projects > ecosystem history: florida bay and the southwest coast > abstract
Historical Trends in Epiphytal Ostracodes from Florida Bay: Implications for Seagrass and Macro-Benthic Algal Variability
We investigated living and fossil epiphytal ostracodes in Florida Bay to determine historical trends in seagrass and algal habitats during the past century. Living assemblages collected in February and July, 1998 from sites throughout Florida Bay revealed that (1) Loxoconcha matagordensis and Malzella floridana are the dominant epiphytal species living on Thalassia; (2) Xestoleberis spp. is most abundant living on macro-benthic algae such as Chondria; and (3) Peratocytheridea setipunctata prefers sandy substrates and is abundant on Halodule.
Temporal trends in epiphytal ostracodes were reconstructed from radiometrically-dated sediment cores from Whipray Basin, Russell Bank, Bob Allen Bank, Pass and Park Keys, the mouth of Taylor Creek and Manatee Bay. These data indicate that there have been frequent changes in the relative frequencies of L. matagordensis, M. floridana, and Xestoleberis over the past century. Prior to the mid-20th century, subaquatic (SAV) ostracode species were relatively rare throughout large parts of central and northeastern Florida Bay. Ostracode assemblages living between 1900 and 1940 were characterized by abundant (10->60%) Peratocytheridea setipunctata. This was a time when Thalassia and macro-benthic algal species were rare to absent at most sites. From about 1930 until 1950, P. setipunctata abundance declined while L. matagordensis and Xestoleberis increased progressively from 0 - 10 % to > 25 - 40 %, depending on the site. This long-term faunal shift in central Florida Bay suggests that, on average, there has been a much greater abundance and/or density of subaquatic vegetation over the past 50 years compared to the prior half century. Since 1950, central and northeastern Florida Bay has experienced high amplitude swings in the proportion of seagrass and algal-dwelling species. Some of these oscillations, such as the decline in L. matagordensis, Xestoleberis, and M. floridana during the 1970s and early 80s, appear to be synchronous across the study area and may represent large-scale dieoffs.
The most important issue regarding the interpretation of these faunal events is whether they represent a local trend at a single mudbank or whether they signify synchronous, large-scale events that characterized the entire region. If these do indeed signify regional changes in Florida Bay benthic habitats, then what is (are) their cause(s)? Both long-term decline in P. setipunctata and the coincident rise in L. matagordensis, M. floridana and Xestoleberis spp. during the mid-20th century and the decline in SAV-dwelling species during the 1970s and 1980s are most likely regional events based on the current available data. Among their many potential causes, a combination of human alteration of the hydrology and natural climatological factors seems to be the most reasonable explanation for observed trends in Florida Bay vegetation. We will discuss the idea that the influence of El Nino and decadal-scale climatological processes on Florida Bay habitats may have been altered, perhaps amplified, by anthropogenic diversion of freshwater inflow. The net result is that since the mid- 20th century, Florida Bay has been "hypersensitive" to climatic and hydrological variability.
The compelling paleoecological evidence that central Florida Bay has experienced oscillations in seagrass and macro-benthic algal habitats, including anomalously high variability during the past 30 years, is also germane to efforts to restore the bay to a natural state. Seagrass and macro-benthic algal habitats were probably very sparse in central and northeastern Florida Bay during the 19th and early 20th centuries, at least relative to the 1950s and 1960s, when epiphytal species flourished. Parts of Florida Bay also experienced diminished amounts of SAV during the 1970s and 1980s. Thus, how one defines the "natural state" of Florida Bay and the desired area of seagrass cover will depend on which time period is selected as the restoration target.
(This abstract was taken from "Programs and Abstracts - 1999 Florida Bay and Adjacent Marine Systems Science Conference". (PDF, 1 MB))
|U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology
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Last updated: 15 January, 2013 @ 12:43 PM (KP)