Dataset: Purple urchin density

Name: Density of purple sea urchins along the California coast, 37.8 to 39.3 N: Andrew Molean State Park to Manchester State Park from 2005-2014 (CHIPS project)
Published: 2014-12-20
Keywords: biota, oceans

Cite This Dataset

Spatial Extent: N:39.28122 E:-122.7068 S:37.89309 W:-123.8038

Project:

Ecological & genetic recovery from a massive invertebrate die-off along the central coast of California (CHIPS)

Principal Investigator:

Brian Gaylord (University of California-Davis, UC Davis-BML)

Co-Principal Investigator:

Michael N. Dawson (University of California-Merced, UC Merced)

Richard K. Grosberg (University of California-Davis, UC Davis)

Student:

Laura J. Jurgens (University of California-Davis, UC Davis-BML)

Lauren Schiebelhut (University of California-Merced, UC Merced)

Contact:

Laura J. Jurgens (University of California-Davis, UC Davis-BML)

Lauren Schiebelhut (University of California-Merced, UC Merced)

BCO-DMO Data Manager:

Nancy Copley (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Version:

2014-12-20

Version Date:

2014-12-20

Restricted:

Validated:

Yes

Current State:

Final no updates expected

Density of purple sea urchins along the California coast, 37.8 to 39.3 N: Andrew Molean State Park to Manchester State Park from 2005-2014 (CHIPS project)

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Description

Twenty accessible rocky intertidal sites were selected to span the ‘kill-zone’ and peripheral locations (see list of sites in Jurgens et al. submitted). Two rocky intertidal areas were sampled per site, usually one on either side of the point of entry onto the beach and separated by approximately 100 m. We used quadrats (1m^2 [4 * 0.25 m^2] or 0.0625 m^2) and swaths (2 m wide transects) to estimate juvenile and adult abundance for each target species.

This data set includes abundances of Strongylocentrotus purpuratus (purple sea urchin) and their burrows on transects along the California coast from 37.9 N to 39.3 N.

Access Restriction: Access to these data are restricted until publication of the associated manuscript, which is currently in review at PLOS ONE. [2015-02-05]

Methods & Sampling

Surveys of S. purpuratus occupancy

We quantified occupied and unoccupied burrows in intertidal bedrock; these burrows are directly attributable to S. purpuratus. The rock walls of burrows are clean while urchins occupy them, but sessile invertebrates such as barnacles, spirorbid worms and anemones rapidly (within weeks) colonize vacated burrows. We used this distinctive indicator to estimate pre-HAB urchin populations, calculating pre-HAB density as the combined density of live urchins plus clean, empty burrows. We calibrated this quantity using the average occupancy rate of burrows at four control sites (Van Damme State Park, Arena Cove, Palomarin, Duxbury Reef). We began mortality surveys at three sites (Phillips Gulch, Windermere Point, Bodega Marine Reserve) within two weeks of initial observations of an harmful algal bloom (HAB), once tides became low enough to access urchin habitat. We completed initial population surveys at the remaining sites during the first three accessible low tide series following the HAB, between October and December 2011.

Data Processing Description

To estimate swath length we first summed the Euclidean distances between consecutive GPS trackpoints. Given the GPS had an error of +/- 3 meters we smoothed the GPS tracks by averaging across two trackpoints and then by three. We selected a window size of two with which to estimate our total transect length to adjust for the noise in our swath transects but to minimize oversmoothing. (see example figure below). We identified and removed outlying trackpoints that led to a Euclidean distance >=8 meters (likely due to temporarily poor satellite signal). The distance was then recalculated between the trackpoints immediately preceding and following the removed trackpoint. Total transect search area was calculated by multiplying the total adjusted transect length by swath width. Total transect search time was estimated using field notes and GPS waypoints and trackpoints, removing 6-second intervals where < 0.05 m were traveled (suggesting this was time during which notes were being written or tissues samples were being collected).

Swath figure: Sample GPS tracks for two transects at Iversen Point, Mendocino County. The blue line is the original unsmoothed track. The red line represents a window size of two, averaging latitudes and longitudes across each pair of consecutive trackpoints. The green line represents a window size of 3, averaging across 3 trackpoints.

BCO-DMO Processing Notes:

added conventional header with dataset name, PI name, version date, reference information
renamed parameters to BCO-DMO standard
added longitude column

Data Files

File
urchin_dens.csv (Comma Separated Values (.csv), 9.12 KB) MD5:471c1e341239c0cf0b8d758926ad96d7 Primary data file for dataset ID 541003

More Information about this dataset

Funding Sources

Funding Source	Award Number
NSF Division of Ocean Sciences	OCE-1243970
NSF Division of Ocean Sciences	OCE-1243958

Deployments

Deployment	Synonyms	Start Date	Platform	Investigator
CalifCoast_Gaylord_CHIPS		2005-01-01	shoreside Calif_shore	Brian Gaylord (Principal Investigator)	data info

Instruments

None available yet

Parameters

Date and time formats are described in python strftime() syntax.

Supplied Name	Supplied description	Supplied Units	Standard Name
site	name of location surveyed	unitless	site
lat	latitude of survey site; north is positive	decimal degrees	lat
lon	longitude; east is positive	decimal degrees	lon
date_survey	first date quadrat-based quantitative surveys were conducted; i.e. date the data here were collected	yyyy-mm-dd	date
quad_num	number of the quadrat in which counts of live urchins and empty burrows were conducted; total of 12	unitless	sample
quad_area	area of the quadrat in which counts were conducted. Quadrats were 50cm per square side.	meter^2	no_bcodmo_term
live_per_quad	number of live Strongylocentrotus purpuratus per quadrat	# urchins	count
live_per_m2	number of live urchins per quadrat scaled by area of quadrat to a count per square meter	# urchins/meter^2	abundance
empty_per_quad	number of clean unfouled & empty S. purpuratus burrows in each quadrat	# burrows	count
empty_per_m2	number of empty burrows per quadrat scaled by area of quadrat to a count per meter square	# burrows/meter^2	abundance
prior_density_m2	prior density estimated using clean empty burrows per square meter plus live urchins per square meter	# urchins/meter^2	abundance
impact_flag	Yes=recent loss of urchins detected; No= no evidence of recent urchin loss in the populations; in each case this assessment was based on the presence of clean empty urchin burrows versus live animals	unitless	flag

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Dataset: Purple urchin density