Ecological aspects of ophiuroids from the phytal of S. W. Atlantic Ocean warm waters

Nine species of ophiuroids — Amphipholis januarii, Axiognathus squamatus, Hemipholis clongata, Ophiocnida scabriuscula, Ophiactis lymani, Ophiactis savignyi, Ophionereis reticulata, Ophioderma appressum and Ophiothrix angulata —were collected in various habitats from the mid-littoral and upper infralittoral on the northern coast of the State of São Paulo, Brazil. The abundance of 6 species occurring in 28 species of algae was investigated. A total of 220 samples was collected at monthly intervals from April, 1969 to May, 1970. The distributional pattern of the populations, as determined by Mobisita's index, shows aggregation of the ophiuroids. No ophiuroid species was limited to one algal species. Each species prefers certain algal species and/or a different level on the shore. The most abundant species on algae was Ophiactis lymani, with a maximum density of 1,510 individuals/100 ml of algae. Four species of ophiuroids occurred inside sponges. The most abundant species in sponges was O. savignyi, with a maximum density of 1,892 individuals/100 g of dry sponge. Two species of ophiuroids occurred inside the bryozoan Schizoporella unicornis. Feeding observations have shown Axiognathus squamatus to capture its food by mucous nets. Decapod crustaceans fed on ophiuroids in aquaria. The copepod Thespesiopsyllus sp. was found in the body cavity of the 2 Ophiactis species. Simultaneous sexual and asexual reproduction were abserved in O. savignyi.     

Life history of the sandy-beach amphipod Dogielinotus loquax (Crustacea: Dogielinotidae) from the outer coast of Washington,USA

Dogielinotus loquax Barnard, a common intertidal macroinvertebrate on exposed ocean beaches near Grays Harbor, Washington, USA, is distributed from mid to mean high tidal levels, with a mean density of 1 830 m^-2 in 1975–1976. Location of maximum density within the intertidal zone is related to surf intensity and varies seasonally. The species is iteroparous and has an average sex ratio of 1:1. Temperature constraints on growth and egg development rates apparently influence the timing of reproduction. Two dominant recruitments occur per year, one in early spring (the summer generation) and another in late summer (the overwintering generation). The sampling design and density estimates permitted estimation of the mortality rate for the summer generation. Shorebird predation is suspected to affect summer generation abundance. Dogielinotus loquax will soon be elevated to the type of a new genus, Proboscinotus (Bousfield and Tzvetkova, in press)Contribution no. 1271 from the Department of Oceanography, University of Washington; Seattle, Washington 98195, USA     

Zonation of the interstitial polychaeteStygocapitella subterranea (Stygocapitellidae) in European sandy beaches

The zonation ofStygocapitella subterranea Knoellner (Polychaeta, Stygocapitellidae) in sandy beaches is compared for several localities along the European coasts. In tidal beaches the species occupies a zone near average high tide level (AHTL), whereas in non-tidal beaches it is found at a fairly long distance from the water line. The regularities observed inS. subterranea indicate that the interstitial fauna may prove well suited for the establishment of a general scheme of zonation in sandy beaches analogous to that for rocky shores proposed byStephenson andStephenson (1949).     

Life history of the sandy-beach amphipod Neohaustorius schmitzi (Crustacea: Haustoriidae)

Neohaustorius schmitzi Bousfield, the dominant macroscopic invertebrate on sandy beaches in North Carolina, USA, is strictly intertidal, and distributed from mean low tide to high tide, with an average density of 790/m². Location of greatest densities within the intertidal zone is dependent upon season and sex. An aggregated distribution is shown. N. schmitzi has 2 generations/year: a winter generation which lives about 8 months, and a summer generation which lives about 4 months. The reproductive season extends from February through October, with spring and summer peaks. Each female appears to produce only 1 brood of young. The number of young ranges from 2 to 14, depending upon the length and generation of the female.     

Mangroves as nursery sites: comparisons of the abundance and species composition of fish and crustaceans in mangroves and other nearshore habitats in tropical Australia

Daytime sampling of mangrove and seagrass (Halophila/Halodule community) habitats every 7 wk at Alligator Creek, Queensland, Australia, over a period of 13 mo (February 1985–February 1986) using two types of seine net, revealed distinct mangrove and seagrass fish and crustacean faunas. Total abundance of fish and relative abundance of small and large fish also varied between habitats and seasonally. Post-larval, juvenile and small adult fish captured with a small seine-net (3 mm mesh) were significantly more abundant (4 to 10 times) in the mangrove habitat throughout the 13 mo of sampling. Mangrove fish abundance showed significant seasonality, greatest catches being recorded in the warm, wet-season months of the year. Relative abundances of larger fish (captured in a seine net with 18 mm mesh) in the two habitats varied throughout the year, but did not show a seasonal pattern. At the same site, small crustaceans were significantly more abundant in the mangroves in all but one dryseason sample. Similar comparisons for three riverine sites, sampled less frequently, in the dry and wet seasons of 1985 and 1986, respectively, showed that in general mangrove habitats had significantly more fish per sample, although the relative abundance of fish in mangroves and other habitats changed with season. Crustacean catches showed a similar pattern, except that densities among sites changed with season. Fish and crustacean abundance in mangroves varied among sites, indicating that estuaries differ in their nursery-ground value. The juveniles of two commercially important penaeid prawn species (Penaeus merguiensis and Metapenaeus ensis) were amongst the top three species of crustaceans captured in the study, and both were significantly more abundant in the mangrove habitat. By contrast, mangroves could not be considered an important nursery for juveniles of commercially important fish species in northern Australia. However, based on comparisons of fish catches in other regions, the results of the present study indicate the importance of mangroves as nursery sites for commercially exploited fish stocks elsewhere in South-East Asia. Contribution No. 378 from the Australian Institute of Marine Science     

The annual reproductive cycles of Uca annulipes,Portunus pelagicus and Metapenaeus affinis (Decapoda: Crustacea) from the South-west coast of India

Employing the gonad index method, the reproductive cycles of three decapod crustaceans, Uca annulipes (Latreille), Portunus pelagicus (Linnaeus) and Metapenaeus affinis (Milne-Edwards) have been studied. In these crustaceans breeding is not continuous all the year round, but extends over several months of the year with distinct peak periods of gonadal activity. The male and female reproductive cycles are not concurrent. The peak of the reproductive cycle of males occurs slightly earlier in the breeding season than that of females. These studies indicate the possibility of production of successive broods of eggs during the same breeding season. In these species, the low saline conditions of the monsoon period are unfavourable for breeding. The medium and high saline conditions during the post-monsoon and pre-monsoon months, respectively, with plenty of planktonic food for the larvae, seem to be the favourable periods for breeding activity.     

Observations on the biology of Donax trunculus and D. vittatus at Ile d'Oléron (French Atlantic coast)

Observations have been made on the biology of two species of the bivalve genus Donax, on two beaches, Vertbois and St. Trojan, on the Ile d'Oléron, French Atlantic coast. The two species displayed different vertical distribution: D. trunculus Linné in the intertidal; and D. vittatus (da Costa) between low-water spring tide (LWST) and 5 to 6m depth, with only the fringe of the population extending to the shore. D. trunculus also showed differential distribution by size or age, the youngest individuals being highest on the shore, and the oldest near LWST. The two species exhibited a similar pattern of seasonal recruitment and growth, but in both there were differences in growth characteristics between the two beaches, individuals at St. Trojan growing to a larger size than those at Vertbois. The mean pattern of mortality in the two areas was similar, and productivity per 100 recruits surviving to the first winter following settlement was greater at St. Trojan than at Vertbois. For D. trunculus the mean population density at Vertbois was higher and the production per unit area on the two beaches was similar. Production to biomass (B) and elimination to biomass (B) ratios were similar for the two beaches for both species, and while production was greater for D. trunculus at both beaches, the B and B ratios were higher for D. vittatus. Comparisons with other published data reveal that the rate of growth of D. trunculus is similar throughout its range from Brittany to the Mediterranean Sea, while that of D. vittatus shows more variation. In both species, there is a trend of increasing P/B and E/B ratios from north to south throughout the geographical range.     

Ontogenetic diel vertical migration of the planktonic copepod Calanus sinicus in the Inland Sea of Japan

The ontogenetic diel vertical migration of the planktonic copepod Calanus sinicus was investigated in the Inland Sea of Japan in June 1989, when the water column was thermally weakly stratified. Because of fewer eggs and less variation in their abundance, nocturnal spawning was not apparent. A pronounced upward migration occurred in NIII. NIII to CIII resided in the upper 20 m layer throughout the day, and from CIV on their median depths descended. CV and adult females underwent significant diel vertical migration, whereas adult males did not migrate. By integrating the results from the present study and those from our previous investigations (in August–September 1988, November 1988 and March 1989), we review seasonal variation in the ontogenetic diel vertical migration of C. sinicus. Spawning was largely nocturnal, reaching its maximum level around dawn, but spawning depth and fecundity changed seasonally. The distribution of pre-feeding stages, NI and NII, was similar to that of eggs. A pronounced upward migration always occurred in the first feeding stage, NIII, and late nauplii and early copepodites always resided in the food-rich upper layer, indicating that upward migration by NIII is feeding migration. As the stages progressed, they extended their vertical distribution range, and CV and adult females usually underwent diel vertical migration. However, the pattern and strength of this migration differed seasonally. Their day depths increased with the increase of relative biomass of planktivorous fish, indicating that predator avoidance induces their diurnal downward migration. High chlorophyll a concentrations in the upper layer (<15 m deep) relative to the lower layer (>20 m deep) amplified their diel vertical migrations. Diel vertical migration of C. sinicus is a phenotypic behavior.     

Breeding and larval distribution of the pteropod Clione limacina in the North Atlantic,Subarctic and North Pacific Oceans

The pteropod Clione limacina (Phipps, 1774) is an arcticboreal, circumpolar species, which is widely distributed in the North Atlantic and Subarctic Oceans; it also occurs in the North Pacific Ocean (in the Oyashio and neighbouring waters) and along the Atlantic coast of North America in the waters of the cold Labrador current to the Cape Hatteras region (35° N). The distribution of C. limacina larvae in the plankton of the Norwegian, Barents and White Seas, the Bear Island-Spitsbergen region of the Greenland Sea, the Newfoundland Grand Bank and the Flemish-Cap Bank region of the North-western Atlantic Ocean, and the Kurile-Kamchatka region of the North-western Pacific Ocean has been studied, and information from literature concerning the reproduction and larval occurrence of the species is summarized. Throughout its distributional are, spawning of C. limacina is characterized by the same general ecological pattern. This species breeds and spawns in all types of water masses occurring within the vertical range which it commonly inhabits — from surface layers to 500 m water depth. In all local populations of the species, the most intensive spawning is correlated with the spring/summer period of annual heating of the local waters, and the highest abundance parallels maximum growth of phytoplankton which serves as food for veligers and early polytrochous larvae. After the end of this period, spawning intensity in all local C. limacina populations declines sharply, but spawning continues at low intensity during the autumn/winter season, being practically continuous throughout the year. Distribution patterns of C. limacina larvae are determined by those of their parental forms (the parental forms spawn in the zones permanently inhabited). The earliest larval stages of C. limacina (veligers) are present predominantly in the upper 100 or 200 m water layer, i.e. in the zone of high phytoplankton abundance. Polytrochous larvae, after becoming predaceous feeders, are distributed throughout the whole water column from the surface to 500 m depth, similar to adult C. limacina. As with the adults, larvae are present (within the species' distribution area) in all types of water masses. Since the beginning of the twentieth century, in the course of the warming of the Arctic Ocean, the southern race of C. limacina (formerly a summer/autumn seasonal invader in the Norwegian Sea) has become a permanent component of the plankton fauna of the Norwegian and Barents Seas in regions influenced by the Norwegian-Northcape Current System.     

Crustacean epifauna of seagrass and macroalgae in Apalachee Bay,Florida, USA

Epifaunal crustaceans on turtlegrass (Thalassia testudinum) and five dominant macroalgae (Anadyomene stellata, Digenia simplex, Halimeda incrassata, Laurencia poitei and Penicillus lamourouxii) were quantitatively sampled bimonthly over a one-year period from September 1979 to September 1980 in a subtropical seagrass meadow in Apalachee Bay, Florida (northeastern Gulf of Mexico). These plant species exhibited a wide range of morphologies, with surface area-to-biomass ratios differing by over 2.5 times. A similar suite of crustaceans occurred on all macrophytes despite differences in shape or architecture among plant species. Relative abundances of many crustaceans, however, varied among plant hosts. Similarity analysis indicated that the epifaunal associates of T. testudinum were distinct from those of the macroalgae. Species richness was generally higher on turtlegrass than on any of the macroalgae. Abundances of total crustaceans per plant biomass or per plant surface area, on the other hand, were greater on all macroalgal species compared to the seagrass. Abundances (per plant biomass or plant surface area) of 14 of the 16 numerically dominant epifaunal species differed significantly among macrophytes. Twelve of the 16 species had greater abundance on one or more macroalgae, while only two species were more abundant on T. testudinum. Almost half of the dominant species had greatest abundances on the branching red alga L. poitei. Although abundances per plant biomass and plant surface area were greater on macroalgae relative to turtlegrass, densities (individuals per meter square of bottom) of animals associated with T. testudinum were significantly greater than those associated with macroalgae, primarily because of the greater abundance of turtlegrass in the grass bed. Both surface area-to-biomass ratios and degree of branching were poorly correlated with epifaunal abundance and number of species. Neither structural feature is an adequate predictor of faunal abundance and species richness among plant species, especially when macrophytes with very different morphologies are compared.     

Seasonal study of planktonic copepods and their benthic resting eggs in northern California coastal waters

Few investigations have examined the occurrence of zooplankton resting eggs in the sea bed of waters deeper than 20 m. In this study the distribution and abundance of planktonic copepods and their benthic resting eggs in coastal waters off northern California, U.S.A., were determined and related to environmental parameters (temperature, salinity, depth, and sediment grain size). Sediment cores, net tows, and CTD profiles were obtained in April and October 1989, and February, April, and October 1990. Water depths in the study area ranged from approximately 60 to 120 m. The mean abundance of eggs was as high as 1.2×10⁵ m^-2 for Acartia clausi Giesbrecht and 1.9×10⁵ m^-2 for Tortanus discaudatus Thompson and Scott. These egg concentrations are comparable to those reported previously for shallower more protected regions. The abundance of eggs in the sediments decreased with increasing depth of the water column. For the region as a whole, eggs were least abundant in muddy sediments. The mean abundance of eggs in the sea bed also varied seasonally and annully. Benthic resting eggs of A. clausi were more abundant in April 1989 than in April 1990, and adults of the species were never found in the plankton samples. The lack of adults is not unusual since results of previous studies indicate that A. clausi is a cold-water species, and in this region water temperatures are colder in summer, than in winter, due to upwelling. Temperature and salinity data indicated that the upwelling season had commenced by the time of the April 1990, but not the April 1989 sampling. Thus, the reduced abundance of benthic eggs in April 1990 may have been due to egg-hatching in response to reduced temperatures. The results suggest that the presence of A. clausi in coastal waters off northern California is linked to recruitment from benthic resting eggs.     

The ecology of two sandy beaches in south west India. III. Observations on the population of Donax incarnatus and D. spiculum

The biology of two species of Donax, D. incarnatus Gmelin and D. spiculum Reeve on two beaches in south west India is described. Two year groups of D. incarnatus were present on both beaches, from settlements during the monsoon period in 1967 and 1968. At Shertallai, both groups were studied through the year, and data on growth, mortality and production are presented. At Cochin, the rate of growth was slower and the maximum size attained smaller, but mortality during the early monsoon precluded study of D. incarnatus through a full year. D. spiculum occurred at Cochin mainly during the pre-monsoon period, and at Shertallai during the post-monsoon. The species has a shorter life-span than D. incarnatus, but its irregular occurrence did not allow detailed production estimates.     

Macroalgae as habitat patch islands for Scutellidium lamellipes (Copepoda: Harpacticoida) and Ampithoe tea (Amphipoda: Gammaridae)

Scutellidium lamellipes and Ampithoe tea live in patches formed by the brown alga Pelvetia fastigiata. The distributions and abundance of both crustaceans were examined on P. fastigiata obtained during 1975 and 1976 from 7 collecting and 6 experimental sites in the mid-intertidal zone at La Jolla, California (USA). At each collecting site, the abundance of each crustacean generally increases with increasing plant size. Following defaunation and transplantation of algae, abundances of both crustaceans on individual plants appear to be governed by equilibria determined by in situ reproduction, immigration and emigration. Immigration rates of both animal species decrease significantly with increasing distance from areas occupied by P. fastigiata. During short-term experiments, neither crustacean was able to establish colonies on defaunated plants placed across a 30 m P. fastigiata-free zone and both species would have to reproduce to persitst on plants transplanted to that site. More frequent immigration and reproduction (and, for S. lamellipes at least, decreasing emigration rates with increasing patch size) would increase abundances and decrease probabilities of local extinction on larger and/or less distant plants. However, even within sites with isolated plants, the smallest plants often are not inhabited by either crustacean. The densitics of both species differ with plant size and distribution. Densities of S. lamellipes are greatest within a large aggregation of P. fastigiata, whereas those of A. tea are greatest on moderate-sized isolated plants at mid-tide levels.     

Corophium multisetosum (Amphipoda: Corophiidae) in Canal de Mira,Portugal: Some factors that affect its distribution

The population ofCorophium multisetosum (L.) from Canal de Mira, Ria de Aveiro, Portugal, was sampled seasonally from December 1985 to September 1986, as part of a larger survey of the benthic invertebrate macrofauna. Its distribution along the channel exposes the species to a range of salinities from freshwater to above 30. A principal components analysis, using the physical and chemical parameters of the sediment as variables and sampling stations as operational taxonomic units, indicated that abundance is negatively correlated with salinity, depth, and the occurrence of sediments rich in particles below 125µm and rich in organic matter. Abundance is positively correlated with temperature. The distribution of the species does not seem to be affected by the occurrence of sediment grades between 125 and 1 000µm. Paired-choice salinity experiments indicated thatC. multisetosum prefers salinities within the range 2.5 to 10. In multi-choice experiments concerning sediment grade, amphipods did not show any significant preference within the 125 to 500µm range, although the 125µm grade was chosen less frequently. The influence of temperature on the overall distribution ofC. multisetosum is discussed.     

Spatial and temporal occurrence of the parasitic dinoflagellate Duboscquella cachoni and its tintinnine host Eutintinnus pectinis in Chesapeake Bay

Eutintinnus pectinis (Kofoid, 1905) Kofoid and Campbell is a seasonally important component of the Chesapeake Bay, USA, microzooplankton. During the summers of 1986 and 1987, E. pectinis populations commonly reached densities well above 10³ cells l^-1 and were often heavily infected by Duboscquella cachoni Coats, 1988, a lethal parasitic dinoflagellate. The temporal and spatial occurrence of D. cachoni suggests that this parasite has a significant impact on E. pectinis populations and may, under appropriate conditions, regulate host abundance. Infection levels above 10% were frequently encountered and epizootic events with 20 to 50% of host individuals parasitized by dinoflagellates were observed over broad areas. Epizootic infections were usually recorded in regions of the Bay that had high concentrations of E. pectinis, and data for vertical profiles, when integrated with depth, showed a significant positive correlation (p0.01) between host abundance and parasite prevalence. However, peak E. pectinis density and maximum levels of parasitism were often not vertically coincident at stations, and a clear relationship between host abundance and parasite prevalence was not evident for data from discrete samples. These vertical distributions and the absence of a correlation between host density and parasite prevalence for discrete samples may reflect death of E. pectinis as epizootics spread through the host population. Bay-wide infection levels averaged 10.4% (±1.73 SE) for eight cruises in 1986 and indicate that parasite-induced mortality removes 7 to 24% of the E. pectinis standing stock per day. Comparison of these values to ingestion rates for copepods on tintinnine ciliates reveals that parasite-induced mortality of E. pectinis is comparable to predation pressure by the dominant mesozooplankton grazers in Chesapeake Bay.     

Ecological studies on a tropical limpet Cellana radiata

Some aspects of the habitat zones, distribution pattern, and population density with reference to tidal levels of the tropical limpet Cellana radiata (Born) are presented. Observations have also been made on the homing behaviour of the limpet. Unlike the temperate limpets, no migration to different tidal levels during different seasons was observed in C. radiata.     

Growth parameters of deep-water decapod crustaceans in the Northwestern Mediterranean Sea: a comparative approach

 Relative and absolute growth were studied in 17 species of deep-water decapod crustaceans, spanning nine families of six different infra-orders, in the Northwestern Mediterranean Sea. The overall maximum abundance of these species lay between 200 m and 750 m (i.e. upper- and mid-slope species). Relative and absolute growth rates were compared by contrasting the slopes of the size–weight relationships for the different species and calculating the von Bertalanffy growth-equation parameters asymptotic length (L _∞ ) and growth rate (k). The size–weight relationships differed significantly as function of the species' life habits. The results revealed a significant decrease in weight relative to size in mesopelagic species (which carry out diel vertical migrations), an almost isometric relationship between size and weight in the less mobile nektobenthic species, and a significant increase in weight relative to size in strictly benthic species. The mean allometric coefficient for each group increased significantly from mesopelagic to benthic species. However, no general trend was observed in the growth-performance index, Φ (an index used to compare absolute growth rates between species, as a function of habit and depth of maximum abundance for all species combined), suggesting that the deep-water decapod crustaceans studied have similar absolute growth rates. Nevertheless, comparison of growth-parameter and growth-performance index values within families did reveal differences. Mesopelagic species of the families Sergestoidae and Pasiphaeidae showed slightly increased growth rates with increasing depth of distribution. Nektobenthic species of the genus Plesionika followed a trend opposite to that shown by mesopelagic species, with a higher growth rate for the shallowest-dwelling species (P. heterocarpus) than the deepest-dwelling species (P. acanthonotus). Taking growth as one of the major components of an organism's energy budget, the growth rates for the decapod crustacean species in this study were significantly lower than those reported in the literature for shallow-water penaeid crustacean species (which are distributed in higher-temperature habitats than deep-water Mediterranean crustaceans) and higher than those reported for mesopelagic myctophid fish species. Hence, the well-defined growth trends shown by deep-water decapod crustacean species in the Northwestern Mediterranean Sea, compared to the less well-defined trends in the other taxa, is discussed in the framework of the overall dynamics of their ecosystem. Received: 25 May 1998 / Accepted: 27 September 1999     

Continuous plankton records: overwintering and annual fluctuations in the abundance of zooplankton

A study of seasonal variations in the pattern of year-to-year changes, for 1948 to 1982, in the abundance of four zooplankton taxa (Pseudocalanus elongatus Acartia clausi, Calanus finmarchicus and Hyperiidea) for the North Sea suggests that an element of the variations, represented at least in part by a quasi-linear downward trend, has its origins in winter and its occurrence through the year is a function of inherent persistence. A downward linear trend is the dominant pattern in the annual fluctuations in abundance of many species of zooplankton throughout the north-east Atlantic and the North Sea. It is argued that it is reasonable to extrapolate from the limited data set included in the detailed study and to assume a winter origin for the pattern wherever it occurs. Some implications for ideas about the dynamics of the plankton ecosystem are considered.     

Locomotor activity patterns and feeding habits in the prawn Palaemon xiphias (Crustacea: Decapoda: Palaemonidae) in Alfacs Bay,Ebro Delta (northwest Mediterranean)

Diel activity rhythms of the prawn Palaemon xiphias Risso, 1818 from Alfacs Bay, Ebro Delta, were studied by time-lapse videorecordings. Activity displayed an endogenous circadian rhythm, with maximum activity at night. Feeding habits were studied by frequency of occurrence and by the points method. The food of P. xiphias consisted mainly of crustaceans; the remains of amphipods, isopods, mysids, copepods, decapods and ostracods were identified. The remaining items consisted of molluscs, polychaetes, ophiuroids, plant material, sand, and unidentified organic debris. The results indicate that P. xiphias is a predator of benthic invertebrates rather than a scavenger or detritus feeder. Diet composition changes with increasing size of the prawn.