According to Jaramillo et al. Thus, groups of sampling strata or a single stratum that were separated by the cluster analyses because the low densities of certain species were not considered as a faunistic zone per se. Species with a sporadic frequency of occurrence e.
The faunistic zones were identified by letters corresponding to each beach N for Navegantes, B for Brava and T for Taquaras , and by numbers indicating their sequential location from the dunes to the sea. In order to identify the abiotic factors responsible for the spatial variability of the mean zonation patterns of the benthic macrofauna throughout the study area between beaches , Canonical Correspondence Analyses CCA were carried out for the three beaches together, using a biotic matrix constructed based on the mean densities of the species for each sampling station.
In the construction of the abiotic matrix, the following environmental factors were considered for each sampling station: mean grain size and sorting, moisture content of the sediment and sediment reworking. The biotic data were transformed by the square root. Environmental Characterization. The beaches studied were characterized by distinct cross-shore gradients of mean grain size, water table depth, water content of sediment and sediment reworking. The accretion-erosion dynamics or sediment reworking increased across the dissipative-reflective continuum and tended to be concentrated at lower levels of the beach profile in this latter state Fig.
The mean grain size increased from the dissipative to the reflective extreme, and tended to increase downshore on the three beaches studied. All the beaches were characterized by moderately well sorted to well sorted sands, and sorting tended to decrease towards the sea Table 1. The different sediment and morphological features of the beaches studied have led to distinct characteristics in relation to water table depth and moisture content of the sediment.
On Navegantes, due to the gentler slope profile, a high water table was present, and was less than 20 cm below the surface of the sediment throughout most of the beach profile.
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By contrast, a deeper water table was observed for Taquaras due to its steeper slope profile. On this beach, the mean water table depth increased sharply from the sea to the dunes, and was more than cm deep along most of the profile. Brava beach presented intermediate depths for this variable Table 1. On the dissipative beach, high moisture levels were observed along most of the profile due to its fine sediment and high-water table. On the reflective beach, high moisture levels were observed only in the swash zone as a result of the coarser sediment and deeper water table Table 1.
Mean Zonation of Benthic Macrofauna. The mean number of faunistic zones did not vary across th e morphodynamic gradient, with a total of 3 zones being identified for each beach. However, the mean extension and specific composition of these zones varied throughout the study area Figs 4 to 6.
On Navegantes, the mean zonation pattern was characterized by the existence of overlapping in the distribution of species, and the occurrence of a single species in more than one faunistic zone Fig. The second zone N2 was located between the mean drift line and the mean upper swash zone limit, and was characterized by the presence of Excirolana armata, Euzonus furciferus, Scolelepis sp.
The lower levels of the beach profile, corresponding to the swash zone, constituted the third faunistic zone N3 and was characterized by Emerita brasiliensis, Lepidopa richmondi, Bowmaniella brasiliensis, Puelche sp. The highest number of species and the greatest mean extension were observed for the lower zone N3 of Navegantes beach. By contrast, the zone formed by O. At Brava beach, the stations located above the upper mean swash zone limit constitute the first faunistic zone B1.
It was characterized by the presence of O. The second faunistic zone B2 was characterized by E. The cluster analysis revealed a third faunistic zone B3 , located below the mean lower swash zone limit and characterized by the isopod M. The group formed by O.
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On Taquaras, the first faunistic zone T1 was located far above the mean drift line. The second faunistic zone T2 , was located between the mean upper swash zone limit and the mean drift line. It should be emphasized that although the cluster analysis identified the formation of a group with station 8 Fig. The faunistic zone comprising O. Relationship Between Zonation and Environmental Factors. The moisture content of the sediment, grain size and sediment reworking were the main environmental factors responsible for the alterations observed for the zonation patterns of the species throughout the study area, and were selected by the Monte Carlo test.
Of the environmental variables considered in this analysis, only the sorting of sediment was not selected Table 2. For the three beaches, the sampling stations on the lower levels of the beach profile were gradually replaced, along Axis 1, by the stations on the upper levels, showing a close relationship with the moisture gradient Fig.
Likewise, species associated with reduced moisture levels occurred in the right quadrant of the diagram, while those related to high moisture levels occurred in the left sector of the graph, following the moisture gradient represented by Axis 1 Fig. The Canonical Correspondence Analysis also revealed that the main differences in zonation throughout the study area were related to the lower beach levels. A clear separation was observed between the sampling stations of the lower levels of Taquaras, Brava and, in particular, Navegantes.
On the other hand, stations on the higher levels of the three beaches were mainly clustered on the right of Axis 1 Fig. On Navegantes, the stations on the lower beach levels were related to a higher number of species, higher moisture levels, reduced sediment reworking and fine sediment. The lower levels of the Brava and Taquaras beaches were associated with lower moisture levels, larger grain sizes, and higher sediment reworking Figs 7 and 8. Furthermore, they harbored a lower number of species.
The cluster of stations on the upper levels of the three beaches in the lower right sector of the graph Fig. Consistent differences in the average zonation pattern of the benthic macrofauna were observed across the morphodynamic spectrum on exposed sandy beaches of Santa Catarina, essentially differing in relation to the composition and extension of the faunistic zones.
Considering that latitudinal variations and exposure to wave action do not constituted factors of variability in this study, the results obtained indicate that the cross-shore environmental gradients associated with the morphodynamic spectrum induced the different zonation patterns observed throughout the study area.
According to the Canonical Correspondence Analysis, these differences mainly resulted from distinctive cross-shore gradients of moisture level, sediment reworking and grain size that exists across the morphodynamic spectrum. The faunistic zone characterized by the crustaceans O. In Taquaras, the extension of the faunistic zone corresponding to the mean swash zone, comprised of E.
These same species formed two distinct zones on Brava beach, corresponding to the mean swash zone E. On Navegantes, the extension of the faunistic zone corresponding to the mean swash zone E. Moreover, on this beach, the greater extension of the high moisture zone also led to the occurrence of a biological zone comprised of E. In other words, although certain species characterized the upper levels O. The zone formed by species which occur preferentially in places characterized by low moisture levels increased in extension to the reflective extreme, following the increase in extension of the zones with low moisture levels.
lokonfpenpecom.ga These results support the observations of Jaramillo et al. In a review of general zonation schemes proposed for sandy beach macrobenthos, McLachlan and Jaramillo conclude that faunistic zones tend to be narrower and clearest at the top of the shore and become increasingly blurred and wide moving downshore. The results obtained in the present study demonstrate that this suggestion does not apply to the entire morphodynamic spectrum. At the reflective extreme, a greater extension was observed for the faunistic zone located at the top of the shore.
Likewise, all the biological zones were clearest in this beach type than in the dissipative state, where a greater overlapping between zones was observed, particularly at the lower levels of the beach profile. The increasing overlapping between biological zones observed towards the dissipative extreme appears to be the result of more gradual horizontal changes in moisture levels across the beach profile. In Taquaras, humidity is not retained by the sediment during low tide because of the presence of coarse sand and the deep water table.
On this beach, high moisture levels occur only in the swash zone, leading to marked discontinuities in this parameter throughout the profile and, as a result, in the establishment of clearly and sharply defined faunistic zones at this extreme. Librarian Administrator Sign In.
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These changes are important as they affect society in a range of different ways, some of which are illustrated in Figure 2, where the time scale represents the duration between events, not the duration of an event. Log in. Page Discussion. Read View source View history. Jump to: navigation , search. Description Toe scour — the short term and relatively small scale removal of sediment from the toe i. This often occurs and recovers completely during the course of a single tide if in the intertidal zone, at least.