Eleuthera

Summer 2002

Geology and Topography of Eleuthera Island Eleuthera and its associated marine environment make up one of the six coastal systems on the Great Bahama Bank.  The long arc of the island creates a sheltered bank environment to the west of the island.  This is a typical long narrow Atlantic margin island, measuring about 90 miles long but rarely exceeding more than 3 miles in width. The largest land masses, and broadest parts of the island, are in the north and south, which also hold the largest water lenses, and to a lesser extent between Tarpum Bay and Rock Sound in the south.

Most of the island is narrow and hilly, especially in the north where there is a breach at the Glass Window. Between the Glass Window and Savannah Sound the island is unusual in having substantial cliffs on both shorelines. The geological structure in this area is a series of overlapping fossil sand dunes forming a low tableland frequently exceeding 100 feet in height. The highest point is 168 feet. Notable outlying islands, usually detached ridges, are Russell Island/St George’s Island (Spanish Wells), Current Island, Harbour Island and Windermere Island, all of which are inhabited. Low-lying rockland is limited in extent, but most evident in North Eleuthera, the name given to the triangular area north of the Glass Window; around Tarpum Bay; and in the far south.

The Eleuthera bank system forms the northeastern extremity of the Great Bahamas Bank, and has a strongly eroding coastline, with some evidence for bank margin collapse in the recent geological past, notably at Glass Window where the scalloped margin suggests bank margin retreat. The karstified surface limestone is generally sufficiently young to be scarified for agricultural purposes, and the island has been much altered by early plantation settlers and later subsistence farmers. Even today Eleuthera is an important agricultural producer with several large commercial farms. 

Being in the northern part of the Bahamas, Eleuthera has a distinct if mild winter season, and is affected by cold fronts from North America. This also amplifies the winter rain in an otherwise dry season, but total rain overall averages just 50” at Rock Sound. Being on the Atlantic fringe it is in the direct line of the Northeast Trade Winds, which blow steadily all the year round, although they take on a more southerly (E-SE) orientation in summer. Summers are hot and relatively wet with most of the rain falling as heavy showers, or from tropical storm or hurricane activity. Eleuthera is in a higher hurricane risk zone than the southern Bahamas and was struck by both Andrew and Floyd in recent years.

HIGHLIGHTS OF THE SUMMER’S EXPEDITIONS

The mission of the summer’s research was to survey as many different types of coastal environments in south Eleuthera as possible. The project started with some preliminary maps of the landcover of South Eleuthera. 

Coastal Surveys of land and sea - The research teams conducted over 64 coastal surveys, covering 48 different sites.  Over 20 surveys were completed at the Island School; this small peninsula created by dredge-and-fill development in the 1960’s was the subject of intense study as a potential restoration project.  The surveys ranged from Powell Point, to Lighthouse Point, and as far north as Savannah Sound. The surveys covered the protected, low-energy mangrove creeks as well as the high-energy beaches and dunes.  The surveys presented a real sampling challenge in facing extreme heat, poison wood, hornet nests, and irritating jellyfish, not to mention the mysterious tides that stranded the boats on sand bars.  The surveys required hours of laboratory work identifying plants and algae samples, drying sediment samples, and sorting algae for biomass estimates. Volunteers worked extra hours in the evening to enter all the data into spreadsheets.   Over 263 species of coastal plants and 114 species of macroalgae were recorded.  The field surveys were used to groundtruth the LandSat 7 landcover maps.  These maps are the first step in developing a master plan for South Eleuthera. 

Water Quality Sampling around Island School – Teams IV and V conducted five days of dawn to dusk water quality sampling.  The water quality sampling started at 6AM and ended at 8PM, with four people taking water samples every 2 hours.  The samples were analyzed for dissolved oxygen, salinity, temperature and turbidity.  Field measurements of current and horizontal secchi disk distance were also taken.  The data showed tidal flushing around the peninsula, and the areas of freshwater input from the Island School.  Water quality characteristics can be matched to wave energy and shoreline sediment composition to predict erosion and areas of water quality degradation.

Interviews with Local Government – College of Bahamas faculty Lionel Johnson and Lester Flowers carried out an interview process on environmental awareness and growth management.  In a long-term environmental education plan, it is essential to identify what people perceive as the most critical environmental issues, and how people envision the island developing in the future.  Eleuthera has had a long history of resort development and failure.  A tremendous amount of environment degradation has occurred with little economic return.  This questionnaire is the first part of a community development plan aimed at empowering local governments to make more informed development decisions.  The product would be a government Master Plan for land use and long-term development.

Training of College of Bahamas faculty – An academic mini-grant from the Environmental Defense Fund funded four CB faculty to participate in the Earthwatch project.  The lecturers received training materials, books and some equipment to apply the coastal survey methods and interviews to their courses at COB.

List of all Survey Stations on Eleuthera

 OBJECTIVES

The research objective is to combine new technologies in remote sensing with landscape ecology to model biological diversity and fisheries production of shallow-water, tropical marine environments. New earth observation platforms have allowed better landcover mapping the coastal vegetation zones above and below the clear water of tropical islands. This research compares the coastal environments, level of coastal development and incidence of hurricane disturbance for ecologically similar islands in the Bahamian archipelago.  This island group is ideal for the study of coastal ecology for several reasons: 1) the archipelago has a range of island sizes, 2) has a range of human development intensities, and 3) has had hurricane disturbances in the past 2, 3, and 4 years. On small tropical islands, the fluxes of nutrients from land to sea, and vice versa, are in critical balance. These systems are described as “oligotrophic”, meaning “few feeding” in environments where nutrients are limited, and algae production and diversity is dependent on nutrient recycling. Carbonate islands of the Bahamas are very sensitive to chronic eutrophication, or the addition of excess nutrients. The consequence of this nutrification is loss of marine diversity, and degradation of critical nearshore marine fisheries habitats.  Fish habitat production is one measurable criterion that could be used to evaluate questions of sustainability for island systems.

There is growing evidence that humans are irreversibly changing the coastal zone with the chronic input of nutrients from non-point sources. This degradation of nearshore marine habitats is manifested in a loss of macroalgae diversity and production that are particularly important to fishes and marine life dependent on nearshore marine habitats as part of their life cycle. The Bahamian archipelago and the Florida Keys are made up of shallow-water carbonate limestone environments with few surface water resources; a critical feature is the continuous solutions of the limestone rock, and permeation of seawater beneath all the islands (Hoffmeister, 1974, Sealey, 1994). The marine and terrestrial habitats adjacent to the shoreline interact ecologically in terms of nutrient flux through rainfall run-off, seepage of ground water, and detrital material moving on and off the islands. Most people in these islands live within 2 km of the sea, and rely on nearshore marine resources for fisheries and tourism.

Threats to nearshore marine environments occur on several levels. The most severe threat is the physical elimination of habitats for the alteration and restructuring of the shoreline to accommodate marina, harbour, and residential development. A second threat comes from the acute and chronic sedimentation generated when coastal vegetation is removed, and the soil/sand exposed to erosion by rain during construction. Often exotic plants are used in landscaping, and native coastal plants are removed permanently leaving little or no vegetation buffer between buildings and the sea. Lastly, a threat exists, though poorly documented in the Bahamas specifically, from nutrient seepage from cesspits systems very close to the sea, or in contact with ground water.  The common means of wastewater treatment and disposal is the use of septic systems or cesspit systems constructed on-site (US.EPA 1991; Cant, 1997). All on-site disposal systems installed on limestone islands are shown to enrich nearshore water with inorganic nutrients and some amount of organic matter (U.S. Environmental Protection Agency, 1983, 1991).

All of these threats can be mapped and integrated into spatial datasets. Although there has been much policy discussion of “sustainable development” of island systems, there remain no real ecological criteria to judge sustainability in these small, fragmented, and highly variable landscapes.  This research seeks to refine a system of coastal habitat classification that is based on linking diversity of both land plant and marine macroalgae.  Nutrient flux between land and sea can be evaluated by analysis of stable isotopes, particularly nitrogen, and an indication as to the source of organic detritus and nutrients to on-shore and near-shore primary production.  However, there is no comprehensive spatial data set to guide field surveys to compare both nutrient flux rates and nearshore fisheries production. An analysis of the patterns of coastal development, coastal energy regime and disturbance history can be accomplished with the construction of a spatial dataset is GIS using existing data sources. From this information, one can address the question of sustainability: are there ecological criteria that can be used to measure over development of the coastal zone?

Using existing LandSat 7 imagery and habitat maps for the island of Eleuthera, the objectives for the 2002 field season were to:

1.)    Survey as many different types of coastal environments as possible, including rocky shores, beaches, mangrove wetlands and developed shorelines. 

2.)    Develop a list of coastal plants and coastal plant communities by transect survey methods

3.)    Develop a list of nearshore algae and epifauna communities by transect survey methods, and

4.)    Establish baseline water quality conditions off the Island School, South Eleuthera as a potential restoration site.

These objectives were met with the help of 5 Earthwatch teams in the field for about 2 months. 

METHODS

The methods employed in the field were fairly straightforward.  Each team member was given a handout on the methods and example data sheets.  Teams were divided into smaller groups during the day to participate in marine or coastal survey teams.  A short description of the methods follows in Table 2.

Participants received training material in the form of datasheets and written protocols.  This was the first summer for the project, thus many of the survey methods were new, and there were some revisions in the datasheets.  The volunteers were a tremendous help in entering all the information into EXCEL spreadsheets for later analyses.  The identification of macroalgae and plants was tedious, and a reference collection of both specimens and photos will be compiled for next summer’s work.

Table 2:  A list of the research components and methods employed for each component.  The methods were carried out by volunteers lead by a staff member.  Volunteers rotated between groups to gain experience with all the different field methods.

VOLUNTEER TASKS and ACCOMPLISHMENTS

(a)               How many Earthwatch volunteers/teams were involved and specifically what tasks did they perform?

58 volunteers participated for five 10-day teams.  Each team conducted surveys around the Island School as part of the initial training, then traveled to new areas.   Table 3 outlines some of the highlights  of the work for each team.

 Table 3: A list of the Earthwatch teams fielded during the 2002 season.  The maximum number of volunteers on each team was 12.  Each team made unique contributions to the coastal survey database.

(b)               Give specific and quantitative measures of the volunteers' contribution to your data collection.

Table 1 lists all the coastal surveys carried out by Earthwatch volunteers over the summer.   One of the biggest accomplishments was the coastal plant survey.  This was difficult and hot work in the coastal zone, but the volunteers with enthusiastic and patient with the pressing of specimens and keying of plant specimens.  We worked to bring together the scientific name with local names and published common names to create a more comprehensive coastal plant database.

With the help of field botanist Keith Bradley, we have started an analysis of plant communities found in different coastal zone environments.  Table 4 lists the plants recorded for south Eleuthera; the scientific names are based on the “Flora of the Bahamian Archipelago” by Correll and Correll.