Temporal variation in protein, carbohydrate, and lipid concentrations in Paramuricea clavata (Anthozoa, Octocorallia): evidence for summer–autumn feeding constraints

Temporal variations in protein, carbohydrate, and lipid levels were studied in a passive suspension feeder, the gorgonian Paramuricea clavata. The samples were collected every month for mature and immature colonies over a three-year period (1997–2000). The relationship between biochemical composition and reproductive output was examined on the basis of the 1998 and 1999 data. In female and male P. clavata colonies, the tissue displayed differences in lipid concentrations only in winter–spring, due to the high lipid levels attained by female colonies in this period. Immature colonies showed significant differences in lipid concentration only with respect to mature females in spring. There were clear seasonal trends in the lipid and carbohydrate levels in P. clavata, with maximum values in winter–spring [male lipid 212±75 SD μg mg⁻¹ of organic matter (OM) and female lipid 274±103 SD μg mg⁻¹ of OM; male and female carbohydrate 68±14 SD μg mg⁻¹ of OM], coinciding with maximum food concentration/quality, and minimum values in summer–autumn (male and female lipid 155±57 SD μg mg⁻¹ of OM; male and female carbohydrate 56±14 SD μg mg⁻¹ of OM), coinciding with low food concentration/quality. The relationship between reproductive output and tissue concentrations of lipids, carbohydrates, and proteins was not straightforward, although there was an evident overlap of the lipid accumulation and the gonadal development. The results of this study show that protein, carbohydrate, and lipid levels may provide a record of episodes in the ecological cycle bearing on the trophic aspects of the target species. The results indicate that information on seasonal biochemical levels may explain benthopelagic coupling processes, provided factors such as natural diet, feeding rates, reproduction, and growth are well understood.     

Reproductive ecology of <Emphasis Type="Italic">Fungiacyathus marenzelleri</Emphasis> from 4100 m depth in the northeast Pacific Ocean

Fungiacyathus marenzelleri (Vaughan, 1906) is a deep-water solitary coral, cosmopolitan in distribution that is found at depths of 300–6,328 m. This study examined gametogenesis, inter-annual variability and reproductive periodicity of F. marenzelleri collected from Station M (34°50′N, 123°00′W) in the northeast Pacific at a depth of 4,100 m. Samples were collected (May, June, October 1996; August 1998; February, June 2001; and June 2002) and histologically processed with spermatogenic stage, oocyte size and fecundity measured. Four stages of spermatogenesis were identified and all males contained multiple stages of sperm development in each seasonal sample. Three stages of oocyte development were identified; previtellogenic (<28–150 μm), vitellogenic (150–300 μm) and late vitellogenic (300–400 μm). Comparison of mean oocyte diameters among sampling dates showed there were no inter-annual variations or seasonal differences. Overall, fecundity was 1,290 (±407) oocytes polyp⁻¹, and with no significant differences between sample months. Fecundity was not polyp-size dependent. This study shows a similar quasi-continuous mode of reproduction to this species examined from the Northeast Atlantic Ocean, but the fecundity is reduced by 50%. The reproductive output may fluctuate in relation to the input of organic material at this site, as shown by non-significant trends in the oocyte size-frequency and fecundity data. A quasi-continuous output of gametes would promote successful fertilisation and wide dispersal of the lecithotrophic larvae.     

Spatial variability in reproductive cycle of the gorgonians <Emphasis Type="Italic">Paramuricea clavata</Emphasis> and <Emphasis Type="Italic">Eunicella singularis</Emphasis> (Anthozoa,Octocorallia) in the Western Mediterranean Sea

Paramuricea clavata (Risso, 1826) and Eunicella singularis (Esper, 1794) are the most representative gorgonian species in hard bottoms sublittoral communities in the Western Mediterranean Sea. Reproductive cycles of two populations of both species were studied in two distinct locations approximately 600 km apart (Medes Islands and Cape of Palos), in order to assess interpopulation variability on a relevant geographic scale. Seasonal variation of lipid concentration levels in the gorgonian tissue was used as a tool to quantify energy storage by each studied population in order to explain possible interpopulation differences in gonadal output. Sex ratio in Medes Islands populations of both species was 1:1, while in Cape of Palos sex ratio was significantly male biased (1:7) in P. clavata, and female biased (1.7:1) in E. singularis populations. Spawning timing occurred in all cases coinciding with a marked increase in sea-water temperature in spring, and after the most successful feeding season, but comparing localities there was a clear temporal shift in the time of gametes release, appearing well linked to the shift in sea-water temperature rising in spring in both sites at the depth where populations are placed. Therefore, in this study the temperature appears as the main synchronizing factor of gonadal development within these populations. Significant differences in gonadal volume per polyp were found in both species owing mainly to differences in the number of gonads per polyp between populations, with Cape of Palos populations displaying higher values in both studied species, suggesting that the exposition to different local conditions may be reverted in a different gonadal output. But the observed patterns in lipid concentrations levels in gorgonians disable us to conclude that lipid concentration levels explain the observed differences in gonadal output found in this study.     

Life cycle of <Emphasis Type="Italic">Pseudocalanus acuspes</Emphasis> Giesbrecht (Copepoda,Calanoida) in the Central Baltic Sea: II. Reproduction,growth and secondary production

The population dynamics of Pseudocalanus acuspes in the Central Baltic Sea were studied from March 2002 to May 2003 on a monthly basis. All stages were present year round with a stage shift from nauplii to older copepodite stages over the course of the year. Biomass, estimated from prosome length, peaked between May and September with maximum recorded values of 594 and 855 mg C m⁻² in May 2002 and 2003, respectively. Differences in biomass between stations up to a factor of 20 were observed especially in April/May and October. Mean egg production rate (EPR) showed a seasonal course and was highest in April 2002 and 2003 with 3.6 and 2.1 eggs f⁻¹ day⁻¹, respectively, corresponding to a mean weight-specific egg production rate (SEPR) of 0.13 and 0.04. Egg production seems to be limited by food from May on. Stage durations determined from moulting experiments turned out to be extremely long. Maximum growth rates based on stage durations of 15–25 days at 4°C in May and July 2003 amounted for 0.03–0.05 day⁻¹ in CI-CIV. Comparing these rates with rates derived from temperature–development relationships for P. acuspes from the literature resulted in five times higher growth rates for the latter case. Secondary production reached values up to 9.1 mg C m⁻² day⁻¹ (method for continuously reproducing populations) and 10.5 mg C m⁻² day⁻¹ (increment summation).     

Population structure and reproductive patterns of the NW Mediterranean deep-sea macrourid Trachyrincus scabrus (Rafinesque, 1810)

Macrourid fish are one of the most abundant marine species on continental margins worldwide. Although they play an important role in the ecosystem, little is known about their overall biology. We report here a large data set of the most abundant macrourid in Mediterranean waters, Trachyrincus scabrus, showing the main population and reproductive characteristics. The study was based on 3,239 specimens collected between 300 and 1,500 m depth on the northwestern Mediterranean in 2003–2004 and 2008–2009. The population showed a depth-related structure with the largest individuals at 1,100 m depth and the smallest (i.e., immature) at shallower depths. Macroscopic and microscopic analyses of the gonads showed that T. scabrus has a highly seasonal reproductive pattern. Spawning females were found during winter when the organic matter fluxes were highest on the continental slope. T. scabrus is a batch spawner with group-synchronous oocyte development and present low average fecundity of 14,191 oocytes.     

Influence of environmental factors and female size on reproductive output in an invasive temperate marine gastropod <Emphasis Type="Italic">Rapana</Emphasis><Emphasis Type="Italic">venosa</Emphasis> (Muricidae)

Life history and reproductive strategies influence population dynamics at the inter- and intra-specific level. Environmental conditions suitable for gonad development and spawning, the reproductive range, may be a smaller portion of the broader species distribution. The only known breeding population of veined rapa whelks (Rapana venosa) in North America is in Chesapeake Bay, USA. There is considerable interest in the potential reproductive range of this non-indigenous species given the rapa whelk’s negative impacts on commercial shellfish species in both its native and introduced ranges. Weight-specific reproductive output is described for wild caught Chesapeake Bay rapa whelks maintained in flow-through mesocosms for 2 years. Measured reproductive output within and between egg capsule deposition seasons (years) in relation to water temperature, salinity, daylength, and female size is used to describe the rapa whelk’s reproductive range. Egg capsule production is influenced by seasonal and absolute water temperatures as well as seasonal daylength cycles. Egg capsule deposition by Chesapeake Bay rapa whelks begins at water temperatures of approximately 18°C and continues for 11–15 weeks. Forty to 70% of female whelks deposited egg capsules in most weeks during this season, producing 150–200 egg capsules female⁻¹ week⁻¹. Water temperatures >28°C caused reduced egg capsule production relative to temperatures of 20–25°C. Egg capsule production was positively related to seasonal changes in daylength, and two peaks of egg capsule deposition were observed in the 2001 and 2002 deposition seasons. The combination of declining daylength and higher water temperatures in late summer was associated with the cessation of egg capsule deposition. A lower average weight specific reproductive output in 130–145 mm SL rapa whelks (average 12 ± 1%) than in 90–106 mm SL rapa whelks (average 22 ± 1% of body weight) may reflect a life history that balances the physiological costs of maintaining a large body mass with the production of many planktonic larvae from multiple clutches of egg capsules per breeding season over a 10–15-year lifespan. Estimates of the cumulative day-degree requirements corresponding to the annual initiation of egg capsule deposition were 238 and 236 for 2001 and 2002, respectively. Reproductive output and day-degree requirements for Chesapeake Bay rapa whelks were similar to values calculated from previous studies of native muricids (Eupleura caudata and Urosalpinx cinerea). A latitudinal range of 30–41° (N and S) is predicted as the realized reproductive range for rapa whelk populations on the basis of the day-degree requirements for native whelks and reproductively active invasive rapa whelk populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of spatial variability and colony size on the reproductive output and gonadal development cycle of the Mediterranean red coral (Corallium rubrum L.)

Red coral (Corallium rubrum, L. 1758) is an over-exploited Mediterranean gorgonian. The gonadal development cycle of this gorgonian is examined at the Costa Brava (NW Mediterranean) taking into account for the first time colony size, depth and spatial horizontal variability. This study compares the gonad development and fertility in two colony size classes (colonies <6-cm height, and >10-cm height, both at 40–45-m depth), and two populations at different depths (16–18-m depth, and 40–45-m depth, both consisting of <6-cm high colonies) in a 15-month period. The fertility of seven size classes (<2 cm to >12 cm high colonies, in 2 cm intervals) was examined in the deep population, where large colonies were present. Furthermore, reproductive output was compared in 6 populations (distributed along more than 70-km coastline) one month before spawning (June). Red coral was found to be dioecious and gonochoric with a sex ratio of 1:1, which differs from other NW Mediterranean populations. On the other hand, fertility of different size classes indicates that small colonies of 2-cm height already produce gonads, which is in line with previous studies. Female and male polyp fertility and sperm sac size increase significantly with colony size [sperm sac diameter: 476±144 μm (mean±SD) and 305±150 μm in the >10-cm and <6-cm height colonies, respectively), whereas no significant effect on oocyte diameter was found (oocyte diameter: 373.7±18.7 μm). Depth staggered spawning, that is, an earlier release of gonads in the shallow populations, was observed in summer 2003, coinciding with the highest temperature gradient between shallow and deep water during the study period. Colonies of <6-cm height were significantly less fertile than colonies >12 cm, thus the recommendation of this study is that a minimum height should be incorporated into fishing regulations. The six studied populations at the Costa Brava showed a comparable reproductive potential, which demonstrates little variability within the homogenous population structure and range of size classes (due to overharvesting) found at the Costa Brava. The study of reproductive output is an important tool for ecosystem management, and this work recommends basing specific exploitation laws for distinctive populations on colony size, which is found to have a larger effect on reproductive potential than mesoscale variability. An erratum to this article can be found at     

Reproductive investment reduces recuperation from exhaustive escape activity in the tropical scallop Euvola zizac

In scallops, mobilization of reserves from the adductor muscle to support maintenance and reproductive activity may impinge upon a major role of the adductor muscle, the movement of the valves during swimming and escape responses. The tropical scallop Euvola ziczac (Linnaeus 1758) invests energy reserves to different degrees during its two periods of reproduction each year. We evaluated the impact of reproductive investment on the escape responses (clapping capacity and recovery after exhaustive exercise) of E. ziczac sampled at different reproductive stages (immature, mature, spawned) during the two reproductive periods in 1997. We compared the escape response capacities with the levels of muscle energetic reserves (glycogen, proteins, and arginine phosphate) and muscle metabolic capacities [activity of the glycolytic enzymes: glycogen phosphorylase (GP), pyruvate kinase (PK), phosphofructokinase (PFK), octopine dehydrogenase (ODH), arginine kinase (AK), and the mitochondrial enzyme, citrate synthase (CS)]. Gonad size, gamete volume fraction, and levels of gonadal protein and lipid were greater for mature scallops during the first than during the second reproduction. Numbers of claps during escape responses (49–57) and levels of muscle arginine phosphate remained similar throughout the different reproductive stages in both reproductive periods. In contrast, recovery was slowed during gonadal maturation in both reproductive periods and during spawning in the first reproduction. Scallops generally took more time to regain their initial clapping capacity during the first (25–40 min) than during the second reproduction (20–30 min). Muscle glycogen decreased markedly during both gonadal maturation and spawning in both reproductions; whereas, muscle proteins decreased only in the first reproduction. The levels of most enzymes decreased during gonadal maturation in both reproductions, and also after spawning, particularly during the first reproduction. We concluded that gonadal maturation and spawning did not decrease clapping capacity of E. ziczac, but decreased its capacity to recover from exhaustive exercise most likely due to decreased levels of energetic reserves and a reduced metabolic capacity of the adductor muscle. Moreover, these effects were probably stronger during the first cycle because of the greater reproductive investment coincident with decreased food availability. Received: 28 April 2000 / Accepted: 21 September 2000     

Survey of deep-dwelling red coral (<Emphasis Type="Italic">Corallium rubrum</Emphasis>) populations at Cap de Creus (NW Mediterranean)

The distribution and population structure of the eurybathic gorgonian Corallium rubrum were studied off Cap de Creus (Costa Brava, Northwestern Mediterranean Sea). Red coral is endemic to the Mediterranean Sea and the adjacent NE Atlantic coast, where it has been over exploited for centuries. This study presents, the first quantitative data on the spatial distribution and structure of a population extending between 50 (common SCUBA limits) and 230 m depth, and compared it with shallow populations previously studied in the same area. Different remotely operated vehicles (ROV) and two methodological approaches were employed during four cruises between 2002 and 2006: 1-Extensive surveys: sea to coast transects in which red coral density and patch frequency were recorded; 2-Intensive surveys, in which parameters describing colony morphology were recorded. Most of the hard substrate between 50 and 85 m depth was inhabited by red coral colonies, showing a patch frequency of 8.3 ± 7.9 SD patches per 100 m-transect (total transect area: 34 m²), and within-patch colony densities of 16–376 colonies m⁻² (mean of 43 ± 53 colonies m⁻²). Below 120 m depth red coral was less abundant, and rather than forming dense patches as in shallow water, isolated colonies were more common. The population structure differed between sites that are easily accessible to red coral fishermen, and remote ones (both at similar depth, 60–80 m), as colonies in easily accessible locations were smaller in height and diameter, and showed a less developed branching pattern. At shallower locations (10–50 m depth) the population structure was significantly different from those at deeper locations, due to the heavy harvesting pressure they are exposed to in the shallows. Twenty-five to forty-six percentage of the deeper colonies were taller than 6 cm, while only 7–16% of the shallow water colonies exceeded 6 cm colony height. Forty-six to seventy-nine percentage of the colonies in deeper waters were large enough to be legally harvested, while only 9–20% of the shallow water colonies met the 7 mm legal basal diameter to be collected. The branching pattern was also better developed in deeper colonies, as up to 16% of the colonies showed fourth order branches, compared to less than 1% of the shallow water colonies (of which 96% consisted of only one single branch). The results thus confirm that C. rubrum populations above 50 m depth are exposed to a higher harvesting intensity than deeper populations in the same area.     

Vertical distribution of <Emphasis Type="Italic">Todarodes pacificus</Emphasis> (Cephalopoda: Ommastrephidae) paralarvae near the Oki Islands,southwestern Sea of Japan

The diel vertical distribution patterns of Japanese common squid, Todarodes pacificus, paralarvae were examined using a Multiple Opening Closing Net and Environmental Sensing System (MOCNESS) in the southwest Sea of Japan near the Oki Islands (Japan) during five late-autumn surveys in 1998–2002. A total of 1,511 paralarvae ranging in mantle length (ML) from 0.7 to 7.3 mm were collected at 63 of the 68 stations surveyed. Most (84%) were collected above 75 m depth and in the mixed layer. The vertical distribution patterns varied little between day and night. Hatchling-sized (<1.0 mm ML) paralarvae were abundant at 0–25 m depth, and paralarval ML increased with increasing sampling depth. Our results suggest that T. pacificus paralarvae do not exhibit large diel vertical migration patterns, but as they increase in size, paralarvae gradually descend in the water column and the variability in depth increases with ontogeny.     

Vertical distribution,population structure and life cycles of four oncaeid copepods in the Oyashio region,western subarctic Pacific

Vertical distribution and population structure of four dominant oncaeid copepods (Triconia borealis, Triconia canadensis, Oncaea grossa and Oncaea parila) were investigated in the Oyashio region, western subarctic Pacific. Seasonal samples were collected with 0.06 mm mesh nets from five discrete layers between the surface and 2,000 m depth at seven occasions (March, May, June, August and October 2002, December 2003 and February 2004). The depth of occurrence of major populations of each species differed by species; the surface–250 m for T. borealis, 250–1,000 m for T. canadensis, 250–500 m for O. grossa and 500–1,000 m for O. parila. The ontogenetic vertical migration characterized by deeper occurrence of early and late copepodid stages, and shallower occurrence of middle copepodid stages was observed in T. canadensis and O. parila. Of the four oncaeid copepods, almost all copepodid stages occurred throughout the study period, suggesting that their reproduction continues throughout the year in the region. Nevertheless, a clear developmental sequence of stage-to-stage was traced for T. canadensis and O. grossa copepodids, implying their generation time to be 1 year. For T. borealis and O. parila copepodids, no clear seasonal succession was observed thus estimation of their generation time was uncertain. The present comprehensive results of vertical distribution and life cycle features for T. borealis, T. canadensis, O. grossa and O. parila are compared with the few published data on oncaeid species distributing in high latitude seas.     

Human impact on <Emphasis Type="Italic">Paracentrotus lividus</Emphasis>: the result of harvest restrictions and accessibility of locations

The sea urchin Paracentrotus lividus is common in the Mediterranean Sea in shallow subtidal rocky habitats, and it is intensely harvested for commercial and recreational purposes. This study is aimed at investigating whether the effects of harvest restrictions of P. lividus in rocky reef habitats interact with the accessibility of locations in structuring sea urchin population (total and commercial-sized individuals). These results are important for generating hypotheses about the influence of human harvesting on P. lividus and for addressing suitable measures of conservation. Paracentrotus lividus was sampled after the end of the sea urchin harvesting period (May–July 2007) within the Gulf of Alghero (North West Sardinia), where the Capo Caccia–Isola Piana Marine Protected Area (MPA) was established since 2002. Paracentrotus lividus was sampled at sixteen locations and attributed in groups of four to 4 combinations of harvest restrictions (Restricted Harvest, RH, vs. Unlimited Harvest, UH) and accessibility (Boat vs. Car), which correspond to a gradient of potential human activity on P. lividus in the ranked order of very low (RHBoatfar), low (RHBoatclose), moderate (RHCar) and high (UHCar). At each location, two depth ranges of 3–7 and 8–12 m were considered. At each of these depths, two areas of about 100-m² size were chosen. The density of P. lividus was assessed in ten quadrats of 1 × 1 m, and the size of 100 individuals (test diameter) was considered. Human activity has been found to significantly affect population structure of P. lividus influencing the proportion of individuals larger than 50 mm. Although harvest was restricted by MPA regulations, a significantly lower abundance of large individuals was found at sites accessible by car. This result highlights that there is an effect of harvest restrictions in relation to accessibility and emphasizes the need to carefully address the enforcement of the MPA toward easily accessible sites. Thus, surveillance and investment in enforcement of marine reserves seem crucial points that may provide the greatest return on maintaining the ecological benefits to the fishery activities.     

Reproduction and imposex in the edible snail <Emphasis Type="Italic">Adelomelon ancilla</Emphasis> from northern Patagonia,Argentina

The edible volutid snail Adelomelon ancilla occurs on the Argentine coast and may have the capacity to serve as source of support for local fisheries. However, knowledge of its reproduction is lacking. Over 3 years (from September 2000 to July 2004) we studied the oviposition at Golfo Nuevo, Patagonia by diving. Monthly collections were performed to examine gonadal stages histologically during 2002–2003. Gamete development stages corresponded with the expected period for oviposition occurring from July to November, a time of increasing day length. Oviposition also took place in March when water temperature attained a maximum of 18°C. Following the spawning period, remaining gametes were resorpted in both sexes. Males contained sperm throughout the year, parasperm and eusperm forms were found within the same acinus. Oogonia/oocytes ranged from 20 to 240 μm in diameter during oogenesis. Females commenced laying egg capsules from a shell length of 114 mm. Reproduction is compared with other fishable volutid snails from the Argentine shelf, and suggests the need to apply certain fishing restrictions if the resource begins to be utilized commercially. The imposex condition was found in snails from some shipping areas. The frequency of this condition declined with distance from the port.     

Phytoplankton growth and microzooplankton grazing rates in a restricted Mediterranean lagoon (Bizerte Lagoon,Tunisia)

Phytoplankton growth and microzooplankton grazing were investigated in the restricted Bizerte Lagoon in 2002 and 2004. The 2002 study, carried out at one station from January to October, showed significant seasonal variations in phytoplankton dynamics. High growth rates (0.9–1.04 day⁻¹), chlorophyll a (Chl a) concentrations (6.6–6.8 μg l⁻¹) and carbon biomass (392–398 μg C l⁻¹) were recorded in summer (July), when several chain-forming diatoms had intensively proliferated and dominated the carbon biomass (74%). In 2004, four stations were studied during July, a period also characterized by the high proliferation of several diatoms that made up 70% of the algal carbon biomass. In 2004, growth rates (0.34–0.45 day⁻¹) and biomass of algae (2.9–5.4 μg Chl a l⁻¹ and 209–260 μg C l⁻¹) were low, which may be related to the lower nutrient concentrations recorded in 2004. Microzooplankton >5 μm were mainly composed of heterotrophic dinoflagellates and ciliates. Microzooplankton biomass peaked during summer (2002 320–329, 2004 246–361 μg C l⁻¹), in response to the enhanced phytoplankton biomass and production. The grazer biomass was dominated by ciliates (71–76%) in July 2002 and by heterotrophic dinoflagellates (52–67%) in July 2004. Throughout the year and at different stations, microzooplankton grazed actively on phytoplankton, removing 26–58% of the Chl a and 57-84% of the primary production. In 2002, the highest grazing impact was observed on the large algae (>10 μm) during the period of diatom dominance. These results have a significant implication for carbon export to depth. Indeed, the recycling of most of the diatom production by the microbial food web in the upper water column would reduce the flux of material to the seafloor. This should be considered when modeling the carbon cycling in coastal environments and under conditions of diatom dominance. During both studies, ciliates had higher growth rates (0.5–1.5 day⁻¹) and a higher carbon demand (165–470 μg C l⁻¹ day⁻¹) than dinoflagellates (0.1–0.5 day⁻¹, 33–290 μg C l⁻¹ day⁻¹). Moreover, when grazer biomass was dominated by ciliates (in July 2002), herbivory accounted for 71–80% of the C ingested by microzooplankton while it accounted only for 14–23% when dinoflagellates dominated the grazer biomass (in July 2004). These results suggest that, in contrast to findings from open coastal waters, ciliate species of the restricted Bizerte Lagoon were more vigorous grazers of the large algae (diatoms) than were dinoflagellates.     

Reproduction and recruitment of scleractinian corals in a high-latitude coral community, Amakusa, southwestern Japan

Reproduction and recruitment in high-latitude coral populations in Japan have been little studied. A comprehensive study of the reproduction and early life history was conducted on nine common scleractinian coral species in Amakusa, southwestern Japan (32°N) from 2001 to 2003 including; (1) fecundity (the proportion of colonies with mature eggs), (2) timing and synchrony of spawning, (3) initial larval settlement pattern, (4) recruitment, (5) post-settlement mortality. The fecundity was high (76.7–100%) in six of seven species examined in 2002 and 2003. Annual spawning of the seven species occurred from mid July to August in 2001–2003, when seawater temperature was at the annual maximum. Spawning was highly synchronised among conspecific colonies and species in 2002 and 2003, with five species spawning five to nine nights after the full moon and another two spawning around the new moon. Temporal patterns of larval settlement of three spawning species during the first 10 days after spawning were similar to those of other spawning species from low latitudes. The number of scleractinian recruits on settlement plates, deployed from July to October (the major recruitment period at the study site), was low (2 recruits/m²) for the three consecutive years. Post-settlement mortality of 1–1.5 month old spat of five species ranged between 88 and 100% over 3–10 months in the field, similar to the values reported for both high and low latitude species (>94–99%). Among the key stages examined, the low recruitment rate may be the most important step in limiting successful reproduction and recruitment of these high-latitude scleractinian populations. The low recruitment rate may be attributable to (1) the reduced influx of larval supply from other coral populations, which are smaller and more isolated at high-latitudes and (2) the longer precompetent larval phase of broadcast-spawning corals which results in an increased chance of larvae being dispersed away from parent populations.     

Life cycle of Pseudocalanus acuspes Giesbrecht (Copepoda, Calanoida) in the Central Baltic Sea: I. Seasonal and spatial distribution

The seasonal and spatial distribution of Pseudocalanus acuspes in the Bornholm Basin (Central Baltic Sea) was studied on 16 cruises between March 2002 and May 2003 from stratified (10 m) multinet samples. The highest abundances were reached in May 2002 and April 2003 (618×10³ and 869×10³ ind. m⁻², respectively). Ontogenetic vertical distribution was stage specific with differences of mean annual weighted mean depth >30 m between nauplii and males; it followed closely the hydrography which was characterized by a permanent halocline and a summer thermocline. The vertical distribution showed a positive correlation with salinity especially in the older developmental stages; the relationship to temperature was negative in the nauplii and copepodite stage I (CI). Most of the stages performed a seasonal migration. The consequences of the vertical distribution patterns in relation to the effects of climate and predation are discussed. A stage shift from nauplii in April/May to CIV and CV as overwintering stages indicated slow seasonal development. However, nauplii were observed all the year round, and the resulting stage structure did not allow to distinguish generations. Changes in the prosome length of females seemed to be related to the advection of water masses with different temperatures rather than to different generations. It could not be clarified whether the strong increase of nauplii and adults after an inflow event of cold, saline North Sea water in the beginning of 2003 was a result of advection or improvement in habitat conditions.     

Lipid (energy) reserves,utilisation and provisioning during oocyte maturation and early embryonic development of deepwater chondrichthyans

We studied the lipid dynamics (lipid contents, classes and fatty acids) during oogenesis and early embryogenesis of 7 viviparous and 3 oviparous deepwater chondrichthyans. Mature pre-ovulated ovarian follicles of all species were high in lipid content, indicative of large energetic expenditure and high maternal investment. Larger lipid reserves were found in viviparous dogshark (28–36% wet weight, ww) compared to oviparous chimaeras (19–24% ww) and catshark, F. boardmani (18% ww). Neutral lipids and monounsaturated fatty acids were the main source of lipidic energy during vitellogenesis and gestation. For most species, there was a peak in total lipid content, levels of storage lipids and essential fatty acids at time of ovulation. Interspecific variation of total lipid yolk reserves and lipid class profiles was largely explained by differences in parity mode, reproductive (continuous vs. non-continuous oocytes development) strategy and depth-related physiological adaptations. Fatty acid profiles were less variable among species with the most important fatty acids including: 16:0, 18:1ω9, 20:1ω9, 20:4ω6 and 22:6ω3. These findings provide a greater biochemical understanding of different maternal-embryonic relationships among chondrichthyans, which can be used as a baseline for subsequent comparative studies.     

Diet and seasonal prey capture rates in the Mediterranean red coral (Corallium rubrum L.)

Gorgonians are passive suspension feeders, contributing significantly to the energy flow of littoral ecosystems. More than in active suspension feeders (such as bivalves, ascidians and sponges) their prey capture is affected by spatial and temporal prey distribution and water movement. Corallium rubrum is a characteristic gorgonian of Mediterranean sublittoral hard bottom communities. This study found a high variability in the annual cycle of prey capture rate, prey size and ingested biomass, compared to other Mediterranean gorgonians. Detrital particulate organic matter (POM) was found throughout the year in the polyp guts and constituted the main proportion of the diet (25–44%). Crustacean fragments and copepods (14–46%) accounted for the second major proportion, while invertebrate eggs (9–15%) and phytoplankton (8–11%) constituted the smallest part of the diet. To verify the importance of detrital POM in the energy input of this precious octocoral species, in situ experiments were carried out during the winter–spring period. The results confirm the importance of detrital POM as the main source of food for C. rubrum [0.13±0.04 μg C polyp⁻¹ h⁻¹ (mean±SD)]. This study also compares the prey capture rates of two colony size classes and two depth strata: Within the same patch, small colonies (<6 cm height) captured significantly more prey per polyp (0.038±0.09 prey polyp⁻¹ h⁻¹) than larger colonies (>10 cm high) (0.026±0.097 prey polyp⁻¹ h⁻¹) and showed a higher proportion of polyps containing prey (17% compared to 10%). Comparing colonies of similar size (<6 cm height) revealed that the colonies situated at 40 m depth captured significantly more prey (0.038±0.09 prey polyp⁻¹ h⁻¹) than the ones at 20 m (0.025±0.11 prey polyp⁻¹ h⁻¹). One pulse of copepods was recorded that constituted 16% of all captured prey during the 15-month period studied in one of the sampled populations. The data suggest that the variability of hydrodynamic processes may have a higher influence on the feeding rate than seasonal changes in the seston composition. The carbon ingestion combined with data on the density of the exploited population results in 0.4–9.6 mg C m⁻² day⁻¹. The grazing impact of current, heavily exploited and small-sized populations is comparable to that of larger Mediterranean gorgonians, suggesting that unexploited red coral populations may have a high impact compared with other passive suspension feeders.     

Mesozooplankton community structure in offshore and coastal waters of the Ionian Sea (eastern Mediterranean) during mixed and stratified conditions

Depth-stratified samples, collected during a period where the water column was vertically mixed (March 2000) and a period of thermal stratification (September 2000), were analyzed in order to investigate the horizontal and vertical distribution patterns and composition of mesozooplankton, especially copepod species assemblages, in a pelagic (Ionian Sea) and a coastal area (Patraikos Gulf) of the eastern Mediterranean. Total mesozooplankton abundance and biomass were significantly lower in the highly oligotrophic offshore waters of the Ionian Sea when compared to the semi-enclosed Patraikos Gulf during both seasons. Small-sized copepods dominated the mesozooplankton community. An ‘offshore’ and a ‘coastal’ copepod assemblage were defined in the surface layer (0–50 m) only during March when differences in environmental conditions (i.e., temperature, salinity and fluorescence) were strong between the two areas. Copepod vertical community structure in offshore waters differed between sampling months. In March one assemblage (0–200 m) was mainly identified, while in September three distinct assemblages (0–50, 50–100 and 100–200 m) were observed, related to different vertical distribution patterns of the various copepod species. A pronounced seasonal change of the dominant copepods was evident in the surface layer, where strong differences in hydrological properties were observed from March to September. Below this layer, the copepod community was relatively stable showing decreasing seasonal differences with increasing depth.     

Vertical distribution and mortality of <Emphasis Type="Italic">Calanus finmarchicus</Emphasis> during overwintering in oceanic waters southwest of Iceland

The seasonal vertical distribution and the predatory regime encountered by Calanus finmarchicus were studied along a transect across the Reykjanes Ridge in the oceanic area southwest of Iceland from data collected during four cruises between November 1996 and June 1997. The mortality for the overwintering period was estimated using linear regressions of density estimates from November 1996 to April 1997. In addition, we also estimated the mortality of the oldest population stages (C4 and older) in April and June by applying the vertical table method. During winter (November/December–January/February), the animals mainly resided at a depth of ∼300–1,500 m in the water of Atlantic origin. Ascent to upper layers took place mainly during March and April, and continued until May. During all cruises, continuous deep-scattering layers were observed, mainly within the range of 400–500 m to 700–800 m depth. Based on sampling with a Harstad pelagic trawl in April, the scattering was mainly ascribed to jellyfish (mainly Periphylla periphylla), small mesopelagic oceanic fishes (several species but Benthosema glaciale and Maurolicus muelleri were most abundant), euphausiids (mainly Meganyctiphanes norvegica) and shrimps (mainly Sergestes arcticus). These species may represent a predatory threat to overwintering C. finmarchicus. From November to April, daily per capita mortality rates were estimated to be (mean ± 95% CL) 0.004 ± 0.0028 for the total data set, and 0.004 ± 0.0033 and 0.004 ± 0.0023 (day^-1) for the Iceland Basin and Irminger Basin, respectively. Mortality rates were higher later in life (mean ± 95% CL) for C5/females (0.13 ± 0.044) and C5/males (0.19 ± 0.051) than for C4/C5 (0.00 ± 0.035) when averaged over all samples taken in April and June 1997. We discuss how the observed distribution and mortality rates of overwintering C. finmarchicus might be related to predatory regime.