Effects of Non-Native Species on Two Life Stages of the Olympia Oyster, Ostrea Lurida, in the Elkhorn Slough Estuary
Marine and estuarine systems worldwide have been altered due to introductions of nonnative species. A common mode of non-native species transport is in ship ballast water that, when released, deposits larvae in new locations. Once established, non-native species compete for resources, reduce native species populations and alter ecosystem services. Some non-native species have been found to be ecosystem engineers, encouraging additional non-native species settlement. Many studies have looked at the competitive interaction between non-native and native species, but few have examined the possibility of a facilitative effect or how additional environmental stressors, such as desiccation, may modify species interactions. This study examined the effect of non-native species on two life stages (adult and juvenile) of the Olympia oyster, Ostrea lurida, a species in decline at two different tidal heights in a central California estuary. In separate experiments, adult and juvenile O. lurida were outplanted on settlement plates in Elkhorn Slough, and two treatments were maintained: (1) manual removal of non-natives every two weeks from half the plates or (2) control treatments that allowed non-native species to colonize and persist. Every two weeks, photographs were taken of each plate in order to calculate changes in percent cover of non-native species and to measure growth of O. lurida in response to the experimental treatment conditions. Results indicated that in the presence of the Australian tubeworm, Ficopomatus enigmaticus, and other non-native species, adult O. lurida exhibited an ~50% increase in area (cm2) on average across the plates. The presence of non-natives consistently resulted in a neutral or positive facilitative effect on oyster growth at two different life stages. The results of this study show that adult O. lurida are able to survive and even benefit from the presence of other species currently found in Elkhorn Slough both above and below MLLW. Juvenile O. lurida demonstrated high initial growth regardless of treatment, with increased growth below MLLW. With this increased understanding, there is much that is unknown about the long-term affect of introduced species on ecosystems and it is important to continue to study their impacts. In particular, the effect of nonnatives on oyster recruitment requires further investigation because the earliest life stages are most likely to be adversely affects by a rapid growing non-native that can monopolize available bare space for settlement. If O. lurida recruitment and juvenile survivorship is further reduced, the local Elkhorn Slough population may be lost.
Deep-sea sedimentary processes in the Argentine Basin revealed by 3.5 kHz echograms
by Adam Klaus, "A thesis presented to the faculty of Moss Landing Marine Laboratories.", Thesis (M.S.) -- San Jose State University, 1986., The regional distribution of eleven 3.5 kHz seismic echo types reveals the areal extent of deep-sea sedimentary processes in the Argentine Basin. A correlation between echo character and the relative abundance of sand and silt layers in piston cores allows the pattern of coarse terrigenous sediment dispersal to be identified. This relationship indicates that the majority of coarse sediment bypasses the continental slope and rise. This coarse sediment is deposited on the proximal abyssal plain with progressively lower amounts basinward, and lower abundances on the shallow margin. Scarps, irregular and blocky hyperbolic zones, and transparent layers along the Argentine continental margin have echo characteristics similar to those of documented gravity-controlled mass flow deposits. A large area of mass flow deposits, covering at least 5x10^4 km^2, is located on the continental rise and adjacent abyssal plain east of the Rio de la Plata. A field of migrating mud waves, approximately 1.0x10^6 km^2 in extent, occurs on the sediment drifts of the central basin. Mud waves range in amplitude up to 137m and average 26m, and have wavelengths of about 3 to 7 km. The presence of migrating mud waves suggests widespread current-controlled sedimentation. It is inferred, however, that these mud waves form in areas of relatively weak flow in the interior basin because the benthic circulation is characterized by strong Antarctic Bottom Water (AABW) flow along the western and southern margins and by weak flow in the central basin. A variety of hyperbolic echoes on the abyssal plain adjacent to the Argentine continental margin, south of the Rio Grande Rise, and in the Georgia Basin, are interpreted as current-produced erosional / depositional bedforms, although downslope sedimentary processes may also produce similar hyperbolic echoes. The distribution of bedforms inferred from seismic echo character suggests that sediment is supplied to the basin principally by gravity-controlled mass flows. Sediment entrained in AABW is a secondary source. Gravity-controlled mass flows are predominantly limited to the Argentine continental margin. Sediment from both sources is winnowed by strong AABW flow along the Argentine continental rise. The fine-grained chaff is transported to the central basin where it is deposited as migrating mud waves in regions of relatively weaker bottom current.