Patterns of abundance and assemblage structure of epifauna inhabiting two morphologically different kelp holdfasts

The mobile fauna associated with two sympatric kelp species with different holdfast morphology (Saccorhiza polyschides and Laminaria hyperborea) was compared to test for differences in the assemblage structure of holdfast-associated mobile epifauna. A total of 24,140 epifaunal individuals were counted from 30 holdfasts of each kelp species. Overall epifaunal abundances exceeded faunal abundances previously reported from holdfasts of other kelps. Three taxonomic groups, Amphipoda, Mollusca, and Polychaeta, accounted for ca. 85% of all individuals. Total abundances increased with the amount of habitat available, quantified either as the volume or the area provided by the holdfasts. The multivariate structure of the epifaunal assemblage did not differ between holdfasts of the two kelp species. However, epifaunal assemblages responded differentially to the habitat attributes provided by each type of kelp holdfast: multivariate variation in the assemblage structure of epifauna was mostly explained by holdfast area and volume for L. hyperborea, and by the surface-to-volume ratio for S. polyschides holdfasts. Therefore, the physical attributes of biogenic habitats, here kelp holdfasts that better predict patterns in the assemblage structure of associated fauna can differ according to their different physical morphology, even though the overall assemblage structure of associated fauna was similar.     

Spatial and temporal variability of the benthic assemblages associated to the holdfasts of the kelp <Emphasis Type="Italic">Macrocystis pyrifera</Emphasis> in the Straits of Magellan,Chile

Macrocystis pyrifera (L.) C. Agardh is a characteristic macroalga in the Magellan region covering almost 30% of the shallow coastal waters. The focus of this study was to analyse the spatial and seasonal patterns in macrofauna communities associated to the holdfasts of Macrocystis pyrifera at two study sites in the Straits of Magellan, South Chile. In total, 114 species from 10 major taxa were isolated from the holdfasts. MDS clearly separated the holdfast fauna collected in different seasons, with autumn and winter collections being richer in terms of species richness and abundance as compared to the spring and summer situation. MDS also clearly separated the holdfast associated faunas of the two study sites, Bahía Laredo and Fuerte Bulnes. The community structure and species composition of the associated macro-invertebrates and vertebrates appeared rather heterogeneous, probably due to the extremely heterogeneous environmental conditions along the entire coastline of the Subantarctic Magellan region.     

Distribution and diversity of polychaetes collected by trawling in Admiralty Bay: an Antarctic glacial fiord

The aim of the study is to determine patterns of distribution, species richness and diversity of polychaetes collected by trawling in Admiralty Bay. Forty-seven species of polychaetes were found in 75 samples collected in 1988 along a depth range from 15 to 500 m. Four polychaete assemblages were distinguished. The most diverse and peculiar assemblage was found in the deepest sublittoral of the central basin from ca. 300–500 m with main constant species Laetmonice producta, Sternaspis sp. and Thelepus cincinnatus. Shallow water assemblages had low diversity and species richness. The most common and eurytopic epifaunal polychaetes were Aglaophamus trissophyllus, Barrukia cristata, Harmothoe spp., Flabelligera mundata and Perkinsiana littoralis. The low species richness in shallow waters of Admiralty Bay is probably associated with depth, influence of glacial streams and suspended matter inflow which is particularly distinct in the shallow water fiord areas.     

Evaluating stress in rocky shore and shallow reef habitats using the macrofauna of kelp holdfasts

Kelp often dominates hard rocky substrata in the coastal watersof temperate, boreal and subantarctic regions of the world's oceans. The habitat providedby kelp holdfasts supports high species richness and high abundance of a range of invertebratetaxa. Studies conducted on the effects of stress on these communities have indicated that theyare sensitive to stressors and that the response is often predictable. With the growing body ofliterature on natural variation in holdfast community structure, studies of the impacts of stressare becoming more readily interpretable making the macrofauna of this habitat a potentiallyimportant tool for evaluating anthropogenic effects on hard substrata in coastal environments. Limitations of the use of holdfast fauna in studies of stress include the fact that brownseaweeds may disappear from polluted areas of reef, and where they persist, holdfaststructure may be altered directly by the stressor. An additional problem is that manipulative,experimental studies are difficult. Artificial holdfasts may provide a means by which thedemonstrated sensitivity of the holdfast community can be combined with a manipulative approach to testspecific hypotheses related to effects of stress in shallow coastal environments.     

Nonlinear multivariate models of successional change in community structure using the von Bertalanffy curve

von Bertalanffy curves were used to describe the nonlinear relationship between assemblages inhabiting holdfasts of the kelp Ecklonia radiata and the volume of the holdfast. This was done using nonlinear canonical analyses of principal coordinates (NCAP). The volume of the holdfast is a proxy for the age of the plant and, thus, the canonical axis is a proxy for succession in the marine invertebrate community inhabiting the holdfast. Analyses were done at several different taxonomic resolutions on the basis of various dissimilarity measures. Assemblages in relatively large holdfasts demonstrated ongoing variation in community structure with increasing volume when the dissimilarity used was independent of sample size. Smaller holdfasts had proportionately greater abundances of ophiuroids and encrusting organisms (bryozoans, sponges, ascidians), while larger holdfasts were characterised by proportionately greater abundances of crustaceans, polychaetes and molluscs. Such linear and nonlinear multivariate models may be applied to analyse system-level responses to the growth of many habitat-forming organisms, such as sponges, coral reefs, coralline algal turf or forest canopies.     

Seasonal changes in taxon richness and abundance of mobile invertebrates inhabiting holdfast of annual kelp Ecklonia radicosa (Phaeophyceae,Lessoniaceae) at the central Pacific coast of Japan

To investigate seasonal changes in the taxon richness and abundance of mobile invertebrates inhabiting holdfasts of the warm temperate annual kelp Ecklonia radicosa, five holdfasts were collected monthly at the central Pacific coast of Japan from April to November 2014. During the study period, there was little variation in holdfast height and diameter, which ranged from 5.9 to 8.5 cm and from 7.1 to 10.8 cm, respectively. In total 7087 animals were collected from 40 holdfasts (177.2 individuals inds./holdfast, on average). The number of mobile invertebrates gradually increased from May (15 ± 9.9 inds./holdfast) to August (346 ± 152.5 inds./holdfast), with over 300 inds./holdfast until October before rapidly decreasing in November (110 ± 85.6 inds./holdfast). Similarly, taxon richness increased gradually from April (4.3 ± 1.0 taxa/holdfast) to August (11.0 ± 3.7 taxa/holdfast), and decreased in November (8.6 ± 2.3 taxa/holdfast). Interestingly, hundreds of mobile invertebrates inhabited holdfasts of kelp plants that had shed their blade in October and November. Taxon composition from August to October and the number of invertebrates from July to November were comparable to data previously reported for perennial kelps. In this study, the importance of annual Ecklonian species as biogenic habitats was demonstrated for the first time.     

Are kelp holdfasts islands on the ocean floor? – indication for temporarily closed aggregations of peracarid crustaceans

During the colonisation process of islands, newly immigrating species often arrive as single individuals. Islands that have received single colonisers may subsequently harbour large populations of a species, while other islands may completely lack this species. Exchange between islands is limited, thereby strongly affecting evolutionary processes. While this concept is widely used in the context of oceanic islands or habitat patches on the mainland, it is rarely used to explain and examine the distribution patterns of marine invertebrates. Benthic marine organisms inhabiting patches with island-like features may also be restricted in their movements between patches. Once established in a patch, it may be more favourable to remain there rather than moving to another patch. Juveniles of species with direct development may recruit to the island patch of their parents. Herein, we examined the peracarid fauna in patches that have island-like features, i.e. kelp holdfasts. The number of peracarid species within an individual holdfast increased with its size. Similarly, the number of individuals per holdfast increased with holdfast size. However, several peracarid species showed a strongly aggregated distribution pattern, being highly abundant in some holdfasts and almost completely absent in others. Our results suggest that these aggregations of conspecifics may be a consequence of the peracarid reproductive biology: fully developed juveniles emerge from the female's marsupium and recruit to the immediate vicinity of their mother, showing little or no tendency to emigrate towards other patches. At present, while it is not known how long peracarid aggregations within kelp holdfasts persist, our data suggest that some juveniles may remain with the natal holdfast and possibly reproduce therein. It is concluded that, during certain time periods, reproduction rates of peracarids in a holdfast may exceed their migration rates between holdfasts.     

Ecological effects of harvesting Lessonia (Laminariales,Phaeophyta) in central Chile

Lessonia nigrescens and L. trabeculata are economically important canopy-forming kelps in Chile. Experimental harvesting of stipes above the first dichotomy reduces stipe movement and inter-stipe friction, allowing the development of a heavy epiphytic load and increased grazing. Complete stipe removal leads to holdfast death as neither species is able to simultaneously regenerate all stipes. The invertebrate fauna inside the holdfast does not respond to upper canopy changes, but mortality does occur in partial or complete plant removals. Kelp removal also affects inter-plant distances, results in increased access of grazers to the outside and inside of kelp holdfasts, reduces recruitment of other algal species, and modifies the morphology of L. trabeculata such that the plants become more susceptible to removal by water movement.     

Invertebrate Community Associated with the Macroalga Halimeda kanaloana Meadow in Maui,Hawaii

An expansive meadow of the native macroalga Halimeda kanaloana has been found in west Maui, Hawaii. This study examined the invertebrate community associated with the H. kanaloana meadow. Analyses of samples collected by SCUBA divers found that the meadow supports a diverse and unique benthic community. The meadow provides a suitable habitat for a variety of epibenthic and epifaunal invertebrates in the otherwise homogeneous sandy habitat. Infaunal polychaete abundances, species richness and Shannon‐Wiener diversity index were also higher inside the meadow. Abundances of epibenthic organisms, and dissimilarities of the polychaete assemblage, inside and outside the meadow were greater at deeper stations. This might be due to an effect of the Halimeda density rather than depth, suggesting that the macroalgal density might play an important role in shaping the benthic community. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ediacaran macroalgal holdfasts and their evolution: a case study from China

A macroalgal holdfast (root-like structure) anchored or grown into sediments is a key trait of metaphytes and eukaryotic algae. Various patterns and taphonomic variants of congeneric holdfasts are preserved on the bedding planes of black shales of the Ediacaran Wenghui biota in South China. The macroalgal holdfast, which commonly consists of a rhizome, rhizoid and pith (perhaps mechanical tissue), can be morphologically classified into ten types within four groups of rhizomes: bare rhizome holdfasts (Grypania, Tongrenphyton and Sectoralga-type holdfasts), canopy rhizome holdfasts (Gemmaphyton, Gesinella, Discusphyton and Baculiphyca-type holdfasts), pithy rhizome holdfasts (Zhongbaodaophyton and pithy-cone-type holdfasts) and differentiated rhizome holdfasts (Wenghuiphyton-type holdfasts). Analysis of the Precambrian macroalgal record indicates that rhizomes played a more important role in the evolution of macroalgal holdfast than rhizoids. The following evolutionary stages of development of macroalgal holdfasts are proposed: (1) growth of the basal thallus into sediments (Grypania-type holdfast); (2) development of a primitive (indistinct) rhizome from the base of a stipe or thallus (Tongrenphyton-type and Sectoralga-type holdfasts); (3) growth of a distinct rhizome with rhizoid (Gemmaphyton-type, Gesinella-type and Discusphyton-type holdfasts); (4) development of a pith in the stipe (Baculiphyca-type holdfast); (5) pith extension into the rhizome (Zhongbaodaophyton-type and pithy-cone-type holdfasts); and (6) rhizome differentiation and development of a complex holdfast system (Wenghuiphyton-type holdfast).     

Diurnal, horizontal and vertical dispersal of kelp-associated fauna

The kelp Laminaria hyperborea is host for a rich fauna of mobile invertebrates. Dispersal patterns of these animals may be crucial for their availability to visual predators like fish, which are known to search for food in these productive habitats. Diurnal, horizontal and vertical dispersal within and out of the kelp forest were studied by analysing colonization of artificial substrata placed among kelps. The species composition of the fauna was different on three parts of the kelp: lamina, stipes (with epiphytes) and holdfast. The artificial substrata were colonized mainly by species associated with kelp. More species and individuals colonized the artificial substrata at night than during the day. The most abundant faunal groups on the kelps and the artificial substrata were amphipods and gastropods. Both groups dispersed at a significantly higher rate at night than during the day. Rapid horizontal dispersal out of the kelp forest was found. The artificial substrata were also colonized quickly by kelp fauna at all vertical levels inside and above the kelp forest. However, species associated with the kelp holdfast tended to disperse close to the bottom, while stipe-associated fauna moved through all parts of the kelp forest and even above the canopy layer. A high dispersal rate appears common amongst the mobile species living on kelp and seems to be advantageous, despite the risks involved in emigrating from the habitat and being exposed to predators. Higher activity at night may reduce availability to predators.     

Seasonal variation in epifaunal communities associated with giant kelp (Macrocystis pyrifera) at an upwelling‐dominated site

Kelp forests are highly productive and species‐rich benthic ecosystems in temperate regions that provide biogenic habitat for numerous associated species. Diverse epifaunal communities inhabit kelp sporophytes and are subject to variations in the physical environment and to changes experienced by the kelp habitat itself. We assessed seasonal variations in epifaunal invertebrate communities inhabiting giant kelps, Macrocystis pyrifera, and their effects on this seaweed. Six seasonal samplings were conducted over a year at an upwelling‐dominated site in northern‐central Chile where physical conditions are known to fluctuate temporally. More than 30 taxa were identified, among which peracarid crustaceans stood out in both diversity and abundance. Species richness and abundance differed among sporophyte sections (holdfast and fronds) and throughout the year. The frond community was dominated by two grazers (the amphipod Peramphithoe femorata and the isopod Amphoroidea typa), while suspension feeders, grazers, and omnivores (the amphipod Aora typica, the isopod Limnoria quadripunctata, and polychaetes) dominated the holdfasts. Abundances of the dominant species fluctuated throughout the year but patterns of variation differed among species. The most abundant grazer (P. femorata) had highest densities in summer, while the less abundant grazer (A. typa) reached its peak densities in winter. Interestingly, the area of kelp damaged by grazers was highest in autumn and early winter, suggesting that grazing impacts accumulate during periods of low kelp growth, which can thus be considered as ‘vestiges of herbivory past.’ Among the factors determining the observed seasonal patterns, strong variability of environmental conditions, reproductive cycles of associated fauna, and predation by fishes vary in importance. Our results suggest that during spring and early summer, bottom‐up processes shape the community structure of organisms inhabiting large perennial seaweeds, whereas during late summer and autumn, top‐down processes are more important.     

Reproductive biomass allocation in three Sargassum species

Allocation of biomass to sexual reproductive (receptacle) tissue and vegetative (holdfast) tissue differed absolutely and relatively in three Sargassum species that form the bulk of the intertidal algal canopy in the northern Gulf of California. Sargassum herporhizum devoted a greater proportion of its thallus mass into its rhizoidal holdfast than did S. sinicola var. camouii or S. johnstonii, whose holdfasts are solid, more compact, and composed of a lower percentage of water. Conversely, more sexual receptacle tissue was produced by these two species with small holdfasts during the spring reproductive period. Sargassum sinicola var. camouii, which is the only species of the three that becomes fertile in the fall, produces a comparable amount of sexual tissue during this second period of reproduction. Removal of Sargassum from single-species patches showed that canopy regrowth by S. herporhizum with its encroaching rhizoidal holdfast was more rapid and complete than that of the other two species, which invest most of their reproductive efforts into sexual propagules that can disperse long distances. Sargassum herporhizum also displayed a more rapid and complete recovery of canopy cover in patches cleared of thalli and in control patches following the annual summer dieback. These two divergent modes of reproductive biomass allocation suggest that ability to encroach upon nearby open sites and ability to colonize distant discrete islands of suitable habitat represent two distinct reproductive strategies requiring different patterns of biomass allocation. Moreover, for energetic reasons, a species may not be able to excel at both modes of reproduction.     

Changes in the fish fauna associated with a sub-Antarctic <Emphasis Type="Italic">Macrocystis pyrifera</Emphasis> kelp forest in response to canopy removal

The fish fauna associated with a Macrocystis pyrifera forest and the effects of the canopy removal on this fauna were studied in the Beagle Channel, Tierra del Fuego. Seasonal changes and differences in the fish communities that inhabit the canopy and the holdfast were also studied. Two patches of kelp forest separated by 200 m were selected. In one, the canopy was removed periodically while the other was used as a control. Samples were collected seasonally, from autumn 1999 to 2001. Fish fauna in the water column was sampled using trammel nets and holdfast fish fauna was sampled by removing the complete holdfast. Different assemblages of fish species were captured in the water column (surface and bottom) and in the holdfast. In the former there were mainly pelagic and benthopelagic species and the latter predominantly demersal species. The principal effect of the canopy removal was a drop in the abundance (and total weight) of Paranotothenia magellanica (doradito), the species with the strongest relationship with the canopy, principally at the surface of the treated patch probably due to a reduction in the availability of refuges. A high degree of seasonality was observed for fish species’ total weight, abundance and diversity, with higher values in summer and autumn. Taking into account our data and available data on kelp growth in the same locality, we suggest of cutting the kelp forest (preferably those farther away from the coast) once a year in winter or early spring, in order to minimize impact on the fish community.     

The macrofaunal community of Ecklonia radiata holdfasts: Variation associated with sediment regime,sponge cover and depth

Abstract The relationship among the Ecklonia radiata holdfast macrofaunal community, sediment content and sponge cover was evaluated for data collected over a four year period at Coffs Harbour, mid-north coast, New South Wales. While several taxa demonstrated significant relationships with these factors, the correlations explained a maximum of 24% of the variation in the data and explanatory power was consequently low. Differences in the composition of the holdfast community were also evaluated at two depths (2m and 6m) at two sites in a mensurative field experiment conducted in summer and winter 1991. The results of both ANOVA and non-parametric multivariate statistical analyses (MDS, ANOSIM, SIMPER) indicated that there were consistent, significant differences between depths over the two sample times. Although some common species demonstrated significant associations with one depth, small differences in the abundance of a large number of species were primarily responsible for the overall differences in community structure between depths. Sediment content and holdfast age were both significantly greater in samples collected from 6 m which may account for some of the depth-related faunistic differences. However, the overall differences between depths are probably related to unmeasured factors such as turbulence due to wave action and holdfast morphology which covary with depth. The results highlight the enormous variability associated with the Ecklonia radiata holdfast macrofaunal community and the consequent necessity to consider as many factors as possible in comparative studies of community structure.     

Temporal, spatial and substrate-dependent variations of Danish hard-bottom macrofauna

Detailed knowledge of the Danish hard-bottom fauna is at present limited because of sampling problems. In this study, two different sampling units were used to yield quantitative results of the fauna on two stone reefs in Kattegat: natural holdfasts of Laminaria digitata and plastic pan-scourers imitating the holdfasts. On the two reefs a total of 135 taxa (102 species) were identified, representing 12 phyla. One species, the bryozoan Cribrilina cryptooecium, has not previously been recorded in Denmark. The fauna was characterized by a mixture of a large number of rare species, yielding high values on the Shannon-Wiener diversity index, and it showed a high degree of spatial and temporal variation. ANOSIM analyses showed a significant difference in species compositions between both sampling location, time and substrate type. The plastic pan-scourers proved to be a valuable substrate for quantitative investigations of the fauna. In contrast, the Laminaria holdfasts were too small and variable to be suitable for such studies. Electronic Publication     

Polychaete populations of the shallow soft bottoms off Terra Nova Bay (Ross Sea, Antarctica): distribution, diversity and biomass

 Diversity, distribution and biomass patterns of polychaetes were studied in the shallow soft bottoms off Terra Nova Bay (Ross Sea, Antarctica). Benthic samples, collected in the austral summer 1989–1990, were sampled using a Van Veen grab at 14 stations distributed between 23- and 194-m depth. A total of 5,768 individuals of polychaetes belonging to 77 species were found. The species richness recorded was high, despite the few biotopes investigated at Terra Nova Bay in this study, especially when compared to that recorded from previous investigations in the same area and from the whole Ross Sea (146 species). Despite the high number of species found, only a few species accounted for 76% of the total abundance: Tharyx cincinnatus (27%), Spiophanes tcherniai (23%), Leitoscoloplos mawsoni (18%) and Laonice weddellia (5%) were mainly distributed in the deeper stations (below 100-m depth), while Aglaophamus ornatus (3%) was the only species abundant in the shallowest stations (above 50-m depth), characterized by gravels and coarse sands. Species richness, diversity and evenness showed an increase with depth. Abundances ranged between 40 to over 12,000 ind/m². Biomass values ranged between 0.9 to 176 g/m² (wet weight). A trophic-guild classification revealed the occurrence of various feeding categories that were, however, numerically dominated by deposit feeders with both discretely motile epiand endobenthic forms, and sessile ones. Both the Bray-Curtis similarity and Correspondence (C.A.) analyses showed stations ordered according to depth and to the local dominance of some species. Both poorly and well-structured polychaete assemblages occurred and they seemed related to depth-related factors, such as degree of environmental disturbance (shallowest bottoms vs deep ones), heterogeneity of the substrate and habitat complexity (gravel and coarse sands vs mixed sediment. The richest and most diverse assemblages of polychaetes were those occurring below 140-m depth, where the substrate was dominated by medium sands, often mixed with a mosaic of rocks and boulders. Received: 30 October 1995/Accepted: 1 May 1996     

Macrozoobenthos of two Antarctic glacial coves: a comparison with non-disturbed bottom areas

There are only few studies on shallow Antarctic benthic communities associated with habitats affected by intense mineral sedimentation inflow. The analysis of macrofaunal communities associated with two shallow, isolated glacial coves was performed in Admiralty Bay (King George Island) and compared with non-disturbed sites. Multivariate analyses (hierarchical classification, nMDS) clearly separated glacial cove communities (two assemblages) from the sites situated outside both basins (two assemblages). The community influenced by the streamflow of glacial discharge of meltwater situated in the area with sandy–clay–silt sediments had a very low species richness, diversity and abundance. It was dominated by eurytopic, motile deposit feeding polychaetes such as Mesospio moorei, Tharyx cincinnatus and Leitoscoloplos kerguelensis as well as the bivalve Yoldia eightsi. The second glacial community of the area located at a grater distance from the outlet of the stream was characterized by sandy–clay–silt and clay–silt deposits and showed also a low diversity and species richness. The most abundant here were peracarid crustaceans, with the dominant opportunistic feeder Cheirimedon femoratus. Community from the non-disturbed area with silty–clay–sand, and silty–sand sediments had higher species richness and diversity. The assemblage of fauna from the sandy bottom has values of those two indexes similar to those found in the disturbed areas.