Overview
This lecture introduces kelp forests in the Salish Sea, focusing on bull kelp (Nereocystis) and giant kelp (Macrocystis), their biology, habitat roles, and ecological importance.
Main Kelp Species in the Salish Sea
- The two main kelps are bull kelp (Nereocystis) and giant kelp (Macrocystis).
- Bull kelp is common in Puget Sound and is identified by a large bulb with many blades.
- Giant kelp has a stipe with multiple gas-filled bladders (pneumatocysts), each supporting a blade.
- Both are brown algae and serve as primary producers, converting sunlight into energy.
Growth, Habitat, and Requirements
- Both species grow rapidly; Macrocystis can grow up to two feet per day.
- They are found from about 15 feet to 100–120 feet deep, requiring clear water for photosynthesis.
- Kelp is sensitive to water pollution and turbidity, which limits light penetration.
- They need abundant nutrients, often supplied by currents from deeper ocean waters.
Kelp Anatomy and Adaptations
- Holdfast anchors kelp to rocks but is not a true root.
- Stipe acts like a stem; Nereocystis has one pneumatocyst with many blades, Macrocystis has multiple pneumatocysts each with a single blade.
- Kelp can move nutrients throughout its structure, similar to vascular plants.
Reproduction and Life Cycle
- The visible kelp form is the sporophyte stage, producing spores (zoospores).
- Spores settle and develop into male or female gametophytes, which produce sperm or eggs.
- Fertilization results in new sporophytes, demonstrating "alternation of generations."
- Both sporophyte and gametophyte stages are vital for kelp persistence.
Ecological and Human Importance
- Kelp forests provide three-dimensional marine habitats, increasing biodiversity and productivity.
- They are foundational ("umbrella") species supporting food webs, shelter, and nursery grounds.
- Kelp washed onto beaches (wrack) provides nutrients to nearshore and deep ocean ecosystems.
- Declines in bull kelp are concerning; restoration efforts involve laboratory cultivation and transplanting.
Key Terms & Definitions
- Bull kelp (Nereocystis) — Kelp species with one large buoyant bulb and many blades.
- Giant kelp (Macrocystis) — Kelp species with many small bladders, each with a blade.
- Holdfast — Root-like anchoring structure for kelp.
- Stipe — Stem-like structure of kelp.
- Pneumatocyst — Gas-filled bladder for buoyancy in kelp.
- Sporophyte — Life stage producing spores.
- Gametophyte — Life stage producing gametes (eggs or sperm).
- Alternation of generations — Life cycle alternating between sporophyte and gametophyte phases.
- Wrack — Dead kelp washed up on the shore.
Action Items / Next Steps
- Review kelp anatomy and reproductive cycle diagrams.
- Research current restoration efforts for bull kelp in the Salish Sea.