Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 4: Spartina Control and Managementab% survival% survival100806040200100806040200San Francisco3 day 15 day 3 day 15 daysmallWillapa Baylarge3 day 8 day 15 day 3 day 8 day 15 daysmalllargeFig. 4: Percent fragment survival 132 days after planting <strong>of</strong> S. alterniflorafrom a) San Francisco and b) Willapa Bay. White = 0 ppt, striped = 15 ppt,black = 35 ppt. All fragments represented here were planted with at leastone attached culm.The proportion <strong>of</strong> surviving fragments per treatmentgroup stabilized by <strong>the</strong> end <strong>of</strong> <strong>the</strong> growing period (Fig. 3).For San Francisco (SF) plants, survival 132 days afterplanting ranged from 45-100% in <strong>the</strong> freshwater treatments,55-90.0% in 15 ppt water and 0 to 5.56% in 35 ppt water.For WB plants, survival ranged from 26.3-81.8% in <strong>the</strong>freshwater treatments, 27.8-88.9% in 15 ppt water and0-11.1% in 35 ppt water.For nearly all SF groups, rhizome fragments immersedfor 3 days prior to planting showed lower rates <strong>of</strong> survivalthan those immersed for 15 days (Figure 4). The samepattern emerged with <strong>the</strong> WB 15 ppt fragments where <strong>the</strong>three-day immersion groups showed much lower survivalthan <strong>the</strong> eight-day immersion groups. Large rhizomefragments consistently had higher viability than smallrhizome fragments. For SF plants, 80.3% <strong>of</strong> large fragmentssurvived compared to only 62.5% <strong>of</strong> <strong>the</strong> small fragments.For WB plants, <strong>the</strong> difference was more pronounced with74.8% <strong>of</strong> large and 36.2% <strong>of</strong> small fragments surviving. SFand WB populations were compared using a two-tailed test<strong>of</strong> two proportions; <strong>the</strong>re were significant differencesbetween <strong>the</strong> proportions surviving in both freshwater (72.5%vs. 55.5%, respectively, p=0.012, α=0.05) and 15 ppt water(70.1% vs. 56.0%, p=0.043, α=0.05). In both <strong>of</strong> <strong>the</strong>secomparisons, SF fragments had higher survivorship. Therewas no notable difference between survival rates for <strong>the</strong> twoTable 2: Summary data for two months <strong>of</strong> drift card releases from three S.alterniflora infested bays.Release Date Willapa HumboldtSeptember 2004SanFranciscoRecovery Rate 57.5% 21.5% 30.5%Quantity <strong>of</strong> recovered cardsNorthSouthInside bayMax distance traveled (km)NorthSouthOctober 20047934295351031275651219304520Recovery Rate 29.5% 0.5% 24.0%Quantity <strong>of</strong> recovered cardsNorthSouthInside bayMax distance traveled (km)NorthSouth563022335locations (3.9% vs. 5.1%) in <strong>the</strong> high salinity treatment (p=0.691, α=0.05).PROPAGULE DISPERSAL STUDYDrift card return rates have been over 20% for five <strong>of</strong><strong>the</strong> six releases performed as <strong>of</strong> November 11, 2004 (Table2). Cards have consistently been found both to <strong>the</strong> north andsouth <strong>of</strong> each release location. In four <strong>of</strong> <strong>the</strong> six releasesperformed to date, cards have been found inside <strong>the</strong>estuaries. The majority <strong>of</strong> cards are staying within 25 km <strong>of</strong><strong>the</strong> release locations, although a few have traveled longerdistances.In Willapa Bay, over 69% <strong>of</strong> <strong>the</strong> September releasecards and 95% <strong>of</strong> <strong>the</strong> October release cards were found to<strong>the</strong> north <strong>of</strong> <strong>the</strong> bay. Maximum northward velocities forSeptember and October releases were 6.9 and 11.2centimeters per second (cm/s) respectively, while maximumsouthward velocities reached 6.7 and 3.4 cm/s.In Humboldt Bay, approximately 72% <strong>of</strong> <strong>the</strong> Septembercards were carried south. Maximum velocity for Septemberrelease was approximately 3.4 cm/s both to <strong>the</strong> north andsouth. Only one card, found after six days approximately sixkm north <strong>of</strong> <strong>the</strong> Humboldt Bay entrance, was recovered fromHumboldt’s October release.1006na64117530- 259 -