ABSTRACT
  1. Fucoid forests are areas dominated by marine brown seaweed in the taxonomic order Fucales that, like the better-known marine foundation species - corals, kelps, seagrasses, salt marshes, and mangroves - are threatened by anthropogenic stressors.
  2. Fucoid forests are fabulous and important because they, like the better-known marine foundation species (i) span large areas, bioregions, and ecosystems, (ii) provide ecological functions such as high productivity and biodiversity, and (iii) support a variety of ecosystem services including habitat for commercial fishery species, food for humans and cultural values.
  3. Fucoid forests are, based on a new citation analysis, forgotten worldwide, because they are described orders of magnitude less than the better-known marine foundation species, in ecology and marine biology textbooks, in Google Scholar and Scopus databases over scientific literature, and in recent reports and reviews about seaweed forests.
  4. Fucoid forests would be less forgotten if more people acknowledge their biological importance and societal value more often and equate their importance to that of the better-known marine foundation species. Perhaps name-recognition would also improve if fucoids are unified under a non-taxonomic common name across teaching, research, management, and conservation, like the better-known marine foundation species. We agree with the marine scientists that have used ‘rockweed’ as such a common name to describe all fucoids, but other seaweed-experts disagree because they (a) do not agree fucoids are forgotten, (b) dislike common names or (c) argue rockweed should only describe fucoid species in the family Fucaceae.
Keywords: Foundation species, brown seaweed, marine forests, habitat-formers, ecological functions, ecosystem services
1. Introduction; a forgotten paper about a forgotten topic? In 2017, an important review was published in Ecology & Evolution, with the objective of highlighting that underwater forests dominated by fucoid seaweeds are vital ecosystems, but have been ‘forgotten’ (Coleman and Wernberg 2017). Today, this paper has been cited 73 times (Scopus search, 31/1-2024), but only by marine biologists and only in research papers that focused exclusively on marine ecosystems. This suggests that take-home messages about the broad importance of fucoid forests have not expanded into general branches of ecology and conservation, perhaps because the paper focused on detailed fucoid biology in a regional context (the subtidal reefs of temperate Australia).
In this viewpoint, we aim to restate and broaden the essential take home message of Coleman & Wernberg (2017) to all readers of Ecology & Evolution: Fucoid forests are globally important ecosystems and should not be forgotten!
2. What are fucoid forests? Fucoids refers to species of seaweeds that belong to the order Fucales (Phaeophycae, i.e., brown macroalgae), a monophyletic taxonomic group represented by over 550 species from 51 genera and 9 families (Algabase 2 Dec 2023) (Bringloe et al. 2020). Most fucoids are large species (by marine standards), that separated over 60 million years ago from the other brown seaweeds (Bringloe et al. 2020). By comparison, the better-known kelps are large brown seaweed in the order Laminariales (Schiel and Foster 2006, Coleman and Wernberg 2017), although some seaweed researchers emphasize ecological function over taxonomy and therefore argue that the term ‘kelps’ should also include large non-laminarian brown seaweed (Fraser 2012, Wernberg and Filbee-Dexter 2019). Terrestrial forests are composed of trees (large wooden angiosperms) that are foundational species of great ecological importance (Ellison et al. 2005, Ellison 2019). In marine biology, areas dominated by relatively large ecologically important foundational species, such as seagrasses (marine angiosperms) and seaweed (red, green, and brown marine macroalga) are generally referred to as marine forests. Furthermore, in marine biology, forests are typically interpreted in a seascape context, where the sizes of the foundation species are viewed from the perspective of the animals that live in, on, and around them (Boström et al. 2011, Tokeshi and Arakaki 2012, Wernberg and Filbee-Dexter 2019). Therefore, seagrasses and seaweeds that are smaller than terrestrial trees are still functionally ‘trees’ (e.g., most marine forest in Australia and Europe are only a few metres tall) (Smale et al. 2013, Bennett et al. 2015, Coleman and Wernberg 2017). Thus, although some researchers split areas dominate by large, intermediate, and small seaweeds, into forests, beds/meadows, and lawns/turfs (Connell et al. 2014, Wernberg and Filbee-Dexter 2019), respectively, areas inhabited by dense stands of fucoids still function as ‘forests’ for the many species living in them.
In short, areas dominated by fucoid seaweeds are fucoid forests.
3. Why are fucoid forests important? First, fucoids cover vast areas, estimated to 2.57 million km2 (Fragkopoulou et al. 2022). This area is larger than the estimated global coverages of other marine foundational species, including the true laminarian kelps (c. 1.70 million km2), seagrasses (c. 1.65 million km2), coral reefs (c. 0.28 million km2), mangroves (c. 0.15 million km2) and salt marshes (c. 0.06 million km2) (Jayathilake and Costello 2018, Davidson et al. 2019, McKenzie et al. 2020, Bunting et al. 2022, Fragkopoulou et al. 2022). Indeed, fucoids are more widely distributed compared to many other marine foundation species, because they are found worldwide in all biogeographical realms (Fig. 1), creating dense forests along large stretches of coastlines, such as in the Baltic sea (Torn et al. 2006), Mediterranean sea (Ballesteros et al. 2009, Rendina et al. 2023), Australia (Coleman and Wernberg 2017), New Zealand (Schiel 1990), many tropical coastlines (Fragkopoulou et al. 2022), and even in the open ocean (Brooks et al. 2018, Wang et al. 2019). For example, in 2018, more than 20 million tons of floating Sargassum natans andS. fluitans covered c. 6,000 km2 in the tropical part of the Atlantic ocean (Fig. 2), forming one of the largest near-monospecific marine habitats on the planet (Wang et al. 2019). Second, fucoids have evolved diverse eco-physiological traits allowing them to create forests (a) from cold polar (e.g., Ascophyllum ) to hot tropical (e.g., Turbinaria ) latitudes, (b) in waves exposed (e.g., Durvillaea ) and sheltered (e.g., Hormosira ) locations, (c) from desiccation stressed intertidal (e.g.,Hormosira ), to light stressed deep waters (e.g.,Cystoseira ), (e) on bottom substrates (most fucoids) and the open pelagic (Sargassum ), and (f) in both brackish waters like the Baltic sea and estuaries (e.g., Fucus ) and fully marine oceans (all fucoids) (King 1981, Torn et al. 2006, Ballesteros et al. 2009, Thomsen and South 2019, Wang et al. 2019, Fragkopoulou et al. 2022, Pessarrodona and Grimaldi 2022). Furthermore, the ability of some fucoids to grow vegetatively allows population to dominate as drift fucoids in sheltered muddy systems, including marshes, mudflats, and mangroves (e.g. Fucus, Hormosira ), and even as epiphytes attached to other fucoids species (Notheia ) (e.g., Schiel and Foster 2006, Tuya and Haroun 2006, Thomsen et al. 2015, Coleman and Wernberg 2017, Martínez et al. 2018, Barboza et al. 2019, Cheung-Wong et al. 2022). Indeed, form-functional trait values that typically increase a species’ ecological importance, are often higher for fucoids compared to similar trait values associated with other marine foundation species. For example, fucoids can be very large and heavy (70 kg and >10 m fronds for Durvillaea species) and long-lived (>50 years for Ascophyllum ) and can hold and dominate space on long time scales (Åberg 1992, Hurd 2003, Menge et al. 2017, Vaux et al. 2023). Furthermore, fucoids, like other marine foundation species, build complex biogenic habitat, represented by many different morphological shapes and sizes of their holdfast, stipes, and fronds (e.g., with bladed or branches morphologies and sometimes air bladders and unique reproductive structures) (Fig. 2). Third, fucoids are, unfortunately, around the world and like other marine foundation species, threatened by stronger heatwaves, sediment-smothering, overgrazing, biological invasions, coastal darkening and eutrophication (Kautsky et al. 1986, Smale and Wernberg 2013, Valdazo et al. 2017, Schiel et al. 2019, Valdazo et al. 2020, Thomsen et al. 2021, Verdura et al. 2021, Fragkopoulou et al. 2022, Pessarrodona 2022, Wernberg et al. 2024). Fucoids should therefore be included in conservation and restoration to the same extent as other marine foundation species (Bellgrove et al. 2010, Bellgrove et al. 2017, Vergés et al. 2020, Eger et al. 2022b, Whitaker et al. 2023). Fourth, fucoids provide ecological functions (e.g., high productivity, supporting complex food webs and biodiversity, modifying environmental conditions) and are consequently considered indicator species for ecosystem health (Schiel and Foster 2006, Kersen et al. 2011, Schagerström et al. 2014, Coleman and Wernberg 2017, Vasconcelos et al. 2019, Benes and Bracken 2020, Pessarrodona et al. 2022, Thomsen et al. 2022). Finally, fucoids also provide essential ecosystem services, such as nutrient retention, carbon sequestration, habitats for commercial fishery species, food for humans, and a variety of cultural benefits (Fig. 3, Ugarte and Sharp 2001, Bellgrove et al. 2017, Coleman and Wernberg 2017, De La Fuente et al. 2019, Vergés et al. 2020, Duarte et al. 2022, Fragkopoulou et al. 2022).
In short, fucoids are important because they, like other marine foundation species, cover vast areas, bioregions, and ecosystems, provide vital ecological functions and ecosystem services, and are also threatened by human activities.
4. Are fucoid forests forgotten? Coleman & Wernberg (2017) argued that subtidal fucoid forests in temperate Australia are forgotten because they identified five times more research papers done on laminarian kelps. Here we list more examples that suggest fucoid forests are forgotten beyond subtidal forests in temperate Australia. First, our citation analysis of Coleman & Wernberg (2017) suggested that this important review, did not, when presented to the broad readership of Ecology and Evolution, move into the non-marine literature (see section 1). Perhaps, this is not surprising because other citation analyses suggest that marine research is cited less frequently by terrestrial researchers than vice versa (Menge et al. 2009b, a). Second, a new keyword search in 10 biology, ecology and marine textbooks taught in many university courses, showed that fucoids are mentioned orders of magnitude less than other marine foundation species. We found that across the 10 textbooks, ‘fucoid’ was only referenced 4 times whereas there were 193 references to ‘kelp’, 1035 to coral, 45 to ‘seagrass’, 198 to ‘mangrove’ and 328 to ‘salt marsh’ (including ‘saltmarsh’) (Krebs 2014, Smith and Smith 2015, Campbell et al. 2017, Fowler et al. 2017, Mittelbach and McGill 2019, Molles Jr and Sher 2019, Clark et al. 2020, Begon and Townsend 2021). Similar discrepancies were found in five marine textbooks used to teach future marine biologists, managers and conservationists, with only 5 references to fucoid compared to 425 to kelp, 2465 to coral, 914 to seagrass, 759 to mangrove, and 411 to salt marsh/saltmarsh (Lalli and Parsons 1997, Verhoef and Morin 2010, Kaiser et al. 2011, Ray and McCormick-Ray 2013, Castro and Huber 2019, Duffy 2021, Keddy and Laughlin 2021). Third, wider searches were done in Scopus and Google Scholar (February 1, 2024) to compare the total available information in reports, theses, and research papers between fucoids and the better known-marine foundation species. We used the same single word searches for each marine foundation species, but also searched for available information related to management, by combining individual marine foundation species with the keywords “AND conservation”. Across all keywords and search engines there was orders of magnitude less information available for fucoids compared to other marine foundation species, with 79-194× more hits for corals, 15-29× more for seagrasses, 37-92× more for mangroves, 39-65× more for saltmarshes (including salt marsh) and 9-16× more for kelps (Fig. 1A, B). Finally, there have been recent, targeted efforts to value seaweed forests more, resulting in several global reports and review papers about their biology, ecology, threats, services, management, restoration, and values to humans (e.g., Eger et al. 2022a, Eger et al. 2022b, al. 2023, Eger et al. 2023, Lutz 2023). However, these outputs have focused almost exclusively on kelp (3,710 references to kelp vs. 10 to fucoids), even though fucoids are equally important foundational species and often co-occur with the kelp (Coleman and Wernberg 2017).
In short, fucoids are forgotten because they are described orders of magnitude less than similar important marine foundation species in biology, ecology, and marine textbooks, in online search engines and in recent global report and reviews about the broad importance of brown seaweed forests.
5. What can be done to better know, teach, study, value and conserve forgotten fucoid forests? Fucoid forests are simple to describe (section 2), are important (section 3), but forgotten (section 4). However, fucoid forests would become better known if more people (outside the world of seaweed experts, see Box 1) acknowledge their biological importance and societal value more often. The aim of our viewpoint is to make more people aware of fucoids and their importance, like they are about kelps, corals, seagrasses, mangroves, seagrasses, and salt marshes. Increased knowledge and appreciation of fucoid forests could then spill over into broader teaching, research, management, conservation and a better understanding of ecosystem interconnectedness (Carr et al. 2003, Webb 2012). Finally, better knowledge and valuation would perhaps also arise if fucoids are unified under a non-taxonomic common name, just like corals, kelps, seagrasses, salt marshes, and mangroves. Some marine scientists have previously used ‘rockweed’ to describe all fucoids (Estes et al. 1989, Steinberg et al. 1995, Van Alstyne et al. 1999a, Van Alstyne et al. 1999b, Tegner and Dayton 2000, Liu et al. 2012, Agatsuma 2014, Duffy 2021, Elsberry and Bracken 2021), and fucoids and rockweeds are listed as synonyms in Webster’s and The Free Dictionaries (“rockweeds are any of various coarse brown algae in the order Fucales”) (Anon. 2021b, a). We agree with these scientists that the rockweed common name - with a published precedence - could potentially increase awareness about fucoids (but also acknowledge that floating Sargassum forests are clearly not ‘attached to rocks’, see box 1). However, many seaweed experts dislike calling fucoids for rockweed (box 1), because they do not agree fucoids are forgotten (but see section 4), loathe common names (a critique that implies that coral, seagrass, kelp, mangrove and salt marsh terminology should also be abandoned) or they argue that rockweed should only describe fucoid species in the Fucaceae family, as is often done in the northern hemisphere (Chapman 1989, McCook and Chapman 1993, Murray and Denis 1997, Denis 2003, Larsen 2012).
In short, we hope fucoids will become better known and valued more. To achieve this objective, more scientists, managers, and conservationists, should elevate fucoids to the level of better-known marine foundation species more often, irrespective of their study field. Perhaps calling fucoids ‘rockweeds’ (or a new common name), in scientific papers, reports, popular articles, talks and wider media, could unify, synthesize, and stimulate research and better communicate their broad ecological and societal importance to a wider audience beyond seaweed experts.