Hilary M. Swain

BULLETIN OF MARINE SCIENCE. 57(1): 252-266. 1995

RECONCILING RARITY AND REPRESENTATION: A REVIEW OF LISTED SPECIES IN THE INDIAN RIVER LAGOON

Hilary M. Swain ABSTRACT The Indian River Lagoon supports 75 species that are listed in need of protection by state or federal entities. A review of these listed species reveals strong taxonomic biases towards vertebrates and a lack of representation for invertebrates. Protecting biodiversity in the lagoon requires recognition of this inadequacy and means by which to rectify the lack of representation. Of the species that are currently listed there is the problem of categorizing these in terms of both vulnerability and potential for management and recovery. This paper prioritizes listed species in the Indian River Lagoon for local management action in relation to three criteria: their geographic distribution; the degree to which they are restricted to a limited number of habitats; and their population sizes. High priority is given to the 30.67% of listed species which have a narrow geographic range, the 60% of the listed species found in the lagoon that are habitat specific, and the 30.67% of species that have relatively large population sizes locally. A few listed species have an adequate level of protection in the existing protected area network whereas the majority (66.67%) are only recorded with low population sizes for any protected area and nine species do not occur at all in any protected area. Management recommendations for these listed species are reviewed in the light of whether a species based approach will really protect biodiversity in the lagoon. Recommendations are also made to address the lack of data concerning population sizes and distribution of listed species. Management for these listed species is only considered worthwhile if a healthy, functioning lagoonal system is maintained.

One of the statements that led to the recognition of the Indian River Lagoon (IRL) as an Estuary of National Significance was that it supports more listed species than any other estuary in the US (Virnstein and Campbell, 1987; FDER, 1989). Breininger et al. (1994) noted that Merritt Island National Wildlife Refuge, at the north end of the lagoon, includes more federally listed species than any other National Wildlife Refuge. They have provided a thoughtful and comprehensive documentation of the significant number of listed species supported on the upland and wetland complex of federal lands bordering the lagoon at the Kennedy Space CenterlMerritt Island National Wildlife Refuge and Canaveral National Seashore. One explanation for the lagoon's rich assemblage of rare species is its ecotonal location, straddling both temperate and sub-tropical ecosystems. This provides habitats for rare species from both climes, particularly the many rare tropical species that have limited U.S. distributions. Another explanation for the large number of rare species is the sheer size of the lagoonal complex, which encompasses about a third of Florida's east coast. Finally, although human development is now a very serious threat to continuing viability of many of these rare species, this development is recent and rare species, which have long since disappeared from heavily urbanized complexes of south Florida, are still present in the IRL region. It is almost universally accepted that any management plan for an estuary, marine park or aquatic preserve such as the IRL, will include the goal of protecting these "rare, threatened and endangered species." This is not a goal one could really argue against but it is a goal which merits further consideration. Rationale behind the thinking is that rare species are the element of biodiversity 252

SWAIN: REVIEW OF LISTED SPECIES IN THE INDIAN RIVER LAGOON

253

under the greatest degree of threat and probability of extinction and loss, and therefore they need to be singled out for special attention. But who decides which species are rare, threatened and endangered? What criteria should be used to determine these designations? Is it critical to protect each and every rare species that occurs within an estuary under consideration? Are there methods of determining which rare species may be most critical to protect in anyone region? How do we coordinate protection of rare coastal species at a regional, state and national level to assure that there is an appropriate level of protection for all? With limited dollars are there some rare species that are more cost effective to protect? Finally, how do we incorporate protection of individual rare species into the broader goals of an ecosystem level of protection? Responsibility for listing species that are rare and in need of protection has typically fallen to state and federal agencies. The U.S. Fish and Wildlife Service (USFWS) and the National Marine Fisheries Service list species at the federal level. At the state level in Florida the Florida Game and Freshwater Fish Commission (FGFWFC) and the Florida Department of Agriculture (FDA) are responsible for publishing lists of endangered, threatened or commercially exploited animals and plants. Some species in Florida, such as sea turtles, are also covered under CITES, the Convention on International Trade in Endangered Species of Wild Flora and Fauna. The status of all Florida species under these formal categories is reviewed annually by FGFWFC (FGFWFC, 1993). There is widespread acknowledgment that many Florida species in need of protection are not included in these formal lists. FGFWFC recently produced a comprehensive review of the status of state vertebrates and recommended many additional species for consideration for listing (Millsap et aI., ] 990). Two state organizations also review the status of Florida species and designate them accordingly. First, the Florida Natural Areas Inventory (FNAI) uses the heritage ranking program developed by The Nature Conservancy to rank species according to their degree of endangerment at both the state and global level (FNAI, 1990a). Second, the Florida Committee on Rare and Endangered Plants and Animals, or FCREPA, is currently in the process of reviewing the status of species in Florida, on a taxonomic group basis, with a new series of publications (Gilbert, ]992; Humphrey, 1992; Moler and Ashton, ] 992). With such a multitude of agencies and categories of listed species, it is hard to develop a consensus as to which rare species may be important locally. Not only do agencies and organizations differ in the categorization of species but they also use a wide variety of criteria to place species into different categories (Pearsall et aI., 1986; Mace and Lande, 1991; Master, 199]). Priorities for listing include the probability of extinction, degree of threat, recovery potential, taxonomic distinctiveness and geographic distributions. From a manager's point of view there is confusion between criteria that designate the degree of threat, or the probability of extinction, versus criteria that can set priorities for management action such as the potential for recovery, feasibility for management and the cost of alternatives (Mace and Lande, 199]). More recent analyses have attempted to prioritize species in Florida in terms of rarity (Burke and Humphrey, 1987) and management action (Millsap et aI., 1990). This paper provides suggestions for prioritizing listed species that occur within the IRL for local management action. Key to development of the methodology outlined here is a seminal paper by Rabinowitz et al. (1986) that used examples of British flora to illustrate how to categorize the term rarity. They argued that species can be perceived to be rare in relation to three criteria: first, their geographic distribution; second, the degree to which they were restricted to a limited

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number of habitats; and third, their population sizes, in particular whether they occur as small populations everywhere or they occur as one large population in at least one location. Using this system of categorizing rarity one can place listed species into one of eight possible types of rarity; for example, the most extreme form of rarity would be a species that is only able to utilize a restricted number of habitats or edaphic conditions, that always occurs in small numbers everywhere, and also has a very narrow geographic range. Management implications of these classes of rarity are that they help determine some priorities for action by showing which species are extremely dependent on a particular region for their survival and also which have population sizes that may be feasible to manage. Within anyone of the eight categories of rarity, fine tuning of the prioritization can then be applied according to the level of endangerment recognized at the state level. A further factor that should be considered when setting priorities for action is the degree to which these species already occur within the existing protected area network. A focus of recent work in conservation biology has been to develop analytical

techniques,

using geographic

information

systems, under the 'gap anal-

ysis' program to identify natural communities and geographic locations supporting extensive biodiversity that fall outside existing protected area networks (Scott et aI., 1993). In this paper, as an extension of this same approach, I raise the priority for management attention for listed species that do not occur within the existing protected area network in the region. Species recommended here for action for the IRL region necessarily differ from those species that would be selected for other Florida estuaries. However, the methodology and approaches laid out in this paper are applicable for any geographical area and also over larger geographical scales. METHODS

Data presented here are extracted from a database originally developed by Larson (1992) for listed species in the northern IRL watershed. The status of listed species for the lagoon was compiled and updated from published and unpublished sources for species including the original FCREPA series (Gilbert, 1979; Kale, 1979; Layne, 1979; McDiarmid, 1979; Ward, 1979; Franz, 1982) and more recent updates are based on Gilbert (1992), Humphrey (1992), Moler and Ashton (1992) as well as Millsap et a!. (1990), FGFWFC (1993) and the most recent unpublished FNAI database lists. The large number of agencies and their categories for listed species are summarized in Table I. Only those species are associated with estuarine or adjacent estuarine wetland habitats were used. Estuarine habitat associations for all listed species in the database were based on Larson, 1992, appendix 3 and determined from published literature (Breininger, 1985; Ashton and Ashton, 1985a, 1985b; FNAl, 1990b; Millsap et aI., 1990; Schmalzer and Hinkle, 1990) and unpublished data provided by Hames (1991) and D. Runde (unpublished FGFWFC database prepared for Millsap et aI., 1990). The listed species associated with estuarine habitats were extracted as a subset of this larger database and updated and analyzed. Species associated with at least seven natural community types (not necessarily all estuarine) were categorized as those with broader habitat preferences, and those with less than seven known habitat associations were categorized as habitat restricted species (for tabulated habitat associations see Larson, 1992, appendix 3). The geographic distribution of each species (number of Florida counties in which they occurred) was determined based on county distribution information provided in FNAI (1990b) and the % of their range in Florida (provided by D. Runde, unpublished FGFWFC database prepared for Millsap et a!., 1990). Species with a wide geographic range were defined as those reported in at least 20 Florida counties or with a large proportion of their distribution outside the state. Species with a narrow geographic range were defined as those reported in fewer than 20 Florida counties or those with a very limited distribution outside the state. The degree of protection and population sizes for listed species in Brevard County were obtained from Breininger et a!. (1994), Schmalzer and Hinkle (1990), the unpublished site files of Brevard County Environmentally Endangered Lands Program (Natural Resources Management Division, Brevard County) and records of M. Hames, FL Native Plant Society (pers. comm.). Protected areas are


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BULLETIN OF MARINE SCIENCE. VOL. 57, NO. I, 1995

defined as lands in public ownership (National Wildlife Refuges, National Seashore, State Park, local Endangered Lands Programs, etc.) rather than those with jurisdictional designations (e.g" Aquatic Preserves). Species that were not reported for any protected area are defined as having N, or no level of protection. Those reported as present, or with small populations or undetermined numbers in at least one protected area, were accorded a L, or low, level of protection. Those that have a significant number (approx. 500+) found on at least one protected area, were accorded a moderate, M, level of protection. Population sizes for species with no information available were estimated using local knowledge including personal communication from M. Hames (FL Native Plant Society) and P. Schmalzer (Bionctics Corporation, KSC). There may be a bias against species reported for the southern sectors of the IRL as there were fewer published data available on distribution of listed species in protected areas in this southern region. RESULTS

There are 75 species associated with the IRL and its adjacent estuarine wetlands that are listed by state or federal agencies or state organizations (Table 2), Some are well known charismatic vertebrates such as Trichechus manatus latirostris and Mycteria americana. The majority (56%) are birds with plants representing a further 16%. Only two invertebrates

Aratus pisonii and Goniopsis cruentata are

included in state databases for the counties bordering the IRL. This is very different from the species composition of the IRL as a whole. Although there is no comprehensive species list available yet for the lagoon, invertebrates dominate any species lists that have been compiled (Virnstein and Campbell, 1987; Morris, 1989; National Estuary Program, 1992), and birds, fishes and flowering plants are a minor component. Only FNAI has a classification system that is comparable across all species listed for the IRL and their data classify most as S2 (vulnerable) and S3 (rare or uncommon) (Fig. 1). A large proportion, 28%, of the species listed by state agencies, such as FDA, are not regarded as under a high degree of threat (i.e., SU, have no state ranking) by FNAI (Table 2). Although the species listed as S 1 and S2 (Table 2) may be the most imperiled and vulnerable at the state level, this does not mean they are necessarily the most appropriate candidates for management at the regional level. If the species listed for the lagoon are divided according to the eight categories of rarity recognized by Rabinowitz et al. (1986), a picture emerges that will help identify priorities for management action (Fig. 2). The IRL may be most critical for the N = 23 (30.67%) listed species that have narrow geographic ranges and a large proportion of their state range lies within the IRL region (Fig. 2). Similarly, 60% of the listed species found in the lagoon are restricted to a limited number of habitats, and these may be the species that are particularly vulnerable to habitat loss and alteration, requiring special management attention (Fig. 2). Finally, only 23 species (30.67%) have relatively large population sizes locally, and these may be the most feasible species to focus on, at a regional level, to ensure management for viable populations (Fig. 2). Using this categorization as a rationale for prioritization, three species stand out as top priority candidates for management in the IRL: Halophila johnsonii, Malaclemys terrapin tequesta and Trichechus manatus latirostris (Table 3). All are species that have, or recently had, large local population sizes; they are fairly habitat specific; and the lagoon represents a significant proportion of their Florida range. They are also species regarded as imperiled or vulnerable at the state level. In contrast, species that have small populations in the lagoon region are much more of a challenge in terms of management priorities. Forty-four percent of the listed species in the lagoon have wide geographic ranges but small population sizes everywhere (Table 3). These species certainly require management-they include some of the rarer S2 and S3 species in the state-but effective manage-

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