Indian River Lagoon Species Inventory
Salt Marshes & Mangroves
of salt marshes and mangrove forests is likely the most broadly
reaching and destructive disturbance in these coastal Florida ecosystems
(Montague & Wiegert 1990).
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.
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 germinans, 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.
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
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).
Bioinvasions 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 tilapia, Sarotherodon 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 range expansion.
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).
Sea Level Rise
Much 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 IRL.
References & Further Reading
Brockmeyer JR., 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 vegetation in marine wetlands in Florida. Florida Sea Grant technical paper TP-60. Sea Grant College, University of Florida. Gainesville, FL. USA.
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: 51-69.
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: 217-222.
Rey, JR & T Kain. 1989. A guide to the salt marsh impoundments of Florida. University of Florida, Florida Medical Entomology Laboratory. Vero Beach, FL. USA.
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.
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