of salt marshes and mangrove forests is likely the most broadly
reaching and destructive disturbance in these coastal Florida ecosystems
(Montague & Wiegert 1990).
Before mosquito control methods like
impoundments were in place, mosquito landings were among the highest
densities ever recorded in the continental United States (Provost
1949), reaching 500 per person per minute in some areas of Florida
Ditching in marshes in the 1930s was ineffective,
and the use of DDT pesticide in the 1940s had adverse effects on
wildlife (Montague & Wiegert 1990). In the 1950s, impounding
marshes became an effective and seemingly less invasive way to control
mosquitoes. Using this method, salt marshes and intertidal mangroves
are closed off to tidal influences and the water is pumped out,
allowing mosquitoes to lay eggs on exposed sediment. The impoundments
are then flooded to kill eggs and larvae. Today, 192 impoundments
are active on the east coast of Florida alone (Rey & Kain 1989).
Many of these areas are still closed systems that allow influx of
freshwater from precipitation and runoff, creating wide variations
in salinity. This, along with the flooding process, can cause dieback
of natural vegetation and establishment of more oligohaline species.
Breeding and spawning behaviors of fishes and invertebrates can
also be restricted in closed systems.
One of the most devastating
effects of impounding was to the dusky seaside sparrow, Ammodramas
maritimus nigrescens, which was driven to extinction in 1987
(Kale 1996). Currently, several areas have begun operating on a
rotational impoundment management (RIM) approach (David 1992). The
RIM plan allows impoundments to be open to regular tidal flows and
wildlife migrations during non-breeding months.
From May to August,
impoundments are closed to control mosquito reproduction. The addition
of culverts to enhance tidal cycles in open impoundments (known
as breached-RIM or restored areas) have helped to increase biodiversity,
correct chemical values for sediments and to re-establish common
vegetation (Brockmeyer et al. 1997, Klassen 1998, Poulakis et al. 2002, Rey &
Mangrove species seem
to respond differently to RIM and restored areas. For example, the
red mangrove, Rhizophora mangle,
reaches higher densities in RIM and restored impoundments; whereas,
the black mangrove, Avicennia
grows best in natural undeveloped areas (Middleton et al. 2008). More information on
mosquito impoundments can be found by
navigating to the impoundment link on the main habitat page.
use changes from the growing population and urbanization in Florida
and throughout the world have altered coastal ecosystems.
mangroves have been removed and both these areas and salt marshes
have been filled with dredged material to create roads, residential
communities and businesses.
Habitat fragmentation has occurred from
this development, fracturing animal communities and leaving ecosystems
more vulnerable to other habitat disturbances (Larson 1995). Fortunately,
substantial mangroves and salt marshes lay within protected areas
such as the Merritt Island National Wildlife Refuge and property
managed by the Florida Department of Environmental Protection. Proper
management provides conservation from further development and encourages
restoration programs that work to increase habitat acreage.
Muck & Nutrients
of fine-grained, organic-rich clays and silt known as muck are introduced
to coastal environments from terrestrial and industrial runoff.
Muck generally settles into depressions in the sediment, and can
reach up to 2 m deep in some areas of the IRL (Trefry et al. 1990). Disturbance from boat
traffic, wind and waves can suspend
muck, creating particulates that cloud the water, reducing sunlight
penetration and retarding plant and algal growth (Trefry et
Transported in the water column by currents, muck
can settle in salt marshes and mangrove forests, possibly smothering
young vegetation. Muck accrual in the IRL has been ongoing for the
past 40 to 60 years. Although less than 10% of the IRL bottom was
covered in muck in 1990, coverage continues to grow (Trefry et
al. 1990, Trefry et al. 2007).
In addition to the
physical stresses caused by this sediment accumulation, muck carries
large quantities of nutrients and toxic substances that can create
health problems or death for a variety of aquatic organisms. Excess
nitrogen and phosphorous can alter the dominant plants in marshes
and mangroves, allowing some species to thrive outside of their
natural elevation (Levine et al. 1998). Recently, dredging
projects in isolated areas of the lagoon, including the St. Sebastian
River, Turkey Creek and Crane Creek, have successfully removed thousands
of cubic meters of muck, along with harmful chemicals like pesticides
that are incorporated into the sediment (Trefry & Trocine 2002).
Coupled with decreases in terrestrial and industrial runoff, further
dredging projects could result in long-term reductions of muck throughout
have become high profile issues affecting ecosystem dynamics in
both aquatic and terrestrial environments. Because salt marshes
and mangroves are unique mixtures of both habitats, invasive species
from land and sea pose threats to biodiversity and ecosystem health.
In Florida, the introduced nutria, Myocastor coypus, contributes
to the loss of marsh acreage by foraging on vegetation (Ford &
Grace 1998). Changes in water flow around salt marshes and mangroves
have allowed for expansion of the invading Brazilian pepper, Schinus
terebinthifolius, and the Australian pine, Casuarina
equistifolia. Closing portions of these habitats for mosquito
impoundments has reduced the salinity, allowing the invasion of
more oligohaline vegetation and animals (FWS 1999) such as the blackchin
melanotheron (Faunce et al. 1999, Poulakis et
al. 2002). Furthermore, disturbed or barren areas will often
be colonized by invasives before native plants can become established.
Efforts are ongoing to remove invasive plants from terrestrial areas,
but aquatic invasions of fishes and invertebrates are often difficult
or impossible to reverse, and can only be managed to prevent further
Salt marshes, mangroves and other coastal ecosystems
can usually recover quickly from natural disturbances such as fire
and hurricanes. However, when disturbance events occur in close
succession, they may have lasting effects on the ecosystems. Hurricanes
produce storm surges, wind and waves that can impact mangroves and
marshes in several ways. Upper marshes and mangrove swamps can experience
an influx of seawater at a salinity to which vegetation is not accustomed,
causing dieback of several plant species. Wind can strip trees and
bushes of foliage and damage the trunk. The white mangrove, Laguncularia
racemosa, is the mangrove species most susceptible to wind
damage (Doyle et al. 1995).
In addition, lower elevations
can experience extreme rates of sedimentation or erosion. Sediment
erosion can wash away much of the vegetation, reducing habitat acreage.
However, sediment accretion could be more harmful, essentially covering
marsh and mangrove areas (Rejmanek et al. 1998) and smothering
sessile benthic invertebrates. One example of rapid sedimentation
occurred in the upper Chesapeake Bay, when over a 70-year period
50% of the sediment accumulation was attributed to one flood event
and a single hurricane (Schubel & Hirschberg 1978). Regeneration
of mangrove forests following substantial storm damage may take
decades, and restored swamps may have altered biodiversity and plant
zonation (Ellison & Farnsworth 1990).
Sea Level Rise
attention has been given to the effects of rising sea level on coastal
ecosystems throughout the world. As intertidal communities, salt
marshes and mangroves are at risk from both the amplitude and rate
of this rise. For the ecosystems to thrive, they must occur at the
appropriate elevation and slope. In fact, one of the most common
reasons for restoration failure in salt marshes is choosing an improper
site based on these parameters (Crewz & Lewis 1991). As sea
level rises, it is possible for marshes and mangroves to shift in
a landward direction if the rate of rise is slow enough for sediment
accretion to occur (Montague & Wiegert 1990). However, coastal
development and steep terrain may inhibit plant migration, changing
zonation in these habitats or flooding them completely. In addition,
compression of the intertidal zone can lead to increased interspecific
competition and loss of biodiversity. See Climate Change and the
References & Further Reading
RE, Rey, JR, Virnstein, RW, Gilmore, RG & L Earnest. 1997. Rehabilitation
of impounded estuarine wetlands by hydrologic reconnection to the
Indian River Lagoon, Florida (USA). Wetlands Ecol. Manag. 4: 93-109.
Crewz, DW & RR Lewis III. 1991. An evaluation of historical attempts to establish
in marine wetlands in Florida. Florida Sea Grant technical
paper TP-60. Sea Grant College, University of Florida. Gainesville,
David, JR. 1992. The Saint Lucie
County Mosquito Control District summary workplan for mosquito impoundment
restoration for the salt marshes of Saint Lucie County. Saint
Lucie County Mosquito Control District. Saint Lucie, FL. USA.
Doyle, TW, Smith III, TJ & MB Robblee.
Wind damage effects of Hurricane Andrew on mangrove communities
along the southwest coast of Florida, USA. J. Coast. Res. 21: 159-168.
Ellison, AM & EL Farnsworth. 2001. Mangrove
communities. In: Bertness, MD, Gaines, SD & ME Hay. Marine community ecology. Sinauer
Associates, Inc. Sunderland,
MA. USA. 550 pp.
Faunce, CH & R Paperno. 1999. Tilapia-dominated
fish assemblages within an impounded mangrove ecosystem in east-central
Florida. Wetlands. 19: 126-138.
Ford, MA & JB Grace. 1998. Effects
of vertebrate herbivores on soil processes, plant biomass, litter
accumulation and soil elevation changes in a coastal marsh. J.
Ecol. 86: 974-982.
FWS. 1999. Coastal Salt Marsh. In: Multi-species recovery plan for South
Florida. US Fish
& Wildlife Service. 553-595.
Kale II, HW. 1996. Recently extinct:
dusky seaside sparrow, Ammodramas maritimus nigrescens. In: Rodgers, JA, Kale II, HW &
HT Smith, eds. Rare
and endangered biota of Florida. Volume V. Birds. 7-12. University
Presses of Florida. Gainesville, FL. USA.
Kemp, SJ. 2008. Autecological effects of habitat
alteration: trophic changes in mangrove marsh fish as a consequence
of marsh impoundment. Mar. Ecol. Prog. Ser. 371: 233-242.
Klassen, CA. 1998. The utilization
of a Florida salt marsh mosquito impoundment by transient fish species. Master's Thesis. Florida
Inst. of Technology. 87 pp.
Leenhouts, WP. 1983. Marsh and
water management plan, Merritt Island National Wildlife Refuge. US Fish and Wildlife Service.
Merritt Island National Wildlife Refuge.
Titusville, FL. USA.
Levine, JM, Brewer, JS & MD Bertness.
1998. Nutrients, competition and plant zonation in a New England
salt marsh. J. Ecol. 86: 285-292.
Middleton, B, Devlin, D, Proffitt, E, McKee,
K & KF Cretini. 2008. Characteristics of mangrove swamps managed
for mosquito control in eastern Florida, USA. Mar. Ecol. Prog.
Ser. 371: 117-129.
Montague, CL & RG Wiegert. 1990.
Salt marshes. In: Myers, RL & JJ Ewel, eds. Ecosystems
of Florida. UCF Press. Orlando, FL. USA. 765 pp.
Poulakis, GR, Shenker, JM & DS
Taylor. 2002. Habitat use by fishes after tidal reconnection of
an impounded estuarine wetland in the Indian River Lagoon (USA). Wetlands Ecol. Manag. 10:
Provost, MW. 1949. Mosquito control
and mosquito problems in Florida. Proc. Annu. Meet. Calif. Mosq.
Control Assoc. 17th. 32-35.
Rejmanek, M, Sasser, C & GW Peterson.
1988. Hurricane-induced sediment deposition in a Gulf Coast marsh. Est. Coast. Shelf Sci. 27:
Rey, JR & T Kain. 1989. A
guide to the salt marsh impoundments of Florida. University
of Florida, Florida Medical Entomology Laboratory. Vero Beach, FL.
Rey, JR & T Kain. 1993. Coastal
marsh enhancement project. Indian River National Estuary Program. Final report contract CE004963-91.
University of Florida IFAS. Vero
Beach, Florida. USA. 29 pp.
Schubel, JR & DJ Hirschberg.
1978. Estuarine graveyards, climatic change, and the importance
of the estuarine environment. In: Wiley, ML, ed. Estuarine
Interactions. 285-303. Academic Press. New York. USA.
Trefry, JH, Metz, S, Trocine, RP,
Iricanin, N, Burnside, D, Chen, NC & B Webb. 1990. Design
and operation of a muck sediment survey. Final report to the
St. Johns River Water Management District. Available from
the St. Johns River Water Management District. Palatka, FL. USA.
Trefry, JH & RP Trocine. 2002. Pre-dredging and post-dredging surveys of trace
metals and organic
substances in Turkey Creek, Florida. Final report to the St.
Johns River Water Management District. Available from the
St. Johns River Water Management District. Palatka, FL. USA.
Trefry, JH, Trocine, RP & DW
Woodall. 2007. Composition and sources of suspended matter in the
Indian River Lagoon, Florida. Florida Sci. 70: 363-382.