Kelp Patches Research Articles

Modeling grazer-mediated effects of demographic and material connectivity on giant kelp metapopulation dynamics

From dispersal-based metapopulations to meta-ecosystems that arise from flows of non-living materials, spatial connectivity is a major driver of population dynamics. One potentially important process is material transport between populations also linked by individual dispersal. Here, I explored material and demographic connectivity in metapopulations of giant kelp Macrocystis pyrifera, a foundation species that produces both detritus and reproductive spores. Kelp detritus (drift) subsidizes grazers, helping maintain the kelp forest ecosystem state. Drift could potentially be exchanged among kelp patches, but this is less studied than spore dispersal. Therefore, I built an ordinary differential equation (ODE) model to investigate conditions under which drift and/or spore connectivity promotes the kelp forest state. I fit statistical models (generalized linear mixed models, GLMMs) to observational data and used the GLMM’s predictions to validate the ODE model. My results suggest kelp patch dynamics are best explained by connectivity of both drift and spores, and that the impacts of these forms of connectivity depend on local grazer (urchin) abundance. Both models predicted greater kelp persistence in well-connected patches across a range of urchin densities. These effects were largely driven by drift, which reduced grazing in recipient patches and thereby enhanced spore recruitment. While testing these predictions will require greater empirical quantification of interpatch drift transport, my findings indicate drift connectivity may be an important spatial process in kelp forest systems. More broadly, this work highlights the role of meta-ecosystem dynamics within a single ecosystem type, reinforcing the need to expand traditional metapopulation perspectives to consider multiple forms of spatial connectivity.

Ecosystem engineering kelp limits recruitment of mussels and microphytobenthic algae

Ecosystem engineers often exert strong effects on the recruitment of other species through modification of the local abiotic and biotic environment. In 2015, artificial reefs in eastern Tasmania (− 42.64693, 148.01481) spanning seven different patch sizes (0.12–7.68 m2) and supporting four densities of transplanted kelp (Ecklonia radiata at 0, 4.1, 8.2 and 16.4 kelp m−2) were used to determine how the patch size and density of this ecosystem engineer influenced the recruitment of microphytobenthic (MPB) algae, and a secondary ecosystem engineer, the mussel Mytilus galloprovincialis. Increasing kelp density and patch size inhibited the establishment of subcanopy MPB algae on settlement slides and reduced the recruitment of mussels in standardised rope fibre habitats (RFHs). The productivity:biomass ratio (P:B) of mussel recruits tended to be lower on small reefs and reefs without kelp, relative to larger reefs with high densities of kelp. Canopy shading and reduced cover of turf algae appeared to negatively impact the recruitment of MPB algae and mussels, whilst reduced sediment accumulation on the reefs due to the kelp was also negatively associated with mussel recruitment. These findings highlight the role of ecosystem engineering by kelp in inhibiting the establishment of other species which may additionally impact community dynamics and primary and secondary productivity. The limited capacity of small kelp patches to inhibit the recruitment of other organisms supports the notion that fragmented patches of ecosystem engineers could be more suspectable to adverse outcomes from species interactions making them less resistant to shifts towards an alternative ecosystem state.

Restored kelp facilitates lobster recruitment but not other mid‐trophic macroinvertebrates

Abstract The patch dynamics of foundation species profoundly affects community assembly and thus has important implications for ecosystem restoration. However, it is unclear how restored kelp patches that vary in size and density will influence the establishment of mid‐trophic level (MTL) macroinvertebrates, a key functional group in coastal ecosystems. Artificial reefs with transplants of the canopy‐forming kelp, Ecklonia radiata, were used to quantify the effect of patch size and kelp density on the densities of MTL macroinvertebrates (primarily decapod crustaceans) and on the recruitment of an ecologically important and commercially valuable lobster species. Densities of MTL macroinvertebrates, which were dominated by hermit crabs, decreased with increasing patch size but responded inconsistently to kelp density. There was, however, an overall positive relationship between MTL macroinvertebrates and the density of small epifaunal grazers (a potential food source), along with a negative association with cover of understorey foliose algae. In contrast, the total abundance and density of lobster recruits was higher on larger reefs, and reefs with kelp had up to double the number of recruits relative to reefs with no kelp. After 12 months, most of the surviving lobster recruits occurred on reefs supporting low and medium densities of kelp. These results show that patchy reef substratum is effective in supporting high densities of some MTL macroinvertebrates, irrespective of kelp presence. Although conversely, larger reefs with restored kelp at natural – or even relatively low – densities appear critical to the recruitment of lobsters, which could motivate and provide positive feedback for kelp restoration projects in some locations. Patch dynamics may be used to support restoration efforts by helping to accelerate the recovery of key species and ecosystem services; however, trade‐offs will exist through different taxa responding to patch characteristics in different ways, some positive and some negative.

Kelp habitat fragmentation reduces resistance to overgrazing, invasion and collapse to turf dominance

Abstract Across many temperate coastlines worldwide, kelp habitat has degraded to be replaced by alternative reef‐states with consequences to ecosystem functioning. Identifying both causes of decline and mechanisms of resilience of remnant kelp habitat is critical for managing and restoring these ecosystems. We use a combination of aerial imagery and field experiments to reveal dynamics of kelp habitat fragmentation during phase‐shift from kelp Ecklonia radiata to overgrazed sea urchin barrens Heliocidaris erythrogramma in Port Phillip bay (Australia). Analysis of aerial images spanning 6 years (2009–2014) revealed fragmentation of kelp patches to result in increase in perimeter‐to‐area ratio during phase‐shift. Sea urchin foraging behaviour also changed from the edge to interior of kelp patches, with destructive grazing at the patch edge. Multiple modes of grazing were observed, with greatest rates of kelp bed decline occurring when urchins simultaneously grazed from the ‘outside‐in’ and ‘inside‐out’ of kelp patches. Overgrazing also triggered establishment of invasive kelp Undaria pinnatifida and proliferation of turf algae. Overgrazing reinforced native kelp decline, with overgrazing exacerbated by reduced provision of drift‐kelp. Synthesis and applications. Perimeter–area ratio of kelp patches can predict phase‐shift, with patch extinction occurring when ratios exceeded a critical ratio of ~0.7. Monitoring dynamics of this critical ratio using aerial imagery provides a novel and cost‐effective indicator of kelp ecosystem resilience for preventing further losses. Targeted culling/harvesting of overgrazing sea urchins along patch edges will enhance native kelp survival and decrease perimeter‐to‐area ratio of remnant kelp patches; reducing risk of phase‐shift to sediment‐trapping turfs and invasive kelp, dually promoting recovery of kelp ecosystems.

Remnant kelp bed refugia and future phase-shifts under ocean acidification.

Ocean warming, ocean acidification and overfishing are major threats to the structure and function of marine ecosystems. Driven by increasing anthropogenic emissions of CO2, ocean warming is leading to global redistribution of marine biota and altered ecosystem dynamics, while ocean acidification threatens the ability of calcifying marine organisms to form skeletons due to decline in saturation state of carbonate Ω and pH. In Tasmania, the interaction between overfishing of sea urchin predators and rapid ocean warming has caused a phase-shift from productive kelp beds to overgrazed sea urchin barren grounds, however potential impacts of ocean acidification on this system have not been considered despite this threat for marine ecosystems globally. Here we use automated loggers and point measures of pH, spanning kelp beds and barren grounds, to reveal that kelp beds have the capacity to locally ameliorate effects of ocean acidification, via photosynthetic drawdown of CO2, compared to unvegetated barren grounds. Based on meta-analysis of anticipated declines in physiological performance of grazing urchins to decreasing pH and assumptions of nil adaptation, future projection of OA across kelp-barrens transition zones reveals that kelp beds could act as important pH refugia, with urchins potentially becoming increasingly challenged at distances >40 m from kelp beds. Using spatially explicit simulation of physicochemical feedbacks between grazing urchins and their kelp prey, we show a stable mosaicked expression of kelp patches to emerge on barren grounds. Depending on the adaptative capacity of sea urchins, future declines in pH appear poised to further alter phase-shift dynamics for reef communities; thus, assessing change in spatial-patterning of reef-scapes may indicate cascading ecological impacts of ocean acidification.

High kelp density attracts fishes except for recruiting cryptobenthic species

As foundation species, kelp support productive and species rich communities; however, the effects of kelp structure on mobile species within these complex natural systems are often difficult to assess. We used artificial reefs with transplanted kelp to quantify the influence of kelp patch size and density on fish assemblages including the arrival of recruiting cryptobenthic species. Large patches with dense kelp supported the highest abundance, species richness, and diversity of fishes, with the addition of dense kelp tripling biomass and doubling richness. The abundance of recruits in artificial collectors declined with patch size and was halved on reefs with sparse kelp compared to reefs with dense kelp or no kelp. These results highlight the importance of dense kelp cover in facilitating biodiversity and indicate that kelp addition could support the recovery of degraded coastal ecosystems. Kelp also apparently drives complex interactions affecting the recruitment/behaviour of some cryptobenthic species.

Fragmented kelp forest canopies retain their ability to alter local seawater chemistry

Kelp forests support some of the most productive and diverse ecosystems on Earth, and their ability to uptake dissolved inorganic carbon (DIC) allows them to modify local seawater chemistry, creating gradients in carbon, pH, and oxygen in their vicinity. By taking up both bicarbonate and CO2 as a carbon source for photosynthesis, kelp forests can act as carbon sinks, reducing nearby acidity and increasing dissolved oxygen; creating conditions conducive to calcification. Recent stressors, however, have reduced kelp forest canopies globally; converting once large and persistent forests to fragmented landscapes of small kelp patches. In a two-year study, we determined whether fragmented kelp patches retained the ability to alter local seawater chemistry. We found that diel fluctuations of multiple parameters of carbonate chemistry were greater in the kelp canopy than in the kelp benthos and in adjacent urchin barrens, consistent with metabolic activity by the kelp. Further, kelp fragments increased pH and aragonite saturation and decreased pCO2 during the day to a similar degree as large, intact kelp forests. We conclude that small kelp patches could mitigate OA stress and serve as spatial and temporal refugia for canopy-dwelling organisms, though this effect is temporary and confined to daylight hours during the growing season.

Kelp patch size and density influence secondary productivity and diversity of epifauna

Habitat‐forming ecosystem engineers are the foundation of many marine ecosystems where they support diverse and productive food‐webs. A reduction in their patch size or density may affect the productivity, biodiversity and stability of these ecosystems. We determined the effects of different densities and patch sizes of Ecklonia radiata (the dominant kelp in southern Australia) on the secondary productivity, species richness, diversity and community structure of understory epifaunal invertebrates and how associated environmental covariates modified by kelp affected those patterns. We assessed sub‐canopy epifauna across 28 artificial reefs with transplanted E. radiata consisting of seven different patch sizes (0.12–7.68 m2) crossed with four kelp densities (0–16 kelp m−2) over two years. Epifaunal secondary productivity associated with both natural algal and standardised rope fibre habitats decreased with patch size and was elevated when kelp was absent, however, it was also high in natural habitat when there was a high density of kelp. Epifaunal productivity was positively associated with sub‐canopy light and water flow but negatively associated with the biomass of the dominant understory alga, Ulva sp. Epifaunal diversity declined with a reduction in reef size as did richness which correlated with a loss of algal species richness. Community structure of epifauna also differed between small and large reefs, between reefs with and without kelp, between rope habitats at the centre and at the edge of reefs, and within natural habitat between reefs supporting high and low densities of kelp. Overall, these results indicate complex effects of E. radiata decline on epifaunal communities, with high secondary productivity associated with dense kelp stands, but also areas without kelp that are dominated by turf algae. While the loss of standing kelp from rocky reefs may result in declines in epifaunal biodiversity, where turf algae replaces kelp, the reefs may still support high secondary productivity.

Seascape genetics of the stalked kelp Pterygophora californica and comparative population genetics in the Santa Barbara Channel.

We conducted a population genetic analysis of the stalked kelp, Pterygophora californica, in the Santa Barbara Channel, California, USA. The results were compared with previous work on the genetic differentiation of giant kelp, Macrocystis pyrifera, in the same region. These two sympatric kelps not only share many life history and dispersal characteristics but also differ in that dislodged P. californica does not produce floating rafts with buoyant fertile sporophytes, commonly observed for M. pyrifera. We used a comparative population genetic approach with these two species to test the hypothesis that theability to produce floating rafts increases the genetic connectivity among kelp patches in the Santa Barbara Channel. We quantified the association of habitat continuity and oceanographic distance with the genetic differentiation observed instalked kelp, like previously conducted for giant kelp. We compared both overall (across all patches) and pairwise (between patches) genetic differentiation. We found that oceanographic transit time, habitat continuity, and geographic distance were all associated with genetic connectivity in P.californica, supporting similar previous findings for M. pyrifera. Controlling for differences in heterozygosity between kelp species using Jost's DEST , we showed that global differentiation and pairwise differentiation were similar among patches between the two kelp species, indicating that theyhave similar dispersal capabilities despite theirdifferences in rafting ability. These results suggest that rafting sporophytes do not play asignificant role in effective dispersal of M. pyrifera at ecologically relevant spatial and temporal scales.

A nonnative habitat-former mitigates native habitat loss for endemic reef fishes.

Animals that select the best available habitats are most likely to succeed in degraded environments, but ecological change can create evolutionarily unfamiliar habitats that may be under- or over-utilized by native fauna. In temperate coastal waters, eutrophication and grazing have driven a global decline in native seaweeds and facilitated the establishment of nonnative seaweeds that provide novel macrophyte habitat. We tested whether a nonnative kelp canopy (wakame Undaria pinnatifida) functions as a viable habitat or ecological trap for several endemic reef fishes on urchin-grazed reefs in southern Australia. We assessed the willingness of fish to utilize native vs. wakame kelp canopy via a laboratory habitat choice experiment and by recording natural recruitment to specially constructed boulder reefs with manipulated kelp canopy. We also compared fish communities on natural reefs using a before-after-control-impact survey of wakame patches, and to assess the quality of wakame habitat for resident fish, compared fitness metrics for fish collected from habitats with native vs. wakame kelp canopy. Endemic fishes did not distinguish between the native or wakame canopy but preferred both to barren reef habitats. On urchin-grazed natural reefs, fish occurred in higher abundance and diversity where seasonal wakame canopy was present. Fitness metrics in fish collected from wakame patches were comparable to those in fish from adjacent native kelp patches. These findings indicate that the nonnative canopy provides a viable habitat for endemic fish and may play a role in sustaining native fauna populations in this degraded ecosystem. More broadly, we recommend that managers consider the role of nonnative habitats within the context of environmental change, as endemic fauna may benefit from nonnative habitat-formers in areas where their native counterparts cannot persist.

Effect of foresting barren ground with Macrocystis pyrifera (Linnaeus) C. Agardh on the occurrence of coastal fishes off northern Chile

Macrocystis pyrifera kelp beds play a significant ecological role along the coast of Chile. Besides their importance as food, protection structures, substrata, microhabitats and nurseries, regularly occurring natural disturbances (e.g. extremes of the climate variability El Niño–Southern Oscillation) and increased kelp exploitation affect these habitats. The present study aimed to test the dependence of reef fishes on Macrocystis pyrifera and to evaluate the effect of an enhanced habitat structure (experimental M. pyrifera bed) on the abundance, composition and spatial distribution on rock, on macroalgae, in the water column and on sand of the reef fish community. Boulders colonised by M. pyrifera were transported into three replicated experimental areas (9 m2 each) located in a barren ground area. Three barren ground areas (9 m2 each) without manipulation were selected as controls. The fish abundance, composition and spatial distribution on rock, on macroalgae, in the water column and on sand were recorded weekly by scuba diving over a period of 3 months, between 15 February 2007 and 13 June 2007 (4 months). Results indicate significantly higher abundances (mean = 225%) of fishes in the forested areas compared to the barren ground controls (mean = 3.71 fishes/9 m2 and 1.14 fishes/9 m2, respectively). Scartichthys gigas/viridis, Chromis crusma, Cheilodactylus variegatus and Isacia conceptionis numerically dominated the fish assemblages of the experimental kelp patches. Each fish species revealed different distributions in the forested areas: Scartichthys gigas/viridis was more abundant on rocks and C. variegatus in the macroalgae, whereas C. crusma and I. conceptionis preferred the water column above the experimental kelp bed. During the experimental time, the kelp lost some blades and some plants became detached. The overall number of fishes correlated with the declining kelp abundance (r = 0.964, p < 0.05). The fish species showed different responses to these changes in the experimental areas: C. variegatus and I. conceptionis declined in abundance, whereas the abundance of Scartichthys gigas/viridis remained constant.

Environmental controls on spatial patterns in the long‐term persistence of giant kelp in central California

AbstractAs marine management measures increasingly protect static areas of the oceans, it is important to make sure protected areas capture and protect persistent populations. Rocky reefs in many temperate areas worldwide serve as habitat for canopy‐forming macroalgae and these structure‐forming species of kelps (order Laminariales) often serve as important habitat for a great diversity of species. Macrocystis pyrifera is the most common canopy‐forming kelp species found along the coast of California, but the distribution and abundance of M. pyrifera varies in space and time. The purpose of this study is to determine what environmental parameters are correlated with and their relative contribution to the spatial and temporal persistence of M. pyrifera along the central coast of California and how well those environmental parameters can be used to predict areas where this species is more likely to persist. Nine environmental variables considered in this study included depth of the seafloor, structure of the rocky reef, proportion of rocky reef, size of kelp patch, biomass of kelp within a patch, distance from the edge of a kelp patch, sea surface temperature, wave orbital velocities, and population connectivity of individual kelp patches. Using a generalized linear mixed effects model (GLMM), the persistence of M. pyrifera was significantly associated with seven of the nine variables considered: depth, complexity of the rocky reef, proportion of rock, patch biomass, distance from the edge of a patch, population connectivity, and wave orbital velocities. These seven environmental variables were then used to predict the persistence of kelp across the central coast, and these predictions were compared to a reserved dataset of M. pyrifera persistence, which was not used in the creation of the GLMM. The environmental variables were shown to accurately predict the persistence of M. pyrifera within the central coast of California (r = 0.71, P &lt; 0.001). Because persistence of giant kelp is important to the community structure of kelp forests, understanding those factors that support persistent populations of M. pyrifera will enable more effective management of these ecosystems.

Factors influencing spatial variation and abundance of a mermithid parasite in sand hoppers.

The impact of parasites on host population dynamics depends on local abundance of the parasites, which may vary considerably across spatial scales. In sand hopper populations, mermithid parasites have major impacts on host dynamics, which may vary among spatially separated populations due to the sand hopper's wide, patchy distribution. The present study compared the abundance and biomass of a mermithid parasite (Thaumamermis zealandica Poinar et al., 2002) in sand hoppers (Bellorchestia quoyana (Milne-Edwards)) both within and among disconnected beaches. In addition, several variables were measured and tested as potentially important predictors of the parasite abundance and biomass. It was found that geographic isolation may only be responsible for minor differences in parasite populations compared with other factors. Host size was identified as the most important predictor of mermithid parasite abundance, but epibiont abundance, kelp patch mass and host density were poor predictors of abundance. These factors were also poor predictors of parasite biomass in hosts. This study further supports the notion that studies aiming to elucidate population dynamics or patterns should sample thoroughly across both spatial and temporal scales.

Drift algal subsidies to sea urchins in low-productivity habitats

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 452:145-157 (2012) - DOI: https://doi.org/10.3354/meps09628 Drift algal subsidies to sea urchins in low-productivity habitats Jennifer R. Kelly1,2,*, Kira A. Krumhansl1, Robert E. Scheibling1 1Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada 2Present address: Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada *Email: jkelly@zoology.ubc.ca ABSTRACT: Highly productive kelp beds off the coast of Nova Scotia, Canada, export a large quantity of detrital material to adjacent low-productivity habitats. We used a combination of dietary tracers (fatty acids, stable isotopes, and gut contents) and gonad index to evaluate the importance and spatial extent of this energy subsidy to green sea urchins Strongylocentrotus droebachiensis offshore from kelp beds along 240 m transects perpendicular to the shore at 4 sites. Gut contents and δ13C values indicated the presence of kelp in the diets of sea urchins collected up to 240 m offshore from kelp beds. We observed a corresponding decrease in gonad index with distance from the kelp at all sites but one, where patches of live kelp offshore from the main kelp bed provided an additional food source. Sea urchins that fed on a large pool of detrital kelp at another site had ~15% larger gonads than sea urchins at other locations. δ15N values were more enriched for sea urchins at 160 and 240 m from the kelp bed, suggesting that these sea urchins consume more animal matter, which was also evident in their gut contents. Our findings suggest that drift kelp represents an important energy source for sea urchins in subtidal habitats on the scale of tens to hundreds of meters offshore from kelp beds and that this resource is increasingly patchy in space and time with distance from the kelp bed. KEY WORDS: Stable isotopes · Fatty acids · Trophic subsidy · Detritus · Kelp beds · Sea urchins · Strongylocentrotus droebachiensis Full text in pdf format PreviousNextCite this article as: Kelly JR, Krumhansl KA, Scheibling RE (2012) Drift algal subsidies to sea urchins in low-productivity habitats. Mar Ecol Prog Ser 452:145-157. https://doi.org/10.3354/meps09628 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 452. Online publication date: April 25, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Biogenic habitat structure of seaweeds change along a latitudinal gradient in ocean temperature

Global warming is affecting all major ecosystems, including temperate reefs where canopy-forming seaweeds provide biogenic habitat. In contrast to the rapidly growing recognition of how climate affects the performance and distribution of individuals and populations, relatively little is known about possible links between climate and biogenic habitat structure. We examined the relationship between several ocean temperature characteristics, expressed on time-scales of days, months and years, and habitat patch characteristics on 24 subtidal temperate reefs along a latitudinal gradient (Western Australia; ~ 34 to 27°S). Significant temperature-related variation in habitat structure was observed, even though the total landscape cover of kelp and fucalean canopies did not change across the climate gradient: monospecific patches of kelp became increasingly dominant in warmer climates, at the expense of mixed kelp–fucalean canopies. The decline in mixed canopies was associated with an increase in the abundance of Sargassum spp., replacing a more diverse canopy of Scytothalia doryocarpa and several other large fucoids. There were no observed differences in the proportion of open gaps or gap characteristics. These habitat changes were most closely related to patterns in minimum temperatures and hot temperature thresholds (days > 20 °C), presumably because temperate algae require cool periods for successful reproduction and recruitment (even if the adults can survive warmer temperatures). Although the observed habitat variation may appear subtle, similar structural differences have been linked to a range of effects on canopy-associated organisms through the provision of habitat and ecosystem engineering. Consequently, our study suggests that the magnitude of projected warming might cause changes in habitat structure and thereby indirectly affect numerous habitat-dependent plants and animals.

Habitat fragmentation, patch size, and the recruitment and abundance of kelp forest fishes

Studies of habitat fragmentation in marine ecosystems are few, despite a high potential for disturbance and the fragmentation of macrophytes that constitute important habitats. In this study, we investigated the relative importance of habitat fragmentation and loss on the recruitment and abundance of fishes associated with giant kelp Macrocystis pyrifera forests. We experimentally fragmented naturally occurring kelp forests at 3 sites along Santa Catalina Island, California, USA, into areas of 100 to 1600 m 2 . We also explored the relationship between kelp patch size and recruit- ment of fishes at smaller spatial scales by constructing kelp plots that were consistent in density but varied in area. The numerical and biomass densities of recruit, older juvenile, and adult fishes across fragment areas differed among species, resulting in linear, exponential, or asymptotic increases in numerical and biomass abundances with fragment size. Overall, fishes exhibited mostly linear rela- tionships between abundance and fragment area, suggesting that kelp-associated fishes are more affected by habitat loss than by fragmentation. When incorporating kelp forests of larger area, how- ever, formerly linear functions became non-linear, indicating that habitat fragmentation may become more important at larger spatial scales. At the scale of small kelp patches, the densities of Paralabrax clathratus and Oxyjulis californica were unrelated to patch size, and recruitment occurred in the smallest patches and was highly variable for both species. These results may provide resource man- agers with important information on the relative effects of habitat loss and fragmentation in the con- servation and management of coastal fishes.

Do sulphuric acid and the brown alga Desmarestia viridis support community structure in Arctic kelp patches by altering grazing impact, distribution patterns, and behaviour of sea urchins?

Macrobenthic community structure and the distribution of the green sea urchin (Strongylocentrotus droebachiensis) were recorded inside and outside (=barrens) of kelp patches (Alaria esculenta) at Kongsfjordneset, Svalbard between August 2002 and October 2006. In manipulative field experiments, conducted at Kongsfjordneset, Svalbard in August 2002, the effect of the presence of the brown seaweed Desmarestia viridis on sea urchin distribution and kelp grazing was determined. Additionally, we studied the effect of sulphuric acid, which is produced and stored by D. viridis, on sea urchin movements in the laboratory at Ny-Alesund, Svalbard, in May 2006. Sea urchin densities were two- to threefold lower in kelp patches than on barrens. The macrobenthic community inside kelp patches hosted 39% more species and was of different species composition than on barrens. Anchored pieces of the kelp A. esculenta were less consumed when surrounded by D. viridis than non-surrounded conspecifics. Changes in pH affected the behaviour of sea urchins. Exposing sea urchins to 500 μl seawater at pH 7.5 caused them to stop, while the exposure of as little as 25 μl at pH 1 caused sea urchins to move in the opposite direction. Acid-mediated escape responses in sea urchin behaviour suggest chemical protection by D. viridis as an additional mechanism to mechanical protection in the generation of kelp refuges. These results improve our understanding of how isolated kelp beds can persist over a wide range of environmental conditions, like wave-sheltered sites, and suggest that changes in community structure may be in part attributable to altered trophic interactions.

Physical disturbance and subtidal habitat structure on open rocky coasts: Effects of wave exposure, extent and intensity

Canopy-forming algae occur across of range of energy environments (i.e., wave sheltered to exposed coasts) where disturbances are frequent (i.e., gap formation) and benthic patterns largely reflect variation in post-disturbance processes. Disturbances vary in extent (area affected) and intensity (degree of damage), and this may affect recolonisation at local scales. On an open oceanic coast, we tested whether habitat structure (patches of canopy algae) differed between heavy and relatively lighter wave exposure (sheltered vs. exposed sides of islands), and whether wave exposure affected the response of prominent habitat-formers to varying disturbance regimes (different sizes of partial and complete canopy removal). Observations of naturally occurring patterns showed sheltered coasts to be characterised by small patches of fucoids, whereas exposed coasts were characterised by large patches of kelp. Canopy-gaps were larger at exposed than sheltered coasts, and mixed canopies constituted > 24% of the subtidal rocky habitat independently of wave exposure. Experimental disturbances showed the local density of kelps to affect recovery through greater recruitment to partial clearings (80% canopy removal). Fucalean algae, on the other hand, mainly recruited into complete clearings (100% removal), but when their recruits were abundant, they also recruited into partial clearings. The covers of filamentous, turf-forming algae increased in all clearings, and more so at exposed than sheltered sites. Extent of disturbance had no detectable effect on recolonisation by canopy-forming algae across the scales examined (i.e., 1.5 m, 3 m diameter loss of canopy). Recolonisation varied among islands kilometres apart, and correlations ( r > 0.85) between cover of canopies and cover of their recruits in clearings at the scale of sites, suggested that differences in propagule supply could account for variation in patterns of recolonisation at scales of kilometres. There was no evidence to suggest that the effect of disturbance depended on wave exposure within the range of exposures tested in this study (i.e. open coasts). We recognise that wave exposure can be fundamental to habitat structure of subtidal rocky coasts, but we suggest that its influence may be mediated by the biological setting (e.g., canopy composition).

Density, habitat use and behaviour of the weedy seadragon Phyllopteryx taeniolatus (Teleostei:Syngnathidae) around Sydney, New South Wales, Australia

The vulnerability of marine fish species, particularly those inhabiting coastal waters, is an increasingly important issue in marine conservation. Although the weedy seadragon Phyllopteryx taeniolatus (Lacepede, 1804), a syngnathid fish endemic to southern Australia, is legally protected in New South Wales, there are no studies on population density, habitat use and behaviour to support this protection. We investigated the abundance, sex ratios and distribution of the weedy seadragon at three sites near Sydney, Australia. The distribution, density and sex ratios of seadragons were temporally stable, suggesting no large-scale seasonal migrations. Estimated population densities varied among sites from 10 individuals per ha to 65 individuals per ha, with sex ratios close to 1 : 1. Survival rates from one encounter to the next (approximately weekly) were high, being slightly lower for males (0.985 ± 0.006, mean ± se) and females (0.987 ± 0.005) compared with juveniles (1.000 ± 0.000). All size classes and both sexes were most common near the border of kelp and sand except when exhibiting hiding behaviour, when they were more often found in kelp beds. Kelp beds were the least-used habitat when feeding. Pregnant males tended to hide more often than other groups and therefore were more frequently found in kelp and kelp patches. Seadragons tended to be solitary, although pairing and grouping behaviour was also observed. Results of the present study show that weedy seadragons are resident in the same area throughout the year and have a strong affinity with heavily weeded rock and/or sand habitat. It is therefore recommended that the current species-based protection laws be used in concert with habitat-protection zones as a necessary measure to ensure the conservation of weedy seadragon populations.

Kelp beds as habitat for American lobster Homarus americanus

The American lobster Homarus americanus and kelp Laminaria longicruris and L. saccharina are prominent and often intimately associated members of the subtidal community in the western North Atlantic Ocean. However, no one has identified the nature of this relationship or specifically investigated whether kelp beds are a superior habitat for lobsters. We conducted field studies in 1990 and 1991 at a coastal site centrally located along the Gulf of Maine. USA, to determine how lobsters use kelp beds as habitat. Identically sized and spaced plots of live and artificial (plastic) kelp were established and monitored for lobster population densities. Adjacent featureless sediment plots of identical size served as controls. Lobster population density and biomass were significantly higher in both real and artificial kelp treatments than in non-kelp control plots (p < 0 0001). The change in lobster density was apparent the day following placement of the expenment, so a secondary trophic effect such as attracting prey into treatments is unlikely to have occurred. Thus, kelp beds can affect local lobster population dens~ties by providing shelter for lobsters, thereby concentrating individuals and increasing the local carrying capacity of potential lobster habitats The effect of kelp beds on the local carrying capacity of lobster habitats was further explored by test~ng how lobsters respond to differing patch sizes. A graded size series of circular patches of artificial kelp was established, in which kelp blade density and total area were held constant for each treatment. Treatments were subdivided into four 1 m', two 2 m*, or one 4 m2 patches. Experiments were surveyed for lobster population density and size structure to determine if statistical differences existed among treatments. Lobster density was significantly greater in the smallest patches (p c 0.001). Moreover, lobsters typically occupied the edges of kelp beds, and their abundance within kelp patches corresponded to the patch's perimeter-to-area relationship. This suggests that 'edge effects' influence the local carrying capacity for lobsters by influencing the lobsters' choice of kelp beds as habitat.