Estuarine and Coastal Marine Science最新文献

Comparisons of egg size and number are made for 10 epifaunal and 16 infaunal species of shallow-water marine or estuarine gammaridean amphipods from the north-western Atlantic. Epifaunal species have significantly more, smaller eggs than infaunal species of the same size and geographic region. Strong latitudinal and seasonal effects are also evident. For several species, egg size increases and egg number decreases in populations at more northern latitudes and in populations breeding during colder seasons. The few exceptions to the above patterns may reflect unique differences in the biology of particular species. A hypothesis is proposed that adult mortality risk is correlated positively with egg number and inversely with egg size.

Zonation of algae and invertebrates was examined on rocky shores in the Severn estuary from 1975 to 1978. These shores were characterised by an absence of macro-algae from MLWS and below. Some littoral algae showed reductions in abundance during the study. In particular, Ascophyllum nodosum and Fucus serratus almost disappeared from the mid shore at one site after 1976, and no significant recolonization had occurred by 1979. Animal species in general showed predictable and constant zonation patterns, but Littorina rudis, Patella vulgata and Elminius modestus all exhibited decreased upper vertical limits in the upper reaches of the estuary.

Three approaches were taken to interpret the zonation patterns and their changes. (i) Exposure to wave action was estimated. Decreasing exposure levels may account for the decline in upper vertical limits of species in the upper estuary. (ii) A survey of silt, salinity and temperature was carried out over complete tidal cycles. High silt concentrations may partially explain the absence of macro-algae below MLWS. (iii) Preliminary experiments compared the effects of grazers in the estuary with those in fully marine conditions. These experiments point to some of the factors which are responsible for the lack of algal recolonization on the shore from which the dominant fucoids disappeared after 1976, but the situation is complex and involves algal reproductive biology as well as grazer activity.

In order to evaluate the influence of the ocean dumping of sewage sludge upon the organic carbon fraction of sediments of the New York Bight, a study of carbon isotopic variations in surface sediments from the area has been completed. On the basis of our ¹³C/¹²C measurements, it appears that: (1) sewage is depleted in ¹³C as compared to average marine organic sedimentary carbon, and (2) δ¹³C values from sediments of the New York Bight show systematic variations which are a direct consequence of the sludge disposal. Based on assumptions regarding inputs of sedimentary carbon to the sea floor in this area, we have modeled these ¹³C/¹²C variations in terms of progressive dilution of normal marine carbon with carbon derived from the ocean dumping of wastewater sludges. The isotopic composition of carbon in sediments from the New York Bight may serve as a quantitative tracer of sewage sludge components.

The interaction of ⁶⁵Zn, ¹⁰⁹Cd and ²¹⁰Pb−²¹⁰Bi with humic acid isolated from marine sediment was investigated by high voltage paper electrophoresis in sea water and 0·55 m NaCl solutions. The experiments were performed in 100, 30 and 10% seawater to simulate also the estuarine conditions. The concentration of humic acid was varied from 3 to 300 mg l⁻¹. The electrophoretic mobility of the radionuclides was measured as function of the concentration of humic acid in the various systems and on aging of these systems from 0 to 7 days. Without addition of humic acid to seawater ¹⁰⁹Cd behaves as a cation, ⁶⁵Zn and ²¹⁰Pb give one cationic and a second nonmobile zone. In 0·55 m NaCl both ⁶⁵Zn and ²¹⁰Pb, give only one cationic zone. By addition of humic acid the radionuclides partly changed their electrophoretic mobility to anionic values and the zone at the starting point became more pronounced than in seawater without addition of humic acid. In general the results obtained confirm that the amounts of humic material dissolved in the open sea are too small to contribute significantly to the chelation of the investigated trace metals while in estuarine waters their contribution to trace metal chelation can play a role.