https://digitalcommons.usm.maine.edu/cbep-graphics-maps-posters/1035/thumbnail.jp

Barker, Seth

Bohlen, Curtis C., PhD

Brewer, Angela D.

Craig, Matthew

Doan, Michael

Lary, Sandra

Neckles, Hilary A.

Sowles, John W.

English

University of Southern Maine: Digital Commons@USM

University of Southern Maine USM Digital Commons Graphics, Maps, and Posters Casco Bay Estuary Partnership (CBEP) 2015 Update on a Continuing Saga: Eelgrass and Green Crabs in Casco Bay, Maine (Poster) Hilary A. Neckles USGS Patuxent Wildlife Research Center Angela D. Brewer Maine Department of Environmental Protection John W. Sowles Seth Barker Curtis C. Bohlen PhD Casco Bay Estuary Partnership See next page for additional authors Follow this and additional works at: https://digitalcommons.usm.maine.edu/cbep-graphics-maps-posters Recommended Citation Neckles, Hilary A.; Brewer, Angela D.; Sowles, John W.; Barker, Seth; Bohlen, Curtis C. PhD; Craig, Matthew; Doan, Michael; and Lary, Sandra, "Update on a Continuing Saga: Eelgrass and Green Crabs in Casco Bay, Maine (Poster)" (2015). Graphics, Maps, and Posters. 36. https://digitalcommons.usm.maine.edu/cbep-graphics-maps-posters/36 This Book is brought to you for free and open access by the Casco Bay Estuary Partnership (CBEP) at USM Digital Commons. It has been accepted for inclusion in Graphics, Maps, and Posters by an authorized administrator of USM Digital Commons. For more information, please contact jessica.c.hovey@maine.edu. Authors Hilary A. Neckles, Angela D. Brewer, John W. Sowles, Seth Barker, Curtis C. Bohlen PhD, Matthew Craig, Michael Doan, and Sandra Lary This book is available at USM Digital Commons: https://digitalcommons.usm.maine.edu/cbep-graphics-maps-posters/36  Conclusions Update on a Continuing Saga:  Eelgrass and Green Crabs in Casco Bay, Maine Hilary A. Neckles1,  Angela D. Brewer2, John W. Sowles3, Seth Barker4, Curtis C. Bohlen5, Matthew Craig5, Michael Doan6, and Sandra Lary7 1USGS Patuxent Wildlife Research Center, Augusta, ME; 2ME Department of Environmental Protection, Augusta, ME; 3North Yarmouth, ME; 4Boothbay, ME; 5Casco Bay Estuary Partnership, Portland, ME; 6Friends of Casco Bay, South Portland, ME; 7USFWS Gulf of Maine Coastal Program, Falmouth, ME   Recent Loss of Eelgrass in Casco Bay Caused By Green Crabs                     Mapping by Seth Barker, produced by: Maine DMR (2001)  Maine DEP & Casco Bay Est. Partnership (2013) • Eelgrass area declined by 56% between the mapping intervals • The majority of loss occurred from 2012 to 2013 • Bioturbation by green crabs identified as a leading cause 2001 2013  Questions 1. Are green crabs continuing to destroy eelgrass in Casco Bay? 2. Are effects of green crabs influenced by other environmental factors?   Large-Scale Eelgrass Change: 2013 – 2014      • Percent cover decreased at all sites • Dramatic loss of area mapped in the highest cover category at CI & MI  • Overall loss of eelgrass area at LCI   Multi-Scale Approach at Targeted Locations Little Chebeague  Island Mackworth Island Broad Cove Cousins Island Study Sites Eelgrass Measurements Green Crab Abundance Environmental Variables • Two traps per transect deployed 24 h every 2 weeks • Baited with standard quantity of frozen alewives  • High-resolution changes in cover during the peak growth season along fixed transects (1-2 per site) parallel to shore in low intertidal/shallow subtidal • Permanent quadrats (12) along transects [methods follow SeagrassNet.org]  • Large-scale changes since 2013 using low-altitude aerial photos • Light attenuation adjacent to each transect measured from duplicate profiles every 2 weeks • Triplicate sediment samples collected from each transect for texture and organic analyses   • Eelgrass loss continued from 2013 to 2014 • Decreases in bed size, patch cover, and shoot density were apparent in different locations • Changes in shoot % cover corresponded negatively to both crab abundance and the proportion of coarse particles in the sediment • At measured values, water clarity would not appear to limit shallow eelgrass production • Results suggest independent or interactive effects of green crabs and sediment texture on eelgrass cover in Casco Bay  August 2013 September 2014 July 2014 August 2013 July 2014 August 2013 September 2014 August 2013  Environmental Variables: June – September, 2014 • Highest number of green crabs occurred at Mackworth Isl. transect • Sediment texture > 10% coarse particles at two sites (Cousins  Isl.-Coarse and Little Cheb.-Coarse) • Seasonal mean attenuation of photosynthetically available radiation (Kd) among sites was 0.46 m-1 to 0.59 m-1, resulting in a minimum of about 24% surface irradiance at the canopy depth at mid-tide Mackworth Island Broad Cove Cousins Island Little Chebeague Percent cover Cousins Island Broad Cove Little Chebeague Island Mackworth Island      From June to September: • At the transect with the greatest total number of crabs, eelgrass % cover decreased despite increase in canopy height, signifying decrease in shoot density (Mackworth Isl.) • The smallest seasonal increases in % cover occurred at the two transects with highest fraction of coarse sediments (Cousins Island-coarse, Little Chebeague-coarse)  * * * * * * * * * * * * * Mackworth Island Broad Cove Cousins Island Little Chebeague High-Resolution Eelgrass Change: June – September, 2014 Mackworth Island Broad Cove Cousins Island Little Chebeague Coarse Coarse Coarse Fine Fine Fine Mackworth Island Broad Cove Cousins Island Little Chebeague Each bar  represents 12 hauls (2 traps per transect  deployed on  6 dates)                 Acknowledgments Crab sampling: Joe Glowa Groundtruthing: Jim Stahlnecker Eelgrass sampling:   Wendy Garland, Bob Houston,   Michael Langlois, Leslie Latt, Jim  Stahlnecker, Alex Sturtevant,   Emily Zimmermann  Target site maps: Becky Schaffner Means compared between dates using repeated measures ANOVA * P < 0.05  

Update on a Continuing Saga: Eelgrass and Green Crabs in Casco Bay, Maine (Poster)

https://digitalcommons.usm.maine.edu/cgi/viewcontent.cgi?article=1035&context=cbep-graphics-maps-posters

Update on a Continuing Saga: Eelgrass and Green Crabs in Casco Bay, Maine (Poster)

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