Lower Trophic Level Species Research Articles

Marine fronts are important fishing areas for demersal species at the Argentine Sea (Southwest Atlantic Ocean)

The high primary and secondary production associated with frontal systems attract a diversity of organisms due to high prey availability; this is why a strong relationship between fronts and pelagic fisheries has been shown worldwide. In the Argentine Sea, demersal resources are the most important, both in economical and in ecological sense; so we hypothesize that fronts are also preferred fishing areas for demersal resources. We evaluated the relationship between spatial distribution of fishing effort and oceanographic fronts, analyzing three of the most important frontal systems located in the Argentine Sea: the shelf-break front, the southern Patagonia front and the mid-shelf front. Individual vessel satellite monitoring system data (VMS; grouped by fleet type: ice-trawlers, freezer-trawlers and jigging fleet) were studied and fishing events were identified. Fishing events per area were used as a proxy of fishing effort and its spatial distribution by fleet type was visualized and analyzed with Geographic Information Systems. Oceanographic fronts were defined using polygons based on satellite chlorophyll amplitude values, and the percentage of fishing events within each polygon was calculated. Results showed a positive association between fronts and fishing activities of the different fleets, which suggests the aggregation of target species in these zones. The coupling of the freezer-trawler and jigging fleets (that operate on lower trophic level species; Macruronus magellanicus and Illex argentinus respectively) with fronts was higher than the ice-trawler fleet, targeting species of higher trophic level (Merluccius hubbsi). Marine fronts represent important fishing areas, even for demersal resources, as the distribution of fishing fleets and fishing effort are positively associated with frontal zones.

Mercury bioaccumulation along food webs in temperate aquatic ecosystems colonized by aquatic macrophytes in south western France

Mercury (Hg) is considered as an important pollutant for aquatic systems as its organic form, methylmercury (MeHg), is easily bioaccumulated and bioamplified along food webs. In various ecosystems, aquatic periphyton associated with macrophyte was identified as an important place for Hg storage and methylation by microorganisms. Our study concerns temperate aquatic ecosystems (South Western France) colonized by invasive macrophytes and characterized by high mercury methylation potentials. This work establishes original data concerning Hg bioaccumulation in organisms (plants, crustaceans, molluscs and fish) from five contrasting ecosystems. For low trophic level species, total Hg (THg) concentrations were low (from 27±2ngTHgg−1dw in asiatic clam Corbicula fluminea to 418±114ngTHgg−1dw in crayfish Procambarus clarkii). THg concentrations in some carnivorous fish (high trophic level) were close to or exceeded the International Marketing Level (IML) with values ranging from 1049±220ngTHgg−1dw in pike perch muscle (Sander lucioperca) to 3910±1307ngTHgg−1dw in eel muscle (Anguilla Anguilla). Trophic levels for the individuals were also evaluated through stable isotope analysis, and linked to Hg concentrations of organisms. A significant Hg biomagnification (r2= 0.9) was observed in the Aureilhan lake, despite the absence of top predator fish. For this site, Ludwigia sp. periphyton, as an entry point of Hg into food webs, is a serious hypothesis which remains to be confirmed. This study provides a first investigation of Hg transfer in the ecosystems of south western France and allows the assessment of the risk associated with the presence of Hg in aquatic food webs.

An assessment of participation, catch and effort in the KwaZulu-Natal shore-based marine linefishery, with comments on management effectiveness

The primary purpose of this study was to evaluate the effectiveness of current management of the KwaZulu-Natal (KZN) shore-based marine linefishery. Methods used included a stratified-random creel survey and an associated questionnaire survey. The study was undertaken between February 2009 and January 2010. Total participation ranged between 41 283 and 68 087 shore-anglers. Results show that there has been little change in participation in the KZN shore-fishery since 1994–1996. In contrast, total angler effort (779 382–843 702 angler-days y−1) has decreased substantially over the past 13 years. Overall catch per unit effort (CPUE) for the KZN shore-linefishery amounted to 0.18 ± 0.3 fish angler−1 h−1 or 0.07 ± 0.13 kg angler−1 h−1. In all, 84 fish species, belonging to 39 families, were recorded in catches of shore-anglers during the study period. Only five species accounted for 75% of the catch recorded along the coast (Sarpa salpa 34.8%, Pomatomus saltatrix 14.7%, Diplodus capensis 14.5%, Pomadasys olivaceum 6.5% and Rhabdosargus holubi 4.9%). The total annual catch for the KZN shore-linefishery was estimated between 249.2 and 276.7 t y−1 (or 636 589–706 995 fish y−1). Analysis of overall CPUE, catch composition and total catch in the shore-based linefishery of KZN suggested that it is currently in a relatively stable condition and that little change has occurred over the past 13 years. However, comparisons of species-specific CPUE values from this study with recent literature suggest that some species (e.g. Argyrosomus japonicus) are severely overexploited. Over the past few decades there seems to have been a gradual transition in landings from long-lived, high trophic-level, piscivorous fish (e.g. A. japonicus) to more short-lived, low trophic-level species (e.g. S. salpa). The results therefore suggest that present exploitation levels may not be sustainable for certain slow-growing, long-lived fish species. Current management regulations appear to have limited effectiveness based on poor angler compliance and knowledge of the regulations. In this regard, it is important to consider alternate management measures that may offer more effective protection to fish and at the same time be more easily understood by all anglers in the linefishery. Recommendations for improved management and the importance of the establishment of an effective MPA network are briefly discussed.

Feeding ecology of harbour porpoises: stable isotope analysis of carbon and nitrogen in muscle and bone

Harbour porpoises are the most common small cetaceans in the North Sea and Dutch coastal waters. To study their trophic level and feeding location, stable carbon and nitrogen isotope ratios (δ13C and δ15N) were analysed in muscle and bone samples collected from 157 porpoises stranded along the Dutch coast (2006–2008). In addition, samples from 30 prey species were analysed. Prey samples showed high δ15N values in species of higher trophic level. In addition, geographic differences in isotopic composition were found, with higher δ15N and δ13C values in prey from more southern, coastal and estuarine areas. Based on muscle δ15N values, we found neonatal enrichment and that larger porpoises, in particular males, seem to feed on lower trophic level species, compared to smaller individuals. Also bone δ15N values show that larger animals had fed on lower trophic levels in distant times. Porpoises from the Eastern Scheldt reveal distinct δ13C values in muscle, but not in bone. This shows that these animals had foraged in the Eastern Scheldt for a longer time period but were not born there. Seasonal variation in bone δ15N and δ13C values revealed two distinct groups of porpoises along the Dutch coast, a winter group (mainly males) that migrated from neighbouring regions and a Dutch subpopulation in summer. These results furthered our insight about shifts in trophic level and feeding location of harbour porpoises from the southern North Sea over time.

Impacts of Fishing Low–Trophic Level Species on Marine Ecosystems

Low-trophic level species account for more than 30% of global fisheries production and contribute substantially to global food security. We used a range of ecosystem models to explore the effects of fishing low-trophic level species on marine ecosystems, including marine mammals and seabirds, and on other commercially important species. In five well-studied ecosystems, we found that fishing these species at conventional maximum sustainable yield (MSY) levels can have large impacts on other parts of the ecosystem, particularly when they constitute a high proportion of the biomass in the ecosystem or are highly connected in the food web. Halving exploitation rates would result in much lower impacts on marine ecosystems while still achieving 80% of MSY.

Unexpected patterns of fisheries collapse in the world's oceans

Understanding which species are most vulnerable to human impacts is a prerequisite for designing effective conservation strategies. Surveys of terrestrial species have suggested that large-bodied species and top predators are the most at risk, and it is commonly assumed that such patterns also apply in the ocean. However, there has been no global test of this hypothesis in the sea. We analyzed two fisheries datasets (stock assessments and landings) to determine the life-history traits of species that have suffered dramatic population collapses. Contrary to expectations, our data suggest that up to twice as many fisheries for small, low trophic-level species have collapsed compared with those for large predators. These patterns contrast with those on land, suggesting fundamental differences in the ways that industrial fisheries and land conversion affect natural communities. Even temporary collapses of small, low trophic-level fishes can have ecosystem-wide impacts by reducing food supply to larger fish, seabirds, and marine mammals.

Trophic indicators to measure the impact of fishing on an exploited ecosystem

There is currently a global call for more use of an ecosystem approach to fisheries management (EAFM) to provide a holistic view of ecosystem-fisheries interactions. Trophic indicators could therefore be used to support the implementation of an EAFM by providing information on the state of the ecosystem. In this paper we propose a set of indicators such as the marine trophic index (MTI), the fishing in balance (FiB), the cut marine trophic index (cutMTI) and the pelagic/demersal index (P/D) to assess the dynamics and the trophic changes in the Black Sea large marine ecosytem from 1970 to 2005. Our analysis shows a heavily exploited ecosystem where overfishing and anthropogenic eutrophication are probably responsible. The decline of the MTI, cutMTI and FiB together with the rising trend of the P/D index could be interpreted as a fishing down marine food web process with a strong decrease in abundance of high trophic level species and a considerable increase of low trophic level species.

Historical Changes in Marine Resources, Food-web Structure and Ecosystem Functioning in the Adriatic Sea, Mediterranean

The Mediterranean Sea has been strongly influenced by human activities for millennia. Although the environmental history of its surrounding terrestrial ecosystems has received considerable study, historical changes in its marine realm are less known. We used a multidisciplinary approach combining paleontological, archeological, historical, fisheries, and ecological data to reconstruct past changes in marine populations, habitats, and water quality in the Adriatic Sea. Then, we constructed binary food webs for different historical periods to analyze possible changes in food-web structure and functioning over time. Our results indicate that human activities have influenced marine resource abundance since at least Roman times and accelerated in the nineteenth and twentieth centuries. Today, 98% of traditional marine resources are depleted to less than 50% of former abundance, with large (>1 m) predators and consumers being most affected. With 37% of investigated species rare and 11% extirpated, diversity has shifted towards smaller, lower trophic-level species, further aggravated by more than 40 species invasions. Species providing habitat and filter functions have been reduced by 75%, contributing to the degradation of water quality and increased eutrophication. Increased exploitation and functional extinctions have altered and simplified food-web structure over time, especially by changing the proportions of top predators, intermediate consumers, and basal species. Moreover, simulations of species losses indicate that today’s ecosystems may be less robust to species extinctions than in the past. Our results illustrate the long-term and far-reaching consequences human activities can have on marine food webs and ecosystems.

Responsible Aquaculture and Trophic Level Implications to Global Fish Supply

Hunger and malnutrition remain among the most devastating problems facing the world's poor and needy, and continue to dominate the health and well-being of the world's poorest nations. Moreover, there are growing doubts as to the long-term sustainability of many existing food production systems, including capture fisheries and aquaculture, to meet the future increasing global demands. Of the different agricultural food production systems, aquaculture (the farming of aquatic animals and plants) is widely viewed as an important weapon in the global fight against malnutrition and poverty, particularly within developing countries where over 93% of global production is currently produced, providing in most instances an affordable and a much needed source of high quality animal protein, lipids, and other essential nutrients. The current article compares for the first time the development and growth of the aquaculture sector and capture fisheries by analyzing production by mean trophic level. Whereas marine capture fisheries have been feeding the world on high trophic level carnivorous fish species since mankind has been fishing the oceans, aquaculture production within developing countries has focused, by and large, on the production of lower trophic level species. However, like capture fisheries, aquaculture focus within economically developed countries has been essentially on the culture of high value-, high trophic level-carnivorous species. The long term sustainability of these production systems is questionable unless the industry can reduce its dependence upon capture fisheries for sourcing raw materials for feed formulation and seed inputs. In line with above, the article calls for the urgent need for all countries to adopt and adhere to the principles and guidelines for responsible aquaculture of the FAO Code of Conduct for Responsible Fisheries.

Coastal dynamics and cultural occupations on Choctawhatchee bay, Florida, U.S.A.

A multidisciplinary project on an archaeological site on theMitchell River, which feeds into Choctawhatchee Bay on the Floridapanhandle, was designed to understand human adaptations to a dynamic hydrological environment during the Middle and Late Archaic period (ca. 8000–3000 B.P.). Now in a freshwater environment, on a sandy terrace above the Mitchell River floodplain, the Mitchell River 1 archaeological site contains an oyster‐shell midden and other features indicating human exploitation of an estuarine environment. Estuarine exploitation at the site occurred over a long span of time, from around 7300 to 3400 2cal B.P., although the site was abandoned two or three times over the millennia. The site was more permanently abandoned after 3400 B.P. Because estuarine shellfish, such as oysters, are low trophic level species, they have been considered marginal resources, and archaeologists modeling collector strategies assume that people will not travel far to obtain them. Under an optimal foraging model, estuarine resources should have been closer to the site than at present. A multidisciplinary team was assembled to address whether a mid‐Holocene sea‐level highstand had produced estuarine conditions in the Mitchell River floodplain during the Archaic. Using microfossils and stratigraphy from a dated core taken in the floodplain due south of the site, the project members attempted to correlate the changing paleoenvironment with human occupation and abandonment of the area. Results indicate that, at ca. 7300 cal B.P., when the Mitchell River 1 site was first inhabited, the floodplain was a shallow, open, sedge marsh. The site inhabitants must have traveled some distance to gather the oysters and other estuarine species that were discarded on the site. The earliest occupation was brief, but the site was reoccupied between 5900 and 5300 cal B.P., when the floodplain had become a Taxodium/Nyssa swamp. Site deposits indicate intensive exploitation of oyster and to a lesser extent Rangia, which may have been closer to the site than at 7300 B .P. but still would have required some travel. At some point, the mouth of the Mitchell River was forced eastward, and the bayhead delta, recognized as a 2‐meter‐deep wedge of sand in the core, was located adjacent to the site. By 4700 cal B.P., brackish water conditions prevailed, although direct evidence of oyster beds in the immediate area is lacking. Unfortunately, scouring of the core sediments sometime after 4700 cal B.P. destroyed the paleoenvironmental record for the lastpart of the Archaic occupation of the site. However, some evidence in Core 1, along with research elsewhere on the Florida panhandle, suggests that catastrophic storms may have played a part in the more permanent abandonment of the site after 3400 B.P.

Restoration in the Face of Climate Change: A Case Study from the Dorset Heaths

This paper demonstrates the potential for restoring a range of habitats by comparing the efficacy of different techniques for restoring lowland dry Atlantic heathland in Dorset, UK, under current and future climatic conditions. The success of different treatments in reducing soil pH and concentrations of the most important macronutrient, phosphorus, on improved pasture adjacent to Hartland Moor National Reserve in Dorset are discussed. The treatments applied were soil removal, soil acidification using elemental sulfur, soil acidification using ferrous sulfate, and nutrient removal. The treatment that most successfully reduced extractable phosphate was soil removal. Nutrient removal produced no significant decrease in extractable phosphate over 7 years study. Soil acidification with sulfur most successfully reduced pH. Under the present climatic conditions, the elemental sulfur treatment produced far more abundant heather growth than soil removal. This study suggest that restoration techniques are likely to change in their relative effectiveness as climate changes and that this may have different consequences for low and high trophic level species.

Predator identity and recruitment of coral-reef fishes: indirect effects of fishing

Studies of food and interaction webs are often simplified by combining different species of predator into guilds, especially predators that are closely related. Such combinations require the assumption that predators are functionally redundant or at least have similar effects on prey abun- dances and community structure. However, few studies have rigorously tested this assumption, par- ticularly with exploited species of marine predators. Moreover, fishing can strongly alter the relative abundances of different predatory species, further highlighting the need to examine the top-down effects of different predators on lower trophic-level species within marine communities. Throughout the greater Caribbean, intensive fishing has depleted populations of Nassau grouper Epinephelus striatus, while populations of the less-targeted coney Cephalopholis fulva have proliferated. In the present study I experimentally tested the effects of these different grouper species on recruitment of other coral-reef fishes to spatially isolated reefs. Recruitment to reefs occupied by Nassau grouper was similar to that on predator-free control reefs, and both treatments accumulated higher relative recruit abundance and diversity than reefs occupied by coney. Thus, even closely related predator species can have substantially different effects on lower trophic levels. Shifts in dominance of preda- tory species may therefore lead to dramatic changes to prey communities. These findings underscore the importance of addressing both the direct and indirect effects of fishing on marine communities.

Changes in the trophic level of Portuguese landings and fish market price variation in the last decades

Fishing can alter the structure of marine food web by selective removal of some species. Changes in marine food webs in Portuguese waters were evaluated based on estimates of the annual mean trophic levels (TLm) and fishing-in-balance index (FiB) of mainland, Azores, Madeira and total Portuguese marine fisheries landings for the period between 1970 and 2006. The log-relative-price-index (LRPI), that translates the relationship between the logarithm of prices of low and high trophic level species, was also calculated for each year. TLm of mainland landings showed a decreasing trend, reflecting changes in the structure of marine food webs, whereas in Azores and Madeira TLm increased. FiB index also showed a downward trend and negative values in mainland waters, which may be associated with unbalanced fisheries. In the period studied LRPI increased, indicating that high trophic level species had become more valuable in relation to species feeding at lower trophic levels. It is likely that the persistence of present trends will compromise the sustainability of fisheries. A better management is needed in order to reverse this decreasing trend in TLm in the long-term using an ecosystem-based approach.

COASTAL DYNAMICS AND CULTURAL OCCUPATIONS ON CHOCTAWHATCHEE BAY, FLORIDA, U.S.A.

Abstract A multidisciplinary project on an archaeological site on the Mitchell River, which feeds into Choctawhatchee Bay on the Florida panhandle, was designed to understand human adaptations to a dynamic hydrological environment during the Middle and Late Archaic period (ca. 8000–3000 B.P.). Now in a freshwater environment, on a sandy terrace above the Mitchell River floodplain, the Mitchell River 1 archaeological site contains an oyster-shell midden and other features indicating human exploitation of an estuarine environment. Estuarine exploitation at the site occurred over a long span of time, from around 7300 to 3400 2cal B.P., although the site was abandoned two or three times over the millennia. The site was more permanently abandoned after 3400 B.P. Because estuarine shellfish, such as oysters, are low trophic level species, they have been considered marginal resources, and archaeologists modeling collector strategies assume that people will not travel far to obtain them. Under an optimal foraging...

Using an Ecosystem Modeling Approach to Explore Possible Ecosystem Impacts of Fishing in the Beibu Gulf, Northern South China Sea

Using the Ecopath with Ecosim software, a trophic structure model of the Beibu Gulf was constructed to explore the energy flows and provide a snapshot of the ecosystem operations. Input data were mainly from the trawl survey data collected from October 1998 to September 1999 and related literatures. The impacts of various fishing pressure on the biomass were examined by simulation at different fishing mortality rates. The model consists of 20 functional groups (boxes), each representing organisms with a similar role in the food web, and only covers the major trophic flows in the Beibu Gulf ecosystem. It was found that the food web of the Beibu Gulf was dominated by the primary producers path, and phytoplankton was the primary producer mostly used as a food source. The fractional trophic levels ranged from 1.0 to 4.02, and the marine mammals occupied the highest trophic level. Using network analysis, the ecosystem network was mapped into a linear food chain, and six discrete trophic levels were found with a mean transfer efficiency of 11.2%. The Finn cycling index was 9.73%. The path length was 1.821. The omnivory index was 0.197. The ecosystem had some degree of instability due to exploitation and other human activities, according to Odum's theory of ecosystem development. A 10-year simulation was performed for each fishery scenario. The fishing mortality rate was found to have a strong impact on the biomass. By keeping the fishing mortality rate at the current level for all fishing sectors, scenario 1 had a drastic decrease in the large fish groups. The biomass of the small and medium pelagic fish would increase to some extent. The biomass of the small and low trophic level species, jellyfish, prawns and benthic crustaceans would be stable. The total biomass of the fishery resources would have a 10% decrease from the current biomass after 10 years. In contrast, the reduced fishing mortality rate induced the recovery of biomass (scenarios 2-4). In scenario 2, the biomass of the large demersal fish and the large pelagic fish would increase to over 16 times and 10 times, respectively, of their current level. In scenario 4, the biomass of the large pelagic fish would increase to over 3 times of its current level. The total biomass of the fish groups, especially the high trophic level groups, would become significantly higher after 10 years, which illustrates the contribution on biomass recovery by relaxing the fishing pressure.

Simulating fisheries management options for the Beibu Gulf by means of an ecological modelling optimization routine

The Beibu Gulf is a semi-enclosed sea surrounded by land territories of China, Vietnam and China's Hainan Island. Historically, the Beibu Gulf supported various commercial, recreational, and artisanal fisheries. Many fisheries are now depleted or had experienced substantial decline in productivity. In this paper, we developed a mass balance model using Ecopath with Ecosim (EwE), to evaluate how the ecosystem may respond to changes in fisheries activities over a period of 20 years. Input data were mainly from the information collected in trawl surveys from October 1998 to September 1999. Four fishery management scenarios, which maximized three independent (fishery profits, employment, and ecosystem) and the combination of the above three objectives were simulated with different vulnerability settings. Results suggested that socioeconomically driven policy caused the ecosystem to be vulnerable whereas maximized ecological stability and the compromise scenarios were generally consistent with different vulnerability settings. To maximize social and economical criteria, the ecosystem structure was shifted to a simplified state where the high trophic level species became depleted and the low trophic level species gained dominance. Therefore, the optimal state (social strategy) had the lowest trophic level, 2.78. When an ecological stability criterion was considered, the model predicted effort should decrease more than 70% for all fishing sectors. A trade-off analysis indicated that ‘Big compromise’ strategy would be optimal to balance fishery and conservation. These results indicate that developing multispecies harvesting strategies is a complex task, and goal functions may be conflicting, while initial model conditions can affect the results.

Reanalyses of Gulf of Mexico fisheries data: Landings can be misleading in assessments of fisheries and fisheries ecosystems

We used two high profile articles as cases to demonstrate that use of fishery landings data can lead to faulty interpretations about the condition of fishery ecosystems. One case uses the mean trophic level index and its changes, and the other uses estimates of fishery collapses. In earlier analyses by other authors, marine ecosystems in the Gulf of Mexico (GOM) and U.S. Atlantic Ocean south of Chesapeake Bay were deemed to be severely overfished and the food webs badly deteriorated using these criteria. In our reanalyses, the low mean trophic level index for the GOM actually resulted from large catches of two groups of low trophic level species, menhaden and shrimp, and the mean trophic level was slowly increasing rather than decreasing. Commercial targeting and high landings of shrimps and menhaden, especially in the GOM, drove the index as previously calculated. Reanalyses of fishery collapses incorporating criteria that included targeting, variability in fishing effort, and market forces discovered many false cases of collapse based simply upon a decline of catches to 10% of previous maximum levels. Consequently, we suggest that the low mean trophic level index calculated in the earlier article for the GOM did not reflect the overall condition of the fishery ecosystem, and that the 10% rule for collapse should not be interpreted out of context in the GOM or elsewhere. In both cases, problems lay in the assumption that commercial landings data alone adequately reflect the fish populations and communities.

‘Fishing down marine food webs’ and spatial expansion of coastal fisheries in India, 1950–2000

The worldwide crisis of fisheries, which are usually managed on a single species basis, has led to calls for ‘ecosystem management’, along with the development of various ecosystem indicators. The Marine Trophic Index (MTI) and the related Fishing-in-Balance (FiB) index are two such indicators, which can be used to draw inferences on the sustainability of fisheries, notably those targeting high-trophic level species, in an ecosystem context. These indices are used here to evaluate the status of marine fisheries in India, based on taxonomically and spatially disaggregated time series of catches covering the years 1950, when 0.6 million tonnes were landed to 2000, when 3.3 million tonnes were landed. We show that the MTI is steadily decreasing in all 13 Indian States and Union Territories, at rates averaging 0.058 trophic level per decade, about the same as in other parts of the world. This decline, however, is not due to the sequential addition of newly exploited species of low trophic level to the multi-species catch from which mean trophic level is calculated. Rather, the MTI values were computed after exclusion of species with trophic levels lower than 3.25. Notably, this excluded Indian oil sardine and penaeid shrimps, the catch of which grew enormously in the 1980s. What has to date maintained the landings of higher trophic level fish in India has been the geographic expansion of the fisheries, which, until the early 1970s, exploited only waters immediately under the coast, while they now reaches to the edges of the continental shelf and beyond. This expansion is quantified here through a ‘spatial expansion factor’, based on a re-interpretation of the Fishing-in-Balance index. This index was proposed earlier to analyse, in an ecosystem context, the interrelationship between mean trophic level and magnitude of the catch, and the trophic transfer efficiency among trophic levels of the food web. The FiB index is shown here to allow, under some specific assumptions about productivity of the exploited areas, inferences on the spatial behavior of fisheries. Based on the newly formulated spatial expansion factor, it is suggested that the Indian shelf fisheries, covered by 2000 about 4 times the area they covered in 1970. However, this expansion had apparently met its natural limits, and catches can be expected to stagnate and ultimately decline, with serious consequences for the marine fisheries sector and consumers in India.

Population structure of a large blue butterfly and its specialist parasitoid in a fragmented landscape

Habitat fragmentation may interrupt trophic interactions if herbivores and their specific parasitoids respond differently to decreasing connectivity of populations. Theoretical models predict that species at higher trophic levels are more negatively affected by isolation than lower trophic level species. By combining ecological data with genetic information from microsatellite markers we tested this hypothesis on the butterfly Maculinea nausithous and its specialist hymenopteran parasitoid Neotypus melanocephalus. We assessed the susceptibility of both species to habitat fragmentation by measuring population density, rate of parasitism, overall genetic differentiation (theta(ST)) and allelic richness in a large metapopulation. We also simulated the dynamics of genetic differentiation among local populations to asses the relative effects of migration rate, population size, and haplodiploid (parasitoid) and diploid (host) inheritance on metapopulation persistence. We show that parasitism by N. melanocephalus is less frequent at larger distances to the nearest neighbouring population of M. nausithous hosts, but that host density itself is not affected by isolation. Allelic richness was independent of isolation, but the mean genetic differentiation among local parasitoid populations increased with the distance between these populations. Overall, genetic differentiation in the parasitoid wasp was much greater than in the butterfly host and our simulations indicate that this difference is due to a combination of haplodiploidy and small local population sizes. Our results thus support the hypothesis that Neotypus parasitoid wasps are more sensitive to habitat fragmentation than their Maculinea butterfly hosts.

Tramas tróficas de peces de arrecifes en la región noroccidental de Cuba. II. Grupos funcionales

A conceptual model of the food webs, mainly with fish, was built in a rocky shore of Havana City with data covering from October 2004 to February 2006. The stomach contents of the most abundant fish was complemented with the literature. We used the Relative Importance Index method to describe diets of carnivorous and omnivorous fish; and a modification of the Relative Abundance method for sponge eaters and herbivorous fish. Agglomerative numeric classification techniques were used to determine the diet's similarity. The matrix was made using Bray-Curtis dissimilarity index. Ten functional trophic groups were formed on the basis of diet similarity. The cascade effect is evidenced in this area by the big top predator shortage and the dominance of a few low trophic level species. The regulator role of top predators is low because of over-fishing: the trophic web of this area is highly altered.