Strong bottom‐up and top‐down control of early life stages of macroalgae

Abstract

In contrast to most pelagic primary producers, benthic macrophytes pass through morphologically distinct life stages, which can be subject to different ecological controls. Using factorial field experiments, we investigated how grazing pressure (three levels) and nutrient supply (four levels) interact in controlling the passage of marine macroalgae through an apparent recruitment ''bottleneck'' at the germling stage. In comparative experiments, we asked whether relative bottom-up and top-down effects on early life stages (Ͻ4 week germlings) vary (1) between the eutrophic Baltic Sea and the oligotrophic NW Atlantic, (2) across seasons in the NW Atlantic, and (3) among annual and perennial macroalgae. In both systems nutrient enrichment favored and grazers suppressed recruitment of green and brown annual algae; however, enrichment effects were much more pronounced in the Baltic, whereas grazer effects dominated in the NW Atlantic. Grazers induced a shift from grazer-susceptible green to more resistant brown algae in the Baltic without reducing total germling density. In the NW Atlantic, grazers strongly reduced overall recruitment rate throughout all seasons. Effects on perennials were similar in both systems with moderate losses to grazing and no effects of nutrient enrichment. Recruit densities and species composition shifted with season in the NW Atlantic. We conclude that the relative effects of grazers and nutrient enrichment depended on the nutrient status of the system, algal life history strategy, and season. Strong bottom-up and top-down controls shape benthic community composition before macroalgae reach visible size.

Light availability indirectly limits herbivore growth and abundance in a high rocky intertidal community during the winter

“…Work elsewhere has demonstrated the importance of both nutrients and consumers in benthic marine ecosystems (Neckles et al 1993;Wootton et al 1996;Hillebrand et al 2000;Menge 2000;Lotze et al 2001). The results presented herein show that light can also interact with consumer pressure to alter the growth and abundance of primary and secondary producers.…”

“…The general acceptance of this view over the past decade has motivated a growing number of studies that have simultaneously manipulated top-down and bottom-up factors. In marine benthic systems, these studies have generally taken the form of factorial manipulations of consumer abundance and nutrient supply (Neckles et al 1993;Wootton et al 1996;Hillebrand et al 2000;Lotze et al 2001). Although nutrient supply is clearly important, very little attention has been devoted to spatial and temporal variability in another fundamental bottom-up factor: light.…”

Physical, chemical, and biotic effects on arctic zooplankton communities and diversity

“…Conversely, when planktivory is weak, zooplankton densities and biomass may be high and phytoplankton abundance low. Similar forces appear to be at work in other food webs (e.g., freshwater benthic [Brönmark et al 1992] and rocky coastal marine [Paine 1966;Lotze and Worm 2001] …”

Depth-specific differences in growth of the reef sponge Callyspongia vaginalis: role of bottom-up effects

“…In marine environments, however, research on these issues has been decidedly one-sided (Menge 1992, Menge et al 1997, with an emphasis on top-down control of rocky intertidal community structure (Paine 1966, 1980, 2002, Dayton 1971, Estes & Palmisano 1974, Lubchenco 1978, Menge 2000. Recently, the emphasis has shifted to examine the role of bottom-up processes acting either in concert with, or independent of, top-down processes (Menge et al 1997, Leonard et al 1998, Lotze et al 2001, Nielsen 2001. In addition, ecologists have broadened the conventional definition of bottomup processes (nutrient supply) to include physical factors such as flow velocity (see Lesser et al 1994, Leonard et al 1998 or food delivery (Menge et al 1997), with their subsequent effects on larval supply and organismal survivorship and physiology.…”