Modeling dispersal of oyster larvae in Chesapeake Bay

Grant awarded to:
Elizabeth North (UMCES)
Tom Gross (NOAA/CRC)
Raleigh Hood (UMCES)
Ming Li (UMCES)
Liejun Zhong (UMCES)

Team includes:
Zachary Schlag

Funded by:
Maryland Department of Natural Resources

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C. virginica larvae
Photo by D. Merrit

___The objectives of this research are to 1) determine the dispersal of Crassostrea virginica and C. ariakensis oyster larvae in Chesapeake Bay using coupled hydrodynamic and larval transport models, and 2) transfer this information to a juvenile/adult demographic model. This research was conducted as part of an Environmental Impact Statement (EIS) to assess the feasibility of introducing a non-native oyster (C. ariakensis) to Chesapeake Bay in addition to assessing alternate restoration strategies for the native oyster (C. virginica).

___Although adult oysters remain fixed in one location, their eggs and larvae spend ~3 weeks as free-swimming plankton in the water column. During this planktonic stage, the young oysters pass through different stages of development, growing from fertilized eggs, to trocophores, to veligers, and finally to pediveligers. The pediveliger stage is the stage at which larvae search for suitable substrate to which they cement themselves, leaving the water column and becoming fixed on the bottom. This “settlement” of the larvae signals the end of the larval dispersal stage and the beginning of the juvenile stage. A suite of physical and biological factors influence larval dispersal and subsequent oyster larvae settlement. Circulation patterns are controlled by tides as well as freshwater flow and wind which can change between years, months, weeks and even days. These patterns, and differences in larval behavior, influence the direction and distance that larvae could be transported and the location where they ultimately settle.

___To predict oyster larval dispersal, we used two numerical models (i.e., computer simulations): a particle-tracking model and a three-dimensional hydrodynamic model of Chesapeake Bay. The coupled bio-physical modeling system has the ability to move particles due to currents velocities and turbulent mixing, and includes algorithms that give the particles “oyster larvae-like” behaviors. We use circulation predictions from 5 years in order to capture a range of physical conditions that likely influence larval dispersal. In addition, we used the best estimate of suitable present-day oyster habitat (oyster bars) and information from laboratory studies on larval behavior.


___Overall results of the larval transport model simulations indicate that:

Weak swimmers have power: The vertical swimming of oyster larvae influenced their encounter with suitable habitat and the distance that they were transported. In addition, swimming behavior influenced the connections between simulated oyster populations in different tributaries. Management implications: Spatial patterns in harvest will not have the same impact on species that have different larval behaviors.

No bar is an island: Few simulated larvae (<4%) returned to the same bar on which they started. This indicates that oyster populations depend on multiple bars. Management implications: Restoring isolated bars may not be the most effective strategy for population restoration.

Basins and bars are not equal: Model results suggest that some tributaries and oyster bars may produce more successful larvae than others because of their location in relation to habitat and circulation patterns. Management implications: this type of information could be used to guide placement of sanctuaries.

___Please see North et al. (2006) and North et al. (2008) (citations below) for more information about the larval transport model and results.

___Please visit the Oyster Larvae Transport Animations page to see animations of larval transport model results.



North, E. W., Z. Schlag, R. R. Hood, M. Li, L. Zhong, T. Gross, and V. S. Kennedy. 2008. Vertical swimming behavior influences the dispersal of simulated oyster larvae in a coupled particle-tracking and hydrodynamic model of Chesapeake Bay. Marine Ecology Progress Series 359: 99-115 (request .pdf)

North, E. W., Z. Schlag, R. Hood, L. Zhong, M. Li, and T. Gross. 2006. Modeling dispersal of Crassostrea ariakensis oyster larvae in Chesapeake Bay. Final report to Maryland Department of Natural Resources, 31 July 2006. 55 pp. Original report pdf. Updated report pdf with Appendices that contain response to and comments from the EIS Larval Transport Peer Review Team.