Oceans Alive! | Life in the Sea | Predators and Prey
Most marine mammals are predators, but some are also preyed upon by other species. Interaction between marine mammals and their prey influences the. Marine resource managers often gauge the health of species based on overall biomass, but a new study of predator-prey relationships in the. Predator-prey relationships. Picture. Seastars prey on mussels and shellfish which would otherwise have no other natural predators.
The entire food web breaks down without the critical links between predator and prey, so we are concerned about the health of all of their populations.
Without healthy prey populations, we cannot sustain our fisheries, either at the midtrophic level, such as sardine and squid, or at the upper-trophic level. The trophic level refers to the position an organism occupies in a food web. We also care about other upper-trophic predators such as seabirds, seals, whales, dolphins, and sharks.
These complicated relationships are why we have developed laws and mandates to protect the whole ecosystem, not just one part.
Predators can be either specialists or generalists. Specialists like brown pelicans need one or two prey types to survive and reproduce, so a lack of either of those causes problems. Generalists may be able to switch between two or more prey types, eating whatever comes their way, but they may still have restrictions—such as prey that is the right size, particularly for a small seabird chick; in the right place, like near a breeding colony where parents must return to feed young or along a migration route; or available at the right time, including during breeding when more food is needed or in winter when other food is scarce.
The prey must also contain enough energy because lack of a particular fatty, energy-rich species such as anchovy can slow predator growth and cause problems with nutrition, eventually leading to unhealthy populations. How do these results apply to other marine ecosystems? Since other predators in the California Current also seem to follow this one-third rule, then other predators in systems around the world may follow it as well.
This rule also seemed to hold for different prey types, including small pelagic fishes, including sardine and anchovy; juvenile predatory fishes, such as rockfish; and invertebrates, like squid.
Do you have recommendations for fisheries managers? Variations in climate are predicted to increase, and fishing can add to climate-induced changes in prey populations. Precautionary fishing cutoffs—above one-fourth to one-third of recent maximum observed prey populations—may not reverse a downward trend in a prey species but may mean the difference between sufficient versus insufficient prey abundance for predators in changing ocean conditions.
One common defense against predators is a protective covering, such as a shell.
Marine Predator-Prey Relationships
Another is to flee the predator. During its evolution, the green sea turtle Chelonia mydas sacrificed speed in favor of a thick, heavy shell carapace. The carapace acts as armor, protecting the turtle's body from the sharp teeth of predators.
But some, like the tiger shark, are powerful enough to bite right through the carapace and kill the turtle. Some species of sea slugs, however, such as Platydoris scabra, have evolved immunity against the toxins of specific sponge families in this case, Microcionidae. This adaptation benefits the slugs in two ways. First, they don't have to compete with many other organisms for the sponges.
The sea slugs can also concentrate the sponge toxins to foil their own predators -- at least until the slugs' predators also evolve immunity to the toxins. Sea sponges, such as those of the Microcionidae family, have escaped predation by all but a few species because they produce foul-tasting and sometimes toxic compounds. These compounds evolved as chemical weapons for use against other sponges, as well as against fouling organisms creatures that grow on top of other creatures, thus decreasing their fitness -- their defensive function was just a lucky side effect.
But some predators, such as sea slugs, have evolved resistance to the toxins and even use those toxins against their own predators. Like many predators, they have evolved as extremely fast swimmers, with streamlined, torpedo-like bodies. And they are efficient killers, using conical, razor-sharp teeth to quickly rip prey to shreds.
In addition, they are resistant to the toxin found in the bodies of many of their prey, such as parrotfish.
Evolution: Survival: Coral Reef Connections
Named for their bright colors and beak-like mouths, parrotfish Scaridae family. Using their beaks and two pairs of crushing jaws, parrotfish are marvelously adapted for crunching and pulverizing chunks of algae-coated coral. They digest the algae and excrete the coral as fine sand. Unfortunately, they are poorly equipped to defend themselves against predators, such as barracuda, but some find protection by schooling with better-armored fish. Algae occur in a kaleidoscope of forms and colors on the reef, but they have one main function: Thus they are called "primary producers.
One important algal group, benthic bottom-dwelling algae, rapidly grows over dead coral and other inert objects, providing a grazing yard for herbivores, such as parrotfish. Their gentle disposition disappears, however, in the presence of another favorite food: When feeding, the butterflyfish turn into vicious predators, darting in to rip off the anemones' fleshy tentacles.
Having evolved resistance to the anemones' toxins, they need only get past clownfish guards to pick off a delicious meal. Packed with miniature toxin-loaded harpoons nematocyststhe tentacles of sea anemones provide an excellent deterrent against almost all would-be predators.
Saddled butterflyfish, though, have evolved resistance to the toxins and apparently relish the tentacles. Still, to grab a meal, the butterflyfish must get past the anemones' second line of defense: One such predator, the smallscale scorpionfish Scorpaenopsis oxycephalaclosely resembles the reef's rocky, algae- and coral-encrusted bottom, where it lies in wait for crustaceans and small fish, such as gobies. Safely tucked in coral crevices or half-buried in sand and rubble, gobies Gobiidae family maintain a low profile on the reef to avoid predation.
In addition, they have evolved independently swiveling eyes that constantly search the water for potential attackers. But their efforts can be foiled by ambush predators, like the smallscale scorpionfish, whose camouflage prevents gobies and other prey from seeing them until it's too late.The Rare and Exotic Animals - National Geographic Documentary
The two fish benefit by the association; a third fish, however, has evolved to take advantage of them both. Using a devious disguise and copycat behaviors to attract larger fish, the fanged ambush predator, called a fangblenny, rips living tissue from surprised prey. In the world of predators and prey, the normal rule is that big creatures eat smaller creatures.
But sometimes the tables are turned, as in the case of the bluestriped fangblenny Plagiotremus rhinorhyncosa small but sinister predatory fish.