Bottom-up regulation of a pelagic community through spatial aggregations

The importance of spatial pattern in ecosystems has long been recognized. However, incorporating patchiness into our understanding of forces regulating ecosystems has proved challenging. We used a combination of continuously sampling moored sensors, complemented by shipboard sampling, to measure the temporal variation, abundance and vertical distribution of four trophic levels in Hawaii's near shore pelagic ecosystem. Using an analysis approach from trophic dynamics, we found that the frequency and intensity of spatial aggregations—rather than total biomass—in each step of a food chain involving phytoplankton, copepods, mesopelagic micronekton and spinner dolphins (Stenella longirostris) were the most significant predictors of variation in adjacent trophic levels. Patches of organisms had impacts disproportionate to the biomass of organisms within them. Our results are in accordance with resource limitation—mediated by patch dynamics—regulating structure at each trophic step in this ecosystem, as well as the foraging behaviour of the top predator. Because of their high degree of heterogeneity, ecosystem-level effects of patchiness such as this may be common in many pelagic marine systems.

[1]  K. Benoit‐Bird,et al.  Diel variation of zooplankton distributions in Hawaiian waters favors horizontal diel migration by midwater micronekton , 2008 .

[2]  D. Ware,et al.  Bottom-Up Ecosystem Trophic Dynamics Determine Fish Production in the Northeast Pacific , 2005, Science.

[3]  Percy L. Donaghay,et al.  Acoustic scattering in the coastal ocean at Monterey Bay, CA, USA: Fine-scale vertical structures , 2010 .

[4]  W. Au,et al.  Prey dynamics affect foraging by a pelagic predator (Stenella longirostris) over a range of spatial and temporal scales , 2003, Behavioral Ecology and Sociobiology.

[5]  K. Benoit‐Bird,et al.  Behavior exceeds physical forcing in the diel horizontal migration of the midwater sound-scattering layer in Hawaiian waters , 2008 .

[6]  John R. Post,et al.  Trophic Relationships in Freshwater Pelagic Ecosystems , 1986 .

[7]  David W. Schindler,et al.  Factors regulating phytoplankton production and standing crop in the world's freshwaters , 1978 .

[8]  D. Cushing,et al.  The ecology of the seas , 1978 .

[9]  George L. Hunt,et al.  Interplay between top-down, bottom-up, and wasp-waist control in marine ecosystems , 2006 .

[10]  Michael S. Twardowski,et al.  Temporal and spatial occurrence of thin phytoplankton layers in relation to physical processes , 2001 .

[11]  M. Hunter,et al.  Playing Chutes and Ladders: Heterogeneity and the Relative Roles of Bottom‐Up and Top‐Down Forces in Natural Communities , 1992, Ecology.

[12]  K. S. Norris,et al.  Behavior of the Hawaiian Spinner Dolphin 'Stenella longirostris' (Schlegel, 1841). , 1979 .

[13]  L. Oksanen,et al.  Exploitation Ecosystems in Gradients of Primary Productivity , 1981, The American Naturalist.

[14]  L. Slobodkin,et al.  Community Structure, Population Control, and Competition , 1960, The American Naturalist.

[15]  S. D. Cooper,et al.  PRIMARY-PRODUCTIVITY GRADIENTS AND SHORT-TERM POPULATION DYNAMICS IN OPEN SYSTEMS , 1997 .

[16]  Whitlow W. L. Au,et al.  Extreme diel horizontal migrations by a tropical nearshore resident micronekton community , 2006 .

[17]  Kelly J Benoit-Bird,et al.  Cooperative prey herding by the pelagic dolphin, Stenella longirostris. , 2009, The Journal of the Acoustical Society of America.

[18]  T. Clarke.  DIETS OF FOURTEEN SPECIES OF VERTICALLY MIGRATING MESOPELAGIC FISHES IN HAWAIIAN WATERS , 1980 .

[19]  T. White,et al.  The importance of a relative shortage of food in animal ecology , 2004, Oecologia.

[20]  I. Boyd.  TEMPORAL SCALES OF FORAGING IN A MARINE PREDATOR , 1996 .