New ecological information onScytalina cerdale (Pisces: Scytalinidae) from a central California rocky intertidal zone

Synopsis New information regarding the ecology ofScytalina cerdale was obtained over a four year period as a consequence of a long-term marine ecological study at the Diablo Canyon Power Plant (DCPP), San Luis Obispo County, California. Twenty intertidal fish surveys were conducted at approximately quarterly intervals, between March 1979 and June 1983, at three separate rocky shore locations (stations). During each survey, a total of 108 square meters (36 m² per station) was searched for fish during periods of low tide. A total of 280S. cerdale were collected, identified, measured, and released back into the same 4 m² area, from the same intertidal station (Diablo Cove), throughout the study period. This limited intertidal occurrence most likely reflectsS. cerdale microhabitat requirements; a combination of intertidal elevation (mean = +0.3 MLLW), substratum specificity (loose gravel, 5–10mm size range, overlying a base of sand and shell fragments), and degree of wave exposure (semi-protected). Throughout the study,S. cerdale was seasonally more abundant during summer months (June through August) and less abundant during winter months (November through February). The only exception to this abundance trend followed the 1982 winter storms, which coincided with an El Niño event, whenS. cerdale abundance uncharacteristically dropped during the subsequent 1983 spring and summer surveys. Mean total lengths did not vary greatly, reflecting the absence of early juvenile fishes, and relatively high mean fish densities (3.5 fish per m² for 20 surveys) were recorded. Qualitative comparisons betweenS. cerdale abundance and seasonal changes in water temperature indicated an inverse relationship. Gravid females, demersal egg masses, and early juvenile individuals were never observed during the four years of the study. This suggests that unlike most other intertidal fishes, particularly other blennioids,S. cerdale may not utilize the intertidal zone for reproductive and recruitment purposes; Diablo Canyon is the most southerly reported distribution for this intertidal species, and therefore, may not entirely represent the species' biology as a whole.     

Field and laboratory observations of spawning periodicity and behavior of a northern population of the Atlantic silverside,Menidia menidia (Pisces: Atherinidae)

Synopsis The spawning periodicity and mating behavior of a northern population of the Atlantic silverside, Menidia menidia, was studied both in the field (Salem Harbor, Massachusetts) and in laboratory experiments. Spawning in the field coincided with new and full moons. Under conditions of unlimited food availability in artificial outdoor pools that received natural celestial illumination or in indoor aquaria receiving no evening illumination, spawning occurred every 1–3 days rather than fortnightly. These results suggest that tidal influences are a primary factor that synchronizes spawning in M. menidia. Published reports of diel time of spawning in both marine and freshwater species of Menidia indicate a generic tendency to spawn during mid-morning. This pattern coupled with high tides that cover suitable spawning substrates during mid-morning only at fortnightly intervals could account for the semilunar spawning cycle in marine populations of Menidia. Although general characteristics of the reproductive ecology of M. menidia in Massachusetts were similar to a thoroughly studied population in South Carolina, several differences were evident. The breeding season was shorter in Massachusetts (late; April–June), and occurred over a much lower range of temperatures (9–21°C). Intensity and frequency of spawning was correlated with the height of high tide. Eggs were deposited only on mats of intertidal, filamentous algae rather than on roots or stems of Spartina alterniflora or other intertidal vegetation. Promiscuous spawning occurred in small, highly male-dominated groups of fish, primarily after the tide had begun to recede, and often at the water's edge. No predation on spawning adults was observed but the mummichog, Fundulus heteroclitus, fed daily on developing embryos during high tide. Contribution No. 81, Massachusetts Cooperative Fisheries Research Unit, Contribution No. 349, Marine Sciences Research Center, State University of New York at Stony Brook.     

Intertidal distribution of infauna in a central California lagoon: the role of seasonal blooms of macroalgae

This study examined the roles of seasonal blooms of green algae, Ulva expansa (Setchell) Setchell et Gardner, and biotic disturbance by burrowing ghost shrimp, Callianassa gigas Dana, and foraging rays, on the intertidal distributions of a phoronid, Phoronopsis viridis Hilton, and a tellinid bivalve, Macoma nasuta (Conrad). Algal removal experiments in 1984 and 1986 demonstrated that heavy seasonal algal cover in the lower zone significantly reduced the abundances of both Phoronopsis and Macoma. Growth of Macoma transplanted into the algal zone was significantly lower in plots with algal cover than in plots regularly cleared of algae. Algal cover did not significantly affect early recruitment of either Phoronopsis or Macoma. Neither ghost shrimp nor rays appeared to reduce the abundances of phoronids or clams, although ray disturbance did result in a significant increase in the proportion of phoronids regenerating dorsal body parts. These results indicate that seasonal algal blooms are capable of producing discrete patterns of infaunal distribution in intertidal sedimentary habitats.     

Biogeochemical pathways of cadmium through an artificially contaminated intertidal mud flat system — a medium-scale enclosure experiment

Summary Two Bremerhaven caissons were used to investigate the interactions of cadmium (Cd) with sea water, particulate matter, sediments, suspended particular matter (SPM), and organisms in enclosed sea water-sediment systems, on the tidal mud flats of Jade Bay (FRG). One caisson was artificially contaminated by continuously injecting cadmium (as a chloride) so as to maintain a Cd concentration of 100 g/l in the inflowing water of each tidal cycle for 22 days. The other caisson was used as a control system. About 30% of the total Cd introduced into the caisson was transferred from the aqueous phase to the other phases during each tidal cycle. Cadmium appears to accumulate in elements of the system in the order SPM, organisms, sediments, water. SPM, initially low in Cd entering the system, rapidly accumulated Cd from solution after the first tidal cycle and the concentration continued to increase during the experiment. Particulate Cd transferred to the sediments results in the development of a Cd-rich layer that attained a depth of 4 cm over the course of the experiment. Among the biota, the blue mussel (Mytilus edulis) progressively accumulated the highest concentrations of Cd whereas other taxa, like polychaetes, accumulated less of the metal. Differnces in Cd accumulation appear to be due to the habitats of the different species and their ability to assimilate Cd from the dissolved and particulate phases. Together, the data indicate that in the contamination of tidal mud flats with aqueous cadmium most of the metal would remain available to the organisms in the aqueous phases and weakly bound to particulate matter. This would present the greatest environmental danger to filter feeders but not to animals living in the sediments.     

An active learning approach to investigate the ecosystem of tide flats using 3D modeling and printing

ABSTRACT

This paper presents an active learning approach that focuses on practical investigation of the ecosystem of tidal flats using 3D modeling and printing for biology students in order to enhance understanding of natural selection. The learning approach for the study followed a 5-step procedure: i) learning about 3D modeling and printing, ii) exploration of the ecosystem of tidal flats, iii) 3D designing of a bird beak, iv) 3D printing of a constructed beak, and v) a natural selection simulation activity. The learning method presented in this study centered on active student exploration of the tidal flats ecosystem using 3D modeling and printing. The learning approach presented in this paper could be implicated at schools to aid in students’ understanding of natural selection as it allows students to firsthand examine simulation changes to a bird beak and benthic communities. This study suggested the active learning method for natural selection as it incorporates student-designed exploration and direct investigative appraisal of the selection process.     

A Lunar Clock Changes Shielding Pigment Transparency in Larval Ocelli of Clunio marinus

Living in the tidal zones of the sea requires synchronization with the dominant environmental influences of tidal, solar, and lunar periodicity. Endogenous clocks anticipate those geoclimatic changes and control the respective rhythms of vital functions. But the underlying mechanisms are only partly understood. While the circadian clocks in animals are investigated employing neurobiological, molecular, and genetic approaches, clocks with a lunar periodicity have been studied with reference to development and behavior only. Sites of their pacemakers, zeitgeber receptors, and coupled endocrine components are unknown. Here, a lunar‐rhythmic change of shielding pigment transparency in the larval ocelli of the intertidal midge Clunio marinus is demonstrated for the first time as a possible access to the neurobiology of lunar timing mechanisms. We studied third instar larvae (Vigo strain) throughout the lunar cycle by light‐ and electron-microscopy as well as by x‐ray fluorescence analysis for the identification of the pigment. Moonlight detection is a prerequisite for photic synchronization of the lunar clock. The larval ocelli of Clunio putatively may function as moonlight receptors and are also controlled by the circalunar clock itself, hence being primary candidates for tracing input and output pathways of the lunar pacemaker. Additionally, the demonstration of a reversible optical change of shielding pigment transparency in Clunio is a novel finding, not reported so far in any other animal species, and reveals a mechanism to enhance photosensitivity under the condition of very dim light. It represents a remarkable change of a sense organ from an imaging device to a radiometer. Its restriction to the developmental stage susceptible to lunar timing elucidates a unique sensory strategy evolved at the level of sensory input. It also raises basic questions about the biochemistry of optically active pigments, like melanin, and their intracellular control.     

Population genetics of <Emphasis Type="Italic">Collisella subrugosa</Emphasis> (Patellogastropoda: Acmaeidae): evidence of two scales of population structure

Marine invertebrate populations usually show high levels of genetic variability that has frequently been associated with spatial and temporal environmental heterogeneity. One of the most heterogeneous marine environments is the intertidal zone, the habitat of Collisella subrugosa, the most widespread and abundant Brazilian limpet. C. subrugosa has planktonic larvae that can disperse over long distances, what can promote gene flow among shores, working against interpopulational differentiation. In this study we investigated the genetic variability and populational substructure of C. subrugosa through analysis of 24 allozyme loci in 14 samples (590 individuals) collected along 2,700 km of the Brazilian coast. The genetic variability was high ( and ), as expected for intertidal species. Genetic differentiation among samples was low (F _ST = 0.03) what may reflect intensive gene flow associated with larval dispersal. However, we detected an isolation-by-distance pattern of population substructure in one sampled region. High levels of heterozygote deficiency were also observed for many loci in each sample. Alternative hypothesis are discussed, and the “breeding groups” is suggested to explain these pattern, indicating the main cause as environmental heterogeneity.     

Temperature and pCO2 jointly affect the emergence and survival of cercariae from a snail host: implications for future parasitic infections in the Humboldt Current system

Ocean warming and acidification are general consequences of rising atmospheric CO₂ concentrations. In addition to future predictions, highly productive systems such as the Humboldt Current System are characterized by important variations in both temperature and pCO₂ level, but how these physical–chemical ocean changes might influence the transmission and survival of parasites has not been assessed. This study experimentally evaluated the effects of temperature (14, 18 and 25 °C) and the combined effects of temperature (∼15 and 20 °C) and pCO₂ level (∼500 and 1400 microatmospheres (µatm) on the emergence and survival of two species of marine trematodes—Echinostomatidae gen. sp. and Philophthalmidae gen. sp.—both of which infect the intertidal snail Echinolittorina peruviana. Snails were collected from intertidal rocky pools in a year-round upwelling area of the northern Humboldt Current System (23°S). Two experiments assessed parasite emergence and survival by simulating emersion-immersion tidal cycles. To assess parasite survival, 2 h old cercariae (on average) were taken from a pool of infected snails incubated at 20–25 °C, and their mortality was recorded every 6 h until all the cercariae were dead. For both species, a trade-off between high emergence and low survival of cercariae was observed in the high temperature treatment. Species-specific responses to the combination of temperature and pCO₂ levels were also observed: the emergence of Echinostomatidae cercariae was highest at 20 °C regardless of the pCO₂ levels. By contrast, the emergence of Philophthalmidae cercariae was highest at elevated pCO₂ (15 and 20 °C), suggesting that CO₂ may react synergistically with temperature, increasing transmission success of this parasite in coastal ecosystems of the Humboldt Current System where water temperature and pH are expected to decrease. In conclusion, our results suggest that integrating temperature-pCO₂ interactions in parasite studies is essential for understanding the consequence of climate change in future marine ecosystem health.     

Parasite-induced trophic facilitation exploited by a non-host predator: a manipulator's nightmare

Parasites with complex life cycles, relying on trophic transmission to a definitive host, very often induce changes in the behaviour or appearance of their intermediate hosts. Because this usually makes the intermediate host vulnerable to predation by the definitive host, it is generally assumed that the parasite's transmission rate is increased, and that the modification of the host is, therefore, of great adaptive significance to the parasite. However, in the ecological "real world" other predators unsuitable as hosts may just as well take advantage of the facilitation process and significantly erode the benefit of host manipulation. Here we show that the intertidal New Zealand cockle (Austrovenus stutchburyi), manipulated by its echinostome trematode (Curtuteria australis) to rest on the sediment surface fully exposed to predation from the avian definitive host, is also subject to sublethal predation from a benthic feeding fish (Notolabrus celidotus, Labridae). The fish is targeting only the cockle-foot, in which the parasite preferentially encysts, reducing the infection intensity of manipulated cockles to levels comparable with those in non-manipulated, buried cockles. Based on the frequency and intensity of the foot cropping and predation rates on surfaced cockles by avian hosts, it is estimated that 2.5% of the parasite population in manipulated cockles is transmitted successfully whereas 17.1% is lost to fish. We argue that the adaptive significance of manipulation in the present system depends critically on the feeding behaviour of the definitive host. If cockles constitute the majority of prey items, there will be selection against manipulation. If manipulated cockles are taken as an easily accessible supplement to a diet composed mostly of other prey organisms, behavioural manipulation of the cockle host appears a high risk, high profit transmission strategy. Both these feeding behaviours of birds are known to occur in the field.     

Reduced byssal thread production and movement by the intertidal mussel<Emphasis Type="Italic"> Hormomya mutabilis</Emphasis> in response to effluent from predators

Laboratory experiments were carried out to investigate byssal thread production by the intertidal mytilid mussel Hormomya mutabilis in response to effluent from the predatory crab Eriphia smithii and the starfish Coscinasterias acutispina. During the early period of the experiment, large H. mutabilis exposed to crab effluent produced a significantly smaller number of functional byssal threads than mussels in crab-free water. No significant difference in the diameter of threads produced in the two treatments was detected. The number of functional byssal threads produced by small H. mutabilis exposed to crab effluent did not differ significantly from that of mussels in crab-free water. However, small H. mutabilis exposed to crab effluent tended to discard fewer byssal bundles, that is, they shifted their attaching sites less frequently than similar mussels in crab-free water. In the presence of waterborne cues from the crab, H. mutabilis tended to reduce both the secretion of byssal threads and movement across the substratum. No significant differences in behaviour were observed between large mussels exposed to effluent from the starfish and those unexposed. The adaptive significance of the responses shown by H. mutabilis is discussed in terms of protection against predators differing in foraging behaviour. Electronic Publication