Bio 160 Marine Ecology
Bella Coladonato
Jessica Midbust
Nick White
40/80, but seems not complete
Giant Kelp (Macrocyctis pyrifera) Canopy Cover and its Seasonality in MontereyBay
1. Introduction
Background:4/4
Seasonal changes drive the growth and development of virtually all biotic ecosystems. Seasons are due to the revolution of the earth around the sun, and the tilt of the earths axis (Allen 1995). Migration, hibernation, and a variety of other physiological and metabolic process are driven by these seasonal changes. Plants for example have evolved cyclical dispersal mechanisms that are cued by changes in season. Other natural process such as storm activity also show seasonal variation. Seasonal weather fluctuations are often seen in oceanic systems which experience changes in ocean currents due to increased wind activity(Graham 1997). An increase in wave action during the winter has a large effect on costal communities, which are easily disrupted by the force and power of waves. Pelagic planktonic communities are at the mercy of wave currents, controlling their dispersal and migrational paths. At times wave action can be to strong to tolerate for near shore invertebrate and algae species, ripping them from the substrate they are attached to.
Central California waters are commonly subjected to harsh waves due to a large magnitude of storm action during much of the year (Graham 1997).The near shore costal communities of California are diverse ecological hotspots.Algal abundance in particular has a drastic effect on costal community structure. Not only is algae photosynthetic, providing over 70 % of earths available oxygen, allowing the persistence of life in terrestrial environments, but it also permits an abundance of growth in marine environments (Graham 1997). In the northern hemisphere the giant kelp Macrocystis Pyrifera, is a widely abundant and dominating brown algae that thrives in highly productive coastal waters (Graham1997).
M.Pyrifera is distributed at depths between 5-20 meters from central California to the southernmost tip of South America (Vanella 2007). M.Pyrifera forms dense forests which provides food and habitat for many species of invertebrates (crabs, sea urchins, mollusks, etc.), fish (rockfish, bass), as well as a variety of seabirds (Vanella2007). All stages of fish (larvae, juvenile, and adulthood) have been found to utilize the presence of kelp forests. All parts of the kelp are utilized by other animals including the holdfasts which may be used as sites for recruitment, providing shelter against macroinvertabrate and fish predators (Vanella 2007). Giant kelp M.Pyrifera plays a vital role in coastal community structure and stability.
Kelp canopy density is thought to be controlled by both biotic and abiotic factors (Graham 1997). Previous studies looking at distribution of M. pyrifera have proposed that community structure in there community is driven by disturbance mediated competition. In this experiment lack of disturbance was shown to favor kelp growth (Graham 1997).
Pattern:2/2
A seasonal pattern was reveled upon examination of theexposed and floating kelp canopy of M.Pyrifera. This pattern was observed at the surface of coastal waters in the MontereyPeninsula. During fall and winter months M.Pyrifera canopy cover density is greatly reduced.
At the beginning of the fall season kelp canopy cover in M.Pyrifera has been observed decreasing by up to 40 percent in previous study site locations (Graham 1997). In this study the greatest reduction in canopy cover was observed after the first large storm of the fall season (Graham 1997). The reduction in kelp forest during the winter months suggest a correlation between seasonal wave activity and kelp population size.
Figure:4/4
Figure 1: Macrocystis Pyrifera canopy abundance along coastal waters in the Monterey
Peninsula in relation to month of the year.
Goal: 2/2
This study will test for factors leading to seasonal variability in giant kelp (M.Pyrifera) canopy cover in the MontereyBayPeninsula.The high productivity of costal waters in the Monterey bay are largely due to the presence ofM.Pyrifera. Giant Kelp reduction can have drastic ecological implications. Recent years have shown a decrease in the abundance of this algae (Dayton 1992). Loss of this species may have the potential to cause trophic cascades, and greatly alter the structure of local ecosystems. In order to understand and prevent the loss ofM.Pyrifera, it is necessary to understand the mechanisms driving its reduction.
We hope to determine whether biotic, abiotic factors or a combination of both are driving the seasonal changes in density cover. The goal of this study is to use a series of field experiments to test and determine exactly what factors are causing the reduction in canopy. We hope to determine whether abiotic factors such as wave activity, biotic factors such as increased predation, or a combination of both cause the pattern of decreased kelp canopy in the winter months.
Hypotheses:6/6
As described earlier, our goal is to determine whether abiotic factors, biotic factors, or both drive the seasonality abundance of giant kelp canopy cover in the MontereyBay. We presume the decrease in kelp canopy is due to a seasonal increase in uprooting (of holdfast) or a seasonal increase in predation. There are several ways to test both the biotic and abiotic factors that can affect kelp canopy cover. The abiotic, or physical, factors can be tested through the following hypotheses.
General hypothesis: Seasonal variability of wave action has a direct correlation to kelp forest canopy cover
Specific: Increased wave action during the winter causes a significant decrease in kelp canopy cover, due to the larger swell of winter months uprooting kelp.
Specific: Calm wave action in the summer months yield high rates of kelp growth. When monitored in protected area, kelp canopy cover should increase significantly.
Null: Wave action throughout the year does not affect kelp forest canopy cover.
The biotic, or biological, factors can be tested through the following hypotheses.
General: Kelp forest canopy cover is driven by grazers.
Specific: Removal of Strongylocentrotuspurpuratus will allow kelp forests to flourish.
Specific: Observe the predatory effects of Strongylocentrotuspurpuratus decreasing giant kelp canopy cover throughout the year.
Null: Kelp forest canopy cover is not affected by grazers.
Material and Methods:
Species description:4/4
The question pertaining to our pattern is; What drives Macrocystis pyrifera canopy abundance throughout the year? This question is important to ask ecologically because fluctuations in ecosystems are crucial for understanding different forms of conservation, sustainability, and preservation.
M.pyrifera has crucial ecological interactions. It's survival is based on three factors; recruitment, growth, and competition. The giant kelp often competes for sun light, due to the fact that it is a 'canopy' kelp, and this competition can be intraspecific (self-shading) as well as interspecific. M.pyrifera main predator is the purple sea urchin, Strongylocentrotus purpuratus. This urchin is involved in a very well known trophic cascade with a keystone predator, sea otters, controlling the urchin population which preys on the giant kelp. Physiologically, giant kelp is most often found in colder water coastal areas, and becomes‘stressed’ with increasing water temperatures, due to a lack in available nutrients. (Gerard 1997).
The area we are focusing M.pyrifera canopy cover distribution is in the MontereyBay of central California. Globally though, M.pyrifera can be found most often above and below the tropics (Raffaelli and Hawkin 1996). Giant kelp populations are known to fluctuate greatly as a result of abiotic and biotic factors. An increase in population size is due to net productivity and recruitment, while a decrease is due to competition, and biomass loss from different types of disturbance (Steneck et al 2002). M.pyrifera experiments are easily observable (which will be a method we use) as well as manipulated, because the phase changes in kelp are very quick and transplant and removal of the kelp is easy to accomplish. (Steneck et al 2002).
In reproduction M.pyrifera start in a microscopic gametophyte stage living in the benthic layer. While in the benthic layer, fertilization occurs and produces a developing sporophyte. The sporophyte attaches a holdfast to the substrate and grows up to the surface, eventually creating a thick canopy (Neushul 1972). Experiments in the MontereyBay show that sporophyte recruitment is negatively correlated to canopy cover, and holdfast growth rates decrease with increasing wave exposure (Graham et al 1997). Steneck et al describes the longevity of M.pyrifera as quick to dissappear and reappear. Episodic events (storms), thermal events, and herbivore outbreaks can cause a large forest of giant kelp to disappear rapidly, but return to normal population levels can occur just as quickly. The growth of M.pyrifera is incredibly dependent on nutrients, water temperature, and light availability. All of these life history traits should be taken into consideration when working with or conducting experiments on giant kelp.
Site Description:4/4
The MontereyBay is characterized by having large kelp forests in its coastal waters. Many species of organisms rely on this ecosystem for survival. One relevant organism is the purple sea urchin, Strongylocentrotus purpuratus. S. purpuratus feeds on the holdfasts of M. pyrifera, destroying an important habitat for many. The sites that will be used are in the coastal waters of the area, which are characterized by a sandy bottom with scattered rocky patches. Macrosystis grows typically in the subtidal zone, from 5-20 meters in depth. This causes the kelp to grow no farther off the coast line than approximately 100 meters. Because the bay is so large and has a crescent shape, there is a great deal of variation in the amount of wave action particular areas receive. Within these areas, there is significant wave fluctuation throughout the year. This area is characterized by small waves during the summer, and large waves during the winter, sometimes exceeding twenty feet in height. During cold upwelling settled nutrients are disturbed and brought into the system, as opposed to the reduced nutrients in warm water (Gerard 1997). The coastline is composed of sandy beaches, and long stretches of marine terraces and 10-50 meter high sea cliffs (Rosenbloom 1994). These structures are composed of Santa Margarita Sandstone (Rosenbloom 1994), which allows for a great deal of erosion due to wave action. This erosion is responsible for the instability of our substrate, creating sand as its final product.
Methods: no mention of stats
Specific Hypothesis:4/5 Increased wave action during the winter causes a significant decrease in kelp canopy cover, due to the larger swell of winter months uprooting kelp.
To observe the influence of wave action on kelp abundance, we will use five sites in the Monterey Bay Each of these five sites will be graded on a scale from 1 to 5; 1 being a measure of low wave action, and 5 being a measure of high wave action. This will be determined by studying data collected by scientists interested in swell activity in the MontereyBay. An Acoustic Doppler Current Profiler (ADCP) is used to document the range of wave energy observed throughout the year.
Each of these sites will have natural Macrosystis growth, and sites will have as similar as possible biotic and abiotic conditions. Kelp canopy cover will be averaged every month for a year. Canopy cover will be measured in meters squared. To test the hypothesis that wave action drives kelp canopy cover, we will compare the average canopy cover in the five sites. If canopy cover decreases as wave action increases, we can conclude that wave action drives kelp canopy cover. This should occur on a gradient following the scale measuring wave action.
Specific Hypothesis:4/5 Removal of Strongylocentrotuspurpuratus will allow kelp forests to flourish.
To test this hypothesis we will remove sea urchins from half of ten study sites. Identical sites will be used to test the control and experimental groups. These sites will be kelp forests in relatively shallow, coastal waters. We will remove all sea urchins from one half of the study sites, constantly prohibiting their return. The other half of help will be left alone to be preyed upon by sea urchins. Kelp canopy cover will be measured at each site every week for two months. Canopy cover will be measured in meters squared. If the canopy cover is significantly less in sites with sea urchin predation than in sites without urchin predation, we can conclude that sea urchin predation drives kelp canopy cover.
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