Samuel C. Snedaker

Pantropical trends in mangrove above-ground biomass and annual litterfall

A major paradigm in biosphere ecology is that organic production, carbon turnover and, perhaps, species diversity are highest at tropical latitudes, and decrease toward higher latitudes. To examine these trends in the pantropical mangrove forest vegetation type, we collated and analysed data on above-ground biomass and annual litterfall for these communities. Regressions of biomass and litterfall data show significant relationships with height of the vegetation and latitude. It is suggested that height and latitude are causally related to biomass, while the relationship with litterfall reflects the specific growing conditions at the respective study sites. Comparison of mangrove and upland forest litterfall data shows similar trends with latitude but indicates that mangrove litterfall is higher than upland forest litterfall. The regression equations allow the litterfall/biomass ratio to be simulated, and this suggests that the patterns of organic matter partitioning differ according to latitude.

Mangroves and climate change in the Florida and Caribbean region: scenarios and hypotheses

The principal scenario concerning the potential effects of climate change on mangrove forest communities revolves around sealevel rise with emphases on coastal abandonment and inland retreat attributable to flooding and saline intrusion. However, at the decade to century scale, changes in precipitation and catchment runoff may be a more significant factor at the regional level. Specifically, for any given sealevel elevation it is hypothesized that reduced rainfall and runoff would necessarily result in higher salinity and greater seawater-sulfate exposure. This would likely be associated with decreased production and increased sediment organic matter decomposition leading to subsidence. In contrast, higher rainfall and runoff would result in reduced salinity and exposure to sulfate, and also increase the delivery of terrigenous nutrients. Consequently, mangrove production would increase and sediment elevations would be maintained. Support for this scenario derives from studies of the high production in saline mangrove impoundments which are depleted in seawater sulfate. This paper also examines other components of climate change, such as UVb, temperature, and storm frequency, and presents a suite of hypotheses and analytical protocols to encourage scientific discussion and testing.

Mangrove species zonation: why?

Mangroves are a taxonomically-diverse group of woody spermatophytes which possess a common ability to survive and perpetuate themselves along sheltered tropical coastlines in saline environments under tidal influence. A halophytic existence is made possible through a wide range of morphological, anatomical and physiological adaptations which has elicited much scientific interest (Walsh, 1974; Chapman, 1976). Although mangroves share a common ability to exist as halophytes in a common environment, they frequently appear in rather predictable mono-specific zones parallel to shorelines, tidal channels, and the banks of rivers and streams influenced by the sea. Thus, mangrove species zonation has been a dominant theme in a voluminous literature on mangroves which exceeds 7,000 titles (B. Rollet, pers. comm.1).

FACTORS INFLUENCING RHIZOPHORA MANGLE L. SEEDLING DEVELOPMENT IN EVERGLADES CARBONATE SOILS

Abstract Nutrient limitation, soil waterlogging, and soil salinity have been hypothesized as the principal factors limiting the development of neotropical mangrove forests. A mesocosm experiment was initiated to investigate these alternative factors, using low-nutrient soils from the south Florida Everglades. Nitrogen (N), phosphorus (P), aeration, and salinity treatment effects on Rhizophora mangle L. seedling leaf area, stem elongation, and biomass development were determined. Phosphorus rather than nitrogen was the important macro-nutrient limiting R. mangle leaf area, and root and leaf biomass development in the mesocosm experiment. A subsequent P enrichment experiment was conducted in the field to substantiate mesocosm findings. Under P enrichment in the field, seedling stem elongation rates increased from 0.03 mm d−1 to 0.20 mm d−1 and leaf area increased from 25 cm2 to 75 cm2, relative to unfertilized controls. Soil aeration stimulated root biomass development 40% in the mesocosm experiment. Sodium chloride at 32‰ resulted in branch initiation with no leaf response; however, hypersaline conditions greater than 45‰ caused denaturing of terminal buds. Thus, without hypersalinity stress, P is identified as a dominant factor limiting R. mangle foliar and stem development in low nutrient carbonate soils. Soil anoxia also influences root development and may moderate stem elongation responses to P fertilization in the field.

Organochlorine pesticide residues in marine sediment and biota from the northern Florida reef tract

Abstract As part of a two-phased study, sediment and biota were collected from Pennekamp Coral Reef State Park and Key Largo National Marine Sanctuary and analysed for organochlorine pesticide residues. Phase 1 consisted of an inter-laboratory comparison using replicates of unspiked field samples. The five participating contract-laboratories differed in methodology, detection limits and their ability to detect pesticides. The highest concentration of pesticide reported in Phase 1 samples was 4.4 ng g−1 wet wt aldrin, found in a fillet of Haemulon plumieri. Based on the inter-laboratory comparison, one laboratory was selected to analyse additional samples collected in Phase 2. Pesticides were detected in 43 of the 52 Phase 2 samples. The highest concentration reported in Phase 2 samples was 2.3 ng g−1 α-BHC in Panulirus argus tail muscle. These results suggest that while most samples contained one or more residues, pesticide concentrations were low and trends in residue profiles were minor.

Diurnal Rates of Photosynthesis, Respiration, and Transpiration in Mangrove Forests of South Florida

The mangrove forests of south Florida extend over an area of 1,750 km2, located primarily within the boundaries of the Everglades National Park and within the region known as the Ten Thousand Islands (Figure 22-1). Davis (1940) described the zonation and succession in some of these areas, and more recent descriptions appear in Craighead (1971). The majority of the literature on mangroves is descriptive; only recently have investigators studied ecosystem function and the role(s) of mangroves in a regional ecosystem. The work of Golley et al. (1962) established baseline information on the primary productivity and respiration for a red mangrove stand in Puerto Rico, and demonstrated its role in exporting organic matter to the adjacent estuarine ecosystem. The regional role of mangrove forest ecosystems in Florida has been documented by Heald (1969) in terms of detritus export, and by Odum (1969) in terms of the role of detritus in the food chains of estuarine and commercial fisheries.

Successional Immobilization of Nutrients and Biologically Mediated Recycling in Tropical Forests

A review of the literature shows a less-than-satisfactory number of detailed studies upon which can be based either a viable synthesis or a test of the major hypotheses on the relationship between nutrients and secondary succession in tropical forests. Data from several of the major works are summarized as an example of the state of our knowledge on the biological immobilization of nutrients. Less understood are processes associated with biologically mediated recycling in tropical forests. Reported examples of functional biological adaptations associated with the storage and/or cycling of nutrients are discussed within the context of theories proposed by others to suggest the most profitable future directions for research. THE PRIMARY PURPOSE OF THIS PAPER is to explore the state of our knowledge relative to both the biological immobilization of nutrients in tropical forest succession and to aspects of subsequent recycling within the more mature forest. Further, an attempt will be made to identify the subject area(s) where the most profitable gains in knowledge might be expected to originate. The few data summarized here are representative of the state of our knowledge, and, although thin and sparse in places, suggest that additional research will most likely result in a significant advancement in our knowledge. The literature dealing with the immobilization of nutrients in tropical forest succession appears bountiful but is, in fact, filled with significant gaps and frequently lacks the kinds of documentation that are requisite for synthesis. For instance, elemental concentrations of the tissues of tropical forest species have been presented in detail for successional species (Snedaker and Gamble 1969) and for species typical of later successional stages (Nye 1958, Ovington and Olson 1970, Stark 1971a and b, Golley et al. 1975). The concentrations of the nutrient elements are, in general, so uniform as to preclude identifying an overall trend associated with succession or a particular stage therein; documentation as to age, soil characteristics, local climate, etc. is either not adequately presented or is not suitably correlated with the measurements. Also, there is no basis for assessing spatial variability which could result in sampling artifacts. It is evident, however, that correlations are possible relating tissue concentrations with the mineral characteristics of the soils, and regional and climatic differences (vide Stark 1971a and b, Golley et al. 1975). Data also exist, along with some level of documentation correlating nutrient stocks with age of succession, but measurements are presented for too few ecosystem compartments and generally only the macronutrients are emphasized. A selection of these data is summarized in table 1. They reveal both significant gaps (measurements for wood biomass are rare even though it is the biomass compartment most closely correlated with the successional stage) and the lack of any significant trend in the stock of foliar nutrients. The data that are available do show the expected: that the total stock of nutrients biologically immobilized does increase with successional developinent as a result of an increasing wood biomass (see also Rodin and Bazilevich 1967). The quantity of nutrients immobilized in the leaves (table 1) does not increase due to an early stabilization in leaf biomass. Data and information on the micronutrients and trace metals are equally limited in the scope of coverage for tropical successional forests and also tropical forests, in general. The most complete data are reported by Golley et al. (1975), Odum and Pigeon (1970), Snedaker and Gamble ( 1 969), Snedaker et al. (1977), and Stark (197 lb), and selected data therefrom on the concentrations of these elements are summarized in table 2. These simply show a much greater variation among sites and successional stages than do the macronutrients and probably reflect both differences in the local surficial geology and the introduction of extraneous materials into the environment, as appears to be specifically the case for tropical mangrove forests. Differences among species in the concentrations of micronutrients and trace metals (vvide Snedaker and Gamble 1969, Ovington and Olson 1970) probably also reflect physiological differences among those species. Of course, one must always be aware of the variation which may be due solely to sampling and analytical techniques, particularly when making interstudy comparisons. 16 TROPICAL SUCCESSION 16-22 1980 This content downloaded from 157.55.39.211 on Tue, 09 Aug 2016 05:06:13 UTC All use subject to http://about.jstor.org/terms TABLE 1. Standing stock biomass (dry weight) and leaf compartment macronutrient inventories in selected tropical lowland successional and mature forests. Leaf compartment (gmis mr2) Vegetation Total age Vegetation biomassa (yrs) Location type (gms mr2) Biomass N P K Ca Mg Reference 1 Izabal, Heliconia 779 779b 9.1 0.5 14.2 2.6 6.8 Popenoe Guatemala fallow (unpublished) 1 Izabal, Mixed spp. 874 874e 11.7 0.9 10.0 5.5 6.0 Tergas 1965 Guatemala fallow 1 Izabal, Mixed spp. 836 706 14.4 1.1 8.3 7.0 4.8 Sncdaker 1970 Guatemala fallow 2 Belgian Mixed spp. 1323 787 10.5 1.2 10.2 ( 7.7 ) Bartholomew et al. Congo fallow 1953 2 Darien, Mixed spp. 1302 362 0.4 4.2 15.7 1.3 Golley et al. 1968 Panama fallow(1 2 Darien, Mixed spp. 2436 296 0.3 5.0 3.5 1.3 Golley et al. 1968 Panama fallowe 2 Guarin, Mixed spp. 1584 260 -Ewel 1968 (in Gamble Colombia fallow et al.) 2 Izabal, Mixed spp. 1419 953 -Snedaker 1970 Guatemala fallow 3 Izabal, Mixed spp. 2287 751 13.9 1.1 9.( 7.1 6.2 Snedaker 1970 Guatemala fallow 4 Guarin, Mixed spp. 4839 495 -Ewel 1968 (in Gamble Colombia fallow et al.) 4 Darien, Mixed spp 3794 594 0.7 8.3 8.0 1.8 Golley et al. 1968 Panama fallow 4 Izabal, Mixed spp 2711 845 13.3 0.8 9.2 6.2 5.4 Snedaker 1970 Guatemala fallow 5 Belgian Mixed spp 7668 563 12.5 0.7 7.9 ( 7.8 ) Bartholomew et al. Congo fallow 1953 5 Izabal, Mixed spp 3667 766 13.1 (.9 9.3 6.6 5.3 Snedaker 1970 Guatemala fallow 6 Izabal, Mixed spp 4467 778 27.6 2.6 19.3 20.9 6.1 Snedaker 1970 Guatemala fallow 6 Darien, Mixed spp 4245 655 -0.7 7.8 17.2 2.5 Golley et al. 1968 Panama fallowd 6 Benin, Acioa barteri 4609 419f 5.2 0.4 2.8 2.9 2.8 Nye and Greenland South fallow 1960 Nigeria 7 Izabal, Mixed spp 4666 1083 Snedaker 1970 Guatemala fallow 8 Belgian Mixed spp 12168 538 12.0 0.7 7.9 ( 8.7 ) Bartholomew et al. Congo fallow 1953 8 Izabal, Mixed spp 6589 1219 Snedaker 1970 Guatemala fallow 9 Izabal, Mixed spp 724

Hypocotyl Function in Seedling Development of the Red Mangrove, Rhizophora mangleL.1

Abstract Propagules of the red mangrove (Rhizophora mangle L.) were subjected to a variety of growing conditions in which light level, anatomical exposure to light, application of the photosynthetic inhibitor DCMU, and genotype were used to infer possible interactions between autonomous photosynthesis and the utilization of internal reserves for the development of roots and shoots. The outgrowth of these organs from hypocotyls was significantly enhanced under conditions favorable for photosynthesis, and chlorophyll-deficient propagules exhibited reduced development compared to sibling wild types. The results suggest that photosynthesis augments processing of carbohydrates derived from maternal sources during early development and differentiation of the hypocotyl, and in combination represent an adaptive trait.