An experimental approach to the study of factors affecting algal colonization in a sublittoral kelp forest

Factors influencing the early colonization by benthic macroalgae and the early successional sequence in a subtidal Ecklonia radiata (C. Agardh) J. Agardh forest in Port Jackson (Sydney) were investigated using controlled experiments involving the microscopic sampling of settlement plates. The preliminary results indicate that the Tolerance model of succession may be applicable. The effect of grazers, and competition between different algal types were important and could, later in the succession, lead to the operation of the mechanisms suggested by the Facilitation or Inhibition models. Controls for the use of settlement plates showed that thick settlement plates led to an over-estimation of initial algal growth compared with the growth on natural patches of substratum. Other results suggested that thick plates excluded grazers. Borders of plates were investigated, but the establishment of algae was random over the plates′ surfaces and border effects were the result of physical or biotic factors acting on algae after settlement. An experiment was developed for use in subtidal areas to test for artifacts due to cages. It was found that the presence of the cages influences the community by attracting small snails. Fish were excluded from some areas to monitor their effects on initial algal growth. Exclusion of fish was found to cause a reduction in algal growth as well as increases in numbers of small invertebrates such as amphipods and copepods. The results suggested that the amount of algae initially present was affected by invertebrate grazers, the abundances of which were, in turn, affected by predation. The species diversity of the early algal growth did not show any consistent trends between high and low grazing pressure. Grazing was important in determining the temporal variability of early growth of individual species. Siltation was positively correlated with early algal growth; a mechanism to account for this effect is suggested. The application of the methods used in this study to future experimental studies of sublittoral community dynamics is considered.     

Movement,activity pattern,and rôle of a hermit crab population in a sublittoral epifaunal community

The movements and activity of hermit crabs in a sublittoral soft-bottom community in the North Adriatic Sea (Gulf of Trieste) were monitored by means of observations by a SCUBA diver and time-lapse photography. Tagging experiments showed that the hermit crabs exhibit a pattern of movement which causes them to remain in a defined area for extended periods. During a two-year period, the radius of activity of a crab is estimated to be under 15 m. This leads to a high recovery rate of tagged shells. The average speed of a hermit crab was 2.1 m/h and the average distance travelled per day was 21.6 m as calculated from the analysis of the time-lapse films. This distance is an order of magnitude larger than that estimated from the tagging experiments (1.1 m/day). The activity of the crabs was restricted to the sediment surface between multi-species clumps. The approximate area of the sediment surface traversed by a crab is 0.4 m²/day. Many inter- and intraspecific encounters were observed, particularly among hermit crabs and the brittle stars Ophiothrix quinquemaculata (D.Ch.) and Ophiura lacertosa (Pennant). The daily activity pattern of the crabs is related to the light and dark phases on the sediment surface. The high density and conspicuous activity of the hermit crabs point to the important rôle of the pagurids in the investigated community.     

Effects of organic enrichment on meiofaunal abundance and community structure in sublittoral soft sediments

In experimental mesocosms established at Solbergstrand, Oslofjord, Norway, organic enrichment was effected by the addition of powdered Ascophyllum nodosum (L.) Le Jol., in quantities equivalent to 50gC·m^?2 and 200gC·m^?2, to boxes of sublittoral soft sediment. After 56 days, the structure of the meiofaunal communities in these treatments was compared with that of the control boxes. At this time the meiofaunal communites at each level of organic enrichment were markedly different from each other and from that in the control sediment. The responses of the two major components of the meiofauna, however, were different. Although the abundance of nematodes was slightly reduced in the high dose treatment this was not accompanied by detectable changes in community structure. Harpacticoid copepods, on the other hand, increased significantly in abundance in the treatment boxes and showed a general trend towards increased dominance and decreased diversity with increasing levels of organic enrichment, although in the low dose treatment there was also an increase in the number of species present. It is also shown that the nematode/copepod ratio is unreliable as a biomonitoring tool and it is suggested that the differential responses in community structure between the nematode and copepod components of the meiofauna might be a better indication of stress at the community level.     

Diversity of carbon use strategies in a kelp forest community: implications for a high CO2 ocean

Mechanisms for inorganic carbon acquisition in macroalgal assemblages today could indicate how coastal ecosystems will respond to predicted changes in ocean chemistry due to elevated carbon dioxide (CO₂). We identified the proportion of noncalcifying macroalgae with particular carbon use strategies using the natural abundance of carbon isotopes and pH drift experiments in a kelp forest. We also identified all calcifying macroalgae in this system; these were the dominant component of the benthos (by % cover) at all depths and seasons while cover of noncalcareous macroalgae increased at shallower depths and during summer. All large canopy‐forming macroalgae had attributes suggestive of active uptake of inorganic carbon and the presence of a CO₂ concentration mechanism (CCM). CCM species covered, on average, 15–45% of the benthos and were most common at shallow depths and during summer. There was a high level of variability in carbon isotope discrimination within CCM species, probably a result of energetic constraints on active carbon uptake in a low light environment. Over 50% of red noncalcifying species exhibited values below ?30‰ suggesting a reliance on diffusive CO₂ uptake and no functional CCM. Non‐CCM macroalgae covered on average 0–8.9% of rock surfaces and were most common in deep, low light habitats. Elevated CO₂ has the potential to influence competition between dominant coralline species (that will be negatively affected by increased CO₂) and noncalcareous CCM macroalgae (neutral or positive effects) and relatively rare (on a % cover basis) non‐CCM species (positive effects). Responses of macroalgae to elevated CO₂ will be strongly modified by light and any responses are likely to be different at times or locations where energy constrains photosynthesis. Increased growth and competitive ability of noncalcareous macroalgae alongside negative impacts of acidification on calcifying species could have major implications for the functioning of coastal reef systems at elevated CO₂ concentrations.     

Diversity and abundance of mollusks in the sublittoral epifaunal community of Punta Patilla, Venezuela

The diversity of a sublittoral epifaunal mollusk community of Punta Patilla, Sucre State, Venezuela, was studied from September 1990 to September 1991. We identified 25 species (14 bivalves and 11 gastropods) of mollusks that inhabit gravel, soft sand and bottoms covered by Thalassia testudinum. Total diversity indices were H' = 3.42. J' = 0.74 and 1-D = 0.85. Monthly diversity reached its maximum in March 1991 (3.12 bits/ ind.), June 1991 (2.88 bits/ind.) and September 1991 (2.95 bits/ind.); minimum diversity was recorded in August 1991 (1.20 bits/ind.). A log series model showed a diversity index alpha = 4.56 for species abundance data and alpha = 3.11 for biomass data. The more abundant species were Chione cancellata, Anigona listeri, Chione granulata and Area zebra among the bivalves, and Chicoreus brevifrons, Turritella variegata and Phllonotus pomum among the gastropods (which present maximum biomass). The average total biomass (56.80 g/m2) is low when compared to reports from other tropical zones.     

Negative effects overpower the positive of kelp to exclude invertebrates from the understorey community

Marine macroalgal forests are one of the most widespread and studied habitats on subtidal coasts, but there remain challenges in understanding why many sessile invertebrates are anomalously absent from understorey communities. In a series of experiments on recruitment of invertebrates, I partitioned the habitat-modifying effects of kelp into their positive and negative effects. Experiments revealed that a reduction of light intensity and removal of sediment by canopies acted to facilitate recruitment, but physical abrasion by the canopy acted as a negative force to overpower these positive effects. Understorey assemblages, therefore, represent biased subsets of taxa from a local pool capable of colonization. On balance, negative effects acted to exclude invertebrates from the understorey community. The asymmetric strength of negative effects not only explains the enigma of exclusion but also indicates that, when it exists, understorey coexistence with canopy plants must reflect a more even match between positive and negative effects.     

On sampling procedures in population and community ecology

In this paper we emphasize that sampling decisions in population and community ecology are context dependent. Thus, the selection of an appropriate sampling procedure should follow directly from considerations of the objectives of an investigation. We recognize eight sampling alternatives, which arise as a result of three basic dichotomies: parameter estimation versus pattern detection, univariate versus multivariate, and a discrete versus continuous sampling universe. These eight alternative sampling procedures are discussed as they relate to decisions regarding the required empirical sample size, the selection or arrangement of sampling units, and plot size and shape. Our results indicate that the decision-making process in sampling must be viewed as a flexible exercise, dictated not by generalized recommendations but by specific objectives: there is no panacea in ecological sampling. We also point to a number of unresolved sampling problems in ecology.     

Application of universally amplifying plastid primers to environmental sampling of a stream periphyton community

To demonstrate the utility of universal plastid primers for probing of environmental samples, we extracted DNA from a tropical stream periphyton community and created two environmental clone libraries. We demonstrate the recovery of DNA sequences corresponding to the major groups of algae observed microscopically in the sample, illustrating the utility of these primers for analysis of environmental samples. Using a touchdown polymerase chain reaction technique, almost 99% of recovered sequences correspond to plastid-containing or cyanobacterial taxa, which allows algae to be targeted to the almost complete exclusion of noncyanobacterial prokaryotes and nonplastid-containing eukaryotes.     

Reproductive bionomics of two sublittoral amphipods in a Bay of Fundy estuary

The reproductive bionomics of two Canadian sublittoral amphipods, Casco bigelowi and Leptocheirus pinguis, are compared in a Bay of Fundy estuary. Casco is semelparous and Leptocheirus iteroparous, although both have a biannual life history. The relatively high reproductive potential of each species, Casco with a reproductive potential of 12.5 and Leptocheirus with 25.5 young per year, is dictated by a combination of wave-caused sediment washout and prédation within the estuary.     

Comparison of gillnet and trawl in diurnal fish community sampling

Hydrobiologia - The fish community in a shallow, eutrophic lake basin in southern Finland was sampled diurnally with gillnets and trawl. The differences in species number, relative abundances and...     

Flux in the sublittoral macrobenthos of Moreton Bay

Several different intertime dissimilarity measures, used with a variety of standardisations of data, were applied to transformed data of macrobenthic species at six sites. These data were obtained over twenty-two times at 8-week intervals. Results were evaluated by stepwise regressions (linear, annual cyclical, longer term cycles). Manhattan metric flux between consecutive times was preferred for most subsequent purposes. This flux divided into positive and negative components which measure, summated over all species, rates of recruitment and depletion. Use of algebraic and absolute sums permits evaluation of an index of homeostasis which measures the counterbalancing of recruitment by some species and depletion by others; this index had a value of ca 0.7. Use of the Manhattan metric with catch standardized data indicated changes of community composition at the (more coastal) Bramble Bay sites with a roughly 3-yr cycle and at the (more oceanic) Middle Banks sites with a roughly 51/2-yr cycle. In the main analyses, sites were considered individually and in various groupings. It was shown that at Bramble Bay the optimum near-annual periodicity gives a 50-instead of a 52-week year, and also that with increased numbers of sites in a grouping, the greater the significance of the near-annual cycles. An hypothesis is outlined involving ‘counterbalancing’ between sites of depletion rates due to mobile predators or ‘disturbers’ (fish and prawns). The counterbalancing of recruitment rates is linked to depletion, and is in line with Caswell's (1978) somewhat theoretical paper in which he suggested the temporary action of predation opens up new cells for colonization. This hypothesis goes far towards ‘explaining’ the known patchiness of benthos in Moreton Bay. Also if mobile predators are a link between areas in proximity with different biotas the ecological unit (2 ‘community’) is necessarily expanded.     

Suspension culture of gametophytes of transgenic kelp in a photobioreactor

Transgenic Laminaria japonica gametophytes producing a recombinant tissue-type plasminogen activator (rtPA) protein, which is an effective third-generation thrombolytic agent for acute myocardial infarction (AMI), were cultured in an illuminated bubble column bioreactor. A maximum final dry cell weight of 1120 mg l⁻¹ was obtained in batch culture with an initial dry cell weight of 126 mg l⁻¹ and with aeration rate of 1.2 l air min⁻¹ l⁻¹ culture, nitrate at 1.5 mM and phosphate at 0.17 mM. The yield of rtPA was 56 μg g⁻¹ dry cell wt. This is the first report regarding cultivation of a transgenic macroalga in a bioreactor.Revisions requested 27 January 2005 and 14 April 2005; Revisions received 6 April 2005 and 17 May 2005     

84 Linking environmental forcing, kelp forest habitat dynamics, and community structure in the northeast pacific

Benthic populations of Euglena viridis exhibit vertical migration behavior on high energy intertidal beaches and along the sand banks of freshwater streams. This study examines similarities and differences in the migratory behavior and cell morphology of populations of E. viridis inhabiting Scripps Beach, La Jolla, California and Coble Brook, Burlington, North Carolina. The timing of migration was measured by counting the number of cells in samples collected from the sediment surface throughout the day. Sediment cores were extracted and sectioned to determine the vertical distribution of the population. Neutral density filters and opaque canisters were used to shade the substratum to 56%, 22%, 2%, and 0% of incident irradiance (Io) to examine the effect of light on cell morphology and migratory behavior. On intertidal beaches, E. viridis exhibited a tidal rhythm in vertical migration with cells migrating below the sediment surface at night (>15 cm) and during daytime high tides. In this habitat, the upward migration response was enhanced at irradiances lower than 100% Io but cell morphology was not altered by shading. On the banks of freshwater streams, E. viridis exhibited a diurnal migratory rhythm with both tear-drop and spherical morphologies observed throughout the day. The population was most concentrated at the surface around solar noon and at night it was located between 1 and 2 cm below the surface. Shading did not enhance upward migration but it did affect cell morphology. These results will be interpreted in the context of the dominant selection pressures in each environment.     

Electron microscopic study of succession in the periphyton community of lake Washington

Microbial succession has been observed on electron microscope grids immersed in lake water for 1, 3, 6, and 10 days. As predicted by ecological theory, the biomass, numbers, and diversity of attached microorganisms increased as succession proceeded. The diversity index of Shannon showed a marked increase from 3.1 at day 1 to 4.2 at day 3. It continued to rise at day 6 and attained the maximum value calculated on day 10 of 4.8. Bacteria were the major pioneer colonizers in this mesotrophic community. Based on these results and the results of other microbiologists who have found bacteria to be the dominant component during the pioneer stage of succession in periphyton communities of varying trophic status, we suggest that microbial heterotrophs may commonly, and perhaps always, be the major component of the early pioneer community of autogenic successions.     

Comparing salinity tolerance in early stages of the sporophytes of a non-indigenous kelp (Undaria pinnatifida) and a native kelp (Saccharina latissima)

The short-term effects of low salinities on the survival of germlings of an introduced kelp Undaria pinnatifida and a native kelp Saccharina latissima were assessed under laboratory conditions. This experiment was designed to compare the differential stress tolerance to salinity of the early life history stages of sporophytes of these two kelps that co-occur on European Atlantic coasts. Germlings (young sporophytes) of both species were exposed for 4 days to salinities ranging from 31 (control) to 26, 21, 16, 11, and 6 psu. Afterwards, they were post-cultured in control seawater (31 psu) for another 4 days to corroborate the viability of injured germlings. Results showed that germlings of the introduced kelp were less resistant to low salinity, surviving to as low as 16 psu; whereas the germlings of the native kelp survived in salinities as low as 11 psu. Despite the observed differences, both species are relatively tolerant to low salinity. Our observations also indicated that, at least in a short term, gametophytes of both species were able to survive in salinities as low as 6 psu. The significance of low-salinity tolerance to the distribution of these kelps and for their offshore cultivation is discussed.     

Feasibility of assessing the community composition of prasinophytes at the Helgoland Roads sampling site with a DNA microarray

The microalgal class Prasinophyceae (Chlorophyta) contains several picoeukaryotic species, which are known to be common in temperate and cold waters and have been observed to constitute major fractions of marine picoplankton. However, reliable detection and classification of prasinophytes are mainly hampered by their small size and few morphological markers. Consequently, very little is known about the abundance and ecology of the members of this class. In order to facilitate the assessment of the abundance of the Prasinophyceae, we have designed and evaluated an 18S rRNA gene-targeted oligonucleotide microarray consisting of 21 probes targeting different taxonomic levels of prasinophytes. The microarray contains both previously published probes from other hybridization methods and new probes, which were designed for novel prasinophyte groups. The evaluation of the probe set was done under stringent conditions with 18S PCR fragments from 20 unialgal reference cultures used as positive targets. This microarray has been applied to assess the community composition of prasinophytes at Helgoland, an island in the North Sea where time series data are collected and analyzed daily but only for the nano- and microplankton-size fractions. There is no identification of prasinophytes other than to record them numerically in the flagellate fraction. The samples were collected every 2 weeks between February 2004 and December 2006. The study here demonstrates the potential of DNA microarrays to be applied as a tool for quick general monitoring of this important picoplanktonic algal group.     

Assessing diversity of arbuscular mycorrhizal fungi in a local community: role of sampling effort and spatial heterogeneity

Diversity of arbuscular mycorrhizal fungi (AMF) was assessed in two 9.2 × 9.2-m plots planted with landscape trees and shrubs at an experimental site in Phoenix, AZ, USA. Twenty-five soil samples were collected in a regular grid pattern from each plot, and AMF species were identified using trap cultures. A total of 12 species were detected, with 7 species detected in one plot and 11 in the other. We found that sampling effort had a major impact on assessing species richness and composition in this local community. Fifteen samples would be necessary to detect 70–80% of species present in each plot. A limited number of additional undetected species are likely to be present in both plots, based on the sampling effort curves and jackknife estimates. Only two species, Glomus eburneum and Glomus microaggregatum, were detected in over 50% of the samples from both plots, and rank–frequency plots revealed a lognormal species distribution. Despite the patchiness of plants in the plots, the number of species detected per point exhibited spatial structuring only at the smallest sampling scale in a single plot, and only a single species in each plot was not randomly distributed. These results indicate that sampling effort and strategy can affect perceptions of AMF community structure.