Peter T. Raimondi

Responses of settling invertebrate larvae to bioorganic films: effects of different types of films

Abstract Larvae of benthic invertebrates are exposed to a variety of chemical cues, many of biological origin, as they near a potential settlement surface. One such cue is the bioorganic film that covers many surfaces, and some laboratory evidence suggests that larvae respond to the presence or absence of such films. Our earlier work has shown that, at two field sites in southeastern Australia, a variety of species recruit at higher densities to substrata bearing such a film, and here we begin to determine the specificity of those responses. Experimental substrata were prepared with films developing in laboratory aquaria and under field conditions for 7 days. These substrata were then exposed in the field, and analysis of 19 sessile taxa, distributed over seven phyla, showed that no species recruited at significantly different densities onto surfaces of these two origins. Field films were prepared by covering substrata with plankton meshes, to exclude larvae, and additional laboratory treatments showed that such handling does not produce different recruitment from that onto substrata that were unnetted. One further experimental treatment was plates that had been placed in sterile seawater, and recruitment onto these surfaces confirmed that both field and laboratory films did have positive (and negative) effects on recruitment. In a second experiment, we prepared laboratory microbial films of four ages: 0, 1, 3, and 6 days. These substrata were immersed in the field for 3 and 6 days in a balanced experiment. Recruitment rates varied significantly with age of film for five of 13 taxa. Two polychaete species and two arborescent bryozoans ( Bugula stolonifera and Bugula neritina ) showed a positive relationship, and the barnacle Balanus variegatus recruited in greater numbers onto less filmed surfaces. Seven other taxa, including one protozoan, a sponge, and five ascidian taxa, showed no relationship with age of microbial film, despite high recruitment rates of these taxa. Summed across all taxa, total recruitment increased with age of film, almost doubling from unfilmed surfaces to those that began the field period with 6-day-old films. Comparison of 3- and 6-day field immersion periods showed that mean daily recruitment of some species, including a number of those responding to the presence of films, was higher on substrata left in the field for 6-days. Some of these patterns were consistent with the hypothesis that laboratory-derived films become supplemented by further microbial organisms in the field, making them even more attractive to settling larvae. An alternative hypothesis, that higher recruitment onto plates immersed for 6 days reflects temporally patchy recruitment, with pulses of recruitment in the latter half of the experimental period, could not be rejected. The experiments show that under field conditions, invertebrate larvae settle at very different rates onto surfaces differing only in the composition of the microbial community. Such settlement choices may be important in determining recolonization sequences following small-scale disturbances.

SPECIES INTERACTION STRENGTH: TESTING MODEL PREDICTIONS ALONG AN UPWELLING GRADIENT

A recent model predicts that species interactions in benthic marine communities vary predictably with upwelling regimes. To test this model, we studied the Pisaster–Mytilus interaction at 14 rocky intertidal sites distributed among three oceanographic regions along a 1300-km stretch of the U.S. West Coast. Regions included an intermittent-upwelling region (northern), a persistent-upwelling region (central), and a region of weak and infrequent upwelling (southern). We quantified predation rates by the sea star Pisaster ochraceus on its main prey Mytilus californianus by transplanting mussels into the sea stars low-zone foraging range and comparing the rate of mussel loss in +Pisaster plots to those in −Pisaster plots. To evaluate the relation between predation rates and key ecological processes and conditions, we quantified phytoplankton concentration and rates of mussel recruitment, mussel growth, mussel abundance, and sea star abundance. Predictions of the model are expressed as responses of predator an...

A physically based model of macroalgal spore dispersal in the wave and current-dominated nearshore

Propagule dispersal in seaweeds is a process influenced by a variety of biological and physical factors, the complexity of which has hindered efforts to understand colonization, persistence, post-disturbance recovery, and dynamics of algal populations in general. In view of this limitation, we employ here modifications to an existing turbulent-transport model to explore the mechanics of nearshore macroalgal spore dispersal and its relationship to coastal hydrodynamic conditions. Our modeling efforts focus on four example species of seaweed whose reproductive propagules span a wide range in sinking speed and height of release above the sea floor: the giant kelp Macrocystis pyrifera, the erect fucoid Sargassum muticum, the small filamentous brown alga Ectocarpus siliculosus, and the flaccid red alga Sarcodiotheca gaudichaudii. Results indicate that both propagule sinking speed and release height can affect dispersal distance substantially, but that the influence of these biological parameters is modulated strongly by the intensity of turbulence as dictated by waves and currents. In rapid flows with larger waves, it is primarily fluid dynamic processes, in particular current velocities, that determine dispersal distance. Additional simulations suggest that patterns of spore dispersal are highly skewed, with most propagules encountering the sea floor within a few meters to hundreds of meters of their parents, but with a sizeable fraction of spores also dispersing as far as kilometers. Such model predictions imply a much greater potential for longer range dispersal than has typically been assumed, a finding with important implications for understanding the demographics of algal populations and for predicting levels of connectivity among them.

SPATIAL AND TEMPORAL PATTERNS OF INVERTEBRATE RECRUITMENT ALONG THE WEST COAST OF THE UNITED STATES

Patterns of recruitment in marine ecosystems can reflect the distribution of adults, dispersal by ocean currents, or patterns of mortality after settlement. In turn, patterns of recruitment can play an important role in determining patterns of adult abundance and community dynamics. Here we examine the biogeographic structure of recruitment variability along the U.S. West Coast and examine its association with temperature variability. From 1997 to 2004 we monitored monthly recruitment rates of dominant intertidal invertebrates, mussels and barnacles, at 26 rocky shore sites on the West Coast of the United States, from northern Oregon to southern California, a span of 1750 km of coastline. We examined spatial variation in the dynamics of recruitment rates and their relationship to coastal oceanography using satellite-derived time series of monthly sea surface temperature (SST). Recruitment rates showed a biogeographic structure with large regions under similar dynamics delimited by abrupt transitions. The seasonal peak in recruitment rates for both mussels and barnacles changed from a late summer-early fall peak in Oregon to winter or early spring in northern California, and then back toward summer in southern California. Recruitment rates varied greatly in magnitude across the latitudinal range. The barnacle Balanus glandula and mussels (Mytilus spp.) showed a decline of two orders of magnitude south of Oregon. In contrast, recruitment rates of barnacles of the genus Chthamalus showed a variable pattern across the region examined. The spatial distribution of associations between raw SST and recruitment rates for all species showed positive associations, indicating recruitment during warm months, for all species in Oregon, northern California, and several sites in south-central California. By considerably extending the spatial and temporal scales beyond that of previous studies on larval recruitment rates in this system, our study has identified major biogeographic breaks around Cape Blanco and Point Conception despite considerable spatial and temporal variation within each region and among species. These large differences in recruitment rates across biogeographic scales highlight the need for a better understanding of larval responses to ocean circulation patterns in the conservation and management of coastal ecosystems.

THE CONSEQUENCES OF COMPLEX LARVAL BEHAVIOR IN A CORAL

The leaf coral Agaricia humilis occurs mainly on the undersides of surfaces in shallow water, a distribution different from the vast majority of corals at our study site in Bonaire, Netherlands Antilles. A series of hypotheses were tested for specific mechanisms that could cause the observed distributions of Agaricia humilis. We found that a suite of larval swimming and settling behaviors, in large part, drives the adult distribution of the species. These behaviors include: (1) swimming behavior that cause larvae to position themselves in shallow water, (2) orientation behavior during settlement that causes larvae to preferentially settle on the undersides of surfaces, and (3) settlement behavior where chemosensory recognition of morphogenic molecules associated with the cell walls of specific crustose red algae is required for induction of settlement and metamorphosis. The consequences of atypical larval behavior are severe and include decreased survivorship, growth, and ability to reproduce sexually.

Responses of settling invertebrate larvae to bioorganic films : effects of large-scale variation in films

Abstract Results of previous studies have shown that at two sites in southeastern Australia (Williamstown and Mornington), some sessile invertebrate species recruit at higher densities onto surfaces that have a microbial film present, and that some species recruit in proportion to the age (0–6days) of that film. Other sessile species, notably colonial ascidians, do not respond to the presence of these films, and some barnacles may avoid the films. We tested whether larvae can detect or respond to differences in the microbial films that develop in different geographic localities and on longer time scales. To do this, we first confirmed that laboratory-developed microbial films induced higher recruitment of benthic invertebrates at a third site, Queenscliff, in Port Phillip Bay, Victoria, Australia. Approximately two-thirds of the sessile species settling at the time of the experiment were more abundant on the filmed surfaces. We then allowed microbial films to develop at all three sites on experimental substrata that were covered with plankton mesh to exclude larvae. The sites were chosen to represent three different rates of development of microbial films. After 1 week, we removed the plankton meshes and reciprocally transplanted experimental surfaces between all three sites. At the same time, we brought a sample from each site back to the laboratory to estimate the number of recruits passing through plankton meshes. We tested two hypotheses using these data, first that settling larvae at a particular site respond more strongly to locally-developed films than to films originating elsewhere and second, that it is the density of the microbial film, rather than its origin, that determines recruitment. Williamstown appeared to have the fastest-growing, most luxurious microbial films, followed by Mornington and Queenscliff. Locally-developed films were not significantly more attractive than foreign films at Mornington or Queenscliff; none of the 15 taxa tested showed higher recruitment rates to the local treatment, and highest recruitment occurred on substrata filmed at Williamstown. At Williamstown, there were differences in recruitment rates to plates with films of different origin, but in each case, films from Williamstown received the most recruitment. These latter results could not separate our two hypotheses, but those from Mornington and Queenscliff suggest that larvae do not recognize and/or respond to films from their local area, but that more heavily-filmed surfaces may be more attractive to settling larvae. The species showing the strongest responses were polychaetes, encrusting bryozoans, and some solitary ascidians. We also compared the attractiveness of laboratory-developed films varying in age up to 1 month and found that some species (serpulid polychaetes and encrusting bryozoans) recruited onto these surfaces at variable rates, while other species, notably ascidians, did not distinguish between the different substrata.

Rock type affects settlement, recruitment, and zonation of the barnacle Chthamalus anisopoma Pilsbury

Abstract The settlement, recruitment, and zonation of the barnacle Chthamalus anisopoma (Pilsbury) on two shores were investigated in the northern Gulf of California. Its upper vertical limit is, on average, 25 cm lower on a basalt shore than on a nearby granite shore, probably because of greater post-settlement mortality on basalt than on granite near the upper limit of its distribution. This difference in mortality may be related to the thermal capacity of each rock type. Results of a reciprocal transplant experiment showed that: 1. (1) there was consistently greater settlement and recruitment on granite stones than on basalt stones at both shores, suggesting that larvae select granite over basalt substrata for settlement; 2. (2) overall, there was more settlement and recruitment to experimental stones at the basalt shore than at the granite shore, suggesting a larger pool of potential settlers at the basalt shore; and, 3. (3) there was no difference between recruitment on granite stones at the granite shore and that on basalt stones at the basalt shore. That is, there was no difference in recruitment between shores on surfaces natural to each shore. These results demonstrate the importance of effects specific to different shores and substrata to intertidal community structure.

Densovirus associated with sea-star wasting disease and mass mortality

Significance Sea stars inhabiting the Northeast Pacific Coast have recently experienced an extensive outbreak of wasting disease, leading to their degradation and disappearance from many coastal areas. In this paper, we present evidence that the cause of the disease is transmissible from disease-affected animals to apparently healthy individuals, that the disease-causing agent is a virus-sized microorganism, and that the best candidate viral taxon, the sea star-associated densovirus (SSaDV), is in greater abundance in diseased than in healthy sea stars. Populations of at least 20 asteroid species on the Northeast Pacific Coast have recently experienced an extensive outbreak of sea-star (asteroid) wasting disease (SSWD). The disease leads to behavioral changes, lesions, loss of turgor, limb autotomy, and death characterized by rapid degradation (“melting”). Here, we present evidence from experimental challenge studies and field observations that link the mass mortalities to a densovirus (Parvoviridae). Virus-sized material (i.e., <0.2 μm) from symptomatic tissues that was inoculated into asymptomatic asteroids consistently resulted in SSWD signs whereas animals receiving heat-killed (i.e., control) virus-sized inoculum remained asymptomatic. Viral metagenomic investigations revealed the sea star-associated densovirus (SSaDV) as the most likely candidate virus associated with tissues from symptomatic asteroids. Quantification of SSaDV during transmission trials indicated that progression of SSWD paralleled increased SSaDV load. In field surveys, SSaDV loads were more abundant in symptomatic than in asymptomatic asteroids. SSaDV could be detected in plankton, sediments and in nonasteroid echinoderms, providing a possible mechanism for viral spread. SSaDV was detected in museum specimens of asteroids from 1942, suggesting that it has been present on the North American Pacific Coast for at least 72 y. SSaDV is therefore the most promising candidate disease agent responsible for asteroid mass mortality.

Rapid effects of marine reserves via larval dispersal.

Marine reserves have been advocated worldwide as conservation and fishery management tools. It is argued that they can protect ecosystems and also benefit fisheries via density-dependent spillover of adults and enhanced larval dispersal into fishing areas. However, while evidence has shown that marine reserves can meet conservation targets, their effects on fisheries are less understood. In particular, the basic question of if and over what temporal and spatial scales reserves can benefit fished populations via larval dispersal remains unanswered. We tested predictions of a larval transport model for a marine reserve network in the Gulf of California, Mexico, via field oceanography and repeated density counts of recently settled juvenile commercial mollusks before and after reserve establishment. We show that local retention of larvae within a reserve network can take place with enhanced, but spatially-explicit, recruitment to local fisheries. Enhancement occurred rapidly (2 yrs), with up to a three-fold increase in density of juveniles found in fished areas at the downstream edge of the reserve network, but other fishing areas within the network were unaffected. These findings were consistent with our model predictions. Our findings underscore the potential benefits of protecting larval sources and show that enhancement in recruitment can be manifested rapidly. However, benefits can be markedly variable within a local seascape. Hence, effects of marine reserve networks, positive or negative, may be overlooked when only focusing on overall responses and not considering finer spatially-explicit responses within a reserve network and its adjacent fishing grounds. Our results therefore call for future research on marine reserves that addresses this variability in order to help frame appropriate scenarios for the spatial management scales of interest.

Evidence that mating group size affects allocation of reproductive resources in a simultaneous hermaphrodite

The results of this study indicate that individuals of the hermaphroditic species Catomerus polymerus allocate proportionately more of their reproductive resources to female function when they occur in small mating groups than when they are in large ones. The most plausible explanation for this result is one provided by Charnov: in small mating groups individual fitness is increased by a bias in energy allocation toward female function.