Vertical Migration and Mortality of Marine Benthos in Dredged Material: A Synthesis

Abstract

This account describes the comparative response of four species of benthic invertebrates t o burial in t,erms of vertical migration and mortality, and provides a synthesis of studies and recommendations upon which t o assess future impacts. The species featured were the bivalve Mercennrin mercennrin, the amphipod crustacean Parahnustorius longirnerus, and the polychactes Scoloplos fragilis and Nereis suceinea.There wns evidence of synergistic effects on burrowing activity and mortality with changes in timc of burial. sediment depth, sediment type and temperature. I n sediment. with silt-clay. h'.succiiten was the most resistant species followed by ,+I. mercenarin, 8. fragilis and P. longimerus.I n sediment without silt-clay the order of percent mortality was reversed. Studies of surface water chemistry and sediment geochemistry showed that dissolved oxygen decreased significantly and ammonia and sulfide increased significantly between the surface and below 2.0 cm within a 15-day period. Based on these results and physiological tolerances from the 1 itrraturc it was concluded that N . niercenaria and N . euccinea would be relatively resistant to chemical effects of spoil disposal, whereas 8. frngi2i.y and P. longirnerus would be less resistant t o such effects.Yert ical migration of benthic invertebrates through dredge disposal can be a viable mcchanism of recolonization under certain conditions. Some effects of burial of benthos can be predicted hnsed on morphology, behavior and physiology. These biological features were discussed with exnniplea dealing with moll~iscs. crustaceans, and polychaetes. Finally, recommendations were made concerning the type of st,ndies t o provide additional data t o aid management agencies in clecision mttking about future dredging and disposal practices.

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“…T he features of climate formation, atmospheric-synoptic processes, commotions and currents of the Caspian Sea, are given according to the information, described in numerous scientific publications and reference books, [1][2][3][4][5][6][7][8][9][10][11] and also according to the Dagestan Center for Hydrometeorology and Environmental Monitoring.…”

“…[1][2][3][4][5][6][7][8][9][10][11] The Caspian Sea is located in relatively low latitudes that resulted in a large influx of solar energy to it. The annual amount of radiation balance over the Caspian Sea is about 3700 MJ/m 2 per year.…”

Experiments on the survival of six brackish macro-invertebrates from the Baltic Sea after dredged spoil coverage and its implications for the field

“…Maurer et al 1986, Essink 1999. The "fatal depth" sensu Essink (1999), describes the limit for the different species to survive burial by burrowing to the new sediment surface.…”

“…The fatal depth can range from a few millimetres to almost one metre (e.g. Maurer et al 1986, Bijkerk 1988, c.f. Essink 1999, Schratzberger et al 2000 and depends largely on the individual's age, size, motility, and its tolerance to oxygen deficiency and sulphide concentrations.…”

“…Until now only a few results from laboratory experiments testing the escape behaviour of marine invertebrates have been published (e.g. Kranz 1974, Maurer et al 1986, Chandrasekara and Frid 1998, Bijkerk 1988, c.f. Essink 1999, Hinchey et al 2006 and in situ (Nichols et al 1978 investigations are even less well documented.…”