Patterns in the cumulative increase in species from foraminiferal time-series
Abstract
Time-series studies are essential for defining short and long-term variability in environments and without such records it is difficult to make well-founded judgments about faunal or environmental change. Datasets of intertidal benthic foraminifera from the Exe and Hamble estuaries, England, intertidal zone of Bahrain, Arabian Gulf, and subtidal Lim channel, Adriatic, have been analysed to provide information on patterns of species richness. Living assemblages comprise one or two dominant species plus two or three subsidiary species and a variable number of ephemeral rare species, the latter being the main control of species richness. The cumulative increase in species from month to month follows a pattern which approximates a log series. None of the datasets follows a broken stick or log normal pattern. The final plateau in cumulative species increase is reached in periods ranging from 5–10 months (Lim channel) to 22–23 months (estuaries). The cumulative maximum number of species gives an estimate of the carrying capacity for species, i.e. the maximum number of species for the environment. The species present in each area represent the species pool related to that environment (e.g. estuarine intertidal zone) together with introductions from a species pool in a different environment nearby (e.g. inner shelf). The time-averaged accumulation of successive live assemblages that form the dead assemblage is not identical with the cumulative total. Some live taxa are unrepresented in the dead assemblage either through taphonomic loss or the introduction of new species that have not yet left a dead record. In addition, the Exe estuary dead assemblage includes a large number of dead tests transported in from the adjacent shelf. It does not conform to any of the three possible patterns. At present the few time-series studies of benthic foraminifera that are available are either intertidal or very shallow water. There remains a need for further studies in a wide range of environments in order to understand more fully the faunal response to dynamic change.<br/Similar works
This paper was published in Southampton (e-Prints Soton).
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