Rocky Intertidal Environments Research Articles

Ecological restoration using intertidal foundation species: Considerations and potential for rockweed restoration

AbstractFoundation species, such as trees, corals, grasses, oysters, and rockweeds, must be common and abundant to effectively modify the physical environment and increase biodiversity by buffering environmental stress. Yet many of these important species have been declining due to disease, climate change, and other factors. A prime example is the precipitous population decline of marine rockweeds, which is attributed to increased urbanization and its accompanying impacts. Rockweeds provide three‐dimensional habitat in harsh rocky intertidal environments and regulate ecosystem functioning, essential roles that no substitute species are capable of filling. Recovery of impacted rockweed populations is typically slow and unpredictable due to their limited dispersal capacity. These issues have motivated efforts to conserve remaining populations of rockweeds and reestablish or enhance depleted ones. Successfully doing so requires a robust understanding of factors that affect survival of the species and the processes that influence ecosystem structure, along with rigorous scientific testing of restoration methods and the factors that affect restoration success. In this comprehensive review, we summarize the current knowledge of rockweed ecology, highlight studies that could inform restoration practices, and recommend ways to improve our ability to implement scalable restoration of rockweeds and accompanying ecosystem‐wide benefits.

Effect of thermal variation on the cardiac thermal limits of a eurythermal marine teleost (Girella nigricans).

Although most animals live in complex, thermally variable environments, the impact of this variability on specific physiological systems is still unresolved. The ectotherm heart is known to change in both structure and function to ensure appropriate oxygen delivery under different thermal regimes, but the plasticity of the upper thermal limits of the heart under stable or variable thermal acclimation conditions remains unknown. To investigate the role of thermal variability on cardiac acclimation potential, we acclimated a eurythermal fish, opaleye (Girella nigricans), to three static temperature treatments (13, 16, and 19 °C) as well as two oscillating treatments which cycled between maximum and minimum temperatures every 12 h (13–19 °C and 16–22 °C). These temperatures and daily thermal ranges were chosen to mimic the conditions observed in the rocky intertidal environments in Santa Barbara, CA, USA where the fish were collected. We hypothesized that increasing temperature would increase upper thermal limits of the heart, and that variable acclimations would result in broader acute thermal performance curves (TPCs) compared to static acclimations. We measured maximum heart rate during acute warming to determine cardiac thermal performance (i.e., the temperature corresponding to the onset of cardiac arrythmia, the temperature at maximum heart rate, absolute maximum heart rate, and the Arrhenius breakpoint temperature) and construct acute TPCs. Rising static acclimation temperatures increased upper thermal limits but had no impact on peak maximum heart rate. The warmest static temperature did, however, cause a narrowing of the acute TPC. Fish acclimated to variable conditions had the same upper thermal limits compared to fish acclimated to static conditions with the same mean temperature in all metrics of thermal performance. Further, there was no significant broadening of the acute TPC. This study suggests that cardiac plasticity is robust to thermal variation in this eurythermal fish.

Effect of Extreme Heatwaves on the Mortality and Cellular Immune Responses of Purplish Bifurcate Mussel Mytilisepta virgata (Wiegmann, 1837) (=Septifer virgatus) in Indoor Mesocosm Experiments

In the rocky intertidal environment, the frequency and duration of heatwaves have increased over the last decade, possibly due to global climate change. Heatwaves often result in lethal or sub-lethal disturbances in benthic animals by changing their metabolic activities. In this study, we investigated the impacts of extreme heatwave stress on the hemocyte functions of Mytilisepta virgata and subsequent mortality to gain a better understanding of the potential causes and consequences of mass mortality events in this mussel during summer. We discriminated three types of hemocytes in the hemolymph, granulocytes, hyalinocytes, and blast-like cells, using flow cytometry and revealed that granulocytes were the major hemocyte involved in cellular defensive activities, such as phagocytosis and reactive oxygen species (ROS) production. For the experiment, mussels were exposed to a 40°C air temperature for 12 h per day over 5 days under laboratory conditions as a simulated semi-diurnal tidal cycle. Mortality began to occur within 3 days after beginning the experiment, and all mussels had died by the end of the experiment. Flow cytometry indicated that the mussels exposed to high air temperatures produced significantly more ROS than did the control mussels within 2 days after the onset of the experiment, which may have caused oxidative stress. Such high levels of ROS in the hemolymph increased DNA damage in hemocytes after 3 days of exposure and decreased the phagocytosis of hemocytes 4 days after the experiment began. The observed mortality and decline in immune capacity suggested that an extreme heat event occurring in the rocky intertidal ecosystem during summer could exert sublethal to lethal impacts on macrobenthic animals.

Near-daily reconstruction of tropical intertidal limpet life-history using secondary-ion mass spectrometry

Measurements of life-history traits can reflect an organism’s response to environment. In wave-dominated rocky intertidal ecosystems, obtaining in-situ measurements of key grazing invertebrates are constrained by extreme conditions. Recent research demonstrates mollusc shells to be high-resolution sea-surface temperature proxies, as well as archival growth records. However, no prior molluscan climate proxy or life-history reconstruction has been demonstrated for the tropical rocky intertidal environment—a zone influenced by warmer waters, mixed tides, trade-wind patterns, and wave-action. Here, we show near-daily, spatiotemporal oxygen isotope signatures from the tropical rocky intertidal environment by coupling secondary ion mass spectrometry analysis of oxygen isotopes with the sclerochronology of an endemic Hawaiian intertidal limpet Cellana sandwicensis, that is a significant biocultural resource harvested for consumption. We also develop a method for reliable interpretation of seasonal growth patterns and longevity in limpets. This study provides a robust approach to explore tropical intertidal climatology and molluscan life-history.

Data Gap Classification for Terrestrial Laser Scanning-Derived Digital Elevation Models

Extensive gaps in terrestrial laser scanning (TLS) point cloud data can primarily be classified into two categories: occlusions and dropouts. These gaps adversely affect derived products such as 3D surface models and digital elevation models (DEMs), requiring interpolation to produce a spatially continuous surface for many types of analyses. Ultimately, the relative proportion of occlusions in a TLS survey is an indicator of the survey quality. Recognizing that regions of a scanned scene occluded from one scan position are likely visible from another point of view, a prevalence of occlusions can indicate an insufficient number of scans and/or poor scanner placement. Conversely, a prevalence of dropouts is ordinarily not indicative of survey quality, as a scanner operator cannot usually control the presence of specular reflective or absorbent surfaces in a scanned scene. To this end, this manuscript presents a novel methodology to determine data completeness by properly classifying and quantifying the proportion of the site that consists of point returns and the two types of data gaps. Knowledge of the data gap origin can not only facilitate the judgement of TLS survey quality, but it can also identify pooled water when water reflections are the main source of dropouts in a scene, which is important for ecological research, such as habitat modeling. The proposed data gap classification methodology was successfully applied to DEMs for two study sites: (1) A controlled test site established by the authors for the proof of concept of classification of occlusions and dropouts and (2) a rocky intertidal environment (Rabbit Rock) presenting immense challenges to develop a topographic model due to significant tidal fluctuations, pooled water bodies, and rugged terrain generating many occlusions.

Structural traits dictate abiotic stress amelioration by intertidal oysters

Abstract Autogenic ecosystem engineers often provide cool microhabitats which are used by associated organisms to reduce thermal extremes. The value of such habitats is, however, dependent on key structural traits of the ecosystem engineer, and the intensity and duration of thermal exposure. Using an experimental mesocosm that mimicked the rocky intertidal environment, we assessed how the spatial configuration of the habitat formed by an autogenic ecosystem engineer, the oyster, influences its capacity to mitigate heat stress experienced by invertebrates during simulated emersion periods on tropical, Hong Kong rocky shores. At the average temperature experienced during summer low tides, oyster habitat ameliorated environmental and organismal temperatures, irrespective of the structural configuration of the oyster bed. As temperatures increased, however, vertically orientated oysters provided microclimates that facilitated cooler invertebrate body temperatures than horizontal beds, which no longer conferred any associational benefit as compared to bare rock surfaces. In the absence of oysters, physiological indicators of stress to associated organisms (i.e., heart rate and osmolality) increased with the intensity and duration of exposure to high temperatures. Such effects were, however, mitigated by association with vertical but not horizontal oyster configurations. In contrast, the osmolality of the oysters was not related to temperature, suggesting they remained in a state of metabolic quiescence throughout emersion. Structural traits such as the spatial configuration of ecosystem engineers are therefore critical to their effectiveness in environmental amelioration. As such, variations in the morphological traits of ecosystem engineers, which have important implications for their ecological role, need to be incorporated into conservation and restoration projects aimed at climate change adaptation. A plain language summary is available for this article.

Mazzaella laminarioides and Sarcothalia crispata as possible bioindicators of heavy metal contamination in the marine coastal zone of Chile.

The suitability of Mazzaella laminarioides and Sarcothalia crispata as heavy metal biomonitors of Cd, Cu, Hg, Pb, and Zn was assessed by comparing bioaccumulation of these elements in different life stages and frond sizes in samples from three locations, San Vicente Bay (industrial area), Coliumo, and Quidico (the latter as a reference station), where different degrees of heavy metal pollution are recorded. Bioaccumulation and bioconcentration factors of Cd, Cu, Hg, Pb, and Zn were evaluated. The two macroalgae species showed similar patterns, with higher values of Cu, Hg, Pb, and Zn in polluted areas. M. laminarioides bioaccumulated higher concentrations of all metals assessed than S. crispata, independent of life stage and frond size. The results also showed significantly higher Cu, Hg, Pb, and Zn concentrations (p<0.05) in water samples from San Vicente Bay than those measured in Coliumo and Quidico. Concentrations of Cd, Hg, Pb, and Zn in San Vicente Bay and Cd, Hg, and Pb in Coliumo and Quidico exceed the mean values considered to represent natural concentrations (Cu=3.00μgL-1; Zn=5.00μgL-1; Pb=0.03μgL-1; Cd=0.05μgL-1; Hg=0.05μgL-1); however, the concentrations recorded do not cause negative effects on the growth and survival of macroalgae. The assessment of heavy metals bioaccumulated in M. laminarioides and S. crispata, particularly Hg, Pb, and Zn, offers a reliable approach for pollution assessment in rocky intertidal environments. Cu and Cd concentrations in seawater samples from San Vicente and Coliumo Bays were significantly higher than in those from Quidico (p value <0.05); no significant differences in Cd concentrations were observed between San Vicente and Coliumo Bays (p<0.05). Exceptionally, Cd is bioaccumulated at high levels independent of its availability in the water, thus reaching high concentrations in control areas. High concentrations of metals like Cu and Zn may limit or inhibit Cd uptake in macroalgae, since the transport channels are saturated by some metals, reducing the accumulation of others. These macroalgae species offer good potential for the development of suitable heavy metal pollution survey tools in rocky intertidal environments.

An approach to the floristics and faunistics of the intertidal zone in El Pulpo rocky shore, Cazones, Veracruz, Mexico.

The rocky intertidal of Veracruz, Mexico is a coastal ecosystem with high biodiversity. However,its relevance has not been recognized compared with other marine ecosystems. The objective of this study was todevelop the first floristic and faunistic lists of the rocky intertidal of El Pulpo beach, located in the municipalityof Cazones, Veracruz. Samples were taken from 2013 to 2016 in the rocky intertidal strip in periods of low tidein order to record the marine biota and the collection of biological material for their taxonomic identification. Inaddition, a bibliographic review was performed to complement the species inventory. Fifty-one species of benthicmacroalgae, one species of phanerogam, 186 species of invertebrates, and five species of vertebrates were recorded totaling 243 intertidal marine species. The Rhodophyta are the most representative of the phycoflora with 29species, while the phylum Mollusca are the most representative of the fauna with 139 species. Most of the marinespecies were recorded in the middle and lower intertidal. Consequently, the lowest richness was recorded in theupper intertidal which consists of filamentous and foliose algae, mollusks and crustaceans with both browsing andfilter habits. This distribution coincides with those described for other rocky intertidal environments. The numberof species recorded in the rocky intertidal of El Pulpo beach demonstrates the relevance of this ecosystem. It isthus necessary to encourage actions for its protection and conservation.

Gastropod shell utilisation pattern by the hermit crab Clibanarius symmetricus (Anomura: Diogenidae) in an Equatorial Amazon estuary

ABSTRACTClibanarius symmetricus is a diogenid hermit crab that is highly abundant in rocky intertidal environments, including the rock outcrops of Amazon estuaries. This study characterises the C. symmetricus shell utilisation pattern in the Marapanim River estuary, Pará, Equatorial Amazon, based on the hypothesis that occupancy patterns would differ, in relation to biometry and diversity of occupied shells, from those of other regions in the range of this species due to the distinct and unique environmental characteristics of equatorial estuaries. Monthly samplings were carried out from August 2006 to July 2007, in the upper and lower areas of the mid-littoral during low tides. A total of seven gastropod species were found as shells occupied by hermit crabs: 93.33% were Thaisella trinitatensis shells, 2.00% Nassarius vibex, 2.00% Neritina virginea, 1.33% Natica marochiensis, 0.67% Parvanachis obesa, and, occasionally, Littorina flava and Phalium granulatum shells, each with only one occurrence (0.33%). Juveniles [cephalothoracic shield length (CL) of less than 3.6 mm] occupied a higher variety of shells, while adults occupied shells with larger meristic variation. Males occupied larger shells. The length of the animal was influenced by shell measurements (total width, aperture width and weight). Clibanarius symmetricus showed occupancy patterns generally similar to those of specimens of the same species previously studied in the Brazilian subtropical region, and this occupancy is explained by shell availability, shell size and weight, and hermit size. However, this study showed lower occupied shell species diversity, and the species with highest occupancy frequency (T. trinitatensis) was not reported in any previous studies on this hermit crab. In addition, the studied population differed in occupancy patterns, with differences between males and females, and between juveniles and adults.

Competition between calcifying and noncalcifying temperate marine macroalgae under elevated CO2 levels

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 464:89-105 (2012) - DOI: https://doi.org/10.3354/meps09892 Competition between calcifying and noncalcifying temperate marine macroalgae under elevated CO2 levels Laurie C. Hofmann*, Sandra Straub, Kai Bischof Marine Botany, Bremen Marine Ecology Center for Research and Education, University of Bremen, Leobener Straße NW2, 28359 Bremen, Germany *Email: l.hofmann@uni-bremen.de ABSTRACT: Since pre-industrial times, uptake of anthropogenic CO2 by surface ocean waters has caused a documented change of 0.1 pH units. Calcifying organisms are sensitive to elevated CO2 concentrations due to their calcium carbonate skeletons. In temperate rocky intertidal environments, calcifying and noncalcifying macroalgae make up diverse benthic photoautotrophic communities. These communities may change as calcifiers and noncalcifiers respond differently to rising CO2 concentrations. In order to test this hypothesis, we conducted an 86 d mesocosm experiment to investigate the physiological and competitive responses of calcifying and noncalcifying temperate marine macroalgae to 385, 665, and 1486 µatm CO2. We focused on comparing 2 abundant red algae in the Northeast Atlantic: Corallina officinalis (calcifying) and Chondrus crispus (noncalcifying). We found an interactive effect of CO2 concentration and exposure time on growth rates of C. officinalis, and total protein and carbohydrate concentrations in both species. Photosynthetic rates did not show a strong response. Calcification in C. officinalis showed a parabolic response, while skeletal inorganic carbon decreased with increasing CO2. Community structure changed, as Chondrus crispus cover increased in all treatments, while C. officinalis cover decreased in both elevated-CO2 treatments. Photochemical parameters of other species are also presented. Our results suggest that CO2 will alter the competitive strengths of calcifying and noncalcifying temperate benthic macroalgae, resulting in different community structures, unless these species are able to adapt at a rate similar to or faster than the current rate of increasing sea-surface CO2 concentrations. KEY WORDS: Competition · Corallina officinalis · Chondrus crispus · Calcification · Ocean acidification · Mesocosm Full text in pdf format PreviousNextCite this article as: Hofmann LC, Straub S, Bischof K (2012) Competition between calcifying and noncalcifying temperate marine macroalgae under elevated CO2 levels. Mar Ecol Prog Ser 464:89-105. https://doi.org/10.3354/meps09892 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 464. Online publication date: September 19, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

PRESERVATION POTENTIAL AND DIVERSITY OF TROPICAL ROCKY SHORE GASTROPOD COMMUNITIES, SAN SALVADOR ISLAND, BAHAMAS

This study explores spatial distribution, species diversity, and preservation potential of modern rocky intertidal gastropod communities from San Salvador Island, Bahamas. Using a hierarchical sampling approach, 17,703 intertidal gastropod specimens representing 9 genera and 15 species were recorded from 480 quadrats along 120 transects at 40 sites sampled at ten localities around the island. All localities are dominated by several species of littorinids and neritids. The rank-abundance structure was comparable across all localities, with the same species dominating at all but one locality. The hierarchical sampling scheme revealed a gradual increase in diversity across sampling levels, with most notable increase observed between site-level and locality-level diversity estimates. Habitat diversity estimates did not vary from bare and exposed surfaces to sheltered pits, crevices, and tide pools. Across energy regimes, there was no meaningful shift in habitat occurrences to more sheltered, protected habitats. Species occurrences in sheltered habitats should augment fossilization potential of those assemblages because, as shown in some paleontological studies, there is evidence of rocky intertidal environments from such settings as tide pools, pits, and crevices. Indeed, when data are restricted to more preservable, sheltered settings only, a good representation of total biodiversity and overall community structure of sampled faunal associations is still retained. Moreover, because the sampled communities appear remarkably homogeneous across and within localities, even a highly fragmentary fossil record (e.g., small area in one locality) would likely collect a substantial fraction of biodiversity and community structure of rocky intertidal communities of San Salvador Island.

Influence of motivation on behaviour in the hermit crab, Pagurus samuelis

Both the need for shelter and the need for food can be motivations that alter animal behaviour. We tested the hypothesis that the hermit crab, Pagurus samuelis, deprived of food, shells, or both will respond differently from control hermit crabs when presented with food and shells concurrently. We measured the number of contacts made with both food and shells, and time elapsed until hermit crabs either began feeding or inserted into shells. We interpreted making few contacts and initiating behaviour quickly to be an indication of short decision time and high motivation; whereas, making many contacts and having long initiation time indicated a long decision time and low motivation to acquire resources. Control (C) hermit crabs made 72% more contacts with food and 53% more contacts with shells than shell-less (S) crabs. Control hermit crabs also made 34% more contacts with food and 35% more contacts with shells than starved and shell-less (StS) hermit crabs. This suggests that S hermit crabs were more motivated to acquire shells than C crabs. In addition, StS hermit crabs chose to insert into provided shells, while hermit crabs remaining in their shells chose to feed. Results indicate that being shell-less is a stronger motivation than being starved, such that finding shelter takes priority over finding food when both are needed. In rocky intertidal environments, resources such as food and shells are likely to be ephemeral. Hermit crabs that are motivated to make appropriate decisions to acquire specific resources may have a distinct advantage over those that are distracted by numerous objects in their environment.

Larval Development of the Hermit Crab Pagurus Edwardsii (Decapoda: Anomura: Paguridae) under Laboratory Conditions

The first description of the larval stages of a representative of the family Paguridae from the SE Pacific coast of South America is presented. Larvae of Pagurus edwardsii, a common hermit crab from the rocky intertidal environment of the Chilean coast, were reared in the laboratory from hatching through the molt to juvenile stage I. Culture conditions included water temperature of |${\rm{11 }} \pm {\rm{ 1}}^\circ {\rm{C}}$|⁠, salinity |${\text{32 }} \pm {\text{ 1}}$|‰, 12h:12h light : dark photoperiod, and feeding with Artemia sp. nauplii. The larval development of P. edwardsii included four zoeal stages (ZI–ZIV) and one megalopal stage; the duration in days for each zoeal stage was: |${\rm{ZI}}:{\rm{ 18}}{\rm{.9 }} \pm {\rm{ 0}}{\rm{.5}}$|⁠, |${\rm{ZII}}:{\rm{ 12}}{\rm{.8 }} \pm {\rm{ 0}}{\rm{.8}}$|⁠, |${\rm{ZIII}}:{\rm{ 5}}{\rm{.9 }} \pm {\rm{ 0}}{\rm{.2}}$|⁠, |${\rm{ZIV}}:{\rm{ 5}}{\rm{.6 }} \pm {\rm{ 0}}{\rm{.6}}$|⁠; and |${\rm{9}}{\rm{.1 }} \pm {\rm{ 0}}{\rm{.4}}$| days for the megalopal stage. Descriptions and detailed illustrations are presented for each of the larval stages. Morphological comparisons made between P. edwardsii and other congeneric species with larval desciptions showed the main characteristics for the diagnosis of zoeal stages are: a) setation of antennal endopod and scaphocerite; b) spination and setation pattern of the basal endite of the maxilulle; c) setal formula of the endopodite of maxilliped 1; d) the segmentation model of the sixth pleomere; and e) the formula for the processes in the posterior margin of the telson. In contrast, the megalopal larva can be recognized by the number of setae on the endopod of maxilliped 3 and the absence of apical hooks on the appendix interna of the pleopods.

Effects of chemical cues on metamorphosis of the Asian shore crab Hemigrapsussanguineus, an invasive species on the Atlantic Coast of North America

The Asian shore crab Hemigrapsus sanguineus (Family Grapsidae) has been recently introduced to the east coast of North America. We present the results of an investigation of the response of postlarvae (megalopae) of H. sanguineus to putative water-soluble cues associated with newly colonized habitat in the Middle Atlantic region of the USA. Specifically, we tested the response of megalopae to exudates from adult H. sanguineus and to exudates from co-occurring native crabs Panopeus herbstii and Dyspanopeus sayi (Family Xanthidae). In addition, we tested the response of P. herbstii and D. sayi megalopae to exudates from adult H. sanguineus and to conspecific exudates. In a separate set of experiments, we also investigated the response of H. sanguineus megalopae to cues associated with substrata found in potential settlement sites. In all experiments, response was measured as the time to metamorphosis of megalopae exposed to the various exudates, as compared to megalopae maintained in filtered offshore seawater. Megalopae of the two native species responded to cues produced by conspecific adults. In addition, P. herbstii megalopae responded to cues produced by adult H. sanguineus. In contrast, H. sanguineus responded only to cues produced by conspecific adults and to cues associated with biofilm-covered substratum from natural rocky intertidal habitat. Thus, it appears that once established, adult H. sanguineus produce cues that promote gregarious settlement, but that initial invasion is not facilitated by response to cues produced by native xanthid crabs. Rather, this initial invasion may be facilitated by cues associated with more general characteristics of rocky intertidal environment.

Assimilation of oil-derived carbon and remedial nitrogen applications by intertidal food chains on a contaminated beach in Prince William Sound, Alaska

Beaches in Prince William Sound, Alaska were heavily oiled by the Exxon Valdez spill in March 1989. Fertilizer supplements designed to stimulate oil degradation by indigenous bacteria were applied to beaches in the rocky intertidal zones. We used stable carbon (δ 13C) and nitrogen (δ 15N) isotopes to monitor trophic interactions following these treatments. Representative macroalgae and consumer organisms were sampled during the summers of 1989 and 1990. Microcosm experiments were conducted to trace bacterial assimilation of fertilizer nitrogen and to compare relative uptake of oil and indigenous substrates during 1990. Fertilizer nitrogen was the dominant source of bacterial nitrogen in the microcosm experiments. Bacteria preferentially assimilated indigenous substrates and used oil as a substrate only after more labile substrates were depleted. Following depletion of indigenous substrates, nitrogen supplements appeared to enhance assimilation of carbon from oil. The δ 13C and δ 15N values of bacteria growing on oil and fertilizer nitrogen were distinct in the rocky intertidal environment, providing a tracer to examine the link between bacterial production and higher trophic levels. No evidence, however, was found for a transfer of carbon or nitrogen assimilated by bacteria to higher trophic levels.

Interindividual Variation in Prey Selection by the Snail Nucella (= Thais) Emarginata

Variation in diet among individuals of a population of carnivorous marine snails in a rocky intertidal environment of central California was analyzed. Nucella emarginata drills and eats barnacles, mussels, and limpets. Out of 128 marked snails, 104 were observed through two or more feeding attacks in the field during the 4—mo study. Fifty—one of these snails were observed through five or more sequential feeding attacks. Three major points are illustrated. (1) Within each study site, individuals close to the same size often chose strikingly different diets. (2) There was a range of dietary specialization and generalization among individuals foraging in the same habitat. Individuals showed a high degree of consistency in their diets. While the population of N. emarginata attacked seven prey species at site A and four prey species at site B, no individual snail observed in this study ate more than three species of prey. (3) Food choices made by each individual were not a simple reflection of the relative abundance of the surrounding prey species or the differences in microhabitat prey distribution that each predator encountered. These conclusions remained the same for several different methods of measuring prey availability. I suggest that Nucella emarginata diet patterns have a variety of causes, which may include ingestive conditioning, learning, and genetic variability.

Human Exclusion from the Rocky Intertidal Zone of Central Chile: The Effects on Concholepas Concholepas (Gastropoda)

The ecological role played by man as a top predator in a rocky intertidal environment of central Chile was studied. Human exclusion from a rocky intertidal stretch of coast (non-harvested area) at Punta El Lacho, for nearly two years, resulted in a substantial density increase of the economically important high trophic level predator muricid Concholepas concholepas. This was followed by a dramatic decline in the cover of the competitive dominant intertidal mussel Perumytilus purpuratus. According to current ecological theory the removal of the competitively superior primary space dominant species led to a pattern of increasing species diversity. We conclude that in the absence of human interference C. concholepas plays the role of a key species in central Chile rocky intertidal environments. We suggest that the interpretation of the structure and dynamics of intertidal landscapes should include the key role played by man. Comparison of monitoring programs between intertidal areas with and without human interference will prove critical to our understanding of such environments.

Analysis of seaweed communities in a disturbed rocky intertidal environment near Whites Point, Los Angeles, Calif., U.S.A.

Analysis of seaweed communities in a disturbed rocky intertidal environment near Whites Point, Los Angeles, Calif., U.S.A.