Algal Beds Research Articles

Palaeocene Rhodophycean Algae from the Ninniyur Formation of the Cauvery Basin, southern India

The sediments of the Ninniyur Formation, Ariyalur are characterised by exceptionally rich assemblages of algae, of which the coralline algae constitute a major component. The present paper documents 32 species of coralline algae, distributed among eleven genera and five unnamed members of sub-family Melobesioideae, from the algal beds of this formation from Ninniyur and the neighbouring areas. An attempt is made to discuss the depositional environment, using actualistic interpretation of the ecological data on the recovered red algae and the associated fossils in conjunction with information on geological aspects gathered from the existing literature. Based on these, it is inferred that the deposits of the Ninniyur Formation were laid down in a transgressing sea within the neritic zone marked by deposition of biogenic accumulations.

The depletion of algal beds by geese: a predictive model and test.

The short-term impact of herbivores on plant productivity has been well studied. Demonstrating long-term effects of grazing on plant populations is much more difficult, but knowledge of such long-term effects is vital in understanding plant-herbivore interactions. We address this issue in a relatively simple plant herbivore system involving the dark-bellied brent goose Branta bernicla bernicla and two marine macroalgae, Enteromorpha spp. and Ulva lactuca, on which the geese graze. In 3years of sampling, goose grazing was responsible for depleting between 23% and 60% of the algae in the autumn, while wave damage caused between 15% and 70% depletion. The degree of depletion in autumn had no effect on the biomass of algae present the following summer, suggesting no long-term consequences of grazing for the population dynamics of the algae. A model simulating the change in mean algal biomass over the autumn and winter, incorporating changes due to depletion by geese, wave action and productivity, successfully described the date at which geese abandoned the algal bed in six different years. These years varied in numbers of geese, strength and timing of storms and initial biomass available. The most important factor determining the date of abandonment of the algal bed was a tradeoff between the timing of storms and the numbers of geese. When storms occur early, most depletion is due to wave action and geese must abandon the bed early, regardless of the numbers grazing there. As the algae become depleted, the geese switch to feeding on saltmarsh, pastures or arable crops. The rate of depletion of algae affects the timing of this movement, and the model presented here enables the switch to be predicted.

Developments in the application of photography to ecological monitoring, with reference to algal beds

Abstract1. The potential for using photographic methods in ecological monitoring of intertidal rocky shores was investigated at two scales: the scale of a bay, and at sampling quadrat level.2. The macroalgal beds at Selwicks Bay, Flamborough Head (north Humberside Coast, England) were used as a case study.3. At each station on three 90 m transects, a photograph was taken of a 50 cm2 quadrat. These images were analysed using SigmaScan™ to measure the cover of algal species. These data were highly correlated with field data collected using a grid quadrat.4. Ground techniques were developed for drawing a scaled overhead map of the bay. The potential for a quantitative survey of the extent of the algal beds using cliff top photographs was investigated. The photographs were merged, and rectified using Arc/Info™ (a Geographical Information System package) to produce scaled overhead images of the bay.5. The two complementary methods developed are suitable for involving amateur naturalists into field‐data collection. They were also designed to meet long‐term statutory monitoring requirements. They are quick, so are well suited to intertidal areas where field sampling windows are limited. In long‐term monitoring strategies, the use of photography produces interactive permanent records of the sample area for back reference. Reporting on the conservation status of sites of European interest could be greatly facilitated by such techniques.6. There are obvious applications for overseas monitoring and base‐line surveys, which demand large data sets to be collected in limited periods of time. Copyright © 2001 John Wiley & Sons, Ltd.

Fish feeding guilds along a gradient of bay biotopes and coral reef depth zones

The study of fish feeding guild structure is a useful method to compare fish communities of complex marine ecosystems. Guild structure was determined in four coral reef depth zones, viz. the fringing reef at depths of 2, 5, 10, and 15 m, as well as in seven shallow-water biotopes within a single bay, viz. notches in fossil reef rock, mangroves, fossil reef boulders, seagrass beds, algal beds at a depth of 2 m, algal beds at a depth of 5 m, and the channel. The study was done in an inland bay on the Caribbean island of Curacao, using a visual census technique. Total fish densities within the different feeding guilds varied considerably between the biotopes, and were generally higher in the reef biotopes and on the boulders than in the remaining bay biotopes. Cluster analysis revealed that the greatest dissimilarity in guild structures in terms of fish densities was that between the algal beds and all other biotopes, followed by that between the reef depth zones and other bay biotopes (notches, mangroves, seagrass beds, channel). The species composition of the guilds also differed considerably among the various biotopes. Species richness within the various guilds showed much smaller differences between the biotopes, but was generally somewhat higher in the reef biotopes. Cluster analysis of guild structures in terms of species richness revealed little dissimilarity among the various biotopes. The coral reef was dominated by omnivores and zooplanktivores, whereas the bay was dominated by zoobenthivores and herbivores. Differences in guild structure between the bay and the adjacent reef indicate differences in food availability.

The Feeding of Juvenile Grooved Tiger Prawns Penaeus semisulcatus in a Tropical Australian Estuary: A Comparison of Diets in Intertidal Seagrass and Subtidal Algal Beds

Diets of both newly settled (2 to 4.9 mm carapace length) and larger pre-emigrating (5 to 10 mm carapace length) juvenile grooved tiger prawns, Penaeus semisulcatus, from two entirely different nursery areas were compared. One site was a subtidal algal bed (Cauleurpa spp) inside a narrow mangrove-lined creek, while the other was a wide intertidal seagrass bed (Enhalus acoroides) on a straight shoreline in a medium size estuary. Both the newly settled and larger prawns consumed a similar range of prey categories in the two nursery areas. Similar high frequency of occurrence of common dietary items (copepods, diatoms and filamentous algae), were found in both sites. For the small prawns, 13 of the 21 prey categories recorded were common in both sites; while 14 of the 21 prey categories were common in the larger prawns. The small prawns had a lower frequency of occurrence than the larger prawns for most of the prey categories, particularly decapod crustaceans, suggesting a restricted diet for the small juveniles. One common prey item at the seagrass site, an insect larva, was not recorded in the algal site.

Day-night shifts of fishes between shallow-water biotopes of a Caribbean bay, with emphasis on the nocturnal feeding of Haemulidae and Lutjanidae

Day-night changes in fish communities were quantified in 6 associated shallow-water biotopes within a single bay: mangroves, seagrass beds, algal beds, channel, fossil reef boulders, and notches in fossil reef rock. All biotopes, except the algal beds, showed a strong reduction in fish density and species richness at night, caused by absence of diurnally active fishes and migrations of Haemulidae and Lutjanidae to the seagrass beds. The fish fauna of the different biotopes showed a relatively high dissimilarity between day and night. This dissimilarity is largely caused by absence of Acanthuridae, Chaetodontidae, Labridae, Pomacentridae, Scaridae and Sparidae at night. These fishes seek shelter at night in, amongst others, the channel, notches and boulders. The balloonfish Diodon holocanthus utilised almost all biotopes as shelter as well as feeding sites. The wide distribution of its preferred food (molluscs) probably explains its distribution in most biotopes at night. The nocturnally active Haemulidae and Lutjanidae, on the other hand, migrated from their daytime shelter sites to the seagrass beds at night to feed. Some of these fishes also migrated to the algal beds to feed. The preference of Haemulidae and Lutjanidae for the seagrass bed as a feeding biotope, instead of other bay biotopes, appears to be related to the relatively high availability of their preferred food (Tanaidacea and Decapoda) as determined by digestive tract analysis. Other bay biotopes showed much lower densities of such food items compared to the seagrass beds.

Importance of shallow-water biotopes of a Caribbean bay for juvenile coral reef fishes: patterns in biotope association, community structure and spatial distribution

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 202:175-192 (2000) - doi:10.3354/meps202175 Importance of shallow-water biotopes of a Caribbean bay for juvenile coral reef fishes: patterns in biotope association, community structure and spatial distribution I. Nagelkerken1,2, M. Dorenbosch2, W. C. E. P. Verberk2, E. Cocheret de la Morinière2, G. van der Velde2,* 1Carmabi Foundation, PO Box 2090, Piscaderabaai z/n, Curaçao, Netherlands Antilles 2Laboratory of Aquatic Ecology, Aquatic Animal Ecology Section, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands *Corresponding author. E-mail: gerardv@sci.kun.nl ABSTRACT: Fish community structure of a non-estuarine inland bay on the Caribbean island of Curaçao was determined in the mangroves, seagrass beds, algal beds, channel, fossil reef boulders, notches in fossil reef rock, and on the adjacent coral reef, using visual censuses in belt transects. Fish communities varied among biotopes, but some overlap was present. Fish density and species richness were highest at the boulders and on the coral reef, and extremely low on the algal beds, whereas the total number of individuals calculated for the entire bay was highest on the seagrass beds. Differences in fish densities between biotopes were related to differences in structural complexity and amount of shelter. Fishes in the bay largely consisted of 17 (mainly commercially important) reef fish species, which used the bay biotopes only as a nursery during the juvenile part of their life cycle. Small juveniles of these species were most often found in the mangroves, whereas at intermediate sizes some were found in the channel. Large individuals and adults were found on the reef, and densities of several of these species were higher on the reef near the bay than on reefs located farther down-current. Fishes which spent their entire life cycles in either the bay or on the coral reef were also found, and the latter group showed a strong decrease in abundance with increasing distance into the bay. The density distribution of individual fish species was not homogeneous within the bay. In the mangroves and seagrass beds, spatial distribution of fishes was correlated with distance to the mouth of the bay, water transparency, amount of shelter, and the structural complexity of the biotope. Juveniles of 3 reef species showed an increase in size on the seagrass beds with distance from the mouth into the bay, whereas 1 bay species showed a decrease in size with this distance. KEY WORDS: Mangroves · Seagrass beds · Coral reef fish · Nursery · Habitat association · Community structure · Habitat complexity Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 202. Online publication date: August 28, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.

The functional and aggregative responses of a herbivore: underlying mechanisms and the spatial implications for plant depletion

Summary 1. The functional and aggregative responses of dark‐bellied brent geese Branta bernicla bernicla feeding on the green algae Enteromorpha intestinalis and Ulva lactuca are described. 2. Bite rate showed maxima at both high and low algal biomass, although the functional response in terms of biomass intake rate was linear (type‐1). The differences in the shapes of these responses can be explained by the fact that bite size declines with decreasing algal biomass. 3. There was little interference between the geese; the rate of aggression was only weakly related to goose density, and time spent feeding decreased only slightly with increasing density. 4. Geese fed on all parts of the algal bed, showing weak, but significant aggregation in patches of higher algal biomass in both October and November. 5. The observed pattern of aggregation was weaker than that predicted by the ideal free distribution with a low value of interference. 6. Simulation models were used to explore four possible behavioural factors leading to this deviation from predictions: cost of travel between patches, constraints on the perception of patch quality, disturbance and short‐term resource guarding. It is concluded that resource‐guarding is likely to be the most important contributory factor.

New observations on the Kildonnan Member, Lealt Shale Formation, Middle Jurassic, Isle of Eigg

Synopsis New exposures prove the position of the Algal Bed in relation to underlying strata at the type section of the Kildonnan Member. A measured section is given and its significance briefly assessed.

The Importance of Scale in Testing the Origins of Alternative Community States

The possibility that different species assemblages may represent persistent alternative community states remains largely unexplored by experimental ecologists because of a variety of conceptual and experimental problems. We discuss some of the conceptual roadblocks to experimentation and propose several avenues for attacking the problem experimentally. We address the conceptual issues involved in (1) the blurring of the distinction between the processes that initiate the switch among alternative states and the positive-feedback processes that maintain those states, and (2) the role of spatial scale in initiating the switch. We suggest that the switch between alternative states requires, first, a disturbance that removes species involved in the positive feedbacks needed for maintenance and, second, the arrival of other individuals that initiate the switch to the alternative assemblage. The removal of the species that maintain the system must be large enough and over a long enough time to allow the arrival and establishment of members of the alternative assemblage, and so we hypothesize that the switch among alternative states is scale dependent. This scenario suggests that the switch among alternative states can be investigated experimentally through the manipulation of the scale of the disturbance and of the arrival of members of the alternative state. Small-scale disturbances should consistently fail to initiate a switch, while larger-scale events should initiate a switch at least part of the time. We also note that in some cases the scale of disturbance and/or the arrival of recruits cannot be manipulated or controlled and suggest that several approaches other than factorial experiments with ANOVA, such as spatial autocorrelation methods, may be useful. We illustrate the potential and the difficulties of various approaches by discussing two systems in eastern North America that may contain alternative states. Mosaics of mussel beds and algal beds occupy rocky coasts from New England northward, and patchworks of forests and heathlands occur in eastern Canada and in the Appalachian highlands. While the study of alternative states in the marine system can be approached experimentally, the scale of disturbance required to switch forests to heathlands is too large for experimentation and must rely on the use of other approaches.

Dimethylsulfide and its oxidation products at two sites in Brittany (France)

Dimethylsulfide (DMS), sulfur dioxide (SO 2), dimethylesulfoxide (DMSO), sulfate (SO 2- 4) and methanesulfonate (MSA) were measured at a coastal site, Pointe de Penmarc’h, over a 25 day period during May and June 1993. Measurements were also performed to estimate the DMS flux from the algal beds around the Penmarc’h lighthouse and from the surrounding sea water. Similar atmospheric measurements were conducted at a second site approximately 2 km inland from Penmarc’h. A comparison between the 2 sites indicates similar patterns of DMS concentration at each site, with values at the inland site being generally 10–15% lower. The concentrations of the aerosol phase products such as methanesulfonic acid and sulfate are examined in the light of air mass origins. The fraction of nss SO 2- 4 produced from biogenic sources is estimated to be less than 25%. The yield of MSA and DMSO from DMS oxidation are assessed from their relative concentrations and estimates of their atmospheric lifetime.

Effects of Periodic Disturbances from Trampling on Rocky Intertidal Algal Beds

Effects of Periodic Disturbances from Trampling on Rocky Intertidal Algal Beds

Spring habitat use and feeding behaviour of Steller's Eider Polysticta stelleri in Varangerfjord, northern Norway

The distribution and abundance of Steller's Eider Polysticta stelleri were studied in Varangerfjord, Norway, in May 1995, immediately prior to the birds' departure for the breeding areas. Almost 80% of the variance in Steller's Eider numbers was explained by a regression model based upon low tide beach width, suggesting strong selection for gently shelving coastal profiles. Such habitat is common but restricted in Varangerfjord and is rare along surrounding coastlines where the species is more scarce. The majority of Steller's Eider and the Common Eider Somateria mollissima were recorded within 200 m of the coast, in contrast to the King Eider Somateria spectabilis, which tended to be more than 200 m from the shore. More detailed observations at one study site showed that Common and Steller's Eiders fed in different ways and in separate areas, despite similar proximity to the shore, although the two species did aggregate together to roost at high tide, particularly during the daytime. Steller's Eider showed a strong tidal rhythm in activity by day and night, roosting at high tide, diving offshore on the ebb and flow tides but resorting to algal beds and sandy‐mud beaches to feed at low tide.

The effects of variable biome distribution on global climate

In projecting climatic adjustments to anthropogenically elevated atmospheric carbon dioxide, most global climate models fix biome distribution to current geographic conditions. Previous biome maps either remain unchanging or shift without taking into account climatic feedbacks such as radiation and temperature. We develop a model that examines the albedo-related effects of biome distribution on global temperature. The model was tested on historical biome changes since 1860 and the results fit both the observed temperature trend and order of magnitude change. The model is then used to generate an optimized future biome distribution that minimizes projected greenhouse effects on global temperature. Because of the complexity of this combinatorial search, an artificial intelligence method, the genetic algorithm, was employed. The method is to adjust biome areas subject to a constant global temperature and total surface area constraint. For regulating global temperature, oceans are found to dominate continental biomes. Algal beds are significant radiative levers as are other carbon intensive biomes including estuaries and tropical deciduous forests. To hold global temperature constant over the next 70 years this simulation requires that deserts decrease and forested areas increase. The effect of biome change on global temperature is revealed as a significant forecasting factor.

Joint ‘bottom-up’ and ‘top-down’ regulation of rocky intertidal algal beds in South Africa

Joint ‘bottom-up’ and ‘top-down’ regulation of rocky intertidal algal beds in South Africa

Seagrass and algal beds as nursery habitats for tiger prawns (Penaeus semisulcatus and P. esculentus) in a tropical Australian estuary

We evaluated the importance of seagrass and algae to two species of tiger prawns (Penaeus semisulcatus and P. esculentus) by detailed sampling at four sites (two seagrass, two algae) in the Embley River estuary, and through sampling 26 sites in 7 adjacent estuaries at one time of year. Samples of tiger prawns were collected in the Embley River estuary with a small beam trawl at night every 2 wk from September to May for 2 yr (1990 to 1992). The two seagrass sites, which were 11 and 13 km from the river mouth, showed less seasonal variation in salinity than the two algal sites, which were 15 and 20 km from the river mouth. The algal beds at the two upstream sites almost disappeared during the wet season, but the biomass of seagrass did not change significantly between the wet and dry seasons. The grooved tiger prawn (P. semisulcatus), the main species at all sites, comprised 88% of the total tiger prawn catch over the two years. They were found at all sites during the pre-wet season, but after the onset of the wet season, they disappeared along with the algae, from the upstream sites. The brown tiger prawn (P. esculentus) was found almost exclusively (97% of the total catch) on the seagrass sites downstream. In the study of several estuaries, juvenile P. semisulcatus were caught at all 26 sites, and P. esculentus were caught in much smaller numbers, at 16 sites. Approximately equal numbers of P. semisulcatus were caught in seagrass and algal beds in the pre-wet season. Very few individuals >10 mm carapace length of either species, were caught. The results from this study highlight the importance of algal beds during the pre-wet season as nursery areas for one species of tiger prawn (P. semisulcatus).

Habitat switching by dark-bellied brent geese Branta b. bernicla (L.) in relation to food depletion.

Seasonal changes in the distribution and feeding behaviour of dark-bellied brent geese Branta b. bernicla (L.) and the biomass of their food plants were studied in three successive winters on the Norfolk coast. The data was used, in conjunction with published information, to show how depletion, productivity and mortality of food plants drive the pattern of habitat switching in this species. It is then possible to explain the habitat shifts observed over the last 35 years and predict future changes. On arrival, geese fed first on algal beds and then on salt marsh, grass and arable fields before returning to feed entirely on the salt marsh in spring. The biomass of green algae, and subsequently the salt marsh vegetation, declined during the autumn and this could be attributed to depletion through goose grazing and natural mortality. As depletion occurred the geese fed more intensively, for a greater percentage of time and with an increasing pace rate, the net result, however, was a declining intake rate (as measured by defaecation rate). The algal biomass at which the geese switched from the algal beds to salt marsh was consistent between years, with heavy storm-induced loss of algae in one year resulting in an earlier switch. That the timing of habitat switches may be explained by depletion of food plants was further supported by historical data: the number of brent geese wintering at the site has increased dramatically over the last 30-35 years and the time of switching from algal beds to salt marsh and from salt marsh to salt marsh and fields has become progressively earlier, as expected from the increased depletion. The expected further increase in brent goose numbers will increase the rate of depletion of intertidal vegetation so that the switches between habitats will be more rapid and the geese will move inland earlier and remain inland longer. The expected increase in the brent goose population will thus result in a disproportionate increase in the levels of conflict between brent geese and agriculture.

Direct observations of groups of mysids in shallow coastal waters of western Japan and southern Korea

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 123:33-44 (1995) - doi:10.3354/meps123033 Direct observations of groups of mysids in shallow coastal waters of western Japan and southern Korea Ohtsuka S, Inagaki H, Onbe T, Gushima K, Yoon YH Groups (swarms, schools or aggregations) of mysids occurring in shallow coastal waters of western Japan and southern Korea were directly observed by SCUBA and skin divers during the day. Formation of groups was seen in 16 species belonging to the family Mysidae. These groups were often polyspecific, composed of 1 dominant species accounting for 50 to 100% of the number of individuals in the group and 0 to 5 guest species. Nipponomysis spp., Prionomysis aspera and Tenagomysis sp. formed flat, carpet-like or discoid swarms over sandy bottoms. Anisomysis aikawai, A. ijimai, A. mixta, A. pelewensis, Anisomysis spp., Lycomysis bispina, Nipponomysis sp., Paracanthomysis hispida, Siriella sp., and an unidentified leptomysid aggregated in shapes of ovals, spheres and columns. L. bispina and P. hispida were associated with algal beds. Other swarms were located near isolated rocks over sandy bottoms, near the edges of corals or along the seashore. Swarms were classified into 2 types in terms of mobility: stationary and migratory; however, the mobility of the swarms was changeable with season and with sexual maturity. Most swarms were made up of various developmental stages, but some swarms of A. aikawai and A. ijimai consisted only of juveniles. Densities of mysids in a swarm ranged from 13 to 571 ind. l-1. Sex ratios (male/female) of immature and mature males and females within a group varied between 0.22 and 2.40. Possible adaptive values of mysid groupings are discussed on the basis of present and previous findings: (1) antipredation, (2) maintenance of favorable position, and (3) feeding. Mysid . Swarm . School . Aggregation . Group Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 123. Publication date: July 20, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Comparison of Hole and Seaweed Habitats of Post-Settled Pueruli and Early Benthic Juvenile Lobsters, Panulirus-Japonicus (Von Siebold, 1824)

The habitats used by pueruli and early bcnthic juvenile Panulirus japonicus were examined at 5 locations along the coast of southern Japan. At Kawazu in the Izu area, from reefs covered by agar algae (Rhodophyta: Gelidiaceae) and Ecklonia cava (Phaeophyta), of a total of 67 juveniles sampled, 64 were sampled from small holes in the rock face and 3 specimens were taken from within the agar algae. At the remaining 4 locations, no agar algal beds occurred and the macroalgae cover was dominated by Laminariaceae and/or Sargassum spp. At these sites, the 81 pueruli and 268 juveniles sampled were observed only within holes on the reef surface and not in association with the macroalgae. Diurnal use of both small holes and the dense foliage of agar algae, allows almost complete concealment of the main part of the body of the juvenile which may not be provided by other macroalgae. Agar algae, however, occur intermittently along the coast of Japan, with extensive beds being found only in the Izu area. It is concluded that holes within the reef face, rather than seaweed, are the main diurnal microhabitat of post-settled pueruli and early benthic juvenile P. japonicus.

Presence of a drifting algal bed in the Mar Piccolo basin, Taranto (Ionian Sea, Southern Italy)

A survey is reported of the drifting algal community in Mar Piccolo, a polluted basin subject to sewage outlets. The key role was played by a few key species, mainly floridean red algae.