Community Biodiversity Surveys in the Rocky Intertidal using Spatially-Nested Methods
Purpose and background: To quantify the abundance (estimated as both percent cover and density) of species in the rocky intertidal zones. This method was used from 2011 through 2015 for sites in Oregon. A longer dataset has been in-place in Oregon from 1997 through present (2016). These surveys are used to document long-term trends in species diversity and richness over time, as well to compare between different sites.
Replicates per Site: One 30-meter transect line per intertidal zone (mid and high zones) or 3 different previously determined areas (low zone)
Number of plots per replicate: 10 quadrats randomly placed per transect line (mid and high zones) or 10 quadrats haphazardly placed per area (low zone)
Materials: 50-meter transect tape, 0.25 m2 stringed quadrat (with 25 squares), datasheet, clipboard, pencils, ID guide (if needed)
Frequency: Surveys should be done every summer around lowest tides of summer.
Identify: Low, Low-Mid, Mid and High Zones to be surveyed
Setting markers: Drill into bedrock and place an anchored lag to mark the beginning and end of each transect line
Measuring elevation: GPS and take tidal heights of each transect line after they have been laid down
Mid and High Zones
- Before you go in the field generate 10 random numbers between 0-30. These numbers will be the distance (in meters) for your ten quadrat surveys along a 30-meter transect, and order then from lowest to highest on the datasheet.
- Run out 30 meter of transect tape where there are markers from the previous years. In mid-zone should run through middle of mussel bed.
As you run out the transect tape keep an eye on the very abundant species (e.g. barnacles, limpets, Littorina, and mussels) to determine of what to subsample and how to subsample them.
- Place the left bottom corner of the 0.25 m2 stringed quadrat on the up slope side of the transect tape at its randomly assigned distance from the 0 m mark.
- After surveying this quadrat, move to the next
- Haphazardly place each 0.25 m2 stringed quadrat with in the designated area, for all 10 quadrats in the area try to capture overall area diversity.
- Estimate percent cover for everything occupying the Primary Space first (this includes the cover of barnacles, mussels, algal holdfasts, crusts, bare rock, sand etc. but NOT mobile invertebrates, these will be counted later). Total Primary Cover count MUST equal 100%.
- Estimate percent cover for all other organisms in the quadrat, this total can be less than or greater than 100%. If there are epibionts present (species attached to another organism) within plot for a particular species, put a slash behind the species name in the column and write epibiont, then split the spot where the percent cover is recorded in half with the top number for the percent cover of species attached to bare rock and bottom number the percent cover of the species that is an epibiont.
For example: if Balanus glandula is found attached to bare rock and on top of Mytilus californianus within a quadrat these two percent covers must be recorded separately.
- In estimating percent cover using a stringed quadrat with 25 squares, each square = 4% and a quarter of each square = 1%. With this in mind you can rapidly get accurate counts of percent cover. (One could also string a quadrat so that a square = 1%, the ones in our lab are 4%)
- Estimate the density of all mobile invertebrates (limpets, chitons, whelks, stars, urchins etc.)
Density counts may need to be subsampled if numbers are going to be in the 1000’s. Determine the area that will be subsampled (10cm x 10cm or 5cm x 5cm, typically in one of the corner squares of the quadrat) and be consistent for all quadrats.
Datasheets for surveys can be found here named ‘Community Survey Blank Datasheet’. Print them out on Write-in-the-Rain paper.
For unknown species (especially algae) bring back to lab to identify/key out.
Identify/key out all unknown species.
File datasheets for later data entry.
Method development literature:
Lubchenco, J., B. A. Menge, S. D. Garrity, P. J. Lubchenco, L. R. Ashkenas, S. D. Gaines, R. Emlet, J. Lucas, and S. Strauss. 1984. Structure, persistence, and role of consumers in a tropical rocky intertidal community (Taboguilla Island, Bay of Panama). Journal of Experimental Marine Biology and Ecology 78:23-73
Menge, B. A. 1976. Organization of the New England rocky intertidal community: role of predation, competition and environmental heterogeneity. Ecological Monographs 46:355-393.
Schoch, G.C., B.A. Menge, G. Allison, M. Kavanaugh, S.A. Thompson, and S.A. Wood., 2006. Fifteen degrees of separation: Latitudinal gradients of rocky intertidal biota along the California Current. Limnology and Oceanography 51:2564-2585.