Age and growth of the naticid gastropod <Emphasis Type="Italic">Polinices pulchellus</Emphasis> (Gastropoda: Naticidae) based on length frequency analysis and statolith growth rings

In Red Wharf Bay, UK the naticid gastropod, Polinices pulchellus, was more abundant and more highly aggregated during the summer months (June–August 2001) than during the winter (December 2000). Whilst small numbers of juvenile P. pulchellus (4–6 mm shell length) were present throughout the year the population consisted mainly of individuals of 12–14 mm shell length. Juvenile snails grew rapidly in size during the winter and early spring; growth then virtually ceased between May and June, following which there was a further period of rapid growth between August and February. Densities ranged between 57 and 4,073 ha⁻¹ and the largest individual collected during this investigation measured 16.2 mm in shell length. Statoliths from adult P. pulchellus revealed the presence of a settlement ring and two prominent growth rings (rings 1 and 2). A curvilinear relationship exists between statolith diameter and shell length in snails up to 16 mm in length. Settlement rings ranged in diameter from 19.7 to 45.2 μm (mean 29.8 μm; SE=0.41) giving an estimated shell length of the settled juvenile of 1.1 mm. The diameter of ring 1 and ring 2 were significantly correlated indicating that rapid growth during the first year is maintained during year 2. Shell lengths estimated from the diameters of the prominent statolith rings and those obtained from length frequency data analysis (LFDA), were broadly congruent strongly suggesting an annual periodicity to the statolith rings. The largest snails (>15 mm) present within this population were estimated to be between 2 and 3 years old. Von Bertallanfy seasonal growth curves obtained from the LFDA predicted values of L∞, K and t ₀ of 14.32 mm, 1.54 and −0.14 years, respectively, suggesting that P. pulchellus rapidly attains its maximum asymptotic size.     

Laboratory culture of the aeolid nudibranch <Emphasis Type="Italic">Spurilla neapolitana</Emphasis> (Mollusca,Opisthobranchia): life history aspects

Spurilla neapolitana from the Eastern Mediterranean was cultured in a self-sustained, temperature-controlled laboratory culture system, and its life cycle is described. Adults were collected from three field sites situated 120 km apart, along the Israeli Mediterranean coastline, between March 2006 and August 2007. Cultures of the life-cycle stages were raised at 24°C. S. neapolitana deposited white, coiled, spiral egg masses containing zygotes. Veliger larvae hatched 3.0 ± 0.4 days post oviposition. The veliger larvae are obligatory planktotrophs, with a minimal larval phase of 22 days. In the lab, larvae settled and metamorphosed following exposure to metabolites derived from distinct prey sea anemone species. Reproductive maturity was reached 42 ± 5 days post metamorphosis, resulting in a laboratory generation time of 67 days (egg to egg). The average life span of reproductive specimens in this study was 157 ± 13 days post-oviposition and they reached a length of 7–10 cm. During this period, an average adult deposited ca. 40 × 10⁶ zygotes. This species has several characteristics that suggest it will be a useful model for laboratory-oriented research. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Reproductive status and body condition of Atlantic bluefin tuna in the Gulf of Maine, 2000–2002

The reproductive status and body condition of 195 (≥185 cm curved fork length, CFL; assigned age 7 and above) Atlantic bluefin tuna were assessed in the Gulf of Maine during the commercial fishing season of June–October, 2000–2002. Given the distance between known spawning and feeding grounds, the prevailing paradigm for Atlantic bluefin tuna (Thunnus thynnus thynnus, L.) suggests that the most likely histological state for females arriving in the Gulf of Maine after spawning would be a resting or quiescent state with little or no perigonadal fat. Alternatively, the presence of mature or mature-inactive histological states in some females supports a more varied or individualistic model for bluefin reproduction. No relationship was found between body condition and reproductive status. Males were found in all reproductive stages, but were more likely to be in spawning condition (stages 4 and 5) or a mature-inactive state (stage 6) in June and July. Female bluefin tuna were found in stage 1 (immature or non-spawning) and stage 6 (mature-inactive). Stage 6 females were only present in June and July and smaller females (<235 cm CFL) were more likely to be in stage 6 than large females (>235 cm CFL) sampled during those same months. The presence of smaller females in stage 6 arriving at the same time as larger females in stage 1 indicates that Western Atlantic bluefin tuna may have an asynchronous reproductive schedule and may mature at a smaller size than the currently accepted paradigm suggests.     

Swimming ability of eels (<Emphasis Type="Italic">Anguilla rostrata,Conger oceanicus</Emphasis>) at estuarine ingress: contrasting patterns of cross-shelf transport?

The transport of eel early life stages may be critical to their population dynamics. This transport from ocean spawning to freshwater, estuarine and coastal nursery areas is a combination of physical and biological processes (including swimming behavior). In New Jersey, USA, the American eel (Anguilla rostrata) enters estuaries as glass eels (48.7–68.1 mm TL) in contrast to the Conger eel (Conger oceanicus) that enters as larger (metamorphosing) leptocephali (68.3–117.8 mm TL). To begin to understand the mechanisms of cross-shelf transport for these species, we measured the potential swimming capability (critical swimming speed, U _crit) under ambient conditions throughout the ingress season. A. rostrata glass eels were collected over many months (January–June) at a range of temperatures (4–21°C), with relative condition declining over the course of the ingress period as temperatures warmed. C. oceanicus occurred later in the season (April–June) and at warmer temperatures (14–24.5°C). Mean U _crit values for A. rostrata (11.7–13.3 cm s⁻¹) and C. oceanicus (14.7–18.6 cm s⁻¹) were comparable, but variable, with portions of the variability explained by water temperature, relative condition, ontogenetic stage, and fish length. Travel times to Little Egg Inlet, New Jersey, estimated using 50% U _crit values, indicate it would take A. rostrata ~30 and ~60 days to swim from the shelf edge and Gulf Stream, respectively. Travel times for C. oceanicus were shorter, ~20 days from the shelf edge, and ~45 days from the Gulf Stream. Despite differences in life stage, our results indicate both species are competent swimmers, and suggest they are capable of swimming from the Gulf Stream and/or edge of the continental shelf to estuarine inlets.     

Brooding of the sub-Antarctic heart urchin, <Emphasis Type="Italic">Abatus cavernosus</Emphasis> (Spatangoida: Schizasteridae), in southern Patagonia

The reproductive cycle of the sub-Antarctic spatangoid sea urchin, Abatus cavernosus, was examined during a 2-year period in southern Patagonia, Argentina. The population studied is the northernmost known coastal population in the austral oceans, and is influenced by a greater annual range of seawater temperature than other Abatus species. The sex ratio of the overall A. cavernosus population did not differ significantly from 1:1, but was not homogeneous across size classes. A clearly defined annual reproductive cycle was found. Spawning occurred from May to July and was synchronous between sexes. Females were observed to be brooding within a 9-month period, from May to February. Juveniles were released during the austral summer, from January to February. The length at which 50% of the females were brooding occurred at a test length of 25.9 mm. A. cavernosus had a large egg size (mean diameter = 1.4 mm) and low fecundity (maximum = 57 eggs per female) compared to closely related species. The number of eggs within each brood pouch was highest in larger anterior brood pouch, which is close to two gonopores, as opposed to the other anterior and two smaller posterior pouches. Significant interannual variation was observed in gonad cycles, fecundity, and embryo development such as: brood size decreased during 2001; adjusted gonad dry weight and fecundity were higher during 2003. Hypotheses concerning the gonadal and brooding cycles and fecundity of sub-Antarctic and Antarctic Schizasteridae are discussed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Spatial distribution,population dynamics and productivity of <Emphasis Type="Italic">Spisula subtruncata</Emphasis>: implications for <Emphasis Type="Italic">Spisula</Emphasis> fisheries in seaduck wintering areas

Bivalves are important in shallow marine habitats, not at least being the major food resource for seaducks such as the common scoter (Melanitta nigra), thousands of which are wintering on the Western Coastal Banks, near the Belgian-French border (North Sea). Next to this ecological importance, fishable stocks of one of these bivalves, Spisula subtruncata, occur in the area. This study aimed at investigating S. subtruncata’s spatial distribution, population dynamics and productivity and its implications for a sustainable Spisula fishery in seaduck wintering areas. The spatial distribution of S. subtruncata was studied in 1994 and 1997 in two areas of the Belgian Western Coastal Banks. The population dynamics and production were investigated by monthly sampling of two stations between April 1995 and April 1996 and a seasonal sampling between April 1996 and April 1998. Spisula subtruncata had a patchy distribution in the deeper (6 m), fine sandy (200 ± 20 μm) sediments of the Abra alba community, mainly found in the western most part of the Western Coastal Banks. In August 1995, an overwhelming and successful recruitment was observed in this area: local densities were as high as 150,000 ind m⁻². Minor, non-successful recruitments were detected in August 1996 and 1997. Due to space limitation, high densities of S. subtruncata are hypothesized to be responsible for the occurrence of aberrant shapes as observed from August 1996 onwards. Growth was described by a seasonally oscillating version of the von Bertalanffy growth function (VBGF): a growth stop was observed from late autumn till early spring. The VBGF parameters K (growth constant) and L _∞ (asymptotic length) were estimated at 0.7–0.9 and 31–33 mm. A combination of length and individual biomass increment showed: (1) a faster length increment of smaller individuals during the second growing period (catching-up phenomenon), (2) a constant length combined with a decreasing individual biomass during the suboptimal winter periods (except for the first winter, when the individual biomass slightly increased), (3) a positive relationship between the individual biomass decrease and the seawater temperature during the winter periods, and (4) a strong increase of the individual biomass in early spring (April 1997 and 1998) because of gametogenesis, followed by a decrease because of spawning (August 1997). The extremely high total production of the 1995 year class in the tidal gully (Potje) during the study period was estimated at approximately 1,500 g ash-free dry weight (ADW) m⁻² or 600 g ADW m⁻² on average per year. Shellfisheries for S. subtruncata within seaduck wintering areas, such as the Western Coastal Banks, should be carefully deliberated since (1) an important food resource for the seaducks will decrease, (2) the ecologically most diverse and rich macrobenthic A. alba community will be heavily affected, and (3) the recovery of Spisula populations after depletion is expected to be erratic.     

Movements of <Emphasis Type="Italic">Ilyanassa obsoleta</Emphasis> (Gastropoda) on an intertidal sandflat

The gastropod Ilyanassa obsoleta (Say) is native to the east coast of North America where it is locally abundant on sandflats, mudflats, and in saltmarsh creeks. The local disturbances created by snails and their movements affect soft-sediment community composition. Movements of individually marked snails were followed on an intertidal sandflat on Cape Henlopen, Delaware, U.S.A. In June 1991, 1,200 snails that had tested as trematode-uninfected were released and over 5 months 554 were sighted 971 times. Mean daily net distance moved was 1.7 m, but snails often moved 10–20 m day⁻¹ and one snail was 180 m distant after 130 days. Net dispersal of the released population was attained in ≈10 days, by which time, a typical distance from release was 15–20 m. Snails were not found crossing sandbars and most moved away from shore into a tidal gully. In June 1993, 500 snails, both uninfected and trematode-infected, were released at the same position and over 6 months, 350 snails were sighted 949 times. Sandbars were again barriers to movement, but their changed positions allowed wider dispersal. Net dispersal was complete in ≈20 days by which time a typical distance from release was 30–40 m. Mean daily net distance moved was 2.2 m, but within 10 days snails had moved 50–100 m. In both years, following initial dispersal, snails (infected or not) took up random directions from move to move. Infected and uninfected snails dispersed equal distances, but had different mean final dispersal directions. Dispersal of I. obsoleta individuals was extensive and affected by shifting sandbar positions and parasitism. Recognizing this will be important in appreciating the ecological dynamics of this gastropod and in determining its effects on soft-bottom communities.Electronic Supplementary Material Supplementary material is available for this article at     

Life cycle of the jellyfish <Emphasis Type="Italic">Rhizostoma pulmo</Emphasis> (Scyphozoa: Rhizostomeae) and its distribution,seasonality and inter-annual variability along the Catalan coast and the Mar Menor (Spain,NW Mediterranean)

Rhizostoma pulmo is one of the most abundant scyphomedusae along the Mediterranean coasts. To understand changes in the population densities of the medusa stage and its relationship with the benthic stage, we describe all developmental stages from the life cycle of R. pulmo, from the scyphistoma stage to young medusae reared in the laboratory. Mature scyphistomae showed a mean total body length of 1.7 mm and the average tentacle number was 16. Asexual reproduction occurred by lateral budding, podocyst and pedalocyst production. Each strobila released up to 8 ephyrae that had a mean total body diameter of 3.5 mm. Moreover, we also present data on the temporal and spatial distribution of the species in the Catalan Sea and the coastal lagoon on Mar Menor (NW Mediterranean) during the years 2007–2009. In the Catalan Sea, the presence of adult R. pulmo was recorded as extended along the whole coast, but most of the observation was concentrated in the central area; the highest abundances were recorded during the months of July and August. The highest number of observations was detected in 2008 in coincidence with the inter-annual variation observed in the Mar Menor lagoon.     

Age,growth and population structure of <Emphasis Type="Italic">Modiolus barbatus</Emphasis> from the Adriatic

Age, growth and population structure of Modiolus barbatus from Mali Ston Bay, Croatia were determined using modal size (age) classes in length frequency distributions, annual pallial line scars on the inner shell surface, internal annual growth lines in shell sections of the middle nacreous layer and Calcein marked and transplanted mussels. The length frequency distributions indicated that M. barbatus attain a length of ∼40 mm in 5–6 years indicating that a large proportion of the population in Mali Ston Bay is <5 years old. Some mussels of ∼60 mm were predicted to be 14 years old using the Von Bertalanffy growth (VBG) equation. Up to the first 6 pallial line scars were visible in young (<6 years) mussels but in older shells the first scars became obscured by nacre deposition as the mussel increased in length and age. The age of the older shells (>6 years) was determined from the middle nacreous lines in shell section, which formed annually in winter between February and March; the wider dark increments forming during summer (June to September). The oldest mussel, determined from the middle nacreous lines, was >12 years, with the majority of mussels aged between 3 and 6 years of age. The ages of mussels ascertained using the growth lines were not dissimilar to the ages predicted from the length frequency distributions. Age at length curves produced using modal size class data were not different from the data obtained using the pallial scar rings and internal growth lines. Taken together these data suggest that M. barbatus attains a length of 40 and 50 mm within 5 and 8 years, respectively. Eighty one percent of individual M. barbatus injected with a Calcein seawater solution (300 mg Calcein l⁻¹), into their mantle cavity successfully deposited a fluorescent line, which was visible in suitably prepared shell sections under ultra violet light. Incorporation of Calcein into the mussel shells was seasonally variable with the lowest frequency of incorporation in mussels marked in February and recovered in May. Seasonal shell growth was observed with significantly higher growth rates in mussels marked in May and removed in August (ANCOVA, F _3,149 = 23.11, P < 0.001). Mussels (∼18 to 22 mm) marked in May and recovered in August displayed maximal growth rates of >2.5 mm month⁻¹ compared with a mean mussel growth rate of 1.2 ± 0.6 mm month⁻¹. At other times of the year mussel shell growth ranged from immeasurable to 1.48 mm month⁻¹.     

Detrimental effects of the isopod, <Emphasis Type="Italic">Edotia doellojuradoi,</Emphasis> on gill morphology and host condition of the mussel, <Emphasis Type="Italic">Mytilus edulis platensis</Emphasis>

There are many reported associations between mussels and other invertebrates, such as pea crabs, polychaetes, turbellarians and copepods, which live in their mantle cavities. The boundary between commensalism and parasitism is often indistinguishable because of insufficient knowledge or because the interaction is variable. Preliminary evidence led to a closer examination of the relationship between the mussel, Mytilus edulis platensis, and an isopod, Edotia doellojuradoi, previously described as commensalism. Monthly intertidal samples of mussels were taken from September 2004 to August 2005 at Caleta Cordova Norte (45°43′S, 67°22′W) in southern Argentina and assessed for the prevalence and abundance levels of isopods. Mussels with and without isopods were measured, examined for evidence of gill damage and their condition (soft tissue dry weight) was determined. The overall isopod prevalence in mussels was 57.9% and infestation varied with mussel length, with maximum occurence at 30.2 mm (medium-sized mussels). Experimental evidence indicated that the position of the isopod inside the mussel depended on the feeding activity of the mussel. Female isopods were observed grasping the ventral food groove of the gill demibranchs and feeding on the mucous food strand produced by the mussel. Juveniles and males were observed clustered together on the dorsal side of the single female in each occupied mussel, suggesting extended maternal care. Gill damage was observed in 58.2% of mussels at the Argentine site and was significantly associated with isopod occurrence. Categorical regression analysis showed that the most important factor associated with the degree of gill lesions was the number of male and juvenile isopods per mussel, followed by the length of female isopods and the developmental stage of juveniles. Conversely, the degree of gill damage decreased with increasing mussel length. Overall, E. doellojuradoi had a significant effect on mussel condition throughout the year, with low flesh weight in mussels with isopods, except during the austral summer and early autumn. In contrast to previous studies, which concluded that the isopod was a commensal, the present study clearly demonstrates that E. doellojuradoi is a parasite of M. edulis platensis. Other symbiotic interactions formerly classified as commensal might not be innocuous on further investigation, especially if samples are taken at multiple sites and at different times of the year.     

Demography of <Emphasis Type="Italic">Halimeda incrassata</Emphasis> (Bryopsidales,Chlorophyta) in a Caribbean reef lagoon

The fate of 100 marked recruits of the rhizophytic alga Halimeda incrassata was followed in Puerto Morelos reef lagoon, Mexican Caribbean (20°52′N, 86°51′W), until death of the last individual from April 2005–2007. Juvenile mortality was relatively high (19%), the half-life of adult thalli was 13 months and maximal lifespan was 2 years. First age of sexual reproduction was 10 months, but only 6% of the marked thalli reproduced sexually. A subsequent static life-table approach (February–April 2008) at two sites indicated low spatial variation in transition probabilities between the life stages. Recruits were found throughout the year (density 2–11 thalli m⁻²) and were mostly of clonal origin. In a disturbed area, the density of sexual recruits was ~0.01 thalli m². Temporal fluctuations in population size depended on mortality rates, which increased slightly after hurricanes Emily (July 2005) and Wilma (October 2005), but might otherwise be regulated by density-dependent processes.     

Population dynamics,reproduction and growth of the Indo-Pacific horned sea star, <Emphasis Type="Italic">Protoreaster nodosus</Emphasis> (Echinodermata; Asteroidea)

The horned sea star (Protoreaster nodosus) is relatively common in the Indo-Pacific region, but there is little information about its biology. This study of the population biology of P. nodosus was carried out in Davao Gulf, The Philippines (7°5′N, 125°45′E) between September 2006 and May 2008. Protoreaster nodosus was found in sand and seagrass dominated habitats at a mean density of 29 specimens per 100 m² and a mean biomass of 7.4 kg per 100 m², whereas a significantly lower density and biomass was found in coral and rock dominated habitats. Adult specimens (mean radius R = 10.0 cm) were found at depths of 0–37 m, whereas juveniles (R < 8 cm) were only found in shallow sandy habitats with abundant seagrass (water depth ≤2 m). Increased gonad weights were found from March to May (spawning period), which coincided with an increasing water temperature and a decreasing salinity. Density and biomass did not change significantly during reproduction, but sea stars avoided intertidal habitats. All specimens with R > 8 cm had well developed gonads and their sex ratio was 1:1. Protoreaster nodosus grew relatively slowly in an enclosure as described by the exponential function G = 7.433 e^{−0.257 × R} . Maturing specimens (R = 6–8 cm) were estimated to have an age of 2–3 years. Specimens with a radius of 10 cm (population mean) were calculated to have an age of 5–6 years, while the maximum age (R = 14 cm) was estimated as 17 years. Potential effects of ornamental collection on the sea star populations are discussed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Predation on egg capsules of <Emphasis Type="Italic">Zidona</Emphasis><Emphasis Type="Italic">dufresnei</Emphasis> (Volutidae): ecological implications

Among the diverse patterns of energy allocation to the offspring of gastropods, the presence of egg capsules to protect embryos is common. Females of the edible snail Zidona dufresnei attach egg capsules to hard substrates in shallow Argentine Patagonian waters (40°45′S, 64°56′W) during spring-summer. Embryonic development takes about 30 days at 22°C. In this study, three likely capsule predator species and the marks left by each on egg capsule walls were identified in laboratory experiments in February 2010. Abundances of predators and egg capsules with evidence of predation were assessed in the field in the summers of 2010 and 2011. Under laboratory conditions (N = 10 replicates per treatment and control), the predation rate by the chiton Chaetopleura isabellei was the highest (up to 90%), followed by the gastropod Tegula patagonica and the crab Neohelice granulata (~20% each). Nearly 60% of 41 capsules found in the field showed signs of predation. According to the marks identified in the laboratory, C. isabellei was responsible for 79% of this predation, and T. patagonica for the rest. Predation appears to be important during the encapsulated early life and could be an agent for selecting for resistant capsule walls and a relatively shorter development time.     

Multi-year observations on the gametogenic ecology of the Antarctic seastar <Emphasis Type="Italic">Odontaster validus</Emphasis>

This study reports the first multi-year observations on the reproductive patterns for an Antarctic predator/scavenger, Odontaster validus (Koehler 1912). Seastars were collected monthly from a shallow site (15–20 m depth) near the British Antarctic Survey (BAS) Rothera Research Station (Adelaide Island, 67°34′S 68°08′W) from July 1997 to January 2001. Reproductive condition, oocyte size frequencies and spermatogenesis were examined in at least ten seastars each month using histological and image analysis techniques. Gonad indices (GI) and pyloric caeca indices (PI) were also examined in the same samples. Female and male GIs varied seasonally, in parallel with a reduction in the proportion of large oocytes and mature sperm in the gonad in August to mid-October following winter spawning. Despite there being remarkable consistency in the timing of spawning from year to year, differences in the reproductive condition of individuals were apparent. Patterns in the digestive tissues also varied with season, peaking in December and reaching a minimum in February in two of the three study years. This weaker annual pattern may partly reflect the varied diet of this predator/scavenger species, which is not directly dependant on the timing and magnitude of the annual phytoplankton bloom. Pooled oocyte size distributions and residual analysis suggested that oogenesis progressed over 18–24 months, with the largest of the two size classes (maximum diameter = 183 μm) being spawned annually. This pattern of oocyte growth and spawning was previously reported in the early 1960s for an O. validus population from McMurdo Sound, which lies south of Rothera by 10° latitude. The extremely catholic diet of this predator/scavenger suggests the reproductive patterns of the seastar will be less susceptible to changes in food supply compared to polar suspension feeders or deposit feeders. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Estimation of the reproductive output of the burrowing shrimp Callianassa tyrrhena : a comparison of three different biometrical approaches

Reproductive output, as the percentage of the mother weight devoted to egg production, was estimated for the burrowing shrimp Callianassa tyrrhena in wet, dry and ash-free dry weight. Three biometrical approaches were used. First, the relationship between the egg mass and the mother weight was determined. A second approach was to estimate the weight loss of the female caused by oviposition. Similar results were obtained from these methods for dry and ash-free dry weight (about 20 and 35%, respectively), but not for the wet weight estimation. The third approach, based on the weight loss of the ovary, did not reveal a constant value for reproductive output throughout the female size range, although it was found that the ovary loses a constant percentage of its weight during oviposition. This discrepancy is due to the fact that the ovary weight shows positive allometry to the weight of the female body. The comparison of the three methods offers insight into the biological events that are related to ovary maturation and oviposition. It is suggested that molting just before oviposition and its inhibition during the yolk accumulation in the ovary play dominant roles in the expression of the reproductive output in the different approaches used. Received: 17 July 1996 / Accepted: 11 September 1996     

Grazing rates of organic matter and living fungal biomass of decaying Spartina alterniflora by three species of salt-marsh invertebrates

 The pathway for the flow of salt-marsh grass production into marsh food-webs is still not well defined. We compared the abilities of three marsh macroinvertebrates [salt marsh periwinkles, Littoraria irrorata (Say) (=Littorina irrorata), salt-marsh coffee-bean snails, Melampus bidentatus (Say); and a talitrid amphipod, Uhlorchestia spartinophila Bounsfield and Heard] to access standing-dead leaves of smooth cordgrass (Spartina alterniflora Loisel). The invertebrates were incubated with naturally-decaying leaves, and the rates of removal of organic matter and living fungal biomass (ergosterol) were measured. The impact of invertebrate activity upon fungal growth rates was measured as rates of fungal-membrane synthesis (incorporation of radioacetate into ergosterol). The removal rates of organic leaf biomass per mg individual biomass were highest for amphipods (700 μg mg⁻¹ d⁻¹) and lowest for periwinkles (90 μg mg⁻¹ d⁻¹), but the relatively large biomass of the snails made their removal rates per individual greater than those of amphipods. Net removal of ergosterol by all three invertebrates was >50% for yellow-brown (early-decay) leaf blades. For fully-brown (advanced-decay) blades, >50% removal of ergosterol was found only for periwinkles; exposure to coffee-bean snails and amphipods resulted in a net ergosterol reduction of ≤20%. The lower net reduction of living fungal biomass by coffee-bean snails and amphipods may have been due to fungal-growth stimulation (2.3-fold stimulation in coffee-bean snails and 1.5-fold stimulation in amphipods). Grazing by periwinkles did not stimulate fungal growth, possibly because of its high intensity. Grazing by these three salt-marsh shredders may affect marsh-grass shoot-decay in different ways. Periwinkles may abbreviate the period of fungal production, and incorporate the decaying material relatively quickly into snail biomass and fecal-pellet rain to the sediments. Coffee-bean snails and amphipods may enhance and prolong fungal production, along with the formation of fecal-pellet rain. All three invertebrates fed preferentially on leaf blades rather than leaf sheaths, and feeding rates of gastropods were higher during the night than during the day. Received: 25 November 1998 / Accepted: 4 November 1999     

Lipid and protein utilisation during early development of yellowtail kingfish (<Emphasis Type="Italic">Seriola lalandi</Emphasis>)

The pelagic yellowtail kingfish Seriola lalandi has become a target species for aquaculture in Asia and Australasia. Australasian production is reliant on larviculture from eggs of captive brood stock; however, knowledge regarding the nutritional requirements of larvae of this species is still scarce, particularly in relation to lipids. As a first step in establishing these requirements, eggs and larvae from captive S. lalandi brood stock were examined for differences in total protein, total lipid and lipid classes between individual spawning events, over the spawning season, and during larval development from fertilisation to 15 days post hatch. Results indicate that total protein egg⁻¹ varied significantly between individual spawning events within a season, but neither total lipid nor total protein egg⁻¹ varied significantly across the spawning season. Brood stock egg lipids were made up of approximately 60% phospholipid, 25% wax and/or sterol esters (WE), 15% triacylglycerol (TAG), and small amounts of sterols and free fatty acids. During the early larval period, both WE and TAG were utilised concurrently for energy. The larvae experienced very high mortality around 5–7 days post hatch, which coincided with very low levels of all neutral lipid classes. Although many other factors may also influence larval mortality, these results indicate that lipid provisioning may be an important factor in larval survival during the critical period around first-feeding in this species. Examination of ratios of TAG:ST, often used as a condition index in fish larvae, suggested that some of the larvae were suffering from starvation. However, as egg-derived WE appears to provide a significant source of energy during the early larval period in S. lalandi, it is suggested that WE should be included in any index of larval nutritional state.     

Size and temperature-dependent variations in intermolt duration and size increment at molt of Northern Shrimp, Pandalus borealis

Growth of Pandalus borealis post-larval stages was measured in relation to size and temperature. Growth characteristics, including intermolt period (IP), molt increment (MI) in size and mass, and tissue allocation in juvenile, male, and female shrimp, were evaluated at 2, 5, and 8°C, the temperature range where this species is generally found in the Northwest Atlantic. Significant variations in growth were associated with temperature and shrimp size. IP (days) increased significantly with shrimp size and was inversely related to temperature. Size (cephalothorax length in mm) and temperature effects were best described by IP = 10^{(0.67 log(CL) − 0.06 T − 1.34)}. The pronounced effect of temperature on IP while MI_S changed little indicated that the main influence of temperature on growth rate of P. borealis was through IP. Specific growth rate (SGR_S) decreased rapidly with size to near zero values in females. Overall, juveniles were much more sensitive to temperature variations than adults, suggesting that temperatures encountered during the juvenile stage will largely influence the growth trajectory of the population.     

Seasonal and interannual variations in size,biomass and chemical composition of the eggs of North Sea shrimp, <Emphasis Type="Italic">Crangon crangon</Emphasis> (Decapoda: Caridea)

In the shrimp Crangon crangon, an important fishery resource and key species in the southern North Sea, we studied temporal variations in size, biomass (dry weight, W) and chemical composition (C, N, protein and lipid) of eggs in an initial embryonic stage. Data from 2 years, 1996 and 2009, consistently revealed that egg size and biomass varied seasonally, with maxima at the beginning of the reproductive season (January), decreasing values throughout spring, minima in June–July, and a slight increase thereafter. This cyclic pattern explains why “Winter eggs” are on average larger and heavier than “summer eggs”. Using a modelling approach, we estimated the duration of oogenesis in relation to seasonally changing seawater temperatures. According to an additive model of multiple explanatory variables, the C content per newly laid egg showed in both years a highly significant negative relationship with day length (r2 = 0.38 and 0.40, respectively; P < 0.0001), a weak positive relationship with temperature (r2 = 0.08 and 0.09; P < 0.05), and a weak negative relationship with phytoplankton biomass (r2 = 0.11 and 0.12; P < 0.05) at the estimated time of beginning oogenesis. Phenotypic plasticity in initial egg size and biomass is interpreted as an adaptive reproductive trait that has evolved in regions with strong seasonality in plankton production and periods of larval food limitation. In contrast to biomass per egg, the percentage chemical composition remained similar throughout the reproductive period. Both the absolute and percentage values also showed significant interannual variations, which caution against generalizations based on short-term studies of reproductive traits of C. crangon and other species of shrimp.     

Size-dependent photosynthetic performance in the giant clam <Emphasis Type="Italic">Tridacna maxima</Emphasis>, a mixotrophic marine bivalve

Giant clams form a symbiosis with photosynthetic algae of the genus Symbiodinium that reside in clam mantle tissue. The allometry of symbiont photosynthetic performance was investigated as a mechanism for the increasing percentage of giant clam carbon respiratory requirements provided by symbionts as clam size increases. Chlorophyll fluorescence measurements of symbionts of the giant clam Tridacna maxima were measured during experiments conducted in September of 2009 using specimens 0.5–200 g tissue wet weight (3–25 cm long), collected from waters around southern Taiwan (N 21°36′, E 120°47′) from July to August of 2009. Light-dependent decreases in effective quantum yield (∆F/F _m′) calculated as the noontime maximum excitation pressure over PSII (Q _m), relative electron transport rates (rETR), and dark-adapted maximum quantum yield (F _v/F _m) all varied as a quadratic function of clam size. Both Q _m and rETR increased as clam size increased up to ~10–50 g then decreased as clam size increased. F _v/F _m decreased as clam size increased up to ~5–50 g then increased as clam size increased. Chlorophyll fluorescence measurements of rETR were positively correlated with gross primary production measured during chamber incubations. Overall, symbionts of mid-sized clams ~5–50 g exhibited the highest light-dependent decreases in effective photosynthetic efficiencies, the highest relative electron transport rates, and the lowest maximum photosynthetic efficiencies, and symbiont photosynthetic performance is allometric with respect to host clam size.