Underwater microscope for measuring spatial and temporal changes in bed-sediment grain size

This paper is not subject to U.S. copyright. The definitive version was published in Sedimentary Geology 202 (2007): 402-408, doi:10.1016/j.sedgeo.2007.03.020.For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the laboratory for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches

Standing Crop and Sediment Production of Reef-Dwelling Foraminifera on O'ahu, Hawai'i

Most of O'ahu's nearshore and beach sands are highly calcareous and of biogenic origin. The pale-colored constituent grains are the eroded remains of carbonate shells and skeletons produced by marine organisms living atop the island's fringing reefs and in the shallow waters near shore. Previous studies have shown that the tests of symbiont-bearing benthic foraminifera compose a substantial portion (up to one-fourth) of these organically produced sands. We sampled a variety of reef flat and slope habitats to obtain standingcrop data and production estimates for several sand-producing genera of reefdwelling formninifera. We found that modem communities of these shelled protists occur in dense numbers islandwide, reaching densities up to 105 individuals per square meter of suitable substrate in the more productive habitats. Further research on the contribution of foraminifera to beach, nearshore, and offshore sands is planned for O'ahu and neighboring islands to describe their roles in the sediment budget more completely

Observations on a Trimorphic Life Cycle in Amphistegina Gibbosa Populations from the Florida Keys

Trimorphic life cycles have been widely postulated for larger foraminifera but have only been documented for Heterostegina. Prior to 1991, extensive laboratory and field studies of Amphistegina spp. revealed evidence only for a classical dimorphic life cycle. In summer 1991, A. gibbosa populations in the Florida Keys were stricken by disease. Specimens collected from stressed populations and maintained in laboratory cultures produced lineages of up to four successive asexual generations. Gametogenesis was observed in some F3 individuals, demonstrating that trimorphic life cycles occur in Amphistegina. To determine if biological trimorphism is manifested as physical trimorphism in protoconch diameters or test size, specimens from field collections and from reproductions in laboratory cultures were sectioned and their protoconchs measured and evaluated. Of 143 individuals randomly-selected from field samples, only five exhibited typical microspheric embryon morphologies; the rest appeared to be megalospheric. Of 32 field-collected specimens that reproduced by multiple fission in culture, three appeared to be microspheric. Of 17 specimens that underwent gametogenesis, all exhibited typical megalospheric embryon morphologies. Of the field-collected specimens suspected to be microspheric, mean protoconch diameter was 19.0 μm (SD 3.4; N 8); mean protoconch diameters of specimens with megalospheric morphologies was 39.1 μm (SD 9.4; N 184). Of the field-collected specimens that reproduced in culture, gamonts were generally larger (TD 1.23 mm, SD 0.19, N 17) than those that reproduced by multiple fission (TD 0.92 mm, SD 0.21, N 32). This study indicates that the life cycle of Amphistegina gibbosa is trimorphic and may include both alternation of generations and successive asexual generations. The latter mode may provide an effective mechanism to rapidly increase population densities. Such a strategy may facilitate population recovery following mortality events, as well as occupation of marginal habitats and colonization of new areas

Standing Crop and Sediment Production of Reef-Dwelling Foraminifera on O\u27Ahu, Hawai\u27I

Most of O\u27ahu\u27s nearshore and beach sands are highly calcareous and of biogenic origin. The pale-colored constituent grains are the eroded remains of carbonate shells and skeletons produced by marine organisms living atop the island\u27s fringing reefs and in the shallow waters near shore. Previous studies have shown that the tests of symbiont-bearing benthic foraminifera compose a substantial portion (up to one-fourth) of these organically produced sands. We sampled a variety of reef flat and slope habitats to obtain standing-crop data and production estimates for several sand-producing genera of reef-dwelling foraminifera. We found that modern communities of these shelled protists occur in dense numbers islandwide, reaching densities up to 105 individuals per square meter of suitable substrate in the more productive habitats. Further research on the contribution of foraminifera to beach, nearshore, and offshore sands is planned for O\u27ahu and neighboring islands to describe their roles in the sediment budget more completely

Borings in Amphistegina (Foraminiferida): Evidence of Predation by Floresina Amphiphaga (Foraminiferida)

The small foraminifer, Floresina amphiphaga, preys upon the relatively large foraminifer, Amphistegina gibbosa, leaving 2-10 characteristic predation holes in the test of the prey

Benthic Foraminiferal Assemblages from Current-Swept Carbonate Platforms of the Northern Nicaraguan Rise, Caribbean Sea

Calcifying organisms with endosymbiotic algae produce a major portion of the calcium carbonate sediments in tropical oceans. In 1982-1983, global coral bleaching events revealed the emergence of serious breakdowns in these important symbiotic associations. In 1991-1992, similar problems appeared in Amphistegina spp., the most abundant reef dwelling algal symbiont-bearing foraminifer worldwide. Since summer 1992, A. gibbosa populations from Conch Reef in the Florida Keys (USA) have been monitored for visible evidence of symbiont loss and associated symptoms. Previous reports have revealed seasonal and size trends in incidences of visible symbiont loss along with trends in reproductive anomalies and shell breakage through 1993. Using data collected through 1996, we statistically tested these postulated trends, with the goals of describing population responses to this multi-year stress event and gaining insight into the underlying cause. Since 1992 the proportions of mottled individuals increased in early spring, peaked in mid summer, and declined in late summer and fall. The summer 1992 peak in bleaching was the most intense, affecting 82% of the population at 18 m whereas only 43% were affected in summer 1996. The disease appears to be degenerative; symbiont loss disproportionately affects the larger size classes. Population densities crashed in fall 1991 and remained low through the spring and summer months of 1992, at which time juveniles (\u3c 0.6 mm diameter) comprised less than 10% of the population. Because Amphistegina spp. typically reproduce asexually in the spring, the lack of juveniles suggested that attempts to reproduce failed, resulting in anomalously low population abundances. Since 1992, the proportion of juveniles has increased steadily and population density has partly recovered. Though the stress has not been identified, the trends and type of damage to the population are consistent with a mechanism related to solar irradiance. Whatever the cause, the potential consequences range from impact on local sediment supply to global carbon budgets