The invasion and spread of non-native, or “exotic,” species is currently one of the most potent, urgent, and far-reaching threats to the integrity of aquatic ecosystems around the world (NRC 1995; NRC 1996; NRC 2002; Ruckelshaus and Hays 1997). Non-native species can simply be defined as “any species or other biological material that enters an ecosystem beyond its historic, native range” (Keppner 1995).
Protection from and management of aquatic species occurs at the federal and state levels. At the federal level, impairment by invasive species is not recognized under the Clean Water Act (ELI 2008). USACE in Jacksonville leads invasive species management with the Aquatic Plant Control Operations Support Center and the Removals of Aquatic Growth Program. The U.S. Department of Agriculture Animal and Plant Health Inspection Services is charged with protection from invasive species (ELI 2008).
In Florida, management of invasive species is coordinated by Florida Fish and Wildlife Commission’s Aquatic Plant Management Program. In 1994, Florida Department of Environment (DEP) included a TMDL water body impairment category of “WEED-exotic and nuisance aquatic plants density impairing water body” (ELI 2008). However, DEP has yet to develop a TMDL for this category. FWC regulates import of vertebrate and invertebrate aquatic species, Florida Department of Agriculture and Consumer Services (FDACS) contributes to prevention of invasive species with importation regulation. Water management districts also contribute with control and restoration programs (ELI 2008). Non-profit organizations, such as the First Coast Invasive Working Group, organize invasive species removal events and education outreach.
The transport and establishment of non-native aquatic species in the St. Johns River watershed is significant due to a number of ecosystem, human health, social, and economic concerns.
126.96.36.199. Ecosystem Concerns
“Generalizations in ecology are always somewhat risky, but one must be offered at this point. The introduction of exotic (foreign) plants and animals is usually a bad thing if the exotic survives; the damage ranges from the loss of a few native competing species to the total collapse of entire communities” (Ehrenfeld 1970). The alarming increase in the number of documented introductions of non-native organisms is of pressing ecological concern (Carlton and Geller 1993). This concern is supported by the evidence that non-native species, within just years of introduction, are capable of breaking down the tight relationships between resident biota (Valiela 1995). Once introduced, exotic species may encounter few (if any) natural pathogens, predators, or competitors in their new environment.
The non-native plant Hydrilla verticillata is the #1 aquatic weed in Florida. Native to Asia, hydrilla was likely introduced to Florida in the 1950s (Simberloff, et al. 1997) and has spread through the Lower St. Johns River Basin since at least 1967 (USGS 2015). Even the smallest fragment of hydrilla can rapidly grow and reproduce into dense canopies, which are poor habitat for fish and other wildlife. Hydrilla is a superb competitor with native species by monopolizing resources and growing throughout months of lower light (Gordon 1998). Huge masses of hydrilla slow water flow, obstruct waterways, reduce native biodiversity, and create stagnant areas ideal for the breeding of mosquitoes (McCann, et al. 1996).
Eutrophic conditions due to excessive nitrate conditions can contribute to proliferation of H. verticillata in historically oligotrophic waters (Kennedy, et al. 2009). In an aquaria experiment with low and high nitrate treatments (0.2 and 1.0 mg nitrate per L, respectively), H. verticillata more than doubled its weight in the high nitrate treatment (547 g dry weight) as compared to the low nitrate treatment (199 g dry weight). By comparison, the native species Sagittaria kurziana and Vallisneria americana did not have a significant difference in weight despite the addition of nitrates. This study suggests that H. verticillata will outgrow native aquatic plants as nitrates continue to increase (Kennedy, et al. 2009).
A number of non-native herbivorous fish are altering native ecosystems in the Lower St. Johns River. Many of these fish are common in the aquarium trade and include the Eurasian goldfish (Carassius auratus; which commonly becomes brown in the wild), Mozambique tilapia (Oreochromis mossambicus), African blue tilapia (Oreochromis aureus), South American brown hoplo (Hoplosternum littorale), and a number of unidentified African cichlids (Cichlidae spp.) (Brodie 2008; USGS 2015). Additionally, several species of South American algae-eating catfish commonly known in the aquarium trade as “plecos,” including the suckermouth catfish (Hypostomus sp.) and vermiculated sailfin catfish (Pterygoplichthys disjunctivus) appear to be established in the Lower St. Johns River (USGS 2015). As most aquarium enthusiasts know, “plecos” are extremely efficient algae eaters, and, when released into the wild, can have profound impacts on the native community of aquatic plants and animals. Recently, the vermiculated sailfin catfish has been eradicated from the Rainbow River following removal of 28 individuals by hand and spear, demonstrating that early removal of invasive species is possible (Hill and Sowards 2015).
Urbanization can contribute to the altering of flow regimes and water quality in the LSJRB (Chadwick, et al. 2012) that may enable invasive organisms to survive. As compared to rural streams where the flow is typically intermittent, urban streams may have perennial flow due to irrigation, leaky sewage tanks and perhaps storm water that was not diverted to retention ponds. The invasive clam Corbicula fluminea contributes significant biomass in two urban perennial streams (Chadwick, et al. 2012). Rangia cuneata was also common on silt-sand substrates near Sixmile Creek and northward in the main river channel to near Cedar River (Mason Jr 1998).
188.8.131.52. Human Health Concerns
Non-native aquatic species can negatively affect human health. Some non-native microorganisms, such as blue-green algae and dinoflagellates, produce toxins that cause varying degrees of irritation and illness in people (Hallegraeff, et al. 1990; Hallegraeff and Bolch 1991; Stewart, et al. 2006). During the summer of 2005, large rafts of toxic algal scum from Lake George to the mouth of the St. Johns River in Mayport, Florida, brought headline attention to toxic bloom-forming algae. The organisms responsible for this bloom were two toxin-producing cyanobacteria (blue-green algae) species: the cosmopolitan Microcystis aeruginosa and the non-native Cylindrospermopsis raciborskii (Burns Jr 2008). C. raciborskii has been recorded throughout tropical waters globally, but appears to be expanding into temperate zones as well throughout the U.S. and the world (Kling 2004; Jones and Sauter 2005). Cylindrospermopsis may have been present in Florida since the 1970s; however, its presence in the St. Johns River Basin was not noted prior to 1994 (Chapman and Schelske 1997; Phlips, et al. 2002; SJRWMD 2005). Genetic studies reveal strong genetic similarities between populations in Florida and Brazil, suggesting the two populations continually mix or came from the same source relatively recently (Dyble, et al. 2002).
Cylindrospermopsis now appears to bloom annually each summer in the St. Johns River with occasionally very high concentrations in excess of 30,000 cells/mL (Phlips, et al. 2002). During the intense bloom of 2005, the Florida Department of Health released a human health alert recommending that people avoid contact with waters of the St. Johns River, because the toxins can cause “irritation of the skin, eyes, nose and throat and inflammation in the respiratory tract” (FDOH 2005). This public health concern will likely continue to menace the Lower St. Johns River Basin in the foreseeable future, particularly when the water becomes warm, still, and nutrient-rich: conditions favorable to the formation of algal blooms.
184.108.40.206. Social Concerns
In general, many non-native species reproduce so successfully in their environment, that they create unsightly masses that negatively impact recreation and tourism. Such unsightly masses, as those created by water hyacinth (Eichhornia crassipes) or hydrilla (Hydrilla verticillata), also shift the way we view and appreciate the aesthetic, intrinsic qualities of our aquatic ecosystems.
220.127.116.11. Economic Concerns
Excessive fouling by successful non-native species can lead to economic losses to industries. In 1986, the South American charrua mussel (Mytella charruana) caused extensive fouling at Jacksonville Electric Authority’s Northside Generating Station on Blount Island, Jacksonville, Florida (Lee 2012a). The charrua mussel probably hitchhiked to the St. Johns River in the ballast water of a ship from South America and continues to persist in the area as evidenced by collections in Mayport, Marineland, and the Arlington area of Jacksonville as recently as 2008 (Frank and Lee 2008). Other non-native fouling organisms identified in the St. Johns River include the Asian clam (Corbicula fluminea), Indo-Pacific green mussel (Perna viridis), and Indo-Pacific striped barnacle (Balanus amphitrite). Cleaning these fouling organisms from docks, bridges, hulls of boats and ships, and industrial water intake/discharge pipes is time-consuming and extremely costly.
Just as importantly, yet often overlooked, non-native species can be serious nuisances on a small scale. They foul recreational boats, docks, sunken ships, and sites of historical and cultural value. Clean-up and control of aquatic pests, such as the floating plant water hyacinth (Eichhornia crassipes), can have high economic costs to citizens, not only in taxpayer dollars, but in out-of-pocket money as well.
4.5.3. Data Sources
Numerous online databases containing non-native species reports were queried. The most comprehensive listing of species is maintained in the Nonindigenous Aquatic Species (NAS) database of the United States Geological Service. Resources to investigate distributions of non-native plants include EDDMAPS, USDA, and the Atlas of Florida Vascular Plants. Additional records and information were obtained from agency reports, books, published port surveys, and personal communication data.
We expect that many more non-native species are found within the LSJRB, but have not been recognized or recorded, either because they are naturalized, cryptogenic, or lack of the taxonomic expertise to identify foreign species, subspecies, or hybrids.
A naturalized species is any non-native species that has adapted and grows or multiplies as if native (Horak 1995). A cryptogenic species is an organism whose status as introduced or native is not known (Carlton 1987).
4.5.5. Current Status
The current status is rated as UNSATISFACTORY. Approximately 80 non-native aquatic species are documented and believed to be established in the LSJRB (Table 4.11). Non-native species recorded in the Lower Basin include floating or submerged aquatic plants, molluscs, fish, crustaceans, amphibians, jellyfish, mammals, reptiles, tunicates, bryozoans, and blue-green algae (Table 4.11). Freshwater species represent >65% of the species introduced into the LSJRB. Non-native aquatic species originate from the Central and South America, the Caribbean, Asia, and Africa (Table 4.11).