Grass beds, reef-kelp forests systems, and coral reefs
Most productive subtidal benthic environments. Dominated by highly active benthic primary producers, which are important not only to fixing carbon, but also in contributing to the structural habitat and providing a substrate for organisms.
Sea Grass Beds
Widespread in shallow water soft sediments. Important foundation species. High primary productivity and structure results a very diverse habitat, providing food and shelter for benthic invertebrates, mobile bottom invertebrates, and fishes.
marine angiosperms, or flowering plants, that are confined to shallow water and extend mainly by subsurface rhizome systems within the sediment
How do sea grasses dominate communities?
Their subsurface structure, upright posture above the sediment surface, and current baffling combine to influence hydrodynamic conditions, microhabitat structure, and food supply within the bed.
A root network within the sediment, capable of taking up nutrients. Grows and extends laterally and sends up shoots. Takes up nutrients mainly from pore waters in sediments. Requires resources to maintain, which may be a problem in low light conditions.
Alternate Reproduction of Sea Grasses
Although sea grasses can extend by means of rhizomes they are, however, flowering plants, and pollen moves between plants in the water currents.
Flowering Vs. Asexual
Population spread by flowering is less important in sea grasses, which appear to reproduce more by asexual spread, through the rhizome system
Colonization of new areas by seedlings is difficult unless the sediment is already physically stable and rich in dissolved nutrients. This can be accomplished by the presence of other plants, such as seaweeds, which stabilize the sediments and add nutrients in forms such as ammonium
Sequence of Colonization
The bare sand goes through turbulent re-suspension. This leads to release of ammonia which promotes seaweed growth that stabilizes the sediment and immobilizes the nutrients. Fleshy epiphytes that grow on leaves decompose and add to the increase in organic matter, sediment nutrients, sediment decomposition, and oxidation. This leads to nutrient regeneration and the growth of sea grasses like Thalassia grass.
Sea grass bed and the marine environment
Sea grass beds reduce current flow, deter the entry of some predators, and may enhance the growth and abundance of infaunal suspension feeders.
Decline of Grazing
Today, grazing is probably reduced in many tropical sea grass beds because major grazers such as the green turtle are missing.
have extended hindguts with a microbiota that is adapted to digesting plant material. The turtle specialize on either high cellulose grass or low cellulose seaweeds
Lack of grazing in higher latitudes
Has a parallel in fish: herbivorous fish are far less frequent in higher latitudes than in the tropics. In warmer waters such as the caribbean and the mediterranean, fish grazing has a major impact on sea grass abundance. It may be that the nitrogen content determines the degree of herbivory.
Horizontal Interaction between eelgrass and seaweeds
If seaweeds are allowed to proliferate, they will overgrow and shade out the eelgrass.
What Dynamic processes produce dominance by seaweeds over sea grasses
Nutrient addition and reduction of suspension feeders
Seaweeds tend to respond much more than eelgrass to increased nutrients. Therefore, in areas adjacent to human habitation, sea grass tends to contain dense growths of rapidly growing seaweeds. Nutrients tend to increase the growth of epiphytes directly on sea grass blades
Reduction of suspension feeders
This might cause local increases in phytoplankton in sea grass beds, which might shade them out and favor seaweeds. Over-harvesting of suspension feeding oysters and other bivalves and the increasing occurrence of nuisance phytoplankton blooms have caused drastic reductions of suspension feed bivalves such as scallops, clams, and mussels.
Importance of Predation in sea grass beds
Predation on animals is clearly a major organizing force on the relative abundance of species in sea grass beds.
A pinfish visual predator that preys on small grazers such as amphipods. It prefers species that are mobile and aggregated. Amphipods and other mobile small crustaceans can hide among sea grass blades, preferably wide bladed sea grasses such as turtle grass.
Decline of sea grasses
Sea grass is otherwise declining at this time, especially in the Caribbean and Atlantic. Due to nutrients from sewage increasing phytoplankton density and decreasing the amount of light that can reach the bottom
Decline of sea grasses are due to
increased fishing reducing the amount of grazing on the epiphytes that live on the blades. Overfishing of top carnivores , and human disturbance from dredging and boat propellers also exert strong negative effects on sea grasses.
Rocky Reef-Kelp Forest system
In many instances these two habitats are part of one system, strongly interlinked by common top predators, grazers, transport of plant detritus, and even species occurrences.
Dominated by brown seaweeds of the group Laminariales. Found throughout the world in shallow open coastal waters. Photosynthesis restrictions are the reasons why kelps are found rarely in waters much deeper than 5-15m. Although they may grow to 25m.
Larger Kelp Forests
restricted to temperatures less than 20ºC, extending to both the Arctic and Antarctic circle.
kelp species widespread and occur in the west coast of North America, Australia, New Zealand, and both coasts of South America and South Africa.
smaller species extend the range of kelp forests to Alaska and the northwestern Atlantic.
There is far more diversity of kelps in the pacific basin than in the Atlantic. Differ in size, and growth rate, so the forests actually range form beds of relatively simple single bladed seaweeds of few meters depths, as in the Atlantic Laminaria beds of Nova Scotia, to wast stands of plants that extend from holdfast on the deep bottoms to stipes and blades floating at the surface as in the Macrocytis beds of the pacific coasts.
Life cycle of kelps
complex. alternates between a large asexual sporophyte to a tiny filamentous gametophyte.
Structure of Kelps
The sporophyte is the "kelp", which consists of a holdfast for attachment to the bottom, a stipe, which looks much like a stem and is strong and flexible, and a leaf like blade, the main site for photosynthesis.
Species Kelp forests support
Sea urchins, blue mussels, abalones, limpets.
Associated with kelp forests, the sea otter is a major predator on sea urchins, mollusks, and fish. They are also a top-down driving force of trophic cascade in eastern pacific kelp communities. Otters, therefore control the pattern of macroalgal productivity, by mediating the herbivore trophic level.
Factors affect kelp communities
Trophic structure is strongly affected by extrinsic factors, such as storms, and intrinsic factors, such as switches of sea urchin behavior.
Trophic Structure Of Kelp Communities
Sea otters sit atop, they prey upon urchins and abalones, the principal grazers in the system.
Shifted their feed preferences to sea otters, probably because of a precipitous decline in alternative prey pinnipeds, including harbor seals and sea lions.
Reorganization of Northern Pacific ecosystem
Is because of the increase in sea surface temperature over the pas few decades and strong fishery pressure in the North Pacific.
Succession in Alaska
In the initial stages of succession, occupation of many layers above the bottom and rapid colonization tended to increase greatly of algal species. However, in the end Laminaria came to dominate and reduce kelp species diversity.
Why does Laminaria species have no graze defenses?
It may be that their extremely rapid growth reflects devotion of resources to escaping predation by a strategy of rapid colonization, growth, and reproduction.
Macrocystis (graze defenses)
Height at full grown
found in the Pacific kelp forests, synthesizes sulfuric acid, which discourages grazing.
has high concentrations of polyphenolics, which discourage urchins from chewing on the fronds.
are consititutional wave resistant features, which are built by a variety of species and are often cemented together. The growth of these structures is aided by zooxanthellae, algae that are symbiotic with the reef building corals.
Includes coralline algae, sponges, and other organisms. They provide the matrix for the growing reef. May precipitate silica.
due to some members of the calcium carbonate secreting group Scleractinia. While some species are solitary and consist of a single polyp and skeleton, most are colonial and consist of hundreds to thousands of polyps that are interconnected by living tissue
Corals that have large numbers of zooxanthellae and calcify at high rates.
Mound shaped and often irregular. They tend to grow slowly, not usually increasing in any linear dimension much more than one centimeter per year.
Usually have either tree-branch forms, or elkhorn shapes. They tend to grow rapidly, on the order of 10cm/yr. The more rapid linear growth sometimes allows branching corals to spread rapidly on the reef.
Overall it is clear that Indo-Pacific reefs are more species rich that Caribbean reefs.
Indo-Pacific biodiversity of many group is greatest in a center of diversity in the area of Thailand, the Philippines, and Indonesia.
specialized single celled algae, and are dinoflagellates that live intracellularly within membrane lined vacuoles in the endodermal tissues of scleractinian corals. They lack the typical biflagellated form of free-living dinoflagellates and are coccoid. They are concentrated in the tentacles.
when stressed, corals appear to expel their zooxanthellae. Bleaching has been observed when corals are diseased, and when temperatures are high.
Benefits of Zooxanthellae
protection from grazing and access to nutrients derived from coral excretion.
Benefits of Corals
1.) Removal of excretory products
2.) Oxygen via photosynthesis
3.) Carbohydrates that can be used for coral nutrition.
4.) enhancement of coral calcification
5.) Aid in synthesis of lipids.
Mechanism of Nutrient uptake
It may be that zooxanthellae take up nitrogen and reduce the overall concentration in coral tissues, creating a concentration gradient that stimulates the further uptake of nitrogen, either actively or passively by diffusion.
Mechanism of calcification
Calcium uptake is greater when hermatypic corals are exposed to light. By removal of carbon dioxide, zooxanthellae may shift the carbonate-bicarbonate carbon dioxide interactions toward conditions favorable for calcium carbonate secretion. Zooxanthellae may also enhance calcification by removing phosphate, which inhibits calcification, or by aiding in the secretion of the organic matrix upon which calcium carbonate is deposited.
Limiting Factors (Light)
Reefs are rarely found in tropical estuaries. Next to temperature, light is probably the most important limiting factor to well developed coral reefs because of the symbiosis with zooxanthellae.
Mycosporine-like amino acids
found in several species, which appear to protect the zooxanthellae from ultraviolet light damage.
Limiting factors (turbidity)
Turbidity and sedimentation both have adverse effects on reef building corals. Turbid waters intercept light and reduce photosynthesis possible. Sedimentation tends to smother coral colonies and inhibit feeding and the extension of the polyps' crowns of tentacles. Blankets of sedimentation may also encourage bacteria growth.
Many species of invertebrates bore into coral skeletons. Parrot dish and surgeonfish rasp away at coral surfaces, and urchins enlarge crevices and bore into colony bases.
Types of Coral reefs
Coral reefs can be divided into atolls and coastal reefs
Horseshoe or ring shaped island chains that cap an oceanic island of volcanic origin. They are open-ocean structures, not usually found near a continental coast. Charles Darwin reasoned that atolls developed when coral grew upward from the top of a sinking volcano on the sea floor.
Usually resides in a stable wind system. The side facing the winds, the windward side, is usually strongly affected by wave action. Corals facing the sea do not grow very well, and a red algal ridge usually accumulates on the seaward side of a broad reef flat. The ridge is caused by algal precipitation of calcium carbonate and trapping of sediment by coralline red algae.
a major feature of coral reefs, these zones are dominated by different species. Factors that determine dominance include: wave and current strength, light, and suspended sediment.
Protected by intertidal reef flats, it has a soft sediment bottom and is dominated by sea grasses, urchins, sea cucumbers, and sparse corals and sea whips.
the mean time that water and entrained larvae and phytoplankton are maintained in the bay.
Flushing Time (Specifics)
If flushing time is short, then larvae and phytoplankton will be mainly flushed out and larval settlement will be poor. But if flushing time is great, then larvae will build up and settle in great densities.
Spartina salt marshes
develop in tidal areas of quiet water, where a variety of salt-tolerant grasses colonize the sediment and then trap fine sediment.
located beneath the sediment surface, it is crucial in maintaining the structure of the marsh sediment and the entire salt marsh.
How salt marshes live in anoxic environments
a cross section of the plants shows the large amount of open space near the surface, which is devoted to air and oxygen transport. Plants cannot use nutrients efficiently without oxygen, so this tissue allows a connection between the aerobic leaves to the stems, which are surrounded usually by anoxic water.
Important of Rhizome system
The rhizomes take up nutrients, but they are also the means by which the plants extend their coverage. Rhizomes extend laterally, and shoots grow above the surface. The asexual spread of the rhizome is usually the major form of local spread.
Spartina salt marshes are excellent examples of the ecosystem engineers concept, where one or a few species create a structural habitat upon which many other species depend.
rich nursery grounds for juvenile crustaceans and fishes
from the low water mark in a tidal creek to the terrestrial environment.
Competition in salt marshes
It is a major determinant of salt marsh plant dominance, but it works in reverse of dominance of invertebrate competition on rocky shores. These plants tolerate salt, but the environment is more physiologically stressful as you go lower in the intertidal, because of lowered oxygen in the sediment, and high salt content of water and pore waters. Spartina alterniflora predominates in the low zone partially because of its superior ability to survive in these stresses. In high zones plants are good competitors because of their ability to produce a dense rhizome system, which outcompetes other species for space and nutrients.
tropical and subtropical in distribution, over 80 magrove species. Growth in lower latitudes are continuous. Rich in marine and terrestrial animal life. Large numbers of falling leaves provide a continual source of detrial material
Mangrove Forests (location)
found along quiet water tropical and subtropical marine coasts in water temperatures greater than 20ºC, but no less than 16ºC .
Mangrove forests are dominated by
shrub or or tree-like mangroves, which are rooted in anoxic muddy sediment that is waterlogged with seawater. They greatly decrease wave energy of shorelines of which they live.
high concentrations in mangrove tissues, helps protect against bacterial invasion
Mangrove root system
usually broadly rooted but only to a shallow depth. Their root system is adapted to the anoxic sediment, and all mangrove species have root extensions that project into the air so that the underground parts of the plant root system can obtain oxygen
surface sediment layer that is high in salt content
Mechanisms for excluding salt in Mangroves
One group of species have salt glands that secrete salt from leaves. In another group of species roots are capable of reducing salt uptake to a degree by an ultrafiltration system. A membrane bound ion channel that can exchange H+ for Na+ accomplishes this.
are rich in invertebrate populations, have high primary productivity, and high supply of particulate organic matter from falling leaves which subsidize animal growth.
environments where oceanic seawater mixes with freshwater input from a discrete source such as a river.
Biological importance of estuaries
Estuaries are among the biologically riches habitats in the world. Supplies of nutrients from freshwater sources and recycling of nutrients from the seabeds combine to support high levels of primary production, which in turn supports large numbers of estuarine benthic invertebrates, fishes, plants, and birds.
the most noticeable gradient in an estuary is that of decreasing salinity as one goes upstream. Tolerance is often exceeded when salinity falls below 10-15 psu
Salinity Transitions I
In estuaries with some degree of vertical density stratification, the salinity is greater on the bottom than at the surface, where freshwater flow moves lower-salinity water downstream. As a result, bottom animals can often penetrate an estuary farther upstream than surface planktonic organisms can.
Salinity Transitions II
The second major salinity is the critical salinity range of 3-8 psu. Many marine groups apparently find it hard to survive in this salinity range, even though many other species are capable of living either in fully fresh water or in waters of higher salinity.
Critical Salinity range (reasons why marine species can't survive)
Mollusks may be incapable of cell volume regulation at salinities this low. Freshwater species, however, can regulate ionic concentrations and maintain a hyperosmotic state. They have lost the ability to regulate cell volume, however, and, therefore, cannot penetrate even the low salinities of the critical salinity range.
Critical Salinity range (reasons why fresh water species can survive)
Many fresh water species are capable of rapid regulation and adjustment to the changing osmotic stress of varying salinity. Stripped bass, salmon, and killfish are just a few examples of fishes that migrate from completely saline water to freshwater in a few weeks or even days.