Talking generalities...
Seaweed is full of various proteins and sugars but not so much oils. So if you mean that you would like to squeeze oil out of the green slime and transesterify it, the answer is no.
If you would like to do something else with it? Maybe.
There are a few issues to deal with; solids %, collection, processing and waste costs.
First, even tho it looks dryish, its not. The more water%, the more energy it will take to turn it into some concentrated energy. This is not a trivial issue.
Then you gotta collect it. Moving high% water feedstocks is really expensive, thermodynamics and economics wise. Biomass chant... 'trucking water and air sux'. Additionally there is the fact that algae washup moves. One day its there and the next it might be out to shore or down the road. Some bays are just natural algal magnets but there is this variation that makes doing business hard. Then you need the right machines and the people willing to smell that stuff day/day.
Then, what are you going to do with it? There is no oil. The sugars are various and we cant even do cellulosic ethanol, much less hemicellulosic algal ethanol. You can Anaerobic digestion but that is a very low economic solution. And AD systems are not 'portable' so you would need centralized location and trucking wet material comes in again. Plus AD leaves alot of biomass left and eventho its hyped as a 'product', the economics sux and getting worse as this stuff becomes larger and larger as more AD systems goes up. The real solution would be to portable gasify/FT system and try to sell the ash but this doesnt exist yet, it will.
Waste issues comes in a few forms, cost and liability and sink. The liability of taking on that has a cost that after 1 E.coli issue and the cost goes thru the roof. There is also the liability of physically collection, 'you ruined my favorite tree' or 'the fishing died' or 'the shore eroded 100ft'... As with any commercial process, waste is a cost. The more complete the answers to the above offers less waste but there will always be something. 10% solids = 90% water and somewhere for that water to go. Also, by putting the load of minerals directly back where you just removed them, that would be like fertilizing your own poop. Good for the collector, bad for everyone else.
There is also the issue of spp. Different times of year will offer up diff spp. So a system that is optimized for one but not be for another, thus you need to have a robust collection/processing system to account for that variability.
Few of my local facts...
Each linear ft of L. Michigan Wisconsin shore line produces ~ 1ton of Chlodophra solids/year. ~ 1/2 of that mass washes up on shore (other half digest and/or die-fall to bottom offshore). I think there is ~ 300miles on Wisc side alone... Ask this poor guy, im sure he has some for you to take.
Those that live by the sword, die by the sword. Id rather die of cholesterol from all the butter Im making and selling...
froggy in Wisconsin