Below are examples of intertidal greens from the surf-swept shores of the northern Oregon coast. A fair number of the green seaweeds pose identification challenges for me, so I’m happy with genus-level identifications when I can get there. Please drop me a line if you see a mistake. My organization loosely follows Kozloff (1993) and Lamb and Hanby (2005), showing species you might encounter in the field, from highest to lowest in the intertidal. I lean on Algaebase for nomenclature and taxonomy. Common names are my choice. I learn a ton by browsing the pages of Druehl and Clarkston (2016) and Kozloff (1993). You’ll find a bunch more easy-to-find references at the bottom of the page.
Let’s explore some green seaweeds!
Ulva intestinalis
In the right setting, frequently at freshwater seeps, U. intestinalis can creep to the highest reaches of the splash zone, above the highest barnacles and limpets. It’s also found in high tidepools.
Ulva intestinalis in the splash zone 
Ulva intestinalis is a notorious seep dweller 
Bleaching at a drying seep | Well above the barnacle zone 
The strands are unbranched cylinders 
Drift U. intestinalis | Galiano Island
Cladophora, sea moss
Cladophora is frequently found with periwinkles, mussels, thatched barnacles, Fucus, and Endocladia.
Cladophora (bright green), part of a diverse high intertidal community 
On the high side of the mussel bed 
You can see why people know Cladophora as sea moss | All the periwinkles agree!
Chaetomorpha (probably)
I think the examples below are Chaetomorpha; there are other unbranched filamentous greens with large cells so I do have some uncertainty. These are all from mid to maybe high tide pools. I’ve highlighted the large cells in the lower right panel below.
Unbranched filaments 
In a semi-protected pool 
You can just about make out the large cells 
Enlarged a little to show off the large cells
Sea lettuce
Leafy, bladed Ulva is common on the exposed coast and flourishes, with lush growth, in semi-protected niches. I won’t speculate what species are represented below.
Long narrow blades draped over a sand-scoured rock 
Low tide reveals a lush growth of Ulva (green) and a splash of Mazzaella 
Ulva and the barnacles beneath 
Leafy Ulva at low tide in a sem-protected site 
You can see why they call it sea luttuce
Ulva taeniata, sea spiral
Sea spiral is a distinctive bladed Ulva. It’s at home in and around sand-filled tidepools.
A lovely strand of sea spiral, Ulva taeniata | Central Oregon 
A disturbed strand of U. taeniata against broad-bladed Ulva | Central Oregon 
Sea spiral in a sand-filled pool | Central Oregon
Acrosiphonia coalita, green rope
Acrosiphonia coalita lives up to its common name | Central Oregon 
Look for A. coalita in the mid to low intertidal | Central Oregon 
Prime rope | Central Oregon
Codium fragile, sea staghorn
Codium fragile with Mazzaella and Cryptosiphonia on an overgrown wall 
Nothing on this shore resembles C. fragile | Central Oregon
Codium setchellii, spongy cushion
Codium setchellii sharing the stage with Dilsea 
Codium setchellii in the low zone 
This one’s greener and less convoluted than most | Central Oregon
References
Druehl, L. D. and B. E. Clarkston. 2016. Pacific Seaweeds: A Guide To Common Seaweeds of the Pacific Coast. 2nd ed. Harbour Publishing Co.
Harbo, R. M. 2011. Whelks to Whales: Coastal Marine Life of the Pacific Northwest. 2nd ed. Harbour Publishing Co.
Kozloff, E. N. 1993. Seashore Life of the Northern Pacific Coast. 3rd ed. University of Washington Press.
Lamb, A. and B. P. Hanby. 2005. Marine Life of the Pacific Northwest. Harbour Publishing.
Mondragon, J., and J. Mondragon. 2010. Seaweeds of the Pacific Coast. Shoreline Press.
Sept. J. D. 2009. The Beachcomber’s Guide to Seashore Life in the Pacific Northwest. Revised ed. Harbour Publishing.
Web Resources
The green algae page on the Netarts Bay Today website is one of the best references you’ll find for the Pacific Northwest.
Biodiversity of the Central Coast has a great page on greens.
Seaweeds of Alaska is a standard reference for the Pacific northwest. It has a great green algae page.
This page was updated on August 19, 2021.
