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Marine Ecology Progress Series

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MEPS 405:39-56 (2010)  -  DOI: https://doi.org/10.3354/meps08511

Fractal measures of habitat structure: maximum densities of juvenile cod occur at intermediate eelgrass complexity

Maria E. Thistle1,6,*, David C. Schneider2, Robert S. Gregory3,4, Nadine J. Wells5,7

1Cognitive and Behavioural Ecology Programme, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1B 3X7, Canada
2Ocean Sciences Centre, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1C 5S7, Canada
3Ecological Sciences Section, Fisheries and Oceans Canada, 80 E. Whitehills Road, PO Box 5667, St. John’s, Newfoundland and Labrador A1C 5X1, Canada
4Department of Biology, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1B 3X9, Canada
5Environmental Science Programme, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1B 3X9, Canada
6Present address: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
7Present address: Science Branch, Fisheries and Oceans Canada, 80 E. Whitehills Road, PO Box 5667, St. John’s, Newfoundland and Labrador A1C 5X1, Canada

ABSTRACT: Habitat patchiness is known to alter the relation of a population to both its predators and its prey. We developed a biologically interpretable measure of habitat complexity to test whether juvenile fish density depends on degree of patchiness. In Newfoundland coastal waters, juvenile fish species, including Atlantic cod Gadus morhua, are associated with eelgrass Zostera marina. However, the association of density with eelgrass cover is dependent upon site and the scale of analysis. We tested for non-monotonic relationships (with an intermediate optimum) between 5 spatial characteristics of eelgrass and density of 3 juvenile (Age-0) fish species: Atlantic cod, Greenland cod G. ogac, and white hake Urophycis tenuis. We used aerial photography to determine eelgrass perimeter and area measurements at multiple scales, fractal dimensions of perimeter (DP) and area (DA), and a measure that combines perimeter and area complexity at these scales (βP/A). Fish densities were estimated at each site using a seine net. We found parabolic relationships between βP/A and density for all 3 species, indicating highest fish densities at sites of intermediate patchiness and edge regularity. Furthermore, we determined that βP/A provided a less ambiguous estimate of spatial configuration than other measures. This intermediate maximum may reflect a trade-off, whereby eelgrass sites of intermediate spatial complexity provide juvenile fish with both optimal protective cover and opportunity to feed. This pattern may apply to any species requiring open areas in which to forage as well as shelter to offset predation risk.


KEY WORDS: Habitat patchiness · Landscape ecology · Eelgrass · Fractal · Multiple scales · Habitat use · Atlantic cod · Greenland cod · White hake


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Cite this article as: Thistle ME, Schneider DC, Gregory RS, Wells NJ (2010) Fractal measures of habitat structure: maximum densities of juvenile cod occur at intermediate eelgrass complexity. Mar Ecol Prog Ser 405:39-56. https://doi.org/10.3354/meps08511

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