Andrea C. Alfaro

Variability in mussel settlement on suspended ropes placed at Ahipara Bay, Northland, New Zealand

Abstract Unique physical and biological conditions at Ninety Mile Beach, northern New Zealand, are responsible for an accumulation of unusually high amounts of mussel spat, Perna canaliculus , found nowhere else in the country. These massive quantities of mussel spat are collected from the beach (>140,000 tonnes/year) and transported to the aquaculture farms, where they supply 80% of the industrys mussel seed requirements. Direct settlement of mussels, P. canaliculus , from the plankton to suspended ropes in the water column was investigated at Ninety Mile Beach, northern New Zealand. Mussel spat-collecting ropes were placed at two sites (inside and outside Ahipara Bay) and at three different depths. The abundances of mussels within three size classes were recorded monthly during two spawning seasons in 1999 and 2000. Small mussels ( 1.0 mm) were relatively more abundant at greater depths (18 m water depth) in September–December. Larger mussels are thought to have transferred from tumbling algae covered with mussels, which are readily transported by hydrodynamic processes near the seafloor. Although higher mussel abundances generally were found at the site inside the bay, these differences were not strongly supported by statistical analyses. The present research provides the first evidence that artificial ropes deployed at Ahipara Bay may be of commercial value to spat collectors on the beach and the mussel farm industry. These ropes could be used as predictors of spatfall arrivals, which are collected at the beach and used to seed the mussel farms. Furthermore, ropes could possibly be used as a new and more reliable means of harvesting the massive quantities of mussel spat available at Ninety Mile Beach, northern New Zealand.

Spatial variability in reproductive behaviour of green-lipped mussel populations of northern New Zealand

The reproductive behaviour of four intertidal and two subtidal mussel populations were investigated within two spatial scales at Ninety Mile Beach, northern New Zealand, where large quantities of seed mussels are collected for aquaculture. Reproductive cycles were compared between intertidal and subtidal populations and among intertidal populations along a 90-km coastal area. Histological sections of mussel gonads were used to identify the reproductive state of individual mussels collected monthly between July 1998 and April 2000. Gonad indices were calculated for populations each month at each site. Frequency distributions of different gametogenic stages were plotted and differences in reproductive cycle among populations were identified. Mussel shell sizes were also recorded and compared among populations. Although all intertidal and subtidal populations had similar temporal variations in reproductive behaviour, spatial patterns among various sites revealed clear differences in reproductive cycles among populations. In particular, mussel shell size and gonad indices were higher for subtidal sites compared to their intertidal counterparts. Among intertidal mussel populations, the northernmost population had the highest maximum shell length, gonad indices and percentage ripe and spawning individuals, followed by two populations at the southern end of Ninety Mile Beach. A small mid-beach mussel population had the smallest mussels with the lowest gonad indices and few spawning mussels during the reproductive season. A prolonged spawning period was observed within the most reproductively active populations (two subtidal populations at the south end and one intertidal population at the north end of the beach) between June and December. However, the reproductive cycle of two intertidal populations at the south end of the beach indicated 2–3 spawning events during the same period. Differences in mussel shell size and reproductive behaviour among sites are likely to be related to variations in environmental conditions along Ninety Mile Beach. M e n C. Al r et

Food and habitat partitioning in grazing snails (Turbo smaragdus), Northern New Zealand

Gut content analyses and fatty acid profiles were used to identity food consumption and assimilation in a dominant grazing snail (Turbo smaragdus) in rocky shore and estuarine habitats, at Waiwera Estuary, northern New Zealand. Gut contents of freshly collected individuals indicated that snails utilize a wide range of food sources within their habitats, including microalgae and foliose-corticated macrophytes (rocky intertidal), and mangrove tissue and filamentous algae (mangrove stand). Laboratory feeding experiments revealed thatT. smaragdus prefers microalgae and possibly filamentous epiphytes, regardless of snail size or habitat of origination. The fatty acid profiles of snails fed different diets (brown algae [Hormosira banksii], diatoms, mangrove pneumatophores, and filamentous green algae [Chaetomorpha sp.]) confirmed the assimilation of the given foods, except for the mangrove treatment, which resulted in a low, long chain, fatty acid (LCFA) signature. Incongruities between the gut content analyses (high number of mangrove particles) and fatty acid profiles (low LCFA signature) of field and laboratory snails exposed to a mangrove diet suggest that snails target microalgal and filamentous epiphyte food sources on the pneumatophores and inadvertently ingest mangrove particles. Snails within all food treatments, except diatoms, had a relatively strong bacterial signature (18∶1n–7, Σ15+Σ17). Bacteria may have readily accumulated in the experimental tanks and been selected by snails as an alternative food source. In the field, snails and other grazers may ingest detritus and biofilms to access dense populations of bacteria. This research highlights the need for a comprehensive and multianalytical approach to elucidate the role of grazers in algal-plant dominated ecosystems.

Two New Species of Retiskenea? (Gastropoda: Neomphalidae) from Lower Cretaceous Hydrocarbon-Seep Carbonates of Northern California

Abstract Two new Mesozoic gastropod species, provisionally attributed to the minute (height < 5 mm) coiled neomphalid genus Retiskenea?, are described from three geographically isolated, Early Cretaceous, hydrocarbon seep-carbonate sites at Wilbur Springs, Rice Valley, and Cold Fork of Cottonwood Creek, northern California (USA). A fourth paleo-seep locality at Paskenta, of probable Upper Jurassic age, also yielded a single specimen of a morphologically similar microgastropod that may be a neomphalid with affinities to the Lower Cretaceous specimens described herein. The limestone lenses are ∼2–260 m in length, ∼1–5 m in diameter, and surrounded by forearc siliciclastics of bathyal turbidites or sedimentary serpentinites in the Upper Jurassic to Lower Cretaceous (Tithonian–Albian) Great Valley Group and its equivalents. The Lower Cretaceous microgastropods are tentatively placed in Retiskenea? based on similar shell characters: size, globose shape, inflated reticulate protoconch, number and distinct inflation of the body whorls, and fine, prosocline sculpture of the final body whorl. The fossils occur in carbonate microbialites that formed in seafloor sediments during archaeal anaerobic oxidation of methane in the zone of bacterial sulfate reduction, associated with H2S- and CH4-rich fluid seepage. The California Retiskenea? fossils commonly are found in gregarious clusters, or closely affiliated with thin worm tubes or, in one case, a larger gastropod. These Mesozoic records increase the total known species attributable to this cold-seep endemic genus from two to four. Its spatial and temporal distribution thus may have spanned ∼9,000 km around the Pacific Rim from at least ∼133 m.y. to the present in 10 subduction-related seep sites from California (possibly Upper Jurassic–Lower Cretaceous), Washington (middle Eocene–Upper Oligocene), and modern offshore Oregon, the eastern Aleutians, and the Japan Trench. If the generic placement of these microgastropod fossils is correct, the California records are the oldest-known occurrences of Retiskenea, consistent with an estimated minimum Mesozoic origin for the ‘hot vent’ Neomphalidae, as inferred from molecular analyses published on other living members of the family.

Characterisation (δ13C and δ15N isotopes) of the food webs in a New Zealand stream in the Waitakere Ranges, with emphasis on the trophic level of the endemic frog Leiopelma hochstetteri

Abstract Leiopelma hochstetteri, the most widespread of New Zealands native frogs, is recognised as threatened, and is fully protected by legislation. As a first step to characterise the diet and trophic level of L. hochstetteri within streams in the Waitakere Ranges, Auckland, stable carbon and nitrogen isotope analyses were undertaken on a variety of sympatric terrestrial and aquatic plant and animal species, including adult frogs. These results show that: (1) aquatic and terrestrial food webs are linked by terrestrial inputs into the stream; (2) invertebrate and vertebrate predators separate well into distinct trophic groups, and (3) L. hochstetteri occupies an intermediate trophic position among predators, with a diet, at least as an adult, comprising terrestrial invertebrates. Shortfin eels and banded kokopu are identified as potential predators of L. hochstetteri, but data for rats are inconclusive. These results have important implications for the conservation of New Zealand native frog species and riparian stream habitat.

Variability of growth, health, and population turnover within mussel beds of Perna canaliculus in northern New Zealand

Abstract The growth and health of intertidal mussel (Perna canaliculus) populations were investigated along an exposed coastline at Ninety Mile Beach, northern New Zealand. A marked and recaptured experiment of young mussels (15–35 mm in shell length) over a year at three sites resulted in significant differences in recovery rates, shell growth, condition indices, age, and degree of shell parasitism. A high recovery rate of fast growing mussels coincided with a high condition index and low shell parasitism. Conversely, a low recovery rate of slow growing populations was associated with a low condition index and a high level of shell parasitism. Anomalous shell conditions included bored shells, wear and sloughing of periostracum, shell erosion, and nacre pits and bulges. Aging of adult mussels (70–80 mm) indicates that in areas of fast population turnover rates, mussels reach adulthood in only 1.1 years compared to the 2.5-year-old mussels found in low turnover areas. These differences are attributed to variations in environmental conditions (e.g., food availability, sediment load) throughout the study area, and highlight the importance of site-specific variability for intertidal populations.

Evaluation of microalgal and formulated diets for the culture of the New Zealand pipi clam Paphies australis

A set of feeding trials was carried out for different microalgal species and processed diets for the culture of the New Zealand pipi, Paphies australis. Five microalgal species (Isochrysis galbana clone T-ISO, Pavlova lutheri, Tetraselmis suecica, Chaetoceros muelleri, and Thalassiora pseudonana clone 3H) and three formulated diets (bakers yeast, wheat flour, and corn flour) were fed to spat, juvenile, and adult pipi for 21 days. Unfed pipi were used in the control group. The spat and juvenile pipi showed a major shell increase with I. galbana while the greatest wet weight increase was obtained with P. lutheri. The shells of adult pipi grew better with corn flour, and the P. lutheri-fed group obtained the greatest wet weight. Results of proximate analysis in adult pipi revealed that proteins and lipids were accumulated in the tissue for all fed groups, while carbohydrate levels were depleted in all treatments including the control group. It is suggested that the gonads have developed during the experiment.

Migration and trail affinity of snails, Littoraria scabra, on mangrove trees of Nananu-i-ra, Fiji Islands

The distribution of mobile species such as grazing snails may be influenced by migration patterns, which often are excluded from ecological studies. To highlight this point, the migration patterns of Littoraria scabra on mangrove trees were investigated during incoming and outgoing tides at Nanaru-i-ra, Fiji Islands. Marked snails were used to track the position of snails, relative to the ground, during advancing and receding tides. Snails were found to move quickly upward during incoming tides, potentially to avoid immersion. During the outgoing tide, snails migrated downward, but at a slower pace than upward movement, presumably as a consequence of active feeding on the newly replenished micro-organisms on the mangrove structures (i.e., stems and roots). Aggregation behavior during migration was also recorded by measuring the distance of marked snails to two nearest neighbors. Affinity to neighboring snails was found to be maintained throughout tidal cycles, although greater affinity was observed during incoming tides compared to outgoing tides. These migratory and aggregation behaviors may be a result of increased feeding and reproductive efficiency.

Use of probiotic bacteria to improve growth and survivability of farmed New Zealand abalone (Haliotis iris)

The effects of two probiotic feeds containing two and three bacterial isolates were evaluated on the growth performance of New Zealand abalone (Haliotis iris). Probiotic bacteria were isolated from the guts of healthy adult abalone. The isolates were screened qualitatively and quantitatively according to their ability to hydrolyse nutrients (i.e. proteins, starch and alginate), produce acid and resist bile salts. Based on the screening results, we developed a multi-strain conglomerate of 2- and 3- probiotic bacterial strains that were supplemented into a commercial abalone feed to use in our experiments. The 2-probiotic conglomerate consisted of Exiguobacterium JHEb1 and Vibrio JH1, and the 3-probiotic conglomerate consisted of Exiguobacterium JHEb1, Vibrio JH1 and Enterococcus JHLDc. The probiotic feeding trial involved abalone juveniles (20–30 mm in maximum shell length). Both probiotic feeds significantly improved abalone growth compared to that of the unsupplemented feed. The 3-probiotic supplemented feed produced a significant shell length increase of 20.9%, a wet weight gain of 19.8% and a five-fold reduction in mortality compared to the controls. The 2-probiotic supplemented feed resulted in significant increases in shell length (15.4%) and reduced mortality (five-fold), but not in weight gain, compared to controls.

Putative involvement of adrenergic receptors in regulation of mussel (Perna canaliculus) larval settlement

Abstract Settlement responses were investigated for mussel (Perna canaliculus) larvae after exposure to catecholamines and their precursor metabolites. Settlement and mortality assays were conducted in Petri plates with chemical treatments (L-phenylalanine, L-tyrosine, L-DOPA, dopamine hydrochloride and epinephrine at various concentrations) and controls. The proteinogenic amino acids L-phenylalanine and L-tyrosine were both effective inducers (~65%) of larval settlement at 10−5 mol l−1 compared with controls (4%). Exposure of larvae to L-DOPA, dopamine and epinephrine resulted in maximum settlement induction (50, 60 and 51%, respectively) at 10−5 mol l−1. Larval mortalities were low (comparable to controls) across all concentrations of L-phenylalanine and L-tyrosine treatments, whereas high mortalities (>60%) were observed for L-DOPA, dopamine and epinephrine at concentrations ≥ 10−4 mol l−1. Our results indicate that P. canaliculus larval settlement is under endogenous regulation by a catecholaminergic mechanism. Furthermore, the inductive effects of all tested metabolites in the epinephrine biosynthesis pathway point to a putative involvement of adrenergic-type receptors in the regulation of larval settlement in this mussel species.