One area that has blossomed in the past eight years is the study of interactions between ocean physics and biology, especially interactions at small scales. A recent review [ Denman and Gargett, 1994] gives 137 references, of which 69 are to works specifically concerning biological-physical interactions. One type of work that seems to be drawing special interest is modeling on the micro-scale. Davis et al. [1991] say in the introduction to their modeling paper that ``workshops... have repeatedly pointed out that the micro-fine scale environment is of critical importance to planktonic growth and survival.'' One puzzle in this field has been whether turbulence increases or decreases the encounter rate between predator and prey (or between plant and nutrient or light). One might think that, by introducing an additional random velocity, turbulence would increase encounter rates, but this must be weighed against the potential decrease in encounter rate due to turbulent dispersion. The model of Davis et al. [1991] indicates that predators are aided in finding prey by low levels of turbulence as long as these levels are too low to disperse patches. Intermediate levels of turbulence do disperse patches, thereby making it more difficult to find prey. Large turbulence velocities homogenize the prey distribution and again the associated velocities increase the encounter rate.
In a review of micro-organism interaction with the physical microenvironment, Pedley and Kessler [1992] quote more than 100 references. One effect they mention is ``bioconvection,'' water motion induced by density gradients of animals, which have density greater than water and for one reason or another tend to swim upward. There were observations of this effect as early as 1911! Could such motions occur in the ocean? Mitchell et al. [1989] say maybe! They survey a number of regions and find that in estuaries and in coastal waters gradients of ``biodensity'' can be of the same order as density gradients caused by temperature or salinity variations. They note, though, that the effect of organisms in changing light absorption and thereby indirectly influencing temperature gradients is probably more important.
Bio-instrumentation: In the 1987 report [ Caldwell, 1987] it was said that ``Still lacking are truly coherent measurements of mixing and bio/chemical parameters. If we could reduce the scale of in-situ bio/chemical measurements to 10 cm and if we could make the measurements from the same instruments as physical mixing measurements, I believe that a new illumination of biological processes would result.'' It's not clear that the ``new illumination'' has yet resulted, but the level of effort in this area has been impressive. Instrument packages have been assembled for this purpose for use on moorings [ Dickey et al., 1993], on towed bodies [ Dunn et al., 1993], on isopycnal floats [ Hitchcock et al., 1989], on surface floats [ Carlson et al., 1988] and on submarines [ Haury et al., 1990]. Attention is finally being paid to routinely getting biological information from standard shipboard Acoustic Doppler Current Profilers [ Flagg and Smith, 1989; Roe and Griffiths, 1993].
One remarkable achievement was the measurement of fluorescence spectra from a profiling instrument [ Desiderio et al., 1993]. This instrument takes in data at a mind-boggling rate: 30 spectra per second, or a spectrum every 2 centimeters as the instrument falls. It appears that it may be possible to assess the species composition of the water column with 2-centimeter resolution [ Cowles et al., 1993]!