[DATE OF SAMPLING UNKNOWN OR NOT APPLICABLE.] Widespread use of septic tanks in 
the Florida Keys increase the nutrient concentrations of limestone groundwaters that 
discharge into shallow nearshore waters, resulting in coastal eutrophication. This study 
characterizes watershed nutrient inputs, transformations, and effects along a land-sea 
gradient stratified into four ecosystems that occur with increasing distance from land: 
manmade canal systems (receiving waters of nutrient inputs), seagrass meadows, 
patch reefs, and offshore bank reefs. Soluble reactive phosphorus (SRP), the primary 
limiting nutrient, was significantly elevated in canal systems compared to the other 
ecosystems, while dissolved inorganic nitrogen (DIN; NH 4 + and N0 3 *), a secondary 
limiting nutrient, was elevated both in canal systems and seagrass meadows. SRP and 
NH 4 + concentrations decreased to low concentrations within approximately I km and 3 
km from land, respectively. DIN and SRP accounted for their greatest contribution (up 
to 30%) of total N and P pools in canals, compared to dissolved organic nitrogen (DON) 
and dissolved organic phosphorus (DOP) that dominated (up to 68%) the total N and P 
pools at the offshore bank reefs. Particulate N and P fractions were also elevated (up to 
48%) in canals and nearshore seagrass meadows, indicating rapid biological uptake of 
DIN and SRP into organic particles. Chlorophyll a and turbidity were also elevated in 
canal systems and seagrass meadows; chlorophyll a was maximal during summer when 
maximum watershed nutrient input occurs, whereas turbidity was maximal during 
winter due to seasonally maximum wind conditions and sediment resuspension. DO was 
negatively correlated with NH 4 + and SRP; hypoxia (DO < 2.5 mg L' 1 ) frequently 
occurred in nutrient-enriched canal systems and seagrass meadows, especially during 
the warm summer months. These findings correlate with recent (<5 yr) observations of 
increasing algal blooms, seagrass epiphytization and die-off, and loss of coral cover on 
patch and bank reef ecosystems, suggesting that nearshore waters of the Florida Keys 
have entered a stage of critical eutrophication. 
1992 0 
Ley, J. A. (1992) Influence of changes in freshwater flow on the use of mangrove prop root 
habitat by fishes. Ph. D. Dissertation. University Florida, Gainesville, FL. 171 pp. 
[DATE OF SAMPLING UNKNOWN OR NOT APPLICABLE.] The hypothesis that seasonal 
changes in freshwater inflow (indicated by salinity) influence habitat use by fishes was 
tested in northeastern Florida Bay. Fishes were sampled monthly for 13 months using 
visual censuses and enclosure nets. Of the 305,589 individuals observed, 91% were 
estuarine residents, numerically dominated by engraulids, atherinids and 
cyprinodontids. Occasional marine and freshwater visitors comprised 2% of the 
individuals, and estuarine transients, 8%. No young-of-the-year estuarine transients 
were observed. Salinity ranged between 0.0 to 58 °/oo upstream, 19.5 to 54 °/oo 
midstream, and 30 to 50 °/oo downstream. The 77 species were grouped for analysis: 
small benthic, small water column, and larger fishes. Abundances of larger fishes were 
consistently lower upstream (0.15 fish nr 2 ), than mid- (0.65 fish nr 2 ), or downstream 
(0.55 fish rrr 2 ). Species of larger fishes numbered fewer upstream (11), than 
midstream (15), and downstream (22). Benthic and water column fish abundances did 
not vary along the gradient. Temporally, fish distribution was uncorrelated with 
salinity. Development of mangrove habitat and submerged aquatic vegetation (SAV) 
were reduced upstream. Fish diets shifted to other foods upstream. Thus, where 
seasonal changes in freshwater inflow were greater (i.e. upstream), species and 
numbers of larger fishes were lower, possibly due to salinity conditions, food 
availability and habitat development. To determine if lower salinity conditions alone led 
to reduced predation, prey fishes were tethered along the gradient. Predator encounter 
rates were not different over the salinity range tested, but were 50% lower at the 
most remote sites. This was perhaps a function of accessibility of the sites to roving 
predators. Water management strategies to increase mangrove development and SAV 
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