The third and final portion of the "Evaluating the Impact Detached Breakwaters have on Habitat Enhancement of American Horseshoe Crabs (Limulus polyphemus) in the Delaware Bay" capstone project revolves around the behavioral influence of the Horseshoe Crabs in relation to the coastal structures. Although the wave analysis and sediment distribution (G.I.S) components can decipher if the structures are achieving their designated purpose of habitat enhancement, the actual usage of the Money Island shoreline by these benthic organisms will dictate if the structures are fulfilling their intended purpose of enchaining the beach for Horseshoe Crab usage (spawning). For this biological assessment, a collaboration with the American Littoral Society (Millville, New Jersey) was completed, where physical surveys of spawning Horseshoe Crabs were completed in May & June of 2023. The survey aimed to determine if the Horseshoe Crabs tend to choose the beachfront behind the detached breakwaters or if they preferred to utilize a different area of Money Island (not directly influenced by the shoreline protection features). 

To accomplish this, a conceptual model was first generated (see image to the left) to display Horseshoe Crab behavior choices, including passage through the channels of the breakwaters (green arrows), usage around the structures (blue curved arrows), complete usage of other areas of the beach (orange arrows). Since these physical structures can impede  Horseshoe Crab spawning, the American Littoral Society (ALS) also accounts for the impingement of the organisms (physically stuck to the structures) and is displayed in red arrows on the conceptual model. American Horseshoe Crab spawning surveys were designated to be conducted on the nights of June 4, 2023, and June 18, 2023. This is due to the fact that Horseshoe Crabs are most active during High-Tide scenarios during New and Full Moon events. *Special Note*: The survey conducted on June 18, 2023, was canceled as per ALS.

June 4, 2022 Survey Methodology:

The Money Island Survey began at approximately 10:30 PM and consisted of two different types of surveys. The first survey was a general walkthrough of the shoreline, while the second was a Quadrant-Based approach. For the Quadrant-Based approach, a 1-square meter Quadrant (see image to left) was used to section off portions of the shoreline at a time. Beginning at the wing wall to the North end of the beach, the quadrant was placed every 3 square meters along the "crab-line" or High Tide line. Once the quadrants were placed, an individual would count the number of male and female specimens in each quadrant. To determine if the organisms preferred to utilize the beach landward of the structures over the adjacent beaches, GPS points were collected at each location where a quadrant survey was conducted. GPS points were collected utilizing the "Maps" application on an Apple iPhone 12. GPS collection via a cellular device was deemed permissible for this study as the exact Northing and Easting are not required. The general locations of the organisms on the beach are sufficient for the analysis. Besides collecting Latitude and Longitude coordinates, the number of specimens in each quadrant was also recorded to utilize for future G.I.S maps. 

Upon completing the biological survey, the data (Lat, Long, # of organism) was transferred to a Microsoft Excel spreadsheet and later imported into an ArcGIS Pro project titled "MI_HSC." Before importing into an ArcGIS project, the Horseshoe Crab data was split between quadrants influenced by the breakwaters and those not influenced by the breakwaters (as per ALS). Inside the ArcGIS Pro project, both of the XY (Lat/Long) data sheets were displayed as point feature classes and shown in a layout alongside the Money Island breakwater feature class and the Money Island Shoreline (2023) feature classes (Full details of these added classes can be found on the Sediment Distribution Methodology page). The symbology of the points was changed to show a "Graduated Symbols" scheme based on the field "# of HSCs per Quad." The graduate symbols indicate that the quadrants with more organisms are shown as larger point files. To distinguish breakwater-influenced quadrants from non-breakwater quadrants, the colors of the points were changed between breakwater-influenced (Red color) and non-breakwater-influenced (Green color). Please see the map below (Full analysis and map can be seen on the Results (Biological) page.

Since only one survey was able to be conducted in the spring of 2023 (June 4, 2023), a full comparison of Horseshoe Crab population data will be analyzed between 2022 and 2023. With the Money Island engineering project concluding in 2021, the American Littoral Society (in conjunction with the New Jersey Department of Environmental Protection) has been researching American Horseshoe Crab usage since 2022. Their research includes Quadrant Surveys (mentioned above), Impingement Surveys (mentioned above), and Tagging Datasheets. By comparing the population datasets, this project aims to see if there is a distinct difference after one year of construction. 

The main focus of the data comparison is whether or not there is an increase in total organisms found along Money Island and their locations along the beach itself. Knowing where the quadrants run along the beach, the population of spawning Horseshoe Crabs can be identified by their approximate location to the detached breakwaters (i.e., landward of the structures or adjacent to them) based on the quadrant survey numbers. For ALS, a total of 100 quadrants are collected during each survey, with #50 representing the split between the beachfront impacted by the breakwaters.

Data Processing Methodology:

• Population Totals:

  • All of the tally sheets from the Quadrant Surveys were added to a Microsoft Excel file with separate sheets for the specific dates associated.

    • Four columns were added for each sheet (Quad #, # of Males, # of Females, & # in Total).

  • The total numbers for 2022 and 2023 were added from all the surveys in the corresponding year on a different Excel sheet.

    • A T-Test was performed to see if a significant difference was present between the two years (based on the 0.05 p-value).

• Population Changes (Sexes):

  • Going off the Excel sheets created in the Population Totals, T-tests were run between the numbers of Males from 2022 & 2023 to see if significant differences were present.

    • T-Tests were also utilized to compare the population numbers of females from 2022 and 2023.

• Impingement Totals:

  • The total of Horseshoe Crab individuals from the impingement surveys was added to a new Microsoft Excel document, and a direct comparison was made. *Special Note*: there was insufficient data to run statistical analysis since very few individuals were stuck on the structures.

  • Physical damage on tagged Horseshoe Crab specimens was also noted on the side in case of a correlation between physical harm and the coastal structures.