King County's 1996/1997 Beach Assessment

Saltwater State Park, Federal Way

Site Description

The park is located in Federal Way in south King County. It is administered by the Washington State Department of Parks and Recreation. The beach is relatively flat and much of the upper beach has been stabilized by rip-rap. There is a large alluvial fan at the mouth of Thomas Creek, which helps maintain a large clam population. The particles in this fan are much smaller than the cobbles that form the fan at Carkeek Park; consequently, this fan is an ideal habitat for hardshell clams. The beach sediment is primarily coarse sand and gravel on the fan and to the south. Adjoining the fan on the north side is a small sand flat. North of there along the rip-rap, the beach is quite narrow and is composed of gravel and cobbles covered with an inch of sand. There are numerous boulders scattered over most of the area. The beach does not seem to be threatened with erosion currently because the vulnerable areas are protected by the rip-rap. The southern portion is replaced with stream sediments after each storm.

Invertebrates

Forty-two (42) invertebrate species were identified on this beach, ranking it fourth highest of the 13 beaches surveyed. Mollusks comprised 60% of the species represented and half of those were bivalves. In addition, five species of crabs were identified. Much of the alluvial fan is covered by mussels.

Limpets
Plate Limpet	Acmaea scutum
Variegated Limpet	Acmaea persona
Shield Limpet	Acmaea pelta
Finger Limpet	Acmaea digitalis
Snails
Sitka Periwinkle	Litorina sitchana
Checkered Periwinkle	Litorina scutulata
Emarginate dogwinkle	Nucella emarginata
Moon Snail	Polinices lewisi
Hairy Triton	Fusitriton oregonense
Fringed Dogwinkle	Thais lamellosa
Bivalves
Native Littleneck	Protothaca staminea
Manila Clam	Tapes japonica
Butter Clam	Saxidomus gigantea
Cockle	Clinocardium nutalli
Softshell	Mya arenaria
Horse Clam	Tresus sp.
Inconspicuous Macoma	Macoma inconspicua
Irus Macoma	Macoma irus
Bay Mussel	Mytilus edulis
Geoduck	Panope generosa
Jingle Shell	Posodesmus cepio
Sea Stars
Mottled Star	Evasterias troschelli
Sea Cucumbers
White	Eupentacta quinquesemita
Barnacles
Acorn Barnacle	Balanus glandula
Small Acorn Barnacle	Chthanalus dalli
Thatched Barnacle	Balanus cariosus
Crabs
Purple Shore Crab	Hemigrapsus nudus
Green Shore Crab	Hemigrapsus oregonensis
Black Clawed Crab	Lophopanopeus bellus
Graceful kelp crab	Pugettia gracilis
Red rock crab	Cancer productus
Shrimp
Sitka shrimp	Heptacarpus sitchensis
Hermit crabs
Tubeworm hermit	Discorsopagurus schmitti
Porcelain crabs
Flattop crab	Petrolisthes eriomerus
Anemones
Colonial anemone	Cribrina elegantisima
Green Anemone	Anthopleura xanthogrammica
Segmented worms
Irridescent worm	Hemipodus borealis
Tube worms
Calcareous tubeworm	Serpula vermicularius
Flatworms
Large speckled	Kaburakia excelsia
Pink	Notoplana litoricola
Isopods
Brown Isopod	Idotea urotoma

Clams

In addition to the availability of suitable habitat, vigilant enforcement by the state parks managers appears to have helped maintain the clam population here. The beach is currently open to recreational harvesting for a short time each year and then is closed.

The clam band here covers about 2 acres, slightly more than one acre on and south of the alluvial fan and slightly less than 1 acre north of the fan, among the boulders. Twenty-two (22) of the 28 holes dug contained one or more clams. The population density averaged 14.8 clams per square foot, the fifth highest of the beaches surveyed. Clams were most numerous at the south end of the park but they tended to be somewhat heavier at the north end.

While the macoma clams numerically made up 40% of the population, they were so small that they accounted for only 3% of the biomass. Conversely, the horse and softshell clams made up only 2% of the count, but they were so large that they accounted for 28% of the biomass. The 325 clams weighed 3,685 grams for an average of 11.3 grams each.

Compared to the average sizes of the clam species for all beaches, the manila, littleneck and butter clams were comparable, but the cockles and macoma clams were much smaller than the averages. While the averages for the horse clam and softshell clams are much higher than the averages, only one each of those species were found. Six (6) of the 26 manila clams and 6 of the 21 littlenecks were legal size. None of the 14 butter clams were of legal size.

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

Seaweed

Five (5) species of green algae and four each of the red and brown algae were identified on this beach. There were three species of Enteromorpha - E. intestinalis, E. plumosa and E. linza. There were also two species of Sea lettuce, Ulva fenestrata and Ulva lactuca. The brown algae were represented by popweed, Pylaiella littoralis, a small bushy filamentous plant, Ralfsia (tar spot) and Sargassum. Four species of Rhodophyta (red algae ) were identified. Ceramium pacificum and Polysiphonia collinsii are pinkish purple algae that grow in lacy filaments that form four to six inch high bushes. Gigartina latissima was found high on the rip-rap. Nori, with single, more-or-less round blades, was found.

Green (Chlorophyceae)

Enteromorpha intestinalis

Enteromorpha plumosa

Enteromorpha linza

Ulva fenestrata

Ulva lactuca

Brown (Phaeophyceae)

Fucus sp.

Pylaiella littoralis

Ralfsia sp.

Sargassum muticum

Red (Rhodophyceae)

Ceramium pacificum

Gigartina latissima

Polysiphonia collinsii

Porphyra perforara

Thomas Creek flows through the park and its course on the beach is marked by a luxuriant growth of Enteromorpha intestinalis, a green marine alga. That alga prefers and efficiently uses fresh water for part of the tide cycle. The alga growth on the beach is conspicuous at long distances and effectively marks the mouths of freshwater streams and seeps. (In fact, it was used in the past by sailors to locate fresh water). Even though the algal growth was luxurious, the diversity was second lowest of the eight beaches surveyed for algae.

Other

The bird population was surveyed twice in January, 1995. Fourteen (14) species were identified, six of which were diving birds (cormorants, mergansers or grebes), while five were surface feeders. Harbor seals have been observed off shore. Sea lions have been observed early in the morning.

Use

Many persons have been observed nearly every day that the beach was surveyed. Some were beachcombing, but many were harvesting seaweed, clams, or crabs.

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Updated: 11/02/98