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.
Predicting stranding patterns of live oiled seabirds, carcass deposition, and carcass retention in Monterey Bay
Beach surveys for live and dead beachcast birds are an economical and practical way of determining seabird population health. Using long-term surveys creates a baseline mortality profile by determining the areas and time of year birds are likely to strand as well as what oceanographic factors cause the deposition and retention of seabird carcasses on beaches. I hypothesized that 1) seabird initial carcass deposition in Monterey Bay would be greater in the southern part of the bay than in the northern part due to oceanographic factors, and 2) seabird carcass retention (how long carcasses stayed on the beach) would be greater in the North Bay than the South Bay due to beach profile characteristics. I utilized BeachCOMBERS beach survey data from 2005 to 2012 to determine patterns of seabird carcass deposition and retention in Monterey Bay and obtained wind speed, wind direction, wave height, tide height, and wave height + tide height (swell impact) from buoys. A backwards multiple regression on the averaged yearly deposition (birds km-1) as affected by oceanographic factors in Monterey yielded significant effects only in the year 2011, with wind speed being the main factor. A two-way ANOVA on the percent of carcasses retained from the previous month with month and zone as independent factors yielded significant effects of both, although location (zone) had a more significant effect. Variability in deposition and retention highlighted the need for continued long-term surveys to accurately determine seabird presence and mortality in Monterey Bay.
Distribution, abundance, habitat use, and respiration patterns of harbor porpoise (Phocoena phocoena) off the northern San Juan Islands, Washington
Boat and shore-based surveys were conducted from June to August 1991 and June to October 1992 to determine harbor porpoise distribution, density, abundance, and habitat use off the northern San Juan Islands, Washington. An estimated 299 harbor porpoise (1.26 harbor porpoise/km2) occurred patchily within 237 km2. Harbor porpoise occurred in water of 10.1° to 16.3°, were generally observed in expected depths>125 m and over shallow slopes (<10%), and less than expected in depths <75 m. Abundance of harbor porpoise in relation to deep waters, flood tides, and tide rips off Point Doughty, Orcas Island, may indicate the importance of these waters as foraging areas. Mean duration of dives for individuals and groups (n = 95) was 6.6 sec (SE = 0.11, n = 1,551) for dives <30 sec and 125 sec (SE = 5.32, n = 156) for dives >30 sec duration.