We addressed the question of bottom-up versus top-down control of marine ecosystem trophic interactions by using annual fish catch data and satellite-derived (SeaWiFS) chlorophyll a measurements for the continental margin of western North America. Findings reveal a marked alongshore variation in retained primary production that is highly correlated with the alongshore variation in resident fish yield. The highest productivity occurs off the coasts of Washington and southern British Columbia. Zooplankton data for coastal British Columbia confirm strong bottom-up trophic linkages between phytoplankton, zooplankton, and resident fish, extending to regional areas as small as 10,000 square kilometers.
"The trophic structure organizes the biological components of an ecosystem and channels the flow of nutrient and energy ; thus, its regulation is a central issue in ecological research (Ware and Thomson 2005; Casini et al. 2008; Llope et al. 2012). "
[Show abstract][Hide abstract] ABSTRACT: Trophic structure and trophic transfer efficiency are among the most fundamental characteristics of an ecosystem. They characterize the transfer of nutrient and energy and are crucial in estimating the yield of harvestable biomass. In this study, we investigated the regulation of trophic structure (phytoplankton, zooplankton, and larval fish abundance) and biomass ratio of zooplankton to phytoplankton (as an indicator of transfer efficiency) in the East China Sea, one of the largest marginal seas in the world and an important fishing ground.
The results showed that when sea surface temperature was below 25°C, temperature co-acted with resource availability (zooplankton for larval fish and phytoplankton for zooplankton) in determining the trophic structure. When sea surface temperature was above 25°C, resource availability dominated the regulation of trophic structure. Biomass ratio of zooplankton to phytoplankton decreased with increasing phosphate concentration.
Our study suggested that the trophic structure of the East China Sea might be controlled by bottom-up processes, and this control is mediated by temperature.
"predation) versus bottom-up (e.g. availability of resources) processes is a difficult one to definitively answer, with much evidence for both cases (Estes et al. 1998; Pace et al. 1999; Richardson and Schoeman 2004; Ware and Thomson 2005; Myers et al. 2007; Frank 2008). The abundance and diversity of coral reef fishes are often thought to be largely controlled from the top-down, in part because of a rich history of apex-predator induced trophic cascades (Myers et al. 2007; Baum and Worm 2009; Ferretti et al. 2010; Rizzari et al. 2014), and in part because of the importance of herbivorous fishes and invertebrates in controlling macroalgal growth and in maintaining a coral-dominated system (Hughes 1994; Bellwood et al. 2006; Mumby et al. 2006; Hughes et al. 2007). "
[Show abstract][Hide abstract] ABSTRACT: The question of whether biological systems are maintained by top-down versus bottom-up drivers is a recurring one in ecology. It is a particularly important question to address in the management of coral reefs, which are at risk from a variety of anthropogenic stressors. Here, we explicitly test whether the abundance of different feeding guilds of coral-associated Chaetodon butterflyfishes are controlled by top-down or bottom-up drivers, and we assess the relative influence of all statistically significant drivers. We find that the abundance and species richness of Chaetodon butterflyfishes are predominately determined by bottom-up drivers. The abundance of corallivores is primarily driven by availability of branching and tabular live corals, whereas the abundance of generalists is most strongly influenced by a negative association with macroalgal cover. We also find evidence of weak top-down control on the abundance of corallivorous butterflyfish by gape-limited mesopredators, but no such effects on generalist butterflyfish. Our findings indicate that conservation of coral reefs for Chaetodon butterflyfishes must include management at a larger spatial scale in order to reduce the effect of coral reef stressors such as declining water quality and climate change, but should also include implementation of fisheries management tools in order to increase local herbivory.
"Bottom-up controls (Ware and Thomson, 2005) are ecosystem adjustments in primary production under nutrient depleted conditions (oligotrophy) caused by stratification of surface waters. Bottom-up control operates through competitive exclusion of phytoplankton species with species having favourable adaptations dominating the community structure and functions in different environmental situations. "
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