Assessment of Bivalve Recovery on Treated Mixed-Soft Beaches in Western Prince William Sound Dennis C. Lees Littoral Ecological & Environmental Services William B. Driskell 22 January 2006 Dennis C. Lees Littoral Ecological & Environmental Services William B. Driskell 22 January 2006 Funded by the Exxon Valdez Oil Spill Trustee Council

Short HistoryShort History –NOAA Shoreline Treatment Effects Study –Infaunal data from geographically limited studies indicated negative effects at Treated sites: Sediment EffectsSediment Effects Impoverished infaunal assemblages, esp. long-lived clamsImpoverished infaunal assemblages, esp. long-lived clams Time-series data suggested recovery was very slowTime-series data suggested recovery was very slow Objectives of this study:Objectives of this study: –Assess persistence of depressed condition of clam assemblages in mixed-soft sediments at Treated sites –Assess relationship between sediment characteristics and depressed condition of clam assemblages in mixed-soft sediments.

Alternative Hypotheses  Sediments -- Coarser and concentrations of organic matter are depressed at Treated sites.  N, S, and H’ -- Higher at Reference sites except for N in infaunal samples.  Short-lived, nestling, pioneering species -- More at Treated sites in infaunal samples.  All large clams -- Fewer at Treated sites  Sediments -- Coarser and concentrations of organic matter are depressed at Treated sites.  N, S, and H’ -- Higher at Reference sites except for N in infaunal samples.  Short-lived, nestling, pioneering species -- More at Treated sites in infaunal samples.  All large clams -- Fewer at Treated sites

Sampling Design & Methods  40 sites - 36 Random & 4 Historic Sites  16 Oiled but Unwashed (Reference) sites and 20 Oiled and Washed (Treated) sites  4 Old NOAA sites to assess consistency from earlier study At Each Site  Five 10-cm core samples for clams and infauna  Three 1/16 m 2 excavation samples for larger clams  1 composite sediment sample for grain size, TOC & TKN  40 sites - 36 Random & 4 Historic Sites  16 Oiled but Unwashed (Reference) sites and 20 Oiled and Washed (Treated) sites  4 Old NOAA sites to assess consistency from earlier study At Each Site  Five 10-cm core samples for clams and infauna  Three 1/16 m 2 excavation samples for larger clams  1 composite sediment sample for grain size, TOC & TKN

SL01

KN554B

Sampling Locations

Typical Pocket Beaches

CH08

KN130B

Common Clams in Excavations ProtothacaProtothaca SaxidomusSaxidomus MacomasMacomas HiatellaHiatella DiplodontaDiplodonta Papermate sp.

Comparison of Sediment Characteristics † Significant difference (p = 0.028) Sediment Variable ReferenceTreated Old NOAA PGS (mm) † 6.8 ± ± ± 3.1 Silt/Clay (%) 3.1 ± ± ± 0.3 TOC (%) 1.1 ± ± ± 0.2 TKN (mg/Kg) 486 ± ± ± 74

Numerical Characteristics for Infaunal Samples Numerical Variable Alternative Hypothesis ReferenceTreated Exact p No. of Indiv. (N) Treat > Ref 51 ± ± No. of Spp. (S) Ref > Treat 4.9± ± Shannon- Wiener H’ Ref > Treat 1.1 ± ±

Numerical Characteristics for Excavation Samples Numerical Variable Alternative Hypothesis ReferenceTreated Exact p N Ref > Treat 65 ± ± S Ref > Treat 3.4 ± ± Shannon- Wiener H’ Ref > Treat 0.6 ± ±

Species Composition Species composition was similar in Infaunal and Excavation samples and, generally, at Reference and Treated sites. Six most abundant species in overall order of abundance by sample type -- four species in common. Infauna Excavation Infauna Excavation Rochefortia - TinyLittleneck clam Arctic nestling clamArctic Nestling clam Littleneck clamPointed macoma Northern horsemusselButter clam Baltic macomaDiplodonta Butter clamBaltic macoma Species composition was similar in Infaunal and Excavation samples and, generally, at Reference and Treated sites. Six most abundant species in overall order of abundance by sample type -- four species in common. Infauna Excavation Infauna Excavation Rochefortia - TinyLittleneck clam Arctic nestling clamArctic Nestling clam Littleneck clamPointed macoma Northern horsemusselButter clam Baltic macomaDiplodonta Butter clamBaltic macoma

Mean Number per m 2 of Clams in Infaunal Samples* SpeciesReferenceTreated Rochefortia †† Arctic nestling clam Littleneck clam † Butter clam ††† *Small species or juveniles of larger species, † p < 0.2 – Longevity < 10 years, †† p < 0.1 – Longevity < 10 years, †† p < 0.1 – Longevity > 15 years, ††† p 15 years, ††† p < 0.01

Comparison of Pioneer and Long-lived Infaunal Clams* Type Ref (no./ m 2 ) Treated (no./m 2 ) T/R Ratio Pioneer % Long-lived % Pioneer/Long- lived Ratio % *Small species or juveniles of larger species – Longevity < 10 years, surface nestlers – Longevity > 15 years, deep burrowers

Mean Number per m 2 of Clams in Excavation Samples* SpeciesReferenceTreated Nestling clam † Littleneck clam ††† Butter clam †† 7955 *Small species or juveniles of larger species – Longevity < 10 years, surface nestlers – Longevity > 15 years, deep burrowers

Comparison of Pioneer & Long- lived Clams in Excavation Samples Species Ref (no./ m 2 ) Treated (no./ m 2 ) T/R Ratio Pioneers % Long-lived % Pioneer/Long- lived Ratio % *Larger size fraction – Longevity < 10 years, surface nestlers – Longevity > 15 years, deep burrowers

Functional Ramifications of Treatment Effects  Large long-lived clams are important prey items for sea otters. Excavation samples provide a better representation of prey-sized clams.  Large long-lived clams in excavations were 40% less abundant at Treated sites.  Ergo, Treated sites are considerably less capable of supporting sea otters.  Large long-lived clams are important prey items for sea otters. Excavation samples provide a better representation of prey-sized clams.  Large long-lived clams in excavations were 40% less abundant at Treated sites.  Ergo, Treated sites are considerably less capable of supporting sea otters.

ConclusionsConclusions As predicted  Sediments at Treated sites -- Coarser than at Reference sites. INFAUNA  H’ was significantly higher at Reference sites and S exhibited strong similar trends.  As predicted, N was higher at Treated sites.  Numerically, small nestling pioneer species dominated species composition at both Treated and Reference sites.  Importance of long-lived species was lower at Treated sites.  Density of pioneer species was >2 times higher than long- lived species at Reference sites but >8.5 times higher at Treated sites. As predicted  Sediments at Treated sites -- Coarser than at Reference sites. INFAUNA  H’ was significantly higher at Reference sites and S exhibited strong similar trends.  As predicted, N was higher at Treated sites.  Numerically, small nestling pioneer species dominated species composition at both Treated and Reference sites.  Importance of long-lived species was lower at Treated sites.  Density of pioneer species was >2 times higher than long- lived species at Reference sites but >8.5 times higher at Treated sites.

ConclusionsConclusions EXCAVATION SAMPLES  Numerical characteristics were depressed at Treated sites.  Density of both long-lived burrowing clams and nestling pioneer species was depressed at Treated sites.  Because treatment caused loss of larger individuals of both pioneering and long-lived species, abundance of both types of clams was significantly lower at Treated sites than at Reference sites. EXCAVATION SAMPLES  Numerical characteristics were depressed at Treated sites.  Density of both long-lived burrowing clams and nestling pioneer species was depressed at Treated sites.  Because treatment caused loss of larger individuals of both pioneering and long-lived species, abundance of both types of clams was significantly lower at Treated sites than at Reference sites.

In Summary Sites treated with HP/HW wash during the EVOS cleanup still exhibited significant though subtle effects from treatment in  Sediment grain size -- Coarser at Treated sites.  Numerical characteristics (N, S, H’) in infaunal and excavation samples -- Generally lower at Treated sites.  Species composition -- Similar qualitatively but differed quantitatively.  Functional aspects of the clam assemblages differed markedly.  Dominant species at Reference and Treated sites both include larger, long-lived deep-burrowing clams.  Because density of large clams is ~40% lower at Treated sites, they can support considerably fewer large predators like sea otters than Reference sites. Sites treated with HP/HW wash during the EVOS cleanup still exhibited significant though subtle effects from treatment in  Sediment grain size -- Coarser at Treated sites.  Numerical characteristics (N, S, H’) in infaunal and excavation samples -- Generally lower at Treated sites.  Species composition -- Similar qualitatively but differed quantitatively.  Functional aspects of the clam assemblages differed markedly.  Dominant species at Reference and Treated sites both include larger, long-lived deep-burrowing clams.  Because density of large clams is ~40% lower at Treated sites, they can support considerably fewer large predators like sea otters than Reference sites.

Acknowledgements Our sponsor, the EVOS Trustee Council Ms. Carrie Holba at ARLIS Terry Kennedy and staff - Cordova Air David and Annette Janka - R/V Auklet Dr. Jon Houghton - Pentec/Hart Crowser Dr. Alan Mearns & Gary Shigenaka - NOAA Dr. Sarah Gerken - UAA Kathleen Lees