Organism responses to habitat fragmentation and diversity: Habitat colonization by estuarine macrofauna

• Published in: Journal of experimental marine biology and ecology Vol. 236; no. 1; pp. 107 - 132
• Main Authors: Eggleston, David B, Elis, Ward E, Etherington, Lisa L, Dahlgren, Craig P, Posey, Martin H
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 31.03.1999; Elsevier Science
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Colonization; Crassostrea virginica; Fragmentation; Fundamental and applied biological sciences. Psychology; Grass shrimp; Habitat selection; Marine; Marine benthos; Palaemonidae; Patchiness; Recruitment; Sea water ecosystems; Synecology; Zostera marina; North Carolina; United States; North America; America; ANW, USA, North Carolina, Back Sound; Grass shrimp; Palaemonidae; Zostera marina; Crassostrea virginica; Habitat selection; Marine benthos; Patchiness; Colonization; Fragmentation; Recruitment; Fauna; Estuaries; Environmental factor; Marine environment; Species diversity; Macrofauna; Population recruitment; Population dynamics; Population density; Ecological abundance; Benthic zone
• ISSN: 0022-0981; 1879-1697
• DOI: 10.1016/S0022-0981(98)00192-0

Ecologists increasingly recognize that their choice of spatial scales may influence greatly their interpretation of ecological systems, and that small changes in the patchiness of habitat resources can produce abrupt, sometimes dramatic shifts in distribution and abundance patterns of a species. Moreover, identification of scale- and habitat-dependent ecological patterns are central to management efforts aimed at predicting the response of organisms to the increasing threat of habitat fragmentation. We used habitat plots containing artificial seagrass, oyster shell, and a mixture of seagrass and shell, placed on unstructured seafloor for 14 days in Back Sound, North Carolina, USA to examine the interactive effects of patch size, habitat diversity and experimental site on colonization by assemblages of estuarine macrofauna. We tested three a priori predictions of the general hypothesis that macrofaunal colonization is scale- and habitat-dependent: (1) colonization (per unit area) will be higher in small patches than in large ones; (2) small macrofauna will show a stronger response to habitat patchiness at a given scale than large macrofauna; and (3) colonization by estuarine macrofauna will be higher in habitat plots containing a mixture of seagrass and oyster shell compared to monotypic plots. Macrofauna responded to habitat patchiness in a complex manner that varied according to habitat type, experimental site, species, taxon, functional group, and animal body size (small: 500 μm–2 mm; large: >2 mm). Of the five out of seven response variables where we observed a significant patch size effect, grass shrimp ( Palaemonidae sp.) and small, mobile crustaceans (i.e., amphipods and isopods) were the only taxonomic or functional groups whose densities were higher in small (0.25 m 2) than large (1 m 2) patches, as predicted. Moreover, there was a disproportionate reduction in macrofaunal abundance and diversity in small patches of oyster shell compared to seagrass and mixed habitat treatments; this pattern was significant for both the total density and numbers of small species but not for large macrofauna. The total density and number of macrofaunal species was not higher in the mixed habitat treatment compared to seagrass or oyster shell. Our study demonstrates that an organism's response to habitat patchiness is dependent upon species, taxa, functional group, and animal body size, and that an organism's response is further modified by habitat type. The patterns observed in this study highlight the importance of scale- and habitat-dependent responses by mobile organisms to complex benthic habitats, and, because of the disproportionate reduction in faunal density and diversity in small versus large patches of oyster shell, heightens concern over the negative impacts to biodiversity through large-scale fragmentation of subtidal oyster reefs in certain regions.