Nereocystis Research Articles

The gelatinous extracellular matrix facilitates transport studies in kelp: visualization of pressure-induced flow reversal across sieve plates.

In vascular plants, important questions regarding phloem function remain unanswered due to problems with invasive experimental procedures in this highly sensitive tissue. Certain brown algae (kelps; Laminariales) also possess sieve tubes for photoassimilate transport, but these are embedded in large volumes of a gelatinous extracellular matrix which isolates them from neighbouring cells. Therefore, we hypothesized that kelp sieve tubes might tolerate invasive experimentation better than their analogues in higher plants, and sought to establish Nereocystis luetkeana as an experimental system. The predominant localization of cellulose and the gelatinous extracellular matrix in N. luetkeana was verified using specific fluorescent markers and confocal laser scanning microscopy. Sieve tubes in intact specimens were loaded with fluorescent dyes, either passively (carboxyfluorescein diacetate; CFDA) or by microinjection (rhodamine B), and the movement of the dyes was monitored by fluorescence microscopy. Application of CFDA demonstrated source to sink bulk flow in N. luetkeana sieve tubes, and revealed the complexity of sieve tube structure, with branches, junctions and lateral connections. Microinjection into sieve elements proved comparatively easy. Pulsed rhodamine B injection enabled the determination of flow velocity in individual sieve elements, and the direct visualization of pressure-induced reversals of flow direction across sieve plates. The reversal of flow direction across sieve plates by pressurizing the downstream sieve element conclusively demonstrates that a critical requirement of the Münch theory is satisfied in kelp; no such evidence exists for tracheophytes. Because of the high tolerance of its sieve elements to experimental manipulation, N. luetkeana is a promising alternative to vascular plants for studying the fluid mechanics of sieve tube networks.

Kelp, cobbles, and currents: Biologic reduction of coarse grain entrainment stress

Models quantifying the onset of sediment motion do not typically account for the effect of biotic processes because they are difficult to isolate and quantify in relation to physical processes. Here we investigate an example of the interaction of kelp (Order Laminariales) and coarse sediment transport in the coastal zone, where it is possible to directly quantify and test its effect. Kelp is ubiquitous along rocky coastlines and the impact on ecosystems has been well studied. We develop a physical model to explore the reduction in critical shear stress of large cobbles colonized by Nereocystis luetkeana , or bull kelp. Observations of coarse sediment motion at a site in the Strait of Juan de Fuca (northwest United States–Canada boundary channel) confirm the model prediction and show that kelp reduces the critical stress required for transport of a given grain size by as much as 92%, enabling annual coarse sediment transport rates comparable to those of fluvial systems. We demonstrate that biology is fundamental to the physical processes that shape the coastal zone in this setting.

Circadian rhythms in the motility (floating versus immersion) in Nereocystis luetkeana

Circadian rhythms in the motility (floating versus immersion) in Nereocystis luetkeana

Degrading detritus: Changes in food quality of aging kelp tissue varies with species

Export of detrital kelp from the photic zone is thought to provide an important trophic subsidy to adjacent food webs. In the San Juan Archipelago, Washington, deep habitats (e.g. >90m) contain abundant, senescent kelp detritus that presumably is colonized by microbes as it sinks. Such aging algal pieces may be of greater nutritional value than fresh material, and may have reduced levels of polyphenolic compounds, which in living kelps deter both bacterial colonization and herbivory. We report here on a diverse set of experiments designed to test the value to consumers of fresh and aged tissue of two kelps with very different biochemical compositions, Nereocystis luetkeana (low polyphenolics) and Agarum fimbriatum (high polyphenolics). We tested 1) short-term food preference and assimilation efficiency in adult isopods; 2) growth rates of juvenile isopods over 10weeks; 3) gonad development in urchins over 18weeks; 4) population growth of copepods over 4weeks and subsequent egg-hatching time; and 5) caloric content, fatty acids, and C:N ratios of fresh and aged tissue of these two kelps, with some additional data for a third kelp species. In a food-choice situation, Nereocystis is strongly preferred over Agarum, and is a superior food by a number of metrics. Aging kelp blades in the dark led to Nereocystis degrading much faster than Agarum. Overall, aging of the two kelp species tended to have opposite effects in various metrics of their value to consumers, so that in many experiments there was a species×age interaction term. Fresh Nereocystis was slightly ‘better’ than aged in terms of isopod growth and preference, gonad development in urchins, and population growth metrics in copepods, while aged Agarum was ‘better’ than fresh in a number of these metrics at least over the time scales of our studies. Degrading kelps show broad changes in fatty acids that differed among species, but we did not find a general increase in N as has been suggested elsewhere. In combination with several other recent studies, our data suggest that the value of different types of detritus to deep trophic webs is likely to be both species- and time-dependent.

Susceptibility of Nereocystis luetkeana (Laminariales, Ochrophyta) and Eualaria fistulosa (Laminariales, Ochrophyta) spores to sedimentation

The establishment of algal spores plays an essential role in adult kelp distribution and abundance patterns. Sedimentation is a key variable regulating algal spore settlement and success, possibly controlling species-specific dominance in situ. Laboratory experiments were used to determine spore attachment and survival rates of two Alaskan canopy-forming kelps, Nereocystis luetkeana (K. Mertens) Postels & Ruprecht and Eualaria fistulosa (Postels & Ruprecht) M. J. Wynne, to various types of sediment loading. Spore attachment for both species was significantly and similarly affected by three sediment treatments: suspended particles; settled sediment covering the substratum; and smothering of attached spores by settling sediment. Spore attachment decreased by approximately 90% at 420 mg sediment L -1 , the highest sediment load tested here, under all three treatments for both species. These results suggest that increases in sedimentation may constrain the success of the spore stages, but sediment does not seem to be a likely factor explaining species-specific distribution patterns. However, while sedimentation affected spores of both species similarly, timing of spore release in relation to times of maximum sediment load in the water might differ for different species, possibly explaining kelp species distribution patterns.

Seasonal variation in kelp phlorotannins in relation to grazer abundance and environmental variables in the Alaskan sublittoral zone

Phlorotannins are common metabolites produced in kelps that can have deterrent functions against grazers. The factors dictating seasonal patterns of phlorotannin content in northeastern Pacific kelps are not well understood. This study assessed density and grazing of the gastropod Lacuna vincta on the annual canopy-forming kelp Nereocystis luetkeana and the perennial understory species Agarum clathratum, Saccharina latissima and S. groenlandica in Kachemak Bay, Alaska. In addition, we assessed seasonal patterns of environmental variables as possible drivers of phlorotannin concentrations. Phlorotannins occurred in all species, with overall lowest levels in N. luetkeana, and with different seasonal patterns among the four species. Lacuna vincta was most dense on N. luetkeana thalli in the summer and had highest grazing rates on this low-phlorotannin species. However, correlations between L. vincta density and phlorotannin content of each kelp species were not significant. Except for N. luetkeana, there were no correlations between phlorotannin levels and environmental variables. We suggest that kelp life history traits may be more important for phlorotannin patterns in these kelp species than grazers or environmental drivers.

Status and habitat associations of the threatened northern abalone: importance of kelp and coralline algae

Northern abalone (Haliotis kamtschatkana kamtschatkana) is a federally listed species of concern. The status of northern abalone and the characteristics of the habitats they associate with were determined showing that northern abalone have declined dramatically in Washington State with present day abundances <10% of those found in 1979. Northern abalone inhabited kelp beds (Nereocystis luetkeana), more than red sea urchin beds (Strongylocentrotus franciscanus) (X2 = 16, d.f. = 1, P < 0.01) or habitats with both kelp and sea urchins (X2 = 13.2, d.f. = 1, P < 0.01). Sites with Nereocystis kelp canopy had twice the percentage cover of encrusting coralline algae compared with sea urchin sites. No juvenile abalone (<75 mm) were found in any of the habitat types raising concerns about recruitment failure. Abalone co-occurred with other molluscs including limpets and scallops. Kelp holdfast microhabitats had significantly higher species richness (t = 2.2, d.f. = 6, P < 0.05), twice the effective number of species and 5x more individuals than sea urchin spine microhabitats. In laboratory choice experiments, juvenile abalone (20 mm) preferred coralline rocks to kelp holdfasts or sea urchin spine canopy. The small snail, Amphissa spp. (5–15 mm) was more abundant inside kelp holdfasts than under sea urchins or in rock cobble, suggesting this may be an important microhabitat. It is recommended that kelp beds with abundant coralline substrate be used for restoration including stocking juveniles and adult aggregations as this biogenic habitat may enhance northern abalone restoration actions. Copyright © 2011 John Wiley & Sons, Ltd.

The motion of kelp blades and the surface renewal model

We consider how the flapping of kelp blades may enhance the flux of nutrients to a blade, by stripping away the diffusive sub‐layer and renewing the fluid at the blade surface. The surface renewal model explains the degree of flux enhancement observed in previous studies under different flow and flapping conditions. We measured the motion of real kelp blades of Laminaria saccharina, Macrocystis pyrifera, and Nereocystis luetkeana under uni‐directional current in a laboratory flume. Observed flapping frequencies coupled with the renewal model, suggest that the flapping of blades in the field has the potential to significantly enhance flux to the blade surface at low current speed, but has little effect on flux at high current speeds.

Photosynthetic response ofNereocystis luetkeana(Phaeophyta) to high light

SUMMARYPhotosynthetic response to high light was determined for Bull kelp,Nereocystis luetkeana(K. Mertens) Postels and Ruprecht in order to understand how this species is affected by short‐term fluctuations in irradiance. Exposure ofN. luetkeanablades to high intensity photosynthetically active radiation (1000 µmol photons m−2s–1) caused increased non‐photochemical quenching of fluorescence and higher de‐epoxidation ratios for xanthophyll pigments indicating that energy‐quenching xanthophylls were used to protect blades against photoinhibition. Despite initiation of these photoprotective mechanisms, maximum photochemical efficiency of photosystem II (Fv/Fm) decreased 40% in response to a 60 min exposure to 1000 µmol photons m−2s–1photosynthetically active radiation indicating that photoinhibition had occurred. Light‐saturated rates of oxygen evolution were not changed significantly by the high light treatment. Recovery of maximum photochemical efficiency of photosystem II to within 8% of initial values occurred after a 300‐min dim light period. Younger sections of the blades were slightly more susceptible to high light damage than older sections. Middle sections of the blades were more prone to light‐induced damage at water temperatures of 7°C or 18°C, as compared to 13°C. Exposure to biologically effective ultraviolet‐B radiation (UV‐Bbe) (up to 4.5 kJ m–2 day–1) in photoinhibitory light conditions did not significantly affect light‐induced damage to photosystem II.

Effects of diet and temperature on ingestion, absorption, assimilation, gonad yield, and gonad quality of the purple sea urchin ( Strongylocentrotus purpuratus)

Sea-urchin ingestion rate, absorption, gonad yield, and gonad quality can be influenced by a variety of factors, including food quantity, food quality, and various environmental conditions. We examined the combined effects of two factors (diet and temperature) on ingestion rate, absorption, assimilation efficiency, and gonad enhancement of the purple sea urchin, Strongylocentrotus purpuratus, over a 12-week period. Four diets [three kelp species ( Macrocystis integrifolia, Nereocystis luetkeana, and Saccharina latissima) and one prepared feed] and three temperatures (8.0 ± 0.4, 12.3 ± 0.3, and 16.2 ± 0.4 °C: mean ± SD) were tested in a completely crossed factorial design. Ingestion rate, gravimetric absorption, and assimilation efficiency of urchins fed the various diets were calculated at weeks 6 and 12. In addition, a number of gonad attributes were quantified at the beginning and end of the experiment including wet weight, percent water content, gonad index, texture, firmness, colour, and flavour. Ingestion rate, gravimetric absorption, and assimilation efficiency were generally significantly affected by both temperature and diet. Wet-weight ingestion rates were significantly higher with the three kelp treatments than with the prepared diet at both weeks 6 and 12. This particular dietary difference was not apparent, however, when ingestion rates were expressed on a dry-weight basis. The highest ingestion rates were recorded for animals held at 12 °C at week 6 and at 16 °C at week 12. Absorption rates and assimilation efficiencies were significantly higher at 16 °C than at 8 °C at week 6 and significantly higher at 16 °C than at the other two temperatures at week 12. Final gonad weight and gonad index were significantly greater in urchins fed the prepared diet than in those fed any of the three kelp species, with little difference among the kelp treatments. Final gonad weight was significantly affected by temperature, but this effect was dependent on diet; temperature had little impact on gonad weight (and index) in the three kelp treatments, but 12 and 16 °C produced significantly heavier gonads than 8 °C for urchins fed the prepared diet. Gonads of urchins fed kelps had more (significantly more in the case of M. integrifolia and N. luetkeana) water than those fed the prepared diet. Gonad colour, texture, and firmness were generally not significantly affected by temperature, diet, or the interaction of these two factors. Gonad flavour was generally (sometimes significantly) better in urchins fed the prepared diet than in those fed the three kelp species. Taking all the measured variables into consideration, we recommend that culture operations utilise a prepared diet at 12 °C to optimise gonad production of S. purpuratus.

Settlement behavior of cyphonautes larvae of the bryozoan Membranipora membranacea in response to two algal substrata

Abstract. Settlement is an important process in the biphasic life histories of many marine invertebrates. Little is known regarding the fine‐scale behavioral mechanisms for finding and attaching to a suitable substratum, particularly under conditions that may impose a potential challenge, such as flow. In this study, we examined the settlement behavior of cyphonautes larvae of the bryozoan, Membranipora membranacea, in response to two different algal substrata. Larvae showed a strong preference for settling on the kelp Nereocystis luetkeana over the red alga Mazzaella splendens. We then tested whether the behavioral mechanisms used by larvae to attach to these algae differed when presented with the challenge of flowing water during settlement. We found that larvae exhibited different behaviors on the two species of algae in flowing water. Larvae were more often observed in direct contact with the preferred alga (N. luetkeana) exhibiting fine‐scale active search behaviors. On the less preferred alga (M. splendens), larvae were less frequently observed in direct contact with the alga, and appeared to be exhibiting broad‐scale passive search behaviors along the surface of the blade. Our results suggest that cyphonautes larvae alter their behavior in response to their preferred settlement habitat.

Further to the Occurrence of Red Abalone, &lt;em&gt;Haliotis rufescens&lt;/em&gt;, in British Columbia

We report on additional occurrences of Red Abalone (Haliotis rufescens Swainson, 1822) that bring the total to seven from British Columbia coastal waters. Possible causes of the presence of Red Abalone include northward (winter) transport via kelp rafts from the Oregon-California area. We tested this hypothesis by performing DNA barcoding analyses on a fragment of kelp holdfast on the surface of one such shell establishing its identity as Nereocystis luetkeana (Mertens) Postels &amp; Ruprecht - a giant kelp with a hollow stipe terminating in a bulbous pneumatocyst (gas-filled float). The occurrence of Red Abalone due to natural processes, besides being important biogeographically, has had important implications for indigenous peoples' pre- and post-contact trade and material culture.

Community level effects of Nereocystis luetkeana in southeastern Alaska

A multispecies approach was used to examine the role of the canopy forming kelp, Nereocystis luetkeana, in structuring kelp communities near Juneau, Alaska (58°22′53 N, 134°38′45 W). Large-scale (1500 m 2) manipulations were used to test direct and indirect effects of Nereocystis on faunal assemblages. Fish and invertebrate abundances were quantified in relation to canopy (canopy, no canopy), depth (bottom, surface), and season (summer, winter) using Standard Monitoring Units for Recruitment of Fish (SMURFs), light traps, and visual surveys. Lacuna vincta directly utilized the canopy of Nereocystis with greatest abundances at canopy sites during the summer. In contrast, a direct negative effect of Nereocystis was observed for schooling Gadidae fishes; six times more fish were observed at sites without canopy kelp. The abundance of juvenile benthic fishes was twice as high at the bottom of sites containing Nereocystis as compared to no canopy sites, providing strong evidence for an indirect effect of canopy presence on community structure. Other invertebrate abundances (i.e., amphipods, copepods) were greater within the bottom strata (sub-canopy) of all sites, regardless of canopy or season. Our results illustrate the importance of a multispecies approach and present novel information for a little-studied, high-latitude kelp system.

How kelp produce blade shapes suited to different flow regimes: A new wrinkle

Many species of macroalgae have flat, strap-like blades in habitats exposed to rapidly flowing water, but have wide, ruffled "undulate" blades at protected sites. We used the giant bull kelp, Nereocystis luetkeana, to investigate how these ecomorphological differences are produced. The undulate blades of N. luetkeana from sites with low flow remain spread out and flutter erratically in moving water, thereby not only enhancing interception of light, but also increasing drag. In contrast, strap-like blades of kelp from habitats with rapid flow collapse into streamlined bundles and flutter at low amplitude in flowing water, thus reducing both drag and interception of light. Transplant experiments in the field revealed that shape of the blade in N. luetkeana is a plastic trait. Laboratory experiments in which growing blades from different sites were subjected to tensile forces that mimicked the hydrodynamic drag experienced by blades in different flow regimes showed that change in shape is induced by mechanical stress. During growth experiments in the field and laboratory, we mapped the spatial distribution of growth in both undulate and strap-like blades to determine how these different morphologies were produced. The highest growth rates occur near the proximal ends of N. luetkeana blades of both morphologies, but the rates of transverse growth of narrow, strap-like blades are lower than those of wide, undulate blades. If rates of longitudinal growth at the edges of a blade exceed the rate of longitudinal growth along the midline of the blade, ruffles along the edges of the blade are produced by elastic buckling. In contrast, flat blades are produced when rates of longitudinal growth are similar across the width of a blade. Because ruffles are the result of elastic buckling, a compliant undulate N. luetkeana blade can easily be pushed into different configurations (e.g., the wavelengths of the ruffles along the edges of the blade can change, and the whole blade can twist into left- and right-handed helicoidal shapes), which may enhance movements of the blade in flowing water that reduce self-shading and increase mass exchange along blade surfaces.

Effect of tidal currents and tidal stage on estimates of bed size in the kelp Nereocystis luetkeana

Aerial or overhead photography is a technique commonly used to measure spatiotemporal variability in surface canopy kelps. To evaluate potential biases in this technique, we used elevated (shore-based) oblique angle photography coupled with in situ measurements of currents and tides to sample 4 independent Nereocystis luetkeana beds at sites adjacent to San Juan Island (Washington State, USA) in 2004 and 2005. Data were collected at high frequency (every 10 min) to quantify the effects of tidal height and tidal currents on the amount of N. luetkeana visible at the surface. Effects of tidal height were highly significant in all 6 time series. Current significantly affected apparent bed size in 5 of the 6 time series, although the magnitude of the effect varied among sites. N. luetkeana beds decrease in apparent size as current velocity increases and as tidal level increases. Currents can fluctuate rapidly, changing by many 10s of cm s–1 over periods as short as 10 min, due in large part to interactions of tides with local topography and bathymetry close to shore, where kelp beds are typically found. As a result, currents can introduce significant variability to estimates of kelp population size collected by remote sensing techniques.

Altered kelp (Laminariales) phlorotannins and growth under elevated carbon dioxide and ultraviolet‐B treatments can influence associated intertidal food webs

AbstractDue to the importance of brown algae, such as kelp (Laminariales, Phaeophyta), within most cool nearshore environments, any direct responses of kelp to multiple global changes could alter the integrity of future coastal marine systems. Fifty‐five‐day manipulation of carbon dioxide (CO2) and ultraviolet light (UVB) within outdoor sea‐tanks, approximating past, present and two predicted future levels, examined the direct influences on Saccharina latissima (=Laminaria saccharina) and Nereocystis luetkeana development and biochemistry, as well as the indirect influences on a marine herbivore (Tegula funebralis; Gastropoda, Mollusca) and on naturally occurring intertidal detritivores. Kelp species displayed variable directional (negative and positive growth) and scale responses to CO2 and UVB manipulations, which was influenced by interactions. Kelp phlorotannin (phenolic) production in blade tissues was induced by elevated UVB levels, and especially enhanced (additively) by elevated CO2, further suggesting that some actively growing kelp species are carbon limited in typical nearshore environments. Negative indirect effects upon detritivore consumers fed CO2‐manipulated kelp blade tissues were detected, however, no statistical relationships existed among UVB‐treated tissues, and test herbivores did not distinguish between phlorotannin‐altered CO2: UVB‐treated kelp blade tissues. Results suggest that past and future conditions differentially benefit these kelp species, which implies a potential for shifts in species abundance and community composition. Higher CO2 conditions can indirectly impede marine decay processes delaying access to recycled trace nutrients, which may be disruptive to the seasonal regrowth of algae and/or higher trophic levels of nearshore ecosystems.

Nested PCR detection of microscopic life-stages of laminarian macroalgae and comparison with adult forms along intertidal height gradients

Recruitment of kelp species (Laminari- ales) to rocky marine habitats relies on the prior establishment of microscopic life-stages (zoospores, gametophytes, gametes and microscopic sporo- phytes). Unlike macroscopic sporophyte stages of kelp, microscopic life-stages have proved difficult to detect and identify in their natural habitat. Using a species-specific PCR-based assay, we developed a method to detect putative microscopic life-stages of 2 northeast Pacific kelp species, Nereocystis luetkeana (Mertens) Postels et Ruprecht and Hedophyllum ses- sile (C. Agardh) Setchell, from rocky intertidal sub- strate samples. Species-specific primers were evalu- ated for specificity and sensitivity. Comparisons of nested and unnested PCR were performed for both species. Nested PCR was used to screen for target species present on rocks obtained along an intertidal height gradient (0.0 to 3.5 m Lowest Low Water (LLW)) from 2 sites at monthly intervals in summer 2005. Vertical distribution patterns of the putative microscopic life-stages and the macroscopic sporo- phyte form were compared at both sites. Putative microscopic life-stages of N. luetkeana were detected at both sites and displayed a widespread vertical dis- tribution with no clear spatial or temporal relation- ship. In comparison, H. sessile putative microscopic life-stage distribution was much more spatially restricted, showing a similar distribution to the macroscopic sporophyte. This study demonstrates the sensitivity, specificity and validity of utilizing molecu- lar techniques to describe the distribution of micro- scopic life-stages of certain kelp species.

Lacuna vincta (Mollusca, Neotaenioglossa) herbivory on juvenile and adult Nereocystis luetkeana (Heterokontophyta, Laminariales)

Herbivory can be an important factor structuring coastal algal communities. Herbivores may preferentially graze particular algal species or tissue types. Mesograzers, despite their small size, can critically weaken kelp thalli and impact entire kelp beds. We propose that when kelp beds are composed of several kelp cohorts, mesograzers will selectively choose to inhabit younger plants and grazing activities will have a greater impact on younger plants. This study investigated the effects of grazing by the littorinid gastropod, Lacuna vincta, on different age classes of the bull kelp, Nereocystis luetkeana by (1) testing food preference of L. vincta on juvenile, first-year adult, and second-year adult Nereocystis blades in the laboratory, (2) determining substrate (blades of different ages) preference of L. vincta in the laboratory, and by (3) estimating in-situ herbivore abundances and densities on juvenile and adult Nereocystis. Results demonstrated that grazing by L. vincta produced greater damage on juvenile than older Nereocystis tissues. Although L. vincta did not select juvenile versus older kelps as substrate in the laboratory, in situ surveys showed that differences existed between age classes with higher L. vincta densities on juvenile than adult kelp. We conclude that at a local scale, L. vincta can be an important structuring factor in Nereocystis populations due to its high density and grazing ability.

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.

A remote sensing approach to estimating harvestable kelp biomass

Regulations of the Alaska Department of Fish and Game require that all fisheries in the state have a harvest management plan. In southeast Alaska two species of floating kelps, Nereocystis luetkeana and Alaria fistulosa, have been commercially harvested since 1992 for use as agrochemicals by the Alaska Kelp Company. However, there is currently no harvest management plan for this fishery. The lack of a formalized management plan is one factor that has kept the kelp industry from expanding in the state. We have employed an aerial digital multispectral imaging system (DMSC) calibrated with ground truthing for performing such an assessment. The system can be flown at varying altitudes to achieve spatial resolutions ranging from 0.5 to 2 m. Rapid ground truthing techniques were developed using morphometric measurements to predict biomass. Analysis of the DMSC imagery showed that good correlations could be developed between the multispectral imagery and kelp biomass estimates collected at the ground-truth sites. Repeatable estimates of kelp bed area derived from the multispectral imagery could be made at varying tidal levels. However, broad scale maps of kelp biomass suitable for estimating harvest rates could not be made at different tide levels. Multispectral imagery suitable for this purpose must be collected at a standard tidal level.