Evolution: Survival: Coral Reef Connections
Eat or Be Eaten: Predators and Prey, Parasites and Hosts Read about different predator-prey relationships on the reef. . to adapt to a wide variety of specialized habitats, gobies have become the most diverse marine fish family in the world. Marine resource managers often gauge the health of species based on overall biomass, but a new study of predator-prey relationships in the. But the marine food chain's top predators are common prey for the most deadly hunters of all—humans. When top predator species are.
Schooling offers some protection from predators, since each fish can be on the lookout, but it requires precise choreography to work well. Schooling fish have evolved special vibration sensors along their lateral sides that allow them to literally feel each other's movements and stay in synch.
Unfortunately, tritons can no longer keep starfish populations in check since they've been overharvested for their beautiful shells.
With too few tritons on the reef, crown-of-thorns starfish populations can explode, jeopardizing the living coral that makes up reefs. Covered with long, venomous spikes, the crown-of-thorns starfish Acanthaster planci is a voracious feeder that can eat living corals because of a unique adaptation: Populations of the starfish were once kept low by a few key predators, namely the giant triton.
Since humans decimated giant triton populations, crown-of-thorns starfish outbreaks periodically kill vast expanses of hard coral. Hard corals have evolved to have large amounts of a wax cetyl palmitate in their tissues. Very few predators can digest the wax, which has allowed corals to flourish and produce massive reefs. Recently, epidemic populations of one predator -- the crown-of-thorns starfish -- have done extensive damage to many reef regions. Armies of grazing starfish leave a wake of destruction in their path, killing up to 95 percent of the hard corals in an area.
They detect prey using an array of finely tuned senses, including electrical current detection. Rows of razor-sharp teeth and powerful jaws allow them to crack though even the thick carapace shell of full-grown sea turtles. One common defense against predators is a protective covering, such as a shell. Another is to flee the predator.
Marine Biome by Jake Walker on Prezi
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. 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: The line between feeding and fleeing is undoubtedly fine for species of prey and must be continually evaluated by prey to minimize vulnerability to predation. Marine mammals may also have indirectly influenced the evolution of nontargeted species in their ecosystems by consuming the predators of these species. The best example of this is the apparent influence of sea otters Enhidra lutris on kelp and other marine algae.
Most species of marine algae use secondary metabolites to defend against herbivores. However, marine algae in the North Pacific have lower levels of chemical defenses where sea otters occur compared to algae species inhabiting the southern oceans where sea otters are not present.
Sea otter predation on sea urchins and other herbivores may have removed selective pressure for species of marine algae to defend themselves against herbivores. Because secondary metabolites are expensive to produce, this may have allowed algae, like kelp, to radiate and diversify without the added cost of evolving and producing antigrazer compounds.
Ecological Time Scales On a shorter time scale than the evolutionary one, predators and prey can directly affect the relative abundance of each other, or they can indirectly affect the abundance of other species. Their interaction may also affect the physical complexity of the marine environment.
Predation by sea otters on sea urchins is probably die best example of how marine mammals can alter ecosystem structure and dynamics. Sea otters were hunted to near extinction in the late s throughout their North Pacific range. Without predation, urchin populations grew unchecked and overgrazed the fleshy algae. Kelp did not replace the underwater barrens until reintroduced sea otters once again began preying upon sea urchins.
Primary production has been estimated to be three times higher in areas where sea otters are present compared to those areas where sea otters are absent, allowing those organisms that feed upon primary production to grow faster and attain larger sizes e. The increase in primary production may even alter settlement patterns of invertebrates. The kelp also provides habitat for fish and suspension-feeding invertebrates to spawn, grow, and flourish. It can also change water motion and reduce onshore erosion and may even block the shoreward movement of barnacle larvae.
Thus a top predator such as the sea otter can change the structure and dynamics of marine ecosystems. Gray whales Eschrichtius robiistus and walruses Odobenus rosmarus are other species of marine mammals whose foraging behavior can also affect community structure. The feeding pits created by gray whales draw times more scavengers and other invertebrates compared to adjacent sediments.
The disturbed sediments may also help maintain the high abundance of gray whale prey and other early colonizing species. Similarly, walruses turn over bottom substrate in their search for clams and other bivalves. There is some evidence that they may feed selectively on certain size classes and certain species and that their defecation may result in the redistribution of sediment.
Thus, the interaction of benthic feeding marine mammals with their prey can result in food for scavengers and habitat for other species. Interactions between predators and prey also influence the shapes of their respective life tables i.
In Quebec, Canada, for example, there are a number of freshwater lakes that are home to land-locked harbor seals Phocavitulirw. Studies have found that the trout in these lakes are younger, grow faster, attain smaller sizes, and spawn at younger ages compared to adjacent lakes without seals. As for marine mammals, they typically have elevated mortality rates during their first few years of life.
This is likely due to a number of factors, including their relative vulnerability to predators and their inexperience at capturing prey and securing optimum nutrition. In the Gulf of Alaska and Bering Sea, killer whales have been implicated as a contributing factor, but not the main one, in the decline of Steller sea lions and harbor seals through the s.
Field observations along the Aleutian Islands indicate that these population declines were followed by a decline of sea otters in the s and that this decline was caused by killer whale predation.Marine Predator-Prey Relationships (accessible preview with captions)
Killer whales may have begun supplementing their diet with sea otters because they could not sustain themselves on the low numbers of remaining seals and sea lions. It is not yet clear what ultimately caused the decline of Steller sea lions and began this spiraling change of events. However, it is apparent from mathematical calculations of population sizes and energetic requirements that there are sufficient numbers of killer whales in Alaska to prevent the recovery of pinniped populations.
Thus, it is conceivable that populations of pinnipeds and otters may not recover to former levels of abundance until the predation by killer whales is reduced by a reduction in killer whale numbers or by a shift in killer whale diet to other species of mammals such as dolphins and porpoises.
In addition to directly affecting the abundance of their prey, marine mammals can indirectly affect the abundance of other species by outcompeting them or by consuming species that prey upon them. Contrary to popular opinion, the harbor seals were likely benefiting salmon because they affected the abundance of hake, a species of fish that is one of the largest predators of salmon smolts. However, the immediate result of the cull was not an increased number of salmon caught, but a decrease and failure of the razor clam fishery.
It turned out that the seals were primarily eating stariy flounder, which fed on the razor clams.
Without the seals, the predatory flounder population grew unchecked. Species such as crabeater seals Lobodon carcinophagaAntarctic fur seals Arctocephalus gazellaleopard seals Hy-drurga leptonyx and penguins chinstrap, Adelie, and macaroni increased and moved the Antarctic marine ecosystem to new equilibrium levels.
Increases were also observed in minke whales Balaenoptera bonaerensis and squid-eating king penguins due perhaps to reductions in the respective abundance of blue whales B.
All of these species appear to have directly benefited from an increase in prey, which was caused by the removal of whales. Penguins and seals may now be hindering the recovery of baleen whale stocks in the Antarctic. Marine mammals are generally considered to be opportunistic foragers who select from a number of alternative prey according to availability.
This is based on the relatively large number of different species that have been reported in the stomachs and feces of marine mammals. Steller sea lions, for example, are known to eat over 50 different species of fish, and even the occasional seabird.