Marine food webs are intricate, dynamic networks that connect microscopic primary producers to top predators across vast ocean spaces. At their base are phytoplankton, which convert sunlight and nutrients into organic matter. These microscopic plants fuel zooplankton populations, which in turn sustain forage fish such as sand lance, capelin, herring, and anchovy—the critical “middle layer” supporting a wide range of predators, including puffins, whales, large fish like cod, seals, and other seabirds.
Puffins—such as the Atlantic Puffin, Horned Puffin, Tufted Puffin, and Rhinoceros Auklet—are central-place foragers during the breeding season, constrained to forage within tens of kilometers of their colonies. They depend heavily on dense, predictable schools of energy-rich forage fish to provision chicks. However, these same prey resources are also targeted by competitors, including baleen whales feeding on krill and small fish, piscivorous fish like cod, pinnipeds such as seals and sea lions, and other seabirds like murres and shearwaters. This overlap creates intense competition, especially when prey availability is limited.
Many marine ecosystems, particularly in the North Atlantic and North Pacific, exhibit a “wasp-waist” food web structure. In this configuration, a relatively small number of mid-trophic species—mainly forage fish—control energy transfer between abundant lower trophic levels (plankton) and diverse upper predators. For puffins, this creates vulnerability: if forage fish populations decline or shift in distribution, the entire upper food web, including seabirds, can be affected disproportionately. Puffins cannot easily switch prey or travel far during breeding, making them especially sensitive to disruptions at this “waist.”
Oceanographic processes such as coastal upwelling play a crucial role in sustaining these food webs. Upwelling brings cold, nutrient-rich waters to the surface, stimulating phytoplankton blooms and cascading productivity through higher trophic levels. Conversely, changes in ocean climate—such as warming sea surface temperatures, altered currents, and marine heatwaves—can disrupt this structure. Warm conditions often reduce nutrient availability, shift plankton communities toward less nutritious species, and drive forage fish deeper or farther offshore, beyond the reach of puffins.
Both bottom-up and top-down forces shape marine food webs, particularly during extreme events like marine heatwaves. Bottom-up effects begin with reduced primary productivity, limiting energy entering the system and ultimately decreasing forage fish abundance. Top-down pressures may intensify simultaneously, as predators concentrate on dwindling prey resources. Fisheries add another layer of complexity: industrial harvest of forage fish can remove key species from the system, exacerbating competition and weakening the resilience of the food web.
For puffins, survival and reproductive success depend on the stability of this finely balanced system. Disruptions—whether from climate change, overfishing, or ecosystem shifts—can ripple rapidly through the food web, underscoring the need for ecosystem-based management that accounts for both ecological connections and the needs of marine predators.