Context: Many nearshore species are distributed in habitat patches connected only through larval dispersal. Genetic research has shown some spatial structure of such metapopulations and modeling studies have shed light onto possible patterns of connectivity and barriers. However, little is known about human impact on their spatial structure and patterns of connectivity. Objectives: We examine the effects of fishing on the spatial and temporal dynamics of metapopulations of sedentary marine species (red sea urchin and red abalone) interconnected by larval dispersal. Methods: We constructed a metapopulation model to simulate abalone and sea urchin metapopulations experiencing increasing levels of fishing mortality. We performed the modularity analysis on the yearly larval connectivity matrices produced by these simulations, and analyzed the changes of modularity and the formation of modules over time as indicators of spatial structure. Results: The analysis revealed a strong modular spatial structure for abalone and a weak spatial signature for sea urchin. In abalone, under exploitation, modularity takes step-wise drops on the path to extinction, and modules breakdown into smaller fragments followed by module and later metapopulation collapse. In contrast, sea urchin showed high modularity variation, indicating high- and low-mixing years, but an abrupt collapse of the metapopulation under strong exploitation. Conclusions: The results identify a disruption in larval connectivity and a pattern of collapse in highly modular nearshore metapopulations. These results highlight the ability of modularity to detect spatial structure in marine metapopulations, which varies among species, and to show early changes in the spatial structure of exploited metapopulations.
Bibliographical noteFunding Information:
This work was supported by NSF Grants OCE-0410439 as part of the Project “Linking Human and Biophysical Processes in the Coastal Marine Ecosystem of Baja California”, and GEO-1211972 as part of the CNH Project “Complexity and Adaptation in Marine Social-ecological Systems”. We also thank Satoshi Mitarai and David Siegel for creating the connectivity data, Laura Rogers-Bennett and Cynthia Catton for the useful information of red abalone and red sea urchin, and the Pisco Project for the abalone and sea urchin data made available in their website ( http://www.piscoweb.org ).
© 2017, Springer Science+Business Media Dordrecht.
- Allee effect
- Larval connectivity
- Marine metapopulation
- Red abalone
- Red sea urchin
- Seascape ecology
- Southern California Bight
- Spatial structure