Spawning of hermatypic corals in Bermuda: a pilot study

This study investigates spawning of 4 hermatypic coral species from the subtropical environment of Bermuda. Laboratory evidence of spawning behaviour is supported by synchronous field observations. Development of scleractinian planulae to postlarval stages is recorded. Diploria strigosa, D. labyrinthiformis, Montastrea annularis and M. cavernosa shed highly buoyant, pigmented eggs (300–440 µm diam.) during July to September 1986. Brief spawning periods, synchronous between conspecific colonies, were recorded for M. annularis (July and August) and M. cavernosa (August) within 1 d of the last quarter of the lunar cycle. In August, there were overlaps amongst the spawning dates of D. strigosa and the Montastrea species. Nocturnal spawning periods differed between M. annularis and M. cavernosa. This constitutes the first evidence from an Atlantic community of overlapping spawning dates amongst several faviid species, and of the accumulation of scleractinian eggs and planulae in surface slicks.     

Age, growth and reproduction of the barrelfish Hyperoglyphe perciformis (Mitchill) in the western North Atlantic

Otoliths ( n = 847) and gonads ( n = 817) were collected from barrelfish Hyperoglyphe perciformis that were captured by commercial fishermen in the waters off South Carolina and Georgia in 1995, 1997 and 2001–2006. Of the otoliths collected, 97% were aged successfully, and specimens sampled ranged from 5 to 85 years, with a median age of 12 years. The von Bertalanffy growth parameters yielded the equation: L_t = 857·8{1 − e^{−0·0985[ t −(−8·95)]}}, where L_t is fork length ( L _F) at time t . Through histological examination, 94% of the gonads assessed were assigned to a sex and reproductive class. Females spawned from September to May with a peak from November to January. Males spawned year round, but had a peak from September to April. The sex ratio (M:F) for this population was 1:1·34. The smallest mature female was 605 mm L _F and the youngest immature female was 697 mm L _F. Estimates of L _F and age at 50% maturity ( L ₅₀ and A ₅₀) for females were 660 mm L _F (95% CI = 633–667 mm L _F) and 6·08 years (95% CI = 3·50–7·27 years), respectively. The youngest mature male was 575 mm L _F and the oldest immature male was 762 mm L _F, and no estimates of L ₅₀ or A ₅₀ were made for males. It was determined that barrelfish exhibit the typical characteristics of long life span, slow growth and high age at maturity seen in other deepwater fishes, and that care should be taken to manage this species accordingly.     

Biology of Galaxiella munda McDowall (Teleostei: Galaxüdae), including a comparison of the reproductive strategies of this and three other local species

The reproductive biology, growth and diet of Galaxiella munda McDowall in a south-western Australian river are described. Monthly trends in gonadosomatic indices, stages in ovarian development and the size and maturity of oocytes show that spawning extended from July to October and peaked in late August to early September. Histology of ovaries indicated that G. munda produced clutches of eggs which it released at intervals. Data on length-frequencies, otoliths and gonads demonstrate that G. munda typically died in the few months after spawning. By age I, the females and males of G. munda had reached 47 mm (≡ 0.54 g) and 43 mm (≡ 0.42 g), respectively. The respective von Bertalanffy growth curve parameters for L., K and to were 48.6 mm, 3.702 and -0.0014 for females and 44.3 mm, 4.217 and -0.0012 for males. Galaxiella munda fed predominantly on terrestrial fauna on the water surface, cladocerans and copepods in the water column, and dipteran larvae in the benthos. Comparisons are made between the above aspects of the biology of G. munda and those recorded for three other locally endemic species ( Galaxias occidentalis Ogilby, Bostockia porosa Castelnau and Edelia vittata Castelnau) and wherever possible with other Galaxiella species. Such comparisons have emphasized the relationship between size and age at first maturity and spawning mode.     

High levels of multiple paternity in a spermcast mating freshwater mussel

Multiple paternity is an important characteristic of the genetic mating system and common across a wide range of taxa. Multiple paternity can increase within‐population genotypic diversity, allowing selection to act on a wider spectre of genotypes, and potentially increasing effective population size. While the genetic mating system has been studied in many species with active mating behavior, little is known about multiple paternity in sessile species releasing gametes into the water. In freshwater mussels, males release sperm into the water, while eggs are retained and fertilized inside the female (spermcast mating). Mature parasitic glochidia are released into the water and attach to the gills of fish where they are encapsulated until settling in the bottom substrate. We used 15 microsatellite markers to detect multiple paternity in a wild population of the freshwater pearl mussel (Margaritifera margaritifera). We found multiple paternity in all clutches for which more than two offspring were genotyped, and numbers of sires were extremely high. Thirty‐two sires had contributed to the largest clutch (43 offspring sampled). This study provides the first evidence of multiple paternity in the freshwater pearl mussel, a species that has experienced dramatic declines across Europe. Previous studies on other species of freshwater mussels have detected much lower numbers of sires. Multiple paternity in freshwater pearl mussels may be central for maintaining genetic variability in small and fragmented populations and for their potential to recover after habitat restoration and may also be important in the evolutionary arms race with their fish host with a much shorter generation time.     

Ocean current variability and the spawning season of Hawaiian reef fishes

Synopsis The spawning patterns of four Hawaiian reef fishes with similar reproductive habits, but different biogeographic distributions were studied from September 1980 to October 1981. Two species are Hawaiian endemics [Centropyge potteri (Pomacanthidae) and Chaetodon multicinctus (Chaetodontidae)] and the other two have pan-tropical Pacific distributions [Ctenochaetus strigosus and Zebrasoma flavescens (Acanthuridae)]. All showed increased spawning activity from January to July, the prevalent pattern among a majority of coastal marine fishes in Hawaii. Environmental correlatives to the period of peak reproduction include cycles of (a) daylight length and temperature which probably function as proximate cues and (b) seasonal variations in ocean current patterns which may ultimately affect survival of larvae and dispersal. Peak reproduction takes place during months when (1) mesoscale eddies most likely occur, and (2) the probability is greatest of drifting objects remaining near the islands.     

Elevated summer temperatures delay spawning and reduce redd construction for resident brook trout (Salvelinus fontinalis)

Redd (nest) surveys for resident brook trout (Salvelinus fontinalis) were conducted annually in a mountain lake in northern New York for 11 years with multiple surveys conducted during the spawning season in eight of those years. Repeated surveys throughout the spawning season allowed us to fit an individually based parametric model and estimate the day of year on which spawning was initiated, reached its midpoint, and ended during each year. Spawning phenology was then assessed relative to (1) mean of maximum daily air temperature and (2) mean of maximum daily water temperature at the lake bottom during summer in each year using a linear model. Elevated temperatures in summer were correlated with a delay in spawning and a reduction in the total number of redds constructed. Increasing the summer mean of maximum daily air temperatures by 1 °C delayed spawning by approximately 1 week and decreased the total number of redds constructed by nearly 65. Lake spawning brook trout select redd sites based on the presence of discharging groundwater that is relatively constant in temperature within and across years, leading to relatively consistent egg incubation times. Therefore, delayed spawning is likely to delay fry emergence, which could influence emergence synchrony with prey items. This work highlights non‐lethal and sub‐lethal effects of elevated summer temperatures on native resident salmonids in aquatic environments with limited thermal refugia.     

Role of evolutionary and ecological factors in the reproductive success and the spatial genetic structure of the temperate gorgonian Paramuricea clavata

Dispersal and mating features strongly influence the evolutionary dynamics and the spatial genetic structure (SGS) of marine populations. For the first time in a marine invertebrate, we examined individual reproductive success, by conducting larval paternity assignments after a natural spawning event, combined with a small‐scale SGS analysis within a population of the gorgonian Paramuricea clavata. Thirty four percent of the larvae were sired by male colonies surrounding the brooding female colonies, revealing that the bulk of the mating was accomplished by males from outside the studied area. Male success increased with male height and decreased with increasing male to female distance. The parentage analyses, with a strong level of self‐recruitment (25%), unveiled the occurrence of a complex family structure at a small spatial scale, consistent with the limited larval dispersal of this species. However, no evidence of small scale SGS was revealed despite this family structure. Furthermore, temporal genetic structure was not observed, which appears to be related to the rather large effective population size. The low level of inbreeding found suggests a pattern of random mating in this species, which disagrees with expectations that limited larval dispersal should lead to biparental inbreeding. Surface brooding and investment in sexual reproduction in P. clavata contribute to multiple paternity (on average 6.4 fathers were assigned per brood), which enhance genetic diversity of the brood. Several factors may have contributed to the lack of biparental inbreeding in our study such as (i) the lack of sperm limitation at a small scale, (ii) multiple paternity, and (iii) the large effective population size. Thus, our results indicate that limited larval dispersal and complex family structure do not necessarily lead to biparental inbreeding and SGS. In the framework of conservation purposes, our results suggested that colony size, proximity among colonies and the population size should be taken into consideration for restoration projects.     

Interannual variation in the reproductive cycle of the New Zealand snapper Pagrus auratus (Bloch & Schneider) (Sparidae)

Changes in reproductive condition in the New Zealand snapper Pagrus auratus (Bloch & Schneider) were monitored in a wild population over three successive years. Recrudescence occurred in spring with spawning beginning in October and continuing for 3 to 5 months. The initiation of spawning varied by up to 3 weeks and was associated with sea surface temperatures of 15–16° C. Theconclusion of spawning was associated with temperatures of 19–21° C but showed greater interannual variation than the onset of spawning. Changes in the gonadosomatic index were accompanied by parallel changes in hepatosomatic index in females but not males, reflecting the role of the liver in vitellogenesis in females.     

Sounds produced by spawning fishes

Synopsis Low frequency sounds are shown to be associated with the spawning of two Caribbean coral reef fishes: the hamlet, Hypoplectrus unicolor (Serranidae) and the striped parrotfish, Scarus iserti (Scaridae). Both fishes produce distinctive sounds while broadcasting gametes in midwater. H. unicolor produces sounds via muscle stimulation of the swimbladder. Fin movements among group spawning S. iserti produce hydrodynamic noise. Although reproductive behaviors of these two species have been previously studied in detail, the association of sounds with mating is new. The mating sounds cannot be easily detected by human hearing underwater but are recordable using a hydrophone. The sounds are distinct and recognizable enough to allow counting and acoustic mapping of mating events in these species.