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

Abstract

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.

Polychaete assemblages as indicators of habitat recovery in a temperate estuary under eutrophication

“…In the absence of macroalgal blooms and anoxic conditions, these species could grow to adult size, as seen for Hediste diversicolor. This species is also tolerant to hypoxia, anoxia and is commonly found under algal mats (Pearson and Rosenberg, 1978;Norkko and Bonsdorff, 1996), but unlike C. capitata, seems able to take advantage of less stressful conditions (Cardoso et al, 2004b), possibly because of its better competitive ability and its capacity to feed as an omnivore, predator, suspension feeder and deposit feeder (Norkko et al, 2000). In contrast to previous studies (e.g.…”

Green and golden seaweed tides on the rise

“…Tonnes of seaweed smothering the shoreline deter tourists and the dense, drifting seaweeds can prevent swimmers and small boats from accessing the sea (Fig. 1); if not removed in time, the algae can turn into a stinking morass, which can produce toxic hydrogen sulphide (H 2 S) from its anoxic interior 1,3 , and have major detrimental effects on the affected coastal ecosystems 1,2,[4][5][6] . Surprisingly, the extensive seaweed tides are mainly the result of only a few genera of macroalgae.…”

Small-scale disturbance and increased nutrients as influences on intertidal macrobenthic assemblages: experimental burial of wrack in different intertidal environments

“…In addition to the frequency, intensity and scale of disturbance, the responses of populations are determined by their inertia, resilience and stability (e.g. Underwood 1989, Norkko & Bonsdorff 1996a,b, Baldwin & Mendelssohn 1998.…”