Below are examples of intertidal greens, mostly from the surf-swept shores of the northern Oregon coast (unless otherwise noted in the captions). Some greens are tricky, even for experts, and I’m not an expert. I’m happy with genus-level identifications, when I can get there. Please drop me a line if you see a mistake or feel like helping me fill a gap. I made this page to organize my own thoughts about greens, and along the way, share different looks at the common ones and their habitats.
My organization loosely follows Kozloff (1993) and Lamb and Hanby (2005), showing species in the order they might be encountered 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.
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. All of the images below are from the splash zone seeps, so I’m guessing they’re all U. intestinalis. But, it’s not restricted to seeps.
Ulva intestinalis in the splash zone 
Lush growth in a drippy seep 
Ulva intestinalis cascading down a drying splash zone seep 
The strands are unbranched cylinders
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Cladophora, Sea moss
Cladophora is frequently found with periwinkles, mussels, thatched barnacles, Fucus, and Endocladia.
Cladophora in a diverse assemblage on the high side of a mussel bed 
A tuft of Cladophora 
You can see why they call it sea moss | Many periwinkles agree!
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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
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Ulva taeniata, sea spiral
Sea spiral is a distinctive bladed Ulva. I don’t notice it too much, but my impression is it’s at home in and around sand-fill 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
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Acrosiphonia
These emerald plaits are probably those of A. coralita, green rope.
Acrosiphonia coalita is known for its ropey strands | Central Oregon 
Sharing a semi-protected space with Ulva | Central Oregon
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Codium, Spongy cushion
Codium is always intriguing. I think all the examples below are C. setchellii
Codium setchellii‘s convolutions are evocative | Central Oregon 
C. setchellii, at home among the reds 
C. setchellii, sharing the stage with Dilsea 
C. setchellii, presumably; greener and less convoluted than most (central Oregon)
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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.
