Feeding mechanisms Flashcards
(34 cards)
Why is understanding feeding ecology essential for studying zooplankton population dynamics?
Feeding ecology directly affects key biological processes like growth, reproduction, and population production. By understanding what zooplankton eat and how they obtain food, we can better grasp their role in structuring marine communities and regulating food web dynamics.
What are ‘bottom-up’ and ‘top-down’ controls in marine ecosystems?
Bottom-up control is driven by the availability of primary producers like phytoplankton, which influence zooplankton abundance. Top-down control involves predation by higher-level consumers such as copepods or fish that regulate prey populations.
What core steps are involved in suspension (filter) feeding by zooplankton?
Suspension feeding generally involves:
1. Drawing water with suspended particles into the body (feeding current),
2. Separating and concentrating food from water,
3. Trapping particles on a filtering structure,
4. Transporting particles to the mouth,
5. Selectively ingesting desired items while rejecting others.
What types of filtering structures are used by different zooplankton groups?
Zooplankton use three primary structures to filter food:
1. Mucous mesh (gelatinous organisms like salps and pteropods),
2. Setae (bristle-like structures used by crustaceans like copepods),
3. Cilia (tiny hair-like projections found in echinoderm larvae and others).
How do pteropods like Cavolinia use mucous webs to feed?
They deploy mucous sheets using their parapodia (wing-like structures) in seconds. These webs hang motionlessly in the water, efficiently trapping phytoplankton and small motile prey. After accumulation, the entire web with embedded food is ingested.
What adaptations do appendicularians have in regards to food capture and uptake?
Their filter structures include:
1. Inlet filters that prevent large, unsuitable particles,
2. Food-concentrating filters that sort particles based on charge and shape,
3. Exit spouts to expel rejected material—making their feeding system highly selective.
How do salps feed, and what makes them unique among mucous feeders?
Salps rhythmically pump water through their body, straining it through a mucous sheet secreted by the endostyle. This mucous sheet rolls into a strand that carries food to the oesophagus. Unlike simple sieving, salps use interception and diffusion to capture even tiny (<1 µm) particles.
Why do salps capture more tiny particles than predicted by size alone?
Their feeding success isn’t just based on mesh size. Instead, mechanisms like direct interception and diffusional deposition help capture ultra-small particles that passively contact the mucous sheet.
How do copepods generate feeding currents?
Copepods use coordinated movements of their first antennae, mouthparts, and swimming legs to create directed water flow that brings food towards them.
What are the motion, viscous, and sensory ‘cores’ around a copepod, and what do they do?
These are concentric zones of influence:
1. The motion core is where water always flows past the copepod,
2. The viscous core is where particles are transported to the mouth,
3. The sensory core is a detection field where copepods sense prey using chemical and mechanical cues.
How do copepods use sensory structures to detect prey?
They have mechanosensory setae and chemosensory sensillae primarily on their antennae. These detect water disturbances and chemical signatures from prey such as chlorophyll or nitrogen-rich compounds.
What prey characteristics affect detection and capture by copepods?
Key factors include: prey swimming speed, presence of toxins or specific nutrients, size, distance from the copepod, and the chemical signature (e.g., C:N ratio, chlorophyll content).
How does the morphology of copepod mouthparts reflect diet type?
Herbivorous copepods have broader, comb-like structures to process phytoplankton; carnivorous types possess sharp, grasping parts suited for larger, mobile prey; omnivores show intermediate traits.
How do copepods select particles based on size?
Their setae and fine setules form a filtering net. The spacing between these structures determines the smallest and largest particle sizes that can be retained, which shifts with copepod body size and developmental stage.
What is ontogenetic niche separation in copepods?
As copepods grow (from nauplius to adult), the spacing between their filtering hairs increases. This means different life stages consume different food sizes, reducing competition between stages.
How do mixed diets affect copepod growth and reproduction?
Studies show that copepods fed a mix of phytoplankton types grow faster and produce more offspring than those on single-species diets. Mixed diets ensure balanced nutrition and reduce deficiencies.
What is the difference between upstream and downstream ciliary feeders?
Downstream feeders (e.g., trochophore larvae) create feeding and swimming currents that flow toward the mouth. Upstream feeders (e.g., pluteus larvae (echinoderm larvae)) must use indirect methods to capture food, as currents are directed away from the mouth.
What is the ‘catch-up principle’ in downstream larval feeding?
This refers to how larvae adjust their swimming and ciliary beat to ensure food particles, which might otherwise pass by, are brought back within reach of their feeding structures.
What are the major strategies used by zooplankton predators to find and capture prey?
Strategies include:
1. Cruising to find slow-moving prey,
2. Ambush feeding to catch fast or motile prey,
3. Using mechanical, tactile, chemical, or visual cues to detect prey,
4. Raptorial capture using specialized mouthparts or tentacles.
How do copepods switch feeding behavior depending on prey type?
For non-motile prey, they use a feeding current (suspension feeding). For motile prey like ciliates, they switch to ambush feeding—sinking quietly then lunging when prey comes close.
Where are carnivorous copepods most abundant and why?
They dominate in oligotrophic tropical and subtropical waters, where nutrients are low and protozooplankton (their prey) are the primary grazers instead of phytoplankton.
What adaptations make chaetognaths effective ambush predators?
They have vibration sensors, photoreceptive eyes, serrated spines, and toxin-producing teeth. Their long, muscular bodies allow fast darting to capture prey like copepods.
How do chaetognaths select their prey?
Prey selection is based on prey size relative to chaetognath head width. They prefer copepods and exhibit limited cannibalism at <10%.
Why does chaetognath feeding level off at high prey densities?
As raptorial feeders, they can only handle a limited number of prey at a time, leading to saturation of their feeding capacity.
