Unit 4 – Biomes, Fresh/Salt Water Zones

Unit 4 – Part 4 Biomes, Fresh/Salt Water Zones, Coral Reefs
Topography can alter climates:
 Mountains impede progress of moisture laden wind creating the Rainshadow Effect (the moisture stays on the windward side
of the mountain leaving the leeward side dry)
 Cities can create microclimates –Urban Heat Island - retains more heat, blocks wind flow so that there is more haz,e smog,
higher temperatures, lower wind speeds, and increased precipitation than surrounding areas.
Biomes are characterized by Climate – temperature and precipitation (as shown below)
Latitude and altitude also affect climates, creating biomes in areas that wouldn’t otherwise be there.
Soils can also affect what biomes are found in some areas.
Climate Graphs (also called climatographs and climatograms) are helpful in determining what biome different geographic areas are in by
correlating precipitation amounts and yearly temperatures with known biome areas. Your textbook shows several different climate graphs
for different biomes.
Specifics about the different biomes is contained in the Biome Matching Quizzes that are done in class.
Aquatic Biomes:
2 major types: saltwater (marine), freshwater
4 major groups of organisms: plankton (photo and zoo), nekton (fish, turtules, whales), benthos (oysters, clams, flounder, crabs, crayfish,
lobster), and decomposers (bacteria)
Food webs and chains are more complex in aquatic environments
See Fig 7-3 for advantages vs disadvantages for living in water
Factors affecting organisms living in the ocean zones: temperature, sunlight penetration, DO, available nutrients
Ocean Zones:
Fresh Water Zones:
Oxygen and nutrients are cycled during spring and fall with vertical mixing – otherwise the zones are stratified (no mixing during winter
or summer due to greater temperature differences)
Describe the amount of each factor (Temp, light, amt sunlight, DO conc., and amt nutrients) found in each zone for both oceans and
Know the major ecological and economic services provided by marine systems (Fig 7-5)
Even though there is adequate light for photosynthesis in the euphotic zone there is little photosynthesis in open ocean due to lack of
nutrients. Most nutrients are found near the shoreline along the continental shelf.
Estuaries contain brackish water (both fresh and salt water) because they are the area that connects both waters.
Refer to Fig 7-13 and 7-14 for ways in which man’s (anthropogenic) activities are causing destruction of coral reefs and marine
Freshwater zones of a lake:
The deepest lake in the world is Lake Baikal in Russia. It is where 2 lithospheric plates are diverging. Thus it is increasing in size each
year. The depth of the lake is over 5,000 ft deep
During the summer and winter, the water in deep temperate zone lakes becomes stratified due to the temperature difference. In the fall and
spring the layers mix during overturns that equalize the temperature at all depths. The overturns bring nutrients up from the bottom as
well as bring oxygen down to the bottom.
Know the difference between oligotrophic, eutrophic, and mesotrophic as it applies to lakes
Know the different types of inland wetlands and functions.
Also know what is meant by wetland mitigation
Coral Reef Notes
Coral reefs can live only in a delicate, balanced marine environment.
They require lots of light and oxygen, clear water, low nitrates and phosphates, a steady temperature, salinity.
Methods of destruction of coral reefs:
 Deforestation (causing sedimentation, fertilizer runoff, etc smothering coral or causing eutrophication that uses up the DO)
 fishing methods (dynamite, cyanide)
 overfishing (less grouper increases the number of damselfish that eat the algae on the coral but create holes. The algae then
proliferate because you can’t get to them in the holes and eventually smother the coral)
 pollution (petroleum, fertilizer from phosphate mining, other chemicals)
 careless recreation (damage from anchors and tourists)
 nutrient runoff (eutrophication from fertilizers and municipal waste plus increase of ‘crown of thorns’ starfish - due to their
favorite food- that decimate reef)
Zooxanthellae algae allow hard corals to build their stony homes by assisting them in the production of calcium carbonate (a mutualistic
symbiotic relationship). They are the most common algae found in coral reefs
Coral reefs exist from the sea surface to as deep as 100 meters below. Growth is highest near the surface
Most coral species require temperatures between 18 and 30 degrees Celsius. A warming of 1 degree to 2 degrees C appears enough to
stress the coral and result in bleaching..
When ocean temperatures increase, coral bleaching (loss of zooxanthellae algae) occurs. The coral turn white and dies. Coral bleaching
happens when the zooxanthellae algae are expelled from the coral polyps.
Causes of bleaching:
 global warming
 El Nino events
 increased UV from decreased stratospheric ozone
Atmospheric CO2 dissolved in water produces carbonic acid that holds the carbonate ion. By holding more carbonate ions the coral can’t
produce as much calcium carbonate.
Coral can live in waters from the surface down to 100 meters. They only grow .5- 2.8 cm a year.
When the Red Sea coral began to die, scientists looked for possible reasons—volcanic dust's smothering the coral, presence of hydrogen
sulfide (H2S), disease, or some combination of causes. When scientists measured water temperatures, though, they found cold water
mixed very thoroughly to great depths. (Cold water is usually found very deep with warmer water near the surface.) Here's what had
happened: The unusually cold surface water had sunk, helping to mix the water column. This helped to also mix nutrients (like
phosphorous) that normally stay deep in the cold water to near the water's surface. This resulted in the growth of thick, red algal blooms.
They are thought to have smothered the coral, blocking out the sunlight. When temperatures returned to normal, the algal blooms died
because they no longer had the nutrients they needed. The reefs were soon healthy again.
This simulation begins 21,000 years ago, at the end of the last ice age. Over time, the continental shelfs flooded, thus creating more
habitat for coral reefs, which flourished. The animation shows the temporal and coral-form evolution of the reef over time. Corals play an
important role in the carbon cycle and there are quite a number of interesting ideas about possible roles they may have played in the
global climate. One hypothesis is that shallow-water carbonate systems may have accounted for a big change of the CO2 seen in ice cores,
corresponding to the period since the last ice age. There is also the possibility of a positive feedback loop: sea-level rises providing more
habitat for coral reefs, the reefs flourish and produce more CO2, the additional CO2 causes additional temperature increase and sea-levels
rise even more. It is an interesting point that coral reefs were once an important source of CO2 released into the atmosphere, but now
they account for only 1-2% of human-generated CO2. In any event, one of the ideas central to this work is that if we can successfully
simulate how reefs grew since the last ice age, we may be able to predict their evolution in the context of global change.
Coral reefs may all smell the same to humans. But to some fish, reefs’ smells have distinct qualities — even when they’re several hundred
miles away.
A new study in the Proceedings of the National Academy of Sciences argues that some reef fish use smelly ocean currents the way New
Yorkers use their subway lines — as the quickest way home.
Scientists have long known that salmon smell their way back to their birth streams, but until now, nobody knew that reef fish did it, too.
In one experiment, the team put cardinal fish larvae into the aquatic equivalent of a subway station. It allowed the fish to chose between
two water trains, one of which was from their home reef. Almost every time, the larvae jumped into the stream that smelled like home,
even when the researchers tried to trick them by switching the odor around.
But the study has attracted critics. They say one big problem is that the chemcial compounds that might be creating the odors are never
But evoluntionary biologist Richard Zimmer of the University of California at Los Angeles says the study raises some intriguing
possibilties. For instance, if these smelly currents turn out to exist, they could be used to lure fish back to reefs that are facing all kinds of
Coral reefs are unique ocean ecosystems in that they have extremely high productivity and diversity, yet they occur in a virtual desert of
organic nutrients. Coral reefs are composed of species that are highly evolved and specialized. This specialization has traditionally been
explained by niche diversification as a result of past competition among previous species requiring similar resources. Clearly, the coral
reef environment must have an affect upon its inhabitants, but the question remains as to the strength of these effects in shaping the
evolution of coral reef fish species.
To avoid predation, coral reef fishes require refuge from predation. This refuge may be provided by the physical makeup of the reef itself,
or through behavioral adaptations of coral reef fishes to reduce their individual threat of being consumed (schooling). The specific
requirements of individual species for refuge space on the reef has been shown to be highly variable among species, with few species
requiring the same resources.
Larval Ecology
Most coral reef fishes have a pelagic, usually larval, stage resulting in a life history with two distinct and very different phases. These
stages differ in almost all characteristics, from morphology to size, habitat, food, and behavior. The duration of the pelagic stage is species
dependent, flexible, and ranges from 9 to well over 100 days.
Coral reef fishes are very fecund, with egg production from 10,000 to over 1,000,000 per female but mortality approaches 100%, with the
majority of the mortality taking place during the pelagic stage. Reef fish larvae eat a wide variety of microzooplankton During their
pelagic stages, reef fishes may be consumed by a wide variety of predators, including corals, pelagic cnidarians and ctenophores, other
larval fishes, and both reef and coastal pelagic adult fishes. The majority of coral reef fish larvae move away from the immediate vicinity
of their natal reef some distance into more open water.
Settlement and Recruitment Ecology
Since coral reefs are patchy habitats and reef fishes are generally sedentary, the only significant recruitment to local reef fish populations
comes form the settlement of planktonic larvae. The intensity of settlement of coral reef fish is variable both during and between seasons.
In more temperate areas, such as One Tree Island on the Great Barrier Reef, this variable is intense, with virtually all settlement occurring
during the summer. An explanation for seasonal cycles of settlement in tropical reef fishes is that settlement cycles simply reflect the
varying breeding capabilities of adults, where seasonal energy surpluses could lead to higher fecundities.
Daily fluctuation in numbers of new recruits have been reported to occur both on lunar cycles. Movement of larvae inshore around the
time of the new moon may help larval survival as the larvae would be passing over reefs on the darkest nights of the month, and tidal
cycles occurring at the new moon may assist inshore migration. The tendency to settle near the time of the new moon may be an
adaptation to reduce visual predation on incoming fish larvae by nocturnal planktivores. .
Interspecific Interactions In the early evolution of our understanding of coral reef fish ecology, interspecific interactions among resident
fishes was used to explain observed patterns in assemblage structure, with emphasis placed on competitive interactions.
Competition: Studies done in the Great Barrier Reef, the Caribbean, and other locations at a wide range of spatial scales, from
microhabitat to much broader geographic scales, invoked competitive interactions. Two closely related species of blennys,
Acanthemblemaria spinosa and A. asperi, compete for the suitable shelter sites, (vacant tube worm holes). A. spinosa, which was shown
to have a higher metabolism, is competitively superior in securing the sites which have the greatest access to planktonic food drifting by,
relegating A. asperi, which has a slower metabolism and lower feeding requirements, to lower sites with less food availability. This study,
which has been mostly ignored by coral reef fish ecologists, provides pretty convincing evidence for niche partitioning.
Lottery Competition for Territories: Evidence suggests that availability of living sites limits the populations of coral reef fishes, with
similar species of fish competing for limited space on the reef. This competition is continuous, yet unlikely to lead to either niche
diversification or competitive exclusion.. Once a fish is in a territory, its optimal strategy for reproductive success would be to stay put,
breed often, and disperse the resulting offspring widely. This strategy would allow an individual to maximize its chances of getting
offspring into suitable living sites as such sites appear. The ‘lottery’ is among newly arriving recruits with similar space requirements,
which enter a lottery for occupying available sites. Once a larvae arrives, it secures its position within the community and should be able
to defend the site against latecomers.
Predation: The risk of predation on coral reefs is great and reef fishes have evolved a variety of mechanisms to minimize the risk.
Piscivorous (fish that eat other fish) reef fishes are diverse in behavior as well as taxonomy, and can be divided into five major categories:
(1) open-water species that pursue their prey, such as jacks; (2) cryptic species that ambush their prey, such as lizardfishes; (3) species
that apparently habituate prey to an illusion that they are nonpredatory, such as groupers and snappers; (4) species that slowly stalk their
prey, such as trumpetfishes; and (5) species that attack prey within crevices, such as moray eels. In addition, a considerable host of
invertebrate and tetrapod piscivores also occur on coral reefs, including anemones, cone snails, mantis shrimps, seastars, seasnakes, and
seabirds. Prey minimize their risk of predation in a number of ways. Various morphological deterrents include tough skins, fin spines,
exceptionally deep bodies, the ability to inflate, swimming abilities, mucous envelopes, cryptic coloration, eyespots, conspicuous
"warning" coloration, toxins and venomous bites. Prey fish also avoid predation through various behavioral patterns including schooling,
spawning, and daily activity patterns. Two direct predictions are that in the absence of piscivores, the density of prey fish occupying a
particular reef would reach a limit imposed by other processes, such as recruitment limitation or competition. Local prey species richness
and/or evenness should shift in predictable ways as predation intensity increases over a broad range.