Big Bend Oyster Research

Transcription

1 Big Bend Oyster Research Drs. Jennifer Seavey, Bill Pine, & Peter Frederick Department of Wildlife Ecology and Conservation, Institute of Food and Agricultural Sciences, 110 Newins-Ziegler Hall, PO Box , Gainesville, FL (352)

2 Research objectives 1. Quantify amount & spatial configuration of changes over the past years 2. Identify why, especially in relation to climate change 3. Plan for conservation/restoration 4. Long-term monitoring program

3 Box B Box A Gulf of Mexico Study Area measuring across gradients of salinity & wave energy

4 Methods- Objective 1 1) Historic photos of focus areas: 1967, 1982, 1995, 2001, ) Ground truthing (for 2010)

5 Oyster bar categories 1) Marsh/oyster 2) Sand/oyster 3) Unresolved Methods: Objective 1 GIS work- digitizing bars -Subtidal oysters and oyster density are not represented.

6 Methods: Objective 1 Digitizing challenges: 1) tides levels 2) accuracy of georeferencing off-shore 3) classification

7 Methods Objective 2- oyster bar density, size class, growth rates, bar attributes

8 Methods: Objective 2 These transects are made by driving two pieces of rebar into the oyster bar at opposite ends of the bar. The two pieces are the same distance apart on each end of the bar. We wrap survey string around the survey bar to create a belt. We measure the length of the belt with a tape. We walk along this belt and count the number of whole, live, oysters in the belt. If the string crosses an oyster, it has to be more than 50% inside the line to be counted.

9 Methods: Objective 2 Using the transect and the tape measure to establish a number line along the grid, we randomly select locations along the bar by generating a random number along and away from the bar

10 Methods: Objective 2 At these locations we place a ¼ m quadrat on the ground and count and measure all the live and dead oysters We do this for a minimum of 100 measurements per oyster bar Overall our response metrics of interest are Size structure to infer growth, survival, and recruitment Proportion of oysters live and dead as a measure of viability These metrics are then examined spatially and temporally as part of a monitoring program to test our hypotheses related to freshwater inputs and energy structuring oyster reef distribution

11 Methods: Objective 2 Experimental monitoring of spat distribution and survival Can we take larval supply out of the equation? Huge question in areas where oyster populations are extirpated. Is this an issue in CK? Is there a gradient in spat settlement? Survival? What is the role of predation?

12 Objective 1: Results

13 Suwannee Reef disappears!

14 Suwannee Reef 2010

15 Offshore reefs were once abundant (Baker et al. 2006, Grinnell 1972, local watermen)

16 Corrigan s Reef - most oysters

17 CA Swamp Flow Suwannee flow? Freshwater?

18 Raabe and Bialkowska-Jelinska, 2010

19 Objective 2: Conclusions 1) Bar locations are not equal 2) Offshore & fresh water sites impacted more & less than others What about type of oyster bar?

20 Total area by bar type % increase AREA (SQ M) % increase Marsh/Oyster Sand/Oyster Unresolved YEAR

21 Distance from shoreline by bar type 700 DISTANCE FROM SHORE (M) Marching Inland Marsh/Oyster Sand/Oyster Unresolved YEAR

22 Sand/Oysters: Total area Inland movement Average Area (SQ M) LC HS CR CR YEAR Average bar size Count Count LC HS CR CR YEAR

23 Marsh/Oysters: Total area Inland movement Average Area (SQ M) LC HS CR CR YEAR Average bar size Count Count LC HS CR CR YEAR

24 Objective 2: Conclusions 1) Offshore bar loss 2) Freshwater sources seem important 3) Sand makes up the majority of bars 4) Marsh & sand appear to be increasing How are Marsh vs. Sand increasing?

25 Tracking bar types at a finer scale

26 Offshore samples Inshore samples Lone Cabbage: where freshwater input is likely building bars Nearshore samples

27 Off shore sites: only sand & gone after 1995 Nearshore: -Sand cm & growth -Marsh change variable Inshore: -Marsh cm & growth -sand steady, except..

28 Nearshore Sand Expanding & flattening sandbars

29 Inshore Marsh 1985 Sand to marsh transition

30 Survey Data

31 Objective 2: Conclusions 1) Offshore bars are very vulnerable 2) Importance of freshwater sources 3) Loss of sand/oysters 4) Future appears to be more marsh/oyster bars 5) Raises questions about the importance of offshore sand bars- do we want to maintain diversity of oyster bar types?

32 Results: Objective 2

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38 Density observations Density consistently highest at inshore reefs, lowest offshore Corrigan s and Horseshoe sites usually highest density Let s look at two sites through time

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41 Viability?

42 Viability? Most oysters alive (>50%) Highest proportion live generally inshore, lowest offshore

43 Size structure?

44 Size structure? Some season variation in size related to spat.. Similar size range between live and dead

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47 Our observations so far Cedar Key region oyster reefs have diverse size structure, stable densities, and apparently high viability Size structure indicates multiple year classes Evidence for recruitment this year Stable proportion live:dead

48 Cooperators & Partners