We examined the net production, decomposition, and microbial utilization of the seagrass Halophil... more We examined the net production, decomposition, and microbial utilization of the seagrass Halophila decipiens during a 6.5 d period in May 1985 in the Salt River Canyon, St Croix, US Virgin Islands. H. decipienscovered 37 % of the Canyon floor between depths of 14 and 32 m with a biomass of 9.15 g dry \vt m-'; its net productivity was ca 0.145 g C m-' d -' Turnover time, estimated by 2 independent methods, was 10.7 d. After 6.5 d H decjpiens incubated in lltterbags buried in the sediment lost 5 6 % of their original ash free dry weight (AFDW) while litterbags incubated on the sediment surface lost only 28 % of their original AFDW. Bacteria grew rapidly on the detritus, doubling in 3.1 d in the surface bags and 3.7 d in the buried bags. Per-cell thymidine incorporation rates peaked within the first 13 h in both treatments but declined thereafter. Final incorporation rates were highest in surface bags. Mean bacterial cell size and bacterial abundance associated with degrading H. decipiens were larger in the buried litterbags. Bacterial biomass, however, was only 29.3 mg cell C g -' AFDW in buried bags and 17.5 mg C g-' AFDVV in surface bags Using bacterial production averaged for the 6.5 d, we estimate that only about 0.26 "10 of the daily detntal input from H. declplens is converted daily into bacterial biomass attached to the degrading plant material. We conclude that, unless the bacterial community on H. decipiens detritus were to use the organic matter more efficiently and were heavily grazed upon, attached bacteria would not make a significant contribution to a deposit-feeding detritivore's energy demands.
Development of planted seagrass beds in Tampa Bay, Florida, USA. 11. Fauna1 components Mark S. ~o... more Development of planted seagrass beds in Tampa Bay, Florida, USA. 11. Fauna1 components Mark S. ~onseca'~', David L. Meyerl, Margret 0. ~a 1 1~
Its mission is to identify, designate, protect and manage the ecological, recreational, research,... more Its mission is to identify, designate, protect and manage the ecological, recreational, research, educational, historical, and aesthetic resources and qualities of nationally significant coastal and marine areas. The existing marine sanctuaries differ widely in their natural and historical resources and include nearshore and open ocean areas ranging in size from less than one to over 5,000 square miles. Protected habitats include rocky coasts, kelp forests, coral reefs, sea grass beds, estuarine habitats, hard and soft bottom habitats, segments of whale migration routes, and shipwrecks.
Eelgrass, Zostera marina, dominates the ecologically important but fragile seagrass communities a... more Eelgrass, Zostera marina, dominates the ecologically important but fragile seagrass communities along the east coast of the United States from North Carolina to Nova Scotia. Grasslike leaves and an extensive root and rhizome system enable eelgrass to exist in a shallow aquatic environment subject to waves, tides, and shifting sediments. Eelgrass meadows are highly productive, frequently rivaling agricultural croplands. They provide shelter and a rich variety of primary and secondary food resources, and form a nursery habitat for the life history stages of numerous fishery organisms. The leaves absorb and release nutrients, provide surfaces for attachment, reduce water current velocity, turbulence and scour, and promote accumulation of detritus. Rhizomes provide protection for benthic infauna and enhance sediment stability. Roots absorb and release nutrients to interstitial waters. Because of their shallow, subtidal existence, seagrasses are susceptible to perturbations of both the water column and sediments. Eelgrass meadows are impacted by dredging and filling, some commercial fishery harvest techniques, modification of normal temperature and salinity regimes, and addition of chemical wastes. Techniques have been developed to successfully restore eelgrass habitats, but a holistic approach to planning research and environmentally-related decisions is needed to avoid cumulative environmental impacts on these vital nursery areas. 64 figures, 16 tables.
Eelgrass, Zostera marina, dominates the ecologically important but fragile seagrass communities a... more Eelgrass, Zostera marina, dominates the ecologically important but fragile seagrass communities along the east coast of the United States from North Carolina to Nova Scotia. Grasslike leaves and an extensive root and rhizome system enable eelgrass to exist in a shallow aquatic environment subject to waves, tides, and shifting sediments. Eelgrass meadows are highly productive, frequently rivaling agricultural croplands. They provide shelter and a rich variety of primary and secondary food resources, and form a nursery habitat for the life history stages of numerous fishery organisms. The leaves absorb and release nutrients, provide surfaces for attachment, reduce water current velocity, turbulence and scour, and promote accumulation of detritus. Rhizomes provide protection for benthic infauna and enhance sediment stability. Roots absorb and release nutrients to interstitial waters. Because of their shallow, subtidal existence, seagrasses are susceptible to perturbations of both the water column and sediments. Eelgrass meadows are impacted by dredging and filling, some commercial fishery harvest techniques, modification of normal temperature and salinity regimes, and addition of chemical wastes. Techniques have been developed to successfully restore eelgrass habitats, but a holistic approach to planning research and environmentally-related decisions is needed to avoid cumulative environmental impacts on these vital nursery areas. 64 figures, 16 tables.
Organismal survival in marine habitats is often positively correlated with habitat structural com... more Organismal survival in marine habitats is often positively correlated with habitat structural complexity at local (within-patch) spatial scales. Far less is known, however, about how marine habitat structure at the landscape scale influences predation and other ecological processes, and in particular, how these processes are dictated by the interactive effect of habitat structure at local and landscape scales. The relationship between survival and habitat structure can be modeled with the habitat-survival function (HSF), which often takes on linear, hyperbolic, or sigmoid forms. We used tethering experiments to determine how seagrass landscape structure influenced the HSF for juvenile blue crabs Callinectes sapidus Rathbun in Back Sound, North Carolina, USA. Crabs were tethered in artificial seagrass plots of 7 different shoot densities embedded within small (1 -3 m 2 ) or large (>100 m 2 ) seagrass patches (October 1999), and within 10 × 10 m landscapes containing patchy (< 50% cover) or continuous (> 90% cover) seagrass (July 2000). Overall, crab survival was higher in small than in large patches, and was higher in patchy than in continuous seagrass. The HSF was hyperbolic in large patches and in continuous seagrass, indicating that at low levels of habitat structure, relatively small increases in structure resulted in substantial increases in juvenile blue crab survival. However, the HSF was linear in small seagrass patches in 1999 and was parabolic in patchy seagrass in 2000. A sigmoid HSF, in which a threshold level of seagrass structure is required for crab survival, was never observed. Patchy seagrass landscapes are valuable refuges for juvenile blue crabs, and the effects of seagrass structural complexity on crab survival can only be fully understood when habitat structure at larger scales is considered.
We examined the net production, decomposition, and microbial utilization of the seagrass Halophil... more We examined the net production, decomposition, and microbial utilization of the seagrass Halophila decipiens during a 6.5 d period in May 1985 in the Salt River Canyon, St Croix, US Virgin Islands. H. decipienscovered 37 % of the Canyon floor between depths of 14 and 32 m with a biomass of 9.15 g dry \vt m-'; its net productivity was ca 0.145 g C m-' d -' Turnover time, estimated by 2 independent methods, was 10.7 d. After 6.5 d H decjpiens incubated in lltterbags buried in the sediment lost 5 6 % of their original ash free dry weight (AFDW) while litterbags incubated on the sediment surface lost only 28 % of their original AFDW. Bacteria grew rapidly on the detritus, doubling in 3.1 d in the surface bags and 3.7 d in the buried bags. Per-cell thymidine incorporation rates peaked within the first 13 h in both treatments but declined thereafter. Final incorporation rates were highest in surface bags. Mean bacterial cell size and bacterial abundance associated with degrading H. decipiens were larger in the buried litterbags. Bacterial biomass, however, was only 29.3 mg cell C g -' AFDW in buried bags and 17.5 mg C g-' AFDVV in surface bags Using bacterial production averaged for the 6.5 d, we estimate that only about 0.26 "10 of the daily detntal input from H. declplens is converted daily into bacterial biomass attached to the degrading plant material. We conclude that, unless the bacterial community on H. decipiens detritus were to use the organic matter more efficiently and were heavily grazed upon, attached bacteria would not make a significant contribution to a deposit-feeding detritivore's energy demands.
Development of planted seagrass beds in Tampa Bay, Florida, USA. 11. Fauna1 components Mark S. ~o... more Development of planted seagrass beds in Tampa Bay, Florida, USA. 11. Fauna1 components Mark S. ~onseca'~', David L. Meyerl, Margret 0. ~a 1 1~
Its mission is to identify, designate, protect and manage the ecological, recreational, research,... more Its mission is to identify, designate, protect and manage the ecological, recreational, research, educational, historical, and aesthetic resources and qualities of nationally significant coastal and marine areas. The existing marine sanctuaries differ widely in their natural and historical resources and include nearshore and open ocean areas ranging in size from less than one to over 5,000 square miles. Protected habitats include rocky coasts, kelp forests, coral reefs, sea grass beds, estuarine habitats, hard and soft bottom habitats, segments of whale migration routes, and shipwrecks.
Eelgrass, Zostera marina, dominates the ecologically important but fragile seagrass communities a... more Eelgrass, Zostera marina, dominates the ecologically important but fragile seagrass communities along the east coast of the United States from North Carolina to Nova Scotia. Grasslike leaves and an extensive root and rhizome system enable eelgrass to exist in a shallow aquatic environment subject to waves, tides, and shifting sediments. Eelgrass meadows are highly productive, frequently rivaling agricultural croplands. They provide shelter and a rich variety of primary and secondary food resources, and form a nursery habitat for the life history stages of numerous fishery organisms. The leaves absorb and release nutrients, provide surfaces for attachment, reduce water current velocity, turbulence and scour, and promote accumulation of detritus. Rhizomes provide protection for benthic infauna and enhance sediment stability. Roots absorb and release nutrients to interstitial waters. Because of their shallow, subtidal existence, seagrasses are susceptible to perturbations of both the water column and sediments. Eelgrass meadows are impacted by dredging and filling, some commercial fishery harvest techniques, modification of normal temperature and salinity regimes, and addition of chemical wastes. Techniques have been developed to successfully restore eelgrass habitats, but a holistic approach to planning research and environmentally-related decisions is needed to avoid cumulative environmental impacts on these vital nursery areas. 64 figures, 16 tables.
Eelgrass, Zostera marina, dominates the ecologically important but fragile seagrass communities a... more Eelgrass, Zostera marina, dominates the ecologically important but fragile seagrass communities along the east coast of the United States from North Carolina to Nova Scotia. Grasslike leaves and an extensive root and rhizome system enable eelgrass to exist in a shallow aquatic environment subject to waves, tides, and shifting sediments. Eelgrass meadows are highly productive, frequently rivaling agricultural croplands. They provide shelter and a rich variety of primary and secondary food resources, and form a nursery habitat for the life history stages of numerous fishery organisms. The leaves absorb and release nutrients, provide surfaces for attachment, reduce water current velocity, turbulence and scour, and promote accumulation of detritus. Rhizomes provide protection for benthic infauna and enhance sediment stability. Roots absorb and release nutrients to interstitial waters. Because of their shallow, subtidal existence, seagrasses are susceptible to perturbations of both the water column and sediments. Eelgrass meadows are impacted by dredging and filling, some commercial fishery harvest techniques, modification of normal temperature and salinity regimes, and addition of chemical wastes. Techniques have been developed to successfully restore eelgrass habitats, but a holistic approach to planning research and environmentally-related decisions is needed to avoid cumulative environmental impacts on these vital nursery areas. 64 figures, 16 tables.
Organismal survival in marine habitats is often positively correlated with habitat structural com... more Organismal survival in marine habitats is often positively correlated with habitat structural complexity at local (within-patch) spatial scales. Far less is known, however, about how marine habitat structure at the landscape scale influences predation and other ecological processes, and in particular, how these processes are dictated by the interactive effect of habitat structure at local and landscape scales. The relationship between survival and habitat structure can be modeled with the habitat-survival function (HSF), which often takes on linear, hyperbolic, or sigmoid forms. We used tethering experiments to determine how seagrass landscape structure influenced the HSF for juvenile blue crabs Callinectes sapidus Rathbun in Back Sound, North Carolina, USA. Crabs were tethered in artificial seagrass plots of 7 different shoot densities embedded within small (1 -3 m 2 ) or large (>100 m 2 ) seagrass patches (October 1999), and within 10 × 10 m landscapes containing patchy (< 50% cover) or continuous (> 90% cover) seagrass (July 2000). Overall, crab survival was higher in small than in large patches, and was higher in patchy than in continuous seagrass. The HSF was hyperbolic in large patches and in continuous seagrass, indicating that at low levels of habitat structure, relatively small increases in structure resulted in substantial increases in juvenile blue crab survival. However, the HSF was linear in small seagrass patches in 1999 and was parabolic in patchy seagrass in 2000. A sigmoid HSF, in which a threshold level of seagrass structure is required for crab survival, was never observed. Patchy seagrass landscapes are valuable refuges for juvenile blue crabs, and the effects of seagrass structural complexity on crab survival can only be fully understood when habitat structure at larger scales is considered.
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