Showing papers in "Advances in Marine Biology in 2001"

Biology of mangroves and mangrove Ecosystems

Abstract: Mangroves are woody plants that grow at the interface between land and sea in tropical and sub-tropical latitudes where they exist in conditions of high salinity, extreme tides, strong winds, high temperatures and muddy, anaerobic soils. There may be no other group of plants with such highly developed morphological and physiological adaptations to extreme conditions. Because of their environment, mangroves are necessarily tolerant of high salt levels and have mechanisms to take up water despite strong osmotic potentials. Some also take up salts, but excrete them through specialized glands in the leaves. Others transfer salts into senescent leaves or store them in the bark or the wood. Still others simply become increasingly conservative in their water use as water salinity increases Morphological specializations include profuse lateral roots that anchor the trees in the loose sediments, exposed aerial roots for gas exchange and viviparous waterdispersed propagules. Mangroves create unique ecological environments that host rich assemblages of species. The muddy or sandy sediments of the mangal are home to a variety of epibenthic, infaunal, and meiofaunal invertebrates Channels within the mangal support communities of phytoplankton, zooplankton and fish. The mangal may play a special role as nursery habitat for juveniles of fish whose adults occupy other habitats (e.g. coral reefs and seagrass beds). Because they are surrounded by loose sediments, the submerged mangroves' roots, trunks and branches are islands of habitat that may attract rich epifaunal communities including bacteria, fungi, macroalgae and invertebrates. The aerial roots, trunks, leaves and branches host other groups of organisms. A number of crab species live among the roots, on the trunks or even forage in the canopy. Insects, reptiles, amphibians, birds and mammals thrive in the habitat and contribute to its unique character. Living at the interface between land and sea, mangroves are well adapted to deal with natural stressors (e.g. temperature, salinity, anoxia, UV). However, because they live close to their tolerance limits, they may be particularly sensitive to disturbances like those created by human activities. Because of their proximity to population centers, mangals have historically been favored sites for sewage disposal. Industrial effluents have contributed to heavy metal contamination in the sediments. Oil from spills and from petroleum production has flowed into many mangals. These insults have had significant negative effects on the mangroves. Habitat destruction through human encroachment has been the primary cause of mangrove loss. Diversion of freshwater for irrigation and land reclamation has destroyed extensive mangrove forests. In the past several decades, numerous tracts of mangrove have been converted for aquaculture, fundamentally altering the nature of the habitat. Measurements reveal alarming levels of mangrove destruction. Some estimates put global loss rates at one million ha y−1, with mangroves in some regions in danger of complete collapse. Heavy historical exploitation of mangroves has left many remaining habitats severely damaged. These impacts are likely to continue, and worsen, as human populations expand further into the mangals. In regions where mangrove removal has produced significant environmental problems, efforts are underway to launch mangrove agroforestry and agriculture projects. Mangrove systems require intensive care to save threatened areas. So far, conservation and management efforts lag behind the destruction; there is still much to learn about proper management and sustainable harvesting of mangrove forests. Mangroves have enormous ecological value. They protect and stabilize coastlines, enrich coastal waters, yield commercial forest products and support coastal fisheries. Mangrove forests are among the world's most productive ecosystems, producing organic carbon well in excess of the ecosystem requirements and contributing significantly to the global carbon cycle. Extracts from mangroves and mangrove-dependent species have proven activity against human, animal and plant pathogens. Mangroves may be further developed as sources of high-value commercial products and fishery resources and as sites for a burgeoning ecotourism industry. Their unique features also make them ideal sites for experimental studies of biodiversity and ecosystem function. Where degraded areas are being revegetated, continued monitoring and thorough assessment must be done to help understand the recovery process. This knowledge will help develop strategies to promote better rehabilitation of degraded mangrove habitats the world over and ensure that these unique ecosystems survive and flourish.

The sea cucumber Holothuria scabra (Holothuroidea : Echinodermata) : Its biology and exploitation as beche-de-mer

Abstract: One of the most intensively studied holothurians, Holothuria scabra has been discussed in the literature since 1833. The species is important for several reasons: (1) it is abundant and widely distributed in shallow soft-bottom habitats throughout the Indo-Pacific; (2) it has a high value on the Asian markets, where it is mainly sold as beche-de-mer; and (3) it is the only tropical holothurian species that can currently be mass produced in hatcheries. Research on H. scabra continues but because of commercial exploitation, wild stocks are declining. This review compiles data from 14 these and 352 technical reports and scientific papers pertaining to the biology, ecology, aquaculture and fisheries of H. scabra . Although several references are likely to have been missed by our investigation, we present the most complete reference list to date, including obscure material published by local institutions and/or in foreign languages. Our main aim was to summarize and critically discuss the abundant literature on this species, making it more readily accessible to all those wishing to conduct fundamental research, or aquaculture and stock enhancement programmes, on H. scabra across its entire geographic range.

The “Exxon Valdez” oil spill in Alaska: Acute, indirect and chronic effects on the ecosystem

Abstract: Following the oil spill in Prince William Sound, Alaska, in 1989, effects were observed across a wide range of habitats and species. The data allow us to evaluate direct and indirect links between shoreline habitats and the coastal ecosystem in general. The intertidal zone sufferred from direct oiling and clean-up treatments such as pressurized hot water, resulting in freeing of bare space on rocks and reductions in fucoid algal cover. Grazing limpets, periwinkles, mussels and barnacles were killed or removed. Subsequent indirect effects included colonization of the upper shore by ephemeral algae and an opportunistic barnacle and, in some regions, spread of Fucus gardneri into the lower shore where it inhibited return of red algae. The loss of habitat provided by the Fucus canopy slowed recovery on high shores, and lowered abundance of associated invertebrates. Abundance of sediment infauna declined and densities of clams were reduced directly. Their recovery was still incomplete by 1997 on oiled and treated shores where fine sediments had been washed down slope during treatment. Impacts in subtidal habitats were less intense than in the intertidal zone. Kelps were reduced in 1989 but recovered rapidly through re-colonization by 1990. Abundances of a dominant crab and seastar were reduced greatly, with recovery of the more mobile species, the crab, occurring by 1991. For about 4 years, there was reduced eelgrass density and hence less habitat for associated animals. Abundance of several toxin-sensitive amphipods declined dramatically and had not recovered by 1995. In general, how ever, many subtidal infaunal invertebrates increased in abundance, especially oligochaetes and surface deposit-feeding polychaetes. This may have resulted from increases in sediment hydrocarbon-degrading bacteria, but may also reflect reduction of predators. Along northern Knight Island, where sea otter populations had not recovered by 1997, green sea-urchins were larger, compared with those in un-oiled parts of Montague Island. This initial response from reduced predation by sea otters, if sustained, could lead to additional indirect effects of the spill. Scavenging terrstrial birds, such as bald eagles and northwestern crows, sufferred direct mortality as adults and reproductive losses, although eagles recovered rapidly. Numbers of intertidal benthic fishes were 40% lower on oiled than on un-oiled shores in 1990, but recovery was underway by 1991. Small benthic fishes living in eelgrass showed sensitivity to hydrocarbon contamination until at least 1996, as evidenced by hemosiderosis in liver tissues and P450 1A enzyme induction. Oiling of intertidal spawning habitats affected breeding of herring and pink salmon. Pink salmon, and possibly Dolly Varden char and cut-throat trout, showed slower growth when foraging on oiled shorelines as older juveniles and adults, which for pink salmon implies lower survival. The pigeon guillemots that suffered from the oil spill showed reduced feeding on sand eels and capelin, which may also have been affected by the spill, and this may have contributed to failure of guillemot recovery. There was an analogous failure of harbor seals to recover. Sea otters declined by approximately 50%, and juvenile survival was depressed on oiled shores for at least four winters. Both black oystercatchers, shorebirds that feed on intertidal invertebrates, and also harlequin ducks showed reduced abundance on oiled shores that persisted for years after the spill. Oystercatchers consumed oiled mussels from beds where contamination by only partially weathered oil persisted until at least 1994, with a resulting impact on productivity of chicks. A high over-winter mortality of adult harlequin ducks continued in 1995–1996, 1996–1997 and 1997–1998. Delays in the recovery of avian and mammalian predators of fishes and invertebrates through chronic and indirect effects occurred long after the iniatial impacts of the spill. Such delayed effects are not usually incorporated into ecotoxicity risk assessments which thus substantially understimate impacts of a spill. Detection of delayed impacts requires rigorous long-term field sampling, so as to observe the dynamics of recovery processes.

Interactions between phytoplankton and trace metals in the ocean

Abstract: This review assesses the degree to which phytoplankton in the contemporary oceans interact with the essential trace metals in their chemical environment as exemplified by the cycling of iron, manganese, cobalt, nickel and zinc. The toxic element cadmium is also considered because of the extent to which it is taken up. The stage is set by a brief consideration of the overall geochemical controls on the composition of sea water and their implications for the milieu within which life evolved. The utilization of the elements within the cells is addressed with the consequent implications for optimizing the uptake of essential elements and controlling the ingress of potentially toxic elements. The impact of the change from an anoxic to an oxygenated atmosphere some 2 billion years ago on the availability of the basic building blocks for living systems is considered. The essential elements have to be delivered to the centres of synthesis in the appropriate ratios. The optimal tailoring of the flows of material into and out of the cell to meet the requirements for maintenance, growth and reproduction requires a carefully regulated internal economy. This internal economy sets the guidelines for the interaction of phytoplankton with the chemistry of their aqueous environment. The uptake mechanisms are explored using data derived from culture experiments indicating a significant degree of biological influence on the chemistry of the essential elements close to the cell surface (the near-field chemistry). The perspective is then widened to consider the implications of these processes for the relative concentrations of the elements and their distribution throughout the world's oceans (the far-field chemistry). Case histories are followed for iron, manganese, copper, zinc, cobalt and nickel reviewing (a) their distribution in the oceans, (b) their biological availability, (c) their uptake and impact upon primary production. This external economy is intimately related to the feedback between the organisms and their environment. The extent of recycling within the ocean system by the mutually dependent processes of photosynthesis and respiration provides a clear measure of the regulatory power of the biological system itself. This is analysed in the context of the Gaia hypothesis. Although the biological processes, to a large degree, control the availability and distribution of the essential trace metals in the oceans, the system does not appear to be optimized. For example cadmium, generally considered to be a non-essential element, is recycled more vigorously than any other element. Zinc in contrast appears to be rendered less accessible as the result of biological activity, and phytoplankton cells in the open ocean are straining at the limit of diffusive transport to obtain sufficient supplies.

Reproduction and development of marine peracaridans

Abstract: Reproduction in peracarid crustaceans is characterized by direct development with the young carried by the female in a ventral brood pouch made from overlapping oostegites. The major exception occurs in thermosbaenaceans where the young develop under a posterior extension of the carapace. Sexual reproduction is the norm, as is standard genetic development of males and females, but intersexes, males with unusual chromosome numbers and hermaphrodites occur in some species. General anatomy of the female reproductive tract is similar for all orders, differing only in the specific details. Asellote isopods develop a unique spermathecal duct for sperm storage. The male reproductive system is much more variable. In some orders it consists of paired tubes, and in others it is unpaired; sperm may be stored in the posterior region of the testes or in vas deferens; and the external genitalia may be located on the coxae or the sternites, with or without penes or other sperm transfer appendages. Sperm morphology has been considered a unifying trait for the Peracarida but, in fact, there are some significant differences among the orders. Peracaridan sperm are aflagellate. Most consist of a head piece and a rigid, non-motile, fibrillar tail of varying design by which the sperm are bundled in spermatophores. Tanaid sperm are round and tailless, and spermatophores are absent. Oogenesis follows a common pattern in those peracarids that have been studied. A period of previtellogenic growth is followed by slow primary vitellogenesis with endogenous yolk synthesis Prior to molting and fertilization, rapid secondary vitellogenesis, utilizing exogenous yolk synthesis, occurs. Life cycles in the more diverse peracaridan orders can be compared. Temperate species often have long overwintering generations interspersed with several shorter summer generations. Polar and deep-sea pericaridans have much longer generations whereas tropical species may produce broods year-round in rapid succession. Mating usually occurs when the mature oostegites appear, with copulation occurring shortly after the female molts. Precopulatory pairing and mate guarding by males using specially modified appendages is common, but some males cruise from one female to another. Sperm is generally deposited into the marsupium where fertilization occurs, but some isopods store sperm for later use. Development follows the general crustacean pattern of superficial cleavage, with the details of organ and appendage formation varying from order to order. Some special brood pouch structures exist, primarily in isopods, and in some tube-dwelling tanaids the young develop in the female's tube rather than in the marsupium. Peracarids generally hatch in the brood pouch as fully developed juveniles or as mancas (without the last pair of thoracic legs). With a few exceptions, brood size is a function of female marsupial volume. The trade-off between egg size and egg number varies with both habitat and, in some cases, with season. Since egg size affects incubation time, these complex interrelationships and the adaptive value of specific reproductive strategies are still unresolved.

Structural, histochemical and functional aspects of the epidermis of fishes

Abstract: Significant progress has been made in the last 30 years in our knowledge of cellular and physiological aspects of fish epidermis This review surveys the histology, histochemistry (including lectin- and immunohistochemistry) and function of the epidermis of various teleosts and cyclostomes in the light of the new data. The epidermis is a multipurpose tissue, although the secretory function is dominant. Mucous secretions are produced by different types of epithelial cells, in particular those located in the superficial layer. Specific unicellular glands in the skin of gnathostome fish are the goblet cells, the sacciform cells and the club cells. In addition, lampreys and hagfish possess specific secretory cell types. Other specialized types are the holocrine venom cells which are aggregated in venom glands, the mitochondria-rich cells (ionocytes) and the photocytes, the latter grouped with other cell types to form photophores that are embedded in the skin. The outer epidermal cells and the mucous goblet cells secrete the epithelial mucous layer, whose carbohydrate composition changes with stress and environmental conditions. The mucus contains neuronal and endothelial forms of nitric oxide synthase (NOS), the enzyme responsible for the production of nitric oxide (NO), a prominent vascular and neuronal messenger that regulates many epithelial functions. The cytokeratins in the skin tissues have different distribution patterns in the various cell types, correlated with specific epithelial differentiation or, in hagfish, the modulation of the viscoelastic properties of skin mucus Club cell and sacciform cell secretions are now considered as storehouses of biologically active substances. Their expression is paralleled with that present in glandular cells of the skin of other lower vertebrates. The fine structure and histochemical properties of club cells are clearly different from those of the venom cells in fish and amphibians. Mitochondria-rich chloride cells (ionocytes), although primarily concentrated in the branchial epithelium, also occur in various areas of the skin. The skin chloride cells, like those in the gill, secrete monovalent ions in sea water and take up ions in fresh water. Fish skin has a diffuse paraneuronal cell system responsible for the production of bioactive compounds that have possible regulating functions. Neuropeptides occur in the Merkel cells, the mechanoreceptors (neuromast hair cells) and the electroreceptors (sensory cells of the ampullary and tuberous organs) of the skin. Basal cells of the taste buds are the source of neuron-specific enolase, serotonin, bombesin and somatostatin. Photophores contain serotonin and adrenalin, which play a neuromodulatory role in the regulation of luminescence. The functions of the skin secretions are primarily protective, as a result of their antimicrobial properties. Further analysis of the components of epidermal cells and unicellular glands of aquatic animals will disclose many protective factors

The parasite fauna of the atlantic cod, Gadus morhua L

Abstract: This review is intended to increase awareness of the value of parasitological studies of the Atlantic cod, which has an exceptionally rich and varied parasite fauna compared with most other species of marine fish. We list 107 named species of protozoan and metazoan parasites recorded from cod, plus many that have been identified to generic or higher taxonomic levels only. This diversity is apparently linked to the omnivorous diet of cod, its occurrence at low salinities where it is exposed to infection by euryhaline parasites that most marine fish do not encounter, and its status as one of the most abundant and widespread piscivorous species in the North Atlantic. Parasitological studies of cod have been undertaken mainly in response to concerns about public health and spoilage effects of the more common and obvious parasites. We also review more academic aspects such as the host range and specificity of cod parasites, their life cycles, zoogeography, population dynamics and host sexual differences to parasitic infection. We also deal in depth with applied aspects such as the role of parasites as pathogens and their use as biological tags in population studies of cod and as indicators of marine pollution. We suggest areas in which further study is most urgently required and try to anticipate which parasites are likely to become important pathogens in the developing mariculture of cod.

Remote sensing of the global light-fishing fleet: An analysis of interactions with oceanography, other fisheries and predators

Abstract: Publisher Summary The use of United States Defense Meteorological Satellite Program Operational Linescan System (DMSP-OLS) data has enabled the precise location of the distribution of the global light-fishing fleet over a six month period in relation to the large and general mesoscale oceanography of the ecological provinces where they occur. The squid catch in these light fisheries can be identified to genera or species in seven ecological provinces where DMSP-OLS imagery reveals light-fishing activities. The DMSP-OLS data provide the information needed to review the relationship between the squid fisheries using lights and other fisheries for finfish with better spatial resolution than has been previously possible using data for FAO statistical areas alone. This chapter demonstrates that 62–70%, and possibly up to something