ALBERT

Description: The ecological balance of nature is defined as an equilibrium between species richness (S) and species evenness (E) such that diversity (H) remains constant with time. Based on this definition, our approach identifies growth or decline in communities as perturbations from stasis and has successfully done so for benthic foraminiferal communities. Here, we examine whether this approach is appropriate for planktonic foraminifera. To do so, we utilized planktonic foraminiferal counts (39 samples, 66% recovery) from Maastrichtian sediments in the Weddell Sea from ODP Hole 690C. A total of 24 species were observed and both 〉63-µm and 〉150-µm fractions were counted. In the 〉63-µm fraction, nine communities were recognized while in the 〉150-µm fraction, there were 12. In both fractions at 70.45 Ma, a boundary was recognized and immediately after this boundary, a community in growth was identified. A trend of increasing diversity upcore was substantiated by regression on individual samples. For our purposes, the 〉150-µm fraction in this data set is sufficient to recognize community trends. The 〉150-µm fraction in Hole 690C has 82% of the sampling time in stasis and an average time per community is 0.85 Ma. The 〉63-µm fraction has 73% of the sampling time in stasis and an average time per community of 1.02 Ma.

Description: An enigma of deep-sea biodiversity research is that the abyss with its low productivity and densities appears to have a biodiversity similar to that of shallower depths. This conceptualization of similarity is based mainly on per-sample estimates (point diversity, within-habitat, or α-diversity). Here, we use a measure of between-sample within-community diversity (β1H) to examine benthic foraminiferal diversity between 333 stations within 49 communties from New Zealand, the South Atlantic, the Gulf of Mexico, the Norwegian Sea, and the Arctic. The communities are grouped into two depth categories: 200–1500 m and 〉1500 m. β1Hdiversity exhibits no evidence of regional differences. Instead, higher values at shallower depths are observed worldwide. At depths of 〉1500 m the average β1His zero, indicating stasis or no biodiversity gradient. The difference in β1H-diversity explains why, despite species richness often being greater per sample at deeper depths, the total number of species is greater at shallower depths. The greater number of communities and higher rate of evolution resulting in shorter species durations at shallower depths is also consistent with higher β1Hvalues.

Description: Many cheilostome bryozoans of diverse phylogenetic origin grow as erect, arborescent colonies with branches of modified planar form composed of two layers of zooids back to back. Regular branching enables a growing colony to expand in surface area, and hence in the number of zooids that feed, reproduce, and perform other vital functions, at an accelerating rate. During growth, branches first all diverge, then increasingly converge, and in late stages of growth begin to interfere with each other's growth and function. Interference can set limits to the width and thickness of branches and hence to the number and size of zooids.Simulation of growth using a 3–dimensional mathematical model shows that a narrow range of possible values of branching angles minimizes branch interference in late growth stages. These values are prevalent in fossil and modern species. Branch spacing at later growth stages is correlated with the distance between branches at first crossing, providing room for feeding organs of the two facing layers of zooids to protrude and function. Interbranch distances dwindle as branches increasingly converge, so emphasis on minimizing interference at a late stage sets a practical limit to growth beyond that stage. To gain this long-term benefit requires adhering to a regular pattern throughout growth. The considerable variation in branching properties in fossil and modern species, and a variability in spacing inherent in the growth pattern itself, limit the amount of usable interbranch space. Despite a higher intraspecific variability, branching properties are as distinctive interspecifically as zooidal properties, and variability is randomly distributed through the colony. A small reduction in variability between fossil and modern species suggests that increasing regularity may provide a selective advantage in the utilization of interbranch space.

Description: Cheilostome bryozoans that grew as rigidly erect arborescent colonies dominate many bryozoan-rich assemblages of Tertiary age, in which they are found most commonly as small dissociated fragments. The regularity with which branching and branch thickening occur in intact colonies of living species provides a basis for quantitative reconstruction of these growth processes in fossils. We propose models to describe branch thickening, develop methods to extend both thickening and branching models to fossils, investigate the thickening and branching properties of four Paleocene and five Oligocene species and compare the properties of these fossils to those of nine living species.The properties investigated are largely mutually independent and species specific irrespective of geologic age and have similar numerical ranges among different assemblages of coeval species. Species are evenly distributed across the range of possible morphologies between observed extremes, without obvious gaps. Statistically significant trends through time are identified in gradients of branch thickening, which have implications for the resistance of colonies to mechanical stress, and in angles of bifurcation, that are important in the way growing colonies occupy space.

Description: The mixed siliciclastic/carbonate sediments of Baffin Bay, Texas, provide a record of the evolution of the Bay for the last 10 ka. Flooding surfaces at 8 ka and 5.5 ka provided an a priori separation of sediments in a core into three groups. Discriminant analysis and interpretation of species composition of the foraminifera from these groups indicated a progression from deltaic to open-bay to hypersaline environments. This traditional paleoecological analysis, however, does not utilize the information available in the relative abundance distribution (RAD) within each community. An approach capable of assessing within community change is provided by S (species richness), H (Shannon information function) and E (evenness) analysis. Using this approach not only can communities be designated without a priori assumptions and environments identified easily, but also the RAD within each community can be evaluated, providing a record of community growth, decline or stasis with time. Stasis, or the ecological balance of nature, is mathematically defined as an equilibrium between S and E such that diversity (H) remains constant with time. This stasis requires that, as the number of individuals (N) gets larger with time, the value of H remains constant. Thus, at stasis a regression between H versus lnN will have a 0 value for the regression coefficient (β1H), here termed the Relative Abundance Distribution Index, RADI. A positive value of RADI indicates community growth, a negative value indicates community decline. In the Baffin Bay core 6, communities were identified from 46 samples using SHE analysis. At ∼9 ka the RADI was positive, indicating the growth of a normal marine community with a high S. A second community, still largely normal marine but with a slightly negative RADI, formed at ∼8 ka. Beginning at ∼6.4 ka, the 3rd and 4th marginal marine communities with highly negative RADIs formed, indicating a sharp decline for ∼1 ka during the formation of Padre Island, which may have taken ∼1000 years. At ∼5 ka the 5th and 6th marginal marine communities were established with RADIs indicating a prolonged period of stasis. The 5th community was dominated by Elphidium with a high percentage of miliolids. The 6th community, established at ∼2 ka, was dominated by Ammonia and a moderate percentage of miliolids. These last two communities, both at stasis, were apparently responding to changes in salinity brought on by changes in rainfall.

Description: Studies of foraminiferal assemblages in intertidal marshes and subtidal creeks usually rely upon sediment samples collected along transects, such that associations with other organisms often go unnoticed. We show that ecologically useful data can be obtained by sampling that is stratified by substrate and microenvironment. The tidal wetland at Lower LaHave, Nova Scotia, Atlantic Canada (44º16′37.39″N, 64º19′46.45″W, area ∼1 km2) comprises mostly sandy sediment occupied largely by the low marsh grass Spartina alterniflora. The wetland is situated next to LaHave Estuary, which is polluted with domestic waste. Microenvironments within the marsh were sampled for total (living + dead) foraminiferal assemblages. The mass of dried sediment examined at each site was used to calculate the foraminiferal number (FN, number of foraminiferal tests per gram of sediment). Sediment samples from the intertidal grass beds reflect a typical low- to high-marsh zonal distribution of benthic foraminifera [FN = 24.7 ± 16.6 g−1 (mean ± standard deviation); n = 716 tests]. Samples from a tidal channel yielded few tests (FN = ∼0.3 ± 0.7 g−1; n = 22). Clutches of the mussel Mytilus edulis occurred in areas of strong current action within the channel and on lower energy slip-off slopes. Mussel clutches from the channel base yielded few tests (FN = ∼0.7 ± 0.7 g−1; n = 25), mostly Miliammina fusca. Clutches from slip-off slopes yielded a significantly richer assemblage (FN = 8.7 ± 4.6 g−1; n = 229) dominated by Elphidium umbilicatulum. We concluded that mussel clutches in low energy areas can be suitable habitat for E. umbilicatulum, either associated with structural complexity of the clutches or with waste products excreted by mussels that may stimulate growth of bacteria or microalgae upon which the foraminifera feed. The results from this study provide a baseline for examining the biotic impact of remediation of the LaHave River on the Lower LaHave wetland.