LINKING MARINE AND TERRESTRIAL FOOD WEBS - ALLOCHTHONOUS INPUT FROM THE OCEAN SUPPORTS HIGH SECONDARY PRODUCTIVITY ON SMALL ISLANDS AND COASTAL LAND COMMUNITIES

This study quantifies the how of energy and biomass from a productive marine system to a relatively unproductive terrestrial system. Biomass from marine food webs (here, the Gulf of California) enters the terre strial webs of islands and coastal areas through two conduits: (1) sho re drift of algal wrack and carrion and (2) colonies of seabirds. Both conduits support dense assemblages of consumers: arthropods are 85-56 0 times more abundant in the supralittoral than inland and 2.2 times m ore abundant on islands with seabird colonies than those without. Mari ne input (MI), not terrestrial primary productivity (TP) by land plant s, provides most energy and biomass for terrestrial communities on 16 of 19 study islands. The ratio of perimeter to area (PIA) significantl y predicts arthropod abundance on islands and is the major determinant of the relative importance of allochthonous how; we expect PIA ratio to be important wherever transport of nutrients, detritus, and organis ms among habitats occurs. Similar transport phenomena generally take p lace, often with significant impact, on coastal habitats and islands w orldwide. Such input subsidizes a diverse array of terrestrial consume rs; in many cases, subsidized consumers reach extraordinarily high den sities and thus can depress their in situ resources. In general, we pr opose that such flow is often a key feature of the energetics, structu re, and dynamics of populations, food webs, and communities whenever a ny two habitats, differing in productivity, are juxtaposed.