King County's 1996/1997 Beach Assessment

Mee Kwa Mooks Park, Seattle

Site Description

This beach is located about one mile south of the Alki lighthouse and is called Schmitz Overlook Park on some maps. An eroded anticline is exposed at several points along the beach. The layers of sediment that make up the formation alternate from clay with organic materials to a clay/sand mixture. The clay/sand composition is less resistant to erosion. The erosion of those layers has created a series of tide pools. Those to the north are quite large. A sea wall along the entire length of the beach protects the upper beach from erosion.

Intertidal Inhabitants

This beach presents several distinct habitats for invertebrate populations. These include sand, sand/gravel/cobble mixtures, boulders and layers of clay. The clay banks are riddled with the burrows of piddocks and various crabs are found under the boulders. There are thousands of sand dollars in the tide pools as well as various shrimp species. There are clams wherever the substrate is suitable and over 2 feet thick.

Invertebrates

Twenty-seven (27) invertebrate species were recorded on the day that the survey was done. In addition, several other species were identified by informal observations. Some of those not included in the survey were red rock crabs, Thais emarginata (emarginate dogwinkle), horse clams, softshell clams, sand macoma, Macoma nasuta (bentnose macoma), dock shrimp, Idotea wosensenskii (olive-green isopod) and Ligyda pallasii (beach cockroach). (Note: The survey was conducted in conjunction with volunteer training and was less extensive than desirable).

Limpets
Shield Limpet	Acmaea pelta
Finger Limpet	Acmaea digitalis
Snails
Sitka Periwinkle	Litorina sitchana
Checkered Periwinkle	Litorina scutulata
Moon Snail	Polinices lewisi
Fringed Dogwinkle	Thais lamellosa
Chitons
Mossy Chiton	Mopalia mucosa
Hairy Chiton	Mopalia ciliata
Bivalves
Native Littleneck	Protothaca staminea
Manila Clam	Tapes japonica
Butter Clam	Saxidomus gigantea
Cockle	Clinocardium nutalli
Pilsbry's Piddock	Zirfaea pilsbryi
Bay Mussel	Mytilus edulis
Jingle Shell	Posodesmus cepio
Barnacles
Acorn Barnacle	Balanus glandula
Thatched Barnacle	Balanus cariosus
Crabs
Purple Shore Crab	Hemigrapsus nudus
Green Shore Crab	Hemigrapsus oregonensis
Northern kelp crab	Pugettia producta
Hermit crabs
Hairy hermit	Pagurus hirsutiusculus
Anemones
Colonial anemone	Cribrina elegantisima
Segmented worms
Sand worm	Nereis virens
Flatworms
Large speckled	Kaburakia excelsia
Nemerteans
Green nemertean	Emplectonema gracile
Isopods
Brown Isopod	Idotea urotoma
Beach Cockroach	Ligia pallasii
Amphipod
Skeleton Shrimp	Caprella kennerlyi

Clams

The clam band is estimated to cover approximately 3.5 acres, the largest of the beaches surveyed. It extended the entire length of the park (see contour map). Thirty-nine of the 58 holes dug contained at least one clam. While the north section of the beach is larger than the south, the substrate of the north beach tends to be too sandy for the manila, littleneck and butter clams. The majority of the clams, both by number and by weight, were found on the south beach, which has a sand/gravel/cobble composition. Littleneck clams dominate both numerically (45%) and by weight (47%). Butter clams comprised 18% of the total weight. While the macoma clams comprised 28% of the total number of the clams, they were only 6% of the biomass.

Check out the following graphs for more information about the clam population:
Numeric composition of clam population
Weight composition of clam population
Numeric distribution of clam population
Biomass distribution of clam population

The 673 clams collected weighed 4811 grams. The average weight of the clams was 7.1 grams. This was the fifth lowest of the beaches, but the population density was 17 per square foot, the fourth highest. The percentages of the legal sized Manila, littleneck and butter clams were relatively low considering the availability of good habitat. Five of the 55 Manila clams (9%) were the seventh highest of the ten beaches on which Manila clams were found. 20% of the littlenecks and butter clams were of legal size-the sixth lowest rates for both species.

It may be that over-harvesting is contributing to the smaller-than-average sizes of several clam species on this beach. The Manila, littleneck, butter and macoma clam averages were about half those for all beaches combined.

Algae

Twenty-two (22) species of algae were identified on the beach (six green, seven brown and nine red algae). At least three of the species are edible and are harvested regularly. One of those edible species is Sargassum, an invasive algae from Asia.

Green (Chlorophyceae)

Arcosiphonia sp.

Cladophora sp.

Enteromorpha intestinalis

Enteromorpha linza

Ulva fenestrata

Ulva lactuca

Brown (Phaeophyceae)

Analipus sp.

Ectocarpus sp.

Fucus distichus

Fucus gardneri

Leathesia difforimis

Petalonia debilis

Sargassum muticum

Red (Rhodophyceae)

Ceramium pacificum

Gigartina cristata

Hymena sp.

Odonthalia floccosa

Plocamium pacificum

Polysiphonia collinsii

Porphyra lanceolata

Porphyra perforara

Prionitis lanceolata

Use

This beach is heavily dug by recreational clam diggers but the sizes of some of the craters indicate that the digging might be at a commercial level in some cases. On several of the days the beach was visited, several people were observed harvesting clams, crabs and seaweed, sometimes in very large quantities.

Red rock crabs did not appear to be as abundant as in 1996. People were observed taking dozens of undersized rock crabs as well as gallons of the smaller purple shore crabs. On one occasion, volunteers requested people to return undersized organisms to the beach and they complied.

Most of the rocks on the beach have been overturned and not returned to their original positions. There are numerous craters appearing on the beach, since some of the harvesters do not fill the holes they dig, although Washington State law requires that they do. The clay banks are being broken up in order to extract the piddocks and the tide pools are being trampled. Presently, this park supports a very diverse population for an urban beach but little is being done to protect it.

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Updated: 11/02/98