Predator regulation of sedimentary fauna in a sub-arctic fjord ecosystem

Quijón, Pedro A. (2004) Predator regulation of sedimentary fauna in a sub-arctic fjord ecosystem. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Historical changes in predator composition in the Newfoundland ecosystem as a result of over-fishing have resulted in a switch from a cod-dominated system to one with abundant decapod crustaceans. In order to understand the consequences of this switch to benthic ecosystems, it is critical to evaluate how epifaunal crustaceans regulate sedimentary communities. An array of exploratory and experimental studies was undertaken in Bonne Bay, a sub-arctic Newfoundland fjord, in order to document predator and prey spatial variation and community responses to predator manipulation. The distribution of snow crab and at least one shrimp species in the main arms of Bonne Bay fjord were found to be related to planktonic larval supply, particularly, late larval stages. The distribution of infaunal prey varied in parallel with predator patterns and, as shown by detailed analysis of the dominant taxon (polychaetes), was related to habitat quality and distribution. Sandy and muddy habitats supported different infaunal communities, and species that occupied a variety of substrates were more broadly distributed inside the fjord and the region. Field exclusion and inclusion experiments carried out in the two main arms of the fjord were complemented with laboratory experiments using the main predators of the fjord: snow crab (Chionoecetes opilio), rock crab (Cancer irroratus) and toad crab (Hyas spp). Results suggest that i) crustacean predation regulates benthic composition, density, and sometimes diversity, ii) predator effects vary spatially, iii) the same infaunal species were important in describing predator exclusion treatments both in the field and in the laboratory experiments, and iv) snow crab and rock crab are the predators that have the strongest effects on infaunal communities. Given that both predators are targeted by the fishery, these results also suggest that the potential impacts of fishing may be even broader than expected through cascading effects on infauna. Finally, the effects of predation on benthic infauna were examined using surrogates or taxonomic categories coarser than species. Although results obtained with data at the family level resemble those with data at the species level, the lack of generality in surrogate performance suggests a cautious use of surrogates in experimental and biodiversity studies.

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