Survival and reproduction of the mussel Xenostrobus securis (Lam.) (Mollusca: Bivalvia: Mytilidae) in a Western Australian estuary

Summary

The Swan estuary is subject to extreme temporal and spatial variations in salinity. Downstream populations of the mussel Xenostrobus securis (Lamarck, 1819) are exposed to a seasonal range from 1·5‰. Cl to 20·0‰. Cl. In summer the estuary is progressively filled with saline water from the sea; in winter it is flooded by fresh river run-off water from the heavy and concentrated winter rains. The autumn fall in salinity is usually very rapid and constitutes a severe physiological shock for organisms inhabiting the estuary.

The physiography and hydrology of the Swan estuary are described. Experiments are reported on the salinity tolerance and behavioural responses to salinity stresses of adult mussels and larval stages.

Adult mussels show no ability to osmoregulate (except possibly at very low salinities). They can tolerate environmental chlorinities at least as high as 31‰. Cl and can withstand sudden dilutions from at least 18‰. down to 1‰.. They are capable of survival at 1‰. for many months.

Closure of the shell valves in response to sudden dilutions of the medium is a behavioural mechanism minimizing physiological shock. Adult mussels remain inactive with the valves closed indefinitely at chlorinities below 2‰.. However, the internal body fluids of the mussels become isotonic with the medium after a few days. Adult salinity tolerance and behavioural responses are sufficient to meet the conditions occurring in the estuary, and adult salinity tolerance is unlikely to limit distribution of the species.

In laboratory dishes eggs may be successfully fertilized, and normal cleavage occurs in water between about 8 to 9‰. and 17·5‰. Cl. This tolerance range of developing larvae imposes upstream limits on the distribution of the mussel and precludes any possibility of larval dispersal between adjacent estuaries by way of the sea.     

Home-range fidelity and use of historic habitat by adult Colorado pikeminnow ( Ptychocheilus lucius ) in the White River, Colorado and Utah

Twelve wild adult Colorado pikeminnow ( Ptychocheilus lucius ), captured in the tailwaters of Taylor Draw Dam on the White River, Colorado, were implanted with radio transmitters and their movement patterns monitored from 1992 to 1994. The spawning migration of these fish was extensive. In 1993, the only full year of the study, the fish migrated an average of 658 km from the White River to spawning sites in the Yampa or Green rivers and back to the White River. Eight of these fish were translocated in the river upstream of the dam in April 1993. These fish and the 4 others below the dam remained in the river until May 1993. All 12 had migrated down the White River to spawning sites in the Green and Yampa rivers by July 1993. The fish that were located above the dam successfully passed over the dam during their downstream migration. Seven fish migrated upstream toward the Yampa River Canyon spawning site and 5 migrated downstream toward the Green River Desolation/Gray Canyon spawning site. Five of 7 Yampa River fish were found at the spawning site. The other 2 were found 5-8 km downstream of the site. One of 5 Green River fish was found at the spawning site, the other 4 between 16 and 62 km upstream of the site. All fish migrated back to the White River by August 1993 and were found near the dam by October 1993. Two fish were recaptured and translocated above the dam in September 1993. Five fish were located below the dam and 2 above the dam in April 1994. By July 1994 seven of the same fish that had migrated toward the Yampa River in 1993 were found at the Yampa Canyon spawning site. At the same time, 3 of 5 fish that migrated toward the Green River in 1993 were found at the Desolation/Gray Canyon spawning site. This included 2 fish that had been found upstream of the site in 1993. The 12 fish traveled an average of 6 km d -1 (range: 4-10 km d -1 ) during the migration period from May through October 1993. Generally, fish moved faster to the spawning site than back from the site to the White River. These fish moved very little within their home ranges in the White River. Six fish tagged in 1992 moved only 0.1-2.3 km in the tailwater reach below Taylor Draw Dam from September 1992 through April 1993. All fish, after their spawning runs, had moved up to or near the dam by October 1993. These fish were not tracked again until April 1994. Their movement patterns in April 1994 were similar to those observed in April 1993. The greatest amount of fish movement in the White River was displayed by the 8 fish placed above Taylor Draw Dam in April 1993 and the 2 placed in Kenney Reservoir in September 1993. They moved 1.1-40.6 km in the river before and after their spawning migration in spring and autumn 1993. These spawning migrations suggest that adult Colorado pikeminnow in the White River were recruited from both Green and Yampa river spawning populations and were presumably imprinted to these respective spawning sites. Those fish placed above Taylor Draw Dam established home ranges in habitats previously occupied by Colorado pikeminnow before the dam was completed. They remained there until they migrated downstream during the spawning period. Although we did not study fish passage, our study demonstrates that adult Colorado pikeminnow will use habitat if access is provided. Translocation of wild adult fish into historic but unoccupied habitats may be a valuable recovery option.     

Population and reproductive biology of the mud crab,Macrophthalmus hirtipes (Jacquinot, 1853) (Ocypodidae), from marine and estuarine habitats

Summary

Monthly samples of the burrowing mud crab, Macrophthalmus hirtipes (Jacquinot 1853) were collected from February 1978 to April 1979 from a marine inlet, Governors Bay (43°38′S, 172°39′E) and from the Avon-Heathcote Estuary (43°33′S, 172°44′E), New Zealand. The estuarine population was generally unimodal and had an annual cycle of population change sustained by a concentrated summer recruitment. In contrast, the bay population was unimodal and bimodal at different times, and recruitment occurred thoughout the year with no clear peak. Both populations had equal sex ratios and were dominated by immature individuals (crabs?10·0 mm carapace width). Estuarine crabs were generally smaller than marine crabs.

At both sites, ovigerous females were found from late May to early March; the smallest egg-bearing female measured CW 10·0 mm at the estuary and CW 10·5 mm at the bay. Cycles of ovarian and embryological development were similar at the two localities. Three peaks of egg oviposition occurred within one breeding season and mature females were capable of producing successive broods. Fecundity was related exponentially to female carapace width and did not alter during the breeding season. Estuarine females carried more eggs than marine females of similar size. Egg volume was related to time of oviposition and eggs laid at the start of the breeding season were significantly larger than those deposited during the second half; however, estuarine eggs showed less reduction in size at this time than did marine eggs.

Estuarine sediments had higher levels of chlorophyll ‘a’, ATP, and microorganism activity and productivity than marine sediments. As M. hirtipes is a detritus feeder, the differences in food resources are believed to account for the elevated fecundity of estuarine crabs. At the bay, salinities were high with little tidal and seasonal variation, whereas in the estuary sea water was diluted significantly both daily and seasonally. The differences in salinity characteristics between the sites may be affecting larval distribution; recruitment in the estuary was concentrated to the summer and in the bay it was almost continuous.     

XLIX.—A list of New Zealand Heteroptera with the description of a remarkable green Aradid representing a new genus

Summary

Christchurch Harbour is the lagoonal estuary of the Rivers Avon and Stour. Due to the low tidal range much of it remains submerged at low water. The microfauna living on the bottom sediment includes Foraminiferida and Thecamoebina. The latter are normally restricted to the lower reaches of rivers but when low salinity conditions prevail in the lagoonal part of the estuary they have a wider distribution. It is shown that a number of species will tolerate brackish water if the calcium content is less than 1 mg-atom/l. Most species show seasonal changes in abundance related partly to temperature changes. It is suggested that fossil Thecamoebina may be more common than has previously been recognized, especially in Pleistocene and Holocene deposits, and that they would be useful paleoecological indicators.     

Lahontan cutthroat trout ( Oncorhynchus clarki henshawi ) spawning and downstream migration of juveniles into Summit Lake, Nevada

The only remaining self-sustaining native population of lacustrine Lahontan cutthroat trout ( Oncorhynchus clarki henshawi ) not affected by nonnative salmonids is in Summit Lake, Humboldt County, Nevada. Annual spawning runs in 1993 and 1994 were monitored at a fish trap on Mahogany Creek, the only spawning tributary for Summit Lake. Number of spawners was similar in both years, with 1290 upstream migrants observed in 1993 and 1255 in 1994. In 1993, 137 postspawners (10.6% of upstream migrants) returned to the lake, and in 1994, 434 postspawners (34.6% of upstream migrants) returned downstream through the fish trap. Two distinct groups of subadult Lahontan cutthroat trout were observed moving downstream in 1994. The first group passed downstream between 27 April and 29 July and included 1188 fish (average fork length = 90 mm). Between 1 August and 31 October, 1160 fish (average fork length = 42 mm) moved downstream. Size differences of these 2 groups suggest that the 1st group comprised fish that had overwintered in Mahogany Creek, while the 2nd group were probably young-of-the-year.     

Two species of caligid copepods (Crustacea) parasitic on marine fishes of Venezuela,with discussion of Metacaligus Thomsen, 1949

Summary

O, I and II group flounders showed a regular increase in length and weight between April and September, but did not grow during the winter months. These immature fish showed highest condition factors and calorific values in summer and lowest in winter. III and ? IV group flounders had highest condition factors and calorific values in winter prior to spawning and lowest when they returned to the estuary as spents in April. Males matured towards the end of their third year and females towards the end of their fourth. Gonad development started in October and peak gonad weights were attained in November (males) and February to April (females).

Diurnal variations in the numbers of fish were very marked on the Sleek of Tarty where larger numbers were caught at night. Little diurnal variation was noticeable on the Forvie Bank mud flat.

Largest numbers of flounders were recorded between May and September when the population was 50–100 times larger than the winter low (January to March). Estimates of the total population size are given, based on observed densities on underwater transects.

Seasonal changes in the population of flounders on the intertidal mud flats were influenced by four major migrations:

• (1)A spring immigration (April and May) of immature (except the O group) and spent fish, the spent females being present in significantly greater numbers than males.

• (2)O group flounders entered the estuary in late June early/July, approximately two months later than the immigration of O group plaice.

• (3)A proportion of III and ? IV group flounders left the mud flats in July and tagging data suggested that they left for the sea.

• (4)The winter emigration of all age classes started in October and continued through the winter, leaving a small population composed mainly of O group and maturing fish. Cormorants preyed mainly on I and II group flounders in winter and probably accounted for the low numbers of these age groups at this time.

     

The carboniferous fossil lycopod Ulodendron landsburgii (Kidston) comb. nov.

Summary

A data gathering system controlled by microcomputer, recording swimming activity, is described. Prior to the breeding season, in a normal day and night regime, the delta prawn Palaemon longirostris shows a circadian swimming rhythm with peak activity at night. As the ovaries ripen and the prawns mate there is evidence of an additional tidal swimming rhythm. Females carrying eggs revert to nocturnal circadian swimming only. In ovigerous females the circadian swimming rhythm persists in continuous darkness with a free-running period of between 22 and 23 hours. The closely related and sympatric species Palaemonetes varians has similar patterns of swimming behaviour. It is suggested that the absence of newly hatched palaemonid larvae in the estuary is a result of the interaction of these adult swimming patterns with tidal flow and nocturnal hatching.     

Invertebrate communities,sediment parameters and food availability of intertidal soft-sediment ecosystems on the north coast of British Columbia,Canada

ABSTRACT

The Skeena River estuary supports commercial and culturally important salmon fisheries. However, considerable development has occurred in the area, and more has been proposed. If anthropogenic development degrades this critical habitat, the Skeena salmon run, that every year contributes $110 million to local economies, may be negatively impacted. Benthic invertebrates are common indicator species, as they often respond to disturbances before commercial species, warning of potential impacts. Unfortunately, invertebrates in the Skeena estuary have not been extensively studied, and we lack the detailed understanding of their community structure and dynamics for them to serve as indicator species in this region. Therefore, present conditions of the Skeena estuary are established here (invertebrate community, sediment conditions and food availability), in order to provide the data required both to anticipate changes associated with potential anthropogenic disturbances and to detect changes in this system if development occurs.     

Notes on the occurrence and biology of Xenoclarias Greenwood (Siluriformes: Clariidae) in Lake Victoria,East Africa

Summary

Xenoclarias inhabits the deeper (>50 m) waters of Lake Victoria. Specimens captured in a bottom trawl ranged in size from 10–22 cm TL (mode, 15–18 cm) and females grew to a larger size than males. Length-weight relationships between sexes were different only in the Kenya waters and resulted in significantly different KTL. Based on gonadal stages, Xenoclarias matured between 14–16 cm (age 1). Fecundity of 6 specimens (Stage VI) ranged from 744–1357 (mean 1009) and egg size from 1·45 to 1·98 mm (mean 1·79 mm).

Based on gravid and spawning females, Xenoclarias spawned prior to the rainy season (January–March) in Kenya and Uganda waters. During periods of increased reproductive activity females were consistently more numerous in samples (2:1) than males. Local meteorological and hydrological conditions may explain the apparently different spawning season in Tanzania waters of the Lake. This genus of small fish is not affected by the artisinal gillnet fishery but may be by the expansion of a bottom trawl fishery in Lake Victoria.     

Responses of pink shrimp Farfantepenaeus brasiliensis (Latreille, 1817) (Penaeoidea) to physico-chemical parameters in a marine protected area: changes in abundance and distribution after 20 years

ABSTRACT

This study analysed the influence of temperature, salinity and sediment texture on the distribution of pink shrimp juveniles (Farfantepenaeus brasiliensis) over a 20-year period. The shrimps were sampled monthly in Fortaleza Bay, north coast of São Paulo, Brazil, in November 1988–October 1989 (period 1) and then 20 years later in November 2008–October 2009 (period 2). In period 1 we captured 80 juveniles whereas in period 2 we captured 226. The abundance and distribution of F. brasiliensis seemed to be modulated by temperature and sediment texture, along with the fishing activity. The management strategies established between the samplings might have been responsible for the higher abundance of juveniles seen during period 2. The strategies included the limitation of fishing effort, regulation of fishing equipment and the establishment of environmental protection areas and temporary fishing ban.     

Not every drought is bad: quantifying reproductive effort in the harlequin frog Atelopus laetissimus (Anura: Bufonidae)

Atelopus laetissimus is an endemic and threatened harlequin frog from the high mountain forests of Sierra Nevada de Santa Marta, Colombia. Knowledge of its reproductive biology is essential for understanding the intraspecific interactions that can help the conservation of Atelopus species. We quantified the energy, measured in body weight, invested by males and females of A. laetissimus for reproduction, and how this energetic investment is related to the survival of individuals and rainfall conditions in habitats during two years (2014 and 2015). Our results show plasticity in terms of reproductive phenology linked to rainfall with short- and long-duration breeding strategies. The first year of this study, 2014, had a precipitation level in accordance with the annual averages at the area. During this time frogs exhibit a short breeding period. Contrary to 2014, 2015 was a year with little precipitation, below the annual averages, which probably facilitated the females’ quick spawning in the creeks and a consequent reduction in the duration of amplexus and low breeding efforts by males. This, in turn, was related to a long breeding period that favors the survival and reproduction of males during the entire year. In 2014 we found a decrease of 25% to 30% body weight of potentially reproductive males, which may be attributed to a prolonged duration of amplectant events.     

The occurrence of Podocotyle atomon (Rud., 1802)(Digenea), Bothriocephalus scorpii (Müller, 1776) (Cestoda), Contracaecum clavatum (Rud., 1809) (Nematoda) and Echinorhynchus gadi Zoega,in Müller, 1776 (Acanthocephala) in the five-bearded rockling,Onos mustelus (L.)

Summary

The variation in the incidence and intensity of infestation of the five-bearded rockling, Onos mustelus (L.) with Podocotyle atomon, Bothriocephalus scorpii, Contracaecum clavatum and Echinorhynchus gadi has been studied for a period of one year, on a shore at Mumbles Head, Swansea.

There is a general increase in the incidence and intensity of infestation by P. atomon and C. clavatum with increase in the length (age) of the host. With E. gadi and B. scorpii, however, infestation decreases in the larger fish.

The seasonal variations in the incidence and intensity of infestation with these parasites are influenced by tidal fluctuations, temperature and by the feeding habits and breeding cycle of the fish.

The frequency distribution of parasite specimens is also described and discussed.     

Aspects of the life history and reproductive biology of the introduced terrestrial amphipod Arcitalitrus dorrieni (Hunt) at two sites in Co. Galway,Ireland

The reproductive biology of Arcitalitrus dorrieni (Hunt) was investigated over a period of 25 months at a deciduous and a coniferous forest site at Kylemore, Co. Galway, Ireland. The species has an annual, univoltine reproductive cycle with ovigerous females found throughout the year. Recruitment of juveniles begins in May–June with a peak of reproductive activity in August–September. The populations at each site show a bimodal size-distribution for most of the year, with a unimodal distribution in March, April and May. Mortality occurs exponentially, and the life-span is 20–22 months. Mean fecundity was 5·65 eggs per female and was dependent on female size, egg size and brood stage. Brood mortality was 37·5% at Addergoole and 29·8% at Tullywee Bridge.     

Notes on the ecology of the Clwyd estuary,north Wales

Summary

No previous ecological work having been attempted in the Clwyd estuary, a 13 month survey was made to assess conditions and provide basic data. A notable feature of this estuary is its physical construction, which, being long in relation to its width, appears to limit the diversity of the benthic fauna. Comments are made on the five most abundant species, Macoma balthica, Scrobicularia plana, Nereis diversicolor, Corophium volutator and Gammarus duebeni. The effect of changing climatic conditions on one species, Gammarus duebeni is described.     

Field studies of Cybocephalus nigriceps nigriceps (J. Sahlberg) (Coleoptera: Cybocephalidae) in Israel

Summary

Cybocephalus nigriceps nigriceps (J. Sahlberg) reproduces in Elat (the Arava region of Israel) during spring and summer. Eggs and larvae are present on date palms during these seasons only, whereas adults occur in the grove throughout the year. The adult population reaches its peak in mid-summer and decreases considerably during spring and autumn. Two main locations in which adults occur during the seasons, were found on date palm trees.

Due to the lack of reproduction and activity during autumn and winter, the predator takes almost no part in the biological control of the parlatoria date scale in these seasons.     

Effects of temperature and salinity on survival and growth of the amphipod Hyale crassicornis (Gammaridea,Hyalidae)

This study explored the survival and growth of the marine amphipod Hyale crassicornis under different conditions of ambient temperature and salinity in the laboratory. In 96‐h exposure experiments at a salinity of 30, H. crassicornis tolerated temperatures between 6 and 28°C (>90% survival). The 96‐h LT₅₀ value (median lethal temperature) at high temperature range for the amphipod was 32°C. The values at low temperature range for adults and juveniles were 3.2 and 4.2°C, respectively, indicating that adults have a higher tolerance to low temperature than juveniles. At 25°C, the amphipods tolerated salinities between 10 and 50 (with >80% survival in 96?h). The 96‐h LS₅₀ values at high and low salinity ranges were 56 and 2, respectively. Growth of the juveniles from instars 1 to 6 was determined under different combinations of temperature and salinity. Growth rate of juveniles cultured at 25°C and a salinity of 20 was the highest (0.114?mm?day^?1) among the combinations of 15–25°C and 10–40 salinity. The moult increment of body length was affected by both temperature and salinity. Yet the intermoult duration of the amphipods was affected by temperature only but not by salinity.     

LXXIII.—Cucumaria tetracentriophora,sp. n., a new dendrochirote Holothurian from South Africa

Summary

A survey of the zoogeography of the eight constituent species of the genus Nerilla demonstrates that they are restricted to temperate and tropical coastal marine and brackish waters. The habitat substrata from which members of the genus have been recorded range in particle size from mud to small stones with an apparent preference for coarse sand and gravel. In addition to particulate substrata, collections have been made from red and green algae, ‘corallines’ and reed stems. Specific measurements of other habitat conditions have been largely limited to salinity and temperature readings.     

Cercaria bucephalopsis haimeana (Lacaze-Duthiers, 1854) (Digenea: Bucephalidae) in the cockle,Cardium edule L. in South Wales

Summary

Some variations in the percentage infection of the cockle, Cardium edule L., on Llanrhidian sands, South Wales with Cercaria bucephalopsis haimeana (Lacaze-Duthiers, 1854) are described.

Vertical variations in percentage infection are related to the population density of the final hosts and the seasonal variation with the breeding cycle of the first intermediate host. Only spent adult cockles, over 18·0 mm long and one year old, are infected, the highest percentage infection occurring in three-year old cockles. A decline in the percentage infection in older cockles suggests an increase in the mortality of infected specimens together with an increase in resistance to infection with age. Medium-sized cockles have a higher percentage infection than smaller and larger cockles of the same age. The parasite causes a decrease in the host's shell growth rate but an improvement in the flesh yield.

The possible reasons for the variations in percentage infection and the effect of the parasite on the host are discussed.     

Spawning behaviour of Engystomops pustulatus (Anura: Leptodactylidae)

Foam nests have evolved independently in several amphibian groups as an adaptive response to prevent predation and desiccation in dry environments. Nests are normally laid on ponds, or in underground galleries, humid forest leaf litter or terrestrial bromeliads. They are built when males or females beat a foam precursor associated with the egg masses extruded by the female. The spawning process requires the synchronic actions of the mating pair to obtain a hemispheric nest that protects the offspring. Herein, we describe the spawning behaviour of Engystomops pustulatus based on videos from 13 nesting couples from the lowlands of western Ecuador. Three variables were measured as indicators of male effort: duration of mixing events, duration of resting periods, and number of kicks per mixing event. We consider that not only male physical effort but also female behaviour influences nest structure. We suggest that nest building requires prolonged and intense physical activity by the male as well as the female’s steady position during spawning and female’s oviposition site selection. Nest building has two phases. In the first phase, the duration of resting periods, the duration of mixing events, and the number of kicks increase and are highly variable. During the second phase the three variables stabilise until the end. The volume of the nest increased mainly during the second phase. In four nesting events we observed kicking movements by the female. To our knowledge, this is the first time that female kicking has been observed in leptodactylid frogs. The function of this behaviour is unknown but our observations suggest that it may be triggered by insufficient male effort. Traditionally, female mate choice in Engystomops has been explained under models of indirect benefits exclusively. We argue that the prolonged male activity during nesting could influence female fitness directly. This will allow the operation of sexual selection via direct benefits.