A regime shift is reflected in the fish community structure of the Indian River Lagoon (IRL)

Author

• Arthur Conwy Jones, Florida Institute of TechnologyFollow

Date of Award

5-2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean Engineering and Marine Sciences

First Advisor

Ralph G. Turingan

Second Advisor

Glenn A. Miller

Third Advisor

M. Toufiq Reza

Fourth Advisor

Richard B. Aronson

Abstract

In 2011, the Indian River Lagoon (IRL) underwent a regime shift due to an intense harmful algae bloom (HAB) that fundamentally changed ecosystem conditions to favor phytoplankton blooms over seagrass, causing massive losses in seagrass coverage. To determine if this regime shift is reflected in the IRL fish community structure, including mass mortality events, I conducted a meta-analysis of long-term data sets of IRL phytoplankton biomass, seagrass coverage, fish kills, and population fluctuations of 14 fish species of interest over a 30-year time frame. Statistical analyses found a strong correlational relationship between phytoplankton biomass and fish mortality events. This is potentially because HAB events can create hypoxic dead zones and release toxins produced by certain algal species, which lead to fish kills. Changepoint analysis in fish mortality events and IRL seagrass coverage at fish kill locations found significant declines in mean and/or variance that reflect the occurrence of superblooms in 2011 and 2016, and indicates that HABs became the primary driver of fish kills after 2016. Changepoints in the average nearest neighbor distance between fish kills and changes in the patterns of K-means clustering of fish kills also suggest that fish kills clustered more strongly by location after 2011. This is potentially due to nutrient input from sewage pollution fueling phytoplankton growth in the IRL. Lastly, changepoint declines in mean abundance in the majority of the 14 IRL fish species that coincided with HAB superbloom events provide evidence of the negative impacts of the loss of seagrass beds that act as essential nursery and foraging habitat, especially on those fish species reliant on seagrass. The response of fish to the regime shift underscores the negative impacts of human activity on the IRL, and makes clear the importance of proactive environmental management and policy to protect this ecosystem.

Recommended Citation

Jones, Arthur Conwy, "A regime shift is reflected in the fish community structure of the Indian River Lagoon (IRL)" (2026). Theses and Dissertations. 1627.
https://repository.fit.edu/etd/1627