Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Supplemental Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Organism sizes on oyster reef quadrats from surveys in Apalachicola Bay and Ocholckonee Bay,  Florida, 2013-2019. Reported are counts, sizes (mm) and relative density.

Site Selection- From Hanley et. al 2019, this was a multi-step process that first involved using ArcGIS to partition the bay’s oyster reefs (commercial and non-commercial) into six zones. Zone assignment was based on the reef’s relative distance by water from the river input (near, mid, far) as well as a reef’s east-west orientation to the river (East Apalachicola and West Apalachicola). Next, we randomly selected three reefs out of all possible reefs (including the experimental reefs) within each zone.

Surveys- Methods for surveys done from 2013-2016 were taken from Hanley et al. 2019.

Surveys 2013-2016-On each reef subtidal reef, we obtained spatially balanced samples by extending four 20 m transects at 90 degree angles from the boat. Along each transect, we overlaid a 0.25 m2 weighted quadrat at the 5, 10, 15, and 20 m marks. For each quadrat, we collected the entire contents of the quadrat into a uniquely labeled mesh bag, transported the bag to the surface, and placed the bag on ice to be processed at the lab. For intertidal reefs, we sampled 2 quadrats per reef, ‘low’ (located at the low water level) and ‘high’ (2 m above the low transect) quadrats centered along a 20 m transect on each reef.

Surveys 2019- Sites were selected from previously sampled reefs. Subtidal surveys were conducted by divers on SCUBA. A buoy was dropped at the sites. The divers attached a 10m transect to the buoy and surveyed the area in the four cardinal directions (North, South, East and West). We characterized the substrate 0.5m on each side of the transect as mud, sand or shell hash, as well as quantified the amount of oyster shells and counted the number of Oyster Drills (Stramonita haemastoma). If there were oysters or shells at meter 5 or meter 10 along the transect then everything in a 0.25m2 quadrat was collected and processed at the lab. We only sampled the intertidal sites in December 2019. We laid a transect across the crest of the reef and then divided the length of the transect by 7 to get a consistent sampling interval. At each sampling interval we recorded the width of the sampling side and then placed a 0.0625m2 quadrat at the midpoint of the sampling width and collected all the contents to be brought back to the lab and processed.

BCO-DMO Processing Notes:
- data submitted in Excel file "Apalachicola_Data_2013-2019_ABP_4.xlsx" sheet "Survey.Quadrat.organism.sizes" extracted to csv
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions
- replaced missing data 'NA' with 'nd'
- joined this table with sheet "Reef Location" table in order to include lat/lon info
- re-ordered columns
- sorted rows by {reef_type}{estuary}{region}{distance}{reef}{transect}

NSF Award Abstract:

Ecosystems can exhibit "tipping points" whereby an environmental disturbance pushes an ecosystem into an altered state from which it does not recover, even when the environment normalizes. This may have happened to valuable oyster reefs in Northwest Florida in 2012, when drought and low river flow allowed predators of oysters to flourish and consume nearly all the oysters. Despite subsequent years of normal rainfall and river flow, oysters have not recovered, suggesting the ecosystem may have crossed a tipping point. However, the timing and magnitude of the disturbance from Hurricane Michael (2018) may have pushed the ecosystem back towards its original, healthy state. In this project, investigators make field observations to gauge how predators and oysters are responding to Hurricane Michael and conduct lab experiments to test how predators and oysters respond to hurricane rainfall conditions. Additionally, they use mathematical models to predict whether effects observed in the field and lab could lead to a shift back past the tipping point. This is a rare opportunity to study how oyster ecosystems can shift back from altered to healthy states. However, a rapid response is essential before seasonal changes in the weather and bay obscure hurricane impacts. This research has several broader impacts. First, it will expand the ecological theory of tipping points. Second, it can support the management of the Apalachicola Bay oyster fishery, such as insight into the likely success of restoration efforts. The team coordinates with the Apalachicola National Estuarine Research Reserve to this end. Finally, research outputs are incorporated into ongoing public education and training efforts.

Ecosystems can rapidly shift from their original, high-value state to a new, degraded one. Such shifts have been observed in many ecosystems, but it is sometimes difficult to identify the mechanisms that mediate the shift beyond a "tipping point" and - to a greater extent - those that could mediate a shift back to the original state. Improving our understanding and predictive capability of tipping points depends on identifying the mechanisms that underlie bi-directional system shifts. In 2012, the oyster reefs of Apalachicola Bay, FL abruptly shifted into an oyster-less state when prolonged drought and low river flow allowed marine oyster predators to flourish. Despite subsequent years of normal rainfall and flow, there has not been a return shift, suggesting this ecosystem may have entered an alternate stable state. The hypothesis of this work is that in 2018 Hurricane Michael provided a sufficient disturbance to shift the system back into the attracting basin for its original state (prior observations support this prediction). This project couples field observations and lab experiments with population modeling to test whether and how Hurricane Michael initiated a reversal shift. A rapid response is essential before seasonal variability in this ecosystem obscures hurricane effects. The proposal's intellectual merit is based on its ability to address a central goal in ecology: identifying and predicting ecosystem tipping points. Combining empirical observations and models is a promising approach to advance this goal, but has not been widely applied in the field, mainly because researchers are not in place at the time of a shift. Hurricane Michael provides a unique opportunity to address this knowledge gap.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.