Hughes B.B.,Moss Landing Marine Laboratories
Journal of Experimental Marine Biology and Ecology | Year: 2010
The effect of foundation species on community assemblages in physically stressful environments has received much recent attention because of the importance of foundation species in ameliorating environmental stress. Many studies have described variable effects of foundation species on community diversity at small scales, but net positive effects over large scales. Egregia menziesii (Turner) J.E. Areschoug is a large and robust perennial kelp that creates a structurally complex habitat on rocky shores of the Northeast Pacific. This study investigated the effects of Egregia sporophytes on benthic assemblages of the rocky intertidal along the central California coast. Egregia sporophytes strongly impacted the structure of associated communities, due to wave-driven whiplash of fronds, shading, or habitat provision. A survey of Egregia populations at 10 stations along 200. km of the central California coast found effects of Egregia density on the intertidal to be consistent among sites. Increased Egregia sporophyte density negatively affected algal species richness, total algal cover, and cover of the most conspicuous species of algae. However, there was a positive relationship with algal crusts, geniculate coralline algae, and sessile invertebrates. Egregia removal experiments at two sites within the study area experimentally tested for the effects of Egregia on intertidal communities. Results from Soberanes Pt. were consistent with survey results because of the negative effect of Egregia on algal species diversity, subcanopy layering, and cover of abundant algal species. However, removal experiments at Pigeon Pt. resulted in a positive Egregia effect on algal diversity and cover of abundant algal species possibly due to lower Egregia densities, lower wave exposure than Soberanes Pt., and stress amelioration. In the lower energy environment, Egregia acted as a sand trap, yet sand accumulation did not negatively impact algal diversity. Negative effects of large brown algae on benthic assemblages have been observed in temperate waters around the world for certain intertidal or subtidal kelp in wave-swept environments allowing for scouring and substrate shading. This study shows that Egregia and morphologically similar brown algal species can have both negative and positive effects on community diversity depending on variation in density and local environmental conditions. Egregia has the opposite effect on community diversity than what has been previously reported for foundation species because it negatively affects biodiversity in stressful environments, but has a positive effect in less stressful environments. © 2010 Elsevier B.V.
Muth A.F.,Moss Landing Marine Laboratories
Journal of Phycology | Year: 2012
Successful kelp recruitment is important for kelp population persistence and associated kelp forest communities. The proximity of settled kelp zoospores is a known requirement for successful kelp recruitment and proximity can be increased as zoospores aggregate. Substrate rugosity can also be an important factor affecting macroalgal settlement and recruitment in wave-swept areas, and may affect kelp recruitment by aggregating zoospores. In this study, kelp zoospores were cultured at different levels of small-scale aggregation and kelp recruitment was quantified. Sporophyte production significantly increased as zoospores became more aggregated indicating that processes that aggregate kelp zoospores have the potential to enhance kelp recruitment. A 13-month field experiment demonstrated differential kelp recruitment onto settlement plates that mimicked surface rugosities of two common rock types within Stillwater Cove, Carmel Bay in central California (Carmelo Formation sandstone and Santa Lucia granodiorite). Significantly more kelp recruited to molds mimicking granodiorite over the yearlong study (granodiorite = 2.7 recruits ± SE 0.50, sandstone = 1.2 recruits ± SE 0.51). There was a significant difference in recruitment between seasons and this variability was due to the fact that spring had the highest average number of kelp recruits per mold. However, the interaction between substrate and season was not significant. This study emphasizes the importance of kelp zoospore aggregation on kelp recruitment and demonstrates that small-scale rugosity affects kelp recruitment. © 2012 Phycological Society of America.
Aiello I.W.,Moss Landing Marine Laboratories |
Christina Ravelo A.,University of California at Santa Cruz
Geosphere | Year: 2012
Sediment of the Bering Sea, derived mainly from biogenic, glaciomarine, and, secondarily, riverine sources, reflects the history of oceanographic changes within the basin and climatic changes on the adjacent continents. Integrated Ocean Drilling Program (IODP) Expedition 323 recovered cores that reveal the evolution of sedimentation in the Bering Sea over the past 5 m.y., a period that includes globally significant events such as the early Pliocene warm period, the onset of extensive Northern Hemisphere glaciation, and the Pleistocene glacial-interglacial and millennial-scale climate cycles. To begin to understand the Bering Sea regional response to and role in these global climate change events, we examined the sedimentary constituents of Expedition 323 sites U1339, U1343, and U1344 on the Bering Slope, and U1340 and U1341 on Bowers Ridge. New particle size and petrographic analyses, combined with shipboard lithostratigraphic and physical property data, are used to characterize sediment types and texture and its distribution through space and time. The sediment comprises mainly two components, opaline diatom valves and siliciclastic grains (mainly clay and fine silt size). Approximately 40% of the variance in particle size can be explained by the abundance and preservation of diatom valves, a rough indicator of biogenic opal productivity. Particle size data indicate that productivity was generally higher during interglacials compared to glacials, and higher during the Pliocene warm period, decreasing as Northern Hemisphere glaciation intensified ~3 m.y. ago. Although the abundance of diatoms in the sediment varied, diatom ooze and diatom mud are the dominant lithologies at Bowers Ridge, indicating that there was a persistent supply of diatoms to the sediment in the open Bering Sea during the past 5 m.y. This study provides a comprehensive view of sediment types and sedimentation processes; future work should be aimed at validating our interpretations of past changes in productivity and siliciclastic sedimentation mechanisms with multiple additional proxies. © 2012 Geological Society of America.
Loeb V.J.,Moss Landing Marine Laboratories |
Santora J.A.,Farallon Institute for Advanced Ecosystem Research
Progress in Oceanography | Year: 2012
The salp Salpa thompsoni has exhibited increased abundance in high latitude portions of the Southern Ocean in recent decades and is now frequently the numerically dominant zooplankton taxon in the Antarctic Peninsula region. The abundance increase of this species in high latitude waters is believed related to ocean warming. Due to its continuous filter feeding and production of dense rapidly sinking fecal pellets S. thompsoni is considered to be an important link in the export of particulate carbon from the surface waters. Hence basic information on the life history of this component of the Antarctic marine ecosystem is essential for assessing its impact given continued climate warming. Here we cover various aspects of the life history of S. thompsoni collected in the north Antarctic Peninsula during annual austral summer surveys of the US Antarctic Marine Living Resources (AMLR) Program between 1993 and 2009. We focus on seasonal and interannual variations in the size composition and abundance of the aggregate (sexual) and solitary (asexual) stages. This information is valuable for refining components of Southern Ocean food web models that explicitly deal with size-structured and life history information on zooplankton. Intraseasonal changes in length-frequency distribution of both stages are used to estimate their growth rates. These average 0.40mmday -1 for aggregates and 0.23mmday -1 for solitaries; together these represent ~7week and ~7.5month generation times, respectively, and a 9month life cycle (i.e., onset of aggregate production year 1 to aggregate production year 2). Based on the maximum lengths typically found during January-March, the life spans of the aggregate and solitary stages can reach at least ~5 and ~15months, respectively. Length-frequency distributions each year reflect interannual differences in timing of the initiation and peak reproductive output. Interannual differences in the abundance of total salps and proportions of the overwintering solitary stage are significantly correlated with El Niño Southern Oscillation indices (SOI and Nino3.4) prevailing over the previous 2years. Massive salp blooms result from two successive summers of elevated solitary production following a reversal from La Niña to El Niño conditions. These results indicate the role of basin-scale atmospheric-oceanic processes in establishing optimal conditions that support aggregate and solitary stage reproduction, development and growth. © 2011 Elsevier Ltd.
Foster M.S.,Moss Landing Marine Laboratories |
Schiel D.R.,University of Canterbury
Journal of Experimental Marine Biology and Ecology | Year: 2010
It is increasingly argued that human-induced alterations to food webs have resulted in the degradation of coastal ecosystems and even their "collapse." We examined the evidence for this argument for Macrocystis pyrifera (giant kelp) forests in southern California. Others have concluded that forests in this region collapsed between 1950 and 1970 as a result of sea urchin grazing driven by overfishing of sea urchin predators (sheephead wrasse and spiny lobsters) and competitors (abalone), and that the kelp forests recovered but are currently sustained as a result of a commercial sea urchin fishery that began in the early 1970s. Our examination of the historical record, primary publications, and previously unpublished data showed that there was no widespread decline in the region between 1950 and 1970, but there were localised declines in mainland kelp forests near the rapidly growing cities of Los Angeles and San Diego. The preponderance of evidence indicates that kelp losses were caused primarily by large increases in contaminated sewage discharged into coastal waters, sedimentation from coastal development, and the 1957-1959 El Niño. Increases in active sea urchin foraging were most likely a secondary effect following dwindling food resources. The forests recovered when sewage treatment improved and sewage outfalls were relocated. The effects of fisheries were explored by correlation analysis between kelp canopy cover and commercial sea urchin landings, and among fisheries landings for sea urchins, abalone, sheephead and lobster. These correlations were generally insignificant, but were often confounded by differences in the spatial scale over which the data were collected as well as factors other than simple abundance that affect the fisheries. However, where area-specific data were available, the landings of sea urchins generally tracked kelp abundance, most likely because roe (gonad) development is directly related to food availability. A literature review showed that although sheephead and lobsters may control sea urchin abundance at small spatial scales within some sites, there is little evidence they do so over large areas. That abalone and sea urchins compete, such that sea urchins increased as a result of abalone harvesting, is largely conjecture based on their similar habitat and food utilization. This study shows that kelp forests in southern California did not collapse, and that declines in some coastal sites were caused primarily by degradation of water quality, increased sedimentation and contamination, and unfavorable oceanographic conditions. We conclude that management by species' protection or reserves will not be effective if poor habitat quality impacts the ability of giant kelp to survive and thrive. © 2010 Elsevier B.V.