Download 2011, Final lecture 12 Mangroves

Pelagic Zone Summary
• Pelagic zone is a three dimensional environment with no
structure to provide shelter or landmarks for orientation
• Epipelagic organisms often possess great speed and
navigational abilities, counter-shading camouflage and
structures that improve buoyancy and aid swimming
• They also grow rapidly and often migrate long distances
• Mesopelagic species often vertically migrate daily, and
migrators are usually better muscled, can withstand large
temperature changes and possess adaptation that aid
buoyancy.
Pelagic Zone Summary
• Oxygen minimum layer selects for reduced oxygen
consumption with depth, reduced athleticism and high
oxygen binding ability in mesopelagic fishes
• Mesopelagic fishes often have large mouths, countershading camouflage, large eyes and use bioluminescence
to find mates, attract prey, and escape predators
• Deep-sea pelagic fish are often small with reduced eyes,
large mouths and are often hermaphroditic or have
parasitic males
• Deep-sea benthic fish are often muscular, with reduced
eyes, big mouths and poor swimming ability. They are
relatively large and long-lived (K-selected).
Coral Reef Summary
• Zooxanthellae are dinoflagellate mutualists that live in
the gastrodermis of hermathypic (reef building) corals
• Hard corals use zooxanthellae during the day and filter feed
at night, while soft corals are obligate filter feeders.
• Hermatypic corals with small polyps rely heavily on
zooxanthellae for nutrition, while corals with large polyps
rely more on filter feeding
• Corals reproduce asexually and sexually by mass spawning
that produces planula larvae
Coral Reef Summary
• Hermatypic corals require sunlight, clear water and warm
temperatures (min of 20 degrees C)
• Pacific coral diversity is much greater than in the Atlantic
• Three types of reefs are: fringing, barrier and atolls
• Reefs have separate zones, including the fore reef (often
with a spur and groove zone), the reef crest (sometimes
with an algal ridge) and the back reef
Coral Reef Summary
• Branching corals occur in shallow, wave swept areas and
massive, foliaceous and plating corals in deep water
• Competition for space can be intense and slower growing
corals are often more aggressive competitors for space than
faster growing corals.
• Corals use mesenterial filaments, sweeper tentacles and
immunological defenses against other corals
• Algae can often outcompete corals for space, if grazers are
not present to control algae
Coral Reef Summary
• Predation on corals can be intense, and much skeletal
material can be abraded by grazers
• Connectivity between coral reefs and adjacent seagrass
meadows and mangrove forests is often high, with many
animals using all these habitats
• Cold water (ahermatypic) corals occur globally and support
abundant fish and invertebrate life
Coral Reef Summary
• Biological interactions are intense on reefs. and there are
many examples of mutualisms
• Many animals possess antipredatory adaptations
• Many organisms abrade the coral skeleton to produce
tons of coral sand every year. The net balance between
coral reef growth and erosion is often small
• Among human threats, herbivore removal, nutrient
enrichment and disease are some of the most important
Mangrove Forests
Mangrove Forests
• Found in coastal areas all over the tropics
• Primarily in brackish water
– salty and fresh mix
• Cover approximately 22 million hectares in
tropical and subtropical coasts, and replace
salt marshes in the tropics
Ecosystem Functions & Threats
• Serve as a buffer between sea and land
–
–
–
–
Lessen impact of intense storms
Reduce erosion and increase sedimentation
Serve as important coastal pioneer species
Act as basis for a complex, biologically diverse, and
productive ecosystem
• Increasingly threatened
– Human development is most intense along coasts
Mangroves
• Not a natural taxonomic group
– Convergence among several groups
• Possibly 16 convergent events
– Based on physiological attributes
– 54 species total world-wide
• 16 Families
– Principally: Avicenniaceae & Rhizophoraceae
– These two families include 25 spp.
• 20 Genera
Mangrove Location
• Found: tropical areas only
– Within the 20ºC isocline
– More southerly on East side of continents
• Due to southward moving warm Equatorial currents there
James A. Danoff-Burg, Columbia
University, [email protected]
U.S. Mangrove Biogeography
• Mangroves around Gulf of
Mexico
- Near northern limit of
distribution
- Occur with salt marshes
• Florida has just 3 species,
while Indo-Pacific has 30-40
species
Black Mangroves on the Chandeleur
Islands
Terminology
• Mangal
– Community of organisms in the mangrove
habitat; also mangrove forest or swamp
• Mangrove
– Trees that flourish in the mangal
• Pneumatophore
– Vertical root structures for air exchange
– Lenticels - tiny pores for air exchange
– Aerenchyma – tissue for air storage and
transport
Characteristics of Mangal
• Inundation with tides
• Increasing salinity towards ocean
• Sandy clay soil
– Nutrient poor
• Nitrogen & Phosphorus are limiting
– Can limit mangrove growth. Best growth near
river mouths (Why?)
• Organic nutrients deposited via siltation
– Fresh water streams & down-shore currents
– Most all are of terrestrial origin
• In sum: Mangal is a harsh place to live
Mangrove Adaptations
• Salt tolerance
– Sequester salt in tissue (bark, stem, root)
– Secrete salt through leaves
– Exclusion by negative hydrostatic pressure
• Frequent inundation
– Aerenchyma tissue & aerial roots for dealing with
soils low in oxygen; hypoxia or anoxia
Mangrove Consequences of
Adaptations
• Greater root mass
– Relative to rest of plant & relative to nonmangrove species
– For water exchange & air exchange
• Lower growth rates
– Consequence of salt & air exchange
• Tradeoff between salt tolerance & frequent
inundation
– Can adapt for one or other, not both
U. S Mangrove Zonation
Pattern
Red Mangroves
(Rhizophora mangle)
• Seaward zone dominated by Red mangrove
- prop roots stabilize trees and are
sediment
traps and “ land builders”
Rhizophora mangle: RED MANGROVE
Red Mangrove Understory
Black Mangroves
(Avicennia germinans)
• possess pneumatophores - specialized root
extensions that penetrate from the sediments to
the atmosphere ( allow plant to respire in
waterlogged, anoxic sediments)
• Most cold tolerant
• Inshore of red mangroves
• specialized glands to excrete salt
Avicennia germinans: BLACK MANGROVE
Black Mangroves
Pneumatophores
SALT ON AVICENNIA LEAF
White Mangroves
(Laguncularia racemosa)
White Mangroves
(Laguncularia racemosa)
• The base of its leaves have two salt-excreting
glands which allow it to get rid of excess salt.
• All mangroves have trouble with cold weather
and freezes, but the white mangrove is the least
cold tolerant of the three common U.S. species
Salt glands on Laguncularia leaves
Conocarpus erectus: BUTTONWOOD
Costs of High Salt Tolerance
• Roots take up water less
freely
• Mangroves grow much
slower than other plants
• Nutrients can be limiting,
and mangroves near river
mouths grow faster than
those away from nutrient
sources
Reproduction
• Pollination by wind or
insects and birds
• Propagules
– Seeds remain on tree for
a period of time
– Seedling dispersed by
waves
– Vivipary. (e.g., red
mangrove Rhizophora)
•Red mangrove seeds
(propagules) germinate on
the tree. When they drop
from the tree they can float
for up to a year.
•Propagules are eventually
carried by the currents until
they reach shallow water
where the root end touches
bottom and sends out roots
and begins to form a new
tree.
Propagules
red
black
white
Associated Organisms
Fauna and Flora
• Bacteria/fungi: initial
litter breakdown
• Epifauna/epibionts:
sponges, hydroids, etc.mutualism w/ rootlets
• Microalgae: limited
production
• Infauna: sediments:
great diversity
• Macroalgae: hi
diversity/biomass
• Crustacea: especially
important for juvenile
shrimp
• Zooplankton: hi
abundance/diversity;
holoplankton- copepods.
meroplankton-70% of
total zooplankton.
• Molluscs: bivalves and
gastropods: detritus
breakdown and fecal
deposits
Fauna and Flora (2)
• Fish: 260 spp. in
Vietnam; up to 20
g/m2 biomass; serves
as critical “nursery”
habitat for seagrass
/coral reef spp.
• Reptiles: crocs, gators,
turtles, lizards, snakes
• Amphibians: 4 species
of marine frogs
• Birds: migratory
passerines: forage/rest:
waders/water birds:
nest/rest
• Mammals: primates
live in Indo-Pacific
mangrove forests
Roles of Mangroves
• Roots are 3-D substratum for
invertebrates
• Basis of detritus food web – leaf fall
occurs year round, greater in rainy
season
• 39% flushed to downstream bays,
lagoons and estuaries
• 60% of leaf litter consumed by
detrivores
Consumers that positively affect
mangroves
• When present, burrowing crabs (ex. fiddlers)
lead to increased production rates and growth.
Burrows aerate the sediments reducing the build
up of H2S (inhibits plant health and root
biomass)
• Oysters on roots add nutrients by depositing fecal
material on the sediments
Consumers that negatively affect
mangroves
• Burrowing isopod – decreases root growth rate
and production rate (50%)
• Barnacles – settle on surface and decrease root
and production rates
• Crab – seedling predation. Australian zonation
pattern is more a function of the crab species that
feed on the seedlings than on the physiological
tolerance or competition
Community Structure
Previously thought to be supported
predominantly by detrital food chains
Litterfall from Rhizophora
Litter and Detritus
Detritus feeders
Peat Production
• Low wave energy, depositional environments
• Primarily root material
• May be several meters thick
Odum (1970)
• Conducted study in the Florida Keys and
Everglades.
• Examined gut contents (>10,000 organisms; 120
species)
• Concluded that detritus was the major energy source
for mangrove community consumers
From Detritus to Detritus
And Not Only Leaves
Odum (1970) Revised
• Since then studies have examined stable isotope ratios
(C, N and S) as a way of tracing food source. This
technique that allows the identity of the source of
energy ingested during the lifetime of the organism
• Algae have different ratios than vascular plants. It has
been found that algal carbon is a much more
important source of energy than Odum (1970) had
concluded. Direct herbivory is also more common
that Odum concluded
Fate of Primary Production in
Mangroves and Salt Marshes
Distributional Factors
• Water and air temperature minima
• Wave action and tidal currents
• Tidal range
• Sediment type and supply
• Water chemistry
• Hurricanes
Mangroves
• Terrestrial woody trees and shrubs that
flourish in tropical estuarine habitats
• Tropical - limited by temperature
– Plants are frost intolerant
– Rarely occur outside winter 20oC isotherm
• Waterlogged soils
– Periodically inundated by tides
– Anaerobic soils
– High salt content
Mangrove Forest
• Also called mangals (and
mangrove swamps)
• Dominant intertidal plant of
tropics and subtropics, 6075% of coastline
• Many species of unrelated
trees and shrubs
• Exposed network of
intertwined roots,
branching into water and
sediment
• Roots contain terrestrial
and marine species
Mangrove distribution
Mangrove Pollination
• Pollination method varies by genus
–
–
–
–
Wind (Rhizophora)
bat or hawk moth (Sonneratia)
birds and butterflies (Bruguiera)
bees (Acanthus, Aegiceras, Avicennia,
Excoecaria, Xylocarpus)
– fruit flies (Nypa)
– other small insects (Ceriops, Kandelia)
Adaptations to High Salt Content
• Tissues have a high salt
tolerance
– Species have different
tolerances
• Exclusion of salt by
roots
• Secreting excess salt
– White mangrove