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Origin and dispersal of invertebrate larvae in the North Atlantic
1074
Oceanographic Abstracts
SCARRATT D. J., 1964. Abundance and distribution of lobster larvae (Homarus american,st in Northumberland Strait. J. Fish. Res. Bd., Canad., 21 (4): 661-680. A method is described for catching the planktonic larval stages ofHomarus asnericanus Milne Edwards, Estimates are made of the abundance and distribution of each of the four stages in the surface waters of part of the Northumberland Strait (southern Gulf of St. Lawrence) for the years 1949-61, with a more critical analysis for the year 1961. Both abundance and survival of the larvae vary from year to year, although they do not appear to be related with measured hydrographical conditions. It is suggested that the distribution of stage I larvae reflects the location of the parent stock and that surface drift carries the developing larvae to possible areas of settlement. There is no conclusive relationship between the larvae and the subsequent stock, although a possible relationship between the abundance of stage I larvae and parent stock density is de.~ribed and briefly discussed. SCHELTEMA R. S., 1964. Origin and dispersal of invertebrate larvae in the North Atlantic. I Abst rac~ only). Am. Zoologist, 4 (3): 299. Benthic invertebrate larvae originating from shallow coastal waters of the shelf and continen~a~ slope sometimes are carried offshore by surface currents. In the open waters of the North Atlantic. the planktotrophic larvae of such organisms are frequently represented. Larvae which have been taken in the Gulf Stream a n d Sargasso Sea include those of sipunculids, brachiopods, polychaetcs. stomatopods, decapod Crustacea, and such types as tornaria, auricularia, bipinnai'ia, plutei, trochol phores, gastropod and lamellibranch veligers and others. That most o f these larvae originate from relatively shallow waters is deduced from the fact that their numbers decrease with increasing dis.. tance from shore. Only those coastal species with long pelagic lives or with mechanisms for delaying metamorphosis can long survive in the open sea. Many species of benthic invertebrate larvae that have been observed are believed to have originateo from tropical latitudes; some probably are from the West Indies and the Caribbean Sea. The transport of certain larvae has been followed over long distances. Two species of sipunculid larvae are of particular interest. These have been traced from the southern coast of Florida, along the Gulf Stream, and as far east as the Azores. It is not unreasonable to suppose from the evidence at hand that these sipunculid larvae are frequently transported across the Atlantic. SCHELTEMA RUDOLF S., 1964. Feeding habits and growth in the mud-snail Nassarius obsolerus. Chesapeake Sci., 5 (4): 161-166. Nassarius obsoletus is primarily a deposit-feeder. The microflora to be found on the surface of sediment of intertidal flats serves as its major source of food. Living bivalves do not form part of the diet as previously reported. Dead organisms such as molluscs, Crustacea, and fish are eaten when available but are not a principal item of food. Occasionally thallus algae are probably also utilized. Ecologically, Nassarius obsoletus may be regarded largdy as a herbivorous species and depositfeeder. In the strict sense, however, it is an omnivore and a facultative scavenger. Growth of Nassarius obsoletus occurs principally during the summer months. The winter is passed in a state of quiescence below mean low water. Zero- and one-year classes are readily distinguished but after the third summer the various age groups can no longer be identified by the lengthfrequency method, The longevity of Nassarius obsoletus cannot be directly determined but some individuals probably live to at least five years. A growth of 1.3 to 1.4 mm per month was estimated during the first two summers in a New England population found in Great Pond, Falmouth, Massac. husetts. An increase in length of 3 to 5 times that at the time of metamorphosis occurs during thc first summer's growth. SCHNEIDER W. A., P. J. FARRELL and R. E. BRANNIAN,1964. Collection and analysis of Pacific Ocean bottom seismic data. Geophysics, 29 (5): 745-771. A total of 500 hours of usable ocean-bottom seismic data recorded on pressure and three components of velocity has been collected in three geographically separate areas of the Pacific Ocean at depths to 20,000 ft. These data are presently being analyzed to determine the extent to which monitoring seismic motion on the ocean floor can assist Project VELA U N I F O R M goals of detection and identification of underground and underwater nuclear blasts. Analysis of three earthquakes and ambient noise recorded simultaneously on the ocean bottom and land reveals : 1. Ocean-bottom signal-to-noise ratios are equal to or less than those seen at a comparative land station; 2. Ocean-bottom signal and noise levels are higher than those obtained at the land station; and 3. Ocean-bottom ambient noise power spectra increase in level towards the microseismic 6to 8-sec peak as do the land data. No strong directional ocean-bottom noise components have been observed. Simultaneous recording of pressure and particle velocity affords the ocean-bottom station a distinct advantage over its land counterpart, through exploitation of the relationships between pressure and vertical velocity which exist for various types of arrivals and modes.
Oceanographic Abstracts
SCARRATT D. J., 1964. Abundance and distribution of lobster larvae (Homarus american,st in Northumberland Strait. J. Fish. Res. Bd., Canad., 21 (4): 661-680. A method is described for catching the planktonic larval stages ofHomarus asnericanus Milne Edwards, Estimates are made of the abundance and distribution of each of the four stages in the surface waters of part of the Northumberland Strait (southern Gulf of St. Lawrence) for the years 1949-61, with a more critical analysis for the year 1961. Both abundance and survival of the larvae vary from year to year, although they do not appear to be related with measured hydrographical conditions. It is suggested that the distribution of stage I larvae reflects the location of the parent stock and that surface drift carries the developing larvae to possible areas of settlement. There is no conclusive relationship between the larvae and the subsequent stock, although a possible relationship between the abundance of stage I larvae and parent stock density is de.~ribed and briefly discussed. SCHELTEMA R. S., 1964. Origin and dispersal of invertebrate larvae in the North Atlantic. I Abst rac~ only). Am. Zoologist, 4 (3): 299. Benthic invertebrate larvae originating from shallow coastal waters of the shelf and continen~a~ slope sometimes are carried offshore by surface currents. In the open waters of the North Atlantic. the planktotrophic larvae of such organisms are frequently represented. Larvae which have been taken in the Gulf Stream a n d Sargasso Sea include those of sipunculids, brachiopods, polychaetcs. stomatopods, decapod Crustacea, and such types as tornaria, auricularia, bipinnai'ia, plutei, trochol phores, gastropod and lamellibranch veligers and others. That most o f these larvae originate from relatively shallow waters is deduced from the fact that their numbers decrease with increasing dis.. tance from shore. Only those coastal species with long pelagic lives or with mechanisms for delaying metamorphosis can long survive in the open sea. Many species of benthic invertebrate larvae that have been observed are believed to have originateo from tropical latitudes; some probably are from the West Indies and the Caribbean Sea. The transport of certain larvae has been followed over long distances. Two species of sipunculid larvae are of particular interest. These have been traced from the southern coast of Florida, along the Gulf Stream, and as far east as the Azores. It is not unreasonable to suppose from the evidence at hand that these sipunculid larvae are frequently transported across the Atlantic. SCHELTEMA RUDOLF S., 1964. Feeding habits and growth in the mud-snail Nassarius obsolerus. Chesapeake Sci., 5 (4): 161-166. Nassarius obsoletus is primarily a deposit-feeder. The microflora to be found on the surface of sediment of intertidal flats serves as its major source of food. Living bivalves do not form part of the diet as previously reported. Dead organisms such as molluscs, Crustacea, and fish are eaten when available but are not a principal item of food. Occasionally thallus algae are probably also utilized. Ecologically, Nassarius obsoletus may be regarded largdy as a herbivorous species and depositfeeder. In the strict sense, however, it is an omnivore and a facultative scavenger. Growth of Nassarius obsoletus occurs principally during the summer months. The winter is passed in a state of quiescence below mean low water. Zero- and one-year classes are readily distinguished but after the third summer the various age groups can no longer be identified by the lengthfrequency method, The longevity of Nassarius obsoletus cannot be directly determined but some individuals probably live to at least five years. A growth of 1.3 to 1.4 mm per month was estimated during the first two summers in a New England population found in Great Pond, Falmouth, Massac. husetts. An increase in length of 3 to 5 times that at the time of metamorphosis occurs during thc first summer's growth. SCHNEIDER W. A., P. J. FARRELL and R. E. BRANNIAN,1964. Collection and analysis of Pacific Ocean bottom seismic data. Geophysics, 29 (5): 745-771. A total of 500 hours of usable ocean-bottom seismic data recorded on pressure and three components of velocity has been collected in three geographically separate areas of the Pacific Ocean at depths to 20,000 ft. These data are presently being analyzed to determine the extent to which monitoring seismic motion on the ocean floor can assist Project VELA U N I F O R M goals of detection and identification of underground and underwater nuclear blasts. Analysis of three earthquakes and ambient noise recorded simultaneously on the ocean bottom and land reveals : 1. Ocean-bottom signal-to-noise ratios are equal to or less than those seen at a comparative land station; 2. Ocean-bottom signal and noise levels are higher than those obtained at the land station; and 3. Ocean-bottom ambient noise power spectra increase in level towards the microseismic 6to 8-sec peak as do the land data. No strong directional ocean-bottom noise components have been observed. Simultaneous recording of pressure and particle velocity affords the ocean-bottom station a distinct advantage over its land counterpart, through exploitation of the relationships between pressure and vertical velocity which exist for various types of arrivals and modes.