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Jack Block Park

Low Tide Adventure. Seattle, Washington


Jack Block Park in West Seattle is built on the site of a former wood treatment plant and shipbuilding facility, with vestigial structures remaining of both. This park is a treat to visit any time, offering a different perspective of downtown Seattle. Bring binoculars and you'll be almost guaranteed to see a sea lion lounging on one of many nearby floating objects. For an extra-great low-tide adventure, take the water taxi from downtown and walk a few minutes east along the trail to Jack Block. As a special bonus, take a look under the bits of dock dotting the shore along the way for more low-tide friends.

There's not a great deal of territory to cover at Jack Block when the tides recede, but there are numerous crevices to peer into. The only areas accessible for exploration are the beach and underneath the main dock. At the lowest of tides, a second dock can be reached heading southwest from the beach.


The majority of tunicates that you can see at Jack Block are of the multi-colored snot variety, more properly known as Botrylloides violaceus. They may be found occupying pretty much any surface that would normally be underwater. Their size and color will vary greatly. These are colonies of once-vertebrate individual zooids that have settled down together in systems commonly known as chain tunicate. They are covered with a shared sheath and excrete waste collectively through a singular opening. Chain tunicates have a matrix of blood vessels that run throughout the colony.

The pink, chewing gum looking guy is a sea squirt, a singular type of tunicate. It is the only one of its kind I have observed in the Seattle area.


Anemones are abundant at Jack Block park. Large, individual anemones can be found dangling from the underside of rocks. Aggregating, or colonial anemones, are present but not abundant. 

Rough Keyhole Limpet

Limpets are very common throughout Puget Sound. They are often found attached to a surface with very little of their body visible. The first image shows the underside of a limpet. This is not an ideal position for the creature as it exposes its tender underbits to predators, such as crows. Keyhole limpets are distinguished from common limpets by the hole on the top of their shell. Keyhole limpets live with a worm that will help defend it from predators!


Mossy, woody and lined chiton proliferate throughout Jack Block park as they do throughout Puget Sound. This individual was covered in seaweed and barnacles. Others have more brilliantly covered shells, though can be easily missed if not paying attention. If you look carefully you are bound to find them on almost every rock revealed by low tide.

Red Sea Cucumbers

Look in between rocks to spot the sea cucumbers at Jack Block. They seem particularly shy in this location. Look out for bright red patches the the shallow waters at the bottom of boulders. Much of the time you will only see their protruding tentacles, and not even that if your approach is indelicate.

Sea Stars

Jack Block is one of many beach parks around Puget Sound where sea stars can regularly be found. What makes this location especially nice for observing them is their relative density in this small area, with the backdrop of an industrial setting. Ocher sea stars in a great spectrum of colors can be found here. Leather stars, though not as common as ocher stars, also make an appearance.


Approaching from Harbor Ave you will need to go a ways into the park before you get to the beach. There is a dock to the northeast which is accessible for people to walk upon. Look in the rocks below this dock. Another dock lies to the west, only accessible at low tide. This one is in a dilapidated state. Look underneath this dock on the fragments that remain. Be mindful of the tide returning as you could be marooned. The beach also has great lookings. The entire area could be thoroughly explored a couple times during a low tide.

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