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     

Latitudinal variation in the life history features of the black turban snail Tegula funebralis (Prosobranchia: Trochidae)

At higher latitudes along the west coast of the USA the herbivorous intertidal snail Tegula funebralis (Adams, 1854) lives longer, grows more slowly, but attains a larger size than further south. To the north, age distributions are less predictable and often far from stationary. The differences, which have some generality, can be explained either by a primary temperature effect joined with increased hazards to planktonic larvae in the north, or else may result from a combination of interactions between intensity of predation, population density and food supply. Growth rates of transplanted individuals suggest a genetic basis for the latitudinal differences.     

Factors influencing clustering in the intertidal snail Cerithium moniliferum

The snail Cerithium moniliferum Kiener at Heron Island (southern end of the Great Barrier Reef) clusters at outgoing tide and disperses at incoming tide. In containers with a constant water level, but exposed to the normal day and night rhythm, the snails cluster and disperse rhythmically for up to several days. Graphical simulation and spectral analysis, preceded by first difference filtering, showed two components, one corresponding to the tidal, and the other to the diurnal rhythm. Snails kept under continuous light also exhibit a two-component rhythm of clustering and dispersal. In containers with high (40 cm) water level and under continuous light or normal day and night rhythm, the two-component rhythm may—for some unknown reason—be replaced by long fluctuations of dispersal, with clustering occurring in the afternoon only in snails kept under normal alternation of day and night. Snails kept for 24 h in dryness prior to putting them into containers with water, remain clustered (sometimes with an initial dispersal “shock”) for a long time, with subsequent slow fluctuations of clustering and dispersal, probably induced by the light conditions. Factors contributing to clustering and dispersal are: (1) increased rate of dropping from container walls at outgoing tide; (2) lack of locomotory activity at low tide; (3) negative geotaxis at incoming tide; (4) positive geotaxis at outgoing tide; (5) attraction of snails by other snails (positive chemotaxis) throughout the rhythm. Sudden exposure to light increases the rate of dropping from the container walls and may be a contributing factor to stronger clustering during the day. Factors 1–4 show endogenous periodicities.     

Habitat complexity impacts persistence and species interactions in an intertidal whelk

Although experiments have shown that habitat structure may influence the distribution of species and species interactions, these effects are still not commonly integrated into studies of community dynamics. Since habitat structure often varies within and among communities, this may limit our understanding of how various factors influence communities. Here, we examined how mussel bed complexity (the presence and thickness of mussel layers) influenced the persistence of whelks (Nucella emarginata) and interactions with a top predator (ochre sea stars, Pisaster ochraceus) and prey (mussels, Mytilus californianus). Results from a mark?Crecapture experiment indicate that whelk recapture rates are higher in more complex habitats, and laboratory experiments demonstrate that habitat complexity affects whelk feeding, growth, and nonconsumptive interactions with a keystone predator. Habitat complexity therefore has direct effects on species and also may lead to trade-offs among feeding, refuge, and other factors, potentially influencing the distribution of whelks and the effects of both whelks and sea stars on intertidal communities. These results demonstrate that habitat structure may play an important role in intertidal communities and other habitats and should be further considered in the experimental design of future studies of community dynamics.     

Accumulation and regulation of heavy metals by the intertidal snail Polinices sordidus

The gastropod Polinices sordidus was collected from an uncontaminated area in Quibray Bay, New South Wales, Australia, in 1990. The snails were exposed for 2 wk to polluted sediments collected from Port Kembla Harbour, Blackwattle Bay, Lake Illawarra, Lake Macquarie in New South Wales, Australia, and the Derwent River in Tasmania, Australia. Metal accumulation and regulation by this species were evaluated. Metal concentrations in snail tissues and total, EDTA and HCl-extractable metals in the sediments were compared. Copper concentrations were extremely varied in snails exposed to the same sediment. This was not the case for other matals tested. No accumulation of copper was found in snails exposed to different sediments. There was no zinc accumulation from sediments containing less then 10 mg Zn/g. P. sordidus could accumulate lead, manganese and iron from some of the sediments. Manganese concentrations in the snail tissues correlated with total, HCl-extractable and, more significantly, EDTA-extractable Mn in the sediments. P. sordidus was not considered to be a good bioindicator of copper and zinc contaimination in sediments; however, this species could be used as an indicator of lead and manganese contamination.     

Function of the shell spine in the predaceous rocky intertidal snail Acanthina spirata (Prosobranchia: Muricacea)

Feeding observations revealed that Acanthina spirata (Blainville, 1832) uses the shell spine in a ramming and prying motion, resulting in the fracturing and/or forcing open of opercular plates in the barnacles Balanus glandula (Darwin, 1854) and Chthamalus fissus (Darwin, 1854). Attacking barnacles by using the shell spine may represent a second widespread feeding mechanism (in addition to drilling) in muricacean gastropods. Specialization of the shell spine for attacking barnacles is advantageous over drilling within the context of an optimal foraging theory. Rockey intertidal field and laboratory experiments at Palos Verdes and Los Angeles, California, respectively, in 1981–1982 revealed, that snails with a shell spine have lower handling times and feed at a greater rate than spineless snails which drill their prey. Spine penetration of prey as opposed to drilling takes considerably less time than a tidal cycle. This is expected to increase the success rate for completion of feeding, since during tidal flux snails risk being dislodged. Plasticity in attack mechanisms allows A. spirata with broken spines to penetrate prey by drilling while undergoing spine repair. Differences exist in spine-feeding by A. spirata on B. glandula and C. fissus. The attack process takes more than twice as long when snails attack B. glandula versus C. fissus. However, there is no difference in the mean number of spine thrusts required to penetrate the opercular plates of the two species. When feeding on the larger barnacle B. glandula, A. spirata ingests significantly greater dry weight per unit handling time than with C. fissus.     

Mate choice in the face of both inbreeding and outbreeding depression in the intertidal copepod Tigriopus californicus

 In species vulnerable to both inbreeding and outbreeding depression, individuals might be expected to choose mates at intermediate levels of genetic relatedness. Previous work on the intertidal copepod Tigriopus californicus has repeatedly shown that crosses between populations result in either no effect or hybrid vigor in the first generation, and hybrid breakdown in the second generation. Previous work also shows that mating between full siblings results in inbreeding depression. The present study again found inbreeding depression, with full sibling mating causing significant fitness declines in two of the three populations assayed. In the mate choice assays, a single female was combined with two males. Despite the costs of both inbreeding and outbreeding, mate choice showed clear inbreeding avoidance but no clear pattern of outbreeding avoidance. This lack of outbreeding avoidance may be attributed either to the temporary increase in fitness in the F₁ generation or to the absence of selection for premating isolation in wholly allopatric populations with infrequent migration. If this inability to avoid unwise matings is common to other taxa, it may contribute to the problem of outbreeding depression when allopatric populations are mixed together. Received: 18 May 1999 / Accepted: 25 January 2000     

Factors influencing food choice by the seaweed-eating marine snail Norrisianorrisi (Trochidae)

Through two-choice gustatory experiments, a␣preference hierarchy was established␣for␣the␣herbivorous gastropod Norrisianorrisi Sowerby, with laminarialean kelps preferred over all other seaweeds. Among the kelps, laminae of Macrocystispyrifera were slightly preferred over Egregiamenziesii, and both were strongly preferred over sporophylls of Eiseniaarborea. E.arborea, the least preferred kelp, was consistently chosen over other algae common in the snail's habitat (Halidrysdioica, Dictyotaflabellata, and Pterocladiacapillacea) and over seaweeds believed to be edible and palatable based on their morphology, structure, and secondary chemistry (Endarachnebinghamiae, Mazzaellaflaccida, and Ulvalobata). The morphologies and structural toughness of tested seaweeds varied significantly as did their nutritional (% carbon, % nitrogen, C:N ratio, and % ash) contents and phlorotannin concentrations; however, snails preferred to feed on kelps regardless of nutritional content, toughness or phlorotannin concentration; and among kelps preferred to feed on the least tough species (based on penetrometer measurements), which also were those containing the lowest phlorotannin concentrations. Preference for kelp was not upheld in experiments using agarose thalli to which freeze-dried powder, of either the kelp Eiseniaarborea or non-kelp Endarachnebinghamiae was added, suggesting the destruction of attractant chemicals during the making of the artificial foods. Our data suggest that the preference of N. norrisi for kelps over other potentially edible and palatable seaweeds may not be related to nutritional content, but instead may have evolved in response to factors such as availability, habitat provision, or refuge from predation. Received: 27 September 1996 / Accepted: 7 October 1997     

Relating bird host distribution and spatial heterogeneity in trematode infections in an intertidal snail—from small to large scale

Shorebird abundance and spatial distribution of larval trematodes in the New Zealand mudsnail, Zeacumantus subcarinatus, were investigated in soft-sediment intertidal bays within Otago Harbour, South Island, New Zealand. In a small-scale study, recruitment of trematodes to caged sentinel snails and the prevalence of infection in free-living snails were examined across a grid of fifteen 50×25 m plots arranged in a representative area of an intertidal bay, in relation to within-plot shorebird abundance (definitive hosts) and tidal height. In a large-scale study, natural spatial variation of larval trematodes in Z. subcarinatus was examined across 12 bays in relation to local abundance of shorebirds. Our results revealed that trematode prevalence in snails was positively correlated with bird abundance across bays (R ²=0.503, P=0.006). In contrast, despite a difference in bird abundance between tidal heights, there was no evidence that trematode prevalence reflected the spatial distribution of birds in the small-scale study, suggesting that factors related to differences in submersion time may override the differential input of trematode eggs from birds.     

The importance of sandflat morphology to recruitment of the intertidal snail Nassarius pauperatus during ten consecutive years at three sites in South Australia

This project was desinged to confirm the temporal consistency of inter-site differences in recruitment of an intertidal gastropod, and to test the hypothesis that these differences are accounted for by differences in shore topography. Annual recruitment of the intertidal sanil Nassarius pauperatus (Lamarck) was estimated at two sandflats in Gulf St Vincent, South Australia, over a period of 12 yr (1979 to 1990). At one sandflat the gradient was slight, the zone containing N. pauperatus was wide, and there were extensive pools of water at low tide, whilst at the other sandflat the gradient was steeper, the zone containing N. pauperatus was narrower, and there were fewer or no pools. Although recruitment at both sites varied temporally, the density of recruits was always higher at the first site. These data, together with data covering 10 yr (1981–1990) from a sandflat where the gradient of the substratum was decreasing due to accretion of sediment, suggest that shore topography is an important determinant of relative recruitment for N. pauperatus in South Australia.     

Feeding preferences and the relationships between food choice and assimilation efficiency in the herbivorous marine snail Lithopoma undosum (Turbinidae)

Preference rankings for 13 macrophytes were established for the subtidal herbivorous snail Lithopoma undosum using two-choice laboratory experiments and consumption rates. L. undosum did not discriminate among three kelp foods (Egregia menziesii, Eisenia arborea and Macrocystis pyrifera) but ate kelp preferentially and more rapidly over all but Ulva spp. among tested macrophytes. Secondary preferences were established for the red alga Pterocladiella capillacea, followed by the coralline Lithothrix aspergillum, whereas the brown seaweeds Zonaria farlowii and Halidrys dioica and the seagrass Phyllospadix torreyi were the least preferred macrophytes. Fastest consumption rates (1.91 g day⁻¹) were measured in trials consisting only of kelp foods. These results indicate that L. undosum exhibits clear feeding preferences even when given less-preferred, non-kelp macrophytes. Using an ash-marker technique, we determined total organic, carbon, and nitrogen assimilation efficiencies (AE%) for six macroalgae used in preference trials. Tested macrophytes were assimilated at different efficiencies but a pattern was not detected between AE (%) and a macrophyte’s position in L. undosum’s preference hierarchy. Highest total organic AEs were found for P. capillacea (61.2%) and H. dioica (59.4%); lowest AEs were detected for E. menziesii (34.9%), a preferred dietary item. Nitrogen was assimilated from red algae with higher efficiencies (74.9–84.3%) than from brown or green algae. These data suggest that the digestive capabilities of L. undosum are better suited for assimilating organic material and nitrogen from less-preferred, non-kelp foods. This supports the hypothesis that factors besides nutritional composition and digestive optimization have played a role in the evolution of feeding preferences in L. undosum and probably other herbivorous snails associated with northeastern Pacific kelp beds.     

Orientation in the intertidal salt-marsh collembolan Anurida maritima

We investigated the cues used by the intertidal insect Anurida maritima (Apterygota: Collembola) to orient to the appropriate zone in which to seek shelter during high tide. Our experiments clearly ruled out any significant role for magnetic, local topographic, slope or celestial cues. Instead, we suggest that the difference between the appearance of the up-shore and the down-shore horizon is the major cue used by the collembolans. When a mirror was used to duplicate either of the two horizons, the insects were not able to orient. The insects moved towards an artificially dark horizon (the reverse of the mirror) placed down-shore, the opposite of their usual direction of movement. The insects had an endogenous circatidal rhythm of phototactic behaviour: most of the population was always negatively phototactic, but between 2 and 7 h after low tide, a significant proportion of the population became positively phototactic. This is the first demonstration of an endogenous tidal rhythm of orientation in an insect. Received: 31 May 1999 / Received in revised form: 1 February 2000 / Accepted: 19 February 2000     

Habitat selection in the tropical polychaeteSpirobranchus giganteus

Total body weight, tube length, abdomen weight and branchial crown weight of individualSpirobranchus giganteus (Pallas) living on four different coral species on the bank reef on the west coast of Barbados were investigated in 1986. Worms onDiploria strigosa were larger in all size parameters than those onMontastrea annularis, which were larger than those onMontastrea cavernosa, which were larger than those onPorites porites. The differences between worms onM. annularis andM. cavernosa were not significant. Variation in worm size on the different corals could result from variation in mortality and/or variation in growth. Whichever the case, larger worms may have higher lifetime reproductive success. Abdomen weight is an index of gamete production inS. giganteus, and increases with increasing body weight for worms on all corals. Moreover, larger worms do not have lower abdomen weight at a given body size than smaller worms. This may imply that faster growth does not reduce gamete production at body size. The coral species on which worms are largest are those most preferred by worm larvae in the laboratory and most heavily colonised by adult worms in the field. The results suggest adaptive habitat selection by planktonic larvae ofS. giganteus.     

Seasonal changes in the structure of an intertidal community

Quantitative (0.25 m²) samples of macrofaunal (>1.0 mm) invertebrates were taken in each season from one habitat of an intertidal sandbar in the North Inlet estuary near Georgetown, South Carolina, USA. During all seasons the community inhabiting the sample site was numerically dominated by two species of haustoriid amphipods (Acanthohaustorius millsi and Pseudohaustorius caroliniensis). Seasonal changes at the community level were clearly controlled by the population dynamics of the numerically dominant species, and qualitative information on life histories was important to the interpretation of analyses' results.This work was supported by the Environmental Technology Center of Martin Marietta Corporation and the Belle W. Baruch Institute for Marine Biology and Coastal Research. It is Contribution No. 138 of the Belle W. Baruch Institute for Marine Biology and Coastal research.     

Community metabolism of intertidal flats in the Ems-Dollard estuary

To obtain an insight into the flux of carbon through intertidal sediments of the Ems-Dollard estuary, the annual cycles of gross benthic primary production and community respiration were measured at six stations, together with a set of environmental parameters. In a stepwise multiple regression analysis it was shown that temperature alone and temperature plus viable bacteria explained 50 and 70% respectively of the observed variation in community respiration. Other variables, including the rate of primary production and amount of organic carbon in the sediment were less important. The rate of primary production could not be fitted adequately into a multiple regression equation. The annual values of community respiration (177–794 gO₂·m^-2·yr^-1) and primary production (82–628 gO₂·m^-2·yr^-1) were within the range of published values. except for one station in the vicinity of a wastewater outfall, which had an extreme production (average 984 gO₂·m^-2·yr^-1). At four stations, annual community respiration exceeded primary production by 40%. It is concluded that the main carbon flux within the sediment, from CO₂ to benthic primary producers, to benthic consumers and from there to CO₂ again,was completed within a month or so, leaving untouched the large bulk of organic matter within the sediment. Possible effects of wastewater discharges on community metabolism are discussed.Publication No. 43 of the project Biological Research in the Ems-Dollard Estuary     

Substrate size mediates thermal stress in the rocky intertidal

Variation in physical factors, such as slope, orientation, and wind exposure, shapes thermal conditions. Variation in substrate size is common in many habitats, but its thermal consequences for organisms are not well characterized. Larger substrates should remain more thermally stable and act as thermal refuges for associated organisms during short, thermally stressful periods such as midday temperature peaks or tidal exposure. In observations and a transplant and thermal integration experiment, we found that larger rock substrates stayed cooler and facilitated greater survival of the barnacle Semibalanus balanoides in the high intertidal relative to small substrates during the hot summer months in southern New England, USA. However, in thermally benign northern New England, rock substrate size had no effect on barnacle distributions, indicating that the thermal effects of substrate size are mediated by regional climate.     

Hydrocarbon metabolism in the intertidal fiddler crab Uca pugnax

The fiddler crab Uca pugnax was examined for its ability to metabolize foreign hydrocarbons. The microsomal mixed function oxidase system was identified in U. pugnax tissues using Aldrin epoxidation rates as the assay. Rates were slow: 96 pM Dieldrin per mg microsomal protein per hour in the hepatopancreas, 438 pM mg^-1 h^-1 in the gill, and 228 pM mg^-1 h^-1 in claw-muscle microsomes. Using standard methods, no difference in rates could be detected between crabs living in clean areas and those living in environments highly contaminated with foreign hydrocarbons. In vivo rates of naphthalene oxidation were measured and used to calculate a clearance time for U. pugnax body tissues based on the aromatic hydrocarbon content of crabs collected from an oil-polluted salt marsh. Calculated clearance time was beyond the life span of the crab. It is concluded that this minimal ability of U. pugnax to metabolize foreign hydrocarbons partially accounts for its sensitivity to oil pollution in the environment.     

Habitat Loss and Changes in the Species-Area Relationship

Abstract: The species-area relationship (SAR) has been used successfully to predict extinction from extent of habitat reduction. These extinction estimates assume that species have uniformly distributed range requirements and a minimum abundance level required for persistence; how many species are lost depends solely on how much habitat is removed, not on where it is removed. We consider another limiting case in which range requirements, rather than abundances, determine extinctions. We used a new method for constructing SARs based on assumptions about geographic ranges of species. Our results show that habitat destruction can change the SAR and consequently the number of species predicted to be lost due to habitat destruction. Our method generates SARs that vary in shape according to the specific distributions of geographic range and occupancy but that have the common feature of being described by a power law with an exponent of <1. When the geographic range of species was included in the SAR, the way habitat was lost became important. Although the SAR before habitat destruction is often used to predict species loss after habitat destruction, assumptions must be clearly stated. To predict the damage caused by habitat loss with our model, it is necessary to know the fraction of aggregated species, the distribution of geographic ranges, the form of habitat destruction, and the sampling protocol. The remaining theoretical challenge is to develop a full theory that links abundance and range.     

Morphological and habitat divergence in the intertidal limpet Patelloida pygmaea

In the intertidal limpet Patelloida pygmaea, two distinctive morphs, the forms pygmaea and conulus, have been recorded. The former possesses a flat elongated shell, and the latter has an extremely high round shell. It has been observed in the field that pygmaea is found on oyster shells Crassostrea gigas. The form conulus uses an unusual substrate for attachment. It is found on the living shells of the intertidal gastropod Batillaria cumingi. Although conulus is normally found only on shells of Batillaria, it can also be found on oyster shells when pygmaea and Batillaria shells are not present in nature. An electrophoretic analysis of allozymes showed that these two forms are reproductively isolated from each other and coexist without gene exchange on the same mudflat. Laboratory experiments showed that pygmaea prefers oyster shells and conulus prefers Batillaria shells as substrates for attachment when both oyster and Batillaria shells are present. The form pygmaea did not attach to Batillaria shells, even when only Batillaria shells were available. However, conulus also attached to oyster shells when Batillaria shells were not available. The proportion of individuals of conulus that attached to oyster shells decreased significantly when pygmaea was attaching to the oyster shells. These results suggest that pygmaea is ecologically more specialized to living on oyster shells than conulus.     

Desiccation as a factor in the intertidal zonation of barnacles

Four species of balanomorph barnacles, Balanus crenatus Brugière, B. balanoides (L.), Elminius modestus Darwin and Chthamalus stellatus (Poli), were studied to assess the susceptibility of intertidal barnacle species to desiccation. Known sized samples of barnacles were exposed to controlled desiccating conditions and subsequent survival and water loss were determined. It is clear that the ability to live high on the shore is dependent on a reduction of the overall permeability to water loss. Because of greater surface area to volume ratios, small stages are particularly prone to desiccation. In normal intertidal emersion periods, small stages of B. crenatus particularly, and also of B. balanoides and E. modestus which are similar in their desiccation resistance, would be susceptible to desiccation at normal temperatures and low humidities. Large barnacles would be more prone to death from high temperatures when the tide is out. The spat of C. stellatus, although surviving much longer than spat of larger dimensions of the other species, must also be prone to prolonged emersion conditions at high shore levels.