Beach-cast Wrack Research Articles

Beach-cast and drifting seaweed wrack is an important resource for marine and terrestrial macroinvertebrates in high latitudes

Seaweeds are foundation species across near-subtidal and intertidal zones, including when detached and free-floating and then cast ashore as wrack. Wrack is sometimes removed by humans for aesthetics or to be used as fertilizer. The study of wrack as an important habitat and resource for macroinvertebrates in high latitudes has been limited. To determine which taxa might be impacted when wrack is removed, the composition and relative abundance of macroinvertebrates were quantified monthly and compared in areas with and without wrack in Kachemak Bay, Alaska. Relationships were assessed between macroinvertebrates and wrack line (tidal height, moisture content, seaweed biomass) and beach characteristics (wave exposure, beach slope, substrate types). Approximately 47,000 animals were counted and a total of 87 taxa were identified from beach-cast wrack, drifting wrack, and bare sediment habitats. Macroinvertebrate communities within beach-cast wrack and bare sediment habitats were significantly different. Beach-cast wrack generally had more terrestrially-derived animals, especially Coleoptera and Diptera. Bare beach sediment was predominantly occupied by Enchytraeida (annelids). Macroinvertebrate communities were most strongly influenced by seaweed biomass and tidal height of the wrack line. Beach-cast wrack and bare sediments were also compared to drifting wrack in shallow, nearshore waters. Drifting wrack was different and generally occupied by more marine-derived animals, especially Amphipoda, Gastropoda, Mytilida, and Polychaeta. Ecological succession in decaying beach-cast wrack was documented, with decomposers (e.g., Amphipoda and Diptera) being early colonizers, and predators (e.g., Coleoptera and Hymenoptera) arriving later. Understanding the importance of this unique and ecologically important habitat to macroinvertebrates is essential, as removals and reductions in wrack availability could influence macroinvertebrate community structure, higher trophic level consumers, and key ecological processes on beaches. This study is the first direct investigation into seaweed wrack-associated macroinvertebrate communities in a sub-Arctic system.

How landscape variables influence the relative abundance, composition, and reproductive viability of macroalgal wrack in a high latitude glacial estuary

Beach-cast wrack is an important resource that is commonly harvested by humans, and its removal can have consequences for coastal ecosystems. To further our understanding of wrack dynamics within high latitude ecosystems, our study objectives were to: 1) quantify spatio-temporal differences in beach-cast wrack biomass and composition, 2) quantify and compare the composition of drifting and beach-cast wrack, 3) determine the reproductive status of beach-cast kelp and rockweed wrack, and 4) compare the efficacy of using drone and on-the-ground surveys to assess beach-cast wrack surface area at different spatial scales. This study was based in Kachemak Bay, Alaska, a high latitude estuarine system where wrack harvest is carefully regulated by the Alaska Department of Fish and Game. Wrack from eleven beaches was surveyed between March and September in 2018 and 2021. Coastline (substrate type, slope, and exposure) and adjacent watershed characteristics (percent glacial cover and range in seawater salinity) were determined for each site and found to correlate with diversity and compositional differences in drifting and beach-cast wrack throughout Kachemak Bay. Reproductive kelp and rockweed wrack were confirmed to be viable at all surveyed sites, which suggests that harvesting wrack has the potential to remove viable propagules from the reproductive pool. On-the-ground and drone-based surveys of beach-cast wrack both revealed similar seasonal patterns of patchy (spring) and continuous (summer) deposition onshore, confirming that aerial drone surveys are a useful and efficient tool for monitoring beach-cast wrack surface area. This study identified several factors that contribute to wrack relative abundance, distribution, composition, and reproductive viability, which can be used by resource managers to develop wrack stock assessment and sustainable harvest strategies.

Effect of upper beach macrofauna on nutrient cycling of sandy beaches: metabolic rates during wrack decay

Sandy beaches constitute a dynamic interface between marine and terrestrial environments, where inflows of organic matter occur mainly in the form of beach-cast wrack. Decomposition and processing of these inputs stand out as central components of ecosystem functioning and the biogeochemical processes associated with nutrient and carbon cycling. To investigate the effect of upper-beach macrofauna on wrack decomposition and carbon cycling, a manipulative experiment was carried out on Ladeira beach (42°34.33″N; 9°3.16″W—NW Spain) and ran for 43 days from 1 June 2011, where wrack decomposition rates and metabolism in the presence or absence of invertebrate macrofauna were assessed. The results showed that activities carried out by macrofauna inhabiting the upper beach are relevant in the decomposition of wrack deposits. Both the weight losses and the degradation rates were significantly higher in treatments with macrofauna access. CO2 fluxes measured throughout the experiment showed that wrack patches act as ‘hot spots’ of biogeochemical activity, supporting higher metabolic rates with maximum values of CO2 flux recorded in this study ~ 12 µmol C m−2 s−1. Microbial activity was estimated as being the main contributor to the respiration measured during wrack decay, but fragmentation and activities carried out by the macrofauna had significant effects on the mass loss, degradation rates and carbon fluxes associated with wrack decay process.

Linking plant communities on land and at sea: The effects of Posidonia oceanica wrack on the structure of dune vegetation

Although terrestrial and marine ecosystems are often perceived as clearly distinct, in coastal areas biological communities on land and at sea are in fact intimately linked. One way in which terrestrial and marine systems interact is through the accumulation of seagrass wrack on beaches, which plays an important role as a nutrient input in coastal dune food webs. Here we test whether accumulated beach-cast wrack also influences the structure and diversity of coastal dune plant communities. Relying on a database of 572 vegetation surveys distributed across the island of Sardinia, we used mixed-effects models to compare the vegetation cover and species richness of plant communities exposed to different amounts of Posidonia oceanica beach-cast wrack. We found that beaches which receive high amounts of P. oceanica wrack have considerably greater vegetation cover (10% on average) than those with fewer deposits. The positive relationship between beach-cast wrack and vegetation cover was especially strong in nearshore plant communities, becoming progressively weaker along the habitat zonation. A similar pattern was found for species richness: beaches with high levels of accumulated wrack had more diverse drift line and foredune plant communities, while habitats further away from the shoreline were unaffected. Our study is the first to present evidence suggesting that activities which reduce wrack accumulation on beaches – either through direct removal of deposits or by causing P. oceanica seabeds to decline – can have effects on both the structure and diversity of coastal dune plant communities. Effective management of Mediterranean coastal dune ecosystems will require developing clear strategies for the removal and relocation of accumulated beach-cast wrack.

Wind-Driven Dynamics of Beach-Cast Wrack in a Tide-Free System

Whereas wrack dynamics on tidally influenced beaches have been studied to some detail, essentially nothing is known about how drift lines in tide-free coastal systems vary in space and time. We provide evidence for high spatial and temporal dynamics of beach-cast wrack on a sand beach in the Western Baltic Sea. Over the course of one year, the amount of weekly deposited macrophyte wrack fluctuated from zero to 3000 g·m-1 shoreline. Wrack mostly accumulated just above the waterline. Part of the beach-cast wrack is frequently re-suspended into coastal water upon extreme high water level events, or wrack patches are translocated landwards by wind-driven changes in water level or along the shoreline by winds. Consequently, the deposited wrack does accumulate, but a steady-state of ca 400 g·m-1 builds up within 2 - 3 weeks. Eelgrass wrack buried in sand decomposed almost twice as fast as on top of the sand or re-suspended in water. Fragmentation of leaves promoted decomposition only when wrack remained on the sand surface. The spatial and temporal distribution of this valuable source of organic matter is unpredictable and depends on wind and wind-driven waves.

Detrital subsidy to the supratidal zone provides feeding habitat for intertidal crabs

Beach-cast wrack of marine origin is considered a spatial subsidy to the marine-terrestrial transition zone. We found that the wrack line on sand and gravel beaches of Vancouver Island was frequented by intertidal purple shore crabs,Hemigrapsus nudus (Dana 1851) and densely colonized by detritivorous talitrid amphipods. Amphipods spend the day buried in sand and forage on beach wrack during the night.H. nudus were found in supratidal wrack putches immediately after nightly high tides in field censuses, but spent most of the day and ebb tides either submerged subtidally or hidden underneath intertidal rocks and boulders. In feeding trials, intertidal shore crabs were capable of preying on talitrid amphipods. We considerH. nudus an omnivore feeding on both fresh and decaying macroalgae as well as animal prey. Although living supratidally, amphipods were significantly preferred over intertidal littorine snails by foraging shore crabs. Handling time of amphipods was significantly shorter than for littorine snails. While amphipods had a reduced risk of predation byH. nudus when buried in the sand, foraging undern eath wrack patches did not reduce predation pressure on amphipods by shore crabs. Rates of amphipod consumption by shore crabs were higher at darkness than daylight. In addition to an apparent day-night rhythm, tidal height and time elapsed since previous high tide had a significant influence on shore crab density wrack. We conclude that beach-cast wrack acts as a spatial subsidy by virtue of providing a valuable food source to talitrid amphipods, which are in turn consumed by shore crabs that ride the nightly high tide into supratidal wrack patches to reduce the risk of passing bare sand on theiry way to a feeding habitat rich in valuable prey.

Marine macrophytes directly enhance abundances of sandy beach fauna through provision of food and habitat

Beach-cast wrack is a prominent feature of beaches of south-western Australia. We examined the fauna of these beaches to explore the generalisation [Polis, G.A., Hurd, S.D., 1995. Extraordinarily high spider densities on islands: flow of energy from the marine to terrestrial food webs and the absence of predation. Ecology 92, 4382–4386] that beach-cast wrack from highly productive marine ecosystems subsidises low productivity of terrestrial ecosystems, to establish whether this generalisation is relevant to oligotrophic marine systems. We sampled three beaches with high and three beaches with low volumes of beach-cast wrack to determine if: (1) the presence of wrack influences the abundance of macroinvertebrates; (2) wrack acts as a food source for beach macroinvertebrates; and (3) the influence of wrack varies between zones above the high water mark. We measured wrack volume and composition, sediment characteristics, the abundance of different epibenthic and infaunal macroinvertebrates taxa, and δ 13C and δ 15N of macrophytes and macroinvertebrates. The mean volume of wrack on high-wrack beaches was 0.27–1.07 m 3 wrack m −2 compared to 0.00–0.09 m 3 wrack m −2 on low-wrack beaches. There were no significant differences in sediment grain size, moisture content or loss on ignition between the two types of beaches or zones. Epibenthic fauna and infauna were consistently abundant on high-wrack beaches (20–291 and 0.5–3.5 individuals 0.64 m −2, respectively), but either absent or extremely rare in low-wrack beaches (0–3 and 0–0.1 individuals 0.64 m −2, respectively). Within high-wrack beaches, there were no significant differences in the abundance of epifauna or infauna among beaches or between zones. The δ 13C values of macroinvertebrates at all sites were most similar to red and brown algae, with the exception of beetles from two beaches, which were closest to seagrasses. Mixing model (Isosource) results for mesograzing amphipods and dipteran flies suggested carbon was assimilated mostly from the seagrass Posidonia spp., the dune grass Spinifex longifolia and red algae for amphipods and from brown algae, red algae and dune vegetation for dipteran flies. We conclude that the presence of marine-derived wrack plays a major role in subsidising production of macroinvertebrates on beaches of south-western Australia. We suggest that marine subsidies can play a role in supporting terrestrial production, even in oligotrophic marine environments.

Species-specific decomposition rates of beach-cast wrack in Barkley Sound, British Columbia, Canada

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 328:155-160 (2006) - doi:10.3354/meps328155 Species-specific decomposition rates of beach-cast wrack in Barkley Sound, British Columbia, Canada Malte Mews1,*, Martin Zimmer1, Dennis E. Jelinski2,3 1Zoologisches Institut: Limnologie, Christian-Albrechts-Universität Kiel, Olshausenstraße 40, 24109 Kiel, Germany 2School of Environmental Studies, Queen’s University, Kingston, Ontario K7L 3N6, Canada 3Present address: Bamfield Marine Sciences Centre, Bamfield, British Columbia V0R 1B0, Canada *Email: mmews@zoologie.uni-kiel.de ABSTRACT: The fate of subtidally drifting macrophytal detritus after its deposition ashore was studied based on short-term mass loss effects and species composition of beach-cast detritus. Different species of macroalgae and seagrass varied in both physical and microbial decay, as well as faunal decomposition rates. Their preferred status as food for detritivorous amphipods also varied. Thus, beach-cast detritus changed in species composition during detritus aging. Estimated turnover rates, based on daily input rates and mass loss rates, ranged from <1 d for Nereocystis luetkeana, Macrocystis integrifolia and Ulva spp. to roughly 30 d for Fucus spp. and Phyllospadix spp. Thus, the dynamics of nutrient fluxes within the marine–terrestrial ecotone depends not only on the spatial distribution and amount of beach-cast detritus, but also on its species composition. KEY WORDS: Marine–terrestrial ecotone · Beach-cast wrack · Decomposition · Macroalgae · Seagrass · Talitrid amphipods Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 328. Online publication date: December 20, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Ecological significance and commercial harvesting of drifting and beach-cast macro-algae and seagrasses in Australia: a review

This review provides an overview of aspects of the ecology of drifting and beach-cast macroalgae and marine angiosperms in respect to present and potential commercial use of that resource in Australia. It sets the scene with sections on industries that utilise macro-algae and seagrasses, the ecology of littoral and nearshore sublittoral ecosystems and the processes of deposition of beach-cast macro-algae and seagrasses on beaches. It then describes the major economic macro-algae and seagrasses that occur as beach-cast wrack, with an emphasis on known information on habitat distribution, geographical range, and harvesting issues. Gaps in scientific knowledge are pointed out. The priority areas of future research were found to be: • The importance of beach accumulations of macro-algae and seagrasses on feeding and nesting shorebirds; • Whether available resource allows for ecologically and economically sustainable harvesting; • A survey of present and potential commercial macro-algae and seagrasses: studying biomass, density and annual production rates, interannual variability of recruitment into living stands, the effect of harvesting on trophodynamics and community structure and the stability of the resource base for economically sustainable harvesting; • An assessment of the importance of wrack in recycling nutrients and detritus to nearshore coastal ecosystems at wider geographical scales than previous work. This research should assess the dependence of offshore production on nutrients and detritus that are broken down in beachwracks.