Marine Science

Marine Science

Marine Science Senior Theses 2010

The Life History of the Loggerhead Musk Turtle, Sternotherus minor, at Rainbow Run, Marion Co., Florida.

Student: Eric Brucks

Thesis Committee: Peter Meylan (chair), Bill Szelistowski, Beth Forys

A life table was generated for a population of the loggerhead musk turtle, Sternotherus minor, at Rainbow River, Marion Co., FL. S. minor is a small turtle (adults about 100 mm) that spends nearly its entire life submerged in its lotic environment. After entering the water as hatchling, it is possible that the only time this species leaves the water is when females emerge to lay eggs. A mark-recapture study was used to determine the population size and structure. X-rays and a literature search were used to determine age-specific fecundity. A population of females over six years of age in a 1.7 km study section of the Rainbow River was estimated to be about 350±218. The total population of that section was estimated to be about 5500±3246 individuals. Reproductive females have relatively low and consistent survivorship, about 70% to 80%. Males have higher survivorship ranging from 80% to over 90%. Fewer than 10% of the eggs laid survive to maturity. The life history of S. minor is unlike that of most other turtles because it does not include a type III survivorship. Adult S. minor females exemplify what appears to be type II survivorship. This is most likely due to the fact that S. minor is small relative to most turtles and subsequently never grows large enough to successfully deter the terrestrial predation females have to face when nesting.

Hide and Go Seek for Keeps: Crypsis of Arrow shrimp Colormorphs

Student: Ben Cournoyer

Thesis Committee: Jonathan Cohen (chair), Shannon Gowans, Nancy Smith

The arrow shrimp, Tozeuma carolinense, is among the most numerically dominant small crustaceans inhabiting seagrass beds along the southern coast of the United States. These Caridean shrimp inhabit the upper region of seagrass blades and feed on epiphytic algae. Despite thousands of this species, it is largely underrepresented in the diets of predatory fish, presumably due to its cryptic morphology and behavior. Here we quantify the degree of crypsis of green and brown colormorphs of T. carolinense to the visual systems of two potential predators, a dichromat (Cynoscion nebulosus) and a trichromat (Sciaenops ocellatus), using a visual chromatic contrast model. Results are given in units of contrast (just noticeable difference) between the spectral reflectances of colormorphs and backgrounds. Contrast varied greatly for both colormorphs among the grass backgrounds. For both dichromatic and trichromatic predators, green-morphs produce less contrast than brown-morphs on live seagrass, while brown-morphs produce less contrast than green-morphs on dead seagrass. Each colormorph had at least one complimentary background on which it would be difficult to discriminate. Model predictions proved to be a good indicator of abundance in a natural population of T. carolinense in Tampa Bay (Fl). Although these shrimp do not rely solely on cryptic coloration for predator evasion, this study indicates that the ability of T. carolinense to match its background likely contributes to their lack of representation in the diets of predatory fish.

Molecular population structure and biogeography of the chain pipefish, Syngnathus lousianae, in Florida waters

Student: Alan Downey-Wall

Thesis Committee: Bill Szelistowski (chair), Carole McIvor, Steve Denison

Population structure in marine organisms is believed to be largely dependent on dispersal ability. This concept is especially applicable to fishes which range widely in dispersal ability due to differences in the form of early life history stages and adult mobility. The chain pipefish, S. louisianae, exhibits characteristics found in poor-dispersal organisms such as non-planktonic eggs and larvae and poor swimming abilities in adults, and might be expected to have highly structured populations within the state of Florida, as does the gulf pipefish, Syngnathus scovelli. In this study I characterized the population structure of S. louisianae using a portion of the mtDNA control region. Fish were collected during 2009 from Fort Pierce on the Atlantic coast, from Pensacola, Apalachicola/St. Josephs Bays, and Tampa Bay on the Gulf coast, and from Long Key in the Florida Keys. A total of 42 haplotypes was found and the most prevalent haplotypes were found on both coasts. A pair-wise comparison of all sites revealed significant genetic differences only between the Atlantic site and the two Gulf of Mexico sites located on the Florida panhandle. A maximum parsimony tree showed no discernable evolutionary relationships associated with geographic location. These data suggest gene flow around the southern tip of the Florida peninsula, previously unrecorded in a syngnathid. The weak population structure and lack of genetic separation between Gulf and Atlantic stocks suggest that S. louisianae has substantially greater dispersal ability than S. scovelli, and has a population structure more comparable to larger fish with high dispersal potential. It is suggested that this dispersal is linked in part to offshore sargassum rafting that occurs in juvenile S. louisianae.

Watching People Watching Dolphins: Studying the interactions between boaters and bottlenose dolphins (Tursiops truncatus) and compliance to voluntary viewing guidelines in Tampa Bay

Student: Michelle McEachern

Thesis Committee:  Shannon Gowans (chair), Beth Forys, Stacey Horstman

There is increasing concern regarding boat interactions with cetaceans. Several studies have found boat presence, especially commercial whale and dolphin watching boats, to negatively affect cetaceans, both on short and long-term time scales. Voluntary codes of conduct and viewing guidelines are often utilized to supplement regulations surrounding marine mammals, but have varying success at reducing impacts. The boating industry is important to the economy and culture of Florida and the Tampa Bay region. The large number of boaters in Florida: however, creates problems in conservation of protected habitats and species. The bottlenose dolphin (Tursiops truncatus) lives in close proximity to humans and is common in Florida waters. The Office of Protected Resources, under the National Marine Fisheries Service, provides viewing guidelines for the southeast region of the United States, which promote proper etiquette when interacting with marine mammals. These guidelines are designed to reduce illegal takes of marine mammals, as defined in the Marine Mammal Protection Act (MMPA) of 1972. The impacts rising from encounters between boaters and bottlenose dolphins are hard to mitigate for various reasons, the most important being a lack of knowledge about encounters involving all types of boaters.

This study is a preliminary investigation of the encounters between bottlenose dolphins and boaters in a small portion of Tampa Bay. We collected observational data on 32 encounters between boaters and bottlenose dolphins, out of 128 bottlenose dolphin sightings occurring in and around Boca Ciega Bay, from June 2, 2009, to July 30, 2009. Almost half of observed dolphins and 41% of resident dolphins were involved in encounters. What is more, 35% of observed dolphins and 30% of resident dolphins were involved in non-compliant encounters. The Gulf of Mexico and upper Boca Ciega Bay may be hotspots for encounters, with greater than expected frequencies of encounters. A majority of encounters were instigated by boaters, were non-compliant with viewing guidelines, and involved recreational boaters. Tourism vessels were non-compliant with viewing guidelines a majority of the time, and committed three of four potential violations of the MMPA. A little less than a third of recreational boaters were non-compliant with viewing guidelines, but the number of recreational boaters contributing to this proportion was half of all non-compliant boaters. The impact resulting from tourism vessels can be mitigated through the adoption of the Dolphin SMART program set to launch in the area in early summer 2010. The impact resulting from recreational vessels should be reduced through comprehensive educational and outreach programs that ensure all boaters receive information pertaining to MMPA regulations and viewing guidelines. In order to understand the encounters between bottlenose dolphins and boaters, and document boat disturbance of dolphins, future research should focus on collecting more detailed boater information and dolphin behavioral data.

Correlation of Side-Scan Sonar Mosaics and Surface Sediment Characteristics at the Mouth of Chesapeake Bay

Student: Heather N. Relyea

Thesis Committee: Laura Wetzel (chair), Gregg Brooks, Kelly Debure, Lt. Jasper Schaer (NOAA)

This study explored the relationship between bottom sample characteristics and backscatter intensities of high-frequency side scan sonar. Bottom samples collected during the summer of 2009, from an area at the mouth of the Chesapeake Bay in Virginia, were compared with side-scan sonar readings taken from the same area by the NOAA hydrographic research ship Thomas Jefferson from 2007-2009. Fifty sediment samples were collected in the study area and analyzed to determine percent carbonate, total organic content, and grain size. These data were then plotted against seven overlapping 455 kHz side-scan sonar mosaics using ArcGIS to visually examine how differences in sediment characteristics correlate with differences in the backscatter intensity. The results of the study clearly indicate a correlation between sediment grain size and backscatter intensity. Total organic content was determined to be inconsequential in this area, and the 50 samples did not show enough variation in percent carbonate to provide any conclusive evidence of correlation in this study. Analysis of the data showed that there is a positive correlation between sediment grain size and side-scan backscatter intensity throughout the range of intensities, with a very strong correlation for high intensity areas and coarse grain sizes, but weaker and more varied correlations in lower intensity areas.

Student Research