Clam recruitment and survival, Crab abundance in Willapa Bay 2024

Description

In June-Sept 2024, seven stations spanning 20 km on intertidal flats of Willapa Bay, Washington (USA) were measured for recruitment of two clam species: Manila clams (Ruditapes philippinarum) and softshell clams (Mya arenaria). Recruitment was operationally defined as 250-500 micron size class and was measured from spat samplers four times during the summer, as well as seasonal recruitment of >500 micron clams that survived to mid-September. (Spat samplers = mesh bags of 15x10 cm, 1 mm mesh size, filled with round gravel) Predator exclosures were established at four tidal elevations at one site, and survival of 1-cm and 2-cm clams was measured over 6 weeks. Crab abundances were determined from traps mid-way through the experiment, including three native (Metacarcinus [Cancer] magister, Cancer productus, Hemigrapsus oregonensis) and one non-native crab species (Carcinus maenas).

Steps to reproduce

1) Find site locations in Willapa Bay, Washington, USA based on WGS84 geolocations 2a) Place 15x10 cm mesh bag of gravel, replaced every month (N=5 bags per site) from June through September 2b) Sieve bag contents to 250-500 microns, count and identify clam recruits 3a) Place 15x10 cm mesh bag of gravel, remaining in place from June through September (N=5 bags per site) 3b) Sieve bag contents to 500 microns, count and identify clam recruits 4a) Place predator exclusion and open experimental units at four elevations (see data file for GPS and elevations). Add 20 small clams (<1 cm) and 5 large clams (2-3 cm) 4b) Sort contents of experimental units after 6 weeks, record number of clams of each size class and measure shell dimension of small clams 5a) Deploy predator traps: A transect at each of the tidal elevations used in 4a) consisted of five cylindrical minnow traps (Gee-40, 50 mm diameter opening, 6.35 mm mesh) and five folding square fukui-style fish traps (13 mm mesh), alternating trap type and each trap separated by 10 m. Traps baited with approximately 100 g of Pacific mackerel (Scomber japonicus) were set on a morning lower-low tide, allowed to soak through the overnight higher-high tide, and retrieved on the following day’s lower-low tide. 5b) Identify, count, and measure carapace width of all crabs in each trap.

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