. Bulletin. Science; Natural history; Natural history. 1971 ASIATIC CLAM INVASION IN CALII ohnia </7. £ -5 Depth intervals in meters Figure 6. Mean particle diameter of El Capitan sedi- ments collected from transects I, 2, and 3. anytime during 1966. The clams were still most abundant between 4 and 14 m. This was probably a result of a time lag in their dispersal, rather than a preference for the sedimental conditions, since they were scarce in this interval during 1967. How- ever, sediment conditions were quite varied at T-l. The shallow depths were predominately sand and gravel (Fig. 6),
. Bulletin. Science; Natural history; Natural history. 1971 ASIATIC CLAM INVASION IN CALII ohnia </7. £ -5 Depth intervals in meters Figure 6. Mean particle diameter of El Capitan sedi- ments collected from transects I, 2, and 3. anytime during 1966. The clams were still most abundant between 4 and 14 m. This was probably a result of a time lag in their dispersal, rather than a preference for the sedimental conditions, since they were scarce in this interval during 1967. How- ever, sediment conditions were quite varied at T-l. The shallow depths were predominately sand and gravel (Fig. 6), whereas, the deeper areas were pre- dominately fine colloidal matter with a high organic content (Table 2). Most Corbicula were again restricted to shallow depths by stratification during 1967, but about 30% were found within the hypolimnion. Hypolimnetic conditions during 1967 were not as severe as during 1964. but oxygen concentrations approached zero by September 1967. While some Corbicula tolerated the low hypolimnion oxygen concentrations and associated stagnation, many may have perished after stratification developed. This could have con- tributed to the great population decrease between January 1966 and August 1967. The effect of reservoir volume changes on Cor- bicula are unknown. Increased volume increases the total bottom area available to the clams. This new area is predominately sand and gravel covered by sparse terrestrial vegetation. Decreased water volumes concentrate the clams and creates less desirable conditions. The rapid drawdowns during 1966 and 1967 may also have contributed to the high mortalities, but Sinclair and Isom (1963) do not recommend water level change for controlling Corbicula. Several factors undoubtedly influenced the clam spatial distribution between transects. Foremost among these considerations are: (1) sediment par- ticle size and i ompi isition (2) n\ paid rn ( u location ol initial introdui tion i ransects l and 2 have similai mean par
Size: 1835px × 1361px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, booksubjectnaturalhistory, booksubjectscience
