Natural Physical Disturbances and Communities of Marine Soft Bottoms

174

In the large archipelago area of the northern Baltic Sea, increasing occurrences of drifting benthic macroalgae have been recorded in the subtidal zone. Their role as a structuring factor on the zoobenthic community has been altered from inducing occasional small-scale disturbances to inducing large-scale mortality of macrobenthic populations. A controlled field experiment was conducted on a sandy bottom in order to test for temporal responses of benthlc invertebrate populations to severe stress imposed by the algal mats. Algae corresponding to amounts recorded in the field were enclosed In netbags and attached to the bottom. Population abundance of the zoobenthic species under algae were compared w~t h control plots for 5 ivk with weekly sanipl~ng. Mass~ve die-offs of benthic populatlons were recorded in both the experiment and under natural occurrences of drift algal mats. The community dominants in abundance (mudsnails Hydrobia spp.) and biomass (bivalve Macoma balthica) exhibited strong population reductions after 9 d of algal stress. Within 5 wk, populat~on crashes were recorded for the sedentary po1ychaett.s Manayunkia aestuanna and Pygosplo elegans, ivh~le populations of the errant polychaete Nereis diverslcolor and tubificid oligochaetes remained stable under the algal mats. Initial short-term recovery after the algae were removed was rapid and do~nlnated by Hydrobia spp. The strong negative effects on key species such as M. balthica may have severe effects on entire food-web dynamics in Baltic coastal ecosystems.

Section: Population Responses To Algal Stressmentioning

confidence: 89%

“…Every species in the food-web will exhibit a broad niche. time in control and under algae adapted to grow and reproduce in a single patch (Thistle 1981). This strategy is probable for the oligochaete species in this study.…”

Section: Population Responses To Algal Stressmentioning

confidence: 99%

Population responses of coastal zoobenthos to stress induced by drifting algal mats

Norkko¹,

Bonsdorff²

1996

174

“…Disturbance may prevent a community from reaching competitive equilibrium (Connell 1978), provide extra resources (Thistle 1981) and, at intermediate intensities, increase diversity (Huston 1979). Studies of disturbance events in marine communities have concentrated on rocky shore and fine sediment habitats; little information is available on the role of disturbance in structuring the communities of mobile gravel-sand sediments.…”

Section: Introductionmentioning

confidence: 99%

Spatial heterogeneity in subtidal gravel generated by the pit-digging activities of Cancer pagurus

Thrush¹

1986

In a coarse gravelly substratum exposed to high current velocities the crab Cancer pagurus was observed to dig pits, approximately 30 cm in diameter and 10 cm deep. Experiments were conducted to identify macrobenthic recolonization processes and differences in abundance between pits and unmanipulated areas. Surveys of the abundance of recently dug pits indicate a frequency of approximately 9 pits 100 mA2. Analysis of species abundances in artificial pits at various times after construction revealed colonizing species to be highly variable. In a second experiment statistically significant differences in the abundances of various species were found between artificial pits and adjacent unmanipulated sediment, but trends in the data were not consistent between experiments. Generally, macrofaunal recolonization processes were haphazard. These results are contrasted with initial recolonization processes in soft sediments. The mobllity and large particle size of the sediment are considered to be important in precluding predictable recoloruzation patterns.

“…McCall 1977) and released resources (e.g. Thistle 1981, VanBlaricom 1982). The opportunists, subject to high mortalities (Grassle & Grassle 1974), are subsequently displaced in a successional process that leads to the return of resident species (McCall 1977(McCall , 1978.…”

Section: Introductionmentioning

confidence: 99%

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

Nichols¹,

Thompson²

1985

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.