Food web interactions in the plankton of Long Island bays, with preliminary observations on brown tide effects

Abstract

We examined the relat~ve Importance of phytoplankton and ciliates as prey for metazoan zooplankton and the role of predation in regulating ciliate populat~ons In 2 Long Island (USA) bays Depth-integrated primary production (mg C m h-') was dominated by nannoplankton < 5 pm In d~a meter throughout the year, ranging from > 9 5 " of total production in mid-summer to an average of about 60%, in winter and early spnng Predator exclusion and addition experiments conducted in microcosms showed that the mortality coeff~cient of cil~ates (d.') from zooplankton predation was higher when larger phytoplankton ( > l 0 pm) contributed less to total primary productivity For adult copepods an Increase In the percentage ciliate contribution compdred to phytoplankton contnbution to total carbon Intake also coinc~ded with the higher prrcrntages of small microdlgal production Egg production rates of Acartia spp were positively correlated to the net growth coefficient of cili~ites In contrast, mlcrometazoa routinely obtalned > 7 0 % of t h~~r total carbon ratlon from phytoplankton, and at times d u n n g spnng and summer, removed 23 to 52' 0 of the total depth-~ntegrated prlmary production In a d d i t~o n to protozoa, w e suggest that microinetazoa part~cularly copepod nauplii, may serve as a trophlc llnk between phytoplankton and mesozooplankton In Long Island bays

Role of zooplankton in the onset and demise of harmful brown tide blooms (Aureococcus anophagefferens) in US mid-Atlantic estuaries

“…Copepod nauplii were the dominant zooplankton in the > 64 µm size category at all sites studied (Fig. 4), a finding consistent with previously published reports on Long Island bays (Lonsdale et al 1996). A recent laboratory study investigating nauplii grazing on A. anophagefferens suggested that nauplii can rapidly graze some, but not all, toxic strains of this alga and thus may contribute to the demise of bloom events (Smith 2005).…”

“…Copepod nauplii are another potentially important grazer of Aureococcus anophagefferens, based on the size particles that these zooplankton are capable of capturing, and may also represent a trophic link between A. anophagefferens and mesozooplankton (Lonsdale et al 1996). Copepod nauplii were the dominant zooplankton in the > 64 µm size category at all sites studied (Fig.…”

“…This process would yield reduced competition for nutrients among small algae, which may otherwise have a similar affinity for low concentrations of nutrients (Raven & Kubler 2002), potentially allowing for a picoplankton which is ungrazed (Aureococcus) to dominate. Since the experimental work in NY also yielded low A. anophagefferens net growth rates in the < 5 µm experimental treatments, despite the absence or rarity of P. ovalis, there are likely other, currently unidentified, small grazers in these systems that consume brown tide and other picoplankton.Copepod nauplii are another potentially important grazer of Aureococcus anophagefferens, based on the size particles that these zooplankton are capable of capturing, and may also represent a trophic link between A. anophagefferens and mesozooplankton (Lonsdale et al 1996). Copepod nauplii were the dominant zooplankton in the > 64 µm size category at all sites studied (Fig.…”

Effect of food concentration and type of diet on Acartia survival and naupliar development

“…Euplotes is even ingested if it is mixed with surplus levels of a well edible diatom. In fact, the presence of the diatom did not even reduce the functional response to Euplotes density, thus indicating a feeding preference for the ciliate, as has been frequently reported from the field (Kleppel et al 1991;Kleppel 1993;Lonsdale et al 1996;Stoecker and Egloff 1987). Adults and copepodites of Acartia have been shown to be able to switch between suspension feeding and ambush feeding, the former being more suitable for immotile prey and the latter for motile prey (Saiz and Kiørboe 1995;Kiørboe et al 1996;Takahashi and Tiselius 2005).…”

“…The traditional view of copepods as herbivores became challenged during recent years (Kleppel et al 1991;Kleppel 1993;Lonsdale et al 1996;Sommer and Sommer 2006;and references therein). The relative importance of herbivory and carnivory (mainly on protozoans) is related to the feeding behaviour: Suspension feeders creating a feeding current to transport immotile or slowly swimming prey to the mouthparts tend to be more herbivorous.…”