Abstract Introduction Acknowledgements Material and Methods Results - Pollen Assemblages and Trends > Faunal Assemblages and Trends    - No Name Bank    - Featherbed Bank    - Card Bank Discussion Significant Findings, Implications And Future Work References Appendices PDF version

Faunal Assemblages and Trends - No Name Bank

The results discussed below all pertain to the core collected at No Name bank in April 2002 (GLW402-NNB).

Faunal Assemblages

Approximately 91 foraminiferal taxonomic groups were identified that include species and species groups (spp.) (Appendix E). The foraminiferal assemblages include rotaliid, textulariid, and miliolid forms. All foraminifera identified were benthic with miliolid and rotaliid forms dominant. The arenaceous textulariids constituted a minor component. No planktonic forms were present. The rotaliids are dominated by the genera Rosalina and Cribroelphidium/ Elphidium. The miliolids are dominated by the genera Quinqueloculina, Triloculina and Miliolinella. Other important genera occurring in the core are Ammonia, Archaias, Articulina, and Bolivina. The textulariids are a minor component of the assemblages represented by the genera Clavulina and Valvulina.

The ostracode assemblages are dominated by Loxoconcha matagordensis, Xestoleberis spp. and bairdiids (a family of marine ostracodes) with lesser amounts of Malzella floridana and other marine species (Appendix F).

The No Name Bank Core has a diverse, generally open-bay to marine molluscan assemblage containing 79 faunal groups (species, genera, and a few family groups) Appendix G). The dominant species in the core are Bittiolum varium, Laevicardium mortoni, Schwartizella catesbyana, Parvilucina multilineata, and Turbo castaneus.

Faunal Trends

The distribution of faunal elements is presented in the interpreted time interval of deposition.

Foraminifera:

Ammonia is present in very low abundance throughout the core but is absent from about 1830-1890 (Figure 14; Appendix E). Archaias also is found in low abundances throughout the core; however there are several significant intervals. From 1640-~1700, Archaias is abundant. Archaias is absent from 1850-1895 and then significantly increases between 1958-1981 before declining to moderate abundances between 1981-1998. Articulina was rarely present in the core until the 1860s. Between 1958 and 1961 Articulina abundance increases from low to high and remains high until about 1991. From 1991 to 1998 there is a decline in this species' abundance.

Figure 14. Downcore log normal plots of the major benthic foraminiferal taxonomic groups present in the No Name Bank Core (GLW402-NNB). [click on graphs for larger versions]

Bolivina is typically an infaunal taxa associated with organic-rich sediments. It was absent to rare throughout the core (Figure 14); however, Bolivina abundance relative to the rest of the core increases from the 1930s to the 1970s.

The Cribroelphidium-Elphidium and Miliolinella have been significant components of foraminiferal assemblages throughout the core (Figure 14). Cribroelphidium-Elphidium were most common between ~1930 and 1980 (especially post-1960), similar to the Bolivina. The Cribroelphidium-Elphidium abundance decreased from 1980-2000. The Miliolinella abundances were particularly high between 1920-1960 and ~1978-2000. Five of the six highest abundances of Miliolinella occurred in samples from 1988-2000.

Quinqueloculina and Triloculina also are common in the core (Figure 14). Quinqueloculina abundances were relatively stable until 1955, when they became more abundant. Triloculina, however, gradually increased in abundance throughout the core, with a significant increase post-1955. Since ~1980, however, Triloculina abundance decreased.

Ostracoda:

The relative proportions of the ostracode taxa fluctuate downcore indicating important environmental changes in the vicinity of No Name Bank during the past four centuries (Figure 15, Appendix F). The more significant ostracode faunal changes include the following. Beginning around 1750, a gradual increase occurs in the bairdiids, a group of marine ostracodes, from < 10 % to 30- 40 %. Bairdiid relative abundance fluctuated between ~1918 and 1924, shifting from 16 to 60 %. Loxoconcha matagordensis, an epiphytal ostracode, increased in abundance from the early 1600s to the late 1700s, then declined sharply; and increased again beginning around 1800 until ~1900. The general trend in abundance of Loxoconcha during the 20^th century is a decline. A progressive decline occurred in the abundance of Xestoleberis spp., an epiphytal species typically found on macro-benthic algae, beginning in the early to mid 1800s and continuing to the 1940s. Malzella floridana, a species tolerant of hypersalinity and often dominant in cores from central Florida Bay (Cronin and others, 2001) was present in persistently low abundances (<10%) throughout the core. However, prior to ~1910 M. floridana was consistently present and fluctuated between 1-13% abundance; after ~1910, it comprised 5% or less of the assemblage, and was completely absent in some intervals.

Figure 15. Downcore plots of key ostracode species from No Name Bank core (GLW402-NNB. Percent abundance of species plotted against year. (See Appendix F for data.) [larger version]

Mollusca:

The lowest portion of the No Name core, from 153 to approximately 140 cm (early 1600s) has relatively high absolute abundance and diversity. However, based on the preservation of some of the mollusks, and observations while cutting the core, the samples from 153-146 cm contain some modern contamination, as well as mixing of fossil debris from the underlying limestone. This mixing contributes to the high molluscan diversity seen in these lowermost samples. Based on these findings, the samples from 153-146 cm were removed from consideration for all analyses.

The lowermost section is dominated by infaunal pelecypod species (Figure 16; Appendix G). The section from the late 1600s to the mid-1800s does not show any signs of contamination, and was dominated by epiphytal species (primarily Bittiolum varium) that dwell on either seagrass or other types of sub-aquatic vegetation. From approximately 1840-1950 mollusks were rare. The species present show a mix of infaunal and epiphytal species in the interval from 1840 to approximately 1920, indicating that vegetation was probably present, but sparse. Around 1940, the number of epiphytal species increased significantly (primarily Turbo castaneus and Bittiolum varium) while the number of infaunal species decreased. Abundance and diversity increased briefly between 1950 and 1970. The uppermost segment of the core has relatively abundant epiphytal species, low numbers of infaunal species, and low abundance and diversity.

Figure 16. Percent abundance of key molluscan taxa in No Name Core (GLW402-NNB). Number of molluscan individuals (absolute abundance) and faunal groups (a rough measure of diversity) are plotted on the right. (See Appendix G for data.) [larger version]

Ostracode Magnesium/Calcium Ratios

Results of the Mg/Ca analyses of ostracodes from No Name Bank core (GLW402 NNB) show interannual to multi-decadal Mg/Ca oscillations (Figure 17, Appendix H). The Mg/Ca is not expressed as absolute salinity in this report. That conversion awaits additional analyses on modern ostracodes and local environmental constraints. However, the shifts from high to low Mg/Ca typically indicate shifts from higher to lower salinities. Prior to the early 1900s, fluctuations in the Mg/Ca had a relatively high amplitude; this shifted to lower amplitude fluctuations during the remainder of the 20^th century. A large sustained shift towards higher ratios occurs from approximately 1850 to 1895.

Figure 17. Average Mg/Ca in mmol/mol (blue line and points), for five valves of Loxoconcha matagordensis from No Name Bank core (GLW402-NNB) and four valves from 1997 Featherbed Bank core (SEI297-FB1). Yellow line is three point moving average. (See appendices H and J for data). [larger version]