In Hawai'i, mangrove trees are introduced species that can rapidly colonize many nearshore en... more In Hawai'i, mangrove trees are introduced species that can rapidly colonize many nearshore environments. Mangroves have been introduced on O'ahu, and Rhizophora mangle in particular has created numerous problems that have led to several mangrove removals and increased interest in long-term man- agement of mangroves. The objective of this project was to quantify current lo- cations of mangroves and their
Belowground biomass is thought to account for much of the total biomass in mangrove forests and m... more Belowground biomass is thought to account for much of the total biomass in mangrove forests and may be related to soil fertility. The Yela River and the Sapwalap River, Federated States of Micronesia, contain a natural soil resource gradient defined by total phosphorus (P) density ranging from 0.05 to 0.42 mg cm -3 in different hydrogeomorphic settings. We used this fertility gradient to test the hypothesis that edaphic conditions constrain mangrove productivity through differential allocation of biomass to belowground roots. We removed sequential cores and implanted root ingrowth bags to measure in situ biomass and productivity, respectively. Belowground root biomass values ranged among sites from 0.448 ± 0.096 to 2.641 ± 0.534 kg m -2 . Root productivity (roots B20 mm) did not vary significantly along the gradient (P = 0.3355) or with P fertilization after 6 months (P = 0.2968). Fine root productivity (roots B2 mm), however, did vary significantly among sites (P = 0.0363) and ranged from 45.88 ± 21.37 to 118.66 ± 38.05 g m -2 year -1 . The distribution of total standing root biomass and fine root productivity followed patterns of N:P ratios as hypothesized, with larger root mass generally associated with lower relative P concentrations. Many of the processes of nutrient acquisition reported from nutrient-limited mangrove forests may also occur in forests of greater biomass and productivity when growing along soil nutrient gradients.
Many tidally influenced freshwater forested wetlands (tidal swamps) along the south Atlantic coas... more Many tidally influenced freshwater forested wetlands (tidal swamps) along the south Atlantic coast of the USA are currently undergoing dieback and decline. Salinity often drives conversion of tidal swamps to marsh, especially under conditions of regional drought. During this change, alterations in nitrogen (N) uptake from dominant vegetation or timing of N recycling from the canopy during annual litter senescence may help to facilitate marsh encroachment by providing for greater bioavailable N with small increases in salinity. To monitor these changes along with shifts in stand productivity, we established sites along two tidal swamp landscape transects on the lower reaches of the Waccamaw River (South Carolina) and Savannah River (Georgia) representing freshwater (≤0.1 psu), low oligohaline (1.1-1.6 psu), and high oligohaline (2.6-4.1 psu) stands; the latter stands have active marsh encroachment. Aboveground tree productivity was monitored on all sites through monthly litterfall collection and dendrometer band measurements from 2005 to 2009. Litterfall samples were pooled by season and analyzed for total N and carbon (C). On average between the two rivers, freshwater, low oligohaline, and high oligohaline tidal swamps returned 8,126, 3,831, and 1,471 mg Nm −2 year −1 , respectively, to the forest floor through litterfall, with differences related to total litterfall volume rather than foliar N concentrations. High oligohaline sites were most inconsistent in patterns of foliar N concentrations and N loading from the canopy. Leaf N content generally decreased and foliar C/N generally increased with salinization (excepting one site), with all sites being fairly inefficient in resorbing N from leaves prior to senescence. Stands with higher salinity also had greater flood frequency and duration, lower basal area increments, lower tree densities, higher numbers of dead or dying trees, and much reduced leaf litter fall (103 vs. 624 gm −2 year −1 ) over the five study years. Our data suggest that alternative processes, such as the rate of decomposition and potential for N mineralization, on tidal swamp sites undergoing salinity-induced state change may be more important for controlling N biogeochemical cycling in soils than differences among sites in N loading via litterfall.
The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries through... more The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries throughout the Indo-Pacific. Understanding crab diets and habitat use should assist in managing these fisheries and could provide additional justification for conservation of the mangrove ecosystem itself. We used multiple chemical tracers to test whether crab movements were restricted to local mangrove forests, or extended to include adjacent seagrass beds and reef flats. We sampled three mangrove forests on the island of Kosrae in the Federated States of Micronesia at Lelu Harbor, Okat River, and Utwe tidal channel. Samples of S. serrata and likely food sources were analyzed for stable carbon (δ 13 C), nitrogen (δ 15 N), and sulfur (δ 34 S) isotopes. Scylla serrata tissues also were analyzed for phosphorus (P), cations (K, Ca, Mg, Na), and trace elements (Mn, Fe, Cu, Zn, and B). Discriminant analysis indicated that at least 87% of the crabs remain in each site as distinct populations. Crab stable isotope values indicated potential differences in habitat use within estuaries. Values for δ 13 C and δ 34 S in crabs from Okat and Utwe were low and similar to values expected from animals feeding within mangrove forests, e.g., feeding on infauna that had average δ 13 C values near −26.5‰. In contrast, crabs from Lelu had higher δ 13 C and δ 34 S values, with average values of −21.8 and 7.8‰, respectively. These higher isotope values are consistent with increased crab foraging on reef flats and seagrasses. Given that S. serrata have been observed feeding on adjacent reef and seagrass environments on Kosrae, it is likely that they move in and out of the mangroves for feeding. Isotope mixing model results support these conclusions, with the greatest mangrove ecosystem contribution to S. serrata diet occurring in the largest mangrove forests. Conserving larger island mangrove forests (> 1 km deep) appears to support crab foraging activities.
Mangroves on Pacific high islands offer a number of important ecosystem services to both natural ... more Mangroves on Pacific high islands offer a number of important ecosystem services to both natural ecological communities and human societies. High islands are subjected to constant erosion over geologic time, which establishes an important source of terrigeneous sediment for nearby marine communities. Many of these sediments are deposited in mangrove forests and offer mangroves a potentially important means for adjusting surface elevation with rising sea level. In this study, we investigated sedimentation and elevation dynamics of mangrove forests in three hydrogeomorphic settings on the islands of Kosrae and Pohnpei, Federated States of Micronesia (FSM). Surface accretion rates ranged from 2.9 to 20.8 mm y -1 , and are high for naturally occurring mangroves. Although mangrove forests in Micronesian high islands appear to have a strong capacity
In Hawai'i, mangrove trees are introduced species that can rapidly colonize many nearshore en... more In Hawai'i, mangrove trees are introduced species that can rapidly colonize many nearshore environments. Mangroves have been introduced on O'ahu, and Rhizophora mangle in particular has created numerous problems that have led to several mangrove removals and increased interest in long-term man- agement of mangroves. The objective of this project was to quantify current lo- cations of mangroves and their
Belowground biomass is thought to account for much of the total biomass in mangrove forests and m... more Belowground biomass is thought to account for much of the total biomass in mangrove forests and may be related to soil fertility. The Yela River and the Sapwalap River, Federated States of Micronesia, contain a natural soil resource gradient defined by total phosphorus (P) density ranging from 0.05 to 0.42 mg cm -3 in different hydrogeomorphic settings. We used this fertility gradient to test the hypothesis that edaphic conditions constrain mangrove productivity through differential allocation of biomass to belowground roots. We removed sequential cores and implanted root ingrowth bags to measure in situ biomass and productivity, respectively. Belowground root biomass values ranged among sites from 0.448 ± 0.096 to 2.641 ± 0.534 kg m -2 . Root productivity (roots B20 mm) did not vary significantly along the gradient (P = 0.3355) or with P fertilization after 6 months (P = 0.2968). Fine root productivity (roots B2 mm), however, did vary significantly among sites (P = 0.0363) and ranged from 45.88 ± 21.37 to 118.66 ± 38.05 g m -2 year -1 . The distribution of total standing root biomass and fine root productivity followed patterns of N:P ratios as hypothesized, with larger root mass generally associated with lower relative P concentrations. Many of the processes of nutrient acquisition reported from nutrient-limited mangrove forests may also occur in forests of greater biomass and productivity when growing along soil nutrient gradients.
Many tidally influenced freshwater forested wetlands (tidal swamps) along the south Atlantic coas... more Many tidally influenced freshwater forested wetlands (tidal swamps) along the south Atlantic coast of the USA are currently undergoing dieback and decline. Salinity often drives conversion of tidal swamps to marsh, especially under conditions of regional drought. During this change, alterations in nitrogen (N) uptake from dominant vegetation or timing of N recycling from the canopy during annual litter senescence may help to facilitate marsh encroachment by providing for greater bioavailable N with small increases in salinity. To monitor these changes along with shifts in stand productivity, we established sites along two tidal swamp landscape transects on the lower reaches of the Waccamaw River (South Carolina) and Savannah River (Georgia) representing freshwater (≤0.1 psu), low oligohaline (1.1-1.6 psu), and high oligohaline (2.6-4.1 psu) stands; the latter stands have active marsh encroachment. Aboveground tree productivity was monitored on all sites through monthly litterfall collection and dendrometer band measurements from 2005 to 2009. Litterfall samples were pooled by season and analyzed for total N and carbon (C). On average between the two rivers, freshwater, low oligohaline, and high oligohaline tidal swamps returned 8,126, 3,831, and 1,471 mg Nm −2 year −1 , respectively, to the forest floor through litterfall, with differences related to total litterfall volume rather than foliar N concentrations. High oligohaline sites were most inconsistent in patterns of foliar N concentrations and N loading from the canopy. Leaf N content generally decreased and foliar C/N generally increased with salinization (excepting one site), with all sites being fairly inefficient in resorbing N from leaves prior to senescence. Stands with higher salinity also had greater flood frequency and duration, lower basal area increments, lower tree densities, higher numbers of dead or dying trees, and much reduced leaf litter fall (103 vs. 624 gm −2 year −1 ) over the five study years. Our data suggest that alternative processes, such as the rate of decomposition and potential for N mineralization, on tidal swamp sites undergoing salinity-induced state change may be more important for controlling N biogeochemical cycling in soils than differences among sites in N loading via litterfall.
The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries through... more The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries throughout the Indo-Pacific. Understanding crab diets and habitat use should assist in managing these fisheries and could provide additional justification for conservation of the mangrove ecosystem itself. We used multiple chemical tracers to test whether crab movements were restricted to local mangrove forests, or extended to include adjacent seagrass beds and reef flats. We sampled three mangrove forests on the island of Kosrae in the Federated States of Micronesia at Lelu Harbor, Okat River, and Utwe tidal channel. Samples of S. serrata and likely food sources were analyzed for stable carbon (δ 13 C), nitrogen (δ 15 N), and sulfur (δ 34 S) isotopes. Scylla serrata tissues also were analyzed for phosphorus (P), cations (K, Ca, Mg, Na), and trace elements (Mn, Fe, Cu, Zn, and B). Discriminant analysis indicated that at least 87% of the crabs remain in each site as distinct populations. Crab stable isotope values indicated potential differences in habitat use within estuaries. Values for δ 13 C and δ 34 S in crabs from Okat and Utwe were low and similar to values expected from animals feeding within mangrove forests, e.g., feeding on infauna that had average δ 13 C values near −26.5‰. In contrast, crabs from Lelu had higher δ 13 C and δ 34 S values, with average values of −21.8 and 7.8‰, respectively. These higher isotope values are consistent with increased crab foraging on reef flats and seagrasses. Given that S. serrata have been observed feeding on adjacent reef and seagrass environments on Kosrae, it is likely that they move in and out of the mangroves for feeding. Isotope mixing model results support these conclusions, with the greatest mangrove ecosystem contribution to S. serrata diet occurring in the largest mangrove forests. Conserving larger island mangrove forests (> 1 km deep) appears to support crab foraging activities.
Mangroves on Pacific high islands offer a number of important ecosystem services to both natural ... more Mangroves on Pacific high islands offer a number of important ecosystem services to both natural ecological communities and human societies. High islands are subjected to constant erosion over geologic time, which establishes an important source of terrigeneous sediment for nearby marine communities. Many of these sediments are deposited in mangrove forests and offer mangroves a potentially important means for adjusting surface elevation with rising sea level. In this study, we investigated sedimentation and elevation dynamics of mangrove forests in three hydrogeomorphic settings on the islands of Kosrae and Pohnpei, Federated States of Micronesia (FSM). Surface accretion rates ranged from 2.9 to 20.8 mm y -1 , and are high for naturally occurring mangroves. Although mangrove forests in Micronesian high islands appear to have a strong capacity
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