Volume-frequency distributions of marine phytoplankton in a temperate neritic environment

Abstract

ABSTRACT. A seasonal study was carried out to determine whether or not volume-frequency distributions of near surface nano-and microplankton were approximated by a power function model in temperate neritic waters. Measurements of buoyancy frequency, the nutrients NO3-N, NO2-N, NH,-N, urea-N, Si(OH),-Si, and PO,-P, phytoplankton photosynthehc pigments, and cell concentrations and volumes were made around a frontal zone in the Strait of Georgia, Canada, at ca 3 w k intervals from Apnl 1983 to September 1984, excluding October to February. The model accounted for a large percentage of the variance in spectra when nano-flagellates and dinoflagellates dominated phytoplankton crops in pre-diatom bloom and nutlient-depleted waters. When diatoms dominated crops, the fit was better in summer than in spring and often was positively correlated to temperature Possible covariance of temperature and grazing by large omnivorous zooplankters on diatoms was considered The exponent of the power function varied around -0.92, derived from linear regression analysis of a log,-transformed allometric equation A geometric mean or functional regression slope was used because the slope varied with the correlation coefficient and because the relationship descnbes an allometric dependence. Results support the use of a power function model to predict volume-frequency spectra of temperate nentic phytoplankton whenever diatoms are not abundant or from the time of the demise of the spring diatom bloom until at least the early fall season when diatoms are abundant. The presence of diatoms such as Laudena boreahs, Skeletonema costatun], and Thalassiosira nordenskiold~i in larger numbers than predicted by their cell volumes invalidates use of the model during spring.

Retention efficiency of 0.2 to 6 µm particles by the appendicularians Oikopleura dioica and Fritillaria borealis

“…-2.4 to -1.1 for b. Although this overlaps partially with the range of b observed in nature for particles >1 µm (from -1.4 to -0.7, Hobson 1988, CavenderBares et al 2001, Rodríguez et al 2001, lower b's indicate that the actual biomass of the smallest submicronic particles is probably higher than could be expected from extrapolation of the biomass density function obtained for particles >1 µm. This, in combination with the fact that power laws do not necessarily apply in all conditions (e.g.…”

“…The exponent of the particle size spectrum in the ocean, b, was allowed to vary between -1.4 and -0.7 in our calculations, which matches approximately the observed range for b in nature (e.g. Hobson 1988, -1.4 to -0.7 in a neritic area; Rodríguez et al 2001, -1.2 to -0.8 in an oceanic system).…”

Patterns and Limitations in Limnoplankton Size Spectra

“…However, the frequency of exceptions to these patterns suggests that the distributions are transient and dynamic as forces both inside and outside the size classes of interest shift the ecological advantage m o n g size classes. Parametric size distributions are at best averaged abstractions, and departures from such idealized distributions must be expected when communities and subcommunities are examined over restricted temp r a l and spatial scales (Hobson 1988). TABLE 8.…”

Temporal variations among planktonic diatom assemblages in a turbulent environment of the southern Strait of Georgia, British Columbia, Canada

“…Furthermore, results of other stu.d.ies show that many of the same species as those observed at the sampling site occur in other regions at about the same time. For example, the spring bloom in the Strait of Georgia is often initially composed of the genus Thalassiosird, including the species pacifica, eccentrica, gravida, nordenskioldi~ and rotula (Parsons et al 1969, Huntly & Hobson 1978, Takahashi et al 1978, Hobson 1981, Sancetta & Calvert 1988, Sancetta 1989, Haigh et al 1992, McQuoid & Hobson 1997, and In some cases, a small form of Skeletonerna costatum (Sancetta 1989) and Lauderia annulata (Hobson 1988 1997) and Paralja sulcata is present during win--3.0 I ter months (Sancetta 1989). Chaetoceros radicans has been observed d.uring spring and sumnler (Sancetta 1989, McQ.uoid & Hobson 1997 and fall (Sancetta 1989) in Saanich Inlet and in the fall in the Strait of Georgia (Haigh et al 1992).…”

“…This coupled to a n unknown but almost certainly large vertical flux of NO3-N into the euphotic zone supports the assumption that division rates of cells are not nutrient lirmted in either Haro Strait or Sidney Channel. As in other regions, the diatoms Skeletonema costatum 480 and Thalassiosira nordenskioldii are impor-40' tant components of the spring bloom in these waters (Parsons et al 1969, Hobson 1988). Information about other species is available at bimonthly intervaIs (Hobson unpubl.…”