Linking Development to the Status of Benthic Communities: Challenges and
Lessons from the Florida Keys
Ricardo N. Calvo, and Debra C. Woithe
URS Corporation, Tampa, Florida
Deborah H. Peterson
U.S. Army Corps of Engineers, Jacksonville, Florida
What is the connection between development and benthic communities in the
Florida Keys? Can we predict the effect of further development on benthic
communities? These questions are central to the establishment of management
policies in the Florida Keys. As part of the Florida Keys Carrying Capacity Study
(FKCCS) we addressed these two questions based on existing data. Our efforts
focused on direct human impacts (e.g., prop scars, groundings and anchoring
damage, snorkeling and diving impacts), as well as indirect impacts of
development (e.g., pollutant loads).
Water Quality and Benthic Communities in the Florida Keys National
Marine Sanctuary. Based on four years of monitoring data, Boyer and Jones
(2002) concluded that, at a Keys-wide scale, the Florida Keys National Marine
Sanctuary (FKNMS) exhibited “very good” water quality. The Upper Keys
generally have lower nutrient concentrations than the Middle or Lower Keys.
Concentration of TN generally decreased from inshore to offshore; the same
occurred for TP, with the exception of the Upper Keys, where TP increased
offshore, oceanside. A median TN:TP ratio of 62.10 suggests a P-limited
environment.
Keller and Itkin (2002) reported statistically significant differences in TN and TP
between Upper and Middle Keys in samples from canals and other nearshore
locations. TN was lower in sampling stations near developed areas (41.3 μm)
than in natural shorelines (52.3 μm). Annual mean was not statistically different
between stations with regard to region (Upper, Middle, Lower Keys), shoreline
type (developed, undeveloped), island side (bayside, oceanside), or season. A
significant correlation between TP and Chl a suggested that P-limitation occurs.
Kruczynski and McManus (2002) provide an extensive discussion of water
quality issues in the Florida Keys. They reviewed TN and TP data for three
canals, and show values between 19.8 and 40.5 μm for TN and between 0.21 and
1.04 for TP; both higher than those observed in open waters. Lapointe et al.
(1994) also measured elevated TN and TP levels (>35 μm and >0.45 μm,
respectively) at sampling stations that received direct nutrient inputs, including a
canal in Big Pine Key.
As part of the FKCCS, Fourqurean and Miller-Rutten (2002) investigated
nearshore (<1 km from shore) benthic communities in the Florida Keys. They
attempted to determine if temporal or spatial variation in benthic communities
was associated with land use activity in the Florida Keys. Both nearshore benthic
communities and their associated nutrient regimes exhibited spatial variation
throughout the Florida Keys. Nearshore benthic communities exhibited very little
variation over the past 40 years, even in the face of tremendous land development
in the Florida Keys. The results provided little evidence to support the hypothesis
that there is a significant relationship between land use and spatial or temporal
variation of nearshore benthic communities and their associated nutrient regimes
throughout the Florida Keys. Results indicate that substrate, not land use, is the
most important factor associated with benthic community distribution and
composition.
Also as part of the FKCCS, URS Corporation developed stormwater and
wastewater pollutant loading models for the Florida Keys. Model runs suggest
that pollutant loads would be greatly reduced with the implementation of
wastewater and stormwater master plans already adopted. However, the link
between pollutant loads, water quality and the status of benthic communities in
the FKNMS remains elusive.
Direct Human Impacts. No comprehensive boat traffic study exists for the
Florida Keys (Leeworthy 1998, Stolpe 1998, Matthews and Donovan 1992,
FKNMS 1996; Kruer 1993). Existing studies and monitoring efforts are
insufficient to establish a connection between population and the number of boats
utilizing the FKNMS or to predict the effect of changing numbers of boats.
The Florida Marine Research Institute (FMRI) developed a map of scarred
seagrass areas (Sargent et al. 1995). We performed multiple regression analyses,
which showed no significant correlation between the distribution of scarred areas
and a series of development surrogates, including development status of the
nearest shore, location of marinas and boat ramps, location of navigational aids,
and location of channels. The distribution of scarred seagrass areas was only
correlated with distance from shore (independently of shoreline type) and water
depth. Similarly, an examination of the FMRI boat groundings database shows
that boat groundings occur mainly near reef areas, in popular, shallow
destinations.
In a Florida study, Tagle (1990) showed divers touched coral heads an average of
seven times during a 30-minute interval, while five percent of divers have more
than 20 incidents per 30-minute dive. No other quantitative assessment of
snorkeling or diving impacts was available. Rouphael and Inglis (1995) claimed
that diver damage to corals is unlikely to have major consequences for local
coral populations, but may be substantive enough to affect the aesthetic appeal of
the sites.
Conclusions and Recommendations. Development may directly and indirectly
affect benthic communities, as evidenced by prop scars, coral damage, and high
pollutant concentrations in canals and other confined waters in the Florida Keys.
However, despite the existence of an extensive and growing body of literature on
the ecological resources and water quality characteristics of the FKNMS
(reviewed in Porter and Porter 2002, Sullivan et. al 1996), the available data are
insufficient to establish a clear connection between development, nutrient
regimes, and nutrient effects on benthic communities in the FKNMS. Available
data are also insufficient to establish predictive relationships between land
development activities and the impacts listed above.
While the relationship between development and benthic communities is of
paramount interest to scientists, resource managers, and other stakeholders in the
Florida Keys, existing data and research programs address the issue only from
limited perspectives. If resource managers are to be able to assess the effect of
future development on the benthic communities of the Florida Keys, research
must focus on establishing predictive relationships between development and the
ecology of benthic communities. A centralized research coordination program,
which brings together and provides overall focus to disparate efforts, may be
necessary to effectively tackle this important scientific and management issue.
Calvo, Ricardo, URS Corporation, 7650 West Courtney Campbell Causeway,
Tampa, FL, 33607, Phone: 813-636-2106, Fax: 813-636-2494,
Ricardo_n_calvo@urscorp.com, Question 4