What are Seagrasses and Why are they Important?
Seagrass meadows are an essential component of the marine ecosystem. Seagrasses perform vital ecological functions such as primary production, stabilizing sediments, increasing habitat complexity and diversity. They act as nursery grounds for fish and invertebrates, maintain water quality, act as contaminant sinks, and form the basis of the marine detrital food web, as well as being directly consumed by marine herbivores like manatees and green turtles.
Why be Concerned about Habitat Protection For Manatees?
A viable population of manatees will not persist without suitable habitat. Florida's increasing human population, and particularly the associated coastal development, is a long-term threat to the manatee's habitat. Historically, coastal development has resulted in degradation of water quality and destruction of seagrasses-the manatee's primary food. Ways to minimize negative effects of coastal development are being explored. The first step is to better understand the manatee's habitat needs and to monitor and assess habitat health and stability. The health of any habitat is important as an indicator of that habitat's ability to sustain a viable population of manatees and other marine species.
What are some of the Impacts to Seagrasses in Florida?
Damage to seagrass communities, which result from accidental grounding and propeller strikes from watercraft, has been recognized as an environmental problem by scientists and natural resource managers since the 1970s. Propeller scars are the result of mechanical excavation of seagrass plants, including the below ground root/rhizome complex, when struck by the propeller and associated engine or steering structures of a watercraft operated in water shallower than the required operational draft of the boat. Damage of this nature can take from between 3-7 years to recover under good conditions, but may be permanent and lead to further seagrass damage in areas with fast moving currents, such as can be found around channels and inlets. Propeller scarring is presumed to result from negligent operation of propeller driven watercraft or operation of such craft with ignorance of navigation rules and markers in shallow waters.
Seagrass Protection Efforts
In the late 1980s, environmental managers from federal wildlife refuges, Florida State parks and aquatic preserves, and county natural resource divisions began addressing the loss of marine and estuarine habitat associated with propeller scarring of seagrass systems. Surveys of badly scarred seagrass resources within managed areas under these authorities resulted in recommendations ranging from creation of focused public education programs to the implementation of no entry zones to protect seagrass communities. Boating restriction zones protecting seagrass from propeller scarring have been in place in Florida waters since 1990, when Lee County first adopted, although never enforced, regulations stipulating that motor powered vessels could not enter identified areas in local waters. Since that time, eleven other zones varying from combustion engine operation exclusion zones to zones stipulating no entry of any kind have been established around the state in Pinellas, Hillsborough, Sarasota, Monroe, Dade and Brevard Counties.
Why are Warm Water Refuges Important to Manatees?
Manatees are regarded as tropical marine mammals. As such, they developed their particular adaptations to an aquatic existence in warm tropical waters. Manatees in Florida are at the northernmost reaches of their range. During the warm season, mostly April to October, manatees freely range throughout the Florida peninsula and to points farther west and north in coastal States of the southeastern U.S. Manatees prefer water temperatures to remain above 68 oF (20 oC). Prolonged exposure to lower water temperatures cause manatees to lose body heat and inadequately digest their food. This can lead to a condition classified as "cold stress" or death.
During the cold season, November to March, water temperatures throughout the state can be below this thermal minimum. Manatees seek out areas with warm water to meet their thermal requirements. Such warm water sources can be natural, such as springs (e.g. Crystal River), or artificial, such as power plant outfalls. Large numbers of manatees, often hundreds, can be found together at these sites during the cold season. Without warm water sources and sites in Florida, manatees would have a difficult time during extremely cold winters in our State.
What's being done?
Habitat staff works with various groups around the state on manatee habitat issues. The Blue Spring Working Group is one such group that meets at Blue Spring State Park each year. The average annual flow of Blue Spring has been reduced by 5% when compared to the historic average annual flow. Consumptive pumping of aquifer water within the spring basin can reduce spring flow by between 5-7% at currently permitted capacity. Although climatic conditions affect spring flows greatly, human use of the aquifer water supplied to this spring has reduced the warm water habitat available to manatees and other wildlife using the spring run. Human population growth within the spring basin is anticipated, and increasing demands on consumptive use of aquifer water is reflected in proposed regional 20 year municipal water use plans. The working group addresses issues like this because the withdrawal levels could reduce spring flows to levels that would not provide the volume of warm water necessary to support the large numbers of manatees using the Blue Spring.
Florida Port Facilities and their Potential Impacts to Manatees - The development, maintenance and expansion of port facilities and inlets represent significant threats to the Florida manatee population due to alteration of habitat, habitat use patterns and direct physical threats from dredging, material transport, vessel access, blasting and other construction activities. It is of paramount importance to review all port and inlet projects with a responsible eye toward manatee and manatee habitat protection. This document addresses port-related manatee concerns.
Seagrass Protection Report (No-motor zones)
Provides a summary of all known seagrass protection zones established prior to January 1998. Marine resource managers throughout Florida were contacted in order to develop this summary. Although there are other boating restriction zones established in Florida for the protection of manatee habitat (e.g. thermal refuge sites; see the Manatee Sanctuary Act, Chapter 62N-22, Florida Administrative Code) and public safety, this report focuses on those zones created for the expressed purpose of seagrass protection. This focus addresses both endangered species foraging habitat and the critical ecological role seagrass communities play in estuarine and marine systems.
Summary of Artificial Warm Water Refugia Issues - This is a synopsis of the FWC's endeavors regarding the topic of artificial warm water refuges.
Foraging Behavior of Manatees During the Cold Season - It has been speculated that during the winter manatees may be limited to foraging in close proximity to a thermal refuge due to their reliance on warm water. If this is typical manatee behavior it would be reasonable to assume that as the winter progresses food resources near the refuge would become depleted, resulting in manatees moving progressively further away from the refuge to other foraging sites. In response to this speculation a literature review was conducted of published research related to manatee foraging behavior to determine if any stereotypic winter foraging habits have been documented.
Manatee Habitat and Human-related Threats to Seagrass in Florida: A Review (165Kb) This review provides and overview of the information regarding manatee habitat in Florida. The purpose of the review is to summarize the existing scientific information concerning:
the ecological requirements of manatees
the behavior associated with manatee foraging
the fresh-water and marine diet of the manatee
the ecological impacts of manatees' feeding on seagrass communities
major threats to manatee habitat related to human activities.
Discussions of habitat requirements for manatees are based on scientific and anecdotal information obtained from published sources.
Proposed Restoration of the Ocklawaha River - Report
Please see our report on The Effects of Proposed Restoration of the Ocklawaha River in the Vicinity of the Rodman Basin on Manatees and Manatee Habitat (142Kb). This report summarizes the history of Rodman Reservoir, historical manatee use, mortality and habitat information for this reservoir and the previously free-flowing Ocklawaha River, and predicted effects on manatee habitat quality and regional manatee populations using this system after planned restoration efforts are completed.
DRAFT FWC Seagrass Survey Protocol Recommendations
Florida International University Seagrass Ecosystems Research Lab
University of Florida Center for Aquatic and Invasive Plant
Southeastern Estuarine Research Society