Predator-prey eddy in heterotrophic nanoflagellate-bacteria relationships in a bay on the northeastern Pacific coast of Japan

T Tanaka,A Taniguchi

doi:10.3354/meps179123

Abstract

A new scheme has been recently proposed by Tanaka et al. (1997; Aquat Microb Ecol 13:249-256) to illustrate the temporal variation in the numerical relationship between heterotrophic nanoflagellates (HNF) and bacteria on both short-term and seasonal scales. To clarify this scheme, seasonal variations in abundance of HNF and bacteria, together with environmental variables, were monitored at 1 to 3 d intervals in Onagawa Bay on the northeastern Pacific coast of Japan. In addition, bacterial growth rates were also measured weekly or bi-monthly. As expected from the marked seasonality of environmental variables, bacterial growth rate showed distinct seasonal variation, being higher in warmer seasons and vice versa. The seasonal variation of bacterial abundance in nature, however, was only 1 order of magnitude, while HNF abundance showed marked seasonal changes. On shorter temporal scales, peaks of bacterial abundance were usually followed by increases in HNF abundance with a lag of 2 to 7 d, and bacterial and HNF abundances changed with 2 to 14 d and 3 to 17 d periods, respectively, indicating so-called predator-prey oscillations. These values generally agree with previously reported values, even though there were temporal and spatial differences. These predator-prey oscillations were confined to a particular region in phase space during a period of ca 1 mo and showed a sequential movement in a anticlockwise and/or clockwise direction. Such movement was termed the predator-prey eddy. On annual scales, the eddy's position and magnitude were different between seasons, but the eddy was confined to a vertically elongated elliptical region in phase space which was similar to findings in our previous study. These results support our contention, namely, that the predator-prey eddy of the HNF-bacteria system always exists and continuously migrates over a certain region of phase space on an annual basis.

Highlights

Based on seasonal monitoring conducted in Onagawa Bay on the northeastern Pacific coast of Japan, we recently proposed a new scheme to illustrate the temporal variation in the numerical relationship between Heterotrophic nanoflagellates (HNF) and bacteria on both shortterm and seasonal scales (Fig. 1, Tanaka et al 1997)
We assumed that the orbit of the HNF-bacteria system in phase space was continuous throughout the year, the data for September and December are presented as examples (Fig.6).Each of the data sets was confined to a particular region which was graphically similar to that predicted by the classical predator-prey model (e.g. Lotka 1925, Volterra 1926, 1939). the sequential movement showed both anticlockwise and clockwise directions in September and only anticlockwise in December, these results demonstrate that the HNF-bacterial relationship in nature is a predator-prey relationship and that the term predator-prey eddy (Tanaka et al 1997) is a fitting description
Our results reveal that both HNF and bacterial abundances in nature continually fluctuate on shorter temporal scales throughout the year, our criterion for the determination of peaks does not premit extensive statistical treatment (Fig. 5)

Summary

Introduction

Heterotrophic nanoflagellates (HNF) are considered to play an important role in regulating bacterial abundance and recycling inorganic nutrients and dissolved organic matter (Fenchel 1982a to d , Azam et al 1983, Andersson et al 1985, Goldman & Caron 1985, Sherr et al 1986).It has been reported that HNF and bacteria are widely distributed and abundant, on the order of 10' to 104,a n d 105to 107cells ml-', respectively (e.g.van Es & Meyer-Reil 1982, Fenchel 1986).O Inter-Research 1999 Resale o f full article not permittedStatistical analysis shows that HNF abundance positively correlates with bacterial abundance across a wide range of aquatic environments (Berninger et al 1991, Sand.ers et al 1992, Gas01 & Vaque 1993). The numerical relationship between bacteria and HNF is often, simplified to a ratio of ca 103:1,and this suggests that both HNF and bacteria respond to changing environmental factors in parallel over wide geographical and temporal scales (Wright & Coffin 1984a). This numerical relationship shows wide variability, up to 2 orders of magnitude (102:1to 104:1,see Sanders et al 1992, their Fig. 2 ). Several reports revealed that the abundances of bacteria and HNF show regular cyclic changes with a certain lag phase, i.e. predatorprey oscillations, when monitoring was done at shorter intervals (Fenchel 1982d, Davis et al 1985, Andersen & S ~ rense n1986, Nakamura et al 1994, Tanaka & Taniguchi 1996)

Methods

Results

Discussion

Conclusion