Optics Introduction

## Introduction

### Major U.S. GLOBEC Objectives

The U.S. Global Ocean Ecosystem Dynamics program (U.S. GLOBEC) is a component of the U.S. Global Change Research Program. Its major objectives have been stated in previously issued reports (e.g., GLOBEC Report No. 1, Initial Science Plan, 1991) and are as follows:

U.S. GLOBEC's overriding goal is to "address the question of how changes in global environment are expected to affect abundances, variations in abundance, and production of animals in the sea" (GLOBEC Rept. 1, p. 5). The approach chosen to accomplish this goal is to develop a fundamental understanding of the mechanisms that determine the mean level and variation in marine animal populations. Toward that end, U.S. GLOBEC is planning investigations of (1) how changes in ocean physics interact with biological processes to control the population dynamics of key species, and (2) how such population-level responses to physical processes affect the structure and stability of ocean ecosystems. Increasing our understanding of the mechanisms and linkages between physical processes, population dynamics and ecosystem structure will lead to improved understanding of how population dynamics and ecosystems will be impacted by climate change.

### Goal of this Workshop

This workshop was intended to evaluate which optical technologies are presently available, which could be modified and which could be developed within the next several years to address some of the specific U.S. GLOBEC objectives mentioned subsequently. The workshop participants were asked to recommend technologies or instrumentation that would be near optimal to accomplish those objectives.

### The Significance of Technology

The importance of advanced technology, specifically for biological oceanography, was emphasized in GLOBEC Report No. 1 (1991) and in the Marine Zooplankton Colloquium 1(1989). Many of the difficulties associated with studying plankton in the water column are obvious. Proto- and metazooplankton live in three dimensions and can respond instantaneously to external stimuli, feeding, swimming and darting about in ways which cannot be observed easily by humans without aid of instrumentation. To quantify and understand those organisms' behaviors, we need to sample or observe continuously, or at frequent intervals, and utilize approaches which do not alter natural behavior (non-invasive approaches). These observations need to be made at space and time scales relevant to the organisms' behaviors and appropriate for the rates being studied.

To make the requisite observations-high frequency, high spatial resolution, large dynamic range and non-intrusive-will require new technology (Marine Zooplankton Colloquium 1, 1989, p.198). Currently available instruments for quantifying the abundance, distribution, and most physiological rates of planktonic animals are inadequate to address the major goals of U.S. GLOBEC. At a U.S. GLOBEC Workshop on Acoustical Technology in April 1991 it was emphasized that acoustical and optical technologies were the "leading candidates from which the necessary tools could be drawn to support the pursuit of GLOBEC's science goals" (GLOBEC Report No. 4, 1991, p. 28).

### Specific U.S. GLOBEC Objectives which could benefit from Optics Technology

To determine population dynamics of planktonic animals it is critical to quantify not only the abundance and distribution of the respective taxa over time, but also to quantify rates of birth, growth and mortality. Feeding rate measurements are valuable because they strongly affect the three above-mentioned variables. Neither acoustical nor optical instruments alone can be used to quantify all of these variables. Rather, these complementary technologies should be used together to provide the needed data (GLOBEC Report No. 4, 1991). Bioacoustic measurements of animals can perceive organisms larger than about 1 mm rather well, and can make accurate, frequent and rapid measurements of animal abundance and distribution. However, without ancillary information on target identification-either by the use of plankton nets, pumps, or optical sampling-current bioacoustical measurements are unlikely to provide the species specific data desired by U.S. GLOBEC. Nets and pumps are not adequate for target identification because in general they do not sample the same parcels of water sampled bioacoustically. Thus, optical instruments, which can provide target identification from the same parcel, will significantly improve the potential of acoustical methods to achieve the major goals of U.S. GLOBEC. Thus, the promise of optics is four-fold: (1) rapid identification of living organisms in situ, (2) quantification of organisms smaller than 1 mm, (3) observation of behavior and rate measurements directly and in situ, and (4) concurrent sampling of organisms, their prey and potential predators at spatial and temporal scales at which the physical environment can be sampled as well.

### Organization of the U.S. GLOBEC Optics Technology Workshop

Workshop participants were provided a background document two weeks prior to the meeting which outlined the goals of the workshop and provided guidance for contributing. The workshop began with several presentations on existing optical instruments which are used to measure the abundance and distribution of zooplankton or to obtain rate measurements. The intent was to inform workshop participants of the status and capability of existing optical instruments to measure zooplankton structure and dynamics in the ocean.

Presentations were made by the following participants who described specific instruments and/or approaches.

P. Donaghay/J. Katz
  Holographic Camera

R. Strickler
  Holography and Schlieren Observations

D. Davis
  Telemetry Developments

U. Kils
  In situ technology, nested camera observations of predator and prey, video image processing

V. Holliday
  Acoustical Estimation incl. MAPS and BITS; nesting of bioacoustical and optical technology; data reduction and analysis

R. Zaneveld
  Coupling of physics and zooplankton food distributions

Discussion following the overview presentations resulted in the delineation of two major zooplankton issues to which the application of optical technology could contribute significantly. These issues are:

1. the determination of zooplankton composition, biomass, and abundance, not only of target species, but also of their principal prey and potential predators, and

2. the quantification of in situ zooplankton dynamics (i.e., rates), specifically studies of behavior, feeding, predation and conspecific interaction (e.g., mating).

Workshop participants formed two working groups to examine in detail the roles that current, planned and future optical based instruments could play in addressing these two issues. The results are provided in the working group reports which follow.