Carkeek Park, Seattle

This page describes the beach and its marine life. For information about the park, its recreational amenities, directions and open hours, please visit City of Seattle's Carkeek Park page (external).

Site Description

This beach adjoins a large urban park in North Seattle.  The adjoining beach is one of those included in the 1974 intertidal studies by Thom and Armstrong because of its proximity to Carkeek Sewage Treatment Plant, which discharged 2,000 feet offshore. In l993 the plant was taken offline and converted to a stormwater treatment facility.

This long beach is bisected by an alluvial fan which has been deposited by Pipers' Creek. The alluvial fan is an inhospitable environment to most intertidal creatures.

The south end of the beach is relatively flat and sandy while the north end is steeper and cobbled. The south beach is made up mainly of gravelly sand, with some patches of sand on the flats and sandy gravel closer to the alluvial fan. The sand/gravel areas seem well suited for clam beds while most of the rest of the area produces few clams. The middle area, the alluvial fan, is elevated and is comprised of unconsolidated sand, gravel and cobbles. The stream has deposited sand and gravel in ridges, which eventually become barriers to the stream. The barriers divert the stream laterally until it reaches the edge of the fan where it spreads out on the beach and deposits the last of its sediment load.

The north end of the beach is a mixture of boulders and concrete chunks sprinkled over a layer of gravel buried beneath a layer of sand about two inches thick. There are a few patches of clay that have been bored by piddocks.

In addition to Pipers' Creek, some drain pipes discharge freshwater to the beach almost continuously. Burlington Railroad, which owns the right of-way along the beach, has rip-rapped along most of the upper beach to protect the railroad bed from erosion. It may be that the beach would be a little wider, providing more intertidal habitat, if the bluffs were allowed to erode and replenish the beach with gravel.

Invertebrates

Fifty-six (56) species have been identified on this beach-the highest number for the beaches surveyed. Besides actual diversity related to the great variety of habitats on the beach, the large number of species could be explained by more rigorous sampling than usual. Not only did we have the benefit of the expertise provided by Lynwood Smith, but we also field-tested some of the identification keys.

Many species were identified. The short-spined sea star, moon snail, Macoma balthica ("baltic macoma") and M. secta ("sand macoma") find the sand flats ideal. The large smooth pieces of rip-rap along the upper beach support a number of limpets, snails and chitons. Feather duster worms, Eudistylia polymorpha, and thatched barnacles cover the large boulders while acorn barnacles and jingle shells find the smaller boulders to be suitable habitat. The long-armed brittle star, shell binder worm, calcareous tube worm, and orange sea cucumber live under the smaller boulders.

Piddocks were observed. Several species of limpets were observed at the high tide line and hidden by large rocks and boulders.

Clams

The clam band covers about 3.5 acres and is bisected by the alluvial fan: one-third north and two-thirds south. The north assessment area is between 40' and 120' wide and extends north 800' from a point 400' north of the footbridge. The south area is from 120' to 240' wide and extends 600' south from a point 800' south of the footbridge (See contour map). The assessment area is the second largest which we surveyed. Thirty-eight (38) of the holes (14 on the north beach and 24 on the south) that were dug contained one or more clams each. Only one fourth of the clams came from the north beach and less than that fraction of the weight since the clams found there tend to be smaller.

Seven hundred and eighteen (718) clams were collected on this beach weighing 6,589 grams. The average per clam weight was 9.2 grams and the density was 18 clams per foot, the third highest density on the beaches.

Littleneck clams dominated the beach both numerically (40%) as well as by weight (56%). Macoma clams are the next most numerous (26%), but the butter clams are second in terms of weight (21%). The manila clams are fairly common on this beach but they are not very large. Of the 119 manila clams collected only 5 (4%) were of legal size. This is the lowest of the eight beaches upon which manila clams were found. Ninety-five (95) of the 286 littleneck clams, or (33%) and 23 of the 104 butter clams (22%) were legal. Those rates were about average for all beaches combined.

Check out the following graphs for more information about the clam populations at Carkeek Park:

• Numeric composition of clam population
• Weight composition of clam population
• Numeric distribution of clam population
• Biomass distribution of clam population

Seaweed

No formal survey of the marine algae was conducted but a few observations were made. The rip-rap support Rockweed and Grapestone. The eelgrass beds to south support epiphytic growths of both Smithora sp. and Punctaria sp. Several species of green seaweed were found here; two were very obvious. Sea lettuce is common on the lower portions of both the north and south beaches wherever there are cobbles for substrate. Sea lettuce is absent from most of the alluvial fan, however. Enteromorpha intestinalis (a green seaweed which grows ribbon-like filaments and is freshwater tolerant) covers most of the cobbles in the stream bed on the alluvial fan.

Other

There was usually a great blue heron present on the beach. A sea lion pup was seen on the beach, and harbor seals were seen offshore.

Use

There is evidence of heavy use of this beach. Harvesting craters are large and common on the south. Some holes, approximately six to ten feet across, could be the result of commercial level extraction. Nearly all the smaller boulders have been overturned recently. The barnacle communities on some of the larger boulders were beginning to show paths worn through them. Scores of red sea cucumbers observed a few years ago are now scarce, according to residents. Trenches have been dug around the bases of some of the rip-rap pieces presumably to expose the chitons, which seek cover during the low-tide events. Over-harvesting seems to have left the beach with smaller than average clams.

The beach is heavily used by families, school groups and individuals for beachcombing and exercising pets. Near the end of the school year, large groups of school children roam the beach where they search for sea creatures. This beach is suffering from this activity. Nearly all of the rocks have been left in an overturned position.