Lecture 16 Oysters and Mangroves Study Guide

Define mangrove.

A salt-tolerant intertidal tree or shrub that grows in tropical and subtropical estuaries where freshwater meets seawater.

Define mangal.

The entire mangrove ecosystem, including trees, roots, sediments, associated fauna, and microbial communities.

Define oyster spat.

A juvenile oyster that has permanently attached to a substrate, marking the start of reef formation.

Define TMII (Trait-Mediated Indirect Interaction).

An indirect effect where a predator changes prey behavior rather than reducing prey abundance.

Define DMII (Density-Mediated Indirect Interaction).

An indirect effect where a predator reduces prey population density, influencing lower trophic levels.

What is a trophic cascade?

A process where predators indirectly influence primary producers by controlling herbivores or intermediate consumers.

Explain the trophic cascade in oyster reefs.

Oyster toadfish prey on mud crabs that consume oyster spat, indirectly increasing oyster survival through top-down control.

How is the oyster reef cascade similar to marsh and seagrass cascades?

All show predators protecting foundation species by controlling herbivores—crabs in oysters, periwinkles in marshes, and grazers in seagrasses.

How does reef complexity influence predator-prey dynamics?

Complex reefs favor behavioral avoidance (TMII), while simple reefs promote direct predator mortality (DMII).

What did Grabowski's experiments show about reef complexity?

On complex reefs, mud crabs reduced feeding due to toadfish presence (TMII); on simple reefs, crabs were consumed (DMII).

Why are oysters considered foundation species?

They build reefs that support communities, filter water, stabilize sediment, and enhance shoreline resilience.

Why are cordgrass, seagrass, and mangroves also foundation species?

Each creates habitat, reduces erosion, and increases biodiversity through physical structure and primary productivity.

List common features of salt marshes, seagrasses, and mangroves.

All are intertidal, detritus-based, sediment-stabilizing, nursery habitats that provide high productivity and carbon storage.

How are these systems different in structure?

Marshes are grassy and temperate, seagrasses are submerged meadows, and mangroves are tropical intertidal forests.

List three major ecological services of oyster reefs.

Wave attenuation, shoreline stabilization, and filtration of excess nutrients and sediments.

List three ecological services of mangroves.

Storm protection, carbon storage, and nursery habitat for fish and crustaceans.

How are oyster reefs, marshes, and mangroves similar in ecological services?

All buffer coastlines, stabilize sediments, and support fisheries through habitat creation and nutrient cycling.

How do oysters improve water quality?

Each adult filters up to 50 gallons per day, removing suspended particles and excess nutrients.

What percentage of global oyster reefs has been lost?

About 85% of historical oyster reefs have been degraded or destroyed globally.

Why have oyster populations declined so dramatically?

Overharvesting, habitat destruction, disease, and eutrophication have caused widespread reef collapse.

How does eutrophication affect oysters?

Excess nutrients fuel algal blooms that reduce oxygen levels and smother reefs.

What diseases threaten oysters?

MSX (Haplosporidium nelsoni) and Dermo (Perkinsus marinus), both prevalent in high-salinity environments.

How does salinity affect oyster distribution?

Low salinity reduces feeding, while high salinity increases predation and disease pressure.

Why do oysters thrive in intermediate-salinity zones?

Moderate salinity minimizes predators and disease while supporting feeding and growth.

How does salinity variability in Louisiana benefit oysters?

Frequent changes in salinity reduce disease transmission and predation, offering a refuge effect.

What limits oyster growth in low salinity?

Osmotic stress inhibits feeding and reproduction.

What limits oysters in high salinity?

High salinity increases parasite loads and predator abundance.

Why is predation risk highest in high-salinity areas?

Marine predators like drills, crabs, and rays are more active and abundant in saline water.

Why are low-salinity areas important for oyster management?

They serve as disease refuges and natural sanctuaries during periods of high salinity or drought.

What role do mangroves play in carbon sequestration?

They store organic carbon in roots and anaerobic sediments, making them powerful blue carbon sinks.

How do mangrove roots promote biodiversity?

Their prop and pneumatophore roots provide complex habitat and refuge for juvenile fish, crabs, and mollusks.

How do mangroves compare to seagrasses in nursery function?

Both offer refuge for young marine organisms, but mangroves shelter larger juveniles due to root complexity.

How do mangroves protect coasts from storms?

Their dense roots and canopies absorb wave energy, reducing storm surge and shoreline erosion.

How does mangrove loss affect human communities?

It increases vulnerability to flooding, damages fisheries, and reduces carbon storage capacity.

What global factors contribute to mangrove decline?

Deforestation for aquaculture, agriculture, coastal development, and rising sea levels.

How do oysters and mangroves differ in geographic range?

Oysters dominate temperate estuaries; mangroves dominate tropical coasts.

How do both systems build and stabilize coastlines?

Oysters cement reefs that buffer waves, while mangroves trap sediment and build land through root accretion.

Why are both oysters and mangroves used in nature-based restoration?

They provide long-term shoreline stability, carbon capture, and habitat while being self-sustaining once established.

How does temperature constrain mangrove distribution?

Mangroves cannot survive prolonged freezing temperatures, limiting them to frost-free coasts.

How does salinity tolerance differ between mangroves and oysters?

Mangroves actively regulate salt through glands and roots, while oysters passively tolerate salinity variation.

What are pneumatophores and what do they do?

Aerial roots that protrude from mangrove sediments, allowing gas exchange in anoxic soils.

How do oyster reefs and mangroves complement one another?

Oysters reduce offshore wave energy; mangroves trap fine sediments closer to shore, creating a multi-layered defense.

How are all coastal foundation species linked ecologically?

They provide habitat, regulate nutrient flow, buffer storms, and form interconnected blue carbon ecosystems.

Compare oyster reefs to rocky intertidal communities.

Both host dense filter-feeder assemblages, but oysters dominate soft sediments and are more influenced by salinity and disease.

Compare oyster reefs to seagrasses.

Both enhance water quality and stabilize sediments, but seagrasses are photosynthetic plants while oysters are suspension-feeding animals.

Compare mangroves to marshes.

Both occupy intertidal zones and provide similar services, but mangroves dominate in warm tropical climates while marshes dominate in temperate regions.

Summarize the key similarity among oysters, mangroves, seagrasses, and marshes.

Each is built around a foundation species that structures habitat, supports biodiversity, and stabilizes the coastline.

Summarize their main ecological difference.

They differ in dominant organisms (plants vs. animals), salinity and temperature tolerance, and specific mechanisms of coastal protection.

How do all intertidal and coastal communities respond to physical stress?

All exhibit zonation driven by gradients of desiccation, temperature, salinity, and wave exposure—organisms occupy zones where they tolerate stress but can still compete effectively.

Which communities are primarily plant-based versus animal-based?

Marshes, seagrasses, and mangroves are plant-based foundation systems, while oyster reefs and rocky intertidal zones are dominated by sessile invertebrates and algae.

How do biotic interactions differ between these ecosystems?

Competition and predation dominate rocky shores and oyster reefs, while physiological tolerance and facilitation dominate marshes, seagrasses, and mangroves.

What ecological principle unites all these systems?

They are all structured by the interplay of physical stress, competition, predation, and disturbance—the same forces emphasized in the Rocky Shore Paradigm.

How does disturbance affect diversity across ecosystems?

Intermediate disturbance maintains diversity in rocky shores and oyster reefs, while excessive disturbance reduces vegetation and stability in marshes, seagrasses, and mangroves.

Which ecosystems are most tolerant of salinity fluctuations?

Oyster reefs and salt marshes tolerate broad ranges; mangroves and seagrasses have narrower ranges but adapt through physiological mechanisms like salt glands or osmoregulation.

How does the role of foundation species differ across systems?

Oysters and corals build rigid habitats; seagrasses, marshes, and mangroves stabilize sediments; rocky algae form canopy-like cover—each structures its community physically and ecologically.

Compare primary productivity among ecosystems.

Seagrasses, marshes, and mangroves have extremely high primary productivity; oyster reefs and rocky shores depend more on external organic input and benthic algae.

How does energy flow differ between plant- and animal-dominated systems?

Plant systems rely on detrital food webs and carbon export; animal systems rely on grazing and suspension feeding.

Which systems provide the strongest shoreline protection?

Mangroves and marshes buffer large-scale erosion, seagrasses stabilize sediments, and oyster reefs and rocky shores break wave energy locally.

How are these ecosystems similar in ecosystem services?

All enhance biodiversity, improve water quality, sequester carbon, and support fisheries through habitat creation and nutrient cycling.

How do successional processes differ among them?

Rocky shores and oyster reefs recover via larval colonization; marshes, seagrasses, and mangroves recolonize through vegetative growth and sediment accretion.

Which systems show the strongest top-down control?

Rocky intertidal and oyster reefs, where predators (Pisaster, toadfish) strongly regulate community structure.

Which systems are most bottom-up controlled?

Seagrasses and marshes, where light, nutrients, and sediment stability drive productivity and diversity.

How does latitude influence community type?

Mangroves dominate tropics, salt marshes dominate temperate zones, seagrasses span both, and oyster reefs occur widely in estuaries.

Compare carbon storage potential across systems.

Mangroves and marshes store vast amounts of blue carbon; seagrasses also store carbon in sediments; oyster reefs contribute primarily through shell carbonate accumulation.

What ecological role is shared by all systems?

They all act as coastal buffers, stabilizing land-water interfaces and supporting nursery habitats essential for marine life.

How does biodiversity differ between systems?

Rocky shores and oyster reefs have high species richness due to microhabitats; marshes and seagrasses have fewer dominant species but complex trophic webs.

What makes these communities interdependent?

They form connected coastal mosaics—oyster reefs protect seagrasses, which trap sediment for marshes and mangroves, linking ecosystem stability across the shoreline.

Summarize the main difference between hard- and soft-bottom communities.

Hard substrates (rocky shores, oysters) favor competition and space limitation; soft substrates (marshes, seagrasses, mangroves) favor facilitation and stress tolerance as key structuring forces.