Subtidal Kelp Research Articles

Can sea urchin grazing of kelp forests in the Arctic make rocky shore systems more vulnerable to oil spills?

In Arctic Norway, the risk of major marine oil spills associated with increasing offshore drilling, land terminal, and maritime transport activities is a cause for concern. Intertidal and subtidal kelp and seaweed communities found in this region are highly productive ecosystems, although sea urchin (Strongylocentrotus droebachiensis)-overgrazed areas (urchin barrens) have been and still are a widespread problem. In the present study, we developed a kelp (Laminaria hyperborea) distribution model and studied fauna distribution, dispersal and recolonisation potentials in seaweed communities, kelp forests and sea urchin-grazed areas to assess sensitivity and vulnerability of these rocky shore communities to additional stress from oil spills, especially if the oil is released close to the coast. Our results suggest that sheltered and moderately exposed rocky shore seaweed communities close to urchin barrens are the most sensitive systems when a combined ecological effect from grazing and oil spill pollution is considered. Our study may have implications for which oil spill countermeasures that represent the best environmental practice (BEP) in the northern coastal areas that already are ecologically stressed because of sea urchin overgrazing.

The importance of kelp to an intertidal ecosystem varies by trophic level: insights from amino acid δ13C analysis

AbstractA fundamental question in ecology is understanding how energy and nutrients move through and between food webs, and which sources of production support consumers. In marine ecosystems, these basic questions have been challenging to answer given the limitation of observational methods. Stable isotope analysis of essential amino acids (EAA δ13C) has great potential as a tool to quantify energy and nutrient flow through marine food webs; however, it has been primarily utilized at large spatial scales. Here, we used EAA δ13C analysis to test for connectivity between adjacent subtidal and intertidal components of a nearshore ecosystem in south central Alaska. We measured δ13C of six EAA from four marine producer groups: subtidal kelp (Laminaria sp.), offshore particulate organic matter (POM), and intertidal red (Neorhodomela sp.) and green (Ulva sp.) algae. In addition, we sampled four intertidal invertebrate consumer species spanning a range of trophic/functional groups: Mytilus sp., Strongylocentrotus droebachiensis, Nucella sp., and Pycnopodia helianthoides. Using canonical analysis of principal coordinates (CAP) and isotope mixing models (MixSIAR), we tested for differences among producer EAA δ13C fingerprints and quantified the contribution of producer EAA to consumers. We compared these results to previously published EAA δ13C data on marine producers to examine the generality of this technique. We found the EAA δ13C fingerprints of subtidal kelps (Laminaria), Ulva, and Neorhodomela were highly distinct from one another. Further, our measured EAA δ13C patterns for kelp and red algae matched those previously reported from other localities, suggesting unique and universal EAA δ13C signatures for these groups. However, CAP could not distinguish between microalgae (POM) and Ulva, possibly due to similar biochemical pathways for the synthesis of EAA. Using these producer fingerprints, we found upper trophic‐level invertebrate consumers, Nucella and Pycnopodia, derived more than 60% of their essential amino acids from subtidal kelps. In contrast, the sampled primary consumers in the system, Mytilus and Strongylocentrotus, relied more heavily on Ulva and/or offshore POM. Our results provide evidence for connectivity between two adjacent nearshore ecosystems and exemplify EAA δ13C as a powerful new tool in tracing energy and nutrient flow within and among marine food webs.

Under pressure: biomechanical limitations of developing pneumatocysts in the bull kelp (Nereocystis luetkeana, Phaeophyceae).

Maintaining buoyancy with gas-filled floats (pneumatocysts) is essential for some subtidal kelps to achieve an upright stature and compete for light . However, as these kelps grow up through the water column, pneumatocysts are exposed to substantial changes in hydrostatic pressure, which could cause complications as internal gases may expand or contract, potentially causing them to rupture, flood, and lose buoyancy. In this study, we investigate how pneumatocysts of Nereocystis luetkeana resist biomechanical stress and maintain buoyancy as they develop across a hydrostatic gradient. We measured internal pressure, material properties, and pneumatocyst geometry across a range of thallus sizes and collection depths to identify strategies used to resist pressure-induced mechanical failure. Contrary to expectations, all pneumatocysts had internal pressures less than atmospheric pressure, ensuring that thalli are always exposed to a positive pressure gradient and compressional loads, indicating that they are more likely to buckle than rupture at all depths. Small pneumatocysts collected from depths between 1 and 9m (inner radius=0.4-1.0cm) were demonstrated to have elevated wall stresses under high compressive loads and are at greatest risk of buckling. Although small kelps do not adjust pneumatocyst material properties or geometry to reduce wall stress as they grow, they are ~3.4 times stronger than they need to be to resist hydrostatic buckling. When tested, pneumatocysts buckled around 35m depth, which agrees with previous measures of lower limits due to light attenuation, suggesting that hydrostatic pressure may also define the lower limit of Nereocystis in the field.

Spatial and short-term variability of larval, post-larval and macrobenthic assemblages associated with subtidal kelp forest ecosystems in Central Chile

ABSTRACTIdentifying patterns of spatial and temporal variability in the composition of communities associated with kelp forests is critical to understand the functioning of this productive, yet vulnerable ecosystem. We used a suite of sampling methods (light attraction and airlift devices) to evaluate the variability of larval, post-larval and macrobenthic assemblages associated with kelp forests (Lessonia trabeculata) in Central Chile (30° to 33°S). Pelagic collections identified two assemblages: early-life stages and emerging macrobenthos, with the later contributing three quarters to the total abundance regardless of the source of illumination (permanent or flashing). Field experiments showed that moon phases affected the structure and composition of the samples. Surveys carried out during new moon showed the highest abundances and taxonomic richness of emergent assemblages. However, species composition varied in both assemblages depending on the moon phase. Although the pelagic assemblages collected at sites with contrasting upwelling intensity did not show differences in community structure, differences in composition were evident for early-life stages. The relationship between pelagic and benthic collections indicated that four decapod crustaceans were represented at both larval and early juvenile stages; however, only the high abundances and densities of Paraxanthus barbiger allowed for estimations of benthic-pelagic coupling. For this species, larval abundances and benthic juvenile densities demonstrated contrasting local and regional patterns, suggesting a decoupling between pelagic and benthic environments. These findings highlight the differential variability in smaller components of kelp forests, but also suggest that post-settlement processes may be driving biological interactions through these highly productive and complex environments.

Exploring the effects of fishing pressure and upwelling intensity over subtidal kelp forest communities in Central Chile

AbstractUnderstanding the processes that drive kelp forest communities is critical for management and conservation of these productive ecosystems. As a way to advance in this direction, we explored the effects of fishing pressure and upwelling intensity over kelp forest communities along the central coast of Chile. We sampled kelp communities in different upwelling conditions associated with contrasting management regimes, namely Territorial User Rights for Fisheries (TURFs) and open‐access (OA) areas. In TURF areas, we found a 2.6‐fold increase in reef fish biomass, higher diversity of all fish trophic groups, mainly dominated by benthic carnivore feeders, and a 1.8‐fold reduction in the number of kelp grazers. On the other hand, upwelling regimes evidence a 1.6‐fold increase in abundance and recruitment of the dominant kelp (Lessonia trabeculata), and also an increase in biomass of planktivorous reef fishes. We found that grazers were capable of reducing kelp condition (measured as canopy foliage index) in OA areas outside the influence of upwelling. Enclosure experiments in the field revealed the effect of grazers on kelps, reducing kelp growth (i.e., blade elongation) and increasing blade tissue loss. Results provide evidence that TURF areas could be important ancillary conservation instruments in kelp forest ecosystems, if key processes of the subtidal community assemblages (e.g., interactions between grazers and reef fish) are maintained. We conclude that human impact interplays with the influence of upwelling in structuring kelp communities.

Impact of grazing by the sea urchin Tetrapygus niger on the kelp Lessonia trabeculata in Northern Chile

The ability of sea urchins to destroy kelp forests, leaving large areas stripped of vegetation and covered by sparse calcareous algae is well known. The reduction in active predators of sea urchins combined with their broad diet makes them an important factor in the structuring of subtidal benthic marine systems. In central and northern Chile, the sea urchin Tetrapygus niger is known to reduce the spread of the subtidal kelp Lessonia trabeculata. However, its impact on the different development stages of L. trabeculata has never been quantified or compared to other possible causes of the loss of material. The objective of this study was to quantify the grazing impact of T. niger on L. trabeculata at different stages of development (recruits, juveniles and adults). An exclusion experiment was conducted to evaluate the grazing effect of T. niger on kelp recruitment within a kelp bed, and kelp transplant experiments were conducted to quantify T. niger's impact on the stipes and fronds of juvenile and adult L. trabeculata. Our results showed that under natural sea urchin densities (10 ind. m−2), T. niger prevented the recruitment of L. trabeculata. Tetrapygus niger completely consumed juvenile plants but only attacked the stipes of adult plants. Tetrapygus niger seems to use different feeding strategies depending on the ontogeny of the plant. Lessonia trabeculata seems unable to defend itself against the impact of intensive grazing by sea urchins, which may be the primary source of mortality of recruits and juveniles of L. trabeculata. However, T. niger's impact on adult plants is limited and shared with other herbivores that graze the fronds, such as fishes and spider crabs.

Climate driven changes in subtidal kelp forest communities in NW Spain

Reconstructions suggest a massive decline of nearly 1400 ha of kelp forest in North Western Spain in 2007. In line with global rising temperatures, we hypothesized that Sea Surface Temperature (SST) surpassed a lethal threshold for kelp. We examined whether changes in SST correlated to the proposed decline in kelp forest. All investigated SST characteristics suggested to affect kelp abundance increased significantly during the past thirty years, reaching extreme values during the last decade. In addition over the past two decades, the landscape formerly dominated by both cold and warm temperate canopy forming and understory species changed to one dominated by warm temperate understory species, resulting in a loss of vertical community structure. Fisheries landing data of kelp associated species was used to support the suggested change in kelp abundance. Subsequent recovery of the kelp appears to be occurring in deeper waters.

Demography and feeding behavior of the kelp crab Taliepus marginatus in subtidal habitats dominated by the kelps Macrocystis pyrifera or Lessonia trabeculata

AbstractWe studied the population and feeding ecology of the kelp crab Taliepus marginatus in subtidal kelp forests dominated by either of two morphologically different kelp species (Macrocystis pyrifera or Lessonia trabeculata) in northern Chile. The sizes and abundances of T. marginatus differed between the two kelp habitats. Kelp crabs were more abundant in the M. pyrifera forest than in the L. trabeculata forest. Size‐frequency distributions showed that juvenile and immature crabs were more common in the M. pyrifera forest than in the L. trabeculata forest, where reproductive adults predominated. The smaller crabs in the M. pyrifera habitat also consumed a higher proportion of kelp tissues than the larger crabs in the L. trabeculata habitat, which had a higher proportion of animal food in their diet. In both kelp forests, individuals of T. marginatus showed a similar pattern of nocturnal feeding over a 24‐h period, consuming more food at night than during the day. The more complex and dense forests of M. pyrifera appear to present better nursery habitats for juvenile kelp crabs than the more open and less dense forests dominated by L. trabeculata. These results suggest that the role of the two kelp habitats for T. marginatus varies during the life cycle of the kelp crabs, with M. pyrifera tending to have nursery function and L. trabeculata being more suitable as a reproductive habitat.

Detrital subsidy from subtidal kelp beds is altered by the invasive green alga Codium fragile ssp. fragile

Invasive species have the potential to alter the dynamics of detrital subsidy from high to low productivity areas through changes in quantity and nutritional quality of detrital material. We examined the effect of the invasive alga Codium fragile ssp. fragile on the nature of detrital export from subtidal algal beds off Nova Scotia, Canada, by comparing changes in mass, nutri- tional quality (%C, %N, C/N ratio), concentration of dimethylsulfoniopropionate (DMSP, a sec- ondary metabolite that deters grazers), and isotopic composition (δ 13 C and δ 15 N) between C. frag- ile and the native kelp Saccharina latissima at 4 wk intervals over 16 wk of degradation in cages on a sand bottom at 19 m depth. C. fragile degraded more slowly, and had a consistently lower C/N and higher DMSP concentration, than S. latissima. Isotope signatures did not differ between algal species: δ 15 N became slightly enriched (~1‰) after 16 wk of degradation, with no change in δ 13 C. We also compared macrofaunal communities associated with degrading thalli of each algal species and found significantly higher abundances of invertebrates (mainly capitellid poly- chaetes) on S. latissima after 8 wk of degradation, resulting in lower evenness (J') and diversity (H') on S. latissima compared to C. fragile. Macrofaunal community composition became similar between algal species at 12 and 16 wk in concordance with decreases in C/N ratio in S. latissima and DMSP concentration in C. fragile. Our results indicate that differences in biochemical compo- sition and the rate of degradation between C. fragile and native kelps result in community-level effects in areas linked to shallow algal beds via the transfer of detritus.

Free-living and particle-associated prokaryote metabolism in giant kelp forests: Implications for carbon flux in a sub-Antarctic coastal area

Extensive beds of large subtidal kelps are characteristic of many temperate and subpolar coastlines. They provide habitats for a wide range of other species and are sites of high primary production that generate large quantities of water-borne particles and dissolved organic compounds that support distinctive communities of prokaryotes. We measured prokaryotic metabolism along transects from the shore to the outside of three giant kelp forests (Macrocystis pyrifera) located in the shelf waters of the Prince Edward Islands (Southern Ocean). Abundance, heterotrophic production (PHP), respiration rates (R-ETS) and growth efficiencies (PGE) were investigated within the particle-associated (PA) and the free-living (FL) communities. Temperature, salinity and inorganic nutrient concentrations indicated distinct hydrological differences among the kelp forests that were related to different levels of freshwater input through island run-off. In contrast, detritus and particulate organic matter concentrations showed a common pattern, decreasing from the near-shore to offshore at all sampling sites, suggesting the retention of organically enriched water masses inshore of the kelp forests. While FL and PA abundances did not differ significantly along transects, FL and PA-PHP and PGE all varied significantly across the kelp forests, following the same pattern across each forest. PA-PGE was significantly higher than FL-PGE in the near-shore waters and farther offshore, while FL-PGE was higher or equal to PA-PGE inside the kelp. This shift can be interpreted in terms of gradients in both the age and origins of organic material across the kelp forests. Higher PA-PGE implies that a larger fraction of organic carbon on colonized particles is converted into prokaryotic biomass and so becomes available to higher trophic levels inshore and offshore of M. pyrifera forests than inside the kelp bed. In contrast, low PA-PGE suggests that a large quantity of carbon passes through the PA-community and is mainly respired within the kelp forest. These results suggest the retention of particles within giant kelp forests. In controlling the metabolic activity of PA and FL prokaryotes, this retention will influence overall carbon flux around the archipelago. In particular, the observation of a common pattern across different M. pyrifera forests has important implications for the role of this species as an autogenic ecological engineer in coastal environments.

Spatial and temporal variation in grazing damage by the gastropod Lacuna vincta in Nova Scotian kelp beds

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 13:163-173 (2011) - DOI: https://doi.org/10.3354/ab00366 Spatial and temporal variation in grazing damage by the gastropod Lacuna vincta in Nova Scotian kelp beds Kira A. Krumhansl*, Robert E. Scheibling Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada *Email: kira.krumhansl@dal.ca ABSTRACT: Population increases of the gastropod Lacuna vincta have been associated with significant damage to kelp blades and decreases in kelp biomass in subtidal kelp beds off Nova Scotia, Canada. We measured the total level and along-blade distribution of grazing damage by Lacuna vincta on the dominant kelp species at 5 sites in Nova Scotia, Canada, over a 15 mo period. Grazing was typically low or absent in the basal regions of blades, consistent with seasonal fluctuations in growth and physical properties of blade tissues. Grazing was largely concentrated in middle and distal sections, although this distribution varied with site exposure and over time. The cover of the invasive bryozoan Membranipora membranacea on the surface of kelp blades did not have a strong effect on grazing by L. vincta. The total level of grazing damage (max. 1% of blade area for Saccharina longicruris and 1.5% for Laminaria digitata) varied seasonally, with peaks in September at some sites. Spatial variation was driven in part by a negative relationship with site exposure. In a field experiment, simulated grazing damage that exceeded a threshold value of 0.5 to 1.0% of blade area caused a significant increase in blade loss during a period of heavy wave action due to a passing hurricane. Our results show that direct reductions in kelp biomass through grazing by L. vincta are relatively small, but can indirectly lead to significant losses of kelp biomass during large wave events. KEY WORDS: Lacuna vincta · Laminaria digitata · Saccharina longicruris · Grazing · ­Mesograzers · Kelp beds · Detritus · Membranipora membranacea Full text in pdf format PreviousNextCite this article as: Krumhansl KA, Scheibling RE (2011) Spatial and temporal variation in grazing damage by the gastropod Lacuna vincta in Nova Scotian kelp beds. Aquat Biol 13:163-173. https://doi.org/10.3354/ab00366 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 13, No. 2. Online publication date: September 06, 2011 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2011 Inter-Research.

Grazing damage and encrustation by an invasive bryozoan reduce the ability of kelps to withstand breakage by waves

Increased breakage of macroalgal fronds during large wave events can significantly reduce canopy cover and biomass. We examined the effects of encrustation by the invasive bryozoan Membranipora membranacea and damage by the snail Lacuna vincta on the ability of kelp blades (Saccharina longicruris, Laminaria digitata, and Laminaria complanata) to withstand wave forces. Using standard materials testing procedures, we documented significant reductions in the maximum stress before breakage, toughness, and extensibility of blade material following bryozoan encrustation. Histological sections of blade tissue indicated a significant degradation of the outer layers of cells following prolonged encrustation by M. membranacea as a likely cause of weakening. Full-thickness perforations and partial-thickness grazing scars also reduced blade strength, suggesting that grazing damage can initiate cracks that lead to blade breakage. Our findings provide a mechanistic link between the damaging effects of mesograzers and encrusting bryozoa on their algal hosts and the export of detrital material from subtidal kelp beds.

Detrital production in Nova Scotian kelp beds: patterns and processes

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 421:67-82 (2011) - DOI: https://doi.org/10.3354/meps08905 Detrital production in Nova Scotian kelp beds: patterns and processes Kira A. Krumhansl1,*, Robert E. Scheibling1 1Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada *Email: kira.krumhansl@dal.ca ABSTRACT: Connectivity via the transport of detrital material from areas of high to low productivity may be an important determinant of secondary productivity and biodiversity in receiving communities. On the Atlantic coast of Nova Scotia, detritus exported from subtidal kelp beds contributes to food webs in communities inhabiting deeper waters offshore. To estimate the amount of energy available via this pathway, we measured rates of detrital production via erosion of kelp blades in kelp beds at 5 sites varying in wave exposure. Specifically, we measured productivity and erosion of the 2 dominant species of kelp, Laminaria digitata and Saccharina longicruris, over 16 mo. We also examined the effect of environmental and biological factors on erosion rates, including temperature, wave exposure, grazing by snails and cover by the invasive bryozoan Membranipora membranacea. We observed clear seasonal and spatial patterns in productivity, with the highest production in spring. Erosion rate was highly variable across sites and seasons, and was strongly related to the cover of M. membranacea and the intensity of snail grazing at the distal end of kelp blades. Both factors cause tissue degradation, abrasions and perforations that weaken blades. Erosion rate was also positively related to water temperature and site exposure. Annual detrital production from the erosion of kelp blades increased linearly with kelp bed biomass, and ranged from 0.5 to 1.71 kg dry weight m–2 (150–513 g C m–2) across sites. These rates equal or exceed annual phytoplankton production off the Atlantic coast of Nova Scotia and estimates of detrital production in seagrass beds in North America. KEY WORDS: Detritus · Grazing · Invasive species · Kelp bed · Laminaria digitata · Membranipora membranacea · Productivity · Saccharina longicruris Full text in pdf format Supplementary material PreviousNextCite this article as: Krumhansl KA, Scheibling RE (2011) Detrital production in Nova Scotian kelp beds: patterns and processes. Mar Ecol Prog Ser 421:67-82. https://doi.org/10.3354/meps08905 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 421. Online publication date: January 17, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Remote sensing with SPOT-4 for mapping kelp forests in turbid waters on the south European Atlantic shelf

Remote sensing has become an increasingly used technique for the thematic mapping of large marine areas. In recent years, many researchers have successfully applied these techniques in different places for benthic mapping in clear waters; however, areas with turbid waters present important limitations that are gradually being solved by recent technological advances. In this context, the main objective of the present study is to develop and validate a methodology for mapping intertidal and subtidal kelp forests in the Galician coast (NW Spain), based on images from SPOT-4 (Satellite Pour l’Observation de la Terre). Three analysis methods have been applied: visual analysis and interpretation, unsupervised classification (cluster) and supervised classification (angular classification and maximum likelihood classification). Classification percentages higher than 70% in all substrates were obtained both using visual analysis and interpretation and maximum likelihood classification.

Variable effects of a kelp foundation species on rocky intertidal diversity and species interactions in central California

The effect of foundation species on community assemblages in physically stressful environments has received much recent attention because of the importance of foundation species in ameliorating environmental stress. Many studies have described variable effects of foundation species on community diversity at small scales, but net positive effects over large scales. Egregia menziesii (Turner) J.E. Areschoug is a large and robust perennial kelp that creates a structurally complex habitat on rocky shores of the Northeast Pacific. This study investigated the effects of Egregia sporophytes on benthic assemblages of the rocky intertidal along the central California coast. Egregia sporophytes strongly impacted the structure of associated communities, due to wave-driven whiplash of fronds, shading, or habitat provision. A survey of Egregia populations at 10 stations along 200 km of the central California coast found effects of Egregia density on the intertidal to be consistent among sites. Increased Egregia sporophyte density negatively affected algal species richness, total algal cover, and cover of the most conspicuous species of algae. However, there was a positive relationship with algal crusts, geniculate coralline algae, and sessile invertebrates. Egregia removal experiments at two sites within the study area experimentally tested for the effects of Egregia on intertidal communities. Results from Soberanes Pt. were consistent with survey results because of the negative effect of Egregia on algal species diversity, subcanopy layering, and cover of abundant algal species. However, removal experiments at Pigeon Pt. resulted in a positive Egregia effect on algal diversity and cover of abundant algal species possibly due to lower Egregia densities, lower wave exposure than Soberanes Pt., and stress amelioration. In the lower energy environment, Egregia acted as a sand trap, yet sand accumulation did not negatively impact algal diversity. Negative effects of large brown algae on benthic assemblages have been observed in temperate waters around the world for certain intertidal or subtidal kelp in wave-swept environments allowing for scouring and substrate shading. This study shows that Egregia and morphologically similar brown algal species can have both negative and positive effects on community diversity depending on variation in density and local environmental conditions. Egregia has the opposite effect on community diversity than what has been previously reported for foundation species because it negatively affects biodiversity in stressful environments, but has a positive effect in less stressful environments.

Predictive modelling of seabed habitats: case study of subtidal kelp forests on the coast of Brittany, France

Predictive modelling to map subtidal communities is an alternative to “traditional” methods, such as direct sampling, remote sensing and acoustic survey, which are neither time- nor cost-effective for vast expanses. The principle of this modelling is the use of a combination of environmental key parameters to produce rules to understand species distribution and hence generate predictive maps. This study focuses on subtidal kelp forests (KF) on the coast of Brittany, France. The most significant key parameters to predict KF frequency are (1) the nature of the substrate, (2) depth, (3) water transparency, (4) water surface temperature and (5) hydrodynamics associated with the flexibility of algae in a flow. All these parameters are integrated in a spatial model, built using a Geographical Information System. This model results in a KF frequency map, where sites with optimum key parameters show a deeper limit of disappearance. After validation, the model is used in the context of Climate Change to estimate the effect of environmental variation on this depth limit of KF. Thus, the effects of both an increase in water temperature and a decrease in its transparency could lead to the complete disappearance of KF.

Three-dimensional resource partitioning between American lobster ( Homarus americanus) and rock crab ( Cancer irroratus) in a subtidal kelp forest

The American lobster ( Homarus americanus) and the rock crab ( Cancer irroratus) commonly coexist, and at high densities, compete for space in subtidal kelp forests in the Gulf of Maine. Competition between the two species was examined in field surveys using visual SCUBA quadrats and complementary laboratory experiments with both live and artificial kelp. Field surveys showed significantly higher crab densities (0.50/m 2 ± 0.08 SE) found up the kelp versus on the ground (0.22/m 2 ± 0.04 SE) when lobsters were present ( P = 0.002). In contrast, crab densities were significantly higher on the ground (0.44/m 2 ± 0.07 SE) as opposed to up the kelp (0.23/m 2 ± 0.06 SE) when lobsters were absent ( P = 0.023). However, the interaction between survey location ⁎ date was significant in five of the eight surveys, suggesting this pattern may not be ubiquitous in all subtidal kelp locations within our study region. Average size of crabs up the kelp or on the ground was not different when lobsters were present or absent ( P > 0.05), and no size correlation was found between lobsters and crabs, irrespective of crab position. Experimental trials in the laboratory confirmed field surveys regardless of the order crabs and lobsters were added into the tank, or the use of live versus artificial kelp, and significant differences were observed in five of the six 5-day experimental trials. Our results suggest that when shelter availability may be limited, kelp could serve as an alternative habitat for rock crabs, perhaps to minimize competition between the two most abundant decapods in the shallow subtidal zone of New England.

Size-related habitat shifts facilitated by positive preference induction in a marine kelp crab

Individual variation in habitat use has important ecological and evolutionary consequences. Here, we combine developmental and functional approaches to study habitat use in Pugettia producta, a marine crab that sequesters pigments from the algae it inhabits and consumes to camouflage with different colored algal habitats. Pugettia from different habitats differ in size and color; individuals living in red intertidal algae are small and red, whereas crabs in amber-colored kelp forests are larger and more amber. We examine the developmental causes (effects of size and experience) and the functional consequences (growth and mortality rates) of size-specific habitat use in Pugettia. We demonstrate that positive preference induction may be a mechanism facilitating size-specific habitat use: prior feeding experience with kelp (in the field or laboratory) increases habitat preferences for kelp but only for larger crabs. Habitat use also has important fitness consequences; small red crabs grow equally fast on both kelp and red algae but suffer much higher mortality in kelp; large red crabs grow faster on kelp diets relative to red algae but experience only marginally higher mortality in kelp. Thus, habitat-specific mortality rates may explain the use of intertidal red algal habitats by small crabs, whereas reduced growth of large crabs on red algae may help trigger shifts to subtidal kelp habitats. Size-specific functional consequences of habitat use may select for developmental processes--such as positive preference induction--that facilitate shifts in habitat use in Pugettia and other phenotypically plastic organisms that shift habitats through ontogeny. Copyright 2010, Oxford University Press.

회귀분석을 이용한 해조류 생물량 측정을 위한 방법론

To estimate seaweed biomass or standing crop, a nondestructive sampling can be beneficial because of not much destroying living plants and saving time in field works. We suggest a methodological procedure to estimate seaweed biomass per unit area in marine benthic habitats by using species-specific regression equations. Percent cover data are required from the field samplings for most species to convert them to weight data. However, for tall macroalgae such as kelps we need density data and their size (e.g., size class for subtidal kelps) of individuals. We propose that the field sampling should be done with 5 replicates of 50 cm x 50 cm quadrat at three zones of intertidals (upper, middle, lower) and three depth points (1, 5, 10 m) in subtidals. To obtain a reliable regression equation for a species, a substantial number of replicate is necessary from destructive samplings. The regression equation of a species can be further specified by different locality and different season, especially for the species with variable morphology temporally and spatially. Example estimation carried out in Onpyung, Jeju Island, Korea is provided to compare estimated values with real weight data.

Flow forces on seaweeds: field evidence for roles of wave impingement and organism inertia.

Hydrodynamic forces dislodge and kill large numbers of organisms in intertidal and subtidal habitats along rocky shores. Although this feature of wave-driven water motion is well recognized, the mechanics of force imposition on compliant organisms is incompletely understood. Here we undertake a field examination of two processes that are thought to impose many of the more dangerous forces that act on flexible benthic seaweeds: impingement of breaking waves directly on emergent organisms, and inertial effects tied to the rapid deceleration of mass that occurs when a passively moving but attached organism abruptly reaches the extent of its range of motion. We focus on two common and important seaweed species: one intertidal kelp (Egregia menziesii) and one subtidal kelp (Macrocystis pyrifera). Results support the concept that wave impingement and inertial effects produce intermittent force transients whose magnitudes commonly exceed values readily attributable to drag. Peak force transients are elevated by as much as a factor of 3 relative to drag in both small and large individuals, consistent with smaller seaweeds being more susceptible to brief impingement forces, and larger seaweeds being more vulnerable to inertial forces. Because both wave impingement and inertial effects vary with the size of an organism, they may have the potential to influence the demographics of physical disturbance in an array of flexible species.