Use of Cost Effective Remote Sensing to Map and Measure Marine Intertidal Habitats in Support of Ecosystem Modeling Efforts: Cobscook Bay, Maine

Abstract

Reliable estimates of the habitat areas of major marine producer groups were needed in support of an ecosystem modeling effort in the macrotidal Cobscook Bay, ME. Results needed to be comprehensive, synoptic, objective, affordable, and on a suitable spatial scale. We chose to address these goals by applying accepted procedures utilizing existing Landsat Thematic Mapper imagery and a computer-generated unsupervised classification.Unsupervised classification of high and low tide Landsat TM images yielded coherent habitat maps that were supported by reference data and independent habitat analyses. The high tide image revealed surface water patterns that supported the existence of a large, Central Bay dipole eddy predicted by a numerical three-dimensional circulation model. Classification of the low tide image resulted in 14 intertidal and water habitat classes being defined. Overall accuracy of the classification was 86%. Good agreement in habitat areas existed between the affordable and easily repeatable satellite survey and four other Cobscook Bay surveys which differed methodologically and temporally. The four studies agreed within 7% of total habitat area and 12% on intertidal habitat area. The area of both brown and green algae in the Bay apparently increased modestly over a 25-year period which saw the introduction of large-scale salmon aquaculture and the advent of intensive dragging for scallops and sea urchins. The increase in both groups is inconsistent with changes induced by nutrient additions observed elsewhere. Landsat imagery appears to be a valuable tool for the management and monitoring of macrotidal environments.