Field Guide to Algae - Green Algae

Acrosiphonia arcta in habitat - bright green on rock

Acrosiphonia arcta
This alga grows as a tufted mat in the lower intertidal zone. It looks unusually fuzzy because it has hooked filaments (see microscopic photograph). This alga is a favorite place for small crustaceans to hide to escape drying stress at low tide. Present winter–summer.

Photos by Joseph Stachelek.

Chaetomorpha melagonium growing vertically

Chaetomorpha melagonium
Chaetomorpha melagonium grows as a thick, beaded tube. The cells are so large that you can see them with your naked eye. Found in tide pools in the lower intertidal zone. Present winter–summer.

Photos by Joseph Stachelek.

Prasiola stipitata growing on rocks

Prasiola stipitata
Prasiola stipitata forms a short green turf (< 1 cm, see microcropic photograph) near bird droppings (an excellent source of nutrients) in the upper intertidal zone. Small, individual blades curve like a mouse ear. Present spring–summer.

Photos by Susan Brawley (left) and Sarah Hall (pop-up).

Ulothrix laetevirens along shoreline

Ulothrix laetevirens
Ulothrix laetevirens forms slippery, dark-green patches on rocks in the upper intertidal zone. Individuals that make up the patches are unbranched filaments. There is a single, band-shaped chloroplast in each cell (see microscopic photograph). Herds of herbivorous periwinkle snails feed at the edge of patches in spring and work their way inward until the patch disappears. Present winter–early summer.

Photos by Sarah Hall.

Ulva lactuca growing along shore

Ulva lactuca
“Sea lettuce” is a flat blade (two cell layers thick) that grows up to 20 cm long. This bright to dark-green sea vegetable is consumed by many invertebrates and also by humans in soups and salads. Blades that have upper white sections have just released reproductive cells; this occurs most often near full and new moons, just after dawn. Ulva lactuca is found in tide pools and in the lower intertidal zone. Present year round, but most abundant in summer–fall.

Photos by Susan Brawley (left) and Sarah Hall (pop-up).

Ulva intestinalis growing in tidepool

Ulva intestinalis
This alga tolerates low salinity and is found in the upper intertidal zone in pools and areas of runoff. Young individuals are slender blades, whereas older individuals form a tube. Gas bubbles accumulate inside the tube and make it float. Gametes and zoospores are released shortly after dawn near new and full moons. Individuals that have released reproductive cells turn white.

Photos by Joseph Stachelek (left) and Sarah Hall (pop-up).

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