Gayana 68(2) supl. t.I. Proc. : 213-214, 2004 ISSN 0717-652X

Poster session ­ PORSEC 2004, Conception, Chile, Nov 29-Dec 3, 2004

HYPERSPECTRAL IMAGING AND GIS: TOWARDS AN OPERATIONAL APPROACH TO MAP SHALLOW, MARINE, INVASIVE ALGAL SPECIES IN OPTICALLY DENSE WATERS

Patrick Gagnon* ^1,2, William Jones¹, Herbert T. Ripley¹, Robert E. Scheibling² & Bruce G. Hatcher²

1. Hyperspectral Data International, 7071 Bayers Road-Suite 119, Halifax, Nova Scotia, Canada, B3L 2C2
2. Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J1
* Email of corresponding author: Patrick.Gagnon@hdi.ns.ca

INTRODUCTION

Non indigenous species (NIS) are increasingly conspicuous in marine and estuarine habitats worldwide, which, clearly, are a significant force of change on native communities globally^(a). The Asian, green alga Codium fragile ssp. tomentosoides is one of the most invasive alga worldwide, with transoceanic and interoceanic spread since the beginning of the last century ^(b). Since it was first reported along the Atlantic coast of Nova Scotia (Canada), a decade ago, C.fragile has become a serious threat for the ecological integrity of shallow, coastal ecosystems, and the economy of the Canadian Maritimes. Our inability to address this problem and to develop adaptation strategies is directly linked to the absence of accurate tools to map the extent, and determine the pattern and race of spread of the alga over synoptic scales. In this study, we present the methodological guidelines of an approach being developed in Nova Scotia to synoptically map shallow, marine, invasive algal species in optically dense waters, using a compact airborne spectrographic imager (casi) and a geographical information system (GIS).

METHODOLOGICAL OVERVIEW

1. The abundance of dominant algal species is determined at random, geo-referenced points in the area of interest using scuba diving techniques. The data are integrated into a geographical information system (GIS);

2. The area to be mapped is segmented into matching flightlines and the casi is deployed at times of optimal atmospheric and oceanic conditions;

3. Selected portions of the sea bottom containing the algal species of interest (C.fragile) are monitored using scuba diving techniques and a submersible video camera, and georeferenced for further habitat classification using casi imagery;

4. The casi data from each flightline is corrected for atmospheric effects, geometric distortions, and attenuation of light by the water column, and further mosaicked into a single image;

5. A supervised classification of the corrected casi data (step 4) is performed using the ground truth data (step3). The resulting distributional maps are exported into a GIS database and compared with the in situ algal distribution data (step 1).

OTHER POTENTIAL APPLICATION

We presented the guidelines of a developing approach to synoptically map the extent of shallow, benthic, algal assemblages in optically dense waters as found along the coast of Nova Scotia. Although we focused on the usefulness of this approach to study the pattern and pace of spread of invasive species such as Codium fragile ssp. tomentosoides, a number of other major coastal applications can be envisioned, including: 1) large-scale and site-specific management of the exploitation of targeted macrophyte resources (e.g., kelp, rock weed, Irish moss) and their associated fisheries (e.g. American lobster, green sea urchin), 2) establishment and control of new and existing fishery and aquaculture areas, 3) delineation and monitoring of marine and coastal protected areas, and 4) implementation of adaptation strategies to marine community changes associated with the global climate change.

LITERATURE CITED

(a) Ruiz, G. M., Carlton, J. T., Grosholz, E. D. & Hines, A. H. 1997. Global invasions of marine and estuarine habitats by non-indigenous species: mechanisms, extent, and consequences. Amer. Zool. 37:621-632.

(b) Trowbridge, C. D. 1998. Ecology of the green macroalga Codium fragile (Suringar) Hariot 1889: invasive and non-invasive subspecies. In: Ansell, A. D., Gibson, R. N. & Barnes, M. [Eds.], Oceanography and marine biology: an annual review. UCL Press, pp. 1-64.