Project completed by Reshmi Joseph

Research Questions / Objectives

This project quantified coral disease prevalence across two reef systems in Mamala Bay (Horseshoe Reef, Kewalo Basin; Turle Canyons, Maunalua Bay), while situating findings within broader patterns observed in Kāneʻohe Bay. Coral disease has emerged as a growing contributor to reef decline globally, yet baseline data remain limited in Hawaiʻi. The primary research questions were:

1. What are the current prevalence rates of key coral diseases (White Syndrome, Growth Anomalies, Pigmentation Response) across multiple coral genera in Maunalua Bay and Kewalo Basin?
2. Do prevalence rates vary significantly between sites, and how do these patterns compare with historical case studies from Kāneʻohe Bay?
3. How do environmental stressors (thermal anomalies, freshwater input, urban runoff) influence spatial patterns of disease prevalence in Oʻahu’s reefs?

Methods

Disease surveys were conducted using 30 × 2 m belt transects at Horseshoe Reef and Turtle Canyons. Coral colonies were identified to genus (Porites, Montipora, Pocillopora, Pavona, Leptastrea, Fungia) and assessed for visible signs of disease: White Syndrome (WS), Growth Anomalies (GA), and Pigmentation Response (PR).

• Diseased vs. total colonies were tallied to calculate prevalence rates.
• Environmental data were integrated, including proximity to land-based inputs: Horseshoe Reef receives runoff from seven storm drains, while Turtle Canyons is influenced by ten watersheds.
• Results were compared to historical prevalence patterns from Kāneʻohe Bay, where Montipora White Syndrome and Porites diseases have been documented since the 1970s

Results

Surveys revealed measurable but site-specific patterns of disease prevalence across Mamala Bay:

• Horseshoe Reef: Overall prevalence was 8.7% (469 diseased out of 5,367 colonies). White Syndrome prevalence was 3.2%, with highest rates in Pocillopora (5.3%). Growth Anomalies reached 3.7%, and Pigmentation Responses 1.9%.
• Turtle Canyons: Overall prevalence was 6.2% (213 diseased out of 3,410 colonies). White Syndrome prevalence was 1.5%, with balanced contributions across Porites, Montipora, and Pocillopora. Growth Anomalies were 1.1%, while Pigmentation Responses were higher at 3.6%.
• Comparisons with Kāneʻohe Bay case studies highlight that Montipora White Syndrome remains a major threat, and that disease prevalence is often highest in southern, runoff-and-sedimentation-impacted areas.

Significance                                                                                                                                          

This study establishes a much-needed prevalence baseline for coral disease in Mamala Bay, providing critical data for monitoring long-term trends and evaluating management interventions. Results confirm that human impacts such as urban runoff and watershed discharge are key drivers of coral disease, with Horseshoe Reef (closest to storm drains) showing the highest prevalence. Importantly, these findings address a major gap in Hawaiʻi’s coral disease literature by directly linking prevalence estimates to site-specific environmental stressors.