The relationship between habitat structure and fish faunas on New Zealand reefs

Reef fish abundances were sampled at 11 shallow reef localities extending over 1000 km of coastline in northern New Zealand. Sampling was restricted to the 4–10-m depth stratum and included six coastal and five island localities. These were either coralline reef flats dominated by echinoids, or algal reefs with high densities of laminarian and fucoid algae. Reefs dominated by macroscopic algae supported large numbers of small fishes, mainly labrids, and few large benthic-feeding fishes. Echinoid-dominated reefs supported a different fish fauna with more large benthic-feeding species. Additional sampling of echinoiddominated reefs and algal stands in deeper water provided confirmation of these findings. A second sampling programme was carried out at a series of eight sites within a single locality covering 5 km of coastline. These spanned a moderate exposure gradient and ranged from algal dominated reefs to typical coralline reef flats with high densities of grazing invertebrates. The relationship between habitat structure and reef fish species composition and size frequency was similar to that of the large-scale sampling programme. Thirdly, observations on reef fish foraging and feeding patterns within a single reef site suggested that larger benthic-feeding reef fishes were less likely to feed within macroscopic algal stands. Experimental reductions of grazing invertebrates designed to produce brown algal stands on echinoid-dominated reef flats supported these observations. Larger individuals capable of removing echinoids and grazing gastropods did not frequent or feed in laminarian and fucoid algal stands. This pattern is discernible at several spatial scales. Our conclusion is that the type of shallow reef habitat, echinoid- as opposed to algal-dominated, will have an important rôle in determining the associated reef fish fauna.     

Selective feeding by the echinoid,Evechinus chloroticus,and the removal of plants from subtidal algal stands in Northern New Zealand

Summary Feeding choice of the echinoid Evechinus chloroticus was examined for six fucoid and one laminarian species of algae. Three experiments were conducted to determine the algal choice by echinoids under controlled conditions. In the first experiment, the seven algal species were presented to echinoids in laboratory conditions. The second experiment had replicates of the algal species placed randomly on a subtidal rocky reef where echinoids were abundant and randomly dispersed. For the third experiment, which was also field-based, replicates of one highly-ranked species, Ecklonia radiata, were presented to naturally dispersed Evechinus. In addition, a series of controlled observations was used to examine the order in which echinoids removed algae from mixed species stands on subtidal boulders and to determine if this was related to the experimentally demonstrated choices of algal species.The results of the first two experiments showed that there were differences between algal species in the amount of material grazed by echinoids. Rankings of algal species from the field experiment were not correlated with rankings from the laboratory experiment. The order of removal of algal species from natural stands was correlated with the laboratory-based experimental rankings of algal species, but not with the rankings from the field-based experiment or with algal species availability. There were differences between algal species in their vulnerability to grazing by echinoids, as measured by regression analyses on the amount of material grazed from algal replicates vs. the number of attached echinoids. Within each species, echinoid numbers exerted a non-linear effect on the removal of algal material. In the third experiment, where only one species of algae was presented, the echinoids still distributed themselves non-randomly amongst replicates, aggregating on some samples.Data on the finer scale distribution of algal species over the entire subtidal reef on which these experiments and observations were conducted indicate that Evechinus are not often presented with a choice of adult plants of several different species in natural stands.The evidence from this study supports the conclusion that feeding preferences by echinoids are labile and do not clearly exert the major influence on the removal of plants from natural stands. Preference, as determined from experimental rankings of algal species, is only one of a number of factors which may affect the removal of algae by echinoids. Other important factors are the density of echinoids present, algal susceptibility to removal, and the distribution and abundances of the various algal species and echinoids relative to each other. It is suggested that algal life history characteristics may be unaffected by echinoids and that coevolutionary arguments are not appropriate for describing echinoid-algal interactions.     

Rhodolith beds at the easternmost extreme of South America: Community structure of an endangered environment

Rhodolith beds are built by the aggregation of free living marine benthic coralline algae. Herein, we described phytobenthic communities associated with subtidal rhodolith beds in northeastern Brazil and tested the hypothesis that depth affects their structure. We compared macroalgal assemblages from depths of 10, 15 and 20 m. The genus Lithothamnion was dominant in these beds. Rhodolith density was similar at different depths, but volume decreases as depth increases. Sixty-seven species of fleshy algae were collected. The red algal order Ceramiales was dominant. A distinct community corresponds to each sampled depth. The shallower depth presented higher values for biomass, number of species, Shannon-Wiener diversity, and Pielou's evenness. When depth and water transparency increased, the number of species and the abundance of macroalgae decreased.     

Arctic rhodolith beds and their environmental controls (Spitsbergen, Norway)

Coralline algae (Corallinales, Rhodophyta) that form rhodoliths are important ecosystem engineers and carbonate producers in many polar coastal habitats. This study deals with rhodolith communities from Floskjeret (78°18′N), Krossfjorden (79°08′N), and Mosselbukta (79°53′N), off Spitsbergen Island, Svalbard Archipelago, Norway. Strong seasonal variations in temperature, salinity, light regime, sea-ice coverage, and turbidity characterize these localities. The coralline algal flora consists of Lithothamnion glaciale and Phymatolithon tenue. Well-developed rhodoliths were recorded between 27 and 47 m water depth, while coralline algal encrustations on lithoclastic cobbles were detected down to 77 m water depth. At all sites, ambient waters were saturated with respect to both aragonite and calcite, and the rhodolith beds were located predominately at dysphotic water depths. The rhodolith-associated macrobenthic fauna included grazing organisms such as chitons and echinoids. With decreasing water depth, the rhodolith pavements were regularly overgrown by non-calcareous Polysiphonia-like red algae. The corallines are thriving and are highly specialized in their adaptations to the physical environment as well as in their interaction with the associated benthic fauna, which is similar to other polar rhodolith communities. The marine environment of Spitsbergen is already affected by a climate-driven ecological regime shift and will lead to an increased borealization in the near future, with presently unpredictable consequences for coralline red algal communities.     

Effects of quantitative and qualitative variation in phenolic compounds on feeding in three species of marine invertebrate herbivores

The deterrent effects of brown algal phenolic compounds and the terrestrial polyphenolic tannic acid on feeding by three species of invertebrate herbivores from central California, including the gastropods Tegula funebralis (Adams) and Tegula brunnea (Phillipi) and the echinoid Strongylocentrotus purpuratus (Stimpson) were examined. Algal phenolics used were the monomeric phenolic phloroglucinol and polyphloroglucinols from Fucus vesiculosus (Linnaeus), Halidrys siliquosa (Linnaeus) Lyngbye and Eisenia arborea Areschoug. All of the polyphenolics deterred feeding by all three herbivores at concentrations of 5 mg · ml⁻¹ in agar disks. Concentrations of 2 mg · ml⁻¹ also generally deterred feeding by the gastropods (these levels were not tested against S. purpuratus). Relative amounts of deterrence by different compounds were similar, especially for the gastropods. Phloroglucinol deterred feeding by the echinoids, but not by T. funebralis. Responses of the echinoids were otherwise similar to the gastropods, but more variable. I also demonstrated deterrence of S. purpuratus by tannic acid using the “tanned” kelp technique of Steinberg (1985). Reactivity of the different phenolic compounds in the Folin-Denis procedure, a common colorimetric assay used to estimate levels of phenolics in plant tissue, was similar. This suggests that measuring phenolic levels in brown algae by this technique will not be greatly confounded by the occurrence of different kinds of phenolic molecules in different brown algae. This result, in combination with the similarity of the deterrent effects of the compounds used in this study, increases the validity of previous studies in the northeastern Pacific Ocean which correlate algal phenolic levels and diets or feeding preferences of invertebrate herbivores. For plants and herbivores in this region, this assay is a reasonable measure of a biologically meaningful phenomenon — levels of phenolic deterrents in the algae.     

The influence of predation and conspecific adults on the abundance of juvenile Evechinus chloroticus (Echinoidea:Echinometridae)

Summary Reefs dominated by red algae, associated with high echinoid densities, are consistent features of the shallow subtidal around northeastern New Zealand. Factors determining the abundance of juvenile Evechinus chloroticus were investigated in such a habitat. Using a factorial design, a field experiment was used to assess the influence of predators and adult E. chloroticus on juvenile abundance. The use of 2 m² exclusion cages enhanced juvenile E. chloroticus abundance over a 16 month period, an effect independent of conspecific adults. We attributed this effect to the exclusion of benthic-feeding, predatory fish. Several species forage over the study area at high densities and are known from gut content analysis to prey on juvenile E. chloroticus in the field. Invertebrate predators are at very low densities in the area. The possibility of caging and site artefacts confounding this interpretation is discussed.Adult E. chloroticus did not directly affect conspecific juvenile densities during the experimental period. However their removal produced a significant change in community structure toward one dominated by macroscopic brown algae. Echinoid removal led to rapid recruitment of laminarian and fucoid algae, predominantly Ecklonia radiata and Sargassum sinclairii. In addition, densities of herbivorous gastropods, particularly the limpet Cellana stellifera decreased in the echinoid exclusion area, as did the feeding rates of predatory fish. The consequences of E. chloroticus removal may be dependent upon the size of the area from which they are excluded.Despite the high densities of predatory fish, a low though consistent number of juvenile E. chloroticus escape predation. We suggest that these represent sufficient input into the adult grazing population to maintain the habitat. This interpretation argues against a key role for predators in structuring shallow water reef communities in northeastern New Zealand.     

Ecology of marine algae on rocky shores and subtidal reefs in temperate Australia

Experiments in intertidal and subtidal rocky marine habitats in temperate Australia have identified the effects of various biological and physical factors on algal assemblages. In intertidal habitats, these involve micro- and macro-algae and grazing by gastropods. In subtidal habitats, interactions among micro- and macro-algae, echinoids, gastropods, micro-invertebrates and sessile invertebrates have been studied. Experimental studies on physical disturbances of algal assemblages have focussed on the effects of desiccation and storms. Most studies have not considered more than one spatial or temporal scale. Few have been concerned with seasonal influences and fewer have been concerned with variation from year to year. Most of the work lacks applicability to biogeographic comparisons. More experimental work across a variety of spatial and temporal scales is required to determine significant biological and physical processes affecting structure of algal assemblages across broad areas of temperate Australia.     

Antarctic patterns of shallow subtidal habitat and inhabitants in Wilke’s Land

Studies of east Antarctic marine assemblages on hard substrata are rare. In relation to sea-ice breakout, we assessed benthic patterns of habitat and inhabitants between islands and bays at each of two depths (6 and 12 m) across the Windmill Islands coast. Island sites experience sea-ice breakout in the austral spring, while bay sites typically retain sea-ice cover into the summer and in some places the cover is virtually permanent. Composition of assemblages differed between sheltered bays and exposed islands. Islands were dominated by macroalgae, which also varied with depth. Immediately below the ice–foot zone at 6 m, substratum space were monopolised by foliose red (Palmaria decipiens) and foliose brown (Desmarestia sp.) algae, whereas at 12 m large canopies of Himantothallus grandifolius was abundant. The understorey consisted of a mixture of turfs and encrusting red algae at 6 m, and coralline algae at 12 m. Sheltered bays had large areas of sediment/algal complex and no canopy-forming macroalgae. We found more sponges and hydroids in bays, and more brittle stars around islands. Experiments testing factors that covary with exposure and depth in Antarctica, such as light, sedimentation and ice scour are necessary to determine processes that maintain these striking patterns.     

40 Years of benthic community change on the Caribbean reefs of Curaçao and Bonaire: the rise of slimy cyanobacterial mats

Over the past decades numerous studies have reported declines in stony corals and, in many cases, phase shifts to fleshy macroalgae. However, long-term studies documenting changes in other benthic reef organisms are scarce. Here, we studied changes in cover of corals, algal turfs, benthic cyanobacterial mats, macroalgae, sponges and crustose coralline algae at four reef sites of the Caribbean islands of Curaçao and Bonaire over a time span of 40 yr. Permanent 9 m² quadrats at 10, 20, 30 and 40 m depth were photographed at 3- to 6-yr intervals from 1973 to 2013. The temporal and spatial dynamics in the six dominant benthic groups were assessed based on image point-analysis. Our results show consistent patterns of benthic community change with a decrease in the cover of calcifying organisms across all sites and depths from 32.6 (1973) to 9.2% (2013) for corals and from 6.4 to 1% for crustose coralline algae. Initially, coral cover was replaced by algal turfs increasing from 24.5 (1973) to 38% around the early 1990s. Fleshy macroalgae, still absent in 1973, also proliferated covering 12% of the substratum approximately 20 yr later. However, these new dominants largely declined in abundance from 2002 to 2013 (11 and 2%, respectively), marking the rise of benthic cyanobacterial mats. Cyanobacterial mats became the most dominant benthic component increasing from a mere 7.1 (2002) to 22.2% (2013). The observed increase was paralleled by a small but significant increase in sponge cover (0.5 to 2.3%). Strikingly, this pattern of degradation and phase change occurred over the reef slope down to mesophotic depths of 40 m. These findings suggest that reefs dominated by algae may be less stable than previously thought and that the next phase may be the dominance of slimy cyanobacterial mats with some sponges.     

Comparative chemical composition of the Barents Sea brown algae

Comparative study of phytochemical compositions of the most widespread brown algae species (one laminarian and four fucoid algae) from Barents Sea has been performed. A modified technique for mannitol determination in brown algae is proposed. It was revealed that fucus algae (fam. Fucaceae) contain 3% (of total dry weight) less mannitol than laminaria (Laminaria saccharina). The contents of alginic acid and laminaran in the Barents Sea fucoids are more than 10% less compared to laminaria. The alga L. saccharina contains almost two times more iodine than the species of fam. Fucaceae. The amounts of fucoidan and sum lipids in the Barents Sea fucoid algae is higher than in Laminaria saccharina (4-7% and 1-3%, respectively). In terms of contents of main biologically active compounds, fucus and laminarian algae from Barents Sea are inferior to none of the Far-Eastern species. The Barents Sea algae may become an important source of biologically active compounds.     

Patterns in shallow subtidal marine assemblages along the coast of New South Wales

Shallow subtidal areas of rocky reefs in central and southern New South Wales may best be described as a mosaic of habitats, the distributions of which are seemingly related to depth, wave exposure and a number of biological processes, particularly herbivory. The Fringe habitat is generally found only in the most shallow waters. Forests of the laminarian alga Ecklonia radiata are often found at intermediate depths. In deeper, or more sheltered water, sponges, ascidians and red algae are more abundant and the abundances of sea urchins and other invertebrate grazers decline. Overlying this broad-brush pattern are patches of crustose coralline algae (the Barrens habitat), the distributions of which are not clearly related to depth. Invertebrate herbivores, and sea urchins in particular, are abundant in the Barrens habitat. The Barrens habitat was most represented at the more southern locations. At the two most northern locations, reefs were shorter in length and dominated by ascidians (Pyura species).     

The mollusc fauna along a depth transect in the Faroe Shetland Channel: Is there a relationship with internal waves?

From boxcore and dredge samples taken along a depth transect across the Faroe Shetland Channel (FSC) in 1997 and 1999, molluscs were sorted and identified. On the basis of their numerical abundance, the stations could be clustered into three groups, reflecting the depth extension of the main water masses in the FSC. Between 400 and 500 m depth, both the number of taxa per sample and the number of specimens, were highest. Bivalves were mainly caught by the boxcorer and the dredge was best suited to collect the epifaunal gastropods. According to the literature, at mid-slope depths, resuspension is increased by the action of internal waves, which leads to the development of intermediate nepheloid layers. This increased concentration of suspended matter may serve as a food source of low quality. Likewise the low amounts of suspended matter with a relatively high quality of particulate organic matter, such as from ∼400 and ∼700 m may act similarly and explain the relative high abundance of filter feeders at these depths. However, in the various multivariate analyses we could not distinguish the fauna from these depths from that collected from other sites. We observed, however, a pattern in the depth distribution of feeding guilds across the slope of the FSC. Deposit feeders demonstrated a trend of decreasing numbers with depth. Filter-feeding taxa were found to have peaks at depths of approximately 350 m, between 500 and 600 m and between 700 and 800 m. This observation supports the idea that the fauna at the deep sites reflects the locally high cross-slope currents and the subsequent increased amounts or availability of food with a better quality, which seems to be related to resuspension events.     

Deep-water rhodolith distribution, productivity, and growth history at sites of formation and subsequent degradation

This study provides the first quantitative measures of deep-water (i.e., below scuba depths) rhodolith development, distribution, abundance, and primary productivity at sites of both active formation and breakdown. The 1.27-km² upper platform surface of San Salvador Seamount, Bahamas, ranges in depth from 67 to 91 m and averages 95.8% cover of rhodoliths that contribute an estimated 391 t organic C·yr⁻¹ to deep-sea productivity. The predominant nongeniculate coralline alga of the slope environment has an extremely narrow PI curve (photosynthesis vs. irradiance) of net primary production (0.005) to slightly beyond 0.24 μmol·m⁻²·⁻¹ PAR) suggesting that some deep-water benthic algae may be acclimated to restricted light ranges. Platform areas contain up to fice-deep accumulations (≈45 cm thick) of rhodoliths with their visible, planar (2-D), crustose algal cover (68.5%) composed of 41% Lithophyllum sp., 14.9% average nongeniculate corallines, and 12.6% Peyssonnelia sp. Platform rhodoliths also contain ≈25% average planar cover of the foraminiferan Gypsina sp. overlying the rock-penetrating chlorophyte Ostreobium sp.

On the steep slopes of the seamount, to a depth of 290 m, rhodoliths that have spilled down from the relatively flat platform average 17.4% cover. These nodules tend to be concentrated in fan-shaped deposits that are most prevalent (33.3% cover) on the west side (leeward) of the mount where they are more abundant near the top of the slope than on the other three sides. Cover of living crustose algae on the deeper slope rhodoliths averages only 22.8% and is made up of 14.8% unidentified nongeniculate corallines, 6% Lithophyllum sp., and 2% Peyssonnelia. Gypsina sp. is not an important component of the slope nodules. Biotic overstory on the seamout slopes is greatly reduced relative to the platform, restricted mainly to bedrock, and consists mostly of Halimeda, gorgonians, and sponges along with scattered patches of small frondose algae.

Over platform depths from 67 to 91 m, rhodoliths are fairly uniform in composition and abundance. Ranging from 4 to 15 cm in diameter, with an average of ≈ 9 cm, they are roughly spherical with smooth living surfaces. The rhodoliths spilling down the steep slopes of the seamount to depths below 200 m are characteristically smaller (mean of ≈5 cm diameter), much rougher, and pittend by boring organisms. As shown by cross sections through the centers of the platform nodules, outer, relatively thin (1–3 cm thick), well-preserved envelopes overlie dead laminated crustose layerse. These layers surround much thicker cores of biotically altered carbonate (mostly coralline, foraminiferan, and coral) that have been extensively reworked by boring sponges, algae, polychaetes, and pelecypods. Borings have been infilled with carbonate detritus and are lithified to various degrees ranging from porous to dense and stony.

Radiocarbon dates indicate that the outermost unaltered envelopes that underlie actively growing crusts are 112–880 yr old ( ), while the innermost unaltered layers average 731 ybp (range = 200–1100 ybp). The consistently abrupt transitions from the intact underlying layers of living.     

QUANTITATIVE DIFFERENCES BETWEEN BENTHIC ALGAL COMMUNITIES ALONG A DEPTH GRADIENT IN LAKE MICHIGAN1,2

This study analyzes the impact of conditions associated with depth upon benthic algal communities in Lake Michigan. Diatom abundance was greater at 9.1 and 14.6 m depths than 6.5, 22.6 and 27.4 m. Shallow (6.5 m), mid-depth (9.1 and 14.6 m) and deep (22.6 and 27.4 m) zones were distinguishable on the basis of community composition, structure and abundance. Dominance of benthic species, high diversity and low abundance in shallow communities probably resulted from substantial substrate disturbance by wave action in this productive zone. Dominance of benthic species, high diversity and high abundance characterized mid-depth communities where less wave disturbance enabled algal accumulation. Preponderance of living planktonic taxa, low diversity and low abundance delineated deep communities where planktonic algae accumulated and low light levels reduced growth of benthic species.     

Comparative chemical composition of the Barents Sea brown algae

Comparative study of phytochemical compositions of the most widespread brown algae species (one laminarian and four fucoid algae) from Barents Sea has been performed. A modified technique for mannitol determination in brown algae is proposed. It was revealed that fucus algae (fam. Fucaceae) contain 3% (of total dry weight) less mannitol than laminaria (Laminaria saccharina). The contents of alginic acid and laminaran in the Barents Sea fucoids are more than 10% less compared to laminaria. The alga L. saccharina contains almost two times more iodine than the species of fam. Fucaceae. The amounts of fucoidan and sum lipids in the Barents Sea fucoid algae is higher than in Laminaria saccharina (4–7% and 1–3%, respectively). In terms of contents of main biologically active compounds, fucus and laminarian algae from Barents Sea are inferior to none of the Far-Eastern species. The Barents Sea algae may become an important source of biologically active compounds.     

DISTRIBUTION AND RECRUITMENT OF SUBTIDAL GENICULATE CORALLINE ALAGE1

Geniculate coralline algae are common members of kelp forest communities. The structure provided by their stiff branches greatly influences the abundance and species composition of benthic animals and can affect associated algae by inhibiting recruitment, but the branches are themselves substrate for a large number of other taxa. However, other than qualitative observations, little is known about the within-site distribution, recruitment, and growth of these algae. We examined the distribution of the dominant corallines at a subtidal site in central California. Abundances of Calliarthron tuberculosum (Post. & Rupr.) Dawson, Bossiella californica ssp. schmittii (Manza) Johans., Calliarthron cheilosporioides Manza, Corallina vancouveriensis Yendo, and unidentifiable juveniles were determined at depths of 10, 15, and 20 m and on horizontal rock, vertical rock, and cobble. Calliarthron tuberculosum was most abundant (≤39% cover) at all depths, growing primarily on horizontal surfaces. Vertical surfaces and cobbles were dominated by B. californica ssp. schmittii (40 and 15% cover, respectively). These two most abundant species had the highest cover at 15 m. Calliarthron cheilosporioides and C. vancouveriensis were relatively rare (<1% cover) and generally grew on horizontal rocks and at shallower depths. Unidentified juveniles were also rare and occurred mainly on horizontal rocks and cobbles at 20 m. The settlement and growth rates of coralline crusts and the initiation and growth rates of young erect fronds from these crusts were determined in clearings made in the spring and fall at the three depths. Crust densities and diameters were highest at 10 m and in spring clearings. Settlement and growth tended to decrease with increasing depth. Trends were similar in fall clearings, but initial settlement was lower. Initiation and growth of fronds decreased with depth and were also higher in fall clearings. These variations in depth and substrata distribution, as well as settlement and growth, suggest there is considerable variation in the population biology between species in this group of subtidal plants.     

Direct observations on the sublittoral marine algae of Argyll,Scotland

Summary The distribution with depth of sublittoral marine algae has been investigated at 11 sites on the west coast of Scotland. More than half of the species found were confined to the sublittoral zone. The greatest variety of species was found in shallow water at sites sheltered from excessive turbulence. With increasing depth the number of species found steadily decreased. There was no evidence of a specifically distinct algal flora confined to deeper water. No algae were found deeper than 36 m below ELWS at any site, but the lower limit of algal growth was reduced to 9 m in a turbid water loch and to 3 m at a site where the herbivorous echinoderm Ophiocomina nigra was abundant. Fairly distinct algal communities were found on different substrates. The major communities recognised underwater were algae attached to stable substrata, algae attached to unstable substrata and epiphytic on other algae, especially on the stipes of Laminaria hyperborea. On stable rock in areas subject to water movement L. hyperborea forest was the dominant vegetation whereas on unstable substrata and in sheltered localities L. saccharina was dominant.     

Distribution of seagrasses along the Indian coast

Seagrass environments, from the main coast of India, Lakshadweep and Andaman Islands, were surveyed for seagrass and marine algal composition. Extensive seagrass meadows and the maximum number of species (seven genera and 12 species) occurred along the Tamil Nadu coast. Seagrasses were observed from intertidal to subtidal regions down to 8 m depth. Thalassia hemprichii (Ehrenberg) Aschers. and Cymodocea serrulata (R. Brown) Aschers. & Magnus were the dominant seagrasses in the subtidal zones. Halophila beccarii Aschers. was restricted to the intertidal mudflats in association with mangroves. The rich growth of seagrasses along the Tamil Nadu coast and Lakshadweep can be attributed mainly to high salinity, clarity of the water and sandy substratum. One hundred species of marine algae were recorded from the seagrass environments of India.