Variability in marine molluscan communities: Historical versus modern drivers over local and regional scales /

Saved in:
Bibliographic Details
Author / Creator:Voorhies, Kristen J., author.
Ann Arbor : ProQuest Dissertations & Theses, 2015
Description:1 electronic resource (146 pages)
Format: E-Resource Dissertations
Local Note:School code: 0330
URL for this record:
Hidden Bibliographic Details
Other authors / contributors:University of Chicago. degree granting institution.
Notes:Advisors: Susan M. Kidwell; John T. Wootton Committee members: David Jablonski; Scott Lidgard.
Dissertation Abstracts International, Volume: 77-02(E), Section: B.
Summary:Historical baselines are critical to evaluating the extent of modern impacts in the marine environment and planning actions for conservation and the future. Unfortunately, we rarely begin collecting information on marine communities before the onset of concern over possible negative impacts on marine communities. Therefore we lack baseline ecological data that represent the state of the un-impacted community. Here I address this issue of missing ecological data by using death assemblages, the dead remains of previously living communities, as an un-tapped source for previously un-observed historical ecological information. I use benthic bivalve communities from Newport, Oregon, a continental shelf where modern marine communities are already being monitored for impacts. First, I establish the validity of death assemblages as a historical baseline by evaluating the similarity between the modern living bivalve communities and the death assemblages that I sampled in the same area as those that have been monitored for the past three years. Evaluating this live-dead similarity revealed limited bias resulting from taphonomic or collection and sampling methods and strong agreement in community patterns of taxonomic composition and rank abundance structure between living and death assemblages. Next, I evaluated one subarea where the living and death assemblages did not agree as strongly in taxonomic composition and rank abundance structure for evidence of ecological changes due to impacts. The poor live-dead agreement revealed previously unrecognized impacts from dredge material disposal, an observation that was not possible with living bivalve communities alone. Dredging activities are an important commercial and economic activity but can be effectively monitored in this area using live-dead agreement and investigating occasions when that agreement weakens. In my third chapter, I evaluate the pattern of an onshore-offshore change in community composition and structure that was reflected in both living and dead bivalve assemblages. Two communities have existed on the shelf historically, one in shallow water less than 50 meters in water depth and a different community in deeper waters below 50 meters in water depth. By testing environmental drivers including oxygen, pH, nutrients, and wave-base, I demonstrate that these benthic bivalve communities are strongly related to the interaction of wave-energy with the environment through wave-base. This finding is critical for future evaluation because current efforts to collect marine renewable energy from wave energy are focused off the coast of Newport, Oregon. Removing wave-energy from this system has the potential to directly impact the composition and structure of marine bivalve communities, which may transfer to higher changes in trophic structure for this region. Finally, I investigate whether the close association of community structure with wave-energy, as seen in Oregon, is apparent in southern Californian communities. If depth, and possibly wave-energy, do appear to correlate consistently with marine community structure from different regions and habitat types then it warrants future work into this previously overlooked physical factor in the ecology of marine communities. I present preliminary evidence in my appendix on an indirect but significant signals for depth-patterning in southern California marine communities across multiple habitat types.