Betina J. Lomovasky

Growth and production of the venerid bivalve Eurhomalea exalbida in the Beagle Channel, Tierra del Fuego

Growth, mortality and productivity of the hard clam Eurhomalea exalbida from Ushuaia Bay, Beagle Channel, were investigated. The parameters of the von Bertalanffy growth function were estimated to be Hl = 74 mm, K = 0.18 y � 1 ,t 0 = 0.15 y. Maximum individual production amounted to 2.74 g shell-free wet mass (SFWM) at 49.5 mm shell height. Animals between 40 mm and 70 mm shell height contributed most to overall population somatic production P of 134 g SFWM m � 2 y � 1 . Mean annual biomass B amounted to 1123 g SFWM m � 2 y � 1 . Annual P/B ratio and mortality rate Z were estimated to be 0.12 y � 1 and 0.14 y � 1 , respectively. Slow growth and low turnover make this population less suitable for sustainable commercial exploitation. D 2002 Elsevier Science B.V. All rights reserved.

Individual age and connective tissue lipofuscin in the hard clam Eurhomalea exalbida

In the hard clam Eurhomalea exalbida, autofluorescent granules were detected in high concentrations in the connective tissue around the intestine and in other tissues. Autofluorescence combined with Sudan black B and PAS positive reactions suggested that these granules were lipofuscin-like. The concentration of this material in the connective tissue (CT) around the intestine was quantified by image analysis and expressed as total area fraction occupied by lipofuscin granules. Lipofuscin concentration was distinctly better related with individual age as determined from stable isotope-validated shell growth bands than with any morphometric parameter. This relationship was described best by a Gompertz model: Lipofuscint=24.79e−e−0.029(Age t−58.578) (N=38; rnl2=0.882). Age was predicted from lipofuscinCT concentration by a von Bertalanffy model: Age t=68.00(1−e−0.146(Lipofuscint+0.028))0.664 (N=38; rnl2=0.933). Our findings suggest that lipofuscinCT concentration in E. exalbida is a function of individual age. If this holds true for bivalves in general, lipofuscin may be a suitable proxy for age in species with less clear shell growth band patterns.

Habitat structure is more important than nutrient supply in modifying mussel bed assemblage in an upwelling area of the Peruvian coast

Upwelling intensity modifies coastal primary production and influences individual traits of habitat-forming species. Along the Peruvian coast, beds of the mytilid Perumytilus purpuratus provide structurally complex habitats that harbour many organisms. We predict that in the nutrient-rich system of Central Peru, the modification of structural complexity would have stronger effects on the Perumytilus community than nutrient addition. We experimentally examined the effects of nutrient addition on the Perumytilus-dominated assemblage and we evaluated the potential effect of varying shell size on the Perumytilus-dominated assemblage. Nutrient addition to the mussel bed with slow-release fertilizers caused no changes in the total macro- and microalgal biomass and did not affect abundances or composition of the assemblage. To explore the effect of structural complexity on the Perumytilus assemblage, we manipulated mussel size with experimental bags containing small and large individuals. Predators, grazers and mobile organisms were more abundant among smaller mussels, with smaller gap volume, whereas the barnacle Jehlius cirratus was more abundant on larger mussels. In conclusion, point-source nutrient addition to the mussel bed did not enhance primary production. However, the modification of structural characteristics related to mussel size induced changes in the faunal assemblage. Thus, it seems that in this nutrient-rich system, nutrient enhancement would not significantly affect Perumytilus and its assemblage, whereas structural habitat seems to play an important role in shaping this community.

Grazing effects of the periwinkle Echinolittorina peruviana at a central Peruvian high rocky intertidal

Echinolittorina peruviana is the most common gastropod in the high intertidal zone of Peru, representing more than 80% of the individuals present at that zone. Experimental removal of snails was used to evaluate their effects on (a) abundance of epilithic biofilm, (b) barnacle recruitment, and (c) abundance of macroalgae under “normal” conditions of the El Niño Southern Oscillation (ENSO). Experiments were carried out from October 2005 to April 2007 at two intertidal levels of a semi-protected rocky shore of central Peru. Results demonstrated that E. peruviana is able to control biofilm abundance and barnacle recruitment at both heights investigated, with marked effects in the lower zone. Erect macroalgae (Ulva spp. and Gelidium spp.) were less affected by grazing; but negative effects were observed on macroalgal crusts. Season and physical stress seem to play a more important role in the abundance of macroalgae in the high intertidal. Our results are similar to those reported elsewhere for high shore littorinids and represent baseline data to understand how the role of intertidal consumers will vary under the cold (La Niña) and warm (El Niño) phases of ENSO on these shores.

The reproductive cycle of Eurhomalea exalbida (Chemnitz, 1795) (Bivalvia: Veneridae) in Ushuaia Bay (54° 50' S), beagle channel (Argentina)

Summary The reproductive cycle of Eurhomalea exalbida (Chemnitz, 1795) in Ushuaia Bay, Beagle Channel, was studied from October 1998 to December 1999. Clams were collected monthly by SCUBA diving at 3–5 m water depth. The degree of sexual maturity was determined histologically (n=338). The sex ratio was 1:1 (Chi-squared p>0.05). First sexual maturity occurred at 39 mm shell height in males and 40 mm in females (i.e., 4 years of age). Five distinct histological stages of sexual maturity could be established in males: (1) early active, (2) late active, (3) ripe, (4) partially spawned with recovery and (5) spent. Females had oocytes ranging from small and immature to large and fully developed in their ovaries throughout the year. Since we could not classify reproductive stages based on a qualitative histological scale of sexual maturity, quantitative measures using an image analyser were used. In males a high percentage of mature individuals were present between January and August. The percentage of early active and partially spawned individuals was highest in November 1998 (70%) and 1999 (60%). In females, the mean number of developed oocytes per unit of gonadal area in a cross section, the mean diameter (minor axis) of oocytes, and the percentage of gonadal area occupied by oocytes were lowest in November, indicating a spawning peak. These results indicate synchronous gonadal development and spawning in males and females. The more intensive spawning activity in November coincides with the higher biomass and production of phytoplankton in spring.

Annual shell growth increment formation in the deep water Patagonian scallop Zygochlamys patagonica

Abstract The Patagonian scallop Zygochlamys patagonica occurs on the SW Atlantic shelf of South America between 36°S to 55°S in beds at depths around 100 m. Stable oxygen and carbon isotope ratio analysis in scallops from four large beds (Uruguay, 36°17′S, Reclutas, 39°20′S, Tango B, 42°30′S, and Beagle, 55°10′S) in combination with condition indexes and oceanography date strongly suggest that shell growth increments in this species are formed annually. Most translucent growth bands coincide with low values of both δ13C and δ18O (i.e., they are formed at times of high remineralization activity and of higher water temperature). This pattern is consistent throughout the distributional range. Given the specific Argentinean shelf oceanography, higher temperatures at this depth occur during austral autumn—beginning winter in the region of Reclutas and Tango B but during summer–autumn at the northern and southern limit of the distributional range. Year-round investigations at Reclutas beds indicate that translucent shell growth bands coincide with a pause in somatic growth during austral winter, when energy investment is shifted from somatic growth to gonad development.

Effects of epibiotic Enteromorpha spp. on the mole crab Emerita analoga in the Peruvian central coast

Epibiotic interactions between macroalgae and crustaceans have rarely been described. We examined the interaction between the mole crab, Emerita analoga and the opportunistic algae Enteromopha spp. in a sandy beach of the central coast of Peru. Enteromorpha spp. was found fouling the carapace of the mole crab that provides the only stable substrate to spore settlement in the beach environment. Epibiosis prevalence was up to 2.1%, and affected mainly larger, ovigerous females. Prevalence presented a seasonal pattern, with peaks during summer. Mole crab body condition was higher when fouled, whereas fecundity was not affected. Fouled mole crabs burrowed at lower speed, which was reversible by the removal of epibiotic algae. The burrowing depth was not affected by epibiosis. Contrary to the expected, the effects of algal epibiosis on demographic and life history parameters of mole crabs, with the exception of body condition, were mainly neutral but important on behavioural traits.

REPRODUCTIVE CYCLE AND ENERGY CONTENT OF TAWERA GAYI (HUPÉ 1854) (BIVALVIA: VENERIDAE) AT THE SOUTHERNMOST LIMIT OF THEIR DISTRIBUTION RANGE

Abstract The reproductive cycle and the energy content of soft parts of Tawera gayi were studied monthly from August 2001 to July 2002 in Ushuaia Bay, Beagle Channel. The degree of sexual maturity was determined histologically. The sex ratio was significantly different of 1:1 (896 females, 796 males, χ2-test, P < 0.05). First sexual maturity occurred at 12 mm shell height in both sexes. In males the reproductive cycle was determined analyzing the monthly percentage of gonadal stages. High percentages (85%–100%) were mature (ripe stage) during a large part of the year (March to September) and in October the 100% of individuals were partially spawned with recovery. An image analyzer was used to determine quantitatively female reproductive cycle. The percentage of gonadal area covered by oocytes was lower in December. The mean number of mature oocytes (diameter >40 μm) by gonadal area and the mean diameter of oocytes reached the lower values during October, November, and December, indicating a spawning peak. This more intensive spawning activity coincides with the phytoplankton bloom in spring. The energy content of soft parts was measured using a microbomb calorimeter in monthly samples during a year. The mean energy content in both sexes was significantly different reaching 20.95 kJ/g AFDW for females and 21.39 kJ/g AFDW for males. The relative condition index attained the lower values in August, September, and October. The monthly values of the energy content did not show significant differences in both sexes. Results of this study indicate that notwithstanding T. gayi lives in a markedly seasonal environment as Subantarctic waters of Beagle Channel shows a protracted gamete production with a principal spawning episode and small pulses of evacuation during the rest of the year.

Coastal upwelling may overwhelm the effect of sewage discharges in rocky intertidal communities of the Peruvian coast

In coastal productive environments, such as upwelling systems, sewage effluents might represent an important input of nutrients affecting intertidal community development and structure. Using descriptive and experimental approaches, the community spatial variation and early succession in relation to a point-source effluent discharge in a rocky intertidal of an upwelling affected area (Ancon Bay, Peru) was analysed. The relative contribution of herbivory to the observed patterns was also analysed. Dissolved nutrient concentrations, macroalgal isotopic signatures and N content revealed a significant input of nutrients at the outfall, although this contribution was not reflected in the algal assemblage, but in higher abundances of mytilids, ophiuroids and limpets. Cover of most sessile organisms (biofilm, Ulva spp., mytilids and barnacles) varied among sites throughout early succession, and grazers only enhanced the cover of the red algae Gelidium spp. Differences in succession patterns could not be attributed to discharge effects. The results of this study suggest that the community development is bottom-up controlled in the entire bay, which is likely to be due to the upwelling that operates at larger temporal and spatial scales. If so, nutrient input derived from coastal upwelling may sometimes overwhelm the role of anthropogenic nutrient loadings in shaping intertidal communities.

Variations in the Biological Characteristics of the Patagonian Scallop (Zygochlamys patagonica) Across the Argentine Shelf Break Front

ABSTRACT Oceanographic fronts and their associated physical processes create strong spatial patterns of food availability that may influence the metabolic processes of bivalves located within these areas. To investigate this prediction, we used mass-size relationships, condition indices, and carbon (C) and nitrogen (N) stable isotopes to evaluate how the biological characteristics of the Patagonian scallop (Zygochlamys patagonica) are influenced by the Shelf Break Front (SBF) and the surrounding chlorophyll a concentration (CSAT). Scallops from 2 transects across the front (38–39°S, 55–56°W, southwest Atlantic Ocean) were sampled with a nonselective dredge in October 2005. The results show that the SBF position, estimated from satellite-derived sea surface temperature, was more stable than the CSAT maximum concentrations. If muscle tissue is considered a better indicator of food shifts as previous studies indicate, scallops located far from the front have lower C isotopic signatures and C/N ratios than scallops located near the front. However, the lack of a shift in scallop organ conditions suggest that spatial differences in food supply are not strong enough during the time of year we sampled to impact scallop development, as may happen at a seasonal scale. Our results show that complicated interactions exist between oceanographic structures, food supply, and scallop life history characteristics.