PERIDINIUM GREGARIUM,A NEW SPECIES OF DINOFLAGELLATE1,2

A dinoflagellate has been found in tidepools on the coast of the Palos Verdes Peninsula in southern California. It is described as a new species, Peridinium gregarium. In the tidepool habitat, great numbers of the organism form cloud-like masses held together by a mucous matrix. The gregarious cloud formation seems to be shared by only one other species of dinoflagellate, Peridinium sociale (Henneguy ex Labbé) Biecheler, 1935.     

Characterization of large basking shark Cetorhinus maximus aggregations in the western North Atlantic Ocean

Cetorhinus maximus aggregations recorded during extensive aerial survey efforts off the north‐eastern United States between 1980 and 2013 included aggregations centring on sightings with group sizes of at least 30 individuals. These aggregations occurred in summer and autumn months and included aggregation sizes of up to 1398 individuals, the largest aggregation ever reported for this species. The aggregations were associated with sea surface temperatures of 13–24° C and chlorophyll‐a concentrations of 0·4–2·6 mg m^?3 and during one aggregation, a high abundance of zooplankton prey was present. Photogrammetric tools allowed for the estimation of total body lengths ranging between 4 and 8 m. Characterization of these events provides new insight into the potential biological function of large aggregations in this species.     

Distribution and abundance patterns of rocky intertidal fishes in central California

Synopsis Distribution patterns and relative abundances were determined for rocky intertidal fishes in central California. Distributions were described relative to a categorization scheme of tidepools based on certain biotic and physical criteria. The fishes displayed a variety of distributions over tidepool categories and showed some segregation within categories.Cottids were the predominant tidepool fishes encountered, withOligocottus snyderi andClinocottus analis comprising 62% of all captures. The cebidichthyidCebidichthys violaceus and the stichaeidAnoplarchus purpurescens were also relatively common and dominated the out-of-water microhabitat.Oligocottus snyderi showed a minor shift in distribution over tidepool categories between seasons, and C. analis showed none, but both species varied substantially in abundance. Temporal changes in abundance of the more common species indicated seasonal trends, but the duration of the census period was insufficient to verify this.It is concluded that while species interactions may have influenced the observed patterns of habitat partitioning, the roles of predation and competition cannot be unambiguously defined. Presently, neither these nor historical factors can be discounted from having significantly influenced the evolution of the intertidal fish community.     

The adaptive significance of aggregation behaviour in the dogwhelk Nucella lapillus (L.)

Summary Three kinds of aggregation behaviour were observed in an exposed shore population of Nucella lapillus. Aggregations on the open rock surface during the summer protected dogwhelks from water movement, and were not found on shores where the topography conferred protection. Feeding occurred mainly within these aggregations, probably because individuals experienced less disturbance there than when isolated. Physical contact was important in holding animals together.Winter and pre-breeding aggregations were usually found in clefts or pools. All age groups formed winter aggregations, but those of immature dogwhelks were not as permanent as those of adults, and the latter merged with the prebreeding aggregations. Winter aggregations protected dogwhelks from dislodgment when their ability to regain a foothold was reduced by low temperatures, while pre-breeding aggregations brought the sexes together for fertilization, but the permanence of adult winter aggregations suggested that reproductive activity may have been occurring within them.     

Nuclear number in cells of some species of Delesseriaceae (Rhodophyta)

The number of nuclei in multinucleate blade cells of 12 species of red algae in the family Delesseriaceae (Rhodophyta) is primarily restricted to a range that is characteristic of the species; in some species larger or older cells in other parts of thalli contain more nuclei than cells in blades. The numbers were similar in laboratory-grown and field-collected specimens and in gametangial and tetrasporangial plants. Most blade cells of Anisocladella pacifica, Sorella spp., and Phycodrys profunda contain 3–5 nuclei. Cells throughout thalli of Phrix gregarium most frequently have one or two nuclei. Other species showed larger ranges. Cells within stipes, midribs, or basal regions of blades of Anisocladella pacifica, Branchioglossum undulatum, Nienburgia andersoniana, Nitophyllum hollenbergii, Platysiphonia clevelandii, and two species of Cryptopleura can have 20+ nuclei, more than in distal blade cells. Chromosome numbers of n = 8–10 for Nienburgia andersoniana, n = 20–26 for Nitophyllum hollenbergii, and n = 7–8 for Phrix gregarium are reported.     

Die Entwicklung vonCodiolum gregarium A. Braun

Zusammenfassung Codiolum gregarium, eine fädigeUrospora sowie Zwergpflanzen sind Glieder eines Entwicklungszyklus. Bei allen drei Erscheinungsformen wurden nur ungeschlechtliche Fortpflanzungszellen beobachtet. Die Entwicklungsabläufe werden entscheidend von der Temperatur beeinflußt (Schema Abb. 5). Wahrscheinlich ist die fädige Generation mitUrospora wormskoldii identisch.(Mit 5 Abbildungen im Text)Es ist nicht erwiesen, daßUrospora penicilliformis (Roth) Areschoug undCodiolum gregarium A. Braun Glieder eines Entwicklungszyklus sind.     

Disintegration of a large concentration of loliginid squid as a response to predation

During hydroacoustic observations in November 2002, a large concentration of chokka squid (Loligo reynaudi) was monitored for three days during fairly constant wind speed and direction, that marginally improved during the period of observations. During this period, the concentration (estimated biomass 48 t) disintegrated into small, separate aggregations. Most often, such dispersal is weather-related, but obviously not in this case. Instead, a bottom trawl made adjacent to the concentration, as well as underwater camera observations revealed an unusually large number of predators, mostly bronze whaler sharks (Carcharhinus brachyurus). Most whaler sharks caught in the trawl had chokka in their stomachs. Therefore, one explanation for the break-up of this squid concentration was the unusual predator activity. Video observations revealed, that these attacks occurred on the bottom where squid spawn; while none were observed in the water column where squid pair, mate and swim in a circular motion preparing for descent to the egg bed. The disintegration of the whole concentration suggested that disrupted spawning affects the upper part of the typical mushroom-shaped structure as well, and squid subsequently disperse and/or move away as a result of predation by whaler sharks.     

Contrasting abundance and contribution of clonal proliferation to the population structure of the corkscrew sea anemone Bartholomea annulata in the tropical Western Atlantic

Clonal propagation is an important life history trait for many sessile organisms, and often leads to the formation of monoclonal aggregations. In the marine environment, sea anemones have been model species for testing theory regarding the evolution of sex and understanding the contribution of sexual versus asexual reproduction to the population structure in facultatively clonal animals. However, little attention has been paid to tropical actiniarians. The corkscrew anemone Bartholomea annulata is common in tropical marine habitats in the western Atlantic and Caribbean; it forms small aggregations (2–4 anemones) on coral reefs and larger aggregations (>10 anemones) in mangrove habitats. We used field surveys and molecular analyses to investigate patterns of distribution, abundance, and genetic structure of aggregations formed by B. annulata on a reef in the US Virgin Islands and in a unique mangrove habitat in the Florida Keys. Abundance was greatest at the abandoned rock quarry mangrove habitat in the Florida Keys, where anemones formed continuously distributed aggregations carpeting the exposed limestone walls. Genetic diversity assessed via intersimple sequence repeats (ISSRs) and six microsatellite loci revealed that asexual reproduction plays only a minor role in the formation of both small and large anemone aggregations. Specifically, ISSR analyses showed that only ~10% of anemone aggregations were clonal in the US Virgin Islands, while microsatellite genotyping identified clonality in only 1 of 35 aggregations. In the Florida Keys, only four clonal genotypes were recovered within aggregations, but eight clones, representing 33% of the total surveyed population, had individuals in multiple aggregations. Thus, population structure of B. annulata appears to rely primarily on sexual reproduction, although asexual reproduction may play a nontrivial role in some environments. Mechanisms that drive the formation of genotypically diverse aggregations remain unknown, but may include attraction toward conspecifics, shared use of preferred habitats, or the local retention of larvae in partially enclosed habitats.     

Eusocial bee male aggregations: spatially and temporally separated but genetically homogenous

Male insects mostly aggregate near sites where sexually reproductive virgin females are found and where mating occur. This reproductive strategy is quite common in Hymenoptera and appears to decrease the chances of inbreeding. In Hymenoptera, inbred mating frequently result in sterile diploid males. Production of diploid males may reach high proportions in small bee populations, and it usually lead to population extinction within a small number of generations. Aggregation of males during a short period of time allow the mixing of local genes. In this paper, we analyzed male aggregations of Tetragonisca angustula (Latreille) (Hymenoptera: Apidae), a eusocial stingless bee, using microsatellite molecular markers. We used population genetic statistics for haplodiploid organisms to address genetic structuring among male aggregations. Our findings indicate that, in general, male aggregations of T. angustula occurring over short time scales and in close proximity are genetically homogeneous as if a single aggregation. We conclude that T. angustula males randomly disperse within a population looking for mating chances rather than settle on a distinct male aggregation. This behavior seems to contribute to the reduction of inbreeding in this species.     

Three-dimensional anatomy of the Tully monster casts doubt on its presumed vertebrate affinities

Tullimonstrum gregarium, also known as the Tully monster, is a well-known phylogenetic enigma, fossils of which have been found only in the Mazon Creek Lagerstätte. The affinities of Tullimonstrum have been debated since its discovery in 1966, because its peculiar morphology with stalked eyes and a proboscis cannot easily be compared with any known animal morphotypes. Recently, the possibility that Tullimonstrum was a vertebrate has attracted much attention, and it has been postulated that Tullimonstrum might fill a gap in the fossil record of early vertebrates, providing important insights into vertebrate evolutionary history. With the hope of resolving this debate, we collected 3D surface data from 153 specimens of Tullimonstrum using a high-resolution laser 3D scanner and conducted x-ray micro-computed tomographic (μCT) analysis of stylets in the proboscis. Our investigation of the resulting comprehensive 3D morphological dataset revealed that structures previously regarded as myomeres, tri-lobed brain, tectal cartilages and fin rays are not comparable with those of vertebrates. These results raise further doubts about its vertebrate affinities, and suggest that Tullimonstrum may have been either a non-vertebrate chordate or a protostome.     

Gregarious foraging in barn swallows after the breeding season

Aerial vertebrate foragers, e.g. insectivorous bats, martins and swallows, often show gregarious behavior such as colonial breeding, communal roosting and aggregating behavior during foraging. Studies of gregariousness in aerial foragers have mostly focused on colonial breeding or communal roosting, and only a few intensive studies have dealt with gregariousness during foraging. Here, we report on large and stable aggregations of barn swallows, Hirundo rustica, observed during daytime after the breeding season in Japan. Relatively large aggregations of 20 or more birds were located around poultry, pig and cattle farms and mounds of manure. The aggregations were stable in size both within-days and between-days. Their activities consisted only of repeated cycles of foraging and resting around the farms where their prey, the large black soldier fly Hermetia illuceus (>10 mm) and other medium (5–10 mm) flies, was dense. Distributions of swallows around the farms overlapped with the distributions of prey, and the size of the aggregations significantly correlated with the abundance of prey.     

Extinction,recolonization, and the genetic structure of tidepool copepod populations

Summary Extinction and recolonization in metapopulations may either increase or decrease genetic differentiation among populations, but recent genetic models predict increased differentiation under most circumstances of recolonization. I examine this prediction empirically using tidepool populations of the marine tidepool copepodTigriopus californicus. The probability of extinction of tidepool populations was sufficiently high to invoke the model's predictions, but varied among populations. Nearly 75% of colonizing groups consisted of 10 or fewer individuals. The genetic effective size of colonizing groups might be as high as 18, depending on assumptions, but colonists probably originated from a subset of local populations. In contrast to my predictions, genetic differentiation was smaller among younger tidepool populations than among older populations on each of three rock outcrops, suggesting that genetic differentiation was reduced by metapopulation dynamics. The discrepancy between the prediction and the results may be explained by the unmet assumptions of classical metapopulation structure underlying the genetic models.     

Population structure and survival in a solitary wasp (Microbembex cubana: Hymenoptera,Sphecidae, Nyssoninae)

Summary This paper documents population structure in a solitary wasp, Microbembex cubana (Hymenoptera, Sphecidae, Nyssoninae), on a small (15 km²) Bahamian island. A relatively isolated portion of this population was studied April–June 1985. The population comprised small aggregations of territorial males and nesting females. Individuals of both sexes were with rare exceptions faithful to a home aggregation during their one- to two-month adult lifespans, conducting all reproductive activities there. Individuals from different aggregations, however, mixed daily during these activities: feeding on nectar, hunting for provisions and retiring to clustered sleeping burrows. Significant variation occurred among the nine breeding aggregations in size, density, sex-ratio (which was on average 2:1 in favor of males) and survival (which was 0.93–0.99 per individual/per day and which was not higher for females than for males). Aggregations retained the same characteristics for longer than the life expectancies of individuals in them.Factors affecting reproductive success and survivorship in M. cubana are complex: they are apparently only partially overlapping between males and females and subject to spatial variation. Patterns in the data suggest several hypotheses about how behavior, morphology and habitat interact to shape population processes. I propose that aggregations arise and are characterized by considerable behavioral inertia because individual M. cubana use conspecifics as sources of information on resource quality. Because M. cubana occurs in secondary habitats, individuals retain flexibility in responding to better opportunities for reproduction, but this population exhibits more viscosity than reported for other ground-nesting solitary Hymenoptera.     

Mating system and spawning cycle in the blenny,Istiblennius enosimae,at Kagoshima,Japan

Synopsis Field observations on reproductive ecology and territoriality of the blennyIstiblennius enosimae, were made in a tidepool at Hanaze Beach, Kagoshima Prefecture, Japan during the summer of 1988. This blenny was herbivorous, and nesting males (> 73 mm SL) maintained territories around nest sites, which were located in rocky crevices of the tidepool. Males courted females wandering near their nests, and spawnings coincided with neap tides. Males guarded the eggs until the embryos hatched at following spring tides. It was suggested that this semilunar spawning cycle guarantees a maximum dispersal of newly hatched embryos away from natal tidepool. Male reproductive success was related to large body size and/or large nest size. There is a size-assortative relationship between male and female among pairs. Egg predation rates by fishes, crabs and sea urchins were not correlated with the body size of male blennies.     

How can river-estuarine planktonic copepods survive river floods?

Distribution of brackish-water zooplankton was surveyed in the Chikugo River estuary, Japan, at 3-h intervals for 24h, including several hours when the river was heavily flooded because of rainfall and discharge from an upstream dam. The populations of the dominant copepods Pseudodiaptomus inopinus and Sinocalanus sinensis were concentrated in the mixing zone of the salt wedge before river flooding. During the period of flooding, they were almost completely swept out from the river, but examination of water trapped by a sediment grab sampler revealed that adults of Pseudodiaptomus inopinus were aggregated immediately above the bottom of the submerged channel outside the river mouth. After the flood, aggregations of both species appeared again in the river together with the salt wedge, and the proportion of adults in the aggregations became significantly higher than before. These results suggest that immature copepods suffer population losses through river flooding, but that the copepods can survive such flooding by means of both behavioral and reproductive mechanisms; that is, adult copepods maintain their position on the bottom of submerged channels outside the river mouth during a river flood and replace the population loss through reproduction after the flood. Channels outside river mouths are thus regarded as important topographic refuges for river-estuarine zooplankton to survive a flood.     

Spawning aggregations of three protogynous groupers in the southern Gulf of Mexico

Spawning aggregations of red hind Epinephelus guttatus, tiger grouper Mycteroperca tigris and yellowfin grouper Mycteroperca venenosa were identified at two coral‐reef systems: Arrecife Alacranes (emergent bank reef) and Bajos del Norte (submerged bank reef) on the continental shelf of the Yucatan Peninsula (Campeche Bank), Mexico. At both reefs, E. guttatus forms large spawning aggregations between February and March. At Bajos del Norte, M. tigris reproduces in a small, low‐density aggregation in May, while M. venenosa aggregates at high densities for spawning between March and May. Multi‐species use of an aggregation site by E. guttatus and M. venenosa was observed at Bajos del Norte. The identified spawning aggregations are apparently stable in location over time, and all three species were commonly observed to spawn within 1 week following the full moon. Development and survival of the larvae spawned in these aggregations are probably aided by a seasonal (spring–summer) upwelling in the north‐east Campeche Bank. A permanent area closure at Bajos del Norte, currently outside any specific fisheries management area or regulations, would provide protection needed for the spawning aggregations of these three species.     

Scramble competition polygyny in the coreid bug (Colpula lativentris)

The mating system of the coreid bug, Colpula lativentris, was studied, and compared with those in other hemipteran bugs. Copulating pairs formed a compact aggregation on a shoot of the Japanese knotweed, Polygonum cuspidatum, and there continued copulation and feeding for more than one day. This aggregation was defined as “a shoot aggregation”. Other than this aggregation composed of copulating pairs, there were loose aggregations on the ground composed of males and females not in copula. This loose aggregation was defined as “a ground aggregation”. Males searched for receptive females mostly in a ground aggregation. Sex ratio was constant and variance of sex ratio was also very small in any shoot aggregations and in large ground aggregations. However, in small ground aggregations, sex ratio was strongly male biased and variance of sex ratio was fairly large. This was because receptive females tended to leave a small ground aggregation and join a large one. These results suggest that a male can attain higher mating success in a larger ground aggregation.     

Patagonian grouper Acanthistius patachonicus (Jenyns, 1840) forms massive spawning aggregations in the Southwest Atlantic

Here we describe massive spawning aggregations and seasonal changes in the large-scale distribution of the Patagonian grouper Acanthistius patachonicus in the Southwest Atlantic based on three sources of information: (a) data from bottom trawl research surveys covering the distributional range of the species within the Argentine continental shelf; (b) folk ecological knowledge gathered from experienced captains of the Argentine industrial trawl fisheries; and (c) sampling of an artisanal trap fishery targeting the Patagonian grouper in a specific location off the coast of Buenos Aires Province. The trawl surveys showed a general pattern of aggregation of Patagonian grouper towards the coast during the reproductive period (September–December). Captains described massive aggregations of the species at specific near-shore locations, where trawl catches of up to 15 t in a single haul were registered during the reproductive season. At a local scale, the artisanal trap fishery described operates exclusively during the reproductive period, targeting near-shore aggregations with a high proportion of individuals releasing gametes onboard. These three sources of information provide evidence of the existence of massive transient spawning aggregations of Patagonian grouper in the Argentine shelf. This is the first report of a reef fish spawning aggregation in the southern region of the Southwest Atlantic. Anecdotal information gathered in this study points to the depletion of many of the aggregations targeted during the 1980s and 1990s by the industrial fleet. At the same time, the spawning aggregation site off Buenos Aires Province has been productive for the last 34 years, being exploited exclusively by traps. The Patagonian grouper is classified as Data Deficient by the International Union for Conservation of Nature, which highlights the need for further research to determine its stock status. Mapping its current spawning aggregations should be a priority to inform the design of a targeted monitoring program and management plan for this species.     

Growth and reproduction of the tidepool sculpinOligocottus maculosus

Growth and reproduction of tidepool sculpins (Oligocottus maculosus) from three sites in Puget Sound, Washington State, USA were characterized. One site was a sandy, gently sloping beach, the second was an exposed rock headland with minimal algal cover, and the third was an exposed rock headland with numerous tidepools containing abundant algal cover. Length-weight relationships for sculpins did not differ significantly between sexes within sites. Population age structure, growth rate and recruitment varied among the three study sites using data pooled across both sexes. Young-of-the-year sculpins comprised 91% of the population at the exposed headland site with minimal algal cover but only 6% at the headland with abundant algal cover. Selective predation by great blue herons (Ardea herodias) upon tidepool sculpins larger than 45 mm total length assisted in the maintainance of these age structures. A maximum gonadosomatic index of 28.5 was calculated; this index correlated poorly with either age, length or somatic weight. Diameters of unshed ova from preserved tidepool sculpins sampled prior to spawning fell into three classes. Comparison of the mean egg size of each mode and the number of modes present in preserved sculpins with similar data from tidepool sculpins that spawned in the laboratory suggested that spawning occurred twice yearly from at least January through August.