Description of Transect Methods and Setup of Web Page,
Outer Island Intertidal Transect


Background

This page is primarily intended for student groups who will be conducting field studies at Outer Island, Stewart B. McKinney National Wildlife Refuge, and for others interested in New England intertidal ecology. For those groups going to Outer Island, this web site can be used to study intertidal zonation prior to conducting their own intertidal transects.

The transect depicted herein was conducted on 12 August 1997 at low tide on the SE shore of Outer Island. Outer Island is located in Long Island Sound and is part of the Town of Branford, Connecticut (just east of New Haven).


Organization of Web Page

The On-line Intertidal Transect consists of several linked modules that can be accessed through the "Index" page (i.e., the Table of Contents). These pages include:

The page combines quantitative data describing the occurrence of dominant intertidal organisms on the shore of Outer Island with a visual presentation (i.e., photos) of these organisms and intertidal zones.

Photographs were taken in succession across the shore beginning at the low tide mark (i.e., water level) and progressing across the shore to the upper level of tidal influence. The photos represent 0.25 m segments in the horizontal dimension.

The web pages for the photographic images are structured in a series of sets of four photos. Each set of four contains a 1.0 m horizontal segment of the shore (i.e., 4 photos x 0.25 m each). The first of these pages shows 0.0 m to 1.0 m across the shore horizontally (i.e., from the low water mark to 1.0 m across the shore). The second, 1.0 m to 2.0 m, and so forth.

Each photographic image is presented in a small frame that can be "clicked on" to link with a full-screen, higher-resolution image of that 0.25 m segment. The pages with sets of four images in 0.25 m segments have solid lines above and below each image. Associated with each solid line are the horizontal distance (in meters from the low water mark) of the location of the top and bottom of each image and the corresponding vertical elevation (in centimeters above mean low water, MLW). Thus, the position of each image is presented vertically (from datum, MLW) and horizontally (from the low water mark at the time the transect was initiated).

Additionally, for each photo the percent cover occupied by dominant, sessile, intertidal organisms is given. These data were collected by visually estimating the coverage of each organism in a 0.25 m-on-a-side (i.e., 0.0625 m2) quadrat frame. Since inertidal organisms can occupy both a "canopy" level and an "understory," these percentages may sum to greater than 100%.

For both the small and enlarged images the vertical dimension of the image contains a horizontal distance of 0.25 m across the shore; the image's horizontal dimension is therefore somewhat greater than 0.25 m.


Description of Intertidal Transect Methods

At predicted low tide (i.e.,Tide Prediction Web Site) a 30 m tape was secured at the low tide mark (i.e., water level) and extended across the shore up to the level of maximum tidal influence. Beginning at the water level (.e., 0.00 m horizontal) a wire frame quadrat, 0.25 m on a side was placed on the shore. The percentage of the quadrat occupied by the dominant, sessile, intertidal organisms was visually estimated. If possible, "canopy-forming" organisms were then moved aside, the quadrat relocated to the original position, and the percentage of space occuped by "understory" organisms was visually estimated. This process was repreated every 0.25 m across the intertidal.

Concurrent with the estimation of percent cover, photographs were taken along the transect. Images were prepared to approximate the 0.25 m quadrat segments. Thus, each image contains a 0.25 m horizontal shore distance in its vertical dimension and a somewhat greater than 0.25 m distance in each image's horizontal dimension. Images were developed onto a Kodak CD-ROM and processed with Adobe Photoshop for this web page.

In addition to estimating the percent cover of organisms in the 0.25 m square quadrats and photographically recording these segments, the vertical elevation of each quadrat was measured and calculated relative to mean low water (datum, 0.00 m).




Index

Penniman@CCSU.EDU
Revised 23 January 1998
URL: http://wwwas.ccsu.ctstateu.edu/depts/biology/intertidal/transc.htm