Ascophyllum Nodosum) in Breiðafjörður, Iceland: Effects of Environmental Factors on Biomass and Plant Height

Home , Ascophyllum, Fucaceae, Fucus distichus, Fucus gardneri, Fucus serratus, Fucus spiralis

Rockweed (Ascophyllum nodosum) in Breiðafjörður, Iceland: Effects of environmental factors on biomass and plant height

Lilja Gunnarsdóttir

Faculty of Life and Environmental Sciences University of Iceland 2017

Rockweed (Ascophyllum nodosum) in Breiðafjörður, Iceland: Effects of environmental factors on biomass and plant height

Lilja Gunnarsdóttir

60 ECTS thesis submitted in partial fulfillment of a Magister Scientiarum degree in Environment and Natural Resources

MS Committee Mariana Lucia Tamayo Karl Gunnarsson

Master’s Examiner Jörundur Svavarsson

Faculty of Life and Environmental Science School of Engineering and Natural Sciences University of Iceland Reykjavik, December 2017

Rockweed (Ascophyllum nodosum) in Breiðafjörður, Iceland: Effects of environmental factors on biomass and plant height Rockweed in Breiðafjörður, Iceland 60 ECTS thesis submitted in partial fulfillment of a Magister Scientiarum degree in Environment and Natural Resources

Faculty of Life and Environmental Science School of Engineering and Natural Sciences University of Iceland Askja, Sturlugata 7 101, Reykjavik Iceland

Telephone: 525 4000

Bibliographic information: Lilja Gunnarsdóttir, 2017, Rockweed (Ascophyllum nodosum) in Breiðafjörður, Iceland: Effects of environmental factors on biomass and plant height, Master’s thesis, Faculty of Life and Environmental Science, University of Iceland, pp. 48

Printing: Háskólaprent Reykjavik, Iceland, December 2017

Abstract

During the Last Glacial Maximum (LGM) ice covered all rocky shores in eastern N-America while on the shores of Europe ice reached south of Ireland where rocky shores were found south of the glacier. After the LGM, rocky shores ecosystem development along European coasts was influenced mainly by movement of the littoral species in the wake of receding ice, while rocky shores of Iceland and NE-America were most likely colonized from N- Europe. Climate change likely facilitates new introductions of southerly species and removal of northern species which may change rocky shore ecosystems in Iceland.

Rockweed (Ascophyllum nodosum) has been harvested commercially in Breiðafjörður since 1975. Plans to increase harvesting create need for information on growth, biomass and distribution. The aim of this study was to determine effects of physical factors on plant size and biomass. Biomass and plant height were determined at 37 stations in Breiðafjörður. Mean biomass of rockweed in Breiðafjörður was 13.5 kg m-2. Biomass and plant height were significantly related to location. Biomass increased from southwest towards northeast in the fjord. Plant height was inversely related to exposure. The relationship between location, rockweed biomass and plant height is likely explained by different local conditions. Mean biomass of rockweed is high in Breiðafjörður, which is close to the northern distribution limits, where rockweed has a relatively slow growth rate and lacks efficient grazers.

Útdráttur

Grjót- og klettafjörur á austurströndum N-Ameríku og vesturströndum Evrópu voru þaktar ís á hámarki síðasta kuldaskeiðs ísaldar, fyrir utan svæði suður af Írlandi í Evrópu. Myndun vistkerfa grjót- og klettafjara í fjörum Evrópu eftir kuldaskeiðið var að mestu leyti vegna fjörutegunda sem fylgdu í kjölfar hörfandi ísaldarjökulsins. Landnám fjörutegunda í grjót- og klettafjörur Íslands var hins vegar líklegast frá N-Evrópu. Líklega munu loftlagsbreytingar auðvelda innleiðingu nýrra suðrænna tegunda og brottflutning norrænna tegunda sem gæti breytt samfélögum grjót- og klettafjara á Íslandi.

Klóþang (Ascophyllum nodosum) hefur verið skorið á Íslandi síðan 1975. Áætlanir um aukinn þangskurð kalla á upplýsingar um vöxt klóþangs, lífmassa og útbreiðslu. Markmið þessara rannsókna var að ákvarða áhrif umhverfisþátta á lífmassa og hæð plantna. Lífmassi og plöntuhæð var kannaður á 37 stöðum í Breiðafirði. Meðal lífmassi klóþangs í Breiðafirði var 13,5 kg m-2. Marktækt samband var á milli lífmassa, plöntuhæðar og staðsetningar. Lífmassi jókst frá suðvestri til norðausturs í firðinum. Einnig var marktækt samband á milli plöntuhæðar og staðsetningar. Samband staðsetningar við lífmassa og plöntuhæð klóþangs skýrist líklega af mun á staðbundnum aðstæðum. Lífmassi klóþangs er hár í Breiðafirði, sem er nálægt norðurmörkum útbreiðslu þess, þar sem klóþang vex tiltölulega hægt en jafnframt eru öflugir grasbítar ekki til staðar.

Table of Contents

List of Figures ...... x

List of Tables ...... xi

Acknowledgements ...... xiii

1 Introduction ...... 15 1.1 Icelandic shores ...... 15 1.2 Most common intertidal algae species in Iceland ...... 18 1.2.1 Serrated wrack (Fucus serratus) ...... 18 1.2.2 Channel wrack (Pelvetia canaliculata) ...... 18 1.2.3 Spiral wrack (Fucus spiralis) ...... 18 1.2.4 Two-headed wrack (Fucus distichus) ...... 18 1.2.5 Bladder wrack (Fucus vesiculosus) ...... 19 1.2.6 Rockweed (Ascophyllum nodosum) ...... 19 1.3 Origin of Icelandic intertidal flora and fauna ...... 20 1.4 Harvesting of rockweed...... 21 1.4.1 Harvesting methods ...... 22 1.4.2 Effects of harvesting on marine organisms ...... 25

2 Objectives ...... 25

3 Methods ...... 26 3.1 Study site ...... 26 3.2 Data collection ...... 26 3.3 Data analysis...... 28

4 Results ...... 29 4.1 General description of Breiðafjörður rockweed shores ...... 29 4.2 Rockweed biomass and environmental factors ...... 32

5 Discussion ...... 34

6 Conclusions ...... 36

References...... 37

Appendix ...... 45

ix List of Figures

Figure 1.1 Shore type prevalence around Iceland...... 15

Figure 1.2 Classification of Icelandic shores based on substrate and exposure...... 16

Figure 1.3 Fucoid species in Iceland...... 17

Figure 1.4 Different harvesting methods...... 24

Figure 3.1 Breiðafjörður study area in Iceland...... 26

Figure 3.2 Example of how transects were laid in sampling stations...... 27

Figure 3.3 Measuring height difference between frame pairs with two graded sticks...... 28

Figure 4.1 Distribution of rockweed biomass and plant height relative to height level in the rockweed zone...... 30

Figure 4.2 The frequency of a number of height levels studied per transect in the rockweed zone...... 31

Figure 4.3 Sampling station "Ytra-Fell" where mud covered the lower parts of the shore...... 31

Figure 4.4 Distribution of rockweed biomass in Breiðafjörður...... 33

x List of Tables

Table 4.1 Generalized additive models (GAMs) that best described the relationship between rockweed biomass and environmental factors...... 32

Table 4.2 Generalized additive models (GAMs) describing the relationship between rockweed plant height and environmental factors...... 33

Acknowledgements

I would like to extend my gratitude to Hafrannsóknastofnun, rannsókna- og ráðgjafarstofnun hafs og vatna (Marine and Freshwater Research Institute) who were instrumental in this research being conducted. Alice Beniot Cattin, Bylgja Sif Jónsdóttir, Hlynur Þorleifsson, Hlynur Pétursson, Julian Burgos, Karl Gunnarsson, Kristinn Guðmundsson, Stefán Áki Ragnarsson, Steinunn Hilma Ólafsdóttir, and Svanhildur Egilsdóttir from the Institute along with Mariana Tamayo from the University of Iceland were all involved in collecting data in the summer of 2016 and I would like to thank them for their work and cooperation.

Special thanks go to Svanhildur Egilsdóttir and Julian Burgos within the Institute. Svanhildur provided valuable advice and Julian was the reason any kind of statistical analysis and modelling was possible.

I want to thank my advisors Mariana Tamayo and Karl Gunnarsson for providing constant positive feedback and without whom my project would never have become reality. Lastly, thanks to Jörundur Svavarsson, my thesis examiner, for all his valuable input and advice.

This work was funded by a grant from AVS R&D Fund of Ministry of Fisheries and Agriculture in Iceland to Karl Gunnarsson.

xiii

1 Introduction 1.1 Icelandic shores

Shores around Iceland have been classified into three categories; rocky shores, exposed sandy shores, and areas of extensive muddy tidal flats (figure 1.1) (Ingólfsson, 2006). The south and southeast coast of Iceland are predominantly exposed sandy shores covered with black, coarse sand. Rocky shores cover over half the shoreline of Iceland, ranging from extremely exposed to fully sheltered, and they are found throughout the country.

Figure 1.1 Shore type prevalence around Iceland. Open circles represent rocky shores, full circles are sandy shores, and full triangles muddy tidal flats (from (Ingólfsson, 2006)).

It has been proposed that roughly 50% (178 km2) of the rocky shore area in Iceland are found in the Bay of Breiðafjörður (Georgsdóttir et al., 2016) and surveys in 2016 estimated that >95% of the fucoid weight in the bay are rockweed. Muddy tidal flats can be found predominantly in lagoons and small bays on the west and southwest coast, as well as in an area on the southeast coast of Iceland. The shores of Iceland have been classified by the degree of exposure and type of substrate in a synthesis on intertidal animal communities (figure 1.2) (Ingólfsson, 2006). On very exposed rocky shores, fucoids are absent but as the shores become more sheltered they become more abundant. The very sheltered shores are characterized by rockweed (Ascophyllum nodosum (Linnaeus) Le Jolis), moderately

15 sheltered shores by bladder wrack (Fucus vesiculosus Linnaeus), and exposed shores by two- headed wrack (Fucus distichus Linnaeus), although they all tend to overlap. The sedimentary shores are divided into either mussel flats (Mytilus edulis Linnaeus) or lugworm (Arenicola marina (Linnaeus)) and ragworm (Hediste diversicolor (O.F. Müller)) flats (Ingólfsson, 2006).

Figure 1.2 Classification of Icelandic shores based on substrate and exposure (Ingólfsson, 2006).

Fucoid dominated rocky shore is the most prevalent shore type around Iceland and therefore plays a substantial role in its ecosystems which is summarized by for example Seeley and Schlesinger (2012). There are six different fucoid species found on the rocky shores of Iceland. Fucoids grow on rocky shores and can be found all around Iceland, barring the shore of the south and southeast coast of the country where black volcanic sand is the dominant substrate (figure 1.1). The most common fucoids are rockweed, bladder wrack, two-headed wrack, and spiral wrack (Fucus spiralis Linnaeus). However, two additional species are found but are restricted to shores of southwestern Iceland; channel wrack (Pelvetia canaliculata (Linnaeus) Decaisne & Thuret), and serrated wrack (figure 1.3). Of these six species, all but channel wrack and spiral wrack are harvested in Ireland and Canada (Morrissey et al., 2001). In Iceland, only rockweed and bladder wrack are harvested.

Figure 1.3 Fucoid species in Iceland. Top left - serrated wrack, top right - channel wrack, middle left - spiral wrack, middle right - two-headed wrack, bottom left - bladder wrack, bottom right - rockweed (photos: Karl Gunnarsson and Svanhildur Egilsdóttir).

17 1.2 Most common intertidal algae species in Iceland

1.2.1 Serrated wrack (Fucus serratus)

Serrated wrack plants range in colour from brown to reddish brown to olive-green and can be 2 meters long with 7-25 mm wide flat fronds. The dichotomous branches have a prominent midrib, no bladders and 3-7 mm long serrations on the edges. The distribution of serrated wrack is on the western shoreline of Europe with relatively recent human introduction to northeastern shores of North America, the Faroe Islands and Iceland, estimated to have taken place during the last 1000 years (Brawley et al., 1999; Coyer et al., 2006). In Iceland, the plants are limited to the southwestern shores of the country, representing the northern limits of serrated wrack’s distribution in the North Atlantic (Jónsson, 1912; Ingólfsson, 2008). Serrated wrack is presently expanding its distribution in Hvalfjörður, Iceland (Gunnarsson et al., 2015).

1.2.2 Channel wrack (Pelvetia canaliculata)

Channel wrack is a small fucoid that grows in the uppermost part of the shore. The dichotomous branches are typically 5 to 10 cm long, 5 mm wide with the edges are folded upwards forming a channel. The colour variation ranges from olive-green to yellow-brown and turn black if the plant is out of the water for a long time (Bunker et al., 2010). Channel wrack grows near the high-water mark, spending a relatively short time covered by the sea. The channeled branches retain water to counteract the desiccation the plants face by growing high up on the shore (Schonbeck & Norton, 1979). Iceland is the northern limit of the distribution of channel wrack, and it has been reported in southwest Iceland (Jónsson, 1903) northwards to the northern shore of Breiðafjörður (Karl Gunnarsson, personal communication, May 2017). This plant also occurs on the Atlantic shores of Europe, from northern Norway to Portugal (Guiry & Guiry, 2017).

1.2.3 Spiral wrack (Fucus spiralis)

Spiral wrack earns its name from its spirally twisted, dichotomous branches. The plant is up to 20 cm long, attached to the substratum with a discoid holdfast. The branches are flat, around 2 cm wide, with a definite midrib, and may contain paired, elongated air bladders one on either side of the midrib, which differ from the spherical air bladders found on bladder wrack. Spiral wrack is a flexible, but firm plant that varies in colour, ranging from dark brown to olive-green (Bunker et al., 2010). It occurs in the upper part of sheltered shores, where the plant’s holdfast attaches to rocky substrates below the zone dominated by channel wrack when it is present. Spiral wrack is found across the Atlantic; covering the east coast of Europe, northeast coast of North America, Iceland, British Isles, and the Faroe Islands (Guiry & Guiry, 2017). In Iceland spiral wrack grows on rocky shores all around Iceland, except the south coast which is dominated by sand (Jónsson, 1903, 1912; Ingólfsson, 2006).

1.2.4 Two-headed wrack (Fucus distichus)

Two-headed wrack is a brown alga which varies considerably in morphology depending on environmental conditions. This alga is brown to dark olive-green in colour, has dichotomous branches with an indistinct midrib, and is secured to the substrate by a circular, conical

18 holdfast (Taylor & Jao, 1937; Bunker et al., 2010). The most common variant is between 30 and 90 cm long with smooth 1 to 2 cm wide branches, growing on semi-exposed shores. On sheltered shores, a variant of two-headed wrack is wider and has sizable oblong air bladders in pairs, one on either side of the midrib. In rock pools of semi-exposed shores, two-headed wrack is between 20 to 40 cm long and has less than half a centimeter wide branches. On bedrocks of highly exposed shores, another variant of two-headed wrack grows, that is short and has a substantial and strong holdfast, and a thick stem (as Fucus inflatus Linnaeus (Jónsson, 1903)). The species can be found in both the North Atlantic and North Pacific Oceans (as Fucus gardneri P.C. Silva (Laughinghouse et al., 2015)). On the European shores of the Atlantic Ocean it grows from the northern British Isles to the Arctic Ocean and on the American shores from Labrador southwards to the state of Maine (Guiry & Guiry, 2017). In Iceland two-headed wrack, similar to spiral wrack, is found on rocky shores all around the country except on the south coast (Jónsson, 1903; Ingólfsson, 2006).

1.2.5 Bladder wrack (Fucus vesiculosus)

Bladder wrack plants are generally large, 15 up to 90 cm long and 0.6 to 2.5 cm wide, with dichotomous branches growing from a circular holdfast. The branches have a definite midrib, spherical, air-filled vesicles in pairs, one on either side of the midrib or three at a branching fork. The colour of bladder wrack ranges from brown to olive-green and its texture is tough (Taylor & Jao, 1937; Bunker et al., 2010). Bladder wrack grows in various conditions, from saline lagoons to exposed rocky shores, as well as on sheltered rocky shores (Jónsson, 1903; Ingólfsson, 2006). This species is confined to the Atlantic Ocean and the Baltic Sea, growing most dominantly on the western shores of Europe, from the White Sea to southern Portugal and the Canary Islands, United Kingdom, Faroe Islands, Iceland and Spitsbergen. Bladder wrack is also found in Greenland, and on the east coast of North America from Newfoundland southwards to the Caribbean Islands (Guiry & Guiry, 2017). Bladder wrack, like spiral and two-headed wrack, is found on rocky shores all around Iceland except on the south coast (Jónsson, 1903; Ingólfsson, 2006).

1.2.6 Rockweed (Ascophyllum nodosum)

Rockweed is a brown, fucoid algae that grows in a distinct zone on rocky shores (Lewis, 1964). It grows from a holdfast in clumps of dichotomously branched main branches and basal shoots, and can reach nearly 3 meters in height (figure 1.3) (Baardseth, 1970). Rockweed has air-filled vesicles on the shoots that lift the plant when the tide rises. Dense growth of a fucoid like rockweed creates an ecosystem that serves as habitat for a multitude of invertebrates, fish, and birds (Rangeley & Kramer, 1998; Hamilton, 2001). The plant varies in colour, being yellow in areas exposed to sunlight and dark green or brown in its shaded parts (Baardseth, 1970). Rockweed has great power of regeneration. If the apex of a rockweed shoot is cut off or damaged, this shoot stops growing in length but it can still grow in thickness and produce new branches from lateral pits found along the branches or develop basal shoots from the holdfast (Baardseth, 1970). A genetically unique holdfast can produce new basal shoots for more than hundred years (Åberg, 1992). These growth characteristics of rockweed are essential to consider for sustainable harvesting. Rockweed can grow densely in sheltered to moderately sheltered shores and form an ecosystem that serves as habitat for a multitude of invertebrates, fish, and birds (Rangeley & Kramer, 1998; Hamilton, 2001). Rockweed is found on European shores of the North Atlantic Ocean extending from northern Portugal, to northern Norway. It is found in the Faroe Islands, Iceland, and southern Greenland and on the east coast North America from Labrador, Canada, southwards to North

19 Carolina, USA (Jónsson, 1912; Baardseth, 1970). In Iceland it is dominant on rocky shores all around Iceland except the south coast (Jónsson, 1903; Ingólfsson, 2006). On the rocky shore, the vertical extent of rockweed has been shown to be shaped by both environmental and biological factors. The upper limit of distribution on sheltered shores is determined by the plant’s ability to withstand high temperatures and desiccation (Schonbeck & Norton, 1978), while the lower limit distribution is controlled by grazing pressure (Lubchenco, 1980). Ice scour affects rockweed at its northern distribution limits so that areas heavily impacted by ice scour are dominated by bladder wrack, and overall the density of rockweed increases with decreasing ice presence (Menge, 1975; McCook & Chapman, 1997). 1.3 Origin of Icelandic intertidal flora and fauna

Looking at past events and how they have shaped the species pool of eastern and western shores of the North Atlantic Ocean can make predictions of future changes more reliable. For example, one past event that led to both differences and similarities in species assemblages was the opening of the Bering Strait, 5.32 million years ago (Gladenkov et al., 2002). This event, known as the trans-Arctic interchange, allowed marine species to move between the Arctic Atlantic and the North Pacific Oceans although for some time after the opening the transfer was mainly to the Pacific due to prevailing currents (Vermeij, 1991). Another large-scale event was glaciation, which was an important driver for regional and local colonization and extinction of species. Human activities in recent times such as fishing and deliberate and accidental introductions of non-native species are also a driver of species composition (Jenkins et al., 2008).

The rocky shore fauna of Iceland is almost entirely of European origin, possibly due to North American northern species dying out when the rocky shores of North America were covered with ice during the LGM (at its maximum 26.5 thousand years ago) (Ingólfsson, 1992; Paul & Schäfer-Neth, 2003; Clark et al., 2009). Similarly, Iceland was entirely covered with ice during this time (Ingólfsson et al., 2010), except perhaps some mountain areas in the north of the country (Rundgren & Ingólfsson, 1999; Ingólfsson et al., 2010). Furthermore, the European rocky shores were also covered by ice to a point south of Ireland (Sejrup et al., 2005). There, a rocky shore habitat was free from ice and possibly facilitated the survival of rocky shore species (Jenkins et al., 2008). The rocky shore species that migrated across the Atlantic in the last 13.000 years probably resemble the species assemblage present in southern Europe during the LGM, which was free of ice. This southern European species assemblage originally moved north in Europe when the glacier started receding and then across the Atlantic to Iceland and north-eastern America. This species assemblage, from south Europe, is presently reflected in the species assemblage of northern Norway (Ingólfsson, 1992). Ingólfsson (1992) studied 92 macrofaunal species of rocky shores in northern Norway and found that 95% (87 species) of them were also present in Iceland. Only 79% (73 species) of the Northern Norwegian species occurred in the Canadian Maritimes, even though the species missing could potentially survive there, thus supporting the hypothesis of European colonization of rocky shore fauna over the Atlantic. Ingólfsson (1992) study also showed that of the rocky shore faunal species that are absent from Iceland but are present in northern Norway (common limpet, Patella vulgata Linnaeus, common periwinkle, Littorina littorea (Linnaeus), the amphipod, Hyale pontica Rathke, and the sea snail Rissoa parva (da Costa)), none have naturally colonized the Canadian Maritimes. The only one of these species that is present in the Canadian Maritime, the common periwinkle, was likely introduced by humans (Chapman et al., 2007; Blakeslee et al., 2008). Both

20 common limpets and common periwinkles are herbivores that can limit macroalgal growth, although common periwinkles have a lesser grazing effect. Both are intensive grazers and while there are presently herbivorous grazers in Iceland, none have the same grazing intensity as the common limpet and common periwinkle (Jenkins et al., 2008). Rising sea temperatures (Jochumsen et al., 2016) might help facilitate the introduction of the common limpet to Iceland as presently the ability of their young to survive the cold, limits their distribution to the north (Bowman & Lewis, 2009). Introduction of such intensive grazers would most likely affect rocky shore macroalgal populations in Iceland, which are currently not subject to aggressive grazing and lead to changes in community structures.

How did the rocky shore species that colonized Iceland arrive there? Iceland is closer to Mainland Europe than North America, the shortest distances between Europe and Iceland are 800 km for Scotland and 940 km for northern Norway. The Faroe Islands, which are midway between Iceland and Norway, could have acted as a stepping stone during species dispersal (Ingólfsson, 2006). These distances mean that only a few methods of dispersal are possible. Active swimming, for example, would only work for fish, and crawling along the bottom over the ocean is highly unlikely for rocky shore species due to great depths and difficult conditions. Other potential dispersal methods are drifting with currents and transportation by fish or birds, which may explain the dispersal of a few species (Ingólfsson, 2006). However, the most likely method of dispersal is by rafting. Rafting could happen by several means, including on ice, driftwood, flotsam, or floating algae. Rafting on algae seems the likeliest mode of dispersal as grazing animals can potentially feed on the algae, and the algae themselves can drift far and wide in the sea (Ingólfsson, 1998, 2006). The rafting methods are all natural ways of species dispersal that may have been operating after the LGM.

The algal vegetation of Iceland is similar to the vegetation of northern Norway indicating similar dispersal routes for algae and rocky shore fauna (Munda, 1991). An example is bladder wrack, which is thought to have survived the LGM on a glacial refuge in southwest Ireland and dispersed north to Scandinavia, the Baltic, Iceland, and then to the Canadian Maritimes in the wake of the receding glacier (Coyer et al., 2011). Rockweed is only present on shores in the North Atlantic Ocean. The divergence of North-American and European rockweed populations happened before glaciation meaning that both populations survived in glacial refuges, one probably in Brittany, France and the other in southern Maine, USA during the LGM (Olsen et al., 2010). 1.4 Harvesting of rockweed

Rockweed is harvested in several countries, particularly in northeastern United States, Canada, France, Ireland, Norway, Scotland, and Iceland. One usage of rockweed is to extract the polysaccharide alginate, which is used in the food-, cosmetic-, and pharmaceutical industry (Þörungaverksmiðjan, 2016). Other industrial products containing rockweed include fertilizers and animal feed supplements (Ugarte et al., 2009). Both in Ireland and Canada rockweed has been harvested for decades. For example, in Ireland, rockweed has been harvested consistently since 1947 and harvesting data shows that the area harvested has not declined in productivity (Guiry & Morrison, 2013). The harvesters use hand cutting methods and harvesting ranges from 3 to 5 years depending on the rate of regrowth (Guiry & Morrison, 2013). In 1995 a new management approach was introduced for rockweed harvesting in New Brunswick, Canada, where the main goal was to secure sustainable

21 harvesting of rockweed (Ugarte & Sharp, 2001). The harvesting took a precautionary approach as information was lacking on the effects of the harvesting on the nearshore ecosystem. The approach set low exploitation rates and set out to ensure no changes in the habitat by controlling cutting height, patchiness, and holdfast removal among other things. This is an area based management that tailors the harvesting plans in accordance to ecological changes or concerns of the habitat (Ugarte & Sharp, 2012). The harvesting methods in New Brunswick and Nova Scotia have changed through the years from cutter rakes, mechanical harvesters, to settling in 1995 on hand cutting with cutter rakes. The mechanical harvesters were considered problematic since they could only access a limited number of very wave sheltered shores in spring and summer (Ugarte & Sharp, 2012). Annual harvesting rate in New Brunswick is set at a maximum of 17% of the harvestable biomass, while in Nova Scotia it is 25% which is considered a conservative management plan (Ugarte & Sharp, 2012). A company (Acadian Seaplants Ltd.) that harvests in Canada does extensive research and uses aerial photos and ground truth measurements to assess rockweed biomass each year to provide data on the state of the stock. Harvesting in Nova Scotia has been continuous for around 40 years with a variable yield of 7.8 to 27.5 t ha-1 until 1995 and since then the annual yield has been consistently maintained at around 20 t ha-1 in the areas harvested (Ugarte & Sharp, 2012). Rockweed harvesting in Norway is not regulated due to the algae being considered property of the landowner and harvesters negotiate with the landowner for permission to harvest. In some cases, there are restrictions in environmental protection laws which restricts harvester’s access to certain areas. The harvesting is done with mechanical harvesters every 4-6 years and the harvesting efficiency is about 60% (Meland & Rebours, 2012). Rockweed is the most abundant fucoid species in Iceland (Jónsson, 1912). This alga is commercially important and has been harvested in Breiðafjörður, Iceland since 1975. Harvesting of rockweed is done during the spring and summer and in the last 4 years, ~13.000 – 14.000 wet tons have been harvested in Breiðafjörður (data from Thorverk).

1.4.1 Harvesting methods

The harvesting of rockweed is mainly done with four different harvesting methods (Briand, 1991), two of which are manual and two are mechanical (figure 1.4). The simplest method, which is used in Ireland and partly in Scotland and France, involves cutting the plants with hand sickles and gathering the cut rockweed into bundles that are tied together and brought to landing facilities (Hebridean Seaweed; Guiry & Morrison, 2013). Another hand cutting method used in Canada involves cutter rakes. In terms of mechanical harvesting, one method is the paddle wheel mechanical harvester, which uses a hydraulic driven finger-bar cutting edge blade at the end of a controllable conveyor belt. The mechanical suction harvester is an additional method employing water jets to propel the machine and cuts the rockweed by sucking shoots up into a pipe with a rotating cutting knife and pumping the cut seaweed into nets. The paddle wheel harvesters were used in Canada from 1972 to 1985 and are presently used in Scotland (Burrows et al., 2010) and Iceland. The suction harvesters were used in Canada from 1985 to 1994 (Sharp & Semple, 1997) and are currently used in Maine, USA (Maine Seaweed Council, 2017) and in Norway, although partly of a different design (Meland & Rebours, 2012). The mechanical harvesters can have difficulty in accessing the resource in exposed sites or when it is windy. A comparison of the suction and paddle wheel mechanical harvesters showed that the suction harvesters cut more biomass than the paddle wheel, and the area cut by a suction harvester had less evidence of harvest than an area harvested by a paddle wheel harvester. The suction cutter had a 16-29% evidence of harvest

22 on rockweed while the paddle wheel had 27-61% (i.e., area showing effects of harvest) (Sharp, 1986). This difference is due to the suction harvesters targeting patches with a high biomass. The paddle wheel harvests by moving repeatedly over the rockweed bed and cutting from the top of the majority of the plants, and per estimations from Iceland in 2016 cuts 30-50% of the total biomass (Gunnarsson unpublished results).

Figure 1.4 Different harvesting methods. Top – manual cutter rake without handle, middle - suction cutter harvester, bottom - paddle wheel harvester (Ugarte & Sharp, 2001).

24 1.4.2 Effects of harvesting on marine organisms

Harvesting of any kind will have effects on the community and habitat. Seeley and Schlesinger (2012) stressed the importance of long-term and ecological research to determine if harvesting is sustainable. Sharp et al. (2006) reviewed the ecological impact of rockweed harvesting in the Canadian Maritimes and evaluated the possible impacts on plant population, community and ecosystem. Impacts on plant population are twofold; loss of biomass and changes in habitat architecture, which vary depending on harvesting methods (Sharp et al., 2006). The community can be impacted in both direct and indirect ways. Direct community impacts involve for example destruction or disturbance of the substrate often because of mechanical harvesters that turn over stones, bycatch of species living attached to the algae being harvested, and effects on the diversity and density of invertebrates living in the canopy (Sharp et al., 2006) but studies such as Hamilton and Nudds (2003) saw no effect from rockweed harvesting on invertebrates living in the rockweed bed. Indirect community impacts entail the removal of a habitat that provides shelter from predators and foraging area (Sharp et al., 2006). Bird species prey on invertebrates that live in the rockweed community and the quantity and height of the plants can have an effect on their feeding activity. For example, the ducklings of the common eider Somateria mollissima (Linnaeus) feed on animals in the rockweed in the first few weeks of their lives while they are unable to dive (Hamilton, 2000; Sharp et al., 2006). Blinn et al. (2008) determined that the fewest number of ducklings were supported on rockweed harvested steep slopes but in areas of gentle slope, harvesting did not affect the number of ducklings. Ecosystem impacts from harvesting have not been studied in Iceland but understanding the effects on components that make up an ecosystem is necessary to be able to evaluate the risks they face (Sharp et al., 2006). For example, macrophytes provide 4% of the total primary production of an area in the Bay of Fundy (Prouse et al., 1984). If rockweed would be providing all the macrophyte primary production, then a harvest of around 17% would result in a 1% reduction in primary production (Sharp et al., 2006).

2 Objectives

Presently there is an interest in increasing the harvesting of rockweed in Breiðafjörður, Iceland. As no reliable estimates are available on the amount of rockweed, it is necessary to estimate the total biomass in the area, factors affecting rockweed growth, sustainable harvest rate and possible ecological effects of the harvesting. The present study focuses on answering the following questions: What is the mean biomass of rockweed in Breiðafjörður? How does wave exposure, slope, geographic location, and possible competition with other fucoids influence the biomass and plant size of rockweed? The information generated will contribute to conservation and sustainable harvesting of rockweed in Iceland.

25 3 Methods 3.1 Study site

The study area is the Bay of Breiðafjörður on the west coast of Iceland (figure 3.1). Breiðafjörður is 125 km long and 50 km wide covering about 6000 km2 with numerous islands and skerries contributing to the long shoreline of the fjord, and it is thought to account for over half of the total rocky shores area of Iceland (Ingólfsson, 2006). Estimates indicate that the area contains over 4,000 islands, islets, and skerries (Björnsson, 2016). The study area within the bay covered the shorelines, east of the 23.5°W longitude but excluding Hvammsfjörður and Gilsfjörður, where salinity is low and growth of fucoids limited. Similarly, the inner most parts of most fjords were mostly mud and sand meaning no rockweed was found there.

Figure 3.1 Breiðafjörður study area in Iceland. Red dots represent sampling stations. 3.2 Data collection

Data on fucoid species coverage and weight was collected at 37 sampling stations in Breiðafjörður (figure 3.1). Sampling was conducted from April to August 2016. The sampling stations were chosen so as to cover the entire study area and at the same time being easily accessible from land or by boat. The work was done around spring tide on days when sea level was lower than 0.3 m over chart datum (Icelandic Coast Guard (Hydrographic department), 2016). At each site, 2 transects were laid out that were about 100 meters apart (figure 3.2), varying a bit depending on local conditions.

Figure 3.2 Example of how transects were laid in sampling stations. Each frame (a,b) was 0.25 m2 and there was a 25 cm height difference between frame pairs. The numbers (1,2,3) represent the levels on the shore, 1 was highest. The total number of frame pairs depended on the vertical extend of the rockweed zone.

Each transect had about 10 pairs of frames (depending on vertical extend of the rockweed zone) from the lower edge of the spiral wrack (Fucus spiralis) population, high on the seashore, to the lowermost rockweed plants near the low water mark. The frame pairs were placed successively with 25 cm difference in height down along the transect line. The height difference between frame pairs was measured with two graded sticks of equal length using the horizon as a reference (figure 3.3). The horizontal distance between frame pairs was also measured. A rectangular frame of 0.25 m2 was used to estimate the cover and biomass of each fucoid species (spiral wrack, Fucus spiralis; two-headed wrack, Fucus distichus; bladder wrack, Fucus vesiculosus; and rockweed, Ascophyllum nodosum) at each level.

Figure 3.3 Measuring height difference between frame pairs with two graded sticks (drawing by Karl Gunnarsson).

For each frame, the height of rockweed plants closest to each corner of the frame were measured. All fucoid plants that had a holdfast inside the frame were then cut 3 cm above the holdfast (to secure regrowth from the same holdfast). The cut plants were then weighed separately by species in a plastic bag or a net with a handheld scale (ElectroSamson scale, Salter Brecknell, USA) to the nearest 0.01 g. A GPS position (Garmin GPSMAP 64s; accuracy: 3.65 meters) was registered for the highest and the lowest frames on each transect. The height of the lowest frame of a transect above sea level was measured at low tide, whenever possible. 3.3 Data analysis

For each transect the slope was calculated from the GPS data and the summary of the vertical distances between frames along the transect. If GPS data was missing, then the slope was calculated from ground measurements of the horizontal distance and the height difference between the squares. Measured sea levels were adjusted for differences in barometric pressure, 10 cm for each 10 millibars above or below the average (Icelandic Coast Guard (Hydrographic department), 2016).

The Relative Exposure Index (REI) for the shoreline in Breiðafjörður was calculated by the Icelandic Institute of Natural History using NOAA’s WEMo 4.0 Model (Malhotra & Fonseca, 2007; Georgsdóttir et al., 2016) REI only describes the relative differences in exposure along the coastline, but the energy of the wave exposure was not estimated. The calculations were based on three different inputs. The first input included five years of averaged data on wind strength and direction from coastal weather stations around Breiðafjörður (data from Icelandic Meteorological Office). The second input was the depth isobaths from nautical charts (Icelandic Coast Guard, Hydrographic department; scale: 1:100,000 and 1:300,000). The third and final data input was the distance from each dot on the shore to the nearest coastline, over open sea. The REI values were evaluated for dots with 25 meters interval along the coastline (Georgsdóttir et al., 2016). To associate an exposure value to each sampling station the average of every exposure value within a 100

28 meter radius of the station was calculated. At stations where exposure values were missing from the 100 meter radius, a 250 meter radius was used instead.

The mean biomass for all stations was calculated by averaging the pairs for each level in each transect and then calculating the average for all the pairs. Preliminary modelling that included linear models, generalized least squares models (GLS), and generalized additive models (GAMs) was conducted to explore the relationship between rockweed biomass and exposure, slope, and location, as well as their interactions. The GLS models used either a power or an exponential function. One half of the GAMs used restrictions on the degrees of freedom (k) and used smooth function (s) for the variables in the models. Models were compared using Akaike information criterion (AIC) which measures the relative quality of the statistical models tested (Akaike, 2011). The final model selected was a GAM in which exposure and slope were included as linear terms and location was modelled as a two- dimensional surface. The model used a tweedie distribution and logarithmic link function, to account for the fact that biomass values cannot be negative. The same GAM model was used to model the relationship between plant height, exposure, and location as a two- dimensional surface. All analysis were performed with R Studio version 3.3.1 (R Studio, 2016).

4 Results 4.1 General description of Breiðafjörður rockweed shores

Rockweed dominated the rocky shores in all stations except the outermost stations in the north and south of Breiðafjörður. These outermost stations were covered with bladder wrack and two-headed wrack. The rockweed shores in Breiðafjörður varied within the fjord, some were mostly muddy with a sparse rockweed vegetation on protruding stones and ridges, while others were completely covered with rockweed. In some sheltered shores, the lower part of the shore was covered with mud. The mud prevents the settlement of new rockweed plants since they need bare rocks for attachment.

The mean biomass of rockweed for all stations was 13.51 kg m-2 (SD: ±2.74). But for the six most exposed shores it was 9.99 kg m-2 (SD: ±2.24), while for the six most sheltered shores it was 16.41 kg m-2 (SD: ±3.38). The biomass of rockweed ranged from 0 to 24 kg 0.25 m-2, although it was mostly below 10 kg 0.25 m-2. For all areas, the biomass of rockweed tended to increase towards the middle and lower parts of the rockweed zone (figure 4.1) although the relationship between shore level and rockweed biomass was not significant (p = 0.378). The same trend was seen with plant height, where the tallest plants tended to occur in the middle of the rockweed zone. A positive correlation was found between plant height and the shore level in the rockweed zone (p < 2*10-16). Plant height ranged from 4 cm to 280 cm; however, the majority of plants were less than 200 cm (figure 4.1).

29 Most commonly the number of levels studied per transect was between 8 and 11, meaning that since the number of levels (frame pairs) represent the range of the rockweed belt, it ranged mostly from 1.75 to almost 2.50 meters in shore height (equivalent to level 8-11 in figure 4.2).

Figure 4.1 Distribution of rockweed biomass and plant height relative to height level in the rockweed zone. The blue lines represent the mean and the grey shaded area is the 95% confidence interval for the mean.

Figure 4.2 The frequency of a number of height levels studied per transect in the rockweed zone. The total number of transects was 74.

The station that had the fewest levels, 4 and 5 per each transect, was in the inner parts of the fjord and here the lower parts of the shore was covered with mud (figure 4.3).

Figure 4.3 Sampling station "Ytra-Fell" where mud covered the lower parts of the shore (photo: Karl Gunnarsson).

31 4.2 Rockweed biomass and environmental factors

The significant results of the four best models tested to explore the relationship between rockweed biomass and the environmental factors (exposure, slope, and location) are shown in table 4.1. Location was positively related to biomass in every model it was included, but exposure and slope were non-significant in all models. The GAMs all had very similar AIC values and the deviance explained was between 36% and 39% depending on factors modelled.

Table 4.1 Generalized additive models (GAMs) that best described the relationship between rockweed biomass and environmental factors. Shown are significance, AIC values, and deviance explained by each model. More detailed results from GAMs can be found in Appendix A.

Model Factors and coefficients Significance AIC Deviance explained GAM5 Slope, exposure, and location Location *** 218.82 39.0% GAM6 Slope and location Location *** 216.44 36.4% GAM7 Exposure and location Location *** 216.83 38.6% GAM8 Location Location *** 213.71 36.8% *** p < 0.001, ** p < 0.01, * p < 0.05

The GAM8 model was used to predict the mean biomass of rockweed (kg m-2) in Breiðafjörður (figure 4.4). This model predicts that as you move from mouth to head in the fjord, from the southwest towards northeast, the mean biomass increases from 9 to 18 kg m-2.

Figure 4.4 Distribution of rockweed biomass in Breiðafjörður. Red dots are sampling stations and their size reflects the mean biomass. Contour lines representing the predicted mean biomass were created using GAM8 model.

The relationship between plant height and environmental factors such as exposure and location are shown in table 4.2. The best model fit was obtained with the GAM5-model. This model had the lowest AIC value, the highest deviance explained, and included slope, exposure, and location. Detailed results on the models are available in Appendix A.

Table 4.2 Generalized additive models (GAMs) describing the relationship between rockweed plant height and environmental factors. Shown are significance, AIC values, and deviance explained by each model. More detailed results from GAMs can be found in Appendix A.

Model Factors and coefficients Significance AIC Deviance explained GAM5 Slope, exposure, and location Exposure *** and 37077.78 7.2% location *** GAM6 Exposure and location Exposure *** and 37079.13 7.13% location *** GAM7 Slope and location Location *** 37186.4 4.31% GAM8 Location Location *** 37188.04 4.24% *** p < 0.001, ** p < 0.01, * p < 0. 05

33 5 Discussion

In Breiðafjörður rockweed biomass increased when moving into Breiðafjörður from southwest to northeast, and plant height increased with decreasing exposure and was significantly related to location. The mean biomass of rockweed for all sampling sites in Breiðafjörður was 13.5 kg m-2. Other published biomass measurements of rockweed in Iceland include Munda (1964) who measured the biomass of rockweed between the rivers Ölfusá and Þjórsá in southern Iceland at 6.3 kg m-2. Ingólfsson (2006) also measured rockweed biomass all around Iceland and found the biomass in the northwest was 5.5 kg m-2, ranging from 3.7 kg m-2 to 7.78 kg m-2 around Iceland. Rockweed biomass measurements in Canada and Scotland are slightly less than those in Breiðafjörður, ranging from 10 to 12 kg m-2 (Cousens, 1981; Sharp, 1981; Burrows et al., 2010). Rockweed biomass can vary enormously from year to year (Cousens, 1981). Ice formed during the winter is one of the main disturbances of rockweed standing crop in sheltered shores in high latitudes (Cousens, 1982; McCook & Chapman, 1997). However, based on sea surface temperature data from Flatey Island in Breiðafjörður (Marine and Freshwater Research Institute, 2017), it seems unlikely that there has been any substantial ice formation and subsequent scouring of rockweed on the shores of Breiðafjörður during the last decades. Since 1997, the winter temperature has not gone below -1°C and seawater freezes around -1.8°C. This indicates that there has been minimal winter sea ice formation in Breiðafjörður for at least 20 years. Winter ice sometimes forms locally close to estuaries and rivers flowing into Breiðafjörður, where the salinity of the water is lower than that of fully saline seawater and has a higher freezing point.

Factors controlling rockweed growth rates will also determine the annual variability in rockweed biomass. Growth rate is affected by; season (which relates to sun exposure and temperature), location within the intertidal zone, plants size and age, wave exposure, and site, (Keser & Larson, 1984; Cousens, 1985; Stengel & Dring, 1997). Biomass can be affected by both biotic and abiotic factors. Abiotic factors such as winter ice, wave action, and harvesting can reduce rockweed biomass. Harvesting, however, has been shown to sometimes enhance the growth of rockweed by producing new lateral shoots and increasing sun exposure in the rockweed bed (Lazo & Chapman, 1996). Tearing, as a consequence of wave exposure and winter ice, can also reduce rockweed biomass (McCook & Chapman, 1997). Biotic factors include grazing, possibly epiphytic load (Kraberg & Norton, 2007), and competition. Grazing rates increase with higher temperatures and the common limpet Patella vulgata is particularly destructive towards rockweed (Davies et al., 2007). The common limpet is not presently found in Iceland, but is present in the Faroe Islands and some dead individuals have been found in southern Iceland (Óskarsson, 1982). With continued ocean warming (Jochumsen et al., 2016) the common limpet might be introduced in Iceland in the future. Competition with other fucoids can limit rockweed growth (Ugarte et al., 2010). Serrated wrack is found in southwest Iceland and has been expanding its distribution northwards in the last few years, and has been shown to compete with rockweed in the lower half of the shore, resulting in a shorter vertical extension of rockweed down the shore (Gunnarsson & Galan, 1990; Ingólfsson, 2008).

Both hard and soft substrata of the eastern and western shores of the North Atlantic Ocean contain the same key taxa and similar community structures (Ingólfsson, 1992; Jenkins et al., 2008). Recent changes in species assemblage are due to human related introductions. Two noteworthy introductions in the Atlantic shores of North America are the European

34 green crab (Carcinus maenas (Linnaeus)) and the common periwinkle (Littorina littorea), which have impacted both hard and soft substrate communities (Jenkins et al., 2008). In Europe, the American slipper limpet (Crepidula fornicata (Linnaeus)) was introduced from North America and is usually associated with negative effects on native fauna, e.g. lower density of juvenile sole (Solea solea (Linnaeus)) in the Bay of Biscay (Le Pape et al., 2004). However, recently it has been suggested that the American slipper limpet may have some positive effects in its introduced habitat, such as protecting mussels from predation (Thieltges et al., 2006). In Iceland, serrated wrack (Fucus serratus) was introduced from Europe at one point between the first human settlement of the country in 874 AD and 1900 (Coyer et al., 2006), and areas covered by this algae have shown an increased grazer density and reduced barnacle cover (Ingólfsson, 2008). Other potential introductions of macroalgae to Iceland are pod-weed (Halidrys siliquosa (Linnaeus) Lyngbye), thongweed (Himanthalia elongate (Linnaeus) S.F. Gray), and the introduced Japanese wireweed (Sargassum muticum (Yendo) Fensholt). The current northern limit of distribution for pod-weed and thongweed is in the Faroe Islands (Nielsen & Gunnarsson, 2001), while for Japanese wireweed it is in south Norway (Rueness, 1997), and if sea temperatures continue rising these limits may extend northwards to Iceland. The dispersal of rocky shore species to Iceland has been contingent on the availability of rocky shore habitats.

Location seemed to be an important factor for both rockweed biomass and plant height. Location is a factor that encompasses a multitude of other factors such as exposure, temperature, salinity, turbidity, and ice formation, which can all affect rockweed distribution and biomass (Cousens, 1985; Stengel & Dring, 1997). Exposure also had a negative effect on plant height, where plant height increased with decreasing exposure. Research shows that rockweed growth rates, measured with internode length, are highest at intermediate exposures (Cousens, 1982), but wave action is least destructive in sheltered shores giving plants time to grow. The greater plant height in sheltered shores can similarly be attributed to less exposed and the lack of winter ice in the inner parts of Breiðafjörður. Sheltered shores have less wave action and typically freeze over when temperature conditions are met. The past winters in Breiðafjörður have been relatively warm, with infrequent winter ice leaving rockweed plants unharmed and allowing them to grow taller.

Rockweed is an important habitat forming species (Rangeley & Kramer, 1998; Hamilton, 2001) that is also of economic importance, being one of the main macroalgae species harvested in Iceland. Data collected for this study has been used to predict the total rockweed biomass for Breiðafjörður. The total biomass was between 1,100,000 and 1,300,000 tons (Gunnarsson et al., 2017) while the total harvest of rockweed in 2015 represented less than 1.5% of that. This harvesting rate is well below the rates reported for Canada. The average exploitation rate in Canada was 11% of the total rockweed biomass but 24% of rockweed on accessible areas only. The accessible areas represented 65% of the total rockweed covered shores (Chopin & Ugarte, 2006; Ugarte & Sharp, 2012). The harvesting methods in Iceland and Canada are different which can affect the amount of accessible area since mechanical harvesters (used in Iceland) can access less of the resource than hand cutting does (Ugarte & Sharp, 2012). The growth of rockweed is probably considerably slower in Iceland than Canada (Marbà et al., 2017), which will affect the rate of regrowth and how much of the resource can be harvested. Research that considers the local conditions in Iceland is needed to determine the actual amount of rockweed available for harvesting. Ugarte and Sharp (2012) maintain that the harvesting of rockweed in the Canadian Maritimes is sustainable as there has been a consistent yield of rockweed. However, Seeley and Schlesinger (2012)

35 contend that to claim sustainability we need to take into account all the factors that affect rockweed growth. Given the numerous factors relating to rockweed growth, Seeley and Schlesinger (2012) argue that management of rockweed harvesting on a large geographic scale is precarious. This study addressed some of the most glaring data gaps in rockweed research in Iceland regarding mean biomass of rockweed Breiðafjörður and identifying environmental affecting rockweed biomass and plant height, as well as research priorities to help foster sustainable use of rockweed.

6 Conclusions

The mean biomass of rockweed in Breiðafjörður was among the highest measured compared to other harvesting countries. Although the mean biomass was high, annual variability of environmental factors can cause higher or lower biomass between the years. This study provides a baseline for management of harvesting and for monitoring rockweed in Breiðafjörður. At present, there is little published research on rockweed in Breiðafjörður, some from Ingólfsson (2006) and Munda (1964), but harvesting amounts are documented by harvesters and rest periods are allowed between subsequent harvesting events. It is in the best interest of the algae industry and other stakeholders to harvest sustainably to guarantee the future use of resources and ecosystem health. Regrowth measurements, determining the acceptable amount of rockweed available for harvesting, and assessing the effects of harvesting on the biota, as well as on ecosystem services and processes are necessary to get a better overview of the harvesting potential of rockweed.

Sustainable harvesting is best achieved and maintained by using reliable and up to date information on the condition of the resource since a sustainable rockweed harvest will maintain ecosystem processes and services, biodiversity in the area, and economic profitability (Schmidt et al., 2011). The importance of adopting a precautionary approach regarding harvesting cannot be understated due to the massive data gaps that need to be addressed, especially long-term ecological research. It is important not to rely solely on research conducted outside Iceland as conditions vary from one area to another. The differences in rockweed biomass density between different places show the importance of local conditions. Breiðafjörður is close to the northern limits of rockweed distribution and lacks the intensive grazers that are common in rockweed in both the eastern and western Atlantic. The data generated from this study serves as an important baseline for further research and monitoring of changes in the distribution and biomass of rockweed in Breiðafjörður. Further research should be carried out to help ensure sustainable harvesting of rockweed, including regrowth experiments and long-term research of effects on ecosystem, especially looking at the effect of harvesting on primary production and intertidal communities in the area.

36 References

Åberg, P. (1992). Size-based demography of the seaweed Ascophyllum- nodosum in stochastic environments. Ecology, 73(4), 1488-1501. doi:Doi 10.2307/1940692 Akaike, H. (2011). Akaike’s Information Criterion. In M. Lovric (Ed.), International Encyclopedia of Statistical Science (pp. 25-25). Berlin, Heidelberg: Springer Berlin Heidelberg. Baardseth, E. (1970). Synopsis of biological data on knobbed wrack Ascophyllum nodosum (Linnaeus) Le Jolis. Rome,: Food and Agriculture Organization of the United Nations. Björnsson, Þ. (2016). Viðtal; 4284 eyjur og sker á Breiðafirði. Breiðfirðingur, 64. Blakeslee, A. M. H., Byers, J. E., & Lesser, M. P. (2008). Solving cryptogenic histories using host and parasite molecular genetics: the resolution of Littorina littorea's North American origin. Molecular Ecology, 17(16), 3684-3696. doi:10.1111/j.1365- 294X.2008.03865.x Blinn, B. M., Diamond, A. W., & Hamilton, D. J. (2008). Factors affecting selection of brood-rearing habitat by common eiders (Somateria mollissima) in the Bay of Fundy, New Brunswick, Canada. Waterbirds, 31(4), 520-529. doi:10.1675/1524-4695- 31.4.520 Bowman, R. S., & Lewis, J. R. (2009). Annual fluctuations in the recruitment of Patella vulgata L. Journal of the Marine Biological Association of the United Kingdom, 57(3), 793-815. doi:10.1017/S0025315400025169 Brawley, S. H., Johnson, L. E., Pearson, G. A., Speransky, V., Li, R., & Serrão, E. (1999). Gamete release at low tide in fucoid algae: Maladaptive or advantageous? American Zoologist, 39(2), 218- 229. Briand, X. (1991). Seaweed harvesting in Europe. In M. D. Guiry & G. Blunden (Eds.), Seaweed resources in Europe: uses and potential (pp. 259-308). Wiley, Chistester. Bunker, F. S. D., Maggs, C. A., Brodie, J. A., & Bunker, A. R. (2010). Seasearch guide to seaweeds of Britain and Ireland: Marine Conservation Society, Ross-on-Wye. Burrows, M. T., Macleod, M., & Orr, K. (2010). Mapping the intertidal seaweed resources of the Outer Hebrides. Scottish Association for Marine Science Internal Report No. 269. Chapman, J. W., Carlton, J. T., Bellinger, M. R., & Blakeslee, A. M. H. (2007). Premature refutation of a human-mediated marine species introduction: the case history of the marine snail Littorina

37 littorea in the Northwestern Atlantic. Biological Invasions, 9(8), 995-1008. doi:10.1007/s10530-007-9098-9 Chopin, T., & Ugarte, R. (2006). Seaweed resources of Eastern Canada. In C. A.T., M. Ohno, & D. B. Largo (Eds.), CD-ROM World Seaweed Resources—an authoritative reference system. Version:1.0 Margraf Publishers GmbH. Clark, P. U., Dyke, A. S., Shakun, J. D., Carlson, A. E., Clark, J., Wohlfarth, B., . . . McCabe, A. M. (2009). The Last Glacial Maximum. Science, 325(5941), 710. Cousens, R. (1981). Variation in annual production by Ascophyllum nodosum with degree of exposure to wave action. Proceedings of the International Seaweed Symposium, 10, 253-258. Cousens, R. (1982). The effect of exposure to wave action on the morphology and pigmentation of Ascophyllum-nodosum (L) Le Jolis in southeastern Canada. Botanica Marina, 25(4), 191-195. doi:DOI 10.1515/botm.1982.25.4.191 Cousens, R. (1985). Frond size distributions and the effects of the algal canopy on the behaviour of Ascophyllum nodosum (L.) Le Jolis. Journal of Experimental Marine Biology and Ecology, 92(2), 231- 249. doi:http://dx.doi.org/10.1016/0022-0981(85)90097-8 Coyer, J. A., Hoarau, G., Costa, J. F., Hogerdijk, B., Serrao, E. A., Billard, E., . . . Olsen, J. L. (2011). Evolution and diversification within the intertidal brown macroalgae Fucus spiralis/F. vesiculosus species complex in the North Atlantic. Molecular Phylogenetics and Evolution, 58(2), 283-296. doi:10.1016/j.ympev.2010.11.015 Coyer, J. A., Hoarau, G., Skage, M., Stam, W. T., & Olsen, J. L. (2006). Origin of Fucus serratus (Heterokontophyta; Fucaceae) populations in Iceland and the Faroes: a microsatellite-based assessment. European Journal of Phycology, 41(2), 235-246. doi:10.1080/09670260600652820 Davies, A. J., Johnson, M. P., & Maggs, C., A. (2007). Limpet grazing and loss of Ascophyllum nodosum canopies on decadal time scales. Marine Ecology Progress Series, 339, 131-141. Georgsdóttir, G. I., Gunnarsson, K., Kristinsdóttir, S., & Guðmundsson, G. (2016). Vistgerðir í fjöru. In J. G. Ottósson, A. Sveinsdóttir, & M. Harðardóttir (Eds.), Vistgerðir á Íslandi. Fjölrit Náttúrufræðistofnunar Nr. 54. Gladenkov, A. Y., Oleinik, A. E., Marincovich, L., & Barinov, K. B. (2002). A refined age for the earliest opening of Bering Strait. Palaeogeography, Palaeoclimatology, Palaeoecology, 183(3-4), 321-328. doi:Pii S0031-0182(02)00249-3. Doi 10.1016/S0031- 0182(02)00249-3 Guiry, M. D., & Guiry, G. M. (2017). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved from http://algaebase.org.

38 Guiry, M. D., & Morrison, L. (2013). The sustainable harvesting of Ascophyllum nodosum (Fucaceae, Phaeophyceae) in Ireland, with notes on the collection and use of some other brown algae. Journal of Applied Phycology, 25(6), 1823-1830. doi:10.1007/s10811-013-0027-2 Gunnarsson, K., Burgos, J., Gunnarsdóttir, L., Egilsdóttir, S., Georgsdóttir, G. I., & Madrigal, V. F. P. (2017). Klóþang í Breiðafirði: útbreiðsla og magn. Hafrannsóknastofnun, unpublished report. Gunnarsson, K., & Galan, A. (1990). Beltaskipting þörunga í skjólsælum klettafjörum og breytingar sem verða við náttúrulegt brottnám sagþangs (Fucus serratus L.). In G. Eggertsson, G. F. Guðmundsson, R. Thorláksdóttir, & S. Sigmundsson (Eds.), Brunnur lifandi vatns (pp. 81-89 (in Icelandic)). Háskóli Íslands - Háskólaútgáfan, Reykjavík. Gunnarsson, K., Þórarinsdóttir, G. G., & Gíslason, Ó. S. (2015). Framandi sjávarlífverur við Ísland. Náttúrufræðingurinn, 85(1/2), 4-14. Hamilton, D., & Nudds, T. (2003). Effects of predation by common eiders (Somateria mollissima) in an intertidal rockweed bed relative to an adjacent mussel bed. Marine Biology, 142(1), 1-12. doi:10.1007/s00227-002-0935-1 Hamilton, D. J. (2000). Community-level interactions between birds and aquatic macrophytes: lessons for a rockweed harvest? In R. W. Rangeley & J. L. Davies (Eds.), Gulf of Maine rockweed: Management in the face of scientific uncertainty: Proceedings of the global programme of action coalition for the Gulf of Maine (GPAC) workshop: Huntsman Marine Science Centre, St. Andrews, New Brunswick, December 5-7, 1999 (pp. 25-29): Huntsman Marine Science Centre. Hamilton, D. J. (2001). Feeding behavior of Common Eider ducklings in relation to availability of rockweed habitat and duckling age. Waterbirds, 24(2), 233-241. doi:Doi 10.2307/1522035 Hebridean Seaweed. Harvesting practices & the manufacturing process. Retrieved on August 2017 from http://www.hebrideanseaweed.co.uk/harvesting-theprocess.html. Icelandic Coast Guard (Hydrographic department). (2016). Sjávarfallatöflur 2016 (pp. 27). Sjómælingadeild Landhelgisgæslunnar. Ingólfsson, A. (1992). The origin of the rocky shore fauna of Iceland and the Canadian Maritimes. Journal of Biogeography, 19(6), 705- 712. doi:10.2307/2845711 Ingólfsson, A. (1998). Dynamics of macrofaunal communities of floating seaweed clumps off western Iceland: a study of patches on the surface of the sea. Journal of Experimental Marine Biology and Ecology, 231(1), 119-137. doi:https://doi.org/10.1016/S0022- 0981(98)00089-6

39 Ingólfsson, A. (2006). The intertidal seashore of Iceland and its animal communities: Zoological Museum, University of Copenhagen. pp. 85. Ingólfsson, A. (2008). The invasion of the intertidal canopy-forming alga Fucus serratus L. to southwestern Iceland: Possible community effects. Estuarine, Coastal and Shelf Science, 77(3), 484-490. doi:http://dx.doi.org/10.1016/j.ecss.2007.10.006 Ingólfsson, Ó., Norðdahl, H., & Schomacker, A. (2010). Deglaciation and Holocene glacial history of Iceland. In A. Schomacker, J. Krüger, & K. H. Kjær (Eds.), Developments in Quaternary Sciences (Vol. 13, pp. 51-68): Elsevier. Jenkins, S. R., Moore, P., Burrows, M. T., Garbary, D. J., Hawkins, S. J., Ingolfsson, A., . . . Woodin, S. A. (2008). Comparative ecology of North Atlantic shores: Do differences in players matter for process? Ecology, 89(11), S3-S23. doi:Doi 10.1890/07-1155.1 Jochumsen, K., Schnurr, S. M., & Quadfasel, D. (2016). Bottom temperature and salinity distribution and its variability around Iceland. Deep Sea Research Part I: Oceanographic Research Papers, 111(Supplement C), 79-90. doi:https://doi.org/10.1016/j.dsr.2016.02.009 Jónsson, H. (1903). The marine algae of Iceland. 2. Phaeophyceae. Botanisk Tidsskrift(25), 141-195. Jónsson, H. (1912). The marine algal vegetation of Iceland. In L. Kolderup-Rosenvinge & E. Warming (Eds.), The botany of Iceland (pp. 1-186): Frimodt. Keser, M., & Larson, B. R. (1984). Colonization and growth of Ascophyllum nodosum (Phaeophyta) in Maine. Journal of Phycology, 20(1), 83-87. doi:10.1111/j.0022-3646.1984.00083.x Kraberg, A. C., & Norton, T. A. (2007). Effect of epiphytism on reproductive and vegetative lateral formation in the brown, intertidal seaweed Ascophyllum nodosum (Phaeophyceae). Phycological Research, 55(1), 17-24. doi:10.1111/j.1440- 1835.2006.00441.x Laughinghouse, H. D., Muller, K. M., Adey, W. H., Lara, Y., Young, R., & Johnson, G. (2015). Evolution of the northern rockweed, Fucus distichus, in a regime of glacial cycling: Implications for benthic algal phylogenetics. Plos One, 10(12). doi:ARTN e0143795. 10.1371/journal.pone.0143795 Lazo, L., & Chapman, A. R. O. (1996). Effects of harvesting on Ascophyllum nodosum (L.) Le Jol. (Fucales, Phaeophyta): a demographic approach. Journal of Applied Phycology, 8(2), 87- 103. doi:10.1007/bf02186311 Le Pape, O., Guerault, D., & Desaunay, Y. (2004). Effect of an invasive mollusc, American slipper limpet Crepidula fornicata, on habitat suitability for juvenile common sole Solea solea in the Bay of Biscay. Marine Ecology Progress Series, 277, 107-115. doi:DOI 10.3354/meps277107

40 Lewis, J. R. (1964). The ecology of rocky shores. London: English Universities Press. Lubchenco, J. (1980). Algal zonation in the New England rocky intertidal community: An experimental analysis. Ecology, 61(2), 333-344. doi:10.2307/1935192 Maine Seaweed Council. (2017). Rockweed harvesting. Retrieved on August 10, 2017 from http://www.seaweedcouncil.org/rockweed- harvesting/. Malhotra, A., & Fonseca, M. S. (2007). WEMo (Wave Exposure Model): Formulation procedures and validation. NOAA Technical Memorandum NOS NCCOS #65. 28p. Marbà, N., Krause-Jensen, D., Olesen, B., Christensen, P. B., Merzouk, A., Rodrigues, J., . . . Wilce, R. T. (2017). Climate change stimulates the growth of the intertidal macroalgae Ascophyllum nodosum near the northern distribution limit. Ambio, 46(Suppl 1), 119-131. doi:10.1007/s13280-016-0873-7 McCook, L. J., & Chapman, A. R. O. (1997). Patterns and variations in natural succession following massive ice-scour of a rocky intertidal seashore. Journal of Experimental Marine Biology and Ecology, 214(1), 121-147. doi:http://dx.doi.org/10.1016/S0022- 0981(96)02751-7 Meland, M., & Rebours, C. (2012). The Norwegian seaweed industry. Bioforsk – Norwegian Institute for Agricultural and Environmental Research. Menge, J. L. (1975). Effect of herbivores on community structure of the New England rocky intertidal region: distribution, abundance and diversity of algae. Morrissey, J., Kraan, S., & Guiry, M. D. (2001). A guide to commercially important seaweeds on the Irish coast: Bord Iascaigh Mhara, Dun Laoghaire, Co. Dublin. Munda, I.-M. (1964). The quantity and chemical composition of Ascophyllum nodosum (L.) Le Jol. along the coast between the rivers Ölfusá and Thjórsa (Southern Iceland). Botanica Marina, 7, 76-89. Munda, I. M. (1991). Shoreline ecology in Iceland with special emphasis on the benthic algal vegetation. In A. C. Mathieson & P. H. Nienhuis (Eds.), Ecosystems of the world 24. Intertidal and littoral ecosystems (pp. 67-81). Elsevier, Amsterdam, 1991. Nielsen, R., & Gunnarsson, K. (2001). Seaweeds of the Faroe Island: An annotated checklist. Fróðskaparrit, 49, 45-108. Olsen, J. L., Zechman, F. W., Hoarau, G., Coyer, J. A., Stam, W. T., Valero, M., & Aberg, P. (2010). The phylogeographic architecture of the fucoid seaweed Ascophyllum nodosum: an intertidal 'marine tree' and survivor of more than one glacial-interglacial cycle. Journal of Biogeography, 37(5), 842-856. doi:10.1111/j.1365-2699.2009.02262.x

41 Óskarsson, I. (1982). Skeldýrafána Íslands : samlokur í sjó, sæsniglar með skel. Reykjavík: Prentsmiðjan Leiftur. Paul, A., & Schäfer-Neth, C. (2003). Modeling the water masses of the Atlantic Ocean at the Last Glacial Maximum. Paleoceanography, 18(3). doi:10.1029/2002PA000783 Prouse, N., Gordon, D. C., Hargrave, B. T., Bird, C. J., McLachlan, J., Lakshminarrayana, J., . . . Thomas, M. L. H. (1984). Primary production: Organic matter supply to the ecosystems in the Bay of Fundy. Canadian Technical Report of Fisheries and Aquatic Science, 1256, 65-96. doi:10.13140/2.1.2215.2483 R Studio. (2016). RStudio: Integrated development for R (Version 3.3.1) [Computer software]. Boston, MA. Retrieved October 1st, 2016 from http://www.rstudio.org/. Rangeley, R. W., & Kramer, D. L. (1998). Density-dependent antipredator tactics and habitat selection in juvenile pollock. Ecology, 79(3), 943-952. Rueness, J. (1997). Algae. In T. Brattegard & T. Holthe (Eds.), Distribution of marine, benthic macro-organisms in Norway: a tabulated catalogue. preliminary Edition. Research Report No. 1997-1: Direktoratet for Naturforvaltning. Rundgren, M., & Ingólfsson, O. (1999). Plant survival in Iceland during periods of glaciation? Journal of Biogeography, 26(2), 387-396. Schonbeck, M., & Norton, T. A. (1978). Factors controlling the upper limits of fucoid algae on the shore. Journal of Experimental Marine Biology and Ecology, 31(3), 303-313. doi:http://dx.doi.org/10.1016/0022-0981(78)90065-5 Schonbeck, M. W., & Norton, T. A. (1979). Drought-hardening in the upper-shore seaweeds Fucus spiralis and Pelvetia canaliculata. Journal of Ecology, 67(2), 687-696. doi:Doi 10.2307/2259120 Seeley, R. H., & Schlesinger, W. H. (2012). Sustainable seaweed cutting? The rockweed (Ascophyllum nodosum) industry of Maine and the Maritime Provinces. Annals of the New York Academy of Sciences, 1249(1), 84-103. doi:10.1111/j.1749- 6632.2012.06443.x Sejrup, H. P., Hjelstuen, B. O., Dahlgren, K. I. T., Haflidason, H., Kuijpers, A., Nygard, A., . . . Vorren, T. O. (2005). Pleistocene glacial history of the NW European continental margin. Marine and Petroleum Geology, 22(9-10), 1111-1129. doi:10.1016/j.marpetgeo.2004.09.007 Sharp, G. J. (1981). An assessment of Ascophyllum nodosum harvesting methods in soutwestern Nova Scotia. Canadian Technical Report of Fisheries and Aquatic Science 1012: v + 1028 p. Sharp, G. J. (1986). Ascophyllum nodosum and its harvesting in Eastern Canada. In M. S. Doty, F. F. Caddy, & B. Santelices (Eds.), Case studies of seven commercial seaweed resources (Vol. 281, pp. 3- 46). FAO Technical Report.

42 Sharp, G. J., & Semple, R. E. (1997). Rockweed (Ascophyllum nodosum). CAFSAC research document, 97(31), 10. Sharp, G. J., Ugarte, R., & Semple, R. (2006). The ecological impact of marine plant harvesting in the Canadian Maritimes, implications for coastal zone management. ScienceAsia, 32(2006), 77-86. doi:10.2306/scienceasia1513-1874.2006.32(s1).077 Stengel, D. B., & Dring, M. J. (1997). Morphology and in situ growth rates of plants of Ascophyllum nodosum (Phaeophyta) from different shore levels and responses of plants to vertical transplantation. European Journal of Phycology, 32(2), 193-202. doi:10.1080/09670269710001737129 Taylor, W. R., & Jao, C.-c. (1937). Marine algae of the northeastern coast of North America. Ann Arbor,: University of Michigan Press. Thieltges, D. W., Strasser, M., & Reise, K. (2006). How bad are invaders in coastal waters? The case of the American slipper limpet Crepidula fornicata in western Europe. Biological Invasions, 8(8), 1673-1680. doi:10.1007/s10530-005-5279-6 Þörungaverksmiðjan. (2016). Saga Þörungaverksmiðjunnar. Retrieved from http://www.thorverk.is/islenska/fyrirtaekid/index.php Ugarte, R., & Sharp, G. (2012). Management and production of the brown algae Ascophyllum nodosum in the Canadian maritimes. Journal of Applied Phycology, 24(3), 409-416. doi:10.1007/s10811-011-9753-5 Ugarte, R. A., Craigie, J. S., & Critchley, A. T. (2010). Fucoid flora of the rocky intertidal of the Canadian Maritimes: Implications for the future with rapid climate change. In J. Seckbach, R. Einav, & A. Israel (Eds.), Seaweeds and their Role in Globally Changing Environments (pp. 69-90). Dordrecht: Springer Netherlands. Ugarte, R. A., Critchley, A., Serdynska, A. R., & Deveau, J. P. (2009). Changes in composition of rockweed (Ascophyllum nodosum) beds due to possible recent increase in sea temperature in Eastern Canada. Journal of Applied Phycology, 21(5), 591-598. doi:10.1007/s10811-008-9397-2 Ugarte, R. A., & Sharp, G. (2001). A new approach to seaweed management in Eastern Canada: the case of Ascophyllum nodosum. Cahiers De Biologie Marine, 42(1-2), 63-70. Vermeij, G. J. (1991). Anatomy of an invasion: The trans-Arctic interchange. Paleobiology, 17(3), 281-307.

Appendix

GAM models for biomass

GAM5 Family: Tweedie (p=1.013) Link function: log Formula: mbiomass ~ exp100 + slope + s(lon,lat) Parametric Estimate Std. Error t value P value coefficients (Intercept) 2.692 0.1562 17.239 <2*10-16 ***

Exposure -8.402*10-6 7.922*10-6 -1.061 0.298

Slope -0.1868 2.756 -0.068 0.946

s(lon,lat)a 2.855 (edfb) 29 (Ref.dfc) 0.418 (F-value) 0.00603 **

R-sq. (adj.) = 0.267 Deviance explained = 39% -REML = 114.06 Scale est. = 1.3597 n = 35 aRepresents the smooth variable. bedf = effective degrees of freedom. cRef.df = original degrees of freedom before deductions for smoothing fits. Significance level: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

GAM6 Family: Tweedie (p=1.252) Link function: log Formula: mbiomass ~ slope + s(lon,lat) Parametric Estimate Std. Error t value P value coefficients: (Intercept) 2.5949 0.1491 17.405 <2*10-16 ***

Slope 0.7136 2.8652 0.249 0.805

s(lon,lat)a 2.511 (edfb) 29 (Ref.dfc) 0.533 (F-value) 0.00124 **

R-sq. (adj.) = 0.262 Deviance explained = 36.4% -REML = 104.54 Scale est. = 0.8174 n = 35 aRepresents the smooth variable. bedf = effective degrees of freedom. cRef.df = original degrees of freedom before deductions for smoothing fits. Significance level: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

45 GAM7 Family: Tweedie (p=1.013) Link function: log Formula: mbiomass ~ exp100 + s(lon,lat) Parametric Estimate Std. Error t value P value coefficients: (Intercept) 2.683 0.07132 37.620 <2*10-16 ***

Exposure -8.306*10-6 7.819*10-6 -1.062 0.297

s(lon,lat)a 2.788 (edfb) 29 (Ref.dfc) 0.418 (F-value) 0.00557 **

R-sq. (adj.) = 0.287 Deviance explained = 38.6% -REML = 115.99 Scale est. = 1.3595 n = 35 aRepresents the smooth variable. bedf = effective degrees of freedom. cRef.df = original degrees of freedom before deductions for smoothing fits. Significance level: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

GAM8 Family: Tweedie (p=1.013) Link function: log Formula: mbiomass ~ s(lon,lat) Parametric Estimate Std. Error t value P value coefficients: (Intercept) 2.63123 0.05424 48.51 <2*10-16 ***

s(lon,lat)a 2.783 (edfb) 29 (Ref.dfc) 0.57 (F-value) 0.00101 **

R-sq. (adj.) = 0.291 Deviance explained = 36.8% -REML = 105.72 Scale est. = 1.3595 n = 35 aRepresents the smooth variable. bedf = effective degrees of freedom. cRef.df = original degrees of freedom before deductions for smoothing fits. Significance level: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

46 GAM tables for plant height

GAM5 Family: Tweedie (p=1.574) Link function: log Formula: plant.height ~ exposure100 + slope + s(lon,lat) Parametric Estimate Std. Error t value P value coefficients: (Intercept) 4.599 0.0546 84.219 <2*10-16 ***

Exposure -2.292 *10-5 3.268 *10-6 -7.013 2.75*10-12 ***

Slope -1.817 1.045 -1.738 0.0823 .

s(lon,lat)a 26.05 (edfb) 29 (Ref.dfc) 8.612 <2*10-16 *** (F-value) R-sq. (adj.) = 0.0671 Deviance explained = 7.2% -REML = 18587 Scale est. = 1.4153 n = 3720 aRepresents the smooth variable. bedf = effective degrees of freedom. cRef.df = original degrees of freedom before deductions for smoothing fits. Significance level: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

GAM6 Family: Tweedie (p=1.577) Link function: log Formula: plant.height ~ exposure100 + s(lon,lat) Parametric Estimate Std. Error t value P value coefficients: (Intercept) 4.512 0.02151 209.762 <2*10-16 ***

Exposure -2.357 *10-5 3.251 *10-6 -7.249 5.11*10-13 ***

s(lon,lat)a 26.24 (edfb) 29 (Ref.dfc) 9.117 <2*10-16 *** (F-value) R-sq. (adj.) = 0.066 Deviance explained = 7.13% -REML = 18589 Scale est. = 1.3984 n = 3720 aRepresents the smooth variable. bedf = effective degrees of freedom. cRef.df = original degrees of freedom before deductions for smoothing fits. Significance level: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

47 GAM7 Family: Tweedie (p=1.593) Link function: log Formula: plant.height ~ slope + s(lon,lat) Parametric Estimate Std. Error t value P value coefficients: (Intercept) 4.43323 0.04308 102.906 <2*10-16 ***

Slope -1.28171 8.4562 -1.516 0.13

s(lon,lat)a 21.1 (edfb) 29 (Ref.dfc) 4.783 <2*10-16 *** (F-value) R-sq. (adj.) = 0.0405 Deviance explained = 4.31% -REML = 18612 Scale est. = 1.3451 n = 3720 aRepresents the smooth variable. bedf = effective degrees of freedom. cRef.df = original degrees of freedom before deductions for smoothing fits. Significance level: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

GAM8 Family: Tweedie (p=1.595) Link function: log Formula: plant.height ~ s(lon,lat) Parametric Estimate Std. Error t value P value coefficients: (Intercept) 4.369060 0.007821 558.6 <2*10-16 ***

s(lon,lat)a 21.33 (edfb) 29 (Ref.dfc) 5.182 <2*10-16 *** (F-value) R-sq. (adj.) = 0.0397 Deviance explained = 4.24% -REML = 18613 Scale est. = 1.3359 n = 3720 aRepresents the smooth variable. bedf = effective degrees of freedom. cRef.df = original degrees of freedom before deductions for smoothing fits. Significance level: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1