Freshwater Invertebrates and Ecosystems

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Questions and Answers

What are some environmental factors that contribute to the paradox of the plankton?

Vertical gradients, differential predation, temporal variability, and symbiosis are key environmental factors.

How do freshwater invertebrates contribute to ecosystem functioning?

They contribute to nutrient cycling, energy flow, and support higher trophic levels through various ecological roles.

What adaptations do freshwater invertebrates have for survival in specific habitats?

Freshwater invertebrates exhibit unique morphological, behavioral, and reproductive adaptations.

What role do sponges play in freshwater ecosystems?

Sponges serve as filter feeders, attaching to solid substrates and cleaning the water. Signup and view all the answers

What are the primary threats to freshwater biodiversity?

Pollution, habitat destruction, climate change, and invasive species are significant threats. Signup and view all the answers

How do hydroids reproduce, and what is their ecological role?

Hydroids reproduce asexually under optimal conditions and prey on small crustaceans and larvae. Signup and view all the answers

What is the lifecycle of mussels, and how do they disperse?

Mussels produce larvae called glochidia, which parasitize fish gills for dispersal. Signup and view all the answers

How does environmental variability influence planktonic communities?

Seasonal changes and variations in light and nutrients disrupt steady states, allowing diverse communities. Signup and view all the answers

What is heterophylly and how does it benefit aquatic plants like Limnophila?

Heterophylly refers to the phenomenon where aquatic plants have different leaf shapes based on the environment; submerged leaves are finely divided for gas exchange, while aerial leaves are broader for photosynthesis. Signup and view all the answers

What are the main threats to freshwater unionid mussels?

The main threats are siltation, toxic compounds, and invasive zebra mussels. Signup and view all the answers

Describe the role of cladocerans in freshwater ecosystems.

Cladocerans, such as Daphnia, graze on green algae and bacteria, helping to control algal blooms. Signup and view all the answers

Describe the primary factors influencing the patterns of plant coverage in aquatic environments.

Plant coverage patterns are influenced by light availability, which affects depth distribution, as well as environmental variations such as silt patterns and grazing by waterfowl. Signup and view all the answers

When does primary productivity typically peak in aquatic macrophytes and why?

Primary productivity usually peaks in summer due to higher sunlight availability, which accelerates photosynthesis and biomass growth. Signup and view all the answers

What adaptations do crustacean zooplankton like clam and copepods exhibit for survival in adverse conditions?

They produce resting eggs that provide a means of survival during unfavorable environmental conditions. Signup and view all the answers

What are the primary differences in macrophyte communities found in reservoirs, natural lakes, and rivers?

Reservoirs are dominated by emergent plants like cattails, natural lakes feature floating species like water lilies, and rivers favor emergent plants with sparse submerged macrophytes due to fast flow conditions. Signup and view all the answers

Explain how the seasons affect phytoplankton dynamics in cold temperate lakes.

In winter, ice limits light causing green flagellates to dominate; spring melt fosters diatom growth, while summer stratification leads to nutrient depletion. Signup and view all the answers

What role does periphyton play in aquatic ecosystems?

Periphyton, consisting of organisms like diatoms and cyanobacteria, forms biofilms on submerged surfaces and produces substances that can inhibit its own growth or benefit aquatic invertebrates. Signup and view all the answers

What is the significance of habitat diversity in freshwater ecosystems?

Greater habitat variety supports higher species richness, contributing to the overall biodiversity of the ecosystem. Signup and view all the answers

How do the respiratory adaptations of aquatic insects differ from those of their terrestrial ancestors?

Aquatic insects have evolved adaptations, such as air-breathing mechanisms, to thrive in water environments. Signup and view all the answers

How do phytoplankton adapt to counter sinking in aquatic environments?

Phytoplankton adapt through low density features like gas vesicles, shape adaptations with spines or flat forms, and motility provided by flagella. Signup and view all the answers

Identify two adaptations phytoplankton use to defend against predation and explain their purpose.

Phytoplankton use spines to deter zooplankton grazing and mucous sheets to protect themselves from digestion in herbivores’ guts. Signup and view all the answers

What role do decapod crayfish play in freshwater ecosystems?

Decapod crayfish are generalist feeders and significantly contribute to freshwater fisheries and ecosystem interactions. Signup and view all the answers

How have modern genomic techniques changed the understanding of phytoplankton taxonomy?

Modern genomic techniques have revealed greater diversity among phytoplankton than traditional taxonomy based on cell wall composition and pigmentation. Signup and view all the answers

What patterns have been observed regarding species richness in relation to latitude in freshwater environments?

Species richness decreases with increasing latitude, suggesting a latitudinal gradient in biodiversity. Signup and view all the answers

Study Notes

Aquatic Macrophytes

Heterophylly: Species like Limnophila or Buttercup have submerged leaves finely divided for gas exchange and aerial leaves broader for photosynthesis. This is regulated by light intensity and hormones like ethylene.
Plant Coverage Patterns: Macrophytes transition from submerged to floating-leaved to emergent forms, often in horizontal patches influenced by environmental factors like siltation or grazing.
Light Availability: Light penetration affects depth distribution but suspended particles or turbulence can reduce it more dramatically than expected.
Primary Productivity: Measured by biomass or oxygen changes. Productivity peaks in summer due to sunlight availability.

Algae

Periphyton: Organisms like diatoms and cyanobacteria form biofilms on submerged surfaces. They can produce substances that affect their own growth or benefit invertebrates.
Phytoplankton: Diverse, including green algae, diatoms, and cyanobacteria. Sinking is countered by adaptations like low-density gas vesicles (e.g., in cyanobacteria) or shape adaptations (e.g., spines in Asterionella).
Reproduction: Primarily asexual via cell division in many algae, while some species use sexual reproduction.

Adaptations Against Predation

Spines: Defense mechanisms seen in Ceratium to deter zooplankton grazing.
Mucous Sheets: Used by some species to protect themselves from digestion by herbivores.

Taxonomy

Basis: Cell wall composition and pigmentation (e.g., chlorophyll a, b).
Modern Techniques: Modern genomic methods reveal greater diversity than traditional taxonomy.

Distribution

Dominance: Some groups (e.g., cyanobacteria) thrive in highly productive water with high nutrient and pH levels.

Competitive Exclusion and the Paradox of the Plankton

Core Idea: Dominance by a few species due to resource competition is predicted, but in reality, many species coexist.
Hutchinson's Proposal: Environmental factors (e.g., vertical gradients, differential predation, and temporal variability) prevent equilibrium. Symbiotic relationships influence coexistence.

Key Themes

Freshwater Invertebrate Diversity: Freshwater habitats support a wide range of invertebrate species.
Adaptations to Freshwater Environments: Species have unique morphological, behavioral, and reproductive adaptations for survival.
Ecological Significance: Freshwater invertebrates are crucial in nutrient cycling, energy flow, and food webs.

Threats to Freshwater Biodiversity

Invasive Species: Species like zebra mussels can disrupt food webs and outcompete native species.
Pollution: Eutrophication, sedimentation, and toxic runoff harm freshwater ecosystems.
Conservation Strategies: Habitat restoration, pollution control, and coordinated water management are vital.

Additional Species

Sponges (Phylum Porifera): Filter feeders in clear water with symbiotic relationships with algae.
Hydroids: Simple body plan with a central cavity, feeding on small invertebrates. Asexual reproduction is prevalent.
Mussels (Class Bivalvia): Two-shelled organisms that filter feed, and some species larvae parasitize fish gills for dispersal.
Rotifers: Tiny organisms with a ciliated feeding corona. Parthenogenesis is common but some species produce colonies.
Crustaceans (Phylum Arthropoda): Segmented bodies with exoskeletons. Reproduce sexually and asexually. Examples include Cladocerans (Water Fleas), copepods, and mysids (Opossum Shrimp).
Insects: Secondary colonists, evolved from terrestrial ancestors. Aquatic larvae and adults exhibit diverse roles within foodwebs.
Other Vertebrates: Include fish, amphibians, reptiles, birds, and mammals.

General Patterns in Freshwater Diversity

Habitat Diversity and Stability: Diverse habitats support higher species richness.
Latitudinal Gradient: Species diversity decreases with increasing latitude.
Size and Stability: Larger, more stable water bodies usually harbor more species.

Seasonal Dynamics in Cold Temperate Lakes

Winter: Ice limits light, and green flagellates are prominent.
Spring: Ice melts; diatom growth and algal blooms occur.
Summer: Stratification occurs.
Autumn: Storm mixing replenishes nutrients; diatoms return.

Case Study: Priest Pot Lake

High Diversity: Supports a high number of species.
Cryptic Diversity: Includes undetected resting stages or groups.
Technological Advances: Environmental DNA (eDNA) enhances species detection.

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Description

This quiz explores the environmental factors influencing the paradox of the plankton and the contributions of freshwater invertebrates to ecosystem functioning. It also covers the adaptations these organisms have developed for survival in specific habitats and the ecological role of sponges in freshwater ecosystems.