Ascophyllum Nodosum) and Associated Epifaunal Communities Following Cutter Rake Harvesting in Maine

Evaluation of short-term changes in rockweed (Ascophyllum nodosum) and associated epifaunal communities following cutter rake harvesting in Maine

Thomas J. Trott

Friedman Field Station, Suffolk University, Edmunds, Maine 04628 Department of Biology, Suffolk University, Boston, Massachusetts 02114

and

Peter F. Larsen

Bigelow Laboratory, PO Box 475, 180 McKown Point Rd. West Boothbay, Maine 04575

Report

Department of Marine Resources Marine Resources Laboratory P.O. Box 8 194 McKown Point Rd. W. Boothbay Harbor, Maine 04575-0008

INTRODUCTION North Atlantic intertidal areas are often dominated by the rockweed Ascophyllum nodosum which can grow to greatest length and mass on wave protected shores. Rockweed is a long-lived canopy alga. In some areas it can achieve near mono-specific cover. The holdfasts and three-dimensional canopy of rockweed beds provide habitat for intertidal invertebrates and fish, and offer a place for attachment of their eggs and epiphytic algae. Rockweed is harvested for use in cosmetics, processed foods, domestic animal feeds and fertilizers. It has been harvested commercially for decades in the Gulf of Maine. Concerns about harvesting have generated numerous publications and workshops (e.g., Rangeley and Davies, 2000). While it is well documented that harvesting rockweed stimulates growth (Lazo and Chapman, 1996; Ugarte, et al., 2006), less attention has been directed towards disturbance effects at the community level. If associated animal communities are affected by rockweed harvesting, then the way that harvesting is done with a cutter-rake would produce a patchwork of disturbance. Harvesting with a cutter-rake removes rockweed in patches over large areas on an incoming tide. Once in a rockweed bed, a harvester targets the largest or bulkier plants in the water that can be reached with his rake. The harvester’s boat moves with the wind and tide to a random position where the bulkiest floating plants are targeted. As a result, the cut plant is chosen by the harvester but position in the bed is not. The goal is to harvest maximum biomass, although the lengths that plants are cut can vary from changes in visibility, the harvester’s stroke and depth perception. Harvesting is conducted in accordance to regulations requiring a 16” length minimum of plant along with its holdfast remain. Potential effects on fauna associated with rockweed at the scale of a rockweed bed would be linked to the patches where targeted plants were removed. The degree of disturbance might fluctuate according to the varying amount of plant removed. A recent increase in harvesting rockweed has raised public concern in Maine and re- stimulated interest to evaluate some basic potential impacts. This study was undertaken to examine the effectiveness of current regulations on cutter-rake harvesting for preventing and/or minimizing impact on rockweed and associated macroinvertebrates. Short-term recovery, two months following a single harvest, was the time course for evaluating disturbance effects.

METHODS A field experiment was conducted using a modified Before-After, Control-Impact (BACI) experimental design with stratified random destructive sampling to evaluate some potential effects of harvesting. The study site was located in Shackford Head State Park, Cobscook Bay, Maine to minimize uncontrolled disturbance from anthropogenic activities (Figure 1). In July 2008, rockweed biomass and associated epifaunal species on rockweed thalli and holdfasts with contiguous substrate were assessed in adjacent control and experimental plots (Figure2). In each plot, four quadrats were sampled per tidal stratum (high, mid, low intertidal). Positions of randomly selected 1/16-m2 quadrats were recorded with GPS. Within each quadrat, plants were sheared just above their holdfasts (<1cm) and transported to the laboratory where they were washed with freshwater under pressure above a 0.5 mm screen to collect mobile epifauna. Material retained on the sieve was preserved in 10% formalin and stained with Rose Bengal. Rockweed samples were drained of excess water and weighed. Individual thalli were examined for attached and remaining mobile epifauna, and eggs. All mobile fauna was saved with sieved material. In the field, epifauna within each quadrat exposed after removing rockweed was collected with forceps. Surfaces were scraped to collect rockweed holdfasts and remaining epifauna (Figure 3). Samples were washed and material retained on a 0.5mm sieve was preserved in 10% formalin and stained with Rose Bengal. Animals were sorted, identified to the lowest taxon possible, and counted. Species names were checked in the World Register of Marine Species database (http://www.marinespecies.org/) to insure use of current valid names. All formalin preserved samples were transferred to ethanol for archiving at the Maine Department of Marine Resources. The impact of harvesting as it is done commercially was a priority so treatments could not be randomly assigned to quadrats within each plot with plants cut at uniform heights. That would not match how rockweed is commercially harvested. Instead, immediately after sampling, rockweed was harvested in the experimental plot by a professional harvester from Acadian Seaplants Limited, New Brunswick, using a cutter rake (Figure 4). The harvester followed Maine Department of Marine Resources harvesting regulations and their activities observed and

documented (Figure 5). During harvesting, plants were not cut below 16 inches or the first branch of the primary thalli. Approximately 1.25 wet tons of rockweed was harvested by one person in 1.5 h and an estimated 17% of the biomass of rockweed in the study area was removed. Both plots were re-sampled in September leaving two months of recovery for the harvested experimental plot. Re-sampling the same quadrat was avoided since the GPS location of each quadrat sampled in July was known. Making a priority on assessing the effects of harvesting rockweed commercially rather than through experimentally consistent, controlled hand removal from much smaller patches placed conditions on how data were analyzed. Although each plot had 12 sample quadrats, these were not independent replicates. This meant that parametric analyses were not valid. Keeping this in mind, analyses performed were for summarizing results observed and not for statistical significance. When statistical significance is given, it is for presentation purposes only. None- the- less, these results are clearly evident in graphical illustrations even without statistics. Another constraint on the experimental design was financial. This dictated the number of plots that could be studied. In keeping with the priority of commercial harvesting effects, having more than one experimental plot was not financially feasible. These caveats need to be held in mind by the reader throughout the presentation of data, results and conclusions. Rockweed biomass and epifauna data were analyzed with a paired BACI design where the differences in measurements before and after in control and experimental plots were tested for using a two-sample t-test. This procedure tests for the significance of impact (Smith et al. 1993; Stewart-Oaten et. al., 1986; Stewart-Oaten and Bence, 2001) which in this case is harvesting. Specifically, before harvest measurements from experimental plots are subtracted from control plot measurements and the mean difference compared using a two-sample t-test with that derived using the same method but with measurements taken after harvesting. Additional tests for differences in epifauna distribution according to habitat were conducted using ANOVA. When warranted, multiple comparison tests were performed using the Student Newman-Keuls Test to identify significant differences among groups. Rockweed biomass was analyzed using simple linear regression to examine relationships. Cluster analysis and non-parametric multidimensional scaling were performed on epifauna data using PRIMER ver. 6 (Plymouth Routines in Multivariate Ecological Research)

(Clarke and Warwick, 2001). Species counts were filtered according to statistical test protocols for cluster analysis and multidimensional scaling. This included eliminating all colonial species from the analysis since these did not represent counts. Also, species which occurred in 10% or less of all samples were designated as rare and removed from the analysis. The remaining species counts which represented the bulk of the data were square root transformed to allow intermediate abundant species to contribute to the similarity matrix calculated using the Bray-Curtis Index. Cluster and non-parametric multidimensional scaling analyses were performed on the resulting Bray-Curtis coefficients. Significant differences (P<0.05) between species grouped according to cluster analysis were determined using the PRIMER SIMPROF routine. For all analyses in this study, α = 0.05 was the level for significance. When statistical significance is given, it is for presentation purposes only for reasons described earlier. RESULTS Harvesting had a significant impact on rockweed Ascophyllum nodosum biomass (t= 2.117, P= 0.046) (Figure 6A). Biomass of rockweed in the experimental plot was greater following harvesting. September biomass was significantly different from July in the harvested plot (Student Newman-Keuls Test, q= 4.032, P=0.007), while the control plot showed no significant change (Figure 6B). There was a significant (P<0.05) direct linear relationship between the number of thalli and weight (Figure 7). Weight of thalli from both control and experimental plots was greater in September. Cluster analysis of epifaunal samples grouped them according to similarity determined using the Bray–Curtis index to identify distinct species assemblages. This produced a dendrogram representing a hierarchy of two levels, habitat and strata (high, mid-, low intertidal), resulting in six significantly distinct groups (SIMPROF, P<0.05) with 65% similarity (Figure 8A). Specifically, epifaunal species collected from thalli and substrate separated into two distinct and significantly different clusters. Within these clusters, samples grouped almost entirely according to strata (high, mid-, low intertidal), except one high intertidal sample (SBSH) clustered with substrate samples from the mid-intertidal. Low, mid- and high intertidal substrate and thalli species assemblages clustered into separate significantly different (SIMPROF, P<0.05) groups. Note that samples did not differ significantly according to sample plot, i.e., control or experimental, regardless of month (either before or after harvesting). The only exception was

substrate assemblages from the low intertidal where month mattered (SIMPROF, P<0.05), but sample plot did not. In other words, for this instance, control and experimental plots were not statistically different (SIMPROF, P>0.05) within the same month although months differed significantly. Ordination of samples based on their rank in the Bray-Curtis similarity matrix using non- parametric multidimensional scaling (MDS) produced an MDS plot or map where the distance between samples was determined by their degree of similarity. The more similar samples are to each other, the closer they appear on the MDS plot. When constructed, samples arranged in the same groups described for cluster analysis (Figure 8B). The low stress value of 0.09 based on the degree of distortion between similarity rankings corresponds to a good ordination with no real prospect of misinterpretation. This means that the groupings are not forced together by the analysis to produce an artificial arrangement but instead represent actual species assemblages. Assemblages of epifaunal species were described according to abundance (numbers of individuals per 1/16 m2) and species richness (number of species) to examine possible impacts of harvesting. A total of 105 putative species were identified (Table 1). The number of species per station ranged from 15 to 39. Extrapolated densities ranged from 1,168 to 34,656 individuals/m2. There was no significant impact of harvesting on the number of individual animals on rockweed thalli (t = 0.742, P = 0.466) or substrate (t = 0.709, P = 0.486) (Figure 9). Overall, the mean abundance of epifaunal species on rockweed thalli and substrate, which includes rockweed holdfasts, differed significantly (Student Newman-Keuls Test, q = 2.813, P < 0.05) with more occurring in substrate samples (Figure 10A). There was no significant difference between control and experimental plots in the number of individuals found on rockweed thalli or substrate in July or September (3-Way ANOVA, F = 0.0433, P = 0.836) (Figure 11). There was no significant impact of harvesting on the number of species found on rockweed thalli (t= 0.653, P = 0.520) or substrate (t= 0.874, P = 0.392) (Figure 12). The number of species found on rockweed thalli did not differ significantly from substrate (3-Way ANOVA, F = 3.866, P = 0.052) (10B). Overall, the number of epifaunal species found on thalli differed significantly between control and experimental plots (Student Newman-Keuls Test, q=7.202, P<0.001) but not from substrate (Student Newman-Keuls Test, q=0.884, P=0.534) (Figure 13). There was no significant difference in the number of species found in control and experimental

plots on either thalli or substrate sampled in July or September (3-Way ANOVA, F = 0.0239, P = 0.877) (Figure 14). There was no significant impact of harvesting on the abundances of the three species of periwinkle, Littorina littorea, L. obtusata and L. saxatilus on either rockweed thalli or substrate (Table 2, Figures 15-17). Periwinkles were distributed differently between habitats. Mean abundances differed significantly between rockweed thalli and substrate for common periwinkle, L. littorea (Student Newman-Keuls Test, q = 4.893, P<0.001), smooth periwinkles, L. obtusata (Student Newman-Keuls Test, q = 4.226, P= 0.004) and rough periwinkles, L. saxatilus (Student Newman-Keuls Test, q =5.608, P<0.001). Common periwinkles were more abundant on substrate than rockweed thalli (Figure 18), but rockweed thalli held more smooth (Figure 19) and rough periwinkles (Figure 20). The mean abundance of smooth periwinkles differed significantly from common periwinkles (Student Newman-Keuls Test, q=4.697, P=0.003), and nearly so from rough periwinkles (Student Newman-Keuls Test, q=2.705, P=0.056). There was enough variation in abundances to make the difference between rough and common periwinkles not significant (Student Newman-Keuls Test, q=1.992, P=0.159).

CONCLUSIONS 1. This study supports previous results that demonstrated cutting rockweed results in increased biomass (Lazo and Chapman, 1996; Ugarte et al., 2006). 2. There was a significant linear relationship between weight and number of rockweed thalli. 3. Weight of thalli from both control and experimental plots was greater in September. 4. Cluster analysis distinguished epifaunal macroinvertebrate assemblages on substrate and thalli as significantly different, and also according to intertidal stratum (high, mid-, low) within these habitats. 5. Multidimensional Scaling (MDS) discriminated 6 distinct species assemblages with 65% similarity based on habitat and intertidal stratum. 6. Species assemblages were not distinctly different before and after harvesting for both experimental and control sample plots at the level of 65% community similarity.

7. There was no significant impact of harvesting on the abundance of epifauna on either substrate or rockweed thalli during the two month duration of this study. 8. More epifauna was found in substrate samples which include rockweed holdfasts than on rockweed thalli. 9. There was no significant impact of harvesting on the species richness of epifauna on either substrate or rockweed thalli during the two month duration of this study. 10. The number of species found on rockweed thalli did not differ significantly from substrate samples. 11. There was no significant impact of harvesting on the abundance of the three species of periwinkle snails (Littorina littorea, L. obtusata, and L. saxatilus) during the two month duration of this study. 12. Common periwinkles were more abundant on substrate than rockweed thalli, but rockweed thalli held more smooth and rough periwinkles. 13. Overall, there were more L. obtusata than L. littorea, though not L. saxatilus. There was no significant difference between the number of L. saxatilus and L. littorea.

Acknowledgements

This work was funded by the Maine Department of Marine Resources, Suffolk University and Bigelow Laboratory. A special thanks to Chris Bartlett, Maine Sea Grant Extension for logistical support in the field and in the laboratory. Much appreciation is given to Patti DeMaria, Saco Middle School teacher, who unselfishly donated her time as a volunteer in all phases of field work. Special thanks are due to Joanne Lardie for her admirable diligence during pre- sorting and polychaete identification. Dr. Lin Lu, Dalhousie University, aided in identification of gastropods, Jon Norenburg, Smithsonian Institution, identified unknown nemerteans, and Seth Tyler, University of Maine, identified unknown flatworms. Thanks to Gerhard Pohle and Ross Mayhew for looking at an unidentified gastropod. Laboratory work was conducted by arrangement with the City of Eastport at the Boat School and at Bigelow Laboratory. We are thankful to Bob Clarke of the Plymouth Marine Laboratory and Allan Stewart Oaten of the University of California, Davis for thoughts on data analysis. This project was greatly improved through discussions with John Sowles and Pete Thayer, Maine Department of Marine Resources.

Literature Cited

Clarke, K.R. and T.M. Warwick. 2001. Change in marine communities: an approach to statistical analysis and interpretation, 2nd edition. PRIMER-E Ltd, Plymouth, UK. Lazo, L. and A.R.O. Chapman. 1996. Effects of harvesting in Ascophyllum nodosum (L.) Le Jol. (Fucales, Phaeophyta): a demographic approach. Journal of Applied Phycology 8: 97-103. Rangeley, R.W. and J.L. Davies (eds.). 2000. Gulf of Maine Rockweed: Management in the Face of Scientific Uncertainty. Proceedings of the GPAC workshop in St. Andrews, New Brunswick, December 5-7, 1999. Huntsman Marine Science Centre Occasional Report 00/1: 94p. Stewart-Oaten, A. and J.R. Bence. 2001. Temporal and spatial variation in environmental assessment. Ecological Monographs 71: 306–339. Stewart-Oaten, A., W.W. Murdoch and K.R. Parker. 1986. Environmental impact assessment: pseudoreplication in time? Ecology 67: 929–940. Smith, E.P., D.R. Orvos, and J.J. Cairns. 1993. Impact assessment using the before-after- control-impact (BACI): Comments and concerns. Canadian Journal of Fisheries and Aquatic Sciences 50: 627–637. Ugarte, R., G. Sharp, and B. Moore. 2006. Changes in the brown seaweed Ascophyllum nodosum (L.) Le Jol. Plant morphology and biomass produced by cutter rake harvest in southern New Brunswick, Canada. Journal of Applied Phycology 18: 351-359.

Table 1. List of taxa encountered during rockweed survey at Shackford Head, Cobscook Bay, Maine.

PHYLUM PORIFERA Sponge PHYLUM PLATYHELMINTHES Acoela Notoplana atomata Uteriporus vulgaris Platyhelminthes B Platyhelminthes D Unknown platyhelminthes PHYLUM CNIDARIA Athecate hydroid Bougainvillia sp. Campanularidae Clava sp. Hydroid Sertularia sp. Thenaria anemone PHYLUM BRYOZOA Bryozoa Flustrellidra hispida PHYLUM RHYNOCHOELA Amphiporus sp. Cerebratulus sp. Lineus sp. Micrura sp. Nemertean Oerstedia dorsalis Red Lineus Tetrastemma candidum Tetrastemma sp. PHYLUM MOLLUSCA Acanthodoris pilosa Buccinum undatum Crenella glandula Hiatella arctica Juvenile gastropod Lacuna vincta Littorina littorea Littorina obtusata 9

Littorina saxatilis Margarites helicinus Mya arenaria Mysella planulata Mytilus edulis Buccinum undatum Onoba aculeus Skeneopsis planorbis ?Stiliger fuscatus Testudinalia testudinalis Unknown nudibranch Velutina laevigata PHYLUM ANNELIDA Apistobranchus tullbergi Capitella capitata Chaetozone setosa Fabricia sabella Gyptis vittatta Harmothoe imbricata Hediste diversicolor Lumbrineris tenuis Maldanidae Microphthalmus aberrans Myrianida sp. Nephtyidae juv. Ninoe nigripes Nothria conchylega Oligochaeta Praxillella praetermissa Spirobis spirorbis Syllidae juv. PHYLUM ARTHROPODA Non-Crustaceans Ant Chironomid larvae Diptera adult Diptera larvae Diptera pupa Halacarus sp. Insect Insect pupa Lepidoptera pupa Mite

Nymphon stromii Phoxichilidium femoratum Spider Wasp Crustaceans Ampelisca abdita Ampelisca agassizi Amphipod B Amphipod C Ampithoe rubricata Caprella linearis Corophium bonnellii Corophium sp. Edotia triloba Eudorella truncatula Gammarus obtusatus Hyale prevosti Ischyrocerus anguipes Jaera marina Metopa sp. Mysid Oniscus asellus Orchestia gammarella Orchestia grillus Orchestia platensis Photis macrocoxa Phoxocephalus holbolli Platorchestia platensis Pontogeneia sp. Semibalanus balanoides Unidentified Amphipod PHYLUM ECHINODERMATA Asterias sp. Strongylocentrotus droebachiensis UNKNOWN Unknown

Table 2. Statistical results testing for significant differences in abundance of periwinkles between control and experimental plots before and after harvesting.

Species Thalli Substrate

t value P value t value P value

Littorina littorea 0.921 0.367 1.363 0.187

Littorina obtusata 1.243 0.227 0.0998 0.921

Littorina saxatilus -0.0688 0.946 1.422 0.169

Figure 1. Study site at Shackford Head, Cobscook Bay, Maine. A. Map illustrating Shackford Head and location of sample plots (red circle). B. View of study site off shore. Observer on shore marks approximate boundary between experimental (left) and control (right) sample plots. Boat on left is harvester. Photograph by Tom Trott. 13

Experimental Plot A Control Plot B 20 m 20 m

1/16 m²

21 m 50 m 11 m

21° 16° 1 8°

Figure 2. Schematic representation of sample plots and BACI experimental design used to evaluate the effects of cutter rake harvesting of rockweed, Ascophyllum nodosum, at Shackford Head State Park, Cobscook Bay, Maine.

B. 25 cm

25 cm

Figure 3. Destructive quadrat sampling of rockweed, Ascophyllum nodosum. A. Before sampling. B. After sampling. Photographs by Tom Trott.

Figure 4. Cutter rake used for commercial harvesting of rockweed, Ascophyllum nodosum, and used to harvest experimental plot. Photograph by Tom Trott.

A. B.

C. D.

Figure 5. Study site at Shackford Head, Cobscook Bay, Maine, before and after harvesting rockweed, Ascophyllum nodosum. Top. Experimental plot (A) before harvesting and (B) after harvesting. Bottom. Control plot (A) before harvesting and (B) after harvesting. Photographs by Tom Trott.

Rockweed Ascophyllum nodosum A. Change in Biomass

1500 SE

+/− July September 1000

500

-500

-1000

Mean Difference between Control and Experimental Plots Experimental and Control between Difference Mean -1500 Month

Rockweed, Ascophyllum nodosum B. Change in Biomass

3000

Experimental (July) Experimental (September) 2500 Control (July) Control (September) Samples +/- SE +/- Samples 2 2000

1500

1000

500 Mean Biomass of Rockeed from 1/16m

0 Sample Plots Figure 6. Changes in biomass of rockweed, Ascophyllum nodosum. A. Mean difference in biomass of rockweed Ascophyllum nodosum (g • 1/16 m2) between control and experimental plots in pre- (July) and post- (September) harvesting. B. Mean biomass of rockweed Ascophyllum nodosum (g • 1/16 m2) in control and experimental plots, pre- (July) and post- (September) harvesting. 18

BIOMASS vs. No. THALLI JULY vs. SEPT

6000 July July Regr 5000 Sept Sept Regr )

2 4000

3000 1/16 m .

2000

Weight (g 1000

0 50 100 150 200 250 300 350 400 Number of Thalli

Figure 7. The linear relationship between number of thalli in a sample of rockweed Ascophyllum nodosum and weight from combined control and experimental plots at Shackford Head State Park, Cobscook Bay, Maine. Weight of thalli increased from July to September.

A. Cluster Analysis of Macroinvertebrates Associated with Rockweed Group average Transform: Square root Resemblance: S17 Bray Curtis similarity 40

60 Similarity

100 TAJL TBJL SAJL SBJL TASL TBSL TBJH TAJH SAJH SBJH SASL SBSL TAJM TBJM TBSH TASH SBSH SAJM SBJM SASH TASM TBSM SASM SBSM Samples

MDS of Macrobenthic Invertebrates Associated with Rockweed B. Transform: Square root Resemblance: S17 Bray Curtis similarity

2D Stress: 0.09 Similarity TASL 60 65 80 TBJL TBSL

SBJL TAJL

SAJL

SASL

SBSL TBJM TASM TAJM TAJHTBJH TBSM SBJM SAJM SASH SBSM TBSH TASH SASM SBSH SAJH SBJH

Figure 8. Macrobenthic invertebrate community similarities in experimental and control samples before and after harvesting, July and September, respectively. A. Dendrogram of cluster analysis results. Red dotted lines connect samples that do not significantly differ (P>0.05). Black horizontal line represents slice at 65% similarity. B. MDS plot. Abbreviations: S = substrate, T = Thalli, A=experimental, B=control, J=July, S=September, H=high intertidal, M=mid-intertidal, L=low intertidal.

Epifaunal Macrofauna A. Abundance on Thalli

600 July SE September +/− 500

400

300

200

100

Mean Difference betweenControl vs. Experimental 0 Month

Epifaunal Macroinvertebrates B. Abundance on Substrate

400 July SE September +/−

200

-200

Experimental Control between vs. Difference Mean -400 Month

Figure 9. Mean difference in abundance of epifaunal macroinvertebrates (no. • 1/16 m2) on rockweed Ascophyllum nodosum between control and experimental plots, pre- (July) and post- (September) harvesting. A. Mean difference of abundance on rockweed thalli in July and September. B. Mean difference of abundance on substrate in July and September.

Epifaunal Macroinvertebrates A. Abundance on Thalli and Substrate

1000

Thalli

SE Substrate +/− 800 Sample 2

600

400

200 Mean Numberof Animals per 1/16m

0 Habitat

B. Epifaunal Macroinvertebrates Species Richness on Thalli and Substrate

Thalli SE 30 Substrate +/−

25 Sample Sample 2

5 Mean Number of Species per 1/16 m

0 Habitat Figure 10. Abundance and species richness of epifaunal macroinvertebrates on substrate (includes holdfasts) and thalli of rockweed Ascophyllum nodosum. A. Abundance on rockweed thalli and substrate. B. Species richness on rockweed thalli and substrate. 22

A. Epifaunal Macroinvertebrates Abundance on Thalli

800

Control (July)

SE Experimental (July) Control (September) +/− Experimental (September)

600 Samples 2

400

200 Mean Numberof Animals from 1.16 m

Sample Plots

Epifaunal Macroinvertebrates B. Abundance on Substrate

1000

Control (July)

SE Experimental (July)

+/− Control (September) 800 Experimental (September) Samples 2

600

400

200 Mean Number of Animals from 1/16 m

0 Sample Plots

Figure 11. Abundance of epifaunal macroinvertebrates on substrate (including holdfasts) and thalli of rockweed Ascophyllum nodosum pre- (July) and post- (September) harvest. A. Abundance on rockweed thalli in July and September. B. Abundance on substrate in July and September. 23

A. Epifaunal Macroinvertebrates Change in Species Richness on Thalli

July September

2 Mean Difference between Control vs. Experimental +/- SE

0 Month

B. Epifaunal Macroinvertebrates Change in Species Richness on Substrate

6 SE July +/− 4 September

-2

-4 Mean Difference between Control vs. Experimental

-6 Month Figure 12. Mean difference in species richness of epifaunal macroinvertebrates (no. • 1/16 m2) on rockweed Ascophyllum nodosum between control and experimental plots, pre- (July) and post- (September) harvesting. A. Mean difference of species richness on rockweed thalli in July and September. B. Mean difference of species richness on substrate in July and September. 24

A. Epifaunal Macroinvertebrates Species Richness on Thalli

Control Experimental 30

Sample

2 25

Mean Number of Species per 1/16 m 5

Sample Plots

B. Epifaunal Macroinvertebrates Species Richness on Substrate

Control Experimental 25

Sample

2 20

5 Mean Number ofSpecies per 1/16m

Sample Plots

Figure 13. Species richness of epifaunal macroinvertebrates on substrate (including holdfasts) and thalli of rockweed Ascophyllum nodosum. A. Species richness on rockweed thalli in control versus experimental plots. B. Species richness on substrate in control versus experimenta l plots. 25

A. Epifaunal Macroinvertebrates Species Richness on Thalli

Control (July) Experimental (July) SE Control (September) +/− 25 Experimental (September)

Samples 2 20

Mean Number of Species from 1/16 m

0 Sample Plots

B. Epifaunal Macroinvertebrates Species Richness on Substrate 25 Control (July)

SE Experimental (July) Control (September)

+/− Experimental (September) 20

Samples 2

Mean NumberMean of Species from m 1/16

Sample Plots

Figure 14. Species richness of epifaunal macroinvertebrates on substrate (including holdfasts) and thalli of rockweed Ascophyllum nodosum pre- (July) and post- (September) harvest. A. Species richness on rockweed thalli in July and September. B. Species richness on substrate in July and September.

A. Common Periwinkles (Littorina littorea) Change in Abundance on Thalli

SE July

+/− +/− September

-5 Mean Difference between Control and Experimental -10 Month

B. Common Periwinkles (Littorina littorea) Change in Abundance on Substrate

10 SE July +/− September

-5 Mean Difference between Control and Experimental -10 Month Figure 15. Mean difference in abundance of the common periwinkle Littorina littorea (no.• 1/16 m2) on rockweed Ascophyllum nodosum between control and experimental plots in pre- (July) and post- (September) harvesting. A. Mean difference of abundance on rockweed thalli in July and September. B. Mean difference of abundance on substrate in July and September. 27

A. Smooth Periwinkles (Littorina obtusata) Change in Abundance on Thalli

200

SE July

+/− +/− September

150

100

0 Mean Difference between Control and Experimental -50 Month

B. Smooth Periwinkles (Littorina obtusata) Change in Abundance on Substrate

SE July

+/− September

-5 Mean Difference between Control and Experimental -10 Month Figure 16. Mean difference in abundance of the smooth periwinkle Littorina obtusata (no. • 1/16 m2) on rockweed Ascophyllum nodosum between control and experimental plots in pre- (July) and post- (September) harvesting. A. Mean difference of abundance on rockweed thalli in July and September. B. Mean difference of abundance on substrate in July and September. 28

A. Rough Periwinkles (Littorina saxatilus) Change in Abundance on Thalli

July September

10 Mean Difference between Control and Experimental +/- SE

0 Month

B. Rough Periwinkles (Littorina saxatilus) Change in Abundance on Substrate

SE July September +/− +/−

-5 Mean Difference between Control and Experimental -10 Month Figure 17. Mean difference in abundance of the rough periwinkle Littorina saxatilus (no. • 1/16 m2) on rockweed Ascophyllum nodosum between control and experimental plots in pre- (July) and post- (September) harvesting. A. Mean difference of abundance on rockweed thalli in July and September. B. Mean difference of abundance on substrate in July and September. 29

A. Littorina littorea Abundance on Thalli

10 SE

+/− Exp July (N=76) Exp Sept (N=68) Control July (N=55) 8 Control Sept (N=6) Samples 2

Mean Number of Snails on Thalli from 1/16 m 1/16 from Thalli on of Snails Number Mean 0 Sample Plots

B. Littorina littorea Abundance on Substrate

20 SE Exp July (N=163) +/− Exp Sept (N=99) Control July (N=162) Control Sept (N=44) Samples

2 15

0 Mean Number of Snails on Substrate from 1/16 m Sample Plots

Figure 18. Mean abundance of common periwinkles Littorina littorea (no. • 1/16 m2) on rockweed Ascophyllum nodosum between control and experimental plots, pre- (July) and post- (September) harvesting. A . Number of common periwinkles on thalli of rockweed. B. Number of common periwinkles on substrate, including holdfasts of A. nodosum. N=Total number of common periwinkles.

A. Littorina obtusata Abundance on Thalli

200 SE Exp July (N=439) +/− Exp Sept (N=497) Control July (N=1474) Control Sept (N=489)

Samples 150 2

100

Mean Number of Snails on Thalli from 1/16 m 0 Sample Plots

B. Littorina obtusata Abundance on Substrate

20 SE

+/− Exp July (N=66) Exp Sept (N=120) Control July (N=83) Control Sept (N=94) Samples Samples 2 15

0 Mean Number of Snails on Substrate from 1/16 m 1/16 from Substrate on Number of Snails Mean Sample Plots Figure 19. Mean abundance of smooth periwinkles Littorina obtusata (no. • 1/16 m2) on rockweed Ascophyllum nodosum between control and experimental plots, pre- (July) and post- (September) harvesting. A. Number of smooth periwinkles on thalli of rockweed. B. Number of smooth periwinkles on substrate, including holdfasts of A. nodosum. N=Total number of smooth periwinkles.

Littorina saxatilus A. Abundance on Thalli

SE Exp July (N=332) +/− Exp Sept (N=176) Control July (N=557) Control Sept (N=419) 60 Samples Samples 2

m 1/16 from Thalli on Snails of Number Mean 0 Sample Plots

Littorina saxatilus B. Abundance on Substrate

20 SE Exp July (N=57) +/− Exp Sept (N=97) Control July (N=74) Control Sept (N=59)

Samples 2 15

0 m 1/16 from Substrate on Snails of Number Mean Sample Plots

Figure 20. Mean abundance of common periwinkles Littorina saxatilus (no. • 1/16 m2) on rockweed Ascophyllum nodosum between control and experimental plots, pre- (July) and post- (September) harvesting. A. Number of rough periwinkles on thalli of rockweed. B. Number of rough periwinkles on substrate, including holdfasts of A. nodosum. N=Total number of rough periwinkles. 32