Depth-Related Patterns of Bioerosion

St.John2011_1What: Field- and lab-based research in carbonate sedimentology/paleobiology.

When: June 20- July 22

Where: Virgin Islands National Park: St. John, U.S. Virgin Islands; Oberlin College, Oberlin OH

Who: Dennis Hubbard and Karla Parsons-Hubbard (space for 6 students)

Project Overview and Goals

Recent studies have clearly demonstrated that the biological breakdown of reef substrate (bioerosion) is an important process in controlling both community structure and the internal fabric of both modern and ancient reefs. Understanding of how the reef edifice is constructed requires accurate measurements of not only calcification, but also processes that break down substrate and subsequently bind and cement that material together into rigid, wave-resistant structures.

This project will collect dead coral samples from two bays within Virgin Islands National Park. One receives only minor terrestrial sediment/nutrient input and the other is much more highly stressed. We will use photographic and video data from the NPS long-term monitoring program to pinpoint the time-of-death for each of approximately 80 corals; the goal is to sample corals that died 1, 2, 3, 4, and 5 years ago. At Haulover Bay, we will collect corals from one site in ca. 5m of water. In Lameshur Bay, we will recover samples from three sites along a depth gradient. At each of the 4 sites, corals that have died at known times over the past five years will be collected to track patterns of post-mortem encrustation and bioerosion. Field work will take two weeks. The second two weeks will be spent in Oberlin where we will cut and describe samples, prepare them for follow-up analyses at students’ home institutions and train participants in the methods that they will use. Each student will leave with a complete set of samples to complete their project during their senior year.

Geologic Background

St.John2011_2To fully understand either modern or ancient reefs, we need to ask questions that effectively tie physical, chemical and biological processes to their depositional products in ways that allow us to understand reef development across both time and space. Looking back in time, how can we use modern reefs to understand their forebears? What controlled the changing pattern of ancient reef-builders and how did they contribute to rigid structures that stood above their surroundings? What factors controlled preservation, taphonomic loss and subsequent diagenetic alteration? How does the preserved fabric of recognizable corals, sediment, encrust-ation, cements and voids allow us to reconstruct the paleoenvironmental conditions under which a particular reef developed? Looking forward, can Quaternary reefs that existed prior to anthropogenic influence provide a “baseline” against which present and future changes might be measured?

All these questions require detailed information on the main players, how they were preserved, and how the resulting fabrics and facies patterns relate to the processes associated with them. The St. John project will provide important information on the effects of sediment/nutrient loading on modern reefs and will also quantify depth-dependent rates of substrate alteration to test new ideas about the role of bioerosion in reef accretion in modern reefs and their ancient forebears.

Potential Student Projects

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A number of possible projects examine the character and pathways of bioerosion at a variety of scales. The following is a list of potential research questions that can be addressed depending on student interests, training and level of support at their home institution.

  • Do the pathways and rates of bioerosion follow a depth-related pattern that is similar to that for calcification by corals and other skeletonizing reef organisms? (1-2 students)
  • To what extent does nutrient loading act as a primary control of the rate of bioerosion? (1 student)
  • How do abundance, diversity, and volume of loss related to micro-boring organisms compare to the same patterns for macro-borers along gradients of depth and nutrient loading? (2-3 students)
  • Are micro-boring patterns likely to be preserved? (1 student)
  • What is the relative importance of carbonate loss due to bioerosion relative to the addition of material by encrustation? (2-3 students)

Logistics/Special Field Conditions

In the field, we will be living in close quarters – either in tents/cabins or aboard our research vessel. The climate is warm and the sun is intense. We will be working on or around the water every day in the field. Even if you are not involved in sampling on a particular day, you will still be needed in the boat to help those working in the water and to help the processing and cataloging of samples on shore. While this type of work does not require unusual strength, it is still rigorous and days can be long.

Recommended/Prerequisites

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Close-up photo of algae (A), sponges (S) and worm burrows (W) in a sample of Acropora palmata.

Courses in general geology, sedimentology, paleontology (and biology) are recommended. SCUBA certification is desirable but not required. Much of the work will be conducted in shallow water and can be done by snorkelers. However, applicants must be reasonable swimmers that are comfortable on a boat and in open water.

More information

Download full project description PDF.

 

 

 

 

 

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