Persistence of an introduced mudflat community in South San Francisco Bay, California

Abstract

The benthic invertebrate community inhabiting the extensive and sedimentologically homogeneous mudflats of South San Francisco Bay has demonstrated a high degree of constancy in both species composition and relative abundance among species throughout 10 yr of observation. The community, composed predominantly of introduced species with opportunistic lifestyles, is dominated numerically by Gemma gernma, Ampelisca abdita, and Streblospio benedicti. The key to the persistent CO-occurrence of these species on the mudflats seems to lie in the combination of (1) the recurrence of minor disturbances of the mudflat habitat (e.g. sediment depositlon/erosion, inundation by low-salinity water) on time scales comparable to that of life cycles; (2) opportunistic life history strategies (rapid maturity, brooding of young, multiple generations each year, ease of local dispersal of both juveniles and adults) that permit continued colonization of the mudflat surface or rapid recolonization after disturbances. Only 1 of the 3 numerically-dominant species. A. abdita, displays an annual periodicity in abundance. S. benedicti and G. gemma, through broadly flexible reproductive strategies permitted in the mild San Francisco climate, can exhibit strong recruitment at any time between spring and autumn. The most extreme community changes, involving temporary reduction or elimination of normally dominant populations, occurred as a result of anomalous disturbances such as unusual buildup and decay of an algal mat during 1 summer and prolonged periods of unusually high freshwater inflow during 2 successive winters. The introduced opportunists routinely CO-occur at high densities. However, one of these, the tube-dwelling amphipod A. abdita, may control the abundance of the native mollusk Macoma balthica.

Synoptic measures of sediment contamination, toxicity and infaunal community composition (the Sediment Quality Triad) in San Francisco Bay

“…Nichols (1979Nichols ( , 1985 noted that natural perturbation~ easily mask possible anthropogenic effects. Nichols & Thompson (1985) could not, in 10 yr of observation of a mudflat community in the Bay, differentiate benthic community change due to other than catastrophic pollution events from natural variation.…”

Population ecology of Polydora ligni (Polychaeta: Spionidae). I. Seasonal variation in population characteristics and reproductive activity

“…(Chesney & Tenore 1985a, Gremare et al 1989), leading to varying population abundance patterns over the long-term (e.g. Nichols & Thompson 1985).…”

Comparison of patterns of spatial variation of microgastropods between 2 contrasting intertidal habitats

“…Each plot was sampled twice, 2 wk apart, in February 2000. Previous studies in soft-sediments (Nichols & Thompson 1985, Livingston 1987, Morrisey et al 1992b) and in mangroves (Underwood & Chapman 1999) have shown large variability in the abundance and composition of fauna over periods of days, weeks or months. Therefore, the replicate cores were sampled to test the hypothesis that the patterns of abundance were consistent over short periods of time and to identify the scale of any spatio-temporal interactions.…”