What is phytoplankton, and why is it so important to life on Earth?

Microscopic photosynthetic organisms that produce about half of Earth's oxygen and form the base of most ocean food webs Tiny fish larvae that drift on ocean currents Single-celled animals that eat bacteria and dead organic matter Microscopic fungi that decompose dead marine organisms

What is the difference between phytoplankton and zooplankton?

Phytoplankton are photosynthetic (plant-like), while zooplankton are animal-like organisms that consume other plankton Phytoplankton are larger than zooplankton Zooplankton produce oxygen while phytoplankton consume it There is no meaningful difference — they are both types of algae

Jellyfish are classified as which type of invertebrate?

Cnidarians — the same group as corals and sea anemones Echinoderms — the same group as sea stars and sea urchins Mollusks — the same group as clams and snails Crustaceans — the same group as crabs and shrimp

What makes the octopus especially remarkable among invertebrates?

It has a highly developed nervous system and is one of the most intelligent invertebrates, capable of problem-solving and tool use It is the longest-lived invertebrate, surviving for over 100 years It is the only invertebrate that can breathe air It has a hard external skeleton that protects it from predators

What is the difference between a squid and an octopus?

Squid have ten arms (including two longer tentacles), a streamlined body, and an internal shell (gladius); octopuses have eight arms and no shell Squid live on the seafloor, while octopuses swim in open water Octopuses are larger than squid and live in deeper water They are the same animal — 'squid' and 'octopus' are interchangeable names

What is a Portuguese Man o' War, and why is it unusual?

It appears to be a single jellyfish-like organism but is actually a colony of specialized individual animals (zooids) working together It is the world's largest true jellyfish, found only in Portuguese waters It is a type of squid that inflates itself with gas to float It is a sea snail with an air-filled shell that allows it to float

Sea stars (starfish) belong to which animal group, and what unusual ability do they have?

Echinoderms; many species can regenerate lost arms and some can regenerate an entire body from a single arm Mollusks; they can change color like octopuses Cnidarians; they sting prey like jellyfish Crustaceans; they shed their exoskeleton as they grow

What is the role of marine worms (polychaetes) in ocean ecosystems?

They are major decomposers and sediment recyclers, and serve as important food sources for fish and invertebrates They are top predators in deep-sea ecosystems Marine worms are not ecologically important They only exist in shallow coastal water and play no deep-sea role

How do clams and mussels (bivalve mollusks) obtain their food?

Filter feeding — they draw water through their gills and extract microscopic plankton and organic particles They are active hunters that chase small fish They absorb nutrients directly through their shells from the water They photosynthesize using algae inside their shells

What is a 'bloom' in the ocean, and when can it be harmful?

A rapid population explosion of algae or plankton; harmful algal blooms (HABs) can produce toxins that kill marine animals and contaminate shellfish A bloom is always beneficial, fertilizing the entire ocean ecosystem Blooms only occur near hydrothermal vents Blooms are caused by fish spawning events rather than plankton growth