Lecture 14 Mangroves and Oysters

What are mangroves?

Tropical, intertidal semi-terrestrial plants that tolerate seawater.

What is a mangal?

Depositional, land building environments where mangroves reside

What are oyster spat?

Oyster larvae that permanently attach to a surface.

What is TMII?

Predator effects on prey traits rather than prey density.

What is DMII?

Changes in the density of one species indirectly affecting another species through modifications in shared resources or interactions with mutual species.

What are trophic cascades in oyster reefs?

toad fish --> mud crabs --> oyster junvenille/spat (fish may indirectly facilitate spat)

Toadfish eat mud crabs which eat juvenile oysters, so toadfish indirectly help juvenile oysters by causing the mud crabs to hide so juvenile oyster populations don't decrease.

How do simple reef cascade differ from complex reef cascade

• Simple reef cascade → Density-mediated indirect interaction (DMII): Toadfish reduce mud crab numbers, leading to lower predation on oyster spat.

• Complex reef cascade → Behaviorally mediated indirect interaction (BMII): Toadfish presence alters mud crab behavior, reducing foraging on oyster spat even if crab density remains the same.

When there is no mud crabs (when there is toadfish and where there is not toadfish), oyster mortality is ____

Mud crabs and No Toadfish, oyster mortality is the ____.

Add both mud crabs and toadish, oyster mortality isn’t ____ but it goes way ____ (compared to no toadfish)

When there is no mud crabs (when there is toadfish and where there is not toadfish), oyster mortality is ~0%

Mud crabs and No Toadfish, oyster mortality is the highest.

Add both mud crabs and toadish, oyster mortality isn’t 0% but it goes way down (compared to no toadfish)

Complex oyster reefs have ___ oyster mortality compared to simple reefs

why

lower

easier to hide, reduce impact of wave action, more balanced food web, better larval settlement

What are some common characteristics of salt marshes, mangroves, and seagrass beds?

A) Decrease local diversity
B) Foundation species enhancing abundance and species richness of nekton
C) Serving as nurseries to nekton
D) Decrease survival of juvenile nekton
E) Detrital-based food webs
F) Carbon Sink

B, C, E, F,

Detrital based food webs (dead organic material primary energy source)

foundation species enhancing abundance and species richness of nekton and benthic invertebrates

serving as nurseries to nekton

carbon sink

What ecological services do oyster reefs provide?

Wave breaks

habitat for commensal organisms

water filtration

How does variation in salinity and predation risk affect oyster distributions?

High vs Low

Salinity and predation risk can limit oyster distributions in estuaries.

• They can’t go further up the bay because it is not salty (salinity of <5)

  • 10-25 PSU is the ideal salinity

• In higher range (below the bay) like 30, there are more predators and disease which prevent them from traveling up the coast
  
  •Low salinity (10-25 PSU) provides refuge from predators and disease-causing microbes

What factors affect the distribution of oysters in estuaries?

Salinity and predation risk.

What limits oysters in low salinity?

Low salinity can limit oysters in estuaries.

What limits oysters in high salinity?

High salinity can limit oysters in estuaries.

How are oyster reefs similar to seagrasses, marshes, and mangroves?

They provide similar ecological services such as

wave breaks

habitat provision

water filtration.

What do oysters do?

Oysters function as

wave breaks

provide habitat for commensal organisms

filter water.

How do oyster reefs reduce erosion?

Intertidal oyster reefs function as a barrier that breaks up wave action, reducing erosion.

What is the impact of oyster reefs on fisheries?

Oyster reefs enhance fisheries by providing habitat for diverse fish assemblages.

How do oysters contribute to water filtration?

Oysters filter feed on plankton, reducing eutrophication and filtering nutrients and phytoplankton.

What is the effect of eutrophication?

Algal blooms, hypoxia, and anoxia-fatal to many benthic inverts

What are the consequences of hypoxia and anoxia?

Fatal to many benthic invertebrates

What happens to copepods and microzooplankton with eutrophication?

Increases in copepods and microzooplankton

What are the threats to oyster reefs?

Overharvesting, disease, non-native species, toxins, fertilizer runoff, alterations in freshwater flow

What is the correlation between infection rate and temperature and salinity?

Infection rate correlates positively with temperature and salinity

What provides refuge from predators and disease-causing microbes for oysters?

Low salinity

What is RSP?

Refuge from predators and disease based on salinity

What is the relationship between larvae settlement and adult oyster presence?

Larvae prefer to settle where adults are

What is the competition between bivalves like?

Thought to be low, but hard to test due to many species growing on and between oysters

What is the role of predators in affecting oyster distributions?

Predators are important, especially with regard to salinity and intertidal/subtidal zones

What happens to oysters during disturbances?

They can get buried, which is detrimental to their survival

What is the indirect facilitation of oyster spat?

Oyster toadfish and mud crabs indirectly facilitate oyster spat

What is the mortality rate of mud crabs on simple reefs?

Most mortality of mud crabs on simple reefs is direct

Where are oysters typically found?

A) In rocky coastal areas, where they require stable, warm temperatures and high salinity
B) In freshwater lakes, where they thrive in low salinity and colder waters
C) In sand and mud, in estuarine environments, and can tolerate a wide range of temperatures
D) In deep oceanic trenches, attached to cliffs with extreme temperature fluctuations
E) In shallow coral reefs, where they are exposed to high salinity and fluctuating temperatures

C) In sand and mud, in estuarine environments, and can tolerate a wide range of temperatures

how does oyster reefs compare to rocky shore paradigm

• space

• monopoly

• tolerance

• disturbance

• predation

• space can be limiting, but not as limiting compared to RI

• No competitive monopoly

• predators important, but they DO NOT suppress competitive monopoly

• disturbances are negative (can bury oysters), so NO IDH

• There is a tolerance refuge, but they DO NOT suppress competitive monopoly

What are services provided by mangroves

protect coastlines

filter water

regulate climate

home to fishes

provide wave breaks

What are mangroves

A) Tropical, intertidal semi-terrestrial plants (shrub to tree size) that tolerate seawater
B) Intertidal, sediment-stabilizing grasslands dominated by halophytic vegetation
C) Subtidal, reef-forming mollusks that create three-dimensional habitat
D) Intertidal, hard-substrate ecosystems influenced by wave action and tidal exposure
E) Tropical, intertidal coral colonies that build reef structures

A. Tropical, intertidal semi-terrestrial plants (shrub to tree size) that tolerate seawater

where are mangroves found and why

A) Tropical and subtropical estuaries
B) Behind coral reefs
C) Open oceanic deep waters
D) Arctic coastal regions
E) Freshwater riverbanks

Found in estuaries and behind reefs

These areas provide sheltered, nutrient-rich environments with low wave action, allowing mangroves to tolerate saline water and flooding, and anchor their complex root systems.

Threats to mangroves

agriculture

aquaculture

coastal development

climate change

pollution

logging

Trophic Cascades _____ in Mangroves

Uncommon

What drives mangrove zonation?

Zonation is driven by tolerance (flooding) to inundation and salt tolerance.

How do hammock plants affect mangrove ecology?

Hammock plants are competitively dominant but not salt-tolerant, outcompeting salt-tolerant species in areas with lower salinity.

What is the effect of disturbances on mangroves?

Disturbances have a negative impact on mangroves, but there is no Intermediate Disturbance Hypothesis (IDH) effect.

How does tolerance influence mangrove distribution in marshes?

Tolerance to salt and flooding is crucial for mangrove survival.

Hammock plants, which are competitively dominant but salt-sensitive, inhabit higher elevations where mangroves cannot thrive.

In contrast, red mangroves dominate in lower elevation (their specific zones) because they are the only plants that can tolerate the conditions in those areas.

Where do hammock plants reside in mangroves

Hammock plants, which are competitively dominant but salt-sensitive, inhabit higher elevations where mangroves cannot thrive.

Where do red mangroves reside in mangroves

In contrast, red mangroves dominate in lower elevation (their specific zones) because they are the only plants that can tolerate the conditions in those areas.

How does RSP compare to mangroves

• space

• no competitive monopoly forms

• Disturbance

• Predation

• Tolerance

• space is not limited

• no competitive monopoly forms

• disturbances are negative, so there is no IDH

• Seed predation is more significant in mangroves, affecting seedling establishment. However, adult mangroves are less affected by predators, as they are larger and more resistant.

• There is a tolerance refuge

Compare Mangroves to Oysters

Similar

Different

similar:

no IDH for either, predation important, both provide water filtration and habitat for organisms

differences:

oyster reefs are space limited to an extent, competition is low impact

mangroves have zonation based on inundation