Seaweeds/Seagrasses

Sea Grasses

  • Eel grass, surf grass, turtle grass

  • Tropical/Temperate oceans

  • Rhizomes - complex root system. Asexual growth via shoots. Nitrogen fixation - when nitrogen is converted into usable forms (ex. ammonia)

  • Shallow water, high light (need to photosynthesize), modest currents, Must Be Submerged

  • Higher plants, flowers, pollen spreads floating on water

  • Succession of species leads to established seagrass beds - seaweed → seagrass

Seagrass beds

  • Zones of high primary production, supports high animal diversity

  • Subtropical/tropical regions - found sub-tidally. Sensitive to nutrients

  • Reduce current flow - establish structure

  • Foundation species - forms habitat for other species

  • Can deter entry of predators, functions as nurseries for juvenile fish

  • Grazing is variable based on species toughness (cellulose content)

  • Main grazers: turtles, sea urchins, manatees - turtles have microbes that help them break down cellulose

  • Important component of coral reef/mangrove systems

Causes of declines in seagrass beds

  • Nutrient pollution - major problem in North America - Pamlico/Albemarle sound has declined 1.5% per year

  • Overfishing - reduced grazing on seagrass epiphytes (algae) which smother seagrass

  • Dredging/Boat traffic - physical disruption of beds

  • Disease - fungal, bacterial “infections”

Seaweeds

Colonial members of kingdom Protista (simplest eukaryotes)

Attach to a substrate, obtain nutrients from the surrounding water (No root system)

Morphological differentiation - Holdfast, stipe, frond (blade), reproductive structures, pneumatocyst for flotation

Complex life cycles: differentially shaped thallus stages (shoot-like) that alternate with dispersing stages (spores)

Classification

Split up into color

  • Green (Chlorophytes) - chlorophylls a and b, stores starch, cell wall made of cellulose. Most similar to Plants. Wide variety of morphologies

  • Brown (Phaeophyta) - Chlorophylls a and c, fucoxanthin, stores laminarin and mannitol, cell wall made of alginate. Dominate rocky low intertidal and shallow subtidal zones. More morphologically differentiated than green seaweeds

  • Red (rhodophyta) - chlorophylls a and d, phycoerythrin and phycocyanin, stores Floridian starch, cell wall made of agar and carrageenan. Most diverse group from soft fforms and calcareous coralline algae. Used for agar extraction

Eating seaweed can alter gut flora to help digest seaweed more effectively

Kelp forests - brown seaweed

  • West coast, rocky zones

  • Rocky-reef complexes are shallow subtidal environments typically found in cooler coastal waters with high nutrients, exposed to open sea

  • Dominated in shallower waters by subtidal kelps/seaweeds and by epifaunal animals in deeper waters (eg. colonial invertebrates such as sea squirts)

  • Patchiness is common, grazed intensely by sea urchins and competition for space

  • Subtidal, rocky reefs - California coast. Colder waters with high nutrient environments, high wave action

Ecosystems

  • Kelp is a foundation species

  • High growth rate - up to centimeters per day

  • Forests can be 1m-20m high

  • Supports diverse communities - many invertebrates (echidnoderms and tunicates), sessile benthic species, suspension feeders, fish