Katie McFarland , Molly - PowerPoint Presentation

Slide1

Katie McFarland, Molly Rybovich, Aswani K. VoletyFlorida Gulf Coast University, Marine and Ecological Sciences, 10501 FGCU Blvd, Fort Myers, FL

Investigation of Environmental

Tolerances

of

the Invasive Green

Mussel,

Perna viridis

,

to Predict the Potential

S

pread in Southwest

FloridaSlide2

Invasion of the Green MusselNative to the Indo-Pacific (Vakily, 1989)SubtidalTropical to subtropicalFirst observed in Tampa Bay in 1999 (Benson et al., 2011; Ingrao et al., 2001)Ballast water and/or biofouling from ships coming to port from the CaribbeanFree swimming larval stage has allowed for a rapid spread throughout Southwest Florida including Estero BayInvasive species can pose a serious threat to ecosystems and infrastructureBiofouling organisms coat boat hulls, docks and pilingsCompete with local bivalves for substrate and foodSlide3

Competition with OystersOysters form permanent 3-dimensional habitat essential to many economically and ecologically important species of fish and crabOyster reefs form natural break walls that help prevent erosion and increase sedimentation Green mussels form more of a 2-dimensional mat over hard substrate and disarticulate upon death Tampa Bay observed a nearly 50% displacement of the oyster population upon the arrival of the green mussel (Baker et al., 2006) While locally green mussels are currently primarily found in the more marine portions of the estuary, some isolated individuals have been found on reefs within the baySlide4

Local Watershed and Environmental CharacteristicsShallow estuaries (average of 3 feet) allow for rapid environmental changes (Estero Bay Aquatic Preserve Management Plan, March 2013)

Desiccation stress: With the already shallow water and most hard substrate in the intertidal region organism living on oyster reefs must be adapted to periods areal exposure

Extreme wet and dry seasons

cause drastic variations in salinity

(Barnes

, et al., 2007)

Winter: 28-38

ppt

Summer: 0-10 pptTemperature remains fairly stable ranging with averages from 16 - 32˚C (Barnes, et al., 2007)

Anthropogenic forces have drastically altered the watersheds of

Southwest

Florida

estuaries

- Estuaries

have gained more tributaries many of which run through areas of increased urbanization Slide5

ObjectivesUnderstand environmental boundaries of the invasive green mussel and predict the potential for spreadSalinity Survival is a clear indication of environmental limitsBut sub-lethal effects can also limit the spread of a new speciesDesiccationAre green mussels capable of occupying hard substrate in the shallow waters of Southwest Florida estuaries? Do green mussels pose a threat to our native oyster reefs?How can we reduce this risk to oysters?Slide6

Methods: Physiological Response to Decreased SalinitiesOsmolalityAn acute salinity change for both oysters and green mussels (5, 10, 15, 20, 25, 30, 35 ppt)Hemolymph was drawn at T = 0, 1, 4, 8, 12, 24, 48, 96, 120 hoursHemolymph osmolality of bivalves was compared with that of the exposure seawater using a vapor pressure osmometerClearance RateClearance rates were measured for both oysters and green mussels following an acute salinity change (10, 15, 25, 35 ppt)Bivalves were fed the phytoplankton T. iso in a static system Algal cell concentration monitored over time using flow cytometerySlide7

Internal Osmolality at Decreased SalinitiesGreen mussels were unable to reach osmotic equilibrium with the external environment at salinities of 5 and 10 ppt after 1 week of exposureOysters reached equilibrium at 10 ppt and above within 24 hours and as low as 5 ppt within the week exposureWell adapted for low salinities prevailing in SW Florida summersSlide8

Changes in Clearance Rates in response to an Acute Salinity DecreaseGreen mussels showed a significant decrease in clearance rates at salinities of 10 and 15 ppt compared to optimal salinities of 25 and 35 pptOysters did not show any significant differences in clearance rate at all salinitiesSlide9

Methods: Survival in Response to Decreased Salinity ExposuresAcute Salinity ChangesSalinity adjusted from 30 ppt to 5, 10, 15, 20, 25, 30 (control), 35 ppt in triplicate tanks (N=20 / tank) Test conditions were maintained for 56 days with survival monitored dailyGradual Salinity ChangeSalinity was adjusted gradually from 30 ppt by 3 ppt every other day to final salinities of 30 (control), 27, 24, 21, 18, 15, 12, 9, 6, 3 ppt in triplicate tanks (N=20 / tank) Final salinities were maintained for an additional 28 daysSlide10

Acute Salinity Decrease Poor survival below 20 ppt and 100% mortality at 5 and 10 pptSlide11

Gradual Salinity Decrease≥97% survival at salinities of 9 ppt and aboveAfter only 13 days at 3 ppt 100% mortality was observedSlide12

Methods: DesiccationGreen mussels and oysters exposed to desiccation under direct sunlight (intertidal exposure), under shade (mangrove canopy) or underwater (subtidal) conditions for 0, 2, 4, 6, and 8 hours Internal temperature of organisms measured using a temperature probe inserted into the shell cavity through a narrow hole that was sealed after insertion

External temperature

measured using an aquarium

thermometer

Survival of oysters and green mussels

were noted

in both experimental and control treatments and expressed as cumulative mortality

B

C

ASlide13

Desiccation: High Temperatures97% mortality in green mussels while oysters showed only 4% mortalityBoth showed similar internal temperatures, but mussels died with increasing frequency as temperature increasedSlide14

Desiccation: Low temperaturesField observations in the winter of 2012High numbers of juvenile recruitment was observed in the intertidal zone in December of 2011A month later in January 2012 found deadLab experiments documented in the literature confirm an intolerance of P. viridis to desiccation under cold air temperatures (Firth et al., 2011; Urian et al., 2011)Slide15

Red Tide BloomsPreviously documented die offs following Red Tide blooms in Tampa Bay (Baker et al., 2012)Field monitoring in Estero Bay (March 2011 – current):During periods of Red Tide observed:Increased mortalitiesSlowed growth Decreased juvenile recruitmentBrevetoxin ELISA’s showed an accumulation of toxins in the tissuesLack of sufficient co-evolution period between Perna viridis and Karenia brevis Trophic Transfer?Slide16

In Conclusion: What is the Potential Threat?Salinity is a limiting factorWhen the change is a acute P. viridis is unable to adaptIf the change is gradual P. viridis may be capable of pushing into lower salinity regions of the estuaryDesiccation With the shallow waters of Estero Bay, P. viridis is unlikely to be able to populate the intertidal zoneAir temperatures can be significantly lower than winter water temperaturesHowever, deep estuaries may be at risk even if salinities drop as low as 15pptOysters were able to adapt to all test salinities and showed high tolerance to desiccation stress even at high internal temperaturesWell adapted to harsh conditions in SW Florida estuariesWill likely remain the dominant intertidal bivalveSlide17

AcknowledgementsFunding: U. S. Department of Education U. S. EPA Marco Island Shell Club South Florida Water Management District Technical and field support: Vester Marine Field and Research StationCoastal Watershed Institute

Lesli Haynes, Robert

Wasno

,

Jeffrey

Devine

, David Segal

Rheannon

Ketover

, Julie Neurohr

and Brooke

Denkert

.Slide18

ReferencesBaker, P., J. S. Fajans, W. S. Arnold, D. A. Ingrao, D. C. Marelli, and S. M. Baker. 2007. Range and dispersal of a tropical marine invader, the Asian green mussel, Perna viridis, in subtropical waters of the southeastern United States. Journal of Shellfish Research 26:345-355.Baker, P., J. S. Fajans, and S. M. Baker. 2012. Habitat dominance of a nonindiginous tropical bivalve, Perna viridis (Linnaeus, 1758), in a subtropical estuary in the Gulf of Mexico Journal of Molluscan Studies 78:28-33.Baker, P., J. S. Fajans, S. M. Baker, and D. Bergquist. 2006. Green mussels in Florida, USA: Review of trends and research. World Aquaculture 37:43-67.Barnes, T., A. Volety, K. Chartier, F. Mazzotti, and L. Pearlstine. 2007. A habitat suitability index model for the eastern oyster (Crassostrea virginica), a tool for restoration of the Caloosahatchee Estuary, Florida. Journal of Shellfish Research 26:949-959.Benson, A. J., D. C. Marelli, M. E. Frischer, J. M. Danforth, and J. D. Williams. 2001. Establishment of the green mussel, Perna viridis (Linnaeus 1758)(Mollusca: Mytilidae) on the west coast of Florida. Journal of Shellfish Research 20:21-30.Estero Bay Aquatic Preserve and Florida Department of Environmental Protection, March 2013. Estero Bay Aquatic Preserve: Management Plan. (Award No. NO11NOS4190077-CM227)Firth, L. B., A. M. Knights, and S. S. Bell. 2011. Air temperature and winter mortality: Implications for the persistence of the invasive mussel,< i> Perna viridis</

i

> in the intertidal zone of the south-eastern United States. Journal of Experimental Marine Biology and Ecology

400

:250-256

.

Ingrao

, D. A., P. M.

Mikkelsen, and D. W. Hicks. 2001. Another introduced marine mollusk in the Gulf of Mexico: the Indo-Pacific green mussel, Perna viridis, in Tampa Bay, Florida. Journal of Shellfish Research 20:13-19.Urian, A. G., J. D. Hatle, and M. R. Gilg. 2011. Thermal constraints for range expansion of the invasive green mussel, Perna viridis, in the southeastern United States. Journal of Experimental Zoology Part A: Ecological Genetics and Physiology 315:12-21.Vakily, J. 1989. The biology and culture of mussels of the genus Perna. The World Fish Center.Slide19