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Biological Effects of Selected Structures and Practices in Galveston Bay System

Biological Effects of Selected Structures and Practices in Galveston Bay System. David Buzan, Liz Singhurst, Grace Chen and Wen Lee. Project Flowchart. Delta Marshes Oyster Reefs. TWDB. TPWD. Circulation & Salinity. Habitat & Species. Structures. Change in PAZ ?. Practices.

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Biological Effects of Selected Structures and Practices in Galveston Bay System

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  1. Biological Effects of Selected Structures and Practices in Galveston Bay System David Buzan, Liz Singhurst, Grace Chen and Wen Lee

  2. Project Flowchart Delta Marshes Oyster Reefs TWDB TPWD Circulation & Salinity Habitat & Species Structures Change in PAZ ? Practices Blue Crab Gulf Menhaden

  3. And We know that: Not all man-made changes are beneficial to the system

  4. The Six Study Cases(dry and wet year conditions) • EC – Existing Conditions • PPO – Power Plant Thermal Release • TCD – Texas City Dyke • HSC – Houston Ship Channel • FID – Freshwater Inflow Diversion • NC – Naturalized Conditions

  5. Trinity Delta Marshes • In upper bay – the oligohaline zone • Cover ~ 54 Km2 • Mixed emergent vegetation - dominated by -Scirpus spp. (bulrush) -Others (arrowheads, alligator weeds…) • Submerged vegetation present - dominated by -Ruppia maritima -Najas spp. -Vallisneriaamericana

  6. Trinity Delta Marshes (cont’d) • Finfish in delta marshes - Sheepshead minnow - Gulf killifish - Bay anchovy - Striped mullet - Atlantic croaker

  7. Trinity Delta Marshes (cont’d) • Shellfish in delta marshes - Grass shrimp - Blue crab - Pink shrimp - Brown shrimp - White shrimp

  8. Mid-Bay Oyster Reefs • 14000 acres in the bay • Distribution and importance • Salinity ( 12 -19 ppt) • Temperature (12 to 30 C) • Dominated by -American oyster -Bay anchovy -Mud crabs -Amphipods -Capitellids

  9. Blue Crab (Callinectesspidus) • Ecologically and commercially important • Estuarine-dependent • R-selected strategists • Secondary consumer • Most abundant in vegetated habitats in mesohaline zone • Densities in open waters peak in May-June

  10. Gulf Menhaden (BrevoortiaPatronus) • Life history/strategy similar to blue crab • Primary consumer • Abundant in open waters with salinities of 10 to 15 ppt • Densities low in summer and high in early winter

  11. Analytical Procedure • Locate the PAZ -explore the historical database trawl - 1982 to 2000 oyster dredge - 1988 to 2003 -find out the PAZ - where the peak abundance occurs and what the salinities are -assumption: increase in PAZ value would be beneficial • Compare PAZ (wet vs. dry year, and among the different structures/practices) - area extent or - location

  12. Analytical Procedure (cont’d) • How to find the PAZ - CF trawl data - Seasons to be included - Spatial distribution in relation to salinity gradient in the bay (GIS) - Comparisons of mean CPUE among salinity zones (ANOVA)

  13. Oyster Reefs PAZ: 10 – 20 ppt

  14. Blue Crab PAZ: 5 – 15 ppt

  15. Gulf Menhaden PAZ: 10 – 15 ppt

  16. Delta Marshes - Assume PAZ of 0 to 5 ppt - Climatic impact – yes wet year = 23 Km2 dry year = 0.7 km2 - Wet - HSC has the most impact - Marsh production Mid-Bay Oyster Reefs - Climatic impact – no PAZ averages 50% - Dry – TCD generates higher PAZ - Changes in current vector ?

  17. From Dry to Wet (1996 to 1992) 1. Mid-bay Isohaline From 20 to 10 ppt 2. Upper Bay Less saline (15-20 to 5-10 ppt)

  18. Mesohaline (10 – 15 ppt) Dry Year HSC TCD 2.7 14.3 Wet Year 26.0 30.8

  19. Blue Crab (5-15 ppt) - Climate – yes dry year = PAZ of 2 % wet year = PAZ of 67 % - Wet year TCD seems to impact more vs. others Gulf Menhaden (10-15 ppt) - Climate – yes dry year = PAZ of 6 % wet year = PAZ of 29 % - Dry year TCD again shows more impact

  20. Relative Impacts of Structures/Practices on Selected Habitats and Species Delta Marsh Oyster Reef Dry Wet Dry Wet Decreasing Impact on PAZ Blue Crab Gulf Menhaden

  21. Summary • Climate has the most impacts on salinity distribution in the bay • Biological effects of structures/practices vary depending on species’ PAZ - If PAZ in upper Bay – HSC - If PAZ in middle Bay – TCD - If PAZ in West Bay – TCD

  22. ***Man-made changes are not all Bad*** • - if we know what change can do • and • -if we know how we can manage it • or • -If we know how to accommodate toit

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