This interactive visualization maps the governance network for shellfish aquaculture in South Carolina. It is a component of an MPA/EVSS dual-degree thesis examining why South Carolina — a state with significant biophysical capacity for shellfish mariculture — has substantially less acreage in active production than its ecological potential would support.
The analysis applies two complementary theoretical frameworks:
Node size reflects betweenness centrality — actors who sit between otherwise disconnected parts of the network and therefore hold disproportionate influence over information and resource flows. Red-orange edges indicate burden-generating relationships. Use the dropdown menus to filter by actor type or search for a specific node.
## 46 peripheral nodes (degree <= 1) excluded from visualization. Retained in centrality calculations.This subgraph isolates the 109 burden-generating edges in the network — relationships where one actor’s regulatory authority, compliance requirement, or administrative process imposes learning, compliance, or psychological costs on the receiving actor (Herd & Moynihan, 2019).
Betweenness centrality identifies actors whose network position mediates flows between otherwise disconnected actors. High betweenness nodes are structural brokers — their removal would disconnect parts of the governance system.
| Actor | Actor Type | Coalition | Betweenness | Degree (All) | Degree (In) | Degree (Out) |
|---|---|---|---|---|---|---|
| South Carolina Shellfish Growers Association (SCSGA) | advocacy | NA | 0.1157 | 20 | 17 | 3 |
| SCDNR Shellfish Management Section | regulatory | regulatory-cautious | 0.1023 | 42 | 11 | 31 |
| SCDES Shellfish Sanitation Section | regulatory | regulatory-cautious | 0.0780 | 34 | 3 | 31 |
| Emily Osborne | science-extension | NA | 0.0716 | 23 | 19 | 4 |
| Andrew Richard | regulatory | NA | 0.0326 | 4 | 2 | 2 |
| Caitlyn Mayer | industry | NA | 0.0116 | 7 | 5 | 2 |
| Matt Gorstein | science-extension | NA | 0.0107 | 7 | 3 | 4 |
| Mike Marshall | regulatory | NA | 0.0074 | 3 | 2 | 1 |
| Minorities in Aquaculture (MIA) | advocacy | pro-expansion | 0.0045 | 2 | 1 | 1 |
| Thomas (Tom) Bierce | industry | NA | 0.0043 | 6 | 5 | 1 |
| William Green | industry | NA | 0.0027 | 5 | 4 | 1 |
| East Coast Shellfish Growers Association (ECSGA) | advocacy | NA | 0.0019 | 2 | 1 | 1 |
| Andrew Speaker | industry | NA | 0.0008 | 6 | 4 | 2 |
| Imani Black | advocacy | NA | 0.0005 | 2 | 1 | 1 |
| Julie Davis | industry | pro-expansion | 0.0004 | 5 | 4 | 1 |
| Trey McMillan | industry | pro-expansion | 0.0004 | 5 | 4 | 1 |
| Jeff Massey | industry | NA | 0.0004 | 6 | 4 | 2 |
| Larry Toomer | industry | NA | 0.0004 | 6 | 4 | 2 |
| Bob Baldwin | industry | NA | 0.0004 | 5 | 4 | 1 |
| Craig Reeves | industry | NA | 0.0003 | 3 | 2 | 1 |
| Actor | Actor Type | Coalition | Degree (All) | Degree (In) | Degree (Out) | Betweenness |
|---|---|---|---|---|---|---|
| SCDNR Shellfish Management Section | regulatory | regulatory-cautious | 42 | 11 | 31 | 0.1023 |
| SCDES Shellfish Sanitation Section | regulatory | regulatory-cautious | 34 | 3 | 31 | 0.0780 |
| U.S. Army Corps of Engineers Charleston Regulatory Office | regulatory | NA | 25 | 0 | 25 | 0.0000 |
| SCDES Bureau of Coastal Management (OCRM) | regulatory | regulatory-cautious | 25 | 0 | 25 | 0.0000 |
| Emily Osborne | science-extension | NA | 23 | 19 | 4 | 0.0716 |
| South Carolina Shellfish Growers Association (SCSGA) | advocacy | NA | 20 | 17 | 3 | 0.1157 |
| Caitlyn Mayer | industry | NA | 7 | 5 | 2 | 0.0116 |
| Matt Gorstein | science-extension | NA | 7 | 3 | 4 | 0.0107 |
| Thomas (Tom) Bierce | industry | NA | 6 | 5 | 1 | 0.0043 |
| Andrew Speaker | industry | NA | 6 | 4 | 2 | 0.0008 |
| Jeff Massey | industry | NA | 6 | 4 | 2 | 0.0004 |
| Larry Toomer | industry | NA | 6 | 4 | 2 | 0.0004 |
| William Green | industry | NA | 5 | 4 | 1 | 0.0027 |
| Julie Davis | industry | pro-expansion | 5 | 4 | 1 | 0.0004 |
| Trey McMillan | industry | pro-expansion | 5 | 4 | 1 | 0.0004 |
| Bob Baldwin | industry | NA | 5 | 4 | 1 | 0.0004 |
| Jeff Spahr | industry | NA | 5 | 4 | 1 | 0.0000 |
| Carrie Spahr | industry | NA | 5 | 5 | 0 | 0.0000 |
| Kim Livingston | industry | NA | 5 | 5 | 0 | 0.0000 |
| Josh Eboch | industry | NA | 5 | 4 | 1 | 0.0000 |
| Coalition | Actor Type | N | Mean Betweenness | Mean Degree |
|---|---|---|---|---|
| conservation | advocacy | 3 | 0.0000 | 1.0 |
| neutral | science-extension | 3 | 0.0000 | 1.3 |
| pro-expansion | advocacy | 1 | 0.0045 | 2.0 |
| pro-expansion | industry | 3 | 0.0003 | 4.7 |
| regulatory-cautious | regulatory | 9 | 0.0200 | 11.2 |
| Metric | Value |
|---|---|
| Active nodes | 95.0000 |
| Edges | 183.0000 |
| Network density | 0.0205 |
| Average path length | 2.4940 |
| Diameter | 5.0000 |
| Clustering coefficient (global) | 0.1484 |
| Burden-generating edges | 109.0000 |
| Non-burden edges | 74.0000 |
| Regulatory authority edges | 112.0000 |
| Collaboration edges | 37.0000 |
| Information edges | 33.0000 |
This network was constructed using a hybrid observed-plus-survey methodology. Edges were coded from documented relationships using a three-tier evidence hierarchy: Tier 1 (formal authority, statutory mandate, signed agreement), Tier 2 (co-membership, documented joint project, survey self-report), and Tier 3 (documented co-attendance, role-overlap inference). Conflict edges require behavioral evidence from the documentary record per codebook Rule 8. Historical nodes (actors no longer active but instrumental in establishing current regulatory structures, including Peter Kingsley-Smith, departed May 2026) are retained in the node roster but excluded from centrality calculations.
Coalition encoding follows the Advocacy Coalition Framework (Sabatier
& Jenkins-Smith, 1993): pro-expansion,
regulatory-cautious, conservation, and
neutral. Administrative burden coding follows Herd &
Moynihan (2019): learning, compliance, and psychological burden types
assigned by role relationship rather than self-report.
All analysis conducted in R using igraph (Csárdi & Nepusz, 2006) and visNetwork (Almende B.V., 2022). Data current as of May 2026.
Chatman, K. (2026). SC Shellfish Aquaculture Governance Network. MPA/EVSS Thesis, College of Charleston / SC Sea Grant Consortium. Beta visualization: rpubs.com/chatmanka