Markov chain analysis of succession in a rocky subtidal community

Author Posting. © University of Chicago Press, 2004. This article is posted here by permission of University of Chicago Press for personal use, not for redistribution. The definitive version was published in American Naturalist 164 (2004): E46-E61.We present a Markov chain model of succession in a rocky subtidal community based on a long-term (1986–1994) study of subtidal invertebrates (14 species) at Ammen Rock Pinnacle in the Gulf of Maine. The model describes successional processes (disturbance, colonization, species persistence, and replacement), the equilibrium (stationary) community, and the rate of convergence. We described successional dynamics by species turnover rates, recurrence times, and the entropy of the transition matrix. We used perturbation analysis to quantify the response of diversity to successional rates and species removals. The equilibrium community was dominated by an encrusting sponge (Hymedesmia) and a bryozoan (Crisia eburnea). The equilibrium structure explained 98% of the variance in observed species frequencies. Dominant species have low probabilities of disturbance and high rates of colonization and persistence. On average, species turn over every 3.4 years. Recurrence times varied among species (7–268 years); rare species had the longest recurrence times. The community converged to equilibrium quickly (9.5 years), as measured by Dobrushin’s coefficient of ergodicity. The largest changes in evenness would result from removal of the dominant sponge Hymedesmia. Subdominant species appear to increase evenness by slowing the dominance of Hymedesmia. Comparison of the subtidal community with intertidal and coral reef communities revealed that disturbance rates are an order of magnitude higher in coral reef than in rocky intertidal and subtidal communities. Colonization rates and turnover times, however, are lowest and longest in coral reefs, highest and shortest in intertidal communities, and intermediate in subtidal communities.This research was supported by National Science Foundation grants DEB-9527400, OCE-981267, OCE-9302238, and OCE-0083976 and by the National Oceanic and Atmospheric Administration’s National Undersea Research Program, University of Connecticut—Avery Point

Consumer mobility predicts impacts of herbivory across an environmental stress gradient

Author Posting. © Ecological Society of America, 2019. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecology, (2019): e02910, doi:10.1002/ecy.2910.Environmental stress impedes predation and herbivory by limiting the ability of animals to search for and consume prey. We tested the contingency of this relationship on consumer traits and specifically hypothesized that herbivore mobility relative to the return time of limiting environmental stress would predict consumer effects. We examined how wave‐induced water motion affects marine communities via herbivory by highly mobile (fish) vs. slow‐moving (pencil urchin) consumers at two wave‐sheltered and two wave‐exposed rocky subtidal locations in the Galapagos Islands. The exposed locations experienced 99th percentile flow speeds that were 2–5 times greater than sheltered locations, with mean flow speeds >33 cm/s vs. <16 cm/s, 2–7 times higher standing macroalgal cover and 2–3 times lower cover of crustose coralline algae than the sheltered locations. As predicted by the environmental stress hypothesis (ESH), there was a negative relationship between mean flow speed and urchin abundance and herbivory rates on Ulva spp. algal feeding assays. In contrast, the biomass of surgeonfishes (Acanthuridae) and parrotfishes (Labridae: Scarinae) was positively correlated with mean flow speed. Ulva assays were consumed at equal rates by fish at exposed and sheltered locations, indicating continued herbivory even when flow speeds surpassed maximum reported swimming speeds at a rate of 1–2 times per minute. Modeled variation in fish species richness revealed minimal effects of diversity on herbivory rates at flow speeds <40 cm/s, when all species were capable of foraging, and above 120 cm/s, when no species could forage, while increasing diversity maximized herbivory rates at flow speeds of 40–120 cm/s. Two‐month herbivore exclusion experiments during warm and cool seasons revealed that macroalgal biomass was positively correlated with flow speed. Fish limited macroalgal development by 65–91% at one exposed location but not the second and by 70% at the two sheltered locations. In contrast, pencil urchins did not affect algal communities at either exposed location, but reduced macroalgae by 87% relative to controls at both sheltered locations. We propose an extension of the ESH that is contingent upon mobility to explain species‐specific changes in feeding rates and consumer effects on benthic communities across environmental gradients.This study was made possible through funding from the National Science Foundation (awards OCE‐1061475, OCE‐1450214, and OCE‐1623867) and the Galapagos Conservancy to JDW, and grants from the Rufford Foundation, the American Museum of Natural History, the Institute at Brown for Environment and Society, and the Bushnell Research and Education Fund to RWL. We are deeply grateful to Max Hirschfeld, Paul Tompkins, Etienne Rastoin, Inti Keith, Anaide Aued, Salome Buglass, Blake Hamilton, Fiona Beltram, Camila Lupi, Calvin Munson, and Maya Greenhill for assistance in the lab and in the field. Captain Nelson Ibarra, Captain Wilton Aguirre, and Captain Viko Rosero provided diving logistics aboard their boats. We also thank Arturo Izurieta, Marta Romolereaux, Heinke Jäger, and the Charles Darwin Research Station for field research support, and Danny Rueda, Jorge Carrion, Jenifer Suarez, and the Galapagos National Park for granting us authorization to carry out this investigation (research permit PC‐06–16). This publication is contribution number 2285 of the Charles Darwin Foundation for the Galapagos Islands

Species diversity in subtidal landscapes: Maintenance by physical processes and larval recruitment. Ecology 80

Abstract. Heterogeneous patterns of species diversity are rarely linked to the processes that maintain them on spatial scales larger than tens of meters. In this study, subtidal landscapes of a New Zealand fjord were used to study the spatial patterns of epifaunal invertebrate species diversity and to test hypotheses about the mechanisms maintaining the patterns. Patterns of species diversity were quantified along 1000-m 2 sections of vertical rock wall habitat at three sites separated by 3-6 km of horizontal distance during AprilAugust 1993. Species diversity data from random 0.25-m 2 quadrats at four depth strata (3, 5, 10, and 18 m) within a 20 ϫ 50 m area were contoured to reveal spatial patterns at each site. General patterns consisted of localized patches of 300-660 m 2 of high diversity (i.e., HЈ [Shannon-Weiner diversity index] of 2.0-3.2/0.25 m 2 and S [species richness] of 28-32 species/0.25 m 2 ) centered at 10 m depth. High-diversity patches, dominated by bryozoans, sponges, and ascidians, were bounded vertically by low-diversity mussel assemblages and horizontally by low-diversity assemblages dominated by encrusting calcareous algae with areas of bare rock. Vertical patterns of diversity were attributed to physical stress from a low-salinity surface layer impinging on shallow areas (e.g., 0-5 m depth) of the landscapes, while horizontal patterns could be partly attributed to large-scale landslides and severe grazing by sea urchins. The hypothesis that the areas of high diversity could be maintained by larval recruitment was tested by deploying an array of recruitment tiles with predator exclusion treatments. Experiments were conducted on the same spatial scale as the documented patterns of diversity (e.g., at 3, 5, 10, and 18 m depth), with tiles placed in and out of the high-diversity patches. Recruitment densities of calcareous polychaetes, bryozoans, and hydroids showed significant depth and habitat effects (i.e., in vs. out of the high-diversity areas) after 3 mo, but no significant effects of predator exclusion treatment. A positive linear relationship between species diversity and number of recruit species in adjacent areas of wall explained 27-57% of the variance. These data also suggested that the size of the high-diversity patches and location within the fjord are important factors affecting this relationship. We suggest that the localized patches of high diversity over hundreds of meters of continuous habitat can be maintained on temporal scales of months either by spatially limited recruitment of short-lived larvae from the patches or by recruitment near established conspecifics. Additionally, there may be a feedback mechanism involving the interaction of increased biogenic structure provided by the high-diversity patches enhancing recruitment. This feedback would then serve to maintain localized areas of high diversity within the extensive areas of low diversity on scales of hundreds to thousands of meters

The relation between productivity and species diversity in temperate-arctic marine ecosystems

Energy variables, such as evapotranspiration, temperature, and productivity explain significant variation in the diversity of many groups of terrestrial plants and animals at local to global scales. Although the ocean represents the largest continuous habitat on earth with a vast spectrum of primary productivity and species richness, little is known about how productivity influences species diversity in marine systems. To search for general relationships between productivity and species richness in the ocean, we analyzed data from three different benthic marine ecosystems (epifaunal communities on subtidal rock walls, on navigation buoys in the Gulf of St. Lawrence, and Canadian Arctic macrobenthos) across local to continental spatial scales (1000 km) using a standardized proxy for productivity, satellite-derived chlorophyll a. Theoretically, the form of the function between productivity and species richness is either monotonically increasing or decreasing, or curvilinear (hump- or U-shaped). We found three negative linear and three hump-shaped relationships between chlorophyll a and species richness out of 10 independent comparisons. Scale dependence was suggested by more prevalent diversity-productivity relationships at smaller (local, landscape) than larger (regional, continental) spatial scales. Differences in the form of the functions were more closely allied with community type than with scale, as negative linear functions were restricted to sessile epifauna while hump-shaped functions occurred in Arctic macrobenthos (mixed epifauna, infauna). In two of the data sets, (St. Lawrence epifauna and Arctic macrobenthos) significant effects of chlorophyll a co-varied with the effects of salinity, suggesting that environmental stress as well as productivity influences diversity in these marine systems. The co-varying effect of salinity may commonly arise in broad-scale studies of productivity and diversity in marine ecosystems when attempting to sample the largest range of productivity, often encompassing a coastal-oceanic gradient

Sea urchin (Eucidaris) quadrat counts at twelve sites in the Galápagos Islands in 2016-2017

Dataset: Sea urchin density Galápagos IslandsSea urchin (E. galapagensis) densities showed high variability across twelve study sites in the Galápagos Islands in 2016-2017. Sea urchin densities ranged from a low of 0.17 individuals per 0.25 square meter quadrat at the Pinzon site to a maximum of 7.7 individuals per quadrat at the Champion site in January 2016. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/872905NSF Division of Ocean Sciences (NSF OCE) OCE-162386

Residence times of consumers in subtidal areas on Isla Baltra, Gal?pagos during 2012 (GMR Trophic Cascades project)

Dataset: consumer residence timesResidence times of consumer species during a trophic cascade experiment conducted at 8- 10 m depth at Isla Baltra, Galápagos Islands from July 13 to July 19, 2012. Data represent counts of consumer species photographed with GoPro cameras at 1 second intervals during daylight hours in two adjacent areas of the bottom, named Baltra crest and Baltra gully. The consumers were photographed in the vicinity of treatments where sea urchins Lytechinus semituberculatus were enclosed in fences on substrates of consumable benthic algae. Data represent raw data of entrance and exit times from image analysis and the calculated difference. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/630458NSF Division of Ocean Sciences (NSF OCE) OCE-106147

Percent algal substrate grazed by sea urchins in trophic cascade experiments in Gal?pagos Islands during 2012 (GMR Trophic Cascades project)

Dataset: urchin grazingPercent algal substrate grazed by sea urchins in trophic cascade experiments in Gal?pagos Islands during 2012. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/635717NSF Division of Ocean Sciences (NSF OCE) OCE-106147

Positive effects of damselfish override negative effects of urchins to prevent an algal habitat switch

1. Understanding the factors that influence habitat persistence is a central theme in ecology, particularly for habitats created by terrestrial and aquatic primary producers that are some of the world’s most extensive and ecologically important. 2. Many species have positive (e.g. farming) or negative effects (e.g. herbivory) on the abundance of primary producers, potentially causing wholesale switches in habitat structure if the net outcome of effects moves toward one extreme (e.g. over-grazing). Predicting the conditions under which such switches occur remains a key challenge for ecologists. 3. The purpose of this study was to understand how co-habiting species of opposing effect (damselfish as habitat facilitators vs. sea urchins as habitat consumers) can directly and indirectly influence the persistence of algal habitats on a tropical coast, including their potential to initiate switches among habitat types (productive ‘turfs’ of filamentous algae vs. ‘barrens’ of encrusting algae). 4. Using a series of five independent experiments, we observed that damselfish facilitated the production of algal turfs both directly, through active farming of selected species, and indirectly, by vigorously attacking and expelling invading urchins from the local area (i.e. preventing herbivory). In contrast, urchins consumed algal turf to directly maintain barrens. 5. The negative effects of urchins on algal turf were strong enough to initiate a habitat switch from turf to barrens, but this was conditional upon the absence of damselfish and the presence of a particular species of urchin. 6. Synthesis. These results build upon our understanding of the dynamics of habitat persistence by demonstrating the conditions where biological interactions of opposing direction (positive vs. negative) maintain or switch habitat types. Such knowledge is central to addressing global concerns about habitat loss and predicting the occurrence of switches to less-productive states

Zip file containing data files and R script

This zip file contains all data files and a R script for the production of all analyses and figures presented in Witman & Lamb 2017: "Persistent differences between coastal and offshore kelp forest communities in a warming Gulf of Maine

Data from: Persistent differences between coastal and offshore kelp forest communities in a warming Gulf of Maine

Kelp forests provide important ecosystem services, yet coastal kelp communities are increasingly altered by anthropogenic impacts. Kelp forests in remote, offshore locations may provide an informative contrast due to reduced impacts from local stressors. We tested the hypothesis that shallow kelp assemblages (12-15 m depth) and associated fish and benthic communities in the coastal southwest Gulf of Maine (GOM) differed significantly from sites on Cashes Ledge, 145 km offshore by sampling five coastal and three offshore sites at 43.0 +/- 0.07° N latitude. Offshore sites on Cashes Ledge supported the greatest density (47.8 plants m-2) and standing crop biomass (5.5 kg m-2 fresh weight) of the foundation species Saccharina latissima kelp at this depth in the Western North Atlantic. Offshore densities of S. latissima were over 150 times greater than at coastal sites, with similar but lower magnitude trends for congeneric S. digitata. Despite these differences, S. latissima underwent a significant 36.2% decrease between 1987 and 2015 on Cashes Ledge, concurrent with a rapid warming of the GOM and invasion by the kelp-encrusting bryozoan Membranipora membranacea. In contrast to kelp, the invasive red alga Dasysiphonia japonica was significantly more abundant at coastal sites, suggesting light or dispersal limitation offshore. Spatial differences in fish abundance mirrored those of kelp, as the average biomass of all fish on Cashes Ledge was 305 times greater than at the coastal sites. Remote video censuses of cod (Gadus morhua), cunner (Tautaogolabrus adspersus), and pollock (Pollachius virens) corroborated these findings. Understory benthic communities also differed between regions, with greater abundance of sessile invertebrates offshore. Populations of kelp-consuming sea urchins Stronglyocentrotus droebachiensis were virtually absent from Cashes Ledge while small urchins were abundant onshore, suggesting recruitment limitation offshore. Despite widespread warming of the GOM since 1987, extraordinary spatial differences in the abundance of primary producers (kelp), consumers (cod) and benthic communities between coastal and offshore sites have persisted. The shallow kelp forest communities offshore on Cashes Ledge represent an oasis of unusually high kelp and fish abundance in the region, and as such, comprise a persistent abundance hotspot that is functionally significant for sustained biological productivity of offshore regions of the Gulf of Maine