An Ocean Food Web: Who’s Eating Who?
I visited the Crary Lab aquarium again today. As I looked at the creatures in the touch and feel tank, I started thinking about food chains and webs. Many food chains (one animal eating a plant, then another animal eating that animal, and so on) make up a food web. The marine (ocean) ecosystem in the Southern Ocean surrounding Antarctica has a wide variety of food chains, making up the ocean web of life. Let’s just look at some of the basics.
Take for example, phytoplankton. These microscopic plants live in all oceans of the world. Every other creature in the ocean depends on them as a producer in the food chain. The first vital link in any food chain is always a plant. Tiny or not, plants use a process called photosynthesis to make their own food. Phytoplankton are so tiny they can only be seen with a microscope. In spring and summer they multiply rapidly in the Southern Ocean. Scientists have counted millions of them in a gallon of water.
Diatoms are the most common phytoplankton in the Southern Ocean. When viewed under high magnification, they are quite beautiful. Their hard shells made out of natural glass (silica) form many unique shapes, as seen in the photos below. Different kinds of diatoms live in the sea-ice and in open water. Reed Scherer, one of the WISSARD scientists, studies diatoms. He shared these photos with me. Reed’s high -powered microscope can take photos of the diatoms under the lens.
Krill, tiny shrimp-like creatures, are the centerpiece of the Antarctic food chains and web. They are important grazers, feeding mainly on the tiny phytoplankton, which they capture using the fine hairs on their front legs. They occasionally eat other krill. Krill are prey (food source) for baleen whales, seals, penguins, and other seabirds.
(photo: retrieved from abc.net.au)
Krill can grow up to six centimeters (close to two and a half inches). Swimming in huge groups, they can stretch hundreds of meters across and 15 to 20 meters (16-21 yards) deep. They look like a swarm of pink in the ocean.
(photo: retrieved from currents.ucsc.edu)
(diagram: retrieved from krillfacts.org)
Krill might be low on the food chain, but they are a critical critter….providing food for so many other creatures in the ocean. They play an important role in the ocean food web.
In the next level of the food chain you would find some of the following creatures: small fish; squid (who eat small fish and small crustaceans, especially krill); sea stars (who are carnivores = meat eaters; they eat clams, small fish, etc.); sea urchins (they eat diatoms or other algae); sea anemones, scallops, nudibranchs (soft, sea-going slugs), jellyfish, chitons, sponges, the Antarctic toothfish, and so much more! Many of these creatures eat phytoplankton or each other. It truly is a complicated web of interrelated creatures!
For a complete “Underwater Field Guide to Ross Island and McMurdo Sound, Antarctica,” follow this link:
(photo by Norbert Wu; retrieved from telegraph.co.uk)
For some unbelievable underwater photography by Norbert Wu, visit the site below. Norbert Wu spent 12 years filming and photographing Antarctica’s life and habitats underwater. He completed over 1,000 dives in the frigid waters of the Ross Sea region.
I found this photo of researchers studying sea stars in Antarctica. Look at the size of that sea star!
(photo: retrieved from faculty.umf.maine.edu)
These sea stars were photographed in the aquarium here in Crary Lab.
(photo: retrieved from tea.armadaproject.org)
And here’s one of my own photos from the aquarium at Crary Lab. It’s the Antarctic toothfish.
Penguins feed on fish, small crustaceans (like krill) and at times squid. The diet of penguins will depend on the geographic location of the species.
Weddell seals eat fish, krill, squid, crustaceans, cephalopods (creatures like an octopus or nautilus; prominent head and sets of arms or tentacles), and sometimes penguins. Crabeater seals have a different diet. Approximately 90% of their diet is krill, with the remainder being cephalopods and fish. The big killer of the seal family here is the leopard seal. It is second to the killer whale among Antarctica’s top predators. It’s canine teeth are one inch long. Although it eats krill, it also eats penguins and less frequently crabeater seals.
The photos below are both taken by a friend from ANDRILL, but unfortunately I cannot remember which person gave me these photographs. Both pictures show Weddell seal mothers and pups.
At the top of the food chain/web, you’ll find the big guys…whales! For the purpose of this blog, I will focus on two species of whales: Killer whales (Orcas) and Minke whales. Scientists study both of those species in the Ross Sea region.
Killer whales live in groups of specialized sub-populations. Each group has adapted to live off resources in their home range. Their menu of prey can vary greatly, depending on geographic location. In the Antarctic austral summer, they hang out near the ice edge and in open channels in the sea ice. Prey in these locations might be baleen whales, seals, or penguins. Killer whales are not limited by habitat features like water temperature and depth; they track prey species and are considered the most widely distributed cetacean (for example whales, dolphins, porpoises).
(photos above and below: from JD, a researcher in McMurdo)
Don’t worry…the scientist is not shooting the killer whale. He is part of a project from NOAA (National Oceanic and Atmospheric Administration) that studies the whales and their movement and patterns. This researcher is preparing to attach a satellite tag to the dorsal fin (fin on the back) of a fish-eating killer whale in McMurdo Sound.
The killer whale below is doing something referred to as spy-hopping. When spy-hopping the killer whale rises out of the water in a slow and controlled motion. It exposes it’s head and it can be compared to a person treading water. If the whale is curious about what it’s viewing, this action can last for a few minutes at a time.
(photo: retrieved from nmfs.noaa.gov)
Cool facts about the killer whale:
** at birth killer whales are about 350 pounds and can be 7 feet 3 inches – 8 feet 6 inches long…WOW!
** adult males can weigh up to 22,000 pounds; adult females can weigh up to 16,500 pounds
** adult males can reach 32 feet long; adult females can reach 28 feet long
** males typically live for about 30 years, but can live as long as 50-60 years; females typically live about 50 years, but can live as long as 80-90 years
** they are highly social animals; they depend on underwater sounds for communication, feeding, and orientation; these sounds can be clicks, whistles, and calls such as squeaks, screams, and squawks
** killer whales are the largest creature in the delphinid (dolphin, whale, porpoise) family
** their color pattern is black on top and white on he underside; white patches near the eyes
Scientists are concerned because killer whales are heavily dependent on ice cover. Changes in the amount of ice cover will mean changes in the available habitat for these whales. Scientists are wondering how adaptable killer whales will be to living in a different habitat. These questions continue to drive their research here in Antarctica.
Below: another type of whale common to this region; the Antarctic Minke.
(photo: by Kike Calvo via AP Images; retrieved from treehugger.com)
Minke whales are baleen whale species which are common in the waters surrounding Antarctica. They’re not just here in the summer months either. They have been spotted in the middle of winter, in heavy pack ice around the continent. In the summer they like to be in open pack ice; where there is open water among floes of ice. Their range can be from the ice edge to far from land. The are inquisitive creatures, and will often come close to ships to check things out.
Baleen is like the bristles (such as a toothbrush has) and is made of the same substance as human fingernails. Baleen is a filter-feeder system inside the whale’s mouth. When the whale opens its mouth to feed underwater, water pours into the mouth. When the whale pushes the water out of its mouth, krill and other animals are trapped by the baleen. That is their way to capture their food. There are 200-300 baleen plates on each side of the a Minke whale’s mouth.
This photo shows you what baleen looks like. This is not necessarily from a Minke whale.
(photo: retrieved from en.wikipedia.org)
What a great picture of Minke whales along the Antarctic coast.
(photo: retrieved from antarctica.gov.au)
Minke whales feed on Antarctic krill and a variety of small schooling fish. Krill are a majority of their diet. The map below shows this whale’s range in the southern hemisphere. Minke whales are considered circumpolar (surrounding the polar region) creatures.
(photo: retrieved from biodiversityexplorer.org)
Cool facts about the Minke Whale:
** at birth, Antarctic Minke whales are 9 feet 2 inches long and can weight 990 pounds….holy cow!
** adults can grow up to 35 feet in length; they can weigh about 20,000 pounds
** they are dark gray above and white below; their head is sharply pointed
Scientists in McMurdo Station study microscopic plants and the animals of every size, from just about every level of the ocean food web. They’ve spent years researching who’s eating who and making discoveries about animal behavior, diet, migration and movement patterns, as well as health of populations and adaptions to changes in climate and ice conditions. I have, by no means, covered every aspect of the marine ecosystems found in the Southern Ocean. I do hope this introduction gave you some new insights into the complex relationships of the marine environment. There is an abundance of wildlife under the ice in the Antarctic region.
What type of marine science might you be interested in? Read more, keep learning, explore the natural world through first-hand experiences, make new discoveries every day!
References I used to write this blog include:
Guide to Marine Mammals of the World; National Audubon Society
The Australian Antarctic Division website: http://www.antarctica.gov.au
“Classroom Antarctica,” Australian Antarctic Division