Chloroplasts in their tissues use the sun's energy to convert carbon dioxide and water into sugar and oxygen for growth through the process of photosynthesis. Like their relatives, seagrasses have leaves, roots and veins, and produce flowers and seeds. Seagrasses belong to a group of plants called monocotyledons that include grasses, lilies and palms. (Courtesy of the Integration and Application Network (), University of Maryland Center for Environmental Science )Įven though seagrasses and seaweeds look superficially similar, they are very different organisms. Algae on the seafloor have a holdfast and transport nutrients through the body by diffusion, while seagrasses are flowering vascular plants with roots and an internal transport system. What Are Seagrasses? A Plant, Not a SeaweedĪlgae or "seaweeds" (left) differ from seagrasses (right) in several ways. Work is ongoing around the world to restore these important ecosystems. Seagrasses provide many important services to people as well, but many seagrasses meadows have been lost because of human activities. Seagrasses provide shelter and food to an incredibly diverse community of animals, from tiny invertebrates to large fish, crabs, turtles, marine mammals and birds. Although they often receive little attention, they are one of the most productive ecosystems in the world. Seagrasses can form dense underwater meadows, some of which are large enough to be seen from space. They evolved around 100 million years ago, and today there are approximately 72 different seagrass species that belong to four major groups. Seagrasses have roots, stems and leaves, and produce flowers and seeds. They are often confused with seaweeds, but are actually more closely related to the flowering plants that you see on land. Seagrasses are so-named because most species have long green, grass-like leaves. Indeed, the team concludes, "this may be occurring in the present population, where 92 percent of the wild fish sampled carry a DNA marker found on the Y chromosome.Seagrasses are found in shallow salty and brackish waters in many parts of the world, from the tropics to the Arctic Circle. This reduces the number of genetic females in the population with each successive generation, and leads to an imbalance in the sex ratio of spawners. If, as in the case of coho salmon and rainbow trout, these males are sexually viable, they can only produce male offspring. But frequent matings between altered females and normal males, both of which carry an X chromosome and a Y chromosome, can yield males with two Y chromosomes. The altered females produced eggs, spawned and then died-the normal Pacific salmon life cycle. Intriguingly, such a reversal does not appear to render the fish reproductively impaired. Both factors might be affecting the Columbia river chinooks: Nagler and his colleagues have detected pesticides and other chemicals that could mimic estrogen in the Columbia's water, and the river's temperature regularly changes with the hydroelectricity-related fluctuating water flows. Earlier studies have shown that hormones can induce sex reversal in trout embryos, and young sockeye salmon will make the switch if exposed to different temperatures. But these new findings document the phenomenon for the first time in a wild fish population. Such reversals are not unheard of, as salmon sex can be reversed experimentally in the lab, Nagler reports. Nagler of the University of Idaho, "is that these females have been 'sex-reversed' and are in fact male." "The best explanation for these results," says lead author James J. According to a report published today in the journal Environmental Health Perspectives, tissue samples collected last year from fall chinook salmon spawning in the Columbia River ( right) show that 84 percent of fish that appeared to be female carried male-specific genetic markers. New findings, though, suggest that in at least one case, what's going on is stranger than anyone had imagined. Researchers have long suspected that degradation of the river ecosystems might play a leading role in the plight of these fish, but the idea had not been fully explored. As a result, a number of them are now endangered or extinct. For years salmon populations in the northwestern U.S.
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