Marine Life Cycles
Spawning and Environmental Cues
A water temperature above degrees Fahrenheit often triggers spawning in various marine species.
During spawning, rivers can appear milky due to the high concentration of sperm and eggs.
Fertilization leads to larval development and dispersal.
Fisheries and Ecology
Spawning aggregations attract fishermen, creating a meeting point between ecology and economy.
Striped bass migrate to canals and estuaries to spawn in late spring and then return to the ocean.
Fishing during spawning season can be highly productive due to the high density of fish.
Striped bass can mate year after year.
Bipartite Life Cycles
Bipartite life cycles involve an adult stage and a larval stage in the plankton.
This type of life cycle is the norm for the majority of marine animals.
Direct development, like in humans, is an exception in the ocean.
Some marine plants, such as kelp, also exhibit bipartite life cycles with spore dispersal.
Challenges in Bipartite Life Cycles
Bipartite life cycles are complex and challenging, with many obstacles at each stage.
Larval forms often look very different from their adult forms, such as in blue crabs and lobsters.
Larval shrimp undergo multiple metamorphic stages and are vulnerable during molting.
Larvae face risks such as predation, starvation, unfavorable environmental conditions (wrong salinity, wrong temperature, lack of oxygen).
Oyster Life Cycle and Hatcheries
Oysters are sessile and release sperm and eggs into the water for spawning.
Oyster larvae are plantotrophic and require a constant food supply.
Oyster hatcheries must provide suitable food for the larvae to thrive.
Larvae need to settle on a hard substrate, like a rock, to survive.
Oyster Seed Holdings and Hatchery Operations
Oyster Seed Holdings is a shellfish hatchery company that spawns adult oysters and grows them to a size suitable for oyster farmers.
Hatcheries can manipulate environmental conditions to induce spawning outside of the natural spawning season (June-August).
Microalgae are grown in large quantities to feed the broodstock and larvae.
Larvae are grown in large tanks and regularly inspected and cleaned.
Oyster Development
Oysters have a two-part life cycle: larval and then benthic (attached).
Larvae swim freely for approximately two weeks before attaching to a substrate.
After attachment, they undergo metamorphosis, changing their internal organs and maximizing gill size.
Oyster Farming
Oyster farmers require specific oyster shell shapes.
The oyster industry demands oysters of a specific size and shape for market success.
Shell shape can be affected by handling and environmental conditions.
Flat shells with minimal tissue are undesirable compared to deep oysters with abundant tissue.
Oyster hatcheries face challenges getting the oysters to the right shape and size.
Oyster Hatchery Challenges and Solutions
Oyster hatcheries involve much trial and error, and it can take years to perfect the process.
Failed oyster stocks can be used to seed natural populations and restore degraded reefs.
Oysters need to survive the initial days after settling to become juveniles and adults.
They must find food and avoid predators.
Post-Settlement Survival Rates of Marine Invertebrates
Many marine invertebrate species, including ascidians, barnacles, bivalves, gastropods, decapods, echinoids, octocorals, and polychaetes, have bipartite life cycles.
These species spend time in the plankton as larvae before settling.
The weekly survival rate after larvae settle varies from C- to A.
However, the mortality rate over a year can range from 75% to 100% for many species.
Death is a common occurrence in the life cycle, and dead organisms become food for survivors.
Factors Affecting Post-Settlement Survivorship
Predation is a significant cause of mortality.
Errors in metamorphosis timing can increase vulnerability.
Storms can displace organisms from their habitats.
Physiological stress due to changes in salinity, temperature (cold snaps or heat waves), can be lethal.
Competition for resources like food and space can also impact survival.
Scallop Life Cycle as an Example
Scallops release sperm and eggs into the water for reproduction.
Larvae spend a long time in the plankton, feeding and developing.
When they settle, they attach to seaweed for about three months before moving into the sediment.
The survival rate of individuals tethered to seaweed is low, with high mortality due to predation and environmental changes.
Predation is a significant factor in mortality during the early stages of settlement.
Fish Life Cycle on Coral Reefs as an Example
Many fish on coral reefs have bipartite life cycles.
Juveniles that have recently settled (naive) have much higher mortality rates than experienced juveniles.
Naive juveniles are less aware of food sources and predators.
Density-Dependent Controls on Population Growth
The number of settlers entering a system affects the number of survivors, but the system adjusts to density.
Density-dependent factors control population growth, such as competition for space and food.
The environment can only support a limited number of individuals.
The number of spaces available is a limiting factor, regardless of the initial number of larvae.
Bottleneck Effect on Populations
Visualize the life cycle as a bottleneck where only a certain number of individuals can pass through each stage.
Each life stage results in more death than survival, leading to a small percentage of original individuals surviving to adulthood.
Visualizing Bipartite Life Cycles
Adults find mates, leading to fertilization and the release of eggs into the water.
Planktonic eggs are vulnerable to predation and unsuccessful fertilization.
Larvae hatch and can be either plantotrophic (feeding) or lysithotrophic (yolk-dependent).
Larvae can starve, be carried away, or experience expatriation.
Settlement involves post-settled survivorship and competition for resources.
The limiting resources gauntlet affects the success of individuals.
Recruitment is the exception rather than the rule, as most individuals do not make it to adulthood.
Spatial Distribution and Larval Dispersal
Larvae have limited control over where they go, especially during the planktonic stage.
The longer larvae spend in the plankton, the farther they can travel.
Species without planktonic larvae are limited in distribution compared to those that spend a long time in the plankton.
Ocean Currents and Species Distribution
The Gulf Stream and other oceanic currents impact larval dispersal.
The gyre in the North Atlantic Basin influences the distribution of species.
Blue mussels and fiddler crabs show different distribution patterns due to these currents.
Blue mussels are found along the coasts of North America and Europe.
Fiddler crabs are limited to the East Coast of the US and the Gulf Coast.
They don't extend to the Caribbean due to unsuitable mangrove habitat.
Life History Trade-Offs
Bipartite life cycles occur because of trade-offs.
Recruitment and competition are challenging.
Coastal areas are heavily occupied.
Larval dispersal allows offspring to find new habitats.
Human development can create new settlement opportunities along the coast.
Larval Dispersal Model
Simulation maps potential spawning points in Irish sea and tracks larvae.
Includes: depth of spawning, season, how the larvae spent time in plankton.
Considers species dynamics in the region, tidal cycles, other cycle.
Migratory Behavior
Larval dispersal is not the only means of spread.
Migration also contributes to distribution.
Species migrate to find food or mates.
Practice problems overview
Determine the larvel mode.
Does species do direct development?
The plantotropic species?
The lisipotropic larvae?
How long do they take to disperse?
Mediterranean Dealfish
Non-migratory mesopelagic fish.
Lives at 100 to 600m deep.
Larvae typically found near the surface.
Distributed all over temperate and tropical seas.
Planktotroph- because it has mouth, anus, and structures for floatation, feeds, does not look like adult, and lives in zooplankton.
Sponge
Adults are sessile.
Females, produce eggs which they then hold on their own bodies.
The males release sperm into the water.
Then the females filter the sperm out of the water to fertilize the eggs.
Once the eggs are fertilized, the eggs released into the water then float around in the plankton for not a very long time for over a couple of hours. Then they settle out.
Lysotropic- very short life, can see shape/yolk
SwissGaurd Basslet
Coral reef fish.
Planktotrophic- eats smaller zoo plankton.
Aquarium trade stops disperse but in the ocean is great dispersal (however limited by water/reef temp.)
Oregon Triton Snail
Lays eggs and consumes each other.
Planktotrophic- they CAN eat (each other)
Deeper water
Corals
Sessile both reproduce asexually and sexually.
When sexually produce larvae that spend about 4 days plankton then settle, metamorphosizes, and grow up oral all over again.
Lysotropic- they spend short time in plankton
Mola Mola, or ocean sunfish, the most fecund animal in the world (with 300,000,000 at a time)
Tiny guys.
Have adapted for anti-predation and to stay afloat with spiky bits.
Planktotrophic- it does/needs to eat.
Spend lots of time planktonic.
Monster Larvae
Monsterlarvae= holoplankton, deep sea fish
(Turns out to be a different life stage though) this is because armor/to avoid predation while in plankton.
Planktorophic- mouth anus long long time. Thought it was different species.
Cusk Eel adaptation
Deep sea fish= deep deep sea/ thousands of meters deep sea.
Lipid rich eggs float top.
External digestive system (stomach outside of body) increase surface area, reduced rate and absorbed nutrient (maybe anti-predator- stinging/ Cnidrian that can sting others may avoid tentacle like structure- therefore not consumable)
Planktotrophic- feeding!! (So not lisitrophic)
Direct development: Brooding deep see squid
She’s gonna carry the eggs around for entire development
Less babies but very likely to fend for self at point of coming into life.
Direct- looks like mom swims like mom.