Influence of upwelling on the chaetognath community along the Southeastern Arabian Sea

Community structure and distribution of chaetognaths were investigated along the upwelled and non-upwelled waters of Southeastern Arabian Sea (SEAS) from the coastal, shelf and open ocean regions. With the onset of monsoon, intense upwelling along the southern part of SEAS (8° 28′ N) and a weak coastal upwelling along the northern counterpart (15° 30′ N) was evident. Zooplankton biomass was observed to be high in the upwelled waters with the dominance of copepods. Chaetognaths were also observed in significant numbers all along the SEAS, however maximum numerical abundance was observed in the southern upwelled waters. Chaetognaths belonging to 10 genera were identified of which genus Flaccisagitta (54%) made the most dominant group along the entire study area followed, in order of abundance, by Serratosagitta (20%), Mesosagitta (18.2%), Sagitta (12.3%), Ferosagitta (11%) and Krohnitta (6.4%). Flaccisagitta were observed to be abundant in the upwelled waters along with Pterosagitta, Serratosagitta, Sagitta, Krohnitta and Ferosagitta whereas genus Mesosagitta dominated the non-upwelled waters of northern transects.

     

INVERTEBRATE‐MEDIATED NUTRIENT LOADING INCREASES GROWTH OF AN INTERTIDAL MACROALGA1

Even in nitrogen‐replete ecosystems, microhabitats exist where local‐scale nutrient limitation occurs. For example, coastal waters of the northeastern Pacific Ocean are characterized by high nitrate concentrations associated with upwelling. However, macroalgae living in high‐zone tide pools on adjacent rocky shores are isolated from this upwelled nitrate for extended periods of time, leading to nutrient limitation. When high‐intertidal pools are isolated during low tide, invertebrate‐excreted ammonium accumulates, providing a potential nitrogen source for macroalgae. I quantified the influence of mussels (Mytilus californianus Conrad) on ammonium accumulation rates in tide pools. I then evaluated the effects of ammonium loading by mussels on nitrogen assimilation and growth rates of Odonthalia floccosa (Esp.) Falkenb., a common red algal inhabitant of pools on northeastern Pacific rocky shores. Odonthalia was grown in artificial tide pool mesocosms in the presence and absence of mussels. Mesocosms were subjected to a simulated tidal cycle mimicking emersion and immersion patterns of high‐intertidal pools on the central Oregon coast. In the presence of mussels, ammonium accumulated more quickly in the mesocosms, resulting in increased rates of nitrogen assimilation into algal tissues. These increased nitrogen assimilation rates were primarily associated with higher growth rates. In mesocosms containing mussels, Odonthalia individuals added 41% more biomass than in mesocosms without mussels. This direct positive effect of mussels on macroalgal biomass represents an often overlooked interaction between macroalgae and invertebrates. In nutrient‐limited microhabitats, such as high‐intertidal pools, invertebrate‐excreted ammonium is likely an important local‐scale contributor to macroalgal productivity.     

Large scale patterns and trophic structure of southern African rocky shores: the roles of geographic variation and wave exposure

In this study we revise the biogeographic delimitation, and large-scale patterns of community structure of the intertidal rocky shores of southern Africa. We use binary (presence/absence) and per-species biomass data collected at fifteen localities and thirty-seven different rocky sites, encompassing the shores of southern Namibia, South Africa and southern Mozambique. Multivariate analyses revealed that the shores of southern Africa (south of 25°) can be divided into three main biogeographic provinces: the west coast or Namaqua province, the south coast or Agulhas province and the east coast or Natal province. The biomass structure of the intertidal rocky shores communities of southern Africa varied at a large scale, corresponding to biogeographic differences, while local-scale variation accorded with the intensity of local wave action. The average biomass of west coast communities was on average significantly greater than that of the south and east provinces. At a local scale, the community biomass on exposed shores was an order of magnitude greater than on sheltered shores, within all biogeographic provinces. Semi-exposed shores exhibited intermediate average biomass. The trophic structure of these communities varied significantly with wave action: autotrophs, filter-feeders and invertebrate predators were more prevalent on wave exposed than sheltered shores, whereas grazers were more abundant on sheltered and semi-exposed shores. Exposed shores were consistently dominated by far fewer species than semi-exposed and sheltered shores, independently of biogeographic differences. Within all biogeographic provinces semi-exposed and sheltered shores were more diverse than exposed shores. West coast intertidal communities therefore had high levels of biomass, but were consistently species-poor. Several working hypotheses that could explain these large and small-scale patterns are presented.     

Ability of invertebrate indices to assess ecological condition on intertidal rocky shores

The implementation of directives such as the European Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD) has promoted the development of several tools and methods for assessing the ecological health of marine ecosystems. Within the scope of the WFD and in terms of rocky shores, several multimetric tools were developed based on the macroalgae biological quality element (BQE), in addition to those based on macroinvertebrates.The WFD requires member states to assess each BQE separately. The present work aimed to test the ability of ecological indices to distinguish sites within anthropogenic disturbance gradients caused by organic enrichment, using macroinvertebrate communities on intertidal rocky shores. Owing to the lack of more specific indices (for rocky shore), indices based on abundance, diversity and/or taxonomic composition were selected from several widely used indices in ecological studies and/or developed for soft-bottom macroinvertebrate communities.Present findings reveal several indices based on diversity and/or taxonomic composition able to distinguish sites within the disturbance gradients, showing increasing quality from the site nearest the source of organic enrichment to that farthest from it, especially indices calculated using biomass data, and in the summer season. Such results open good perspectives for the use of intertidal macroinvertebrate communities from rocky shores, and also help add the perspective of this biological quality element in the ecological quality assessment of coastal waters.     

Intertidal assemblages on seawalls and vertical rocky shores in Sydney Harbour,Australia

Abstract Understanding the ecological role of artificial structures, such as seawalls, in shallow coastal waters is necessary in order to plan sound strategies of conservation and management of natural habitats. In Sydney Harbour (NSW, Australia), about 50% of the foreshore is made of retaining seawalls This study evaluates the changes caused to natural assemblages of organisms by these structures, by comparing intertidal assemblages between seawalls and vertical rocky shores. The following hypotheses were tested: that assemblages on seawalls would differ from those on rocky shores at mid‐, but not at low‐shore levels; where assemblages differ between habitats, there would be differences in cover/abundances of widespread species; patterns would be consistent among locations and through time; the variability of assemblages at the scales of 10s of cm and metres would differ between seawalls and rocky shores at mid‐ and low‐shore levels. To test these hypotheses, assemblages on seawalls and rocky shores were sampled at three locations, at roughly 4‐monthly intervals, over a period of about 18 months. Results indicated that mid‐shore assemblages on seawalls were different from those on rocky shores, but this was not the case at low‐shore levels. Few taxa were unique to either habitat. Cover of common species of algae and sessile animals and abundances of mobile grazers were variable with few consistent patterns. Variability at the scales sampled differed between habitats and heights on the shore. Seawalls and rocky shores, in general, supported a similar suite of species, but patterns of abundance and variation differed among locations and from height to height in each habitat. The implications of these findings for the future management of seawalls are briefly considered.     

Impacts of sewage outfalls on rocky shores: Incorporating scale,biotic assemblage structure and variability into monitoring tools

Coastal systems, such as rocky shores, are among the most heavily anthropogenically-impacted marine ecosystems and are also among the most productive in terms of ecosystem functioning. One of the greatest impacts on coastal ecosystems is nutrient enrichment from human activities such as agricultural run-off and discharge of sewage. The aim of this study was to identify and characterise potential effects of sewage discharges on the biotic diversity of rocky shores and to test current tools for assessing the ecological status of rocky shores in line with the EU Water Framework Directive (WFD). A sampling strategy was designed to test for effects of sewage outfalls on rocky shore assemblages on the east coast of Ireland and to identify the scale of the putative impact. In addition, a separate sampling programme based on the Reduced algal Species List (RSL), the current WFD monitoring tool for rocky shores in Ireland and the UK, was also completed by identifying algae and measuring percent cover in replicate samples on rocky shores during Summer. There was no detectable effect of sewage outfalls on benthic taxon diversity or assemblage structure. However, spatial variability of assemblages was greater at sites proximal or adjacent to sewage outfalls compared to shores without sewage outfalls present. Results based on the RSL, show that algal assemblages were not affected by the presence of sewage outfalls, except when classed into functional groups when variability was greater at the sites with sewage outfalls. A key finding of both surveys, was the prevalence of spatial and temporal variation of assemblages. It is recommended that future metrics of ecological status are based on quantified sampling designs, incorporate changes in variability of assemblages (indicative of community stability), consider shifts in assemblage structure and include both benthic fauna and flora to assess the status of rocky shores.     

Impacts of Nutrient Reduction on Coastal Communities

Eutrophication due to high anthropogenic nutrient loading has greatly impacted ecological processes in marine coastal waters and, therefore, much effort has been put into reducing nitrogen and phosphorus discharges into European and North-American waters. Nutrient enrichment usually resulted in increase of biomass and production of phytoplankton and microphytobenthos, often coinciding with shifts in species composition within the primary producer community. Consequences of increasing eutrophication for higher trophic levels are still being disputed, and even less is known about the consequences of nutrient reduction on coastal food webs. Here, we present 30-year concurrent field observations on phytoplankton, macrozoobenthos and estuarine birds in the Dutch Wadden Sea, which has been subject to decades of nutrient enrichment and subsequent nutrient reduction. We demonstrate that long-term variations in limiting nutrients (phosphate and silicon) were weakly correlated with biomass and more strongly with community structures of phytoplankton, macrozoobenthos and estuarine birds. Although we cannot conclusively determine if, and if so to what extent, nutrient enrichment and subsequent nutrient reduction actually contributed to the concurrent trends in these communities, it appears likely that part of the variance in the studied coastal communities is related to changes in nutrient loads. Our results imply that nutrient reduction measures should not ignore the potential consequences for policies aimed at bird conservation and exploitation of marine living resources. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of nutrients and currents on the genomic composition of microbes across an upwelling mosaic

Metagenomic data sets were generated from samples collected along a coastal to open ocean transect between Southern California Bight and California Current waters during a seasonal upwelling event, providing an opportunity to examine the impact of episodic pulses of cold nutrient-rich water into surface ocean microbial communities. The data set consists of ∼5.8 million predicted proteins across seven sites, from three different size classes: 0.1–0.8, 0.8–3.0 and 3.0–200.0 μm. Taxonomic and metabolic analyses suggest that sequences from the 0.1–0.8 μm size class correlated with their position along the upwelling mosaic. However, taxonomic profiles of bacteria from the larger size classes (0.8–200 μm) were less constrained by habitat and characterized by an increase in Cyanobacteria, Bacteroidetes, Flavobacteria and double-stranded DNA viral sequences. Functional annotation of transmembrane proteins indicate that sites comprised of organisms with small genomes have an enrichment of transporters with substrate specificities for amino acids, iron and cadmium, whereas organisms with larger genomes have a higher percentage of transporters for ammonium and potassium. Eukaryotic-type glutamine synthetase (GS) II proteins were identified and taxonomically classified as viral, most closely related to the GSII in Mimivirus, suggesting that marine Mimivirus-like particles may have played a role in the transfer of GSII gene functions. Additionally, a Planctomycete bloom was sampled from one upwelling site providing a rare opportunity to assess the genomic composition of a marine Planctomycete population. The significant correlations observed between genomic properties, community structure and nutrient availability provide insights into habitat-driven dynamics among oligotrophic versus upwelled marine waters adjoining each other spatially.     

Response of macroalgae and macroinvertebrates to anthropogenic disturbance gradients in rocky shores

The compliance of macroalgal and macroinvertebrate assemblages to anthropogenic disturbance gradients (e.g., nutrient enrichment) was investigated at intertidal rocky shores. Macroalgae and macroinvertebrates presented parallel behavior, both showing shifts in the communities’ structural variation along the gradients, in which an higher number of opportunistic species (and higher abundances) were found in more stressful sites (close to the disturbance source), in contrast to less disturbed sites (far from the disturbance source), which showed higher presence of more sensitive species (and higher abundance of several of them).The macroinvertebrate abundance and taxonomic composition, which are parameters required by the Water Framework Directive (WFD) to be included in tools for the ecological quality status assessment, responded to the disturbance gradient. Results suggest that the macroinvertebrate biological element might be considered an indicator of disturbance in intertidal rocky shores as good as the macroalgae, and therefore the development of a specific methodology based solely on benthic macroinvertebrates of rocky shores, presently a gap in the ecological quality status assessment for the WFD, seems feasible.     

Climate‐driven trends and ecological implications of event‐scale upwelling in the California Current System

Eastern boundary current systems are among the most productive and lucrative ecosystems on Earth because they benefit from upwelling currents. Upwelling currents subsidize the base of the coastal food web by bringing deep, cold and nutrient‐rich water to the surface. As upwelling is driven by large‐scale atmospheric patterns, global climate change has the potential to affect a wide range of significant ecological processes through changes in water chemistry, water temperature, and the transport processes that influence species dispersal and recruitment. We examined long‐term trends in the frequency, duration, and strength of continuous upwelling events for the Oregon and California regions of the California Current System in the eastern Pacific Ocean. We then associated event‐scale upwelling with up to 21 years of barnacle and mussel recruitment, and water temperature data measured at rocky intertidal field sites along the Oregon coast. Our analyses suggest that upwelling events are changing in ways that are consistent with climate change predictions: upwelling events are becoming less frequent, stronger, and longer in duration. In addition, upwelling events have a quasi‐instantaneous and cumulative effect on rocky intertidal water temperatures, with longer events leading to colder temperatures. Longer, more persistent upwelling events were negatively associated with barnacle recruitment but positively associated with mussel recruitment. However, since barnacles facilitate mussel recruitment by providing attachment sites, increased upwelling persistence could have indirect negative impacts on mussel populations. Overall, our results indicate that changes in coastal upwelling that are consistent with climate change predictions are altering the tempo and the mode of environmental forcing in near‐shore ecosystems, with potentially severe and discontinuous ramifications for ecosystem structure and functioning.     

Positive and negative effects of mesograzers on early‐colonizing species in an intertidal rocky‐shore community

The ecological consequences of human‐driven overexploitation and loss of keystone consumers are still unclear. In intertidal rocky shores over the world, the decrease of keystone macrograzers has resulted in an increase in the dominance of herbivores with smaller body (i.e., “mesograzers”), which could potentially alter community assembly and structure. Here, we experimentally tested whether mesograzers affect the structure of rocky intertidal communities during the period of early colonization after the occurrence of a disturbance. A manipulative field experiment was conducted to exclude mesograzers (i.e., juvenile chitons, small snails, amphipods, and juvenile limpets) from experimental areas in an ecosystem characterized by the overexploitation of keystone macrograzers and predators. The results of multivariate analyses suggest that mesograzers had significant effects on intertidal community structure through negative and positive effects on species abundances. Mesograzers had negative effects on filamentous algae, but positive effects on opportunistic foliose algae and barnacles. Probably, mesograzers indirectly favored the colonization of barnacles and foliose algae by removing preemptive competitors, as previously shown for other meso‐ and macrograzer species. These results strongly support the idea that small herbivores exert a firm controlling effect on the assembly process of natural communities. Therefore, changes in functional roles of top‐down controllers might have significant implications for the structure of intertidal communities.     

Composition dynamics of epilithic intertidal bacterial communities exposed to high copper levels

Copper has a dual role for organisms, both as micronutrient and toxic element. Copper mining activities have an enormous ecological impact because of the extraction process and the consequent release of copper-containing waste materials to the environment. In northern Chile, mainly in the Cha?aral coastal area, this phenomenon is clearly evident. The released waste material has caused a strong modification of the area, and copper enrichment of beaches and rocky shores has provoked a decrease in the richness and diversity of many species of macroorganisms. However, the effects that copper enrichment has on microbial (e.g. bacterial epilithic) communities associated with the rocky shore environment are poorly understood. Using a culture-independent molecular approach, field sampling and laboratory microcosm experiments, we determined the effects of copper enrichment on bacterial communities inhabiting the rocky shore environment. Field samples showed a strong effect of copper on the structure of the natural bacterial epilithic communities, and microcosm experiments demonstrated rapid changes in bacterial community when copper is added, and reversibility of this effect within 48?h after copper is removed.     

NUTRIENTS AND THE PRODUCTIVITY OF ESTUARINE AND COASTAL MARINE ECOSYSTEMS

SUMMARY

Recent research on estuarine and coastal marine systems has revealed two particularly interesting things about nutrients and productivity. First is the observation that these areas are among the most intensively fertilized environments on earth. Second is the common finding that much of the characteristically high primary productivity of these shallow waters is supported by nutrients released or recycled by pelagic and benthic microheterotrophs. Since nutrient inputs to coastal areas have probably been increasing and are likely to continue to do so, it is particularly important to understand the relationship between nutrient loading and nutrient cycling and the extent to which their interactions may set the levels of primary and secondary production in coastal systems.

That some direct relationship exists between the input of nutrients and the productivity of higher trophic levels has been a principle of marine ecology since the turn of the century. It is surprisingly difficult, however, to find quantitative evidence showing that estuaries, lagoons, or other coastal waters respond to eutrophication by producing a larger biomass of animals. Part of this difficulty arises because the amount of nitrogen or phosphorus incorporated in animal tissue is a very small term in the total nutrient budget of an estuary, and the accuracy and precision of ecological field measurements may not be adequate to the task. In addition, the response of natural systems to nutrient enrichment is compounded by changes in climate, hydrography, harvesting effort and technology, and pollution.

Attempts to avoid some of these problems by carrying out controlled nutrient addition experiments in the field or with mesocosms have been much rarer in marine ecology than in limnology. The results that are available for such studies seem to suggest that there is a modest enhancement of primary production with nutrient addition, but that most of this extra organic matter is rapidly consumed, presumably by microheterotrophs. In other words, as nutrient inputs rise, so does the rate of nutrient recycling. Only a small fraction of the added nutrients appears as an increment in the production of higher trophic levels.     

Structure and function of anthropogenically altered microbial communities in coastal waters

Human-based (anthropogenic) nutrient and other pollutant enrichment of the world's coastal waters is causing unprecedented changes in microbial community structure and function. Symptoms of these changes include accelerating eutrophication, the proliferation of harmful microalgal blooms, excessive oxygen consumption (hypoxia, anoxia), increasing toxicity, altered routes and fluxes of organic and inorganic matter cycling, and disruption of food webs. Biogeochemical and trophic consequences are expanding on local, regional and global scales.     

34 Pieces of a puzzle: biogeography of southeast farallon Island,California

Rocky intertidal communities in cold waters on open shores tend to have a stable, predictable makeup worldwide. The structure of the environment, the morphology and life history of species, the economics of species behavior and the dynamics of population changes all contribute to the distribution of species in a given habitat. South East Farallon Island, in the Pacific Ocean off the northern California coast, hosts an intertidal community typical in many ways of other rocky intertidal communities. However, two orders of marine algae one might expect to be there, the Fucales and Laminariales, are unexpectedly uncommon on this island. In this paper some of the possible environmental, morphological and life history factors contributing to and restricting the distribution of marine algae in the intertidal zone on South East Farallon Island are considered.     

Top-down and bottom-up community regulation in marine rocky intertidal habitats

Strong top-down control by consumers has been demonstrated in rocky intertidal communities around the world. In contrast, the role of bottom-up effects (nutrients and productivity), known to have important influences in terrestrial and particularly freshwater ecosystems, is poorly known in marine hard-bottom communities. Recent studies in South Africa, New England, Oregon and New Zealand suggest that bottom-up processes can have important effects on rocky intertidal community structure. A significant aspect of all of these studies was the incorporation of processes varying on larger spatial scales than previously considered (10’s to 1000’s of km). In all four regions, variation in oceanographic factors (currents, upwelling, nutrients, rates of particle flux) was associated with different magnitudes of algal and/or phytoplankton abundance, availability of particulate food, and rates of recruitment. These processes led to differences in prey abundance and growth, secondary production, consumer growth, and consumer impact on prey resources. Oceanographic conditions therefore may vary on scales that generate ecologically significant variability in populations at the bottom of the food chain, and through upward-flowing food chain effects, lead to variation in top-down trophic effects. I conclude that top-down and bottom-up processes can be important joint determinants of community structure in rocky intertidal habitats, and predict that such effects will occur generally wherever oceanographic ‘discontinuities’ lie adjacent to rocky coastlines. I further argue that increased attention by researchers and of funding agencies to such benthic–pelagic coupling would dramatically enhance our understanding of the dynamics of marine ecosystems.     

36 Nutrients and harmful algal blooms: general issues and examples from the northern gulf of mexico

Rocky intertidal communities in cold waters on open shores tend to have a stable, predictable makeup worldwide. The structure of the environment, the morphology and life history of species, the economics of species behavior and the dynamics of population changes all contribute to the distribution of species in a given habitat. South East Farallon Island, in the Pacific Ocean off the northern California coast, hosts an intertidal community typical in many ways of other rocky intertidal communities. However, two orders of marine algae one might expect to be there, the Fucales and Laminariales, are unexpectedly uncommon on this island. In this paper some of the possible environmental, morphological and life history factors contributing to and restricting the distribution of marine algae in the intertidal zone on South East Farallon Island are considered.     

Climate-induced changes in bottom-up and top-down processes independently alter a marine ecosystem

Climate change has complex structural impacts on coastal ecosystems. Global warming is linked to a widespread decline in body size, whereas increased flood frequency can amplify nutrient enrichment through enhanced run-off. Altered population body-size structure represents a disruption in top-down control, whereas eutrophication embodies a change in bottom-up forcing. These processes are typically studied in isolation and little is known about their potential interactive effects. Here, we present the results of an in situ experiment examining the combined effects of top-down and bottom-up forces on the structure of a coastal marine community. Reduced average body mass of the top predator (the shore crab, Carcinus maenas) and nutrient enrichment combined additively to alter mean community body mass. Nutrient enrichment increased species richness and overall density of organisms. Reduced top-predator body mass increased community biomass. Additionally, we found evidence for an allometrically induced trophic cascade. Here, the reduction in top-predator body mass enabled greater biomass of intermediate fish predators within the mesocosms. This, in turn, suppressed key micrograzers, which led to an overall increase in microalgal biomass. This response highlights the possibility for climate-induced trophic cascades, driven by altered size structure of populations, rather than species extinction.     

The use of sea temperature in characterizing the mesoscale heterogeneity of phytoplankton in an embayment of the southern Benguela upwelling system

The role of meteorological events and hydrography in determiningchanges to the phytoplankton community was investigated in anembayment exposed to a narrow band of coastal upwelling. Dailysampling demonstrated the importance of advective processesdriven by meteorological forcing in controlling rapid shiftsin the biomass and species composition of the phytoplanktoncommunity. Samples of similar phytoplankton composition wereassociated with different stages of the upwelling cycle, asdefined by an index of biological ageing of upwelled waters.Relationships between the physical, chemical and biologicalfields were defined from time-senes measurements. The time elapsedfollowing upwelling, required for the determination of biologicalrates, was estimated from the rate of heating. A primary productionestimate of 2.14 g C m^–2 day^–1 was derived fromdetermination of the rate of nutrient depletion, whereas a phytoplanktonbiomass-nutrient consumption equation provided an estimate of3 92 g C m ^–2 day^–1. Both rates were within therange of estimates obtained from in vitro tracer methods.     

Trophic structure of macrobenthic communities on the Portuguese coast. A review of lagoonal,estuarine and rocky littoral habitats

This work is based on a compilation and treatment of data obtained on several studies regarding the macrobenthos trophic structure, carried out in different habitats of the Portuguese coast: a lagoon, rocky subtidal shores and estuarine eelgrass beds. Macrobenthic organisms were assigned to four distinct trophic groups (filter feeders, detritivores, herbivores and carnivores). Detritivores were the dominant trophic group in soft-bottom communities. Filter feeders dominated in subtidal rocky shores while eelgrass communities were equally represented by detritivores and herbivores. Current intensity and sediment deposition are discussed as factors affecting the observed distribution. Nevertheless, different sampling methods used in these studies and the lack of information on feeding habits of some species can also influence the results obtained.