Department of Environmental Sciences

Sourcing sediment from adjacent inlets for placement on eroded downdrift beaches is an increasingly common practice, as an inlet sources’ proximity to a placement site reduces the transportation cost of a project and is considered a beneficial use of the dredge material (BUDM). This project aimed to compare two nourishment projects using adjacent inlet sediment sources for changes in water quality, morphology, and sedimentology at two geographically similar locations in southeast Florida. In 2023, Jupiter Beach Park (Jupiter, FL) and South Inlet Park Beach (Boca Raton, FL) were nourished using sediment from the adjacent inlet system. Jupiter was nourished with sediment from the inlet’s sand trap and Boca Raton was nourished with sediment from the ebb shoal. Suspended sediment concentration (SSC) in the water column is closely associated with other properties of water including temperature, salinity, and dissolved oxygen.
A sudden increase in suspended sediment in nearshore water can be triggered by anthropogenic activity, like nourishment, as well as natural occurrences, like storms. Sampling began prior to the initiation of nourishment (February) and continued throughout hurricane season (May – November). Sediment samples were analyzed for moment method statistics (i.e., mean, standard deviation/sorting) at half-phi intervals above 63μm. Fine sediment (<63μm) was dried and weighed. Surface and bottom water samples were collected and measured for SSC, dissolved oxygen, temperature, and salinity to analyze changes in response to nourishment.

Large-scale seagrass mortality events have been linked to internal hypoxia and exposure to phytotoxins in the sediment, such as hydrogen sulfide (H2S). Although seagrasses can transport oxygen (O2) to belowground tissues (rhizomes and roots) and into surrounding sediment to prevent H2S intrusion, reoccurring seagrass mortality events from H2S exposure continue. In the present study, I examined the potential of tropical seagrass Thalassia testudinum to transport O2 effectively to belowground tissues and diffuse O2 into Florida Bay sediment around the root rhizosphere or sediment-root interface to constrain H2S diffusion into the roots. My approach was to (1) examine the spatial distribution of O2 in the rhizosphere during the light and dark with 2-D planar optode sensors, (2) examine patterns of root O2 loss (ROL) with O2 dye tracing experiments, and (3) measure O2 and H2S dynamics in internal tissues and rhizospheres. My results indicate that T. testudinum effectively sustains oxidation in belowground tissues to constrain H2S, but minimal evidence of ROL into the rhizosphere.

Freshwater harmful algal blooms (HABs) are increasing in severity and frequency. These blooms are devastating to the communities surrounding these bodies of water due to their numerous health, economic, and environmental impacts (Hallegraeff et al. 1995; Smith 2003; O’Neil et al. 2012; Bláha et al. 2009; V. H. Smith et al. 1999). In Florida, runoff containing fertilizers, human wastes, or industrial wastes contribute to the eutrophication in these lakes and contribute to these freshwater blooms (Val H. Smith 2003; Heisler et al. 2008; O’Neil et al. 2012). M. aeruginosa, a toxic cyanobacterium, often devastates Lake Okeechobee. M. aeruginosa die off creates anoxic conditions and produces a toxin that causes major environmental loss. This project is aimed to increase knowledge on how organic phosphorus compounds affect the growth of the axenic M. aeruginosa and investigate the postulated interactome (Cook et al. 2020). Through these experiments, it was shown that axenic M. aeruginosa cannot utilize organic phosphorus compounds and therefore shows no growth when grown in this media. This research is critical to furthering our understanding of the mechanisms behind these blooms and to mitigating them.

By regulating the abundance of prey populations, predators can directly and indirectly influence food web interactions in ways that influence ecosystem function. Predator functional responses quantify how predator foraging rate changes with prey abundance. Due to the large numbers of individuals needed for these experiments, most studies are conducted on small, abundant taxa. Consequently, we know relatively little about the functional responses of many marine taxa, especially those that are large and highly mobile. We present a novel method for studying predator foraging behaviors by integrating two innovative approaches: passive acoustics to document the occurrence of underwater predation events in concert with a recently developed statistical method that uses the times between predation events to estimate functional response parameters. We demonstrate and expand on the application of these methods by quantifying the shape of the predator functional responses for whitespotted eagle rays (Aetobatus narinari) preying on hard clams (Mercenaria mercenaria).

Coastal wetlands across the Indian River Lagoon (IRL) on the east coast of Florida have been impounded for mosquito control purposes, which have been known to have adverse effects on overall fish populations. The objective of this project was to assess the use of culverts by species of larval fish at three impounded mangrove sites in the IRL. Light traps were used to collect samples of larval fish (both inside the basins and in the surrounding lagoon) which were humanely euthanized, preserved, and examined under a digital microscope. A total of 3,926 fish were collected from 24 taxa in 576 samples over the year-long study. Larval seasonality generally followed known reproductive seasonality of the species captured. Inside the impoundments were dominated by species known to spawn in and around mangroves such as the Gambusia holbrooki and Poecilia latipinna. Species that spawn in the IRL or in coastal waters that subsequently use the IRL as a nursery (such as Anchoa mitchilli and Gobiosoma robustum) had relatively low catches in the impoundments. Larvae of the main sportfishery species that have juveniles known to utilize the studied impoundments (Megalops atlanticus, the Atlantic tarpon, and Centropomus undecimalis, the common snook), were rarely caught inside the impoundments or in the surrounding IRL. The low numbers of IRL and offshore spawning larvae that enter the impoundments may be hindered by restricted water flow through culverts connecting the habitats, or by their inability to survive the low DO conditions often found inside the impoundments, especially during the summer. The lack of larval tarpon and snook in the light collections suggest that these species metamorphose from the larval to juvenile stage outside of the impoundments, before they enter the mangrove-dominated nursery habitats. The results of the study can be used to further modify impoundment restoration and management strategies to enhance their role as fish nursery habitats.

Animals face both natural and sexual selection pressures, and at times, these pressures conflict with one another. This results in a tradeoff between sexual and natural selection. In my thesis, I examine aspects of Bachman’s sparrows’ behavior and morphology in relation to weather conditions in light of these two conflicting pressures.
Large bill size is selected for by the natural selection pressures of thermoregulation. Smaller bills are selected for by the sexual selection pressures of song quality. Both thermoregulation and song are important behaviors/processes that have fitness implications. By looking at bill size in relation to thermoregulatory ability and song quality I examined the tradeoff between these two selection pressures acting on the bill of Bachman’s sparrows

Pleurogonius malaclemys is a digenean trematode with a life cycle that begins in Ilyanassa obsoleta as a first and second intermediate host and Malaclemys terrapin as a definitive host. The fluke matures and reproduces within terrapins and, therefore, relies on terrapins for dispersal. Thus, we hypothesized that the genetic structure of flukes would reflect contemporary changes in the connectivity of terrapin populations. Flukes were sampled by dissecting mudsnails collected from eight sites along the eastern United States. Following amplification of the COI mitochondrial marker, 21 haplotypes were identified and a high degree of structure was detected. We propose that this suggests the parasite could serve as a tool for monitoring terrapin populations. This study sets a foundation for the genetic diversity of the fluke, and provides a first step towards developing the species as a proxy for studying terrapin population size, connectivity, and health, which may help conserve both species.

Macroinvertebrates make up a large fraction of secondary production in wetlands
and are strongly influenced by hydrologic alterations. However, little is known of the
effect flow has on macroinvertebrate production and community composition in wetlands.
Reintroducing measurable water velocities (1-5 cm/s) to the oligotrophic (phosphoruslimited)
Everglades has the potential to affect macroinvertebrate production and
community structure by increasing the supply of phosphorus (P) to periphyton, changing
basal food quality, and physically altering the habitat. In Chapter 2, I investigated the
potential effects of flow-mediated nutrient-loading on the growth rate of herbivorous
grazers, apple snails (Pomacea maculata), by growing periphyton on standard substrates,
in four sloughs within a landscape-scale flow addition experiment; two sloughs received
elevated flow velocities (2.9-5.2 cm/s) and two control sloughs (0.3-0.4 cm/s). Snails fed
periphyton from the flowing sloughs gained more than 3.7-fold greater total mass than
snails fed periphyton from the control sloughs. The highest velocity slough produced the
greatest snail growth. Snail growth was correlated with P accumulation and C:P ratios in
the periphyton. Water column nutrients were low and the water column TP differences among sloughs could not fully explain differences in periphyton nutrients or snail growth.
Increasing flow above background conditions by as little as 2.4 cm/s in this oligotrophic
wetland altered periphyton food quality by flow loading, which subsequently increased
growth rates of primary consumers. In Chapter 3, I investigated potential changes in
macroinvertebrate standing stock biomass and community composition caused by flow by
conducting two sweep net surveys. Surveys were conducted within two groups of sloughs,
flow sloughs (6 sloughs) and control sloughs (12 sloughs), within the same landscape-scale
flow addition experiment as the growth experiment. Surveys were conducted from January
to March in 2018 and 2021. Biomass was compared between the flow sloughs and control
sloughs using generalized linear models. Community composition was analyzed at the
slough level using Bray-Curtis similarity. Biomass of macroinvertebrates was similar
among transects in 2018 but higher in the flow sloughs in 2021 with the highest biomasses
further from the L67A (velocities <2cm/s). The two highest flowing sloughs (typically
>3cm/s) had a different community composition from the other 16 sloughs in both 2018
and 2021 with a predator resistant non-native snail appearing in 2021. The results of the
surveys show an increase in macroinvertebrate production in the flow sloughs possibly
related to increased nutritional value of food, however, with higher biomass further from
the L67A and the invasion of a predator resistant snail at the high flow sloughs, it also
appears that there is increased top-down pressure on the macroinvertebrates at the sloughs
closer to the L67A (were cover from predation has been reduced). The overall results of
these studies indicate flow produces more nutritional food for herbivorous
macroinvertebrates and increases standing stock biomass but can change the community
composition when periphyton cover is reduced.

The effect of artificial reefs on natural reefs is poorly understood. This study focused on Aquarius Reef Base (ARB), an underwater habitat offshore of Key Largo, Florida, and 14 natural reef sites spanning 4 habitats, on the surrounding Conch Reef. Food web models were created for ARB and natural reef habitats. Biomass at each habitat was quantified by fish surveys. Using Ecopath, species were organized into functional groups with supporting data from previous research for other inputs. ARB’s food web was found to have a large predator biomass with insufficient prey biomass to sustain the population, suggesting that these predators must forage on nearby natural reefs where the predator/prey ratio is smaller. Between 0.57km2 and 1.79km2 of natural reef is estimated to be a sufficient spatial subsidy for the large predatory biomass at ARB when the biomass is added as determined by the seascape around the artificial reef.

Distribution and abundance of water impacts population dynamics and habitat structure within a wetland ecosystem. It is known that drought can interfere with trophic dynamics and temporarily free crayfish from the threat of predation by population limiting fish predators in seasonal freshwater wetlands. Less is known about wet season water depths, and their effect on predator prey interactions. In order to address this, I conducted a two-and-a-half-year study in which I experimentally manipulated the wet season water depth in four 8 ha replicate wetlands of the central Everglades, allowing two wetlands to be flooded as natural rainfall patterns would allow (unconstrained hydro-pattern) and two wetlands to experience a constrained hydro-pattern in which the maximum depths to which they were flooded was limited. I discovered that crayfish, small marsh fish, and large bodied predatory fish populations were unaffected by the water depth difference between the hydro-pattern treatments. Unlike fauna, flora did respond to the hydro-pattern treatments with stem densities increasing in the wetlands under the constrained hydro-pattern treatment.