[Advances in Marine Biology] Advances in Marine Biology Volume 30 Volume 30 || The Biology of Seamounts

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<ul><li><p>The Biology of Seamounts </p><p>A.D. Rogers </p><p>Marine Biological Association of the United Kingdom, The Laboratory, Citadel Hill, Plymouth, PLl 2PB, UK </p><p>1. Introduction.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 2. Geology and Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 3. The Effects of Seamounts on the Pelagi stems . . . . . . . . . . . . . . . . . . . . . 311 </p><p>3.1. Primary production and seamount fisheries . . . . . . . . . . . . . . . . . . . . . . . . 31 1 3.2. The structure of pelagic communities over seamounts . . . . . . . . </p><p>4.1. Sampling seamount benthos. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 4.2. The biology of hard substrata.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 4.3. The biology of soft substrata.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320 </p><p>. . . . . . . . . . . . . . 323 4.5. Hydrothermal vent communities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 </p><p>5.1. The geographic affiniti eamount organisms.. . . . . . . . . . . . . . . . . . 326 5.2. Reproductive and genetic isolation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 </p><p>6. Commercial Exploitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 6.1. Seamount fisheries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 6.2. The pelagic armourh . . . . . . . . . . . . . . . . . 6.3. The orange roughy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 6.4. Precious corals . . . . . . . . . . . . . . . .................... 6.5. Overexploitation of species . . . . . . . . . . . . . . . . . . 6.6. Exploitation of geological and physical resources . . . . . . . . . . . . . . . . . . 339 </p><p>. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 </p><p>4. Benthic Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 </p><p>4.4. Seamounts penetrating oxygen minimum layers </p><p>5. Species Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 </p><p>Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 </p><p>1. INTRODUCTION </p><p>The presence of numerous seamounts in the worlds oceans, especially in the Pacific, has only become known to the scientific community in the last </p><p>ADVANCES IN MARINE BIOLOGY VOL 30 ISBN CL1242613C3 </p><p>Copyright 0 I994 Academic Press Limired A11 righrr of reproduction in any form reserved </p></li><li><p>306 A.D. ROGERS </p><p>50 years (Hess, 1946; Menard and Dietz, 1951; Menard and Ladd, 1963). C.L. Hubbs was one of the first biologists to work on the biology of seamounts and as early as 1959 he posed a number of fundamental problems regarding seamount faunas. These included: What species inhabit seamounts and with what regularity and abundance? How do species disperse to and become established on seamounts? Do seamounts represent stepping stones for transoceanic dispersal of species? Are demersal or pelagic fishes sufficiently abundant on seamounts to provide profitable fisheries? What factors are responsible for the abundance of life over seamounts? </p><p>These questions remain relevant today, and despite a large quantity of work since Hubbs (1959), most of them remain incompletely answered. Biological investigations of seamounts have been very scattered in terms of the geographical areas covered and aspects of biology studied. The quality of data has also varied considerably often according to particular taxonomic expertise of the investigators and on methods of data collection. Dissemination of data and attendant conclusions on the biology of seamounts has also been hampered by language barriers. For example, quantities of useful Russian data on seamounts have been inaccessible to English-speaking biologists due to the difficulties in obtaining complete translations of scientific papers. </p><p>The following review draws together the scattered literature on the biology of seamounts. It summarizes current knowledge on the effects of seamounts on pelagic ecosystems, factors that influence the structure of seamount communities, the establishment, maintenance and genetic isola- tion of populations on seamounts and on the effects of commercial exploitation on seamounts organisms. In summarizing current knowledge in these areas, many of which are related directly to the problems posed by Hubbs more than 30 years ago, this review also points out the areas in which data are lacking or contradictory and where further research is required. A map showing the approximate position of the seamounts discussed in this review is given in Figure 1. </p><p>Figure 1 Map showing approximate position of the seamounts discussed in this review. 1, Norfolk Ridge; 2, Cobb seamount; 3, Axial seamount; 4, Fieberling seamount; Fieberling I1 seamount; Hoke seamount; Jasper seamount; Stoddard seamount; Nidever Bank; Banco San Isidro; 5, Red Volcano; 6, Volcano 7; 7, San Salvador seamount; 8, Atlantis I1 seamount; 9, Comer Rise seamounts; 10, Great Meteor seamount; 11, Dacia seamount; 12, Josephine seamount; Gettysburg seamount; 13, Marsili seamount; 14, Vema seamount; 15, Equator seamount; 16, Minami-Kasuga seamount; 17, Conical seamount; 18, Southeast Hancock sea- mount; 19, Mid-Pacific Mountains; 20, Horizon Guyot; 21, Magellan Rise; 22, Emperor seamount chain; 23, Peepa seamount; 24, North Hawaiian Ridge; 25, Cross seamount; 26, Loihi seamount; 27, Challenger Plateau; 28, Ritchie Bank; 29, North Chatham Rise. </p></li><li><p>308 AD. ROGERS </p><p>Recent reviews have covered aspects of the biology of seamounts especially those in Keating et al. (1987) but this literature has had limited circulation amongst biologists. Furthermore in recent years much impor- tant work has been published on seamounts especially in respect to current topography interactions, the biology of the soft benthos on seamounts and on the biology of commercially valuable species of fish associated with seamounts. The combination of this new data with that obtained in previous studies provides a complete picture of the current knowledge of the biology of seamounts which will be of use to marine biologists , fisheries biologists and oceanographers. </p><p>2. GEOLOGY AND OCEANOGRAPHY </p><p>Seamounts are undersea mountains which rise steeply from the sea bottom to below sea level. They have been defined as having an elevation of more than 1000m with a limited extent across the summit (Menard, 1964; US Board of Geographic Names, 1981). Features that have elevations between 500 and 1000 m have been defined as knolls and those that have a relief of less than 500m as hills (US Board of Geographic Names, 1981). These definitions have not been adhered to in literature on the biology, geology and oceanography of such features and most are referred to as seamounts regardless of size (i.e. Epp and Smoot, 1989). </p><p>Seamounts are a variety of shapes but are generally conical with a circular, elliptical or more elongate base. Eaamples of typical seamount shapes are Conical seamount (Fryer and Fryer, 1987; circular), Great Meteor seamount (Pratt, 1963; elliptical) and Horizon Guyot (Karig et hl., 1970; elongate) (see Figure 2 (a), (b) and (c)). They are usually of volcanic origin (Epp and Smoot, 1989) though some are formed by vertical tectonic movement along converging plate margins (see Fryer and Fryer, 1987). Seamounts often occur in chains or clusters known as provinces (Menard and Dietz, 1951; Menard, 1964) which may be associated with seafloor hotspots (Epp and Smoot, 1989). It has been estimated that there are over 30000 seamounts with a height of over loo0 m in the Pacific ocean (Smith and Jordan, 1988), approximately 810 (over 100m in height) in the Atlantic (Epp and Smoot, 1989) and an indeterminate number in the Indian ocean. </p><p>Seamounts provide a striking contrast to the surrounding flat sediment- covered abyssal plain. Their profiles can show declivities of up to 60 (Sagalevitch et al., 1992), much greater than anywhere else in the deep sea. Hard substrata atypical of the deep-sea environment are common on seamounts and may take the form of calderas (Levin and Nittrouer, </p></li><li><p>THE BIOLOGY OF SEAMOUNTS 309 </p><p>P </p><p>Figure 2 Contour maps showing the shape of three typical seamounts. (a) Conical seamount (after Fryer and Fryer, 1987). (b) Great Meteor seamount (after Hinz, 1969). (c) Horizon Guyot (after Smith et al., 1989). </p></li><li><p>31 0 A.D. ROGERS </p><p>1987), terraces (Pratt, 1963; Hinz, 1969; Rad, 1974), pit craters (Levin and Nittrouer, 1987), canyons (Raymore, 1982), caves (Heydorn, 1969), pinnacles (Hughes, 1981; Raymore, 1982), knobs (Boehlert and Genin, 1987), crevices (Heydorn, 1969), rocks (Raymore, 1982), cobbles (Ray- more, 1982) and marine organisms (Levin et al., 1986). Hydrothermal precipitates may form crusts, mounds and chimneys on seamounts (Levin and Nittrouer, 1987). Some seamounts, known as guyots (Hess, 1946), have flat summits, formed by wave erosion when they were above sea level (Hinz, 1969). The tops of such seamounts are frequently covered in biogenic sediments such as foraminiferan sands (Pratt, 1963; Karig et al., 1970; Hinz, 1969; Levin and Nittrouer, 1987). These may be sup- plemented by sediments of a volcanic origin which may be composed of a variety of materials such as fragments of basaltic glass and tephra (Natland, 1976). Lithogenic sediments, transported from the continental margin, may also be present and authigenic sedimentation, principally from the precipitation of ferromanganese oxides, may also form signi- ficant components of seamount sediments (Levin and Nittrouer, 1987). Hydrothermal sediments may be found on some young and active seamounts such as Red Volcano located near the East Pacific Rise (Lonsdale et al., 1982). </p><p>Seamounts have complex effects on ocean circulation, which are poorly understood (Roden, 1987; Eriksen, 1991). This is because of the great diversity in seamount size, shape and distribution (in relation to neigh- bouring seamounts), the complexity of the currents impinging upon them and the importance of Coriolis forces and stratification on current- topography interactions (Roden, 1987; see also Brink, 1989; Zhang and Boyer, 1991). </p><p>Observations of the effects of seamounts on ocean circulation have been at a range of scales from the macroscale to effects in the immediate vicinity of a seamount. At a large scale, seamounts in the Emperor seamount chain have been shown to deflect both the Kuroshio extension and subarctic currents (Roden et al., 1982, Roden and Taft, 1985; Vastano et al., 1985; also see Roden (1991) for Fieberling seamount). At a smaller scale, effects of seamounts on ocean currents include the formation of trapped waves (Eriksen, 1982a, 1991; Brink, 1989; Genin et al., 1989) and the reflection, amplification and distortion of internal waves (Bell, 1975; Wunsch and Webb, 1979; Eriksen, 1982b, 1985, 1991; Kaneko et al., 1986). Diurnal and semidiurnal tides may be amplified over seamounts leading to fast tidal currents (&gt;40 cm s-l) around some seamounts (Chapman, 1989; Genin et al., 1989; Noble and Mullineaux, 1989). </p><p>The production of jets and eddies may also be a feature of the interaction of seamounts with ocean currents (Vastano and Warren, 1976; </p></li><li><p>THE BIOLOGY OF SEAMOUNTS 31 1 </p><p>Roden, 1991). Eddies may be trapped over seamounts to form closed circulations known as Taylor columns (after G.I. Taylor who first studied the effects of obstacles on rotating flows (Taylor, 1917)). These are thought to occur when a steady current impinging on a seamount causes an uplifting of isotherms (upwelling). This compresses vortex lines and induces anticyclonic vorticity generating a closed eddy over the seamount (Huppert and Bryan, 1976). Observations of Taylor columns or Taylor column-like structures have been observed over several seamounts including the Great Meteor seamount (Meincke, 1971), Atlantis 11 seamount (Vastano and Warren, 1976), seamounts of the Emperor seamount chain (Cheney et al. , 1980), the Corner Rrse seamounts (Richardson, 1980), Fieberling seamount (Genin et al., 1989; Roden, 1991), Fieberling 11, Hoke and Stoddard seamounts (Roden, 1991) and Cobb seamount (Dower et al. , 1992). Taylor column-like effects have also been noted near smaller abyssal hills and bumps (Owens and Hogg, 1980; Gould et al., 1981). Taylor columns can last for considerable periods of time over seamounts. Richardson (1980) tracked the path of an anticyclonic eddy over the Corner Rise seamounts, using freely drifting buoys, for 6 weeks before it left the seamounts and drifted away. </p><p>3. THE EFFECTS OF SEAMOUNTS ON PELAGIC ECOSYSTEMS </p><p>3.1. Primary Production and Seamount Fisheries </p><p>The concentration of commercially valuable fish species around sea- mounts is well documented (Hubbs, 1959; Hughes, 1981; Uchida and Tagami, 1984; Parin and Prutko, 1985; Alton, 1986; Boehlert, 1986; Sasaki, 1986; Seki and Tagami, 1986; Yasui, 1986; Genin et al., 1988; Parin et al . , 1990; Fonteneau, 1991; Gerber, 1993). It has been suggested that this is due to increased densities of prey organisms (i.e. macroplank- ton) over seamounts which in turn are caused by enhanced primary productivity due to topographic effects on local hydrographic conditions (see above). In oligotrophic waters it has been suggested that the uplifting of isotherms into the euphotic zone by seamounts, as a result of Taylor column formation, can introduce biogenes into nutrient-poor water and cause an increase in primary production (Genin and Boehlert, 1985; Tseytlin, 1985; Voronina and Timonin, 1986; Boehlert and Genin, 1987; Dower et al. , 1992). </p><p>Evidence for enhanced primary productivity leading to concentrations of fish and zooplankton over seamounts is, however, sparse. There is evidence that waters over seamounts do show increased primary produc- </p></li><li><p>31 2 A.D. ROGERS </p><p>tivity. Lophukin (1986), for example, studied ATP concentrations across 12 Atlantic seamounts. In almost all cases a dome-like layer of upwelling water, poor in microplankton, was detected directly over the seamount whilst high concentrations of chlorophyll A, ATP and microplankton were detected over the seamount flanks. High concentrations of chloro- phyll A above seamounts have also been detected by Bezrukov and Natarov (1976), Genin and Boehlert (1985) and Dower et al. (1992). </p><p>Genin and Boehlert (1985) measured temperature and chlorophyll A concentrations across the Minami-kasuga seamount on the Manana ridge on three separate dates with the second and third samples being taken 2 and 17 days after the first. The first sample showed a cold temperature dome (upwelling) over the seamount with high concentrations of chlor- ophyll between 80 and 100m. This was not due to decreased grazing by zooplankton, since concentrations of zooplankton...</p></li></ul>

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