Population Dynamics of Nassarius reticulatus (Gastropoda, Prosobranchia) in Gullmar Fjord, Sweden
1980; Inter-Research; Volume: 3; Linguagem: Inglês
10.3354/meps003051
ISSN1616-1599
Autores Tópico(s)Marine and fisheries research
ResumoThe population dynamics of Nassarius reticulatus (L.) (Gastropoda, Prosobranchia) was investigated in Gullmar Fjord on the Swedish west coast from 1973 to 1979.A fairly well-defined population on a shallow, sandy bottom in Kvarnbukten Bay (36 000 m*) was intensively studied.Settling of veliger larvae was very irregular and normally only took place where the organic content of the substrate was fairly high, i. e. in deeper water.The snails, especially small ones ( S 15 mm), were greatly attracted to detritus-rich substrates, whereas larger ones congregated on canion.The snails in Kvarnbukten Bay spent their first 3 years in the settling area living mainly on detritus.The change in diet may be a factor influencing the intraspecific competition between small and large snails.When nearly 4 years old (ca.15 mm) they become sexually mature.From then on most of them participated in the yearly migrations: in April and May from winter quarters in deeper water (1-5 m depth) to the shallow part of the bay (0-1 m) where they spent the summer, and then back again in September to December.Growth rate was fast during the first 3 years with a length increment of about 5.5 mm year-', but then decreased considerably, also becoming individually very variable.Maximum age was about 15 years.Fecundity was high: ca.6000 eggs female-' year-'; females spawned every year.Mortality rate during the planktonic phase was high but there were few predators on larger snails, parasitism in shallow water probably being the most important cause of losses at this age.Temperature was one of the main proximate factors affecting locomotory activity, migration, spawning and growth.Threshold temperatures for various activities were narrowly defined.Irregular settling of larvae and hence sporadic recruitment to the shallow parts of the bays seemed to be the main reason for population fluctuations in different bays.Advantages of inshore migration (temperature and availability of food) seemed to balance disadvantages (mainly parasitism) and this may explain the dimorphism in migratory habits.As a whole these snails show several special adaptations to the varying environment in this non-tidal, soft bottom littoral.Flg. 1 .Map of Kvarnbukten Bay.HWL: high-water level (= 0.25 m above MWL); MWL: mean-water level; LWL: low-water level (= 0 25 m below MWL).Inset: stratification for sampling purposes
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