Weddell seals hunt in both pelagic and benthic-demersal habitats. Marine habitats can be broadly divided into pelagic and demersal habitats. Alternatively, marine habitats can be divided into pelagic and demersal habitats. They feed on pelagic and benthic fish. Alternatively, marine habitats can be divided into pelagic and demersal zones. Juveniles mostly prey on small notothenioids, krill, squid and pelagic fishes. The distinction between demersal species of fish and pelagic species is not always clear cut. Tropicbirds are a family of tropical pelagic seabirds. Herrings consume copepods, arrow worms, pelagic amphipods, mysids, and krill in the pelagic zone. The pelagic ecosystem is based on phytoplankton. Notothenioids are found in many different niches like semipelagic, cryopelagic, pelagic, and benthic zones. These sediments include igneous crust, turbidite sediments, and pelagic sediments. Phytoplankton are found drifting in the water column of the pelagic zone. Sex-ratio of adult populations of pelagic copepods is usually skewed towards dominance of females. This is expected to cause an overall shift towards pelagic phytoplankton production.