Variations in benthic community structure in a sub-tropical estuary

Abundances of macroinfaunal invertebrates in sand dollar (Dendraster excentricus) beds and in adjacent areas free of sand dollars were studied at 10 intertidal sites in the Pacific Northwest region of the USA and Canada. Each site was sampled once in late summer of 1977. There were no significant differences in overall diversity of species between the beds and adjacent areas; nor did cluster analysis indicate a sand dollar bed community. However, a polychaete (Armandia brevis) was significantly more abundant inside the beds than just outside them. Conversely, in comparison to the beds, adjacent regions contained significantly more specimens of the following species: a bivalve (Transennella tantilla), several tubicolous crustaceans (Corophium spp., Ampelisca agassizi, and Leptochelia savignyi) and two polychaetes (Glycinde polygnatha and Malacoceros arenicola). Sediment characteristics at each study site were not correlated with the presence or absence of sand dollars; moreover, a comparison among the 10 sites revealed no sediment characteristics typical of sand dollar beds. At most of the sites, significantly fewer tube-building invertebrates occurred inside sand dollar beds than outside. The discussion considers the possibility that mechanical disturbance by the sand dollars tends to exclude some macroinvertebrates (especially tubicolous ones) from sand dollar beds.     

Population ecology and secondary production of the polychaete Loimia medusa (Terebellidae)

In soft-sediment marine and estuarine habitats, population dynamics of resident species are an important aspect of commnity structure and function, yet the population dynamics of many members of these communities remain poorly studied. The population dynamics and secondary production of the infaunal terebellid polychaete Loimia medusa (Savigny) were investigated in a shallow sand habitat of the York River, Chesapeake Bay, Virginia, between June 1989 and December 1990. Monthly sampling throughout 1 yr revealed that individuals were present year-round with maximum densities of 60 ind m^-2 and a life span of 1 yr. Abundances were highest from August through September when two cohorts recruited to the population. Mean individual growth was highest in summer, and appeared to be a function of temperature rather than food limitation. Adults were reproductive from May through October and exhibited high fecundity; the number of oocytes segment^-1 ranged from 201 to 15840 among worms. Larvae initially appeared approximately 1 mo after gametes were first observed in adult L. medusa, and these larvae appeared to spend less than 1 mo in the plankton. Abundances of larvae in the water column were significantly higher around new moon, suggesting lunar spawning periodicity. New recruits attained sexual maturity within 2 mo of settlement. Secondary production was 3.3 g ash-free dry wt m^-2 yr^-1 and the P/B (production/biomass) ratio was 3.0. Despite equilibrium species characteristics such as large size, high fecundity, and planktonic larvae, L. medusa exhibits some characteristics typically ascribed to opportunistic species, namely, the capacity for rapid growth and maturation, a short life span and a relatively high P/B ratio. This mixture of life history characteristics emphasizes that there is no simple dichotomy between opportunistic and equilibrium species. We caution that the dominance of large infaunal polychaetes in soft-bottom estuarine and marine environments may not be a useful indicator of undisturbed habitats.     

Settlement of larval blacklip abalone, Haliotis rubra, in response to green and red macroalgae

Surfaces from the habitat of adult Haliotis rubra were tested as inducers of larval settlement to determine the cues that larvae may respond to in the field. Settlement was high on the green algal species Ulva australis and Ulva compressa (Chlorophyta), the articulated coralline algae Amphiroa anceps and Corallina officinalis, and encrusting coralline algae (Rhodophyta). Biofilmed abiotic surfaces such as rocks, sand and shells did not induce settlement. Ulvella lens was also included as a control. Treatment of U. australis, A. anceps and C. officinalis with antibiotics to reduce bacterial films on the surface did not reduce the settlement response of H. rubra larvae. Similarly, treatment of these species and encrusting coralline algae with germanium dioxide to reduce diatom growth did not significantly reduce larval settlement. These results suggest that macroalgae, particularly green algal species, may play an important role in the recruitment of H. rubra larvae in the field and can be used to induce larval settlement in hatchery culture.     

Dynamics and biological cycle of a Melinna palmata (Ampharetidae) population during the recolonisation of a dredged area in the vicinity of the harbour of Brest (France)

The reproductive cycle and growth parameters were studied in a Melinna palmata population, for 3 yr after dredging, in the vicinity of the harbour of Brest, France. This species first settled in May 1979, 8 mo after dredging had ceased. Measurements of the diameter of coelomic oocytes indicated that spawning took place from August to October and settlement in autumn and early winter. The first settled cohort displayed a high growth rate (0.25 mm width mo^-1 in summer) and a low longevity (22 mo); the growth rate of the second settled cohort was not significantly different from the first, but its longevity was higher (28 mo); the third settled cohort had a lower growth rate (0.15 mm width per month), but lower mortality and therefore a longer life expectancy. A fourth cohort appeared in August 1981 but was not followed because of the termination of the study. M. palmata colonised the dredged area in two ways: by settlement of juveniles in autumn and by probable immigration of young and adults in May. The population increased in number and biomass from the end of dredging (August, 1978) to June 1981 and decreased after this period. The demographic strategy of this species changed from r- to K-selection during this recolonization as a result of intraspecific and interspecific competition.     

Spatial and temporal patterns of reproduction,larval settlement,and recruitment of the compound ascidian Aplidium stellatum

Spatial and temporal variation in recruitment of the compound ascidian Aplidium stellatum was examined on a shallow-water limestone outcropping in the Northeastern Gulf of Mexico from 1983 to 1985. Fifty-two percent of the recruits appeared on vertical surfaces, which were rare at this site. In the laboratory, tadpole larvae of A. stellatum consistently settled on vertical vs horizontal surfaces in a 2 to 1 ratio, regardless of the area of vertical surface offered. This settlement response was insufficient to account entirely for the field recruitment pattern, suggesting greater mortality of newly-settled individuals or larvae on horizontal vs vertical surfaces. Fifty-six percent of the variation in recruitment over 21 months could be explained by variation in the percentage of zooids brooding larvae in adult colonies. Over 28 consecutive months, the percentage of zooids brooding larvae was positively correlated with egg counts of the previous month (r ²=0.75), which in turn were weakly correlated with monthly average water temperature (r ²=0.36). These results suggest that larval production contributed substantially to temporal variation in recruitment of A. stellatum. The short larval life of tadpoles of A. stellatum and the relative isolation of the population were probably responsible for the correlation between recruitment and larval production.     

Population dynamics and reproduction of Mysella bidentata (Bivalvia: Galeommatacea) in Galway Bay,Irish west coast

Mysella bidentata (Montagu) is found in high densities in an Amphiura filiformis (O. F. Müller) community in Inner Galway Bay, west coast of Ireland. As part of an ongoing investigation at one station within this community, the population dynamics and reproductive pattern of this bivalve were investigated during the period November 1978-December 1981. Monthly sampling over the 3 yr period revealed a mean population density of 745±672 individuals m^-2. Recruitment occurred during August-October and three year-classes were identified. Growth rates were assessed by analysis of length-frequency histograms and winter growth checks. Individuals from the Y1 and Y2 year-classes functioned as hermaphrodites during the 1980 and 1981 reproductive seasons. The Y0 year-class contained both males and hermaphrodites. Results are compared with available information on the same species from other locations.Contribution No. 225 from the School of Marine Sciences, University College, Galway Ireland     

Annual fluctuation of life-history traits in the mud crab Macrophthalmus japonicus

Interannual fluctuation of life-history traits in the mud crab Macrophthalmus japonicus (De Haan) was studied for a 7-yr period (1981 to 1987) in an intertidal mudflat in the estuary of the Tatara-Umi River, Fukuoka, Japan. Density of juveniles fluctuated greatly, and maximum annual density was low in 1981 to 1984 (22.0 to 44.0 m^-2) and very high in 1985 to 1987 (98.5 to 188.6 m^-2). In 1980, recruits may have been very few, though there is no data on or before 1980, because no crab of the 1980 cohort was found during the study period. Density of adult crabs was almost stable (11.0 to 32.6 m^-2), perhaps because of density-dependent mortality. Under the high density conditions prevailing from 1985 to 1987 crabs grew slowly and longevity was shorter. Male chela and female abdomen were dwarfish, and females produced few and small broods. The changes of life-history traits under high density conditions were thought to result from strong intraspecific competition for space.     

Energetics,competency, and long-distance dispersal of planula larvae of the coral Pocillopora damicornis

Pocillopora damicornis (Linnaeus) were collected from Enewetak Atoll, Marshall Islands, in 1980–1981) and Kaneohe Bay, Hawaii, in 1982. Their planula larvae contained 17% protein, 70% lipid, and 13% carbohydrate by dry weight. Calculations based on stored energy reserves and daily metabolic expenditure indicate that planulae could survive approximately 100 d and still settle successfully. Competency experiments demonstrated that larvae settled and metamorphosed after 103 d. This period of time is sufficient to allow immigration of larvae from the Central Pacific to the eastern Pacific, and supports the hypothesis of long-distance dispersal of larvae for the origin of present eastern Pacific populations of P. damicornis.     

Population dynamics and reproductive cycle of Pholoë minuta (Polychaeta: Sigalionidae) in Galway Bay

Pholoë minuta (Fabricius) is a prominent member of the Amphiura filiformis (O.F. Müller) subcommunity in Galway Bay, Ireland. The aim of the present investigation was to study the population dynamics and reproductive cycle of P. minuta in this area. Monthly sampling over a 2 yr period (November 1978–October 1980), at a permanent station (18 m) with a fine sand substrate, revealed a mean density of 96 individuals per 0.1 m². The width of the fifth elytron was correlated with total body length and was used as a basis for analysing population structure. Four distinct year classes were evident and estimates of recruitment levels and growth rates were calculated. P. minuta is polytelic and reproduces for the first time when approaching 3 yr of age. Spawning occurred in March—April and appeared to be associated with a seasonal low in bottom-water temperature.     

Induction of settlement and metamorphosis in the sand dollarEchinarachnius parma: Evidence for an adult-associated factor

Larvae of the northern sand dollarEchinarachnius parma (Lamarck), reared from adults collected from Eagle Head, Nova Scotia, Canada, in 1988 and 1989, metamorphose in significantly greater numbers on sand conditioned by adults than on non-conditioned sand. The metamorphic factor has a molecular weight < 1000 and is destroyed by heating. Larvae are capable of sensing this cue in the water column under static conditions. Substrata of varying particle size and surface texture can be conditioned by adults to induce metamorphosis. Substrata conditioned in the dark, and conditioned sand treated with antibiotics also induce metamorphosis suggesting that the factor is not produced by adult-associated bacteria or microflora. In nature, this adult-associated factor may direct settlement of larvae to established sand dollar beds resulting in the aggregated distribution of this species.     

Otolith ring deposition in relation to growth rate in herring (Clupea harengus) and turbot (Scophthalmus maximus) larvae

Larvae of Clyde spring-spawning Clupea harengus L. and hatchery-produced Scophthalmus maximus (L.) were reared from hatching through metamorphosis in 1980 and 1981 in laboratory tanks and in large enclosures under various light, temperature, and feeding regimes in order to study otolith ring deposition and growth under different conditions. Ring deposition and growth rates were significantly affected by rearing conditions in both species. The ring deposition rates observed under the conditions tested ranged from 0.34 to 0.92 rings d^-1 in herring larvae, and from 0.07 to 1.0 rings d^-1 in turbot larvae. Growth rates ranged from 0.11 to 0.42 mm d^-1 in herring and from 0.05 to 0.27 mm d^-1 in turbot. The number of otolith rings was dependent on the growth rate of the individual larva. At the population level, higher ring deposition rates were observed in faster growing populations. In herring larvae, the relationship between average growth rate and average ring deposition rate was logarthmic, reaching an asymptote at 1 ring d^-1 for growth rates approaching 0.40 mm d^-1. The relationship was linear for turbot larvae for the range of growth rates observed.     

Population dynamics of the acorn barnacles, Tetraclita squamosa and Tetraclita japonica (Cirripedia: Balanomorpha), in Hong Kong

Tetraclita squamosa and Tetraclita japonica are common, intertidal barnacles. In Hong Kong, the population dynamics of the two species exhibited spatial and temporal variation on two semi-exposed shores. T. squamosa produced egg masses from May–June and annual settlement and recruitment occurred from June–July. In contrast, settlement and recruitment of T. japonica was sparse from March–May, but intensified in July–October. Mature gonads and egg masses were, however, only present from September–November, suggesting the larvae from the two settlement pulses originated from other locations as well as Hong Kong populations. Settlement intensity and post-recruitment mortality of the two species varied between sites, possibly due to spatial variation in free rock space, physical transport of larvae and abundance of food in the water column.Communicated by T. Ikeda, Hakodate     

Effect of microbial films on settlement of bryozoan larvae (Bugula simplex,B. stolonifera and B. turrita)

The influence of microbial films on larval settlement was studied for sympatric species of cellularioid cheilostome bryozoans (Bugula simplex, B. stolonifera, and B. turrita). Settlement experiments were conducted in the laboratory in 1981 with and without a choice of filmed or unfilmed substrates. When given a choice of substrates, the larvae of all three bryozoan species significantly preferred the filmed substrate. When not given a choice of substrates, both B. simplex and B. turrita larvae tended not to settle on the unfilmed substrate, while the filmed and unfilmed substrates were equally attractive to B. stolonifera. Microbial films enhanced the settlement of all three species.     

Recruitment,growth, and diel vertical migration of Euphausia pacifica in a temperate fjord

The pelagic crustacean Euphausia pacifica Hansen was sampled with a multiple-sample 1.0 m² Tucker trawl and a multiple-sample 1.0 m² vertical net in Dabob Bay, Washington on 17 dates between May 1985 and October 1987. Size (stage) structure and abundance of the population were determined for each date, while vertical distribution and diel migration were determined for 13 dates. Although internannual variability in both timing and magnitude of events occurred, consistent patterns were discernable. The population produced a large pulse of larvae (2 to 5 mm) in late spring of each year, apparently in response to the vernal phytoplankton bloom. Much lower abundances of larvae occurred during summer and autumn of each year, and larvae were completely absent during winter. Recruitment to the juvenile (6 to 9 mm) and adult (10 mm) stages was strongest during the summer, with abundances of these individuals peaking in summer and autumn. Individual growth rates, determined by modal progression analysis, were calculated for E. pacifica. Rates ranged from zero for some adult cohorts during the winter to 0.12 mm d^-1 for larvae during spring. The latter are among the highest ever reported for this species in the field. The vertical distributions and diel vertical migrations (DVM) of E. pacifica varied seasonally and between size (stage) classes. At night, all size classes were distributed in the surface layer (upper 25 m) irrespective of season or year. During the day, the larger/older stages were always distributed at middepths (50 to 125 m). In contrast, the daytime distribution of the larvae was more variable, being concentrated at the surface during spring and early summer of 1985, and at increasing depths later in the summer and autumn of 1985 and again in spring of 1986. This resulted in invariant DVM in the juveniles and adults, but variable DVM in the larvae, the latter of which is hypothesized to be a response to variable abundances of zooplanktivorous fish.     

Tidal height,rather than habitat selection for conspecifics,controls settlement in mussels

Settlement is a major determinant of intertidal populations. However, the energy costs of lost larvae are very high. Accordingly, arrival and attachment on suitable substrata are essential requirements for species’ survival. On the intertidal, the presence of cues left by adult or juvenile conspecifics could be vital for the successful establishment of larvae arriving on the shore. Two mussel species, the indigenous Perna perna and the invasive Mytilus galloprovincialis, co-occur on the lower eulittoral zone on the south coast of South Africa. P. perna dominates the low and M. galloprovincialis the high mussel zones, with co-existence in the mid mussel zone. This study tested the hypothesis of settlement selectivity for conspecifics in these two mussel species, to understand whether the final adult distribution of mussels on the shores is determined by active behavioural and chemical mechanisms. Preferential selection by larvae for conspecifics was tested in the field during the peak settlement period in 2004 in natural mussel beds across zones and through manipulative experiments in the mid-zone where the species co-exist. On natural beds, settlement was determined by counts of settlers attached over 48 h onto artificial collectors. Collectors were placed on beds of P. perna and M. galloprovincialis present at both high- and low-adult densities, as well as in mixed beds. On such natural beds, settlers of both species consistently favored low-zone P. perna beds. Settlement patterns over 24 h onto experimentally created mussel patches consisting of P. perna, M. galloprovincialis or the two species combined beds, set in the mixed zone, did not conform with the results of the natural beds study: settlers of both species settled with no discrimination among different patches. The results indicate that mussels, which are sedentary, lack attraction to conspecifics at settlement. This highlights the importance of tidal height in setting settlement rates, and of post-settlement events in shaping populations of these broadcast spawners.     

Microdistribution of the marine copepodOithona davisae in the shallow waters of Ariake-kai mud flats,Japan

The microdistribution ofOithona davisae Ferrari and Orsi inhabiting shallow waters of Ariake-kai, western Kyushu, Japan, was investigated in 1980–1981 by means of a pumping method. Water samples (10 l) were repeatedly collected from the surface to the bottom at intervals of 0.5 m. This species was dispersed when the tidal current ran fast (more than 20 cm s^–1), but aggregated in the upper layer during the period of slow current. Their density was highest when the current stopped. Aggregation ofO. davisae presumably induced the continuous flat swarm near the surface. It is to be expected that the shallow waters in Ariake-kai would be favorable as nursery grounds for the fish larvae and juveniles which depend on the presence of such swarms.Contribution no. 51 from the Aitsu Marine Biological Station     

Life history characteristics of a coral reef sponge

Study of the life history characteristics of the common Red Sea sponge Mycale fistulifera (Poecilosclerida: Demospongiae) reveals several traits which may categorize it as an opportunistic species: (1) at least part of the population is reproductively active throughout the year, providing a continuous supply of larvae for settlement; (2) sponges may produce and release a large number (152±39 larvae d^-1) of brooded larvae; (3) released larvae are capable of fast settlement and metamorphosis (minutes to 30 hours post-release); (4) the turnover of the population is high and population size varies with time. From 48 initial sponges plus 94 recruits, only 25 remained alive after 14 months of observation; (5) most members of the population (>70%) have a small body size (<30 cm²); (6) sexual maturity may occur at an early age. These traits facilitate continuous establishment of M. fistulifera in new spaces on the reef; (7) M. fistulifera, preferred substrate is another opportunistic species, the coral Stylophora pistillata which it overgrows.     

Spawning and larval development of the black turban snail Tegula funebralis (Prosobranchia: Trochidae)

An understanding of spawning and larval development can be fundamental to interpreting the abundance, distribution, and population structure of marine invertebrate taxa. Tegula funebralis (A. Adams, 1855), the black turban snail, has been the focus of numerous ecological studies on the Pacific coast of North America. To date, there are only conflicting and anecdotal reports of spawning, and there is no information on larval or juvenile development for this conspicuous and abundant species. On 19 September 1995, two individuals of T. funebralis were observed free-spawning gametes into seawater in tanks at the Oregon Institute of Marine Biology. Embryos and larvae were subsequently reared to metamorphosis and beyond. Development was pelagic and similar to development described for other trochids, and larvae were observed not to feed at any stage. Larvae began to metamorphose at 5.7 to 6.7 d and settled at 260 μm shell length. Juveniles grew ≃ 10 μm in shell length per day and appeared to feed on detritus. Juveniles lacked some adult diagnostic shell characters, including two columellar nodes and a closed umbilicus. In the field, small (<3 mm) juveniles occurred in the adult habitat on all sampling dates between October and March. Small juveniles were found only under rocks and were most abundant under rocks partially buried in coarse sand, suggesting that juveniles may utilize a specific microhabitat within the adult T. funebralis habitat. Received: 7 October 1996 / Accepted: 17 October 1996     

Seasonal and diel variation in movement rhythms of sand dollar, Peronella lesueuri (Valenciennes 1841), in Cockburn Sound, Western Australia

Rates and direction of movement in the sand dollar Peronella lesueuri were measured in summer and winter in Cockburn Sound, a large coastal embayment in south-western Australia. P. lesueuri was found to have a diurnal activity pattern throughout the year and had a greater movement rate in the summer (mean of 5.3 cm h^?1, day; 3.9 cm h^?1, night) than in the winter (mean of 2.7 cm h^?1, day; 2.0 cm h^?1, night). Seasonal change in temperature and physiological requirements by the sand dollar are the most likely reason for the seasonal differences. Reasons for diurnal variation were not clear. Direction of movement was found to be random at both times of the year. Based on these movement rates, one sand dollar can bioturbate an approximate area of 0.1 m² day^?1 and 36.4 m² year^?1. At a conservative density estimate of 0.5 sand dollars per m² it takes approximately 20 days for the sand dollars to rework the entire area of the sediments in the habitats they occupy.     

Spatial and temporal variation in coral recruitment on the Great Barrier Reef: Implications for dispersal hypotheses

Over 15 000 coral recruits were counted on settlement plates from three mid-shelf reefs and six fringing reefs in the northern section of the Great Barrier Reef during two summers (1986 and 1987) and one winter (1987). The density of coral recruits on some settlement plates from a fringing reef was up to 4.88 cm^–2, the highest value ever reported. Mean density of recruits was greater on fringing reefs (81.1 recruits/settlement plate) than on mid-shelf reefs (15.6 recruits/settlement plate), but there was greater spatial variation in abundance of recruits between the fringing reef sites. Other differences between the mid-shelf reefs and the fringing reefs were that different taxa were dominant, and that settlement orientation differed, with mid-shelf recruits settling preferentially on horizontally oriented surfaces and fringingreef recruits preferring vertical surfaces. Of the three midshelf reefs, Green Island reef recorded the highest recruitment rate for each of the two summers, despite having a depauperate adult coral population following predation by the asteroidAcanthaster planci. This suggests that coral larvae frequently travel between reefs. In contrast with an earlier study, there was no consistent difference in abundance of recruits between forereef and backreef locations. Overall, the results indicated great spatial variation in the availability of coral larvae, both on the scale of whole reefs and within-reef habitats.