Modern ecology seeks to develop a unified theory of biodiversity that predicts species abundances and distributions for diverse ecosystems. Evelyn G. Hutchinson wrote about how the ecological theater is played out on various scales of space and time while Simon Levin wrote that understanding pattern and scale is the central problem of ecology. The niche-based theory, developed by Hutchinson, states that maintenance of diversity results from differences in traits or responses to the environment, defined as niches. Stephen Hubbell proposed a neutral theory that assumes all individuals in a community are equivalent in rates of reproduction and death and that diversity is a balance of speciation and extinction. While the niche-based theory struggles to explain coexistence of many species in communities that have more species than resources, known as the Paradox of the plankton, the neutral theory has been successful at describing ecological patterns such as species-area relationships and species abundance distributions. It cannot, however, predict changes in diversity among regions due to habitat fragmentation and environmental heterogeneity. Using spatially implicit models and species abundance data, Hubbell, Maria Dornelas, and colleagues showed evidence for and against the neutral theory in tropical forest and coral reef systems, respectively. Furthermore, although alpha diversity (species richness) has been studied extensively, few studies have examined beta diversity (species turnover) which influences diversity at large scales. Robert Whittaker first described beta diversity as the variation in species’ composition among sites, which can be calculated as a probability represented as a function of distance between two individuals that they will not be of the same species. For this study, the null hypothesis that the structure of coral assemblages over a large biogeographic range, such as Southeast Asia or the eastern to western tropical Pacific (i.e, Rapa Nui to the Pitcairn Islands), is governed by a spatial pattern consistent with the neutral theory. To accomplish this, I would utilize large-area imaging to collect data from the regional species pool that include the local reef communities and quantify beta diversity. By testing the neutral theory against coral diversity patterns, I will assess its generality and provide insight into mechanisms of biodiversity maintenance in these increasingly threatened ecosystems. If my results differ from assumptions of neutral theory, further research will examine species’ distributions along the neutral-niche continuum, such as the role of environmental fluctuations (i.e., spatio-temporal environmental stochasticity).

In 1952, Alan Turing examined how a spherical embryo develops into a complex-shaped organism. He devised mathematical models to explain how molecular ingredients of a bundle of cells, termed morphogens, diffuse and react to drive the development or specialization of cells and tissues. In 1972, developmental biologists Hans Meinhardt and Alfred Grier described morphogens as short-range activators that diffuse slowly and long-range inhibitors that diffuse rapidly in a reaction-diffusion system. The activator is autocatalytic and speeds up its own rate of formation while producing wave patterns through random fluctuations in its concentration levels. The inhibitor, however, stops the autocatalysis, and produces stationary waves with different wavelengths that result in regular-spaced patterns of blobs or patches, called Turing instabilities. The dynamics of biochemical reactions can be applied to animal and plant populations; the collisions and reactions that take place between molecules are proxies for interactions between organisms. The interplay of the physical environment, life-history, and morphological traits have been shown, albeit in a few examples, to influence potential regular patterning in coral reefs that emerge along a continuum of scale - from fine-scale patterns in the architecture of colonial skeletal morphology perpendicular to waves generated by wind to clusters of colonies on a reef characteristic of life stage and taxonomic identity and lastly to large-scale reef distribution pattern of reef islands oriented in a series along predominating current direction. I will study the population dynamics of corals and hypothesize that a scale dependent feedback emerges with facilitation (positive feedback) and competition (negative feedback). During facilitation, the aggregation of conspecifics enhances protection from physical disturbances such as waves. Here, growth and survival are autocatalytic, and populations increase with higher densities of individuals. However, as colonies become more numerous, food resources transported downstream by currents are depleted, causing increased competition over large areas of the reef. I hypothesize that the rate of aggregating behavior is slow compared to more rapid wave forces, which quickly inhibit the unlimited growth of coral populations by physically dislodging them from the reef substrate. In mussel beds, density-dependent movement of mussels has been shown to act synergistically with scale-dependent feedbacks to produce regular banded patterns, a phenomenon akin to phase separation in mixed fluids. Therefore, Turing instabilities and phase separation combine to potentially aggregate competing conspecific corals (like mussels) to high density so they can find safety in numbers while sharing food.

The Florida Keys National Marine Sanctuary is a living laboratory for scientific research that protects, conserves, and enhances its natural resources while allowing and managing public and private uses that are compatible with the primary goal of resource protection. The FKNMS includes 1,400 km^2 of coral reefs in several distinct habitats influenced by waters of Florida Bay, the Gulf of Mexico, and the Florida Current. Although both large-scale flow patterns and local bathymetry influence water movements in the Florida Keys, regular and seasonally pronounced reversals of that overall flow pattern and local gyres contribute to retention of microscopic biota (i.e., disease pathogens) influenced by those water masses.

Currently, a disease outbreak called the stony coral tissue disease (SCTLD) has affected several species of coral in southeast Florida since 2014 and has spread through the Florida Keys National Marine Sanctuary. In accordance with the vision and mission to study and conserve the Florida Keys National Marine Sanctuary, I will introduce seascape pathology as a field of study to enhance understanding of the SCTLD outbreak by identifying the environmental and biotic mechanisms underlying the dynamics of disease transmission. This approach will incorporate effective restoration techniques already adopted by NOAA and FKNMS6 to terminate disease progression while increasing abundance of critically endangered acroporid corals (Acopora palmata and A. cervicornis). My research will slow the outbreak of SCLTD, increase biodiversity of natural resources, and enhance management strategies of the Florida Keys National Marine Sanctuary.

Background

The health of coral reefs around the world is in decline and many species of reef-building corals are threatened by diseases that are increasing in number, prevalence, and geographic extent. Tissue loss diseases categorized as “white plague” are damaging coral populations worldwide. White-plague diseases are characterized by multiple rings of necrotic tissue that form on the surface of coral colonies. and have been reported in the Upper Keys in 1975 from the upper Florida Keys, in 1995, and throughout FKNMS with SCTLD. Environmental factors contribute to host-pathogen dynamics, but the underlying factors allowing the emergence and continued spread of SCTLD are not yet understood. For directly transmitted diseases, the spacing between adjacent coral colonies (i.e., host behavior) will be the primary determinant of the scale of spatial spread. Ocean currents and local oceanographic forcings, however, may play roles in determining connectivity and affect disease spread rates.

Spatial modeling methods and landscape metric analyses have already proved useful for investigating the spread of pathogens in plant populations. Although fine-scale or experimental pathology studies are common in marine science, reef scientists must understand disease at a regional scale to apply appropriate restoration and management practices. Seascape pathology can help discern which site factors affect susceptibility by coupling the analysis of water currents associated with the distribution of host corals may provide a more thorough understanding of SCTLD than separate studies of environment and host patterns. My study will examine the complex ways that coral hosts, mode of disease transmission, and environment interact during a disease outbreak.

Research Questions

1. What is the relative role of local physical oceanographic factors (i.e., local currents and eddies) in SCTLD transmission?

2. What roles do the patterning of the underlying coral host population play in direct contact and SCTLD transmission?

3. Will unsusceptible coral taxa be able to ameliorate the detrimental effects of the SCLTD outbreak?

4. How can scientists enhance proactive restoration efforts in conservation management plans that are suitable for sustainable ecological control of coral diseases?

Hypotheses

1. Elevated prevalence of SCTLD is inversely related to the distance of local oceanographic forcings such as eddies and ocean currents.

2. Coral density and aggregation are positively related to disease transmission rates.

3. Outplanting of the unsusceptible coral species, A. cervicornis, onto reef areas with elevated disease risk will decrease transmission of SCTLD to uninfected coral.

Data collection

I will utilize cutting-edge large-area imaging technology developed by scientists from the collaborative 100 Island Challenge research group (Scripps Institution of Oceanography and the Department of Computer Science and Engineering at the University of California, San Diego) that uses three-dimensional digital models of coral reefs to quantify ecological data. In June 2019, SIO conducted 85 large-area images (100 m^2) of reefs throughout the Florida Keys Marine National Sanctuary. I will apply the τ-statistic described below and identify areas of elevated prevalence, or “hotspots”, of SCTLD, defined as the area of reef around a single infected colony with SCLTD where a higher prevalence of SCLTD infected colonies is expected. Using physical oceanographic data collected from the SEAKEYS network of C-MAN monitoring buoys, I will test the hypothesis that reefs closer to local currents and gyres have higher disease prevalence than those further away. In 2021, I will resurvey the same reefs to obtain fine-scale temporal data of disease transmission and identify areas of elevated risk, defined as the area of reef around a single colony infected with SCTLD where colonies are more likely to acquire SCLTD from that colony. I will test the hypothesis that spatial structure of host colonies influences epidemic spread rates. Beginning in 2021, I will choose three reef plots with substantial elevated risk to outplant fragments (12 - 24 cm) of A. cervicornis or A. palmata. Large-area images will be recorded quarterly for one year to test if areas of elevated disease risk diminish with unsusceptible outplanted acroporid coral.

Statistical tests

In statistics, a kernel is three-dimensional function that weights events (i.e., colonies infected with SCTLD) within its sphere of influence according to their distance from the point at which the intensity is being estimated. In my study, the probability distribution of distances (d1, d2) between the location of an infector and infectee define the spatial transmission kernel and will be calculated using the τ-statistic:

τ(d1,d2) = λ(d1,d2)/λ

Where λ is the average incidence (i.e. rate of disease occurrence) across the entire coral assemblage. Meeting the management, scientific, and societal importance of FKNMS This project will satisfy goals, objectives, and actions outlined in the Draft environmental impact statement for Florida Keys National Marine Sanctuary: A Restoration Blueprint, 3.5.5 Draft management plan (Alternative 3, preferred). I will communicate my research and provide new tools for coral reef conservation via broader impacts of social outreach, STEM education, and marine conservation. I will develop a web-based application with graphical user-interfaces and animations of the oceanographic processes and coral disease dynamics that will allow competent biologists, curious naturalists, and concerned managers to explore coral reefs in critical and novel ways with accessible technology. My research will prove beneficial for those who depend on for sources of food, recreation, and coastal protection and provide tools to quantify and predict disease outbreaks and future spatial seascapes.

Tangible Outcomes

1. Four annual project reports and one final report submitted to the Nancy Foster Scholarship.

2. Minimum of three peer-reviewed journal articles published by journals such as Coral Reefs, Ecology, Nature, or Science.

3. Web-GIS based user-interface application displaying areas of elevated SCTLD prevalence and risk overlaid with local physical oceanographic forcings and coral population spatial patterns.

Conclusion and future research

My project will provide baselines for monitoring dynamics of coral hosts and their pathogens in ecological time. Future research will examine how spatial patterns of disease related mortality can be used as indicators of the proximity of coral reefs to a catastrophic change. The health of coral reefs has adversely been impacted by local anthropogenic factors that have already caused high mortality of reef corals over large areas. The power to detect and quantify explicit spatial patterns of live, dead, and diseased coral before environmental will allow stakeholders to make timely and informed decisions regarding the management of these natural resources.

Introduction

Rapa Nui (Easter Island) is one of the most remote islands in the Pacific, lying at the southeastern-most part of Polynesia and range of reef-building scleractinian corals. To date, nothing is known of the colony sizes of the two main coral taxa at Rapa Nui: Porites lobata and Pocillopora spp. The purpose of this study was to examine variation in the mean size of the two coral taxa at different locations and depths at Rapa Nui.