We review the effects of fishing on benthic fauna, habitat, diversity, community structure and trophic interactions in tropical, temperate and polar marine environments and consider whether it is possible to predict or manage fishing-induced changes in marine ecosystems Such considerations are timely given the disillusionment with some fishery management strategies and that policy makers need a scientific basis for deciding whether they should respond to social, economic and political demands for instituting or preventing ecosystem-based management Fishing has significant direct and indirect effects on habitat, and on the diversity, structure and productivity of benthic communities These effects are most readily identified and last longest in those areas that experience infrequent natural disturbance The initiation of fishing in an unfished system leads to dramatic changes in fish community structure As fishing intensity increases the additional effects are more difficult to detect Fishing has accelerated and magnified natural declines in the abundance of many forage fishes and this has lead to reduced reproductive success and abundance in birds and marine mammals However, such donor-controlled dynamics are less apparent in food webs where fishes are the top predators since their feeding strategies are rather more plastic than those of most birds and mammals Fishers tend to target species in sequence as a fishery develops and this leads to changes in the composition of the fished communities with time The dramatic and apparently compensatory shifts in the biomass of different species in many fished ecosystems have often been driven by environmental change rather than the indirect effects of fishing Indeed, in most pelagic systems, species replacements would have occurred, albeit less rapidly, in the absence of fishing pressure In those cases when predator or prey species fill a key role, fishing can have dramatic indirect effects on community structure Thus fishing has shifted some coral reef ecosystems to alternate stable states because there is tight predator–prey coupling between invertebrate feeding fishes and sea urchins Fishing has reduced, and locally extirpated, populations of predatory fishes These reductions do not have a consistent effect on the abundance and diversity of their prey: environmental processes control prey populations in some systems, whereas top-down processes are more important in others By-catch which is discarded during fishing activities may sustain populations of scavenging species, particularly seabirds We conclude by identifying the circumstances in which new research is needed to guide managers and stress the importance of unfished control sites for studies of fishing effects We discuss the advantages and disadvantages of closed area management (marine reserves) and the conditions under which such management is likely to provide benefits for the fishery or ecosystem

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The effects of fishing on marine ecosystems

Although invasive species are widely recognized as a major threat to marine biodiversity, there has been no quantitative global assessment of their impacts and routes of introduction. Here, we report initial results from the first such global assessment. Drawing from over 350 databases and other sources, we synthesized information on 329 marine invasive species, including their distribution, impacts on biodiversity, and introduction pathways. Initial analyses show that only 16% of marine ecoregions have no reported marine invasions, and even that figure may be inflated due to under-reporting. International shipping, followed by aquaculture, represent the major means of introduction. Our geographically referenced and publicly available database provides a framework that can be used to highlight the invasive taxa that are most threatening, as well as to prioritize the invasion pathways that pose the greatest threat.

Assessing the global threat of invasive species to marine biodiversity

▪ Abstract Biological invasions of marine habitats have been common, and many patterns emerge from the existing literature. In North America, we identify 298 nonindigenous species (NIS) of invertebrates and algae that are established in marine and estuarine waters, generating many “apparent patterns” of invasion: (a) The rate of reported invasions has increased exponentially over the past 200 years; (b) Most NIS are crustaceans and molluscs, while NIS in taxonomic groups dominated by small organisms are rare; (c) Most invasions have resulted from shipping; (d) More NIS are present along the Pacific coast than the Atlantic and Gulf coasts; (e) Native and source regions of NIS differ among coasts, corresponding to trade patterns. The validity of these apparent patterns remains to be tested, because strong bias exists in the data. Overall, the emergent patterns reflect interactive effects of propagule supply, invasion resistance, and sampling bias. Understanding the relative contribution of each component re...

Invasion of Coastal Marine Communities in North America: Apparent Patterns, Processes, and Biases

SYNOPSIS. Non-indigenous species (NIS) are increasingly conspicuous in marine and estuarine habitats throughout the world, as the number, variety, and effects of these species continue to accrue. Most of these NIS invasions result from anthropogenic dispersal. Although the relative importance of different dispersal mechanisms varies both spatially and temporally, the global movement of ballast water by ships appears to be the largest single vector for NIS transfer today, and many recent invasions have resulted from this transfer. The rate of new invasions may have increased in recent decades, perhaps due to changes in ballast water transport. Estuaries have been especially common sites of invasions, accumulating from tens to hundreds of NIS per estuary that include most major taxonomic and trophic groups. We now know of approximately 400 NIS along the Pacific, Atlantic and Gulf coasts of the U.S., and hundreds of marine and estuarine NIS are reported from other regions of the world. Although available information about invasions is limited to a few regions and underestimates the actual number of NIS invasions, there are apparent differences in the frequency of NIS among sites. Mechanisms responsible for observed patterns among sites likely include variation in supply of NIS, and perhaps variation in properties of recipient or donor communities, but the role of these mechanisms has not been tested. Although our present knowledge about the extent, patterns and mechanisms of marine invasions is still in its infancy, it is clear that NIS are a significant force of change in marine and especially estuarine communities globally. Taxonomically diverse NIS are having significant effects on many, if not most, estuaries that fundamentally alter population, community, and ecosystems processes. The impacts of most NIS remain unknown, and the predictability of their direct and indirect effects remains uncertain. Nonetheless, based upon the documented extent of NIS invasions and scope of then* effects, studies of marine communities that do not include NIS are increasingly incomplete.

Global Invasions of Marine and Estuarine Habitats by Non-Indigenous Species: Mechanisms, Extent, and Consequences'

Marine invasive alien species: a threat to global biodiversity

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Non-native Marine Species in British Waters: A Review and Directory

We examined the effects of fishing with crustacean traps on benthic species in Great Britain by means of qualitative and quantitative experiments. Experimental sites were selected where fishing using pots or creels was practised regularly and where species perceived to be potentially sensitive to damage were present. The effect of Nephrops creels on different sea pen species was studied in Scottish sea lochs. Sea pens were observed to bend in response to the pressure wave before the creel made contact. After smothering and even uprooting, they re-established themselves when in contact with muddy substrate. Observations of lobster and crab pots being hauled from rocky substrates in southern England, revealed that the habitats and their communities appeared relatively unaffected by potting. The slow-growing, long-lived, pink sea fan Eunicella verrucosa were observed to flex under the weight of pots as they passed and then returned back to an upright position. Quantitative studies, undertaken in south England and west Wales, were based on surveys carried out along transect lines before and after a month of pot fishing for crabs and lobsters. The results suggest that four weeks of fairly intense fishing did not have immediate detrimental effects on the abundance of the species selected for study, although some individual ross coral colonies (Pentapora foliacea) were damaged.

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Effects of crustacean traps on benthic fauna

1. Preliminary estimates of the relative sensitivity of sea bed types and benthic species to physical disturbance, particularly fishing activity, have been made in order to identify areas where further studies are required and to help formulate management plans for sites of marine conservation importance.

 2. Physical disturbance is considered in the context of a single encounter with fishing gear followed by a recovery period during which there is no fishing, but with a view to qualifying, in the future, the effect of multiple fishing events. Disturbance is considered in terms of the physical action of the gear on the sea bed and the unit area over which this action occurs.

 3. The effects of a wide range of gears are considered. Static gears, which can be employed on a variety of substrata, generally result in low level impacts for single fishing events and impacts are localized compared with the effects of mobile gears, which can extend over considerable areas.

 4. The theoretical sensitivity of individual species is assessed on the basis of how well they cope with an encounter with fishing gear and on their likely recovery from destruction in terms of their reproductive strategies.

 5. Species considered of key importance in the structuring of communities are suggested and examples of particularly sensitive species, which are therefore likely indicator species of physical disturbance, are listed.

 6. Fragile, slow recruiting animals are considered to be most susceptible to disturbance, while the least sensitive species are generally fast growing and have good recruitment. ©1996 by John Wiley & Sons, Ltd.

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Disturbance of benthic species by fishing activities: a sensitivity index

1. The occurrence of non-native marine macro fauna and flora, which have become established in the wild British waters, are summarized. The effects of these non-natives on the native fauna and flora and on commercial and recreational interests are reviewed.



 2. Sixteen species of marine algae (11 rhodophytes, three chromophytes and two chlorophytes), five diatoms, one angiosperm and 31 invertebrates were identified as non-native. The majority of these species are red algae, polychaete worms, crustaceans and molluscs.



 3. Species were introduced directly from primary sources within their natural range, or from secondary sources to which they had previously been introduced. They have only become established where introduced from similar latitudes of both hemispheres.



 4. More than half the total number of species are considered to have been introduced to Britain in association with shipping, whilst half of the non-native marine algae are believed to have been introduced in association with deliberate introductions for mariculture.



 5. Of the species that had spread, the marine plants did so fairly rapidly, while the invertebrates tended to spread more slowly. The methods of spread were often the same as their method of introduction for both flora and fauna.



 6. The direct effects of non-native species on the marine environment in British waters are not as detrimental as those reported from elsewhere in the world. Some commercially important species have been introduced, but some associated pests and parasites have accompanied them.



 7. Control methods, where applied to populations of nuisance species, are fairly ineffective and no non-native marine species have been deliberately eradicated from British waters. Ways of avoiding introduction of further non-natives by mandatory and voluntary means are discussed. ©1996 by John Wiley & Sons, Ltd.

Non‐native marine species in British waters: effects and controls

The capacity for oxygen uptake of a respiratory organ can be estimated using morpho-metric techniques, the two essential measurements being respiratory surface-area and thickness of the tissue barrier across which oxygen diffuses. In cephalopods, the gills are the main site of respiratory exchange and this study was designed to estimate oxygen uptake capacity of the gills of four different genera of cephalopods. A preliminary study was required to determine the form and structure of the gills. Light microscopy showed the surface of the gills to be highly folded, particularly in Octopus. A level of microscopy was chosen at which the outline of the smallest folds of the epithelium and the blood vessels of the gills could be easily resolved. Stereological techniques were then employed to obtain values for the respiratory surface-area related to body weight (cm2 g-1), tissue barrier thickness (μm) and oxygen-diffusing capacity (ml O2 min1 Torr·1 kg1). Values for these three variables obtained for the different species were as follows: Octopus vulgaris 2·9 cm2 g-1, 10 μm, 0·05 ml O2 min-1 Torr-1 kg1; Alloteuthis subulata 10·6 cm2 g1,6 μm, 0·27 ml O2 min-1 Torr-1 kg-1; Nautilus sp. 4·9 cm2 g-1,15 μm, 0·05 ml O2 min-1 Torr1 kg-1; Sepia hatchlings 13·3 cm2 g-1, 4 μm, 0·52 ml O2 min-1 Torr-1 kg-1.

N. Clare Eno

Papers

Non-native Marine Species in British Waters: A Review and Directory

Effects of crustacean traps on benthic fauna

Disturbance of benthic species by fishing activities: a sensitivity index

Non‐native marine species in British waters: effects and controls

The morphometrics of cephalopod gills