russell J. Schmitt (UCSB) and Andrew J. Brooks (UCSB)

Project Rationale:

A number of entities, including MMS, have devoted considerable effort and resources to the long-term monitoring of various components of the coastal marine ecosystems in the Southern California outer-continental shelf (OCS) region. The primary goals of such monitoring programs are to estimate the current state of the biota and to identify long-term trends in population demographics. Data from such studies are vital to resource and regulatory agencies as they provide critical baseline information needed for accurate assessment of potential effects arising from such particular activities as offshore oil and gas production. The fundamental need for such information is evidenced by the growing number of coastal marine monitoring programs that have been implemented in Southern California.

The behavior of the California Current System plays a critical role in determining the conditions of the nearshore marine environment off Southern California. The typically high productivity of this system is attributed to coastal upwelling which brings deeper, nutrient-rich water to the surface near shore. This high supply rate of nutrients enhances primary productivity, which in turn increases secondary productivity of the nearshore pelagic and benthic food webs. Time series studies of the California Current System conducted by the California Cooperative Fisheries Oceanic Investigations since the 1940’s have revealed distinct seasonality within a year, and periodic wholesale change during El Niño Southern Oscillation (ENSO) events that have relatively brief (1-2 years) durations. There is abundant evidence that the California Current System has undergone a longer, interdecadal length change since the late 1970’s and early 1980’s. One manifestation off Southern California of this apparent regime shift was a rapid, large, and persistent increase in seawater temperature. Between 1976-1977, mean annual surface temperatures in the Southern California Bight rose an average of 1^oC or more above the mean for the previous two decades. Associated with this warming event were a number of changes in other physical processes and events that can influence marine biota. Among the more important manifestations in Southern California of these altered physical conditions was a decrease in productivity in surface waters near shore. Although the exact physical explanation is still under study, it appears reasonably certain that the amount of nutrients upwelled into surface waters has declined during this recent period of elevated seawater temperature. There is compelling evidence that the abundances of many coastal species off Southern California have undergone dramatic declines over the past 1-2 decades in response to falling productivity in near shore, surface waters.

The vast amount of long-term data on nearshore biota collected by a large number of separate monitoring programs in the Southern California OCS region represents a relatively untapped “gold mine” of information for environmental managers. The occurrence of a regime shift in the ocean climate in the North Pacific in the past two decades provides a unique opportunity to determine whether and how various components of the biota respond to this source of perturbation. Data from long-term monitoring programs not only indicate the current state and recent history of the biota, they can revel much about the ecological structure of various coastal ecosystems, including the dynamical behavior and regulation of different food webs. Such knowledge provides managers with better understanding and enhanced predictive ability regarding the potential impacts to these ecosystems from other potential sources of disturbance. Further, analyses of existing data sets can expose whether and how our ability to estimate or interpret responses of the biota may be constrained by present monitoring practices.

Research Progress :

Our MMS-UC CMI funded research encompasses two main objectives: (1) the analysis and synthesis of existing long-term monitoring data and (2) the continued annual surveys of subtidal reef communities at Santa Cruz Island.

(1) The analysis and synthesis of existing long-term monitoring data.

We have obtained all of our originally targeted data sets and have converted these data from their original hard copy format into a standardized digital format.

We are identifying biologically meaningful measures of population responses to the decline in productivity for use in our meta-analyses. This has involved the conversion of the raw abundance data contained in many of the original data sets into a standardized measures of abundance. To date, we have completed this process for all of the fish species contained in our datasets and are using this reduced data set to develop many of the time series techniques, e.g. data de-trending and smoothing functions, needed for many of our proposed analyses. Preliminary population trajectory analysis of these fish data indicates a continuation of the observed declines in population abundances.

(2) The continued annual surveys of subtidal reef communities at Santa Cruz Island.

Our monitoring of the abundances of surfperches, their invertebrate prey, and the cover of benthic microhabitats has continued at the 11 permanent study sites on the south coast of Santa Cruz Island. Sampling of fish (via visual counts along permanent band transects) and of the cover of benthic microhabitats (via random point contact methods) has been conducted annually. All samples collected for the purpose of identifying potential invertebrate prey are sorted and the individual organisms identified to the lowest taxon possible each year. All data have been error checked and entered into the appropriate data sets.