The above image was shot handheld using a Canon 20D with Canon 100-400L.
Golden gardens is one of the best places in Seattle for tidepool photography. At low tide you can shoot a variety of creatures like Sea Stars, Anemone, etc. Also dont forget to use a polarizer when shooting the tidepool creatures - it will help get rid of the glare. All the good tidepool locations are at the northern end of the park past the turtle pond. Wading boots are a great asset if you want to do tidepool photography.
Make sure you get there at low tide - the beach is much more interesting at low tide. A good website to lookup the tide charts for the seattle area is http://www.dairiki.org/tides/. Even better if you can get there during the lowest tide of the year. This is usually in June/July. In my opinion this is the best time of the year to shoot the Great blue Herons. The normally skittish herons are so preoccupied with the bounty of fish available that they tend to ignore the photographers :)
There is also a small freshwater pond located in the park. Its a great place to shoot Red slider turtles, Mallards, Red winged blackbirds etc.