scholarly journals After 15 years, no evidence for trophic cascades in marine protected areas

2021 ◽  
Vol 288 (1945) ◽  
pp. 20203061
Author(s):  
Katrina D. Malakhoff ◽  
Robert J. Miller
Keyword(s):  
Marine Protected Areas ◽  
Indirect Effects ◽  
Sea Urchins ◽  
Marine Reserves ◽  
Strongylocentrotus Purpuratus ◽  
Trophic Cascades ◽  
Giant Kelp ◽  
Direct And Indirect Effects ◽  
Predator Density ◽  
Northern Channel Islands

In marine ecosystems, fishing often targets predators, which can drive direct and indirect effects on entire food webs. Marine reserves can induce trophic cascades by increasing predator density and body size, thereby increasing predation pressure on populations of herbivores, such as sea urchins. In California's northern Channel Islands, two species of sea urchins are abundant: the red urchin Mesocentrotus franciscanus , which is targeted by an economically valuable fishery, and the virtually unfished purple urchin Strongylocentrotus purpuratus . We hypothesized that urchin populations inside marine reserves would be depressed by higher predation, but that red urchins would be less affected due to fishing outside reserves. Instead, our analyses revealed that purple urchin populations were unaffected by reserves, and red urchin biomass significantly increased in response to protection. Therefore, urchin biomass overall has increased inside reserves, and we found no evidence that giant kelp is positively affected by reserves. Our results reveal the overwhelming direct effect of protecting fished species in marine reserves over indirect effects that are often predicted but seldom clearly documented. Indirect effects due to marine reserves may eventually occur in some cases, but very effective predators, large reserves or extended time periods may be needed to induce them.

scholarly journals Effects of five southern California macroalgal diets on consumption, growth, and gonad weight, in the purple sea urchin Strongylocentrotus purpuratus

2014 ◽  
Author(s):  
Matthew C Foster ◽  
Jarrett E Byrnes ◽  
Daniel C Reed
Keyword(s):  
Sea Urchin ◽  
Sea Urchins ◽  
Strongylocentrotus Purpuratus ◽  
Macrocystis Pyrifera ◽  
Reproductive Capacity ◽  
Giant Kelp ◽  
Mixed Diet ◽  
Gonad Weight ◽  
Consumption Growth ◽  
Purple Sea Urchin

Consumer growth and reproductive capacity are direct functions of diet. Strongylocentrotid sea urchins, the dominant herbivores in California kelp forests, strongly prefer giant kelp (Macrocystis pyrifera), but are highly catholic in their ability to consume other species. The biomass of Macrocystis fluctuates greatly in space and time and the extent to which urchins can use alternate species of algae or a mixed diet of multiple algal species to maintain fitness when giant kelp is unavailable is unknown. We experimentally examined the effects of single and mixed species diets on consumption, growth and gonad weight in the purple sea urchin Strongylocentrotus purpuratus. Urchins were fed single species diets consisting of one of four common species of macroalgae (the kelps Macrocystis pyrifera and Pterygophora californica, and the red algae Chondracanthus corymbiferus and Rhodymenia californica (hereafter referred to by genus) or a mixed diet containing all four species ad libitum over a 13-week period in a controlled laboratory setting. Urchins fed Chondracanthus, Macrocystis and a mixed diet showed the highest growth (in terms of test diameter, wet weight and jaw length) and gonad weight while urchins fed Pterygophora and Rhodymenia showed the lowest. Urchins consumed their preferred food, Macrocystis at the highest rate when offered a mixture, but consumed Chondracanthus or Macrocystis at similar rates when the two algae were offered alone. The differences in urchin feeding behavior and growth observed between these diet types suggest the relative availability of the algae tested here could affect urchin populations and their interactions with the algal assemblage. The fact that the performance of urchins fed Chondracanthus was similar or higher than those fed the preferred Macrocystis suggests purple sea urchins could sustain growth and reproduction during times of low Macrocystis abundance as is common following large wave events.

Experience and benefits of Marine Reserves for conservation, science and society

2015 ◽  
Author(s):  
Mark Costello ◽  
Bill Ballantine
Keyword(s):  
Marine Protected Areas ◽  
Small Area ◽  
Marine Reserves ◽  
Trophic Cascades ◽  
Economic Benefits ◽  
Science And Society ◽  
Reference Sites ◽  
Brood Stock ◽  
The Public ◽  
Do So

Experiences with Marine Reserves (no-take Marine Protected Areas) in New Zealand and internationally are reviewed. Reserves became popular with the public and provided economic benefits. In one reserve, ‘spill-over’ of lobsters counter-balanced lost fishing. The reserves provided the controls that showed the effects of fishing on ecosystems through depleted populations and habitat change due to trophic cascades. Studies in other countries indicated that these trophic cascades were common globally. Research has shown that reserves protect benthic and pelagic species, including those that move outside the reserves. Marine Reserves can provide benefits to (1) conservation of species and habitats, (2) science as controls for fishing effects, and (3) fisheries as reference sites that conserve natural genetic and population structure, host brood-stock, and provide spill-over to nearby fisheries. They should be distributed geographically in networks that include replicated examples of habitats and species. To do so, they need to be suitably located, large enough, and enforced to fulfil these opportunities. However, these benefits remain limited by the relatively small area occupied by marine reserves within and between countries.

scholarly journals Effects of five southern California macroalgal diets on consumption, growth, and gonad weight, in the purple sea urchin Strongylocentrotus purpuratus

2014 ◽  
Author(s):  
Matthew C Foster ◽  
Jarrett E Byrnes ◽  
Daniel C Reed
Keyword(s):  
Sea Urchin ◽  
Sea Urchins ◽  
Strongylocentrotus Purpuratus ◽  
Macrocystis Pyrifera ◽  
Reproductive Capacity ◽  
Giant Kelp ◽  
Mixed Diet ◽  
Gonad Weight ◽  
Consumption Growth ◽  
Purple Sea Urchin

Consumer growth and reproductive capacity are direct functions of diet. Strongylocentrotid sea urchins, the dominant herbivores in California kelp forests, strongly prefer giant kelp (Macrocystis pyrifera), but are highly catholic in their ability to consume other species. The biomass of Macrocystis fluctuates greatly in space and time and the extent to which urchins can use alternate species of algae or a mixed diet of multiple algal species to maintain fitness when giant kelp is unavailable is unknown. We experimentally examined the effects of single and mixed species diets on consumption, growth and gonad weight in the purple sea urchin Strongylocentrotus purpuratus. Urchins were fed single species diets consisting of one of four common species of macroalgae (the kelps Macrocystis pyrifera and Pterygophora californica, and the red algae Chondracanthus corymbiferus and Rhodymenia californica (hereafter referred to by genus) or a mixed diet containing all four species ad libitum over a 13-week period in a controlled laboratory setting. Urchins fed Chondracanthus, Macrocystis and a mixed diet showed the highest growth (in terms of test diameter, wet weight and jaw length) and gonad weight while urchins fed Pterygophora and Rhodymenia showed the lowest. Urchins consumed their preferred food, Macrocystis at the highest rate when offered a mixture, but consumed Chondracanthus or Macrocystis at similar rates when the two algae were offered alone. The differences in urchin feeding behavior and growth observed between these diet types suggest the relative availability of the algae tested here could affect urchin populations and their interactions with the algal assemblage. The fact that the performance of urchins fed Chondracanthus was similar or higher than those fed the preferred Macrocystis suggests purple sea urchins could sustain growth and reproduction during times of low Macrocystis abundance as is common following large wave events.

scholarly journals Decadal trends in marine reserves reveal differential rates of change in direct and indirect effects

2010 ◽  
Vol 107 (43) ◽  
pp. 18256-18261 ◽  
Author(s):  
R. C. Babcock ◽  
N. T. Shears ◽  
A. C. Alcala ◽  
N. S. Barrett ◽  
G. J. Edgar ◽  
...  
Keyword(s):  
Indirect Effects ◽  
Marine Reserves ◽  
Direct And Indirect Effects ◽  
Rates Of Change

scholarly journals Sea urchins mediate the availability of kelp detritus to benthic consumers

2019 ◽  
Vol 286 (1906) ◽  
pp. 20190846 ◽  
Author(s):  
Christie E. Yorke ◽  
Henry M. Page ◽  
Robert J. Miller
Keyword(s):  
Food Webs ◽  
Sea Urchins ◽  
Strongylocentrotus Purpuratus ◽  
Kelp Forest ◽  
Macrocystis Pyrifera ◽  
Mesocosm Experiment ◽  
Kelp Forests ◽  
Giant Kelp ◽  
Trophic Role ◽  
Benthic Consumers

Detritus can fundamentally shape and sustain food webs, and shredders can facilitate its availability. Most of the biomass of the highly productive giant kelp, Macrocystis pyrifera , becomes detritus that is exported or falls to the seafloor as litter. We hypothesized that sea urchins process kelp litter through shredding, sloppy feeding and egestion, making kelp litter more available to benthic consumers. To test this, we conducted a mesocosm experiment in which an array of kelp forest benthic consumers were exposed to 13 C- and 15 N-labelled Macrocystis with or without the presence of sea urchins, Strongylocentrotus purpuratus . Our results showed that several detritivore species consumed significant amounts of kelp, but only when urchins were present. Although they are typically portrayed as antagonistic grazers in kelp forests, sea urchins can have a positive trophic role, capturing kelp litter before it is exported and making it available to a suite of benthic detritivores.

Reconciling conflict between the direct and indirect effects of marine reserve protection

2012 ◽  
Vol 39 (3) ◽  
pp. 225-236 ◽  
Author(s):  
NICK T. SHEARS ◽  
DAVID J. KUSHNER ◽  
STEPHEN L. KATZ ◽  
STEVEN D. GAINES
Keyword(s):  
Indirect Effects ◽  
Prey Species ◽  
Sea Urchins ◽  
Marine Reserve ◽  
Reproductive Potential ◽  
Direct And Indirect Effects ◽  
Size Selectivity ◽  
Potential Conflict ◽  
Predation Rates

SUMMARYNo-take marine reserves directly promote the recovery of predatory species, which can have negative indirect effects on prey populations in reserves. When harvesting also occurs on prey species there is potential conflict between the direct and indirect effects of protection, and reserves may not have conservation benefits for prey species. For example, sea urchins are fished in many regions, but may decline in reserves due to increased predation rates. To investigate this potential conflict, this paper compares density, size, biomass and reproductive potential of both a harvested and an unharvested urchin species between a long-term reserve and unprotected sites in California. Consistent with density-mediated indirect interactions, densities of the unharvested species were 3.4-times higher at unprotected sites compared to reserve sites. However, for the harvested species, densities were comparable between reserve and unprotected sites. Both species were consistently larger at reserve sites, and the biomass and reproductive potential of the harvested species was 4.8- and 7.0-times higher, respectively, than at unprotected sites. This is likely due to differences in size-selectivity between harvesting and predators, and potential compensatory effects of predators. While the generality of these effects needs to be tested, these results suggest mechanisms whereby reserves can benefit both predator and prey species.

Direct and indirect effects of dynamic social impact

2005 ◽  
Author(s):  
Dana M. Binder ◽  
Martin J. Bourgeois ◽  
Christine M. Shea Adams
Keyword(s):  
Indirect Effects ◽  
Social Impact ◽  
Direct And Indirect Effects
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