In contrast to the study of ecosystems, organismal ecology focuses on individuals and species. CBL scientists in this area address two fundamental questions: How does a species or organism function in this environment? And, how does the environment influence that species or organism? Investigating aquatic life ranging from minute sedimentary worms to predatory fishes, CBL's ecologists are furthering knowledge of the physiological characteristics of organisms, their place in the food web, and the physical and chemical processes influencing or in some cases, resulting from their activities. Another important factor they consider is species variability; understanding individual variation within species is key to understanding how communities have developed as they have, as well as how individuals and species respond to change.

A research area within organismal ecology is ecotoxicology how individuals and niches respond to a new biotic or abiotic stress. Such studies not only increase knowledge of the consequences of anthropogenic stresses, but also of how variation plays into evolutionary processes, for instance, how it can enable one species to outcompete another.

CBL Student research Projects:

• Biodiversity in marine sediments
• See Fisheries for ecological research on fish

Sediment Dwellers and Geochemical Cues

Professor Roberta Marinelli, in conjunction with Dr. Sarah Woodin, University of South Carolina, has demonstrated that a wide variety of sediment-dwelling organisms use information concerning oxygen and ammonium concentrations in sediments to make initial decisions about where to live after their larval life in the plankton. Often, this variation is linked to other physical and biological processes that may be beneficial or detrimental to an individual's growth and success in a given location. As organisms age, the importance of certain geochemical cues, such as ammonium, appears to shift. Whereas ammonium is a negative cue for new juveniles, it appears to have beneficial effects later in life due to its positive effect on benthic primary production. Given such ontogenetic shifts in the importance of chemical cues in the early stages of life, Dr. Marinelli's laboratory continues to focus on identifying important substances and determining their distribution in nature and their effect on organisms throughout their lives. This research, sponsored by the National Science Foundation, is one of several projects in Dr. Marinelli's laboratory investigating the importance of small-scale geochemical processes to community ecology in marine sediments.

A juvenile polychaete, (species Arenicola cristata), seen here among sediment grains, was one of the benthic organisms used in Dr. Roberta Marinelli's research on geochemical cues and organismal behavior.

Chesapeake Ecotoxilogical Research Project

Dr. Thomas Miller is involved in one of the first studies to show the sublethal levels effects on estuarine animals from a complex mixture of contaminants in a real-world environment. The multi-institutional investigation into contamination in the Chesapeake Bay addresses shortcomings in the way most ecotoxilogical research is performed.* Typically, studies test individual chemicals to the LC50 standard, the level of concentration that is lethal to 50% of tested organisms. However, contaminants in the environment generally do not exist at lethal doses, nor do they exist in isolation. Dr. Miller's lab has studied the effects of contamination on anthropods and mummichogs placed in tanks containing sediment from the Baltimore Harbor, Maryland, or the Elizabeth River in Norfolk, Virginia. Sediments from both places contained polyaromatic hydrocarbons, common industrial contaminants. At this exposure level, the anthropods incurred a 20% loss in production, primarily in terms of growth. In the real world, such a loss in production not only would affect the anthropods, but also the fish relying upon them for food. Among the mummichogs, they found that the offspring of contaminated mothers had diminished growth and survival rates, even though the offspring were raised in uncontaminated situations. This finding was particularly relevant to the Chesapeake Bay, where many fishes are migratory. Miller's study could have implications for managing resources, if, for example, his models demonstrate that contaminated sediment leads to a loss in fishery yield.

*Funded by the National Oceanic and Atmospheric Administration

Dr. Thomas Miller has been involved in one of the first studies to show the sublethal levels effects on estuarine animals from a complex mixture of contaminants in a real-world environment.

Sediment Modification by Organisms

Sedimentary organisms, such as worms and clams, are immersed in a physical and chemical matrix that they continually modify through feeding, burrowing, and respiratory activities. Their physical and chemical changes affect the ecological community in which they reside; they also alter the distribution of acoustically important sediment properties through the creation of air spaces and bubbles and the movement of particles and shell fragments. Dr. Roberta Marinelli, in collaboration with Drs. Sarah Woodin and David Wethey of the University of South Carolina, are examining how the relocation of individuals affects the physics, chemistry, and biology of sediments. Three factors that promote relocation among sediment dwellers include resource availability; the geochemical environment, such as rates of organic matter degradation and the fate and concentration of dissolved compounds in sediments; and the density and activity of surrounding biota. Their research seeks to develop new technologies, including pressure sensors, PIT tags, and ultrasound, to measure how frequently organisms move (as a result of experimentally imposed conditions) and the physical (solid and fluid) consequences of these movements. The results have implications for geochemical and physical processes and ecological interactions in sediments. Collectively, the experiments and new technologies also provide information regarding the spatial distribution of physical and chemical properties in sediments of operational importance to the Navy.

Research sponsored by the Office of Naval Research.

Parasite Resistance in Snails

Dr. Thomas Miller's laboratory has been investigating the population dynamics of a wide range of species. One recent study has quantified interactions between parasite resistance and heavy metal tolerance in a tropical snail (Biomphalaria glabrata) that is an intermediate host for trematode parasites that cause schistosomiasis. Parasite resistance in this snails goes hand in hand with sensitivity to the heavy metal cadmium, meaning that if a snail is resistant to the parasite, it also is sensitive to cadmium. The research involved quantifying rates of individual survival and population growth at different levels of cadmium exposure. This model system provides evidence for how natural selection that acts on different stages of the snail's life cycle affects overall population growth.

Biocomplexity of Marine Stromatolites

Layered deposits of calcium carbonate known as stromatolites are the oldest macroscopic evidence of life on earth. Neither biotic fossils nor abiotic structures, stromatolites are complex interactions of microbes, sediments and the environment. Modern stromatolites are still forming in the Bahamas, and CBL's Professor Roberta Marinelli has been investigating them with The Research Initiative on Bahamian Stromatolites (RIBS), a multi-investigator project funded under the National Science Foundation's Biocomplexity Program. The RIBS team is seeking to understand the internal biological and chemical processes associated with microbial and mineral growth, as well as environmental factors, such as light, currents, sediment supply, that determine growth and proliferation of stromatolite reefs. Professor Marinelli is engaged in measuring and manipulating the physical parameters that affect stromatolite success. This includes the long-term wave and current environment and turbulence characteristics affecting sediment supply and the shear stresses at the surface of stromatolite heads and reefs. Her group also is measuring the light, which drives photosynthetic activity important to microbial processes, and sediment resuspension to learn if sediments in sufficient supply to promote accretion or burial of existing stromatolite heads and reefs. Combining the collected data with that from microbial ecologists, the project will develop both ecological and geochemical models of stromatolite growth.
 

Photo: Research Initiative on Bahamian Stromatolites

Stromatolites are complex interactions of microbes, sediments and the environment. Professor Roberta Marinelli is investigating processes that affect their growth and success.