Classification: Echinoderms
Diversity: Echinoderms are a phylum of marine animals. The adults are recognizable by their radial symmetry, and include such well-known animals as starfish, sea urchins, sand dollars, and sea cucumbers as well as the sea lilies. Echinoderms are found at every ocean depth, from the intertidal zone to then abyssal zone. The phylum contains about 6,000 species, making it the second largest grouping of deuterostomes after the chordates. Echinoderms are also the largest phylum that has no freshwater or terrestrial representatives. The characteristics that distinguish Phylum Echinodermata include: radial symmetry, internal skeleton, and water-vascular system. Echinoderms appear to be quite different that other advanced animal phyla, having radial (five-point wheel shape) symmetry as adults, rather that bilateral (worm-like) symmetry as in tother three cell-layer animals. Life History: Echinoderms have an internal skeleton made of bony plates of calcium carbonate. They deposit this material after extracting dissolved calcium and carbonate (bicarbonate)ions from sea wate r. In some species, such as the sea urchin, plates of the skeleton are locked together to form a rigid structure, On the other hand, most sea stars and brittle stars can flex their 'arms' indicating that the skeleton has gays and flexible plate junctures. Sea cucumbers have no real skeleton; only tiny remnant ossicles or bony plates. Many echinoderms have spines, the spines are part of the internal skeleton and are covered by epidermis. Another phylum-level characteristic of echinoderms is the water vascular system, this system function primarily in movement, but oxygen exchange, and molecular nutrient uptake are also known functions of this system. Sea stars feed by forcing their stomachs out of their bodies, onto, or into, their pray. Then, they secrete powerful digestive enzymes to break down the prey in its own body. The food molecules pass into the body fluid for distribution to the skin and other parts of the sea stars body. In most sea stars, undigested material is pushed out the oral opening, while some material is eliminated through a small anus located on the top surface. Also, on top are five gonopores, openings where eggs or sperm are shed directly into the sea. Echinoderms are usually dioecious, male and female reproductive systems in separate individuals. Larval development goes through several stages on the way to becoming a baby sea star. After gastrulation, the larval series had bilateral symmetry until metamorphosis when the animal assumes the radial symmetry of the adult. Ecological Roles: Species in the ocean interact within the ecosystem in a number of ways. These interactions are categorized according to the effect the interaction has on each species, the duration, and the nature of the relationship. The effects of species interactions are classified as zero effect, positive effect, or negative effect: 0, +, or - respectively: neutralism (0,0), amensalism (-,0), commensalism (+,0), synnecrosis (-,-), Mutualism (+,+), Predation (+,-) and Parasitism (-,+). The duration of these interactions range from brief, such as when a flowering plant is pollinated, to permanent, as with most symbiotic organisms. Population Interactions: Further complicating species interactions, there are population interactions in marine ecosystems to consider. Competition among species plays an important role in ecological regulation. The two forms of competition are: interference (or contest) competition and exploitation (or scramble) competition. Interference competition occurs when the dominant species keeps its competition away from a resource. Scramble competition describes a situation in which a population depletes a resource making it less available to its competition. The amount of competition is increased when resources are limited. Inter specific competition is competition between two or more species populations for limited resources. Intraspecific competition is the struggle that occurs between organisms in a population when resources are limited. Mortality, growth, and the ability to reproduce are all related to the number of organisms in a particular environmental niche. When density becomes too high, mortality increases, growth decreases, and the ability to reproduce is inhibited. Human Impacts: Ecosystems are controlled by a multitude of factors, each influencing the other. Almost all living organisms rely on the energy from the sun. Organisms at the base of the food chain, such as phytoplankton and plants, use the sun's energy directly. Organisms higher on the food chain receive energy from the sun indirectly. The only organisms on the planet capable of producing energy without the sun are microorganisms called chemoautotrophs that often live near deep sea vents and synthesize energy through a chemical process. Within an ecosystem there are trophic levels based on feeding relationships including producers, primary consumers, secondary consumers, tertiary consumers, and decomposers. Many organisms consume both plants and animals (omnivores) and prey on a variety of species to avoid starvation in case their primary prey becomes scarce; therefore they are sometimes categorized into more than one trophic level depending on the circumstances. Abiotic factors like temperature, light, nutrients, and salinity play a large part in the control of growth, location, and abundance of marine populations. Lastly, species within a population are also regulated by competition, predation, parasitism and disease. Every part of the complex web of biotic and abiotic factors fits together to make a system that is balanced and capable of withstanding most changes. Sources: https://www.ebiomedia.com/prod/BOechinoderms.html http://marinebio.org/oceans/ecological-regulation/ |