C

5,000

4,000

CAC Pit

Old Orchard Shoal

4,000

CAC Pit

Old Orchard Shoal

Figure 18.4. Seasonal variations in abundance at two locations in Lower Bay. Data from Cerrato and Scheier (1984).

Jan79 Jul79 Jan80 Jul80 Jan81 Jul81 Jan82 Jul82 Jan83 Jul83 Jan84

Sampling Date

Figure 18.4. Seasonal variations in abundance at two locations in Lower Bay. Data from Cerrato and Scheier (1984).

to be comparable, suggesting that the differences in taxonomy between surveys did not have a major influence on the outcome of the Mantel tests.

Analysis of spatial and faunal associations in data sets collected during the same season, but one to three years apart, indicated considerable annual variability in the benthic community. Correlations from Mantel tests were significant but weaker than seasonal correlations (Tables 18.7 and 18.8), evenif the extremely low correlations for the spatial comparison between 1957 and 1960 are excluded as possible artifacts of their small sample size (n = 10). Diaz and Boesch (1979) did not feel that changes in the benthic community during 1957-60 were associated with initiation of sewage treatment in early 1958. So the low annual correlations involving the 1957 and 1960 data cannot be explained by faunal succession.

Comparing the benthos on a decadal time scale, the abundances of many species increased substantially between the early regional studies (195760 and 1973-74) and the later studies (1986-87 and 1994-95) (Table 18.3 and Fig. 18.3). No species that was consistently abundant in 1957-60 or 197374 was rare in 1986-87 or 1994-95. Species both from Lower Bay and those in Raritan and Sandy Hook Bays increased, indicating that the pattern was bay wide. It is also evident from Table 18.3 that fewer species were present during 1957-60 and 1973-74 compared to later surveys. This is especially obvious for amphipod and other crustacean groups. These observations cannot be explained by seasonal or sieve size differences, since methods can be matched for any comparison involving these earlier studies and the 1986-87 study. High abundances of some species such as Stre-blospio benedicti and Ampelisca abdita in October 1994 or June 1995 could, however, reflect sieve size differences.

Abundances of a number of species were especially different in 1973-74 compared to other sampling periods. Numerical dominants such as the amphipodsAmpeliscaspp. and Unciolaserrata, the gastropod Ilyanassa obsoleta, and the bivalve Mya arenaria were conspicuously low during January 1973 (Table 18.3). The almost complete absence of these species persisted throughout the more limited 1973-74 sampling in Sandy Hook Bay (see Table 18.3). Although less obvious, several species, including the polychaetes Nephtys incisa, Polydora ligni, Spiofilicornis, Streblospio benedicti,

Figure 18.5. Seasonal changes, indicated clockwise, in the distribution of high and low abundance areas in the Lower Bay Complex. The contour line delineates geometric mean abundance for all four sampling periods (1,778 individuals per m2). The darker area is above and the lighter area is below the mean. Data from Cerrato et al. (1989).

Figure 18.5. Seasonal changes, indicated clockwise, in the distribution of high and low abundance areas in the Lower Bay Complex. The contour line delineates geometric mean abundance for all four sampling periods (1,778 individuals per m2). The darker area is above and the lighter area is below the mean. Data from Cerrato et al. (1989).

the gastropod Ritaxis punctostriatus, and the bivalve Mulinia lateralis, actually increased during this same period. Very often these species had high abundances during only one or two seasons (e.g., Polydora ligni in July 1973 and Streblospio benedicti in July and October 1973).

Most investigators have concluded that the ben-thic community present during the January 1973 regional study was different than other periods (McGrath, 1974; Berg and Levinton, 1984; Diaz and Boesch, 1979). McGrath (1974), based on a preliminary analysis of only forty samples, characterized the benthic community in 1973-74 as "impoverished" when compared to other regions, although reanalysis by Steimle and Caracciolo-Ward, (1989) using the entire data set showed that the fauna in 1973-74 was somewhat more abundant and diverse than McGrath initially suggested. Diaz and Boesch (1979) incomparing Dean's 195760 data with McGrath's 1973-74 survey thought that the differences for dominants such as Ampelisca abdita, Mya arenaria, and Ilyanassa obsoleta could not be due to differences in sieve size (1.5 mm for Dean and 1.0 mm for McGrath) since the finer mesh sieve in McGrath's study would tend to retain more, not fewer, individuals. Despite other methodological differences, they believed the 1973-74 fauna densities were "extraordinarily low." Comparison of the July 1986 1.0 and 1.5 mm sieved samples in Cerrato etal. (1989) suggests that except for several small species, most differences in retention between 1.0 and 1.5 mm screens were

Table 18.7.

Mantel tests of faunal associations (inverse analysis)

Was this article helpful?

0 0

Post a comment