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Student Research

A description of Morgan's summer research project:

            With approximately 12,000 acres of marine habitat, the San Diego Bay is the largest naturally occurring marine embayment between San Francisco and Scammon’s Lagoon (central Baja CA) and is home to a wide diversity of species (Allen et al. 2002). This important ecosystem is highly productive, with an abundance of juvenile fish that grow up in the extensive nursery habitat of eelgrass. Nearby ecosystems are supported by production in the San Diego Bay, as the fish migrate out into the open ocean once they have reached adulthood. The fish species not only support ecologically important and endangered avian species, but also recreational and commercial fisheries.

In 2005 and 2008, the Vantuna Research Group at Occidental College conducted a survey of the fish populations in the San Diego Bay, continuing work that had been completed from 1994 to 1999. From 1994-1999, surveys were taken quarterly and in 2005 and 2008, they were done in both April and July of each year. This study is scheduled to again take place in April and July of 2012. The goal of this ongoing research is to identify and calculate the use of the fishery populations in the bay, recognize the habitats and their nursery function that are support juvenile fish species, and ascertain which areas of the bay are supporting populations of fish that are classified as forage species for endangered avian species in the environment (Pondella and Williams 2009). The studies have been researching nursery area function, fish species and composition, ecological importance of the species, fish assemblage structure, water quality parameters, and fish density and biomass estimates, among other physical and chemical factors.

I contend that the function of the nursery area is one of the most important aspects of the study, as the health of the environment in which juvenile fish grow up in is integral to the health of the ecosystem as a whole. The entire bay thrives because of the high population of these species and the eelgrass in which the fish live driving the process. In past research, it was found that measurements at eelgrass sites yielded nearly twice as many individual fish and fish species than samples taken at non-vegetated sites (Hoffman et al. 1986). However, though the bay supports a wide variety of marine life, it is heavily polluted by runoff from Chollas Creek, one of the most polluted waterbodies in San Diego County (San Diego Coastkeeper, 2010), and from the shipyards and Navy facilities that reside in the bay. The presence of copper at unhealthy levels has been detected in the bay, with concentrations in the sediment high enough to have adverse effects on benthic fauna (Biggs et al. 2011).  Eelgrass populations are declining worldwide, and scientists suspect that in addition to pollution, other causes such as development, commercial fishing, and changes in climate are contributing to this change. Eelgrass is used for shelter for fish larvae settling in estuaries and by juvenile fish before it is time for some of them to migrate from the freshwater bay into the ocean (Jenkins and Wheatley 1997). As a nursery habitat and a vital primary producer, eelgrass is extremely important and the loss of it will have far reaching consequences.

I plan to study the presence of eelgrass in the San Diego Bay, which will help aid in determining the health of the bay’s ecosystem. Estuary dependant fish species, such as the slough anchovy (Anchoa delicatissimma), heavily rely on the bay as a nursery habitat.  In the 2008 survey, the slough anchovy was found to be the most abundant species, comprising 35.5% of the catch (Table 1), and the species of highest ecological importance based upon the variables %Number, %Weight, and %Frequency (Pondella and Williams 2009). The slough anchovy was also found to be the dominant species in three out of the four Ecoregions (Figure 1). I propose to look for a correlation between the fish density of the slough anchovy and the presence of eelgrass in the upcoming April and July 2012 surveys. Using GIS files of the eelgrass shown in Google Earth, I will be able to georeference the areas in which eelgrass has been growing in the bay. With maps from 2004 (Figure 2), and one recently done this summer, I can determine the loss/growth of the eelgrass. Considering the rising changes in global climate and the increasing toxicity found in the waters, I hypothesize that there will be a measurable difference.

As a member of the Vantuna Research Group, I will accompany the group down to San Diego this April and July. Four main stations are surveyed- north, north-central, south-central, and south (Figure 3).

Figure 2. San Diego Bay 2004 Eelgrass Survey (US Navy SWDIV Naval Facilities Engineering Command, Port of San Diego, 2004)

Figure 3. Sampling locations of the North (1), North-Central (2), South-Central (3) and South (4) Ecoregions in San Diego Bay. (Pondella and Williams 2009)

 

At each of these sites, I will note if we encountered eelgrass and compare this to satellite images of the region in years past. I will examine the concentration of the slough anchovy, an important forage species that spends its life in the estuary environment. One of the main questions to be answered will be whether or not there a positive correlation between the density of the slough anchovy and the occurrence of eelgrass. Because of the past surveys, I have data on the number of slough anchovies collected in the bay in previous years. I will then be able to compare this information to the samples obtained during the upcoming 2012 survey.

Table 1. Total abundance of fishes collected in San Diego Bay during April and July 2008 by Ecoregion. (Pondella and Williams 2009)

Figure 1. Total catch of the five numerically dominant species by Ecoregion (Pondella and Williams 2009).

 

 

When surveying the fish in the bay, the same protocol will be used this year as in years past. At each of the four Ecoregions (Figure 2), five subhabitats will be sampled (intertidal vegetated, intertidal non-vegetated, nearshore vegetated, nearshore non-vegetated, and deep channel). Gear to be used includes a large seine, a small seine, a square enclosure, a beam trawl, a purse seine, and a semi-balloon otter trawl. At each station, the fish are counted and measured. I will note at each site whether or not there is eelgrass growth present and count/measure all slough anchovies found. This can then be compared to numbers found in years past. Though slough anchovies have been sampled in years past, there has been no further investigation into precisely which areas of the bay they are found relative to the presence of eelgrass. The water at each Ecoregion is tested for water temperature, salinity, dissolved oxygen, and pH; I can use this data in comparison to years past in order to detect the changes that have been occurring in the environment. By looking at the presence of eelgrass and the corresponding population of slough anchovies over time, I will examine if manmade and/or natural factors are causing a change in their environment. 

 

Works Cited:

 

Allen, Larry G., Amy M. Findlay and Carol M. Phalen. “Structure and Standing Stock of Fish Assemblages of San Diego Bay, California from 1994 to 1999.” Southern California Academy of Sciences. 101(2), 2002, pp. 49-85. 13 May 2011.

 

Biggs, Trent W. and Heather D’Anna. “Rapid increase in copper concentrations in a new marine, San Diego Bay.” Marine Pollution Bulletin. (2012) doi: 10.1016/j.marpolbul.2011.12.006.

 

Pondella, Daniel J. and Jonathan P. Williams. “Fisheries Inventory and Utilization of San Diego Bay, San Diego California for Surveys Conducted in April and July 2008.” Vantuna Research Group. February 2009.

 

San Diego Coastkeeper "Toxic Sediment in San Diego Bay.". 2010. Web. 12 Feb. 2012. <http://www.sdcoastkeeper.org/learn/restoring-san-diegos-toxic-waters/current-work-on-toxic-waters/sediment.html>.