Extinction-colonization dynamics structure genetic variation of spotted sunfish (Lepomis punctatus) in the Florida Everglades

The population genetics of aquatic animals in the Florida Everglades may be strongly influenced by extinction and colonization dynamics. We combined analyses of allozyme and microsatellite loci to test the hypothesis that two levels of population structure are present for spotted sunfish (Pisces: Centrarchidae: Lepomis punctatus) inhabiting the Everglades. We hypothesized that annual cycles of marsh dry-down increase local-scale genetic variation through a process of local extinction and colonization; we hypothesized that barriers to gene flow by levee/canal systems create a second, regional level of genetic variation. In 1996 and 1997, we sampled spotted sunfish from 11 Everglades sites that were distributed in three regions separated by levees. We documented patterns of genetic variation at 7 polymorphic allozyme loci and 5 polymorphic microsatellite loci. Most genetic variation was present among local populations, according to both types of genetic markers. Furthermore, samples from marsh sites were heterogeneous, while those from canals were not. These data supported our hypothesis that dry-down events and local population dynamics in the marsh have a significant effect on population genetic structure of spotted sunfish. We found no support for our hypothesis that water-management structures superimpose a second level of genetic structure on this species, possibly because canals obscure historical structure by facilitating gene flow or because the complete canal system has been in place for fewer than 20 generations of this species. Our data suggests a continent-island (canal-marsh) structure of populations with high gene flow among regions and recurrent mixing in marshes from canal and creek habitats.     

Density-habitat relationships of mangrove creek fishes within the southeastern saline Everglades (USA), with reference to managed freshwater releases

The Comprehensive Everglades Restoration Plan aims to make considerable changes to the quantity, quality, and timing of freshwater delivery to the southeastern saline Everglades (SESE), a mangrove ecosystem located between the freshwater Everglades and downstream estuarine embayments. Whereas fishes inhabiting seasonally-inundated areas of the SESE and the shorelines of downstream embayments have been examined, those utilizing the creeks connecting these ecotones have not. To evaluate the functional role of the creek habitat and the possible impact of future hydrologic changes on the fishes inhabiting them, 228 underwater visual surveys were performed at three locations of the SESE over a three-year period. Fish abundance data was related to structural habitat, water level, and salinity over various time periods. The SESE contains taxa from both the freshwater Everglades and downstream embayments, but does not appear to function as a nursery for most fishery taxa. Abiotic variability and fish diversity increased with distance from major freshwater sources. Though there were significant differences in the physical structure of mangrove trees among locations, few meaningful correlations between these parameters and the density of individual fish taxa were found. Small prey-base fishes (<10 cm TL) utilize the expansive ephemeral wetlands (i.e., upper mangle) during wet periods, and were concentrated into deeper creeks when these wetlands became dry. Densities of these fishes increase on the upper mangle with increased flooding (hydroperiod), and we observed greater densities of larger species in the creeks when hydroperiods exceeded 240 days. Based on these results, we recommend that water management create water releases which result in a wet period of ca. 240 days, followed by a gradual dry period lasting ca. 90 days.     

Differential skeletal preservation at Windover Pond: causes and consequences

In this paper, we evaluate the causes of differential skeletal preservation in the Windover Pond skeletal series (8BR246). We collected data on sex and age for approximately 110 individuals, and calculated a preservation score for each individual based on the presence of 80 skeletal landmarks. Our research questions evaluated the relationship between bone preservation and individual age and sex, and between the presence of preserved brain material and skeletal preservation, and the effects of burial location on bone preservation. The results indicate variability in average preservation for the sample (micro = 0.53, SD = 0.22) with an apparent lack of sex-specific (P = 0.79) or age-specific (P = 0.37) differences in preservation. The relationship between brain and skeletal preservation (P = 0.15) was not significant. The horizontal distribution of burials was not significantly correlated with skeletal preservation (north: r = -0.10, P = 0.93; east: r = 0.09, P = 0.45); however, vertical depth was a significant predictor of preservation (r = -0.31, P = 0.005), indicating that skeletal preservation decreased as burials were located closer to the ground surface. The observed variability in preservation scores may be related to the partial drying and resubmergence of the uppermost burials for the last few millennia. Comparison of Windover element-specific survival rates with previous analyses based on terrestrial samples (Galloway et al. [1997] Forensic taphonomy, Boca Raton: CRC Press; Waldron [1987] Death, decay and reconstruction, Manchester: Manchester University Press; Willey et al. [1997] Am J Phys Anthropol 104:513-528) affirms the relationship between element weight or density and bone survival. The unique taphonomic context of our study sample effected little change in bone deterioration processes.     

FIRST REPORT OF GYMNODINIUM PULCHELLUM (DINOPHYCEAE) IN NORTH AMERICA AND ASSOCIATED FISH KILLS IN THE INDIAN RIVER, FLORIDA

Fish and invertebrate kills were reported from September to October 1996 in the Indian River, Florida, coincident with blooms of the dinoflagellate Gymnodinium pulchellum Larsen 1994. This is the first report of a bloom of this species in the Americas. Fish and invertebrate species affected were common snook ( Centropomus undecimalis ), striped mullet ( Mugil cephalus ), hardhead catfish ( Arius felis ), red drum ( Sciaenops ocellatus ), sheepshead ( Archosargus probatocephalus ), black drum ( Pogonias cromis ), blue crab ( Callinectes sapidus ), and shrimp ( Penaeus spp.). However, Gymnodinium pulchellum has previously caused fish kills in Japan and Australia. Examination of archived phytoplankton samples from a fish kill reported in the same area of the Indian River in August 1990 confirmed the presence of high concentrations of G. pulchellum. Fish kills associated with Alexandrium monilatum and potentially Pfiesteria -like species in the Indian River also are discussed. Scanning electron microscopy provided additional morphological detail on this distinct but little-known dinoflagellate.     

Effects of fish predation and seaweed competition on the survival and growth of corals

On Caribbean coral reefs, high rates of grazing by herbivorous fishes are thought to benefit corals because fishes consume competing seaweeds. We conducted field experiments in the Florida Keys, USA, to examine the effects of grazing fishes on coral/seaweed competition. Initially, fragments of Porites divaracata from an inshore habitat were transplanted into full-cage, half-cage, and no-cage treatments on a fore-reef. Within 48 h, 56% of the unprotected corals in half-cage and no-cage treatments (62 of 111) were completely consumed. Stoplight parrotfish (Sparisoma viride) were the major coral predators, with redband parrotfish (S. aurofrenatum) also commonly attacking this coral. Next, we transplanted fragments of P. porites collected from the fore-reef habitat where our caging experiments were being conducted into the three cage treatments, half in the presence of transplanted seaweeds, and half onto initially clean substrates. The corals were allowed to grow in these conditions, with concurrent development of competing seaweeds, for 14 weeks. Although seaweed cover and biomass were both significantly greater in the full-cage treatment, coral growth did not differ significantly between cage treatments even though corals placed with pre-planted seaweeds grew significantly less than corals placed on initially clean substrate. This surprising result occurred because parrotfishes not only grazed algae from accessible treatments, but also fed directly on our coral transplants. Parrotfish feeding scars were significantly more abundant on P. porites from the half and no-cage treatments than on corals in the full cages. On this Florida reef, direct fish predation on some coral species (P. divaracata) can exclude them from fore-reef areas, as has previously been shown for certain seaweeds and sponges. For other corals that live on the fore-reef (P. porites), the benefits of fishes removing seaweeds can be counterbalanced by the detrimental effects of fishes directly consuming corals. Received: 31 May 1997 / Accepted: 2 September 1997     

Does Mangrove Leaf Chemistry Help Explain Crab Herbivory Patterns?

We examined feeding by the mangrove tree crab Aratus pisonii in Tampa Bay, Florida, in relation to the percent dry weight of carbohydrate, protein, phenolics, condensed tannins, ash, carbon, nitrogen, carbonmitrogen ratio, water content, and sclerophylly for leaves of the red mangrove Rhizophora mangle. Comparisons of leaf chemistry were made among leaves that experienced variable levels of crab damage. Because R. mangle is the crab's preferred food source based on damage patterns in the field, comparisons of R. mangle leaf chemistry were made in relation to that of the black mangrove Avicennia germinans and the white mangrove Laguncularia racemosa. We observed a negative relationship between level of leaf damage and percent dry weight of nitrogen, carbohydrates, condensed tannins, and sclerophylly. In contrast, a positive relationship was found between leaf damage and the carbon:nitrogen ratio. The chemical constituents that provided the best explanation for differences in damage among the three mangrove species include condensed tannins, nitrogen, carbon:nitrogen ratio, carbohydrates, phenolics, water content, and ash. The results from this study suggest that chemistry only partially explains food preference by A. pisonii. It appears that A. pisonii feeding behavior and preference may be influenced by a more complex series of factors and interactions, which may include reproduction by, predation on, and interspecific competition with A. pisonii.     

TRENDS IN MANATEE (TRICHECHUS MANATUS LATIROSTRIS) COUNTS AND HABITAT USE IN TAMPA BAY, 1987–1994: IMPLICATIONS FOR CONSERVATION

Aerial surveys ( n = 88) were used to document locations and count sightings of manatees ( Trichechus manatus latirostris ) in the inshore waters of Tampa Bay, Florida, between November 1987 and May 1994. We made 5,358 sightings of manatees in 1,958 groups. Calves represented 8% of the manatees sighted. Counts were significantly higher in winter ( = 79, n = 29 flights) than in non-winter ( = 46, n = 47) months. Counts of manatees in winter increased significantly during the study, but warm-season counts did not. Regression models demonstrated a relationship between counts and environmental factors. Year-round counts were related to air temperatures and seasons, with highest counts in winter. However, in the winter season, counts were significantly correlated only with wind speed, not air temperature. Yearround counts were predicted to be curvilinear with highest counts at 15°C average air temperature. Areas used differed with season: in cold weather, 76% of all sightings occurred in zones with warm-water sources. High-use areas were identified for summer months. Spatial filter analysis was used to compare manatee density in high-use areas between two two-year time periods. The data indicate that (1) manatee use of Tampa Bay was high and increasing in winter, (2) there are particular zones of the bay where conservation of manatees and habitat should be a priority, and (3) sufficient information has been collected for management agencies to develop and implement manatee protection plans.     

PREHENSILE USE OF PERIORAL BRISTLES DURING FEEDING AND ASSOCIATED BEHAVIORS OF THE FLORIDA MANATEE (TRICHECHUS MANATUS LATIROSTRIS)

The use of perioral bristles (modified vibrissae) by 17 captive Florida manatees and approximately 20 wild manatees was analyzed. Captive manatees were fed six species of aquatic vegetation normally eaten in the wild (four freshwater species and two seagrasses). Inanimate objects were placed in the holding tanks with manatees at Lowry Park Zoological Gardens (Tampa, FL) to determine the degree to which perioral bristles were used in exploration and to define the range of manipulative behavior. In addition, behavioral observations were made on the use of perioral bristles during social interactions with conspecifics. Observations were recorded using a Hi8-format video camera. Florida manatees possess an unusually large degree of fine motor control of the snout and perioral bristles. The large and robust perioral bristle fields of the upper lip were used in a prehensile manner during feeding. Bristle use by manatees feeding on submerged vegetation differed from that seen during feeding on floating vegetation. Other behavioral use of the perioral bristles shows variation depending upon the situation encountered. The degree of plasticity of perioral bristle use supports our hypothesis that the vibrissal-muscular complex of the Florida manatee has evolved to increase the efficiency of grazing and browsing on aquatic vegetation and to fully maximize the potential of the manatee as a generalist feeder. The manipulative and sensitive nature of the manatee snout is likely a manifestation of a complex sensory and motor system which has evolved for marine mammal aquatic herbivores living in shallow turbid habitats.     

Treponematosis in regional and chronological perspective from central Gulf Coast Florida

Examination of five central Gulf Coast Florida archaeological skeletal series (n = 547) from the late prehistoric and early historic periods reveals the presence of pathological lesions characteristic of treponemal infection. These skeletal remains of native American populations represent a crucial time regarding hypotheses about the exchange of syphilis between the Old and New World or the mutation of one treponemal infection into another. Comparison of the lesions with those observed in modern studies of treponemal infection does not support an interpretation of veneral syphilis. The data from this study and from other archaeological skeletal series indicate the presence of a treponemal disease prior to European contact. The skeletal elements from Florida do not suggest that the disease changed dramatically following contact with Europeans. It is possible that cases of nonspecific postcranial pathology can be explained by the presence of this disease in the Florida populations. This study indicates that a treponemal disease was endemic throughout the region by at least A. D. 1000. © 1993 Wiley-Liss, Inc.