Population Biology of Mussels (Aulacomya Maoriana, Mytilus Galloprovincialis and Perna Canaliculus) From Rocky Intertidal Shores in Wellington Harbour, New Zealand

<p>This study examines the population ecology and dynamics of three co-existing mussel species (Aulacomya maoriana, Mytilus galloprovincialis and Perna canaliculus) in Wellington Harbour, New Zealand. The present study investigates the role of multiple environmental factors and their multiple effects on the intertidal mussel population. Wellington Harbour is a complex system, supporting speciose intertidal invertebrate communities. CTD data loggers recording seawater temperature, turbidity, chlorophyll a concentration and salinity at Evans Bay, Seatoun, Matiu-Somes Island and Petone provided the environmental data. The data suggest the existence of distinct zones within Wellington Harbour, with different hydrological regimes present at each zone. Consistently high salinity (35.08 + 2.9 PSU) and chlorophyll a concentration (9.42 + 4.33 μg l-1) were found at Evans Bay, while these parameters displayed a degree of temporal variation and were significantly lower at Seatoun (31.5 + 4.17 PSU and 2.15 + 2.1 μg l-1) and Matiu-Somes Island (33.26 + 0.99 PSU and 1.23 + 1.79 μg l-1). At Petone, a site located near the Hutt river mouth, salinities were reduced (31.59 + 3.21 PSU) while chlorophyll a levels were similar to those at Matiu-Somes Island (1.64 + 1.08 μg l-1). Mean turbidity values were similar at Seatoun and Evans Bay (11.51 + 18.53 FTU and 11.89 + 5.52 FTU, respectively), with mean turbidity slightly reduced at Petone (8.20 + 11.16 FTU) and elevated at Matiu-Somes Island (15.35 + 11.12 FTU). Further, CTD data revealed similar seawater temperature at all sites, with mean values oscillating around 13 - 15ºC. The ecology of larval stages was expressed in this study by quantifying the rates at which mussel larvae settled on the experimental substrate. A year-round spawning, as well as temporal and spatial variability in mussel recruitment at four experimental sites was revealed. Evans Bay was the site with consistently higher recruitment rates but not the mean recruit numbers (721 + 879 larvae), while the highest number of recruits (9851 larvae) was recorded at Petone (1041 + 2112 larvae). Recruitment rates were lower at Seatoun (729 + 536 larvae) and Matiu-Somes Island (410 + 636 larvae). However, only at Seatoun was this variability clearly linked to the environmental conditions of water turbidity, chlorophyll a concentration, and salinity. The post-larval ecology part of this study concentrates on the condition index and gonad mass, and the degree of infestation with a parasitic pea crab Pinnotheres novaezelandiae studied at four sites. Spatial and temporal variation in condition index and gonad mass was revealed in all three species investigated, with both condition index and gonad mass of adult mussels being highest at Matiu-Somes Island (14.59 + 4.41 and 0.21 + 0.16 g), followed by Kau Point (13.47 + 6.99 and 0.17 + 0.10 g), Seatoun (13.32 + 7.79 and 0.11 + 0.10 g) and Evans Bay (11.99 + 2.78 and 0.14 + 0.14 g). Condition index was significantly correlated with gonad mass, and was highest in Aulacomya maoriana (15.85 + 9.38), followed by Perna canaliculus (12.52 + 4.39) and Mytilus galloprovincialis (11.66 + 5.91). The condition was generally reduced in mussels infested with the pea crab Pinnotheres novaezelandiae, although the overall infestation rate was low (3.28%). In order to describe the pattern of mussel community development, patches of bare rock were experimentally created in the mid-intertidal zone. Subsequently, predatorexclusion cages were set up in those areas and monitored regularly. The abundance of main groups of intertidal taxa settling on the cleared substrate was expressed in terms of percent cover, and was highest at Evans Bay (59.57 + 80.27%), lowest at Kau Point (13.96 + 26.18%) and intermediate at Seatoun (22.56 + 41.64%). However, the bottomup factors were visibly linked to the community development at Seatoun. The full cage experimental treatment provided the maximum protection from predation and desiccation, therefore the community recovery was most pronounced under this treatment. Mytilus galloprovincialis was revealed as the most competitive mussel species, in some cases able to colonise the entire available substrate and exclude other two mussel species. Further, seasonality of mussel response to wave action and desiccation was investigated. Mussel species-specific strength of attachment to the rocky substrate was expressed in kg (effectively the force) required for the mussel to be removed from the rocky substrate at shores facing south and north in Wellington Harbour. The strength of attachment was highest in Perna canaliculus (5.81 kg + 2.27), followed by Aulacomya maoriana (3.63 kg + 1.63) and Mytilus galloprovincialis (3.44 kg + 1.70). Mussel strength of attachment was generally higher at south-facing sites, due to stronger waves generated by southerly winds. In a separate experiment, in which mussels were exposed to air at six different shore levels within the intertidal zone, desiccation tolerance was highest in Mytilus galloprovincialis on the south-facing sites (LD50=0.62m and 0.87 for north- and south-facing sites, respectively), followed by Aulacomya maoriana (LD50=0.65 and 0.75m for north- and south-facing sites, respectively) and Perna canaliculus (LD50=0.20 and 0.35m for north- and south-facing sites, respectively). LD50 desiccation exposure values were lower in all three species found on the north-facing shores, indicating that mussels on those shores are less tolerant to desiccation-induced stress and therefore died more rapidly.</p>

Population Biology of Mussels (Aulacomya Maoriana, Mytilus Galloprovincialis and Perna Canaliculus) From Rocky Intertidal Shores in Wellington Harbour, New Zealand

<p>This study examines the population ecology and dynamics of three co-existing mussel species (Aulacomya maoriana, Mytilus galloprovincialis and Perna canaliculus) in Wellington Harbour, New Zealand. The present study investigates the role of multiple environmental factors and their multiple effects on the intertidal mussel population. Wellington Harbour is a complex system, supporting speciose intertidal invertebrate communities. CTD data loggers recording seawater temperature, turbidity, chlorophyll a concentration and salinity at Evans Bay, Seatoun, Matiu-Somes Island and Petone provided the environmental data. The data suggest the existence of distinct zones within Wellington Harbour, with different hydrological regimes present at each zone. Consistently high salinity (35.08 + 2.9 PSU) and chlorophyll a concentration (9.42 + 4.33 μg l-1) were found at Evans Bay, while these parameters displayed a degree of temporal variation and were significantly lower at Seatoun (31.5 + 4.17 PSU and 2.15 + 2.1 μg l-1) and Matiu-Somes Island (33.26 + 0.99 PSU and 1.23 + 1.79 μg l-1). At Petone, a site located near the Hutt river mouth, salinities were reduced (31.59 + 3.21 PSU) while chlorophyll a levels were similar to those at Matiu-Somes Island (1.64 + 1.08 μg l-1). Mean turbidity values were similar at Seatoun and Evans Bay (11.51 + 18.53 FTU and 11.89 + 5.52 FTU, respectively), with mean turbidity slightly reduced at Petone (8.20 + 11.16 FTU) and elevated at Matiu-Somes Island (15.35 + 11.12 FTU). Further, CTD data revealed similar seawater temperature at all sites, with mean values oscillating around 13 - 15ºC. The ecology of larval stages was expressed in this study by quantifying the rates at which mussel larvae settled on the experimental substrate. A year-round spawning, as well as temporal and spatial variability in mussel recruitment at four experimental sites was revealed. Evans Bay was the site with consistently higher recruitment rates but not the mean recruit numbers (721 + 879 larvae), while the highest number of recruits (9851 larvae) was recorded at Petone (1041 + 2112 larvae). Recruitment rates were lower at Seatoun (729 + 536 larvae) and Matiu-Somes Island (410 + 636 larvae). However, only at Seatoun was this variability clearly linked to the environmental conditions of water turbidity, chlorophyll a concentration, and salinity. The post-larval ecology part of this study concentrates on the condition index and gonad mass, and the degree of infestation with a parasitic pea crab Pinnotheres novaezelandiae studied at four sites. Spatial and temporal variation in condition index and gonad mass was revealed in all three species investigated, with both condition index and gonad mass of adult mussels being highest at Matiu-Somes Island (14.59 + 4.41 and 0.21 + 0.16 g), followed by Kau Point (13.47 + 6.99 and 0.17 + 0.10 g), Seatoun (13.32 + 7.79 and 0.11 + 0.10 g) and Evans Bay (11.99 + 2.78 and 0.14 + 0.14 g). Condition index was significantly correlated with gonad mass, and was highest in Aulacomya maoriana (15.85 + 9.38), followed by Perna canaliculus (12.52 + 4.39) and Mytilus galloprovincialis (11.66 + 5.91). The condition was generally reduced in mussels infested with the pea crab Pinnotheres novaezelandiae, although the overall infestation rate was low (3.28%). In order to describe the pattern of mussel community development, patches of bare rock were experimentally created in the mid-intertidal zone. Subsequently, predatorexclusion cages were set up in those areas and monitored regularly. The abundance of main groups of intertidal taxa settling on the cleared substrate was expressed in terms of percent cover, and was highest at Evans Bay (59.57 + 80.27%), lowest at Kau Point (13.96 + 26.18%) and intermediate at Seatoun (22.56 + 41.64%). However, the bottomup factors were visibly linked to the community development at Seatoun. The full cage experimental treatment provided the maximum protection from predation and desiccation, therefore the community recovery was most pronounced under this treatment. Mytilus galloprovincialis was revealed as the most competitive mussel species, in some cases able to colonise the entire available substrate and exclude other two mussel species. Further, seasonality of mussel response to wave action and desiccation was investigated. Mussel species-specific strength of attachment to the rocky substrate was expressed in kg (effectively the force) required for the mussel to be removed from the rocky substrate at shores facing south and north in Wellington Harbour. The strength of attachment was highest in Perna canaliculus (5.81 kg + 2.27), followed by Aulacomya maoriana (3.63 kg + 1.63) and Mytilus galloprovincialis (3.44 kg + 1.70). Mussel strength of attachment was generally higher at south-facing sites, due to stronger waves generated by southerly winds. In a separate experiment, in which mussels were exposed to air at six different shore levels within the intertidal zone, desiccation tolerance was highest in Mytilus galloprovincialis on the south-facing sites (LD50=0.62m and 0.87 for north- and south-facing sites, respectively), followed by Aulacomya maoriana (LD50=0.65 and 0.75m for north- and south-facing sites, respectively) and Perna canaliculus (LD50=0.20 and 0.35m for north- and south-facing sites, respectively). LD50 desiccation exposure values were lower in all three species found on the north-facing shores, indicating that mussels on those shores are less tolerant to desiccation-induced stress and therefore died more rapidly.</p>

The zombification and reanimation of purple urchins (Strongylocentrotus purpuratus) in response to food availability

To survive periods of starvation, organisms can reduce their metabolism and/or decrease energy allocation to reproduction. This is especially important for coastal rocky reefs where widespread kelp deforestation has become increasingly common in recent decades. This deforestation often results in the formation of urchin barrens that have high densities of herbivorous sea urchins and little macroalgae for them to consume. While it is clear that these barrens can persist for years to decades, it is unclear how the urchins within them survive such prolonged periods without regular access to macroalgae. Here, we show that urchin metabolism and gonad mass both decrease significantly when the urchins are starved, and that these urchins regain normal metabolic activity and gonad masses when access to food is restored. However, if urchins occur in barren areas that receive drift algae from nearby kelp forests, it appears they can maintain normal metabolic activity and gonad mass. Together, our results provide experimental evidence that reducing metabolism may be a primary strategy for avoiding starvation in urchins occurring within barrens. Our results can be especially important to researchers looking to restore kelp forests and to urchin fishers who seek to harvest these urchins for their gonads but currently cannot because their gonads are of poor quality. Additionally, this has important implications for consumers in other ecosystems where access to energetic resources is spatially or temporally variable and can point to new avenues of research to explain how organisms adjust their energetic needs to survive extended periods of starvation.

Switches, stability and reversals: the evolutionary history of sexual systems in fish

Sexual systems are highly diverse and have profound consequences for population dynamics and resilience. Yet, little is known about how they evolved. Using phylogenetic Bayesian modelling on 4740 species, we show that gonochorism is the likely ancestral condition in teleost fish. While all hermaphroditic forms revert quickly to gonochorism, protogyny and simultaneous hermaphroditism are evolutionarily more stable than protandry. Importantly, simultaneous hermaphroditism can evolve directly from gonochorism, in contrast to theoretical expectations. We find support for predictions from life history theory that protogynous species live longer than gonochoristic species, are smaller than protandrous species, have males maturing later than protandrous males, and invest the least in male gonad mass. The large-scale distribution of sexual systems on the tree of life does not seem to reflect just adaptive predictions and thus does not fully explain why some sexual forms evolve in some taxa but not others (William’s paradox). We propose that future studies should take into account the diversity of sex determining mechanisms. Some of these might constrain the evolution of hermaphroditism, while the non-duality of the embryological origin of teleost gonads might explain why protogyny predominates over protandry in this extraordinarily diverse group of animals.

MORPHOFUNCTIONAL CHARACTERISTICS OF GONAD OF THE GABLE-ROLL NEOGOBIUS MELANOSTOMUS (PALLAS, 1814) OF THE LOWER NISTRY DURING THE SPAWN

The results of studies of the reproductive system of sexually mature females of the round goby Neogobius melanostomus (Pallas, 1814) from the Lower Dniester during the spawning season are presented. The age of sexual maturation and the timing of spawning of fish in the conditions of this basin are determined. Asynchrony in the development of germ cells has been identified, which provides four-time spawning during the entire breeding season of fish. Throughout the entire reproductive cycle, larger females with greater body weight and gonad mass are the first to spawn.

Pattern of energy allocation during the gametogenesis of the asteroid Cosmasterias lurida (Forcipulatida: Stichasteridae) from the Beagle Channel, Ushuaia, Argentina

Energy allocation patterns during the reproductive cycle of echinoderms may be determined by the different energy requirements of the organisms. In this study, we describe the energy reserves variation in the gonads, pyloric caeca and stomach among the gametogenic stages of a population of Cosmasterias lurida from the Beagle Channel, Argentina. Adult individuals of C. lurida were collected from the subtidal zone of Ushuaia Bay during four seasonal sampling periods (August 2010 to June 2011). Indices, energy density (kJ/g ash-free dry mass) and energy content (kJ) of gonads, pyloric caeca and stomach were determined. Oocytes number and diameter were evaluated. Cosmasterias lurida had a major peak of gonadal index (GI) in mature gonads (M), with a great decrease towards the spawning (PS/PSR) and remature (RM) periods. No variation was observed in the energy density of the gonads (EDG). The energy content of the gonads (ECG) presented a similar pattern to the GI. Thus, the gonadal storage cycle can be explained through the variation in gonad mass more than in its energy density. Females had higher ECG and EDG values than males, which suggest a greater energy contribution in females during the reproductive cycle. The stomach and the pyloric caeca indices, energy density and energy content remained unaltered among the stages. The energy density of pyloric caeca (EDPC) was higher in mature males than in mature females. Likewise, the energy density of the stomach (EDS) was overall higher in males than in females. This inverse pattern between sexes in relation to the EDG may suggest a transference of energy from the pyloric caeca and stomach to gonads during maturate stage playing a storage role for reproduction. Rev. Biol. Trop. 65(Suppl. 1): S197-S206. Epub 2017 November 01.

Differences in egg quantity and quality among hatchery- and wild-origin Chinook salmon (Oncorhynchus tshawytscha)

Each year, millions of hatchery-raised juvenile salmon are released into the wild to help bolster salmon populations all over North America. These fish often differ from their wild-origin conspecifics in terms of survival and reproductive success after release, but our understanding of their reproductive investment is limited. We examined differences in egg number (gonad mass and fecundity) and quality (mass, lipids, fatty acids) between spawning hatchery- and wild-origin Chinook salmon (Oncorhynchus tshawytscha) from Lake Ontario. Hatchery-origin females were found to not differ significantly in body size, age, egg total lipids, and fatty acid content of eggs relative to wild-origin females, but hatchery-origin females allocated significantly less body mass and neutral lipids into egg and gonadal development compared with wild-origin females. We also examined diets of both groups of females using stable isotopes and found that carbon and nitrogen stable isotopes suggested limited differences in the diet between hatchery- and wild-origin adult females. The results from the present study provide evidence that the differing environmental conditions and associated selection pressures of captive environments during early life in hatchery settings can alter certain life-history traits later in adult development, namely gonad mass and egg size, and could contribute to differences in their performance in the wild.

Variation in sperm morphometry of the African cyprinid Barbus neumayeri (Neumayer’s barb)

In this study, we explored variation in sperm morphometry of the African cyprinid Barbus neumayeri Fischer, 1884 (Neumayer’s barb) across seven sites with a wide range in dissolved oxygen, from hypoxic swamps to intermittent normoxic streams to well-oxygenated rivers. We explore whether fish physiological condition (K) or hypoxia can affect the reproductive traits, and whether condition–hypoxia dependence of sperm traits including head length (LH), head width (WH), flagellum length (LF), and hydrodynamic ratio (HR) vary across sampling sites. Significant differences were found in fish total length (P = 0.0212), as well as in K, left and right testis masses, total gonad mass, and gonadosomatic index (P < 0.0001 for all traits). Total gonad mass was lower in hypoxic sites than in well-oxygenated sites. Interestingly, the left and right testes from normoxic environments were double the size of testes from hypoxic environments. Despite little variation in sperm flagellum length, sperm heads were longer in swamps than in streams or rivers, giving the sperm head a more hydrodynamic shape. This variation in HR may be beneficial in the more stagnant waters of the swamp compared with the other environments. Future studies are necessary to understand whether variation in sperm morphology correlates with sperm swimming performance and male reproductive capacity.

Evidence for neither the compensation hypothesis nor the expensive-tissue hypothesis in Carassius auratus

In many taxa, the left and right testes often differ in size. The compensation hypothesis states that an increase in size of one testis can compensate for a reduced function in the other testis. Moreover, the expensive-tissue hypothesis predicts that an increase in investment of a metabolically costly tissue is offset by decreasing investment in the other metabolically costly tissues. Here we tested these two hypotheses in Carassius auratus, by analysing difference between left and right testes mass, and between brain mass and both gut length and gonad mass (testes mass in males and clutch mass in females). We found no difference between left and right testis mass and no correlations between relative testis size and body measurements. These findings suggest that the left testis cannot serve a compensatory role. Nonetheless, contrary to the predictions of the expensive-tissue hypothesis, brain mass was positively correlated with both gut length and gonad mass within each sex. This positive correlation between brain mass and other organs (gut, gonad and clutch tissues) suggests that organisms may compensate for substantial variation in investment in tissues without sacrificing other expensive tissues.

Reproductive Strategy ofLabeobarbus batesii(Boulenger, 1903) (Teleostei: Cyprinidae) in the Mbô Floodplain Rivers of Cameroon

Aspects of the reproductive strategy of African carp,Labeobarbus batesii, were investigated from May 2008 to October 2009 in the Mbô Floodplain of Cameroon. Samples were collected monthly from artisanal fishermen. The total length and total body mass of each specimen were measured to the nearest mm and 0.01 g, respectively. Sex was determined by macroscopic examination of the gonads after dissection. The sex ratio was female skewed (overall sex ratio: 1 : 1.42). Females reach sexual maturity at a larger size (213 mm) than the males (203 mm). The mean gonadosomatic index ranges from0.32±0.17% to1.91±1.15%, whereas the meanKfactor ranges from0.90±1.09to1.10±0.13. These two parameters are negatively correlated. The reproduction cycle begins in mid-September and ends in July of the next year, and they are reproductively quiescent for the rest of the year.Labeobarbus batesiiis a group-synchronous spawner with pulses of synchronised reproduction spread over a long period. The mean absolute, potential, and relative fecundities are2898±2837oocytes,1016±963oocytes, and9071±7184oocytes/kg, respectively. The fecundity is higher and positively correlated with the gonad mass than with body size. Its reproductive biology suggests thatL. batesiiis suitable for pond culture.