Ch. 16: Marine Communities

1. Ch. 16: Marine Communities

2. Main Concepts • A community is all the living things in a defined area. The organisms of a community will interact with and depend on each other, often in complex ways. • An organism’s habitat is its “address,” its niche is its “occupation.” • The distribution of organisms in communities is rarely random; clumped distribution is the most common. • Though among Earth’s most rigorous habitats, high-energy rocky and sandy shores are heavily populated by diverse organisms able to take advantage of the abundant nutrients found there.

3. Main Concepts • Highly productive salt marshes and estuaries shelter a great variety of benthic life forms and serve as nurseries for some pelagic organisms. • Coral reef communities are exceptions to the general rule that tropical oceans are unproductive. Closely cycled nutrients and zooxanthellae in coral organisms make high productivity, and high biodiversity, possible. • The open ocean below 3,000 meters (10,000 feet) is among the least densely populated habitats on Earth. Lack of food is the main limiting factor. • The deep-sea floor is the ocean’s most uniform habitat. It is populated by large numbers of mostly small, highly specialized organisms.

4. Main Concepts • Earth’s largest community has only recently been discovered. It consists of bacteria and archaeans living in the minute spaces within solid rock, and may extend to a depth of perhaps 7 kilometers (4.4 miles). • Deep vent communities near black smokers and atop cold seeps depend for energy on chemosynthesis by bacteria and archaeans. • Whale fall communities may act as “stepping stones” for organisms that colonize hydrothermal vents. • Symbiosis is the co-occurrence of two species in which the life of one is closely interwoven with the life of the other. The types of symbiosis are mutualism, commensalism, and the most common symbiosis, parasitism.

5. The Resourceful Hermit Hermit crab: • Faces the same challenges of any organism: find food, avoid predators, find mates.

6. The Resourceful Hermit • Adaptations include: • Sensors on antennae and mouth parts to find food • Good eyesight • Muscular coordination • Tough exoskeleton • Blue bands around tips of legs for attracting mates

7. The Resourceful Hermit • Uses shell as protective, temporary “home” to protect vulnerable and delicate hind-body parts • Hermit crabs engage in “house hopping,” always looking for better shell. • May evict snails from their shells before snail is done with it. • Two crabs may fight for lengthy periods of time (hours to days) over one shell. • Two crabs may occupy opposite ends of a worm tube simultaneously. • Two crabs may swap shells (frequently with “renter’s remorse” occurring almost immediately).

8. Marine Communities • Community:

9. Marine Communities • Community: a group of interacting populations of organisms in a particular location. • Population:

10. Marine Communities • Community: a group of interacting populations of organisms in a particular location. • Population: a group of individuals of the same species living together in a specific area. • Physical and biological characteristics of a location dictate what populations and, thus, what community, lives there. • Members of a community usually share similar environmental tolerances.

11. Marine Communities The scale on which a community is considered can vary greatly.

12. Marine Communities Deep open-ocean community = largest marine community • Sparsely populated • Permanently dark • Little food availability • Mating opportunities are rare • In some spp. the male burrows into the female’s body upon first meeting and remains there permanently.

13. Marine Communities • Isolated rocks on seafloor = may be the smallest marine communities • Inhabited by larvae of various spp., seaweeds, worms, snails, and small fish.

14. Marine Communities • Single grain of sand, or individual fish scale may be considered an entire microscopic community.

15. Organisms within Communities Communities depend on availability of energy. • Energy source may be the sun (for photosynthesis) or inorganic chemicals, e.g. iron, sulfate, and manganese ions (chemosynthesis). • Primary producers use these sources of energy to assemble carbon, hydrogen, and oxygen into foods (e.g. glucose). • The energy is passed from producer to consumer and to other consumers in a food web.

16. Organisms within Communities

17. Organisms within Communities Habitat: the physical location occupied by a species or community; its “address.” Niche: the ecological role carried out by the organism or population; its “occupation.” • Each population in a community has its own “job” for which its characteristics (e.g. size, shape, color, behavior, feeding habits, etc.) suit it.

18. Organisms within Communities • Biodiversity (biological diversity): a measure of species richness in a given area; the variety of spp. in a given area. • A community with high biodiversity is characterized by complex interactions among spp.

19. The Influence of Physical and Biological Factors The location and composition of a community are both influenced by physical and biological factors. • Physical factors: temperature, pressure, salinity, etc. • Biological factors: crowding, predation, grazing, parasitism, shading from light, generation of waste, competition.

20. The Influence of Physical and Biological Factors • Limiting factor: any physical or biological factor that prevents an organism from feeding, growing, reproducing successfully, defending itself, or otherwise functioning successfully, i.e. any factor that limits an organism’s success in a community, e.g. low water temperature for tropical fish may cause them to become too sluggish to capture food, or avoid predators (see Fig. 16.2, p. 393).

21. Physical & Biological Factors • Stenothermal (steno = narrow): referring to organisms with a narrow tolerance for temperature fluctuations. • Eurythermal (eury = wide, broad): referring to organisms with a wide thermal tolerance. • Stenohaline(halos = salt): referring to organisms that require a stable saline environment. • Euryhaline: referring to organisms that can withstand a wide range of salinity. • Same ideas apply to stenobaric (baros = pressure) and eurybaric.

22. Physical & Biological Factors

23. Physical & Biological Factors • Usually more than one environmental factor changes simultaneously. • Even slight changes, which alone may not harm an organism, when combined with others, may be lethal to the organism: synergistic effects. • The proper balance of physical and biological factors must be maintained to ensure the success and longevity of any community.

24. Physical & Biological Factors • Ecology (oikos = house; logos = study): the study of interactions of organisms with one another and with the environment.

25. Competition • The availability of food, light, space and other resources will determine the number and composition of populations within a community. • Competition may occur between . . .

26. Competition • . . . members of the same species (intraspecific competition): • Some individuals in a population will be larger, stronger, faster, more adept at gathering food, etc. • These will survive; others will either move to a new location, or die. • Those that are most successful will produce the greatest number of offspring, which will possess their parents’ adaptive traits. • This kind of competition hones population to its environment.

27. Competition • . . . or members of different species (interspecific competition): • One sp. may be so successful that it eliminates competing populations. • Extinction of one sp. by another in this fashion is probably rare. • Such competition can  the restriction of one population by another, e.g. . . .

28. Competition . . . Chthamalus and Collisella (Fig. 16.3, p. 394). • Larvae of both spp. attach to the rocks in the intertidal. • Faster-growing limpets (Collisella) push the weaker barnacles (Chthamalus) off the rocks in lower zone. • Limpets cannot tolerate the dry conditions of the upper zone. • Limpets dominate the lower zone; barnacles the upper zone. • Mid-zone is occupied by both spp. in lower densities due to the competition that exists there.

29. Competition “Complete competitors cannot coexist.”

30. Growth Rate & Carrying Capacity • Given unlimited resources, a population introduced to a new environment will reproduce exponentially. • The population growth curve will follow a J-shaped pattern (see Fig. 16.4, p. 394). • Happens very rarely.

31. Growth Rate & Carrying Capacity • Typically, limiting factors slow the population growth rate, resulting in an S-shaped population growth curve.

32. Growth Rate & Carrying Capacity • Environmental resistance: the sum of the effects of the limiting factors in an environment.

33. Growth Rate & Carrying Capacity Carrying capacity: the population size that a community or environment can support indefinitely under a stable set of environmental conditions. • But environmental conditions do change: • An upwelling may cease • A new predator may be introduced • Climate may change • Food supplies may dwindle • A new parasite may invade the population • All of these could  population crash

34. Distribution of Organisms • Population density: the number of individuals per unit area (or volume) • In general, more benign habitats where physical factors remain near the optimum possess a greater variety of niches and a greater biodiversity, e.g. coral reefs, rain forests. • Rougher habitats are home to fewer organisms and fewer spp. of organisms, i.e. lower biodiversity, e.g. deserts, beaches. • Organisms are rarely distributed randomly throughout their habitat.

35. Distribution of Organisms • Random distribution (Fig. 16.5a, p. 395): distribution in which the position of one organism does not influence the position of another in anyway. • Implies that resources and conditions are exactly the same everywhere throughout the habitat. • Very rare in nature with possible exception of abyssal plain benthic communities.

36. Distribution of Organisms • Clumped distribution (Fig. 16.5b): distribution of organisms within a community in small, patchy aggregations, or clumps. • Occurs when conditions for growth are optimal in small areas because of physical protection (e.g. cracks in an intertidal rock), nutrient concentration (e.g. a dead body on the ocean floor), initial dispersal (e.g. near the position of a parent), or social interaction (e.g. chemical, or active defense). • The most common distribution pattern.

37. Distribution of Organisms • Clumped distribution

38. Distribution of Organisms • Uniform distribution (Fig. 16.5c): distribution of organisms within a community characterized by equal space between individuals, e.g. the arrangement of trees in an orchard. • The rarest type of distribution in nature. • Garden eel distribution approaches this pattern.

39. Distribution of Organisms • Uniform distribution (?)

40. Change in Marine Communities • Communities change over time, but marine communities generally do not evolve as rapidly as terrestrial communities.

41. Change in Marine Communities • Causes of slow change include: • Seafloor spreading • Climate cycles • Atmospheric composition • Newly evolved spp.

42. Change in Marine Communities • Community members can change the physical makeup of their environment. • The accumulation of coral and sediments on a coral reef can influence ocean current patterns, ocean temperature, and the composition of dissolved gases.

43. Change in Marine Communities • Rapid changes can occur in marine environments. • Volcanic eruptions • Landslides • Asteroid impacts

44. Change in Marine Communities • Human activities can  rapid changes • Damming a river • Dumping excess nutrients into a nearshore area • Discharging toxic wastes into ocean

45. Change in Marine Communities Define the following: • Succession • Climax community • Pioneer species

46. Change in Marine Communities • Climax community: a stable, long-established community of self-perpetuating organisms that tends not to change with time, e.g. a forest. • Severe external forces can  change in a climax community, e.g. dramatic changes in current patterns, epidemic diseases, or an influx of fresh water, or pollutants.

47. Change in Marine Communities • Once disturbed, a climax community may be reestablished through the process of succession, the orderly changes of a community’s species composition from temporary inhabitants to long-term inhabitants.

48. Change in Marine Communities • With the original community members disrupted, habitats and niches are left vacant for occupation by pioneer spp. • These spp., in turn, will alter the community, making it more suitable for other spp. to take up residence. • Eventually, the climax community may return, or a new climax community may become established.

49. Examples of Marine Communities • Rocky Intertidal • Seaweed • Sand Beach and Cobble Beach • Salt Marshes and Estuaries • Coral Reef • Open Ocean • Deep-Sea Floor • Deep Rock • Hydrothermal Vent and Cold Seep • Whale Fall

50. Rocky Intertidal Communities Intertidal zone: the marine zone between the highest high-tide point on a shoreline and the lowest low-tide point • Sometimes subdivided into four separate habitats by height above tidal datum, typically numbered 1 to 4, land to sea. • One of the most densely populated areas, despite the harsh conditions.