Fish/Zone Associations

Fish/Zone Associations

Aron Kingsbook

Overall score: 78/100

Title [[3/4 – this title is a bit difficult to read and you should probably have mentioned species-habitat associations]]

Varying fish species abundance and composition at different depth zones in Hopkins Marine Station, Pacific Grove, California.

Clarity [[10/14 – be careful with things like amount vs number, they are similar but should be used in different contexts. Also you need to read everything slowly out loud to yourself before you turn it in to make sure it all makes sense and is said as simply as you can. Some of these sentences are hard to understand!]]

INTRODUCTION: [[15/20]]

For decades ecologists have studied how species-rich ecosystems like rainforests, coral reefs, and kelp forests are able to maintain their broadhigh levels of diversity. Several hypotheses like “niche diversification” and “the intermediate disturbance hypothesis”[[quotes make it look like you’re making fun of those hypotheses, not what you intend]] attempt to explain this phenomenon. The iIntermediate disturbance hypothesis posits that species diversity is maintained with a certain level of disturbance in the ecosystem. Too little disruption can lead to dominant species out competing others, while too much (like an earthquake or a wildfire) can wipe out all species. Niche diversification is the theory that diversity will be greatest when the majority of species occupy specialized habitats and utilize specific resources within the ecosystem. This allows for a greater number of species to co-exist in an environment because inter-species competition diminishes. For example, studies on the amount number of dominant predators in an ecosystem have shown that when few species determine lower trophic level abundance, they are ecosystem is more susceptible to trophic cascades that can destroy or drastically alter their ecosystem. (Byrnes 2005, Duggins et al. 1989, Estes et al 1998) In contrast, environments with a larger variety of species along all trophic levels are better able to cope with disruptions in the habitat. (Byrnes 2005). These studies help in understanding what maintains diversity, which is necessary for the development of methods to control environmental destruction.

Kelp forests are one of the most diverse and productive ecosystems in the world, yet relatively few studies have been performed on them. They grow in cold-temperate waters, in contrast to warm tropical environments that rainforests and coral reefs require, making it more difficult to conduct research. Since wetsuit technology has improved drastically [since when?], increased research has shown that kelp forests thrive in extremely nutrient rich waters and are inhabited by a wide variety of invertebrates, fish, and algae. In addition, these species are able to develop specialized habitat associations because kelp forests contain several types of substrate and relief. Observational studies have supported the theory of niche diversification for inter-species [[what does this mean??]] in kelp forests. A study on inshore rockfish found that species will utilize and predate different areas of a kelp forest during the upwelling season. (Hallacher & Roberts 1985) Furthermore, Watanabe et al. (1984) observed three different species of Tegula inhabiting distinct zones at Hopkins Reef as a result of predation and recruitment. [[you need to pull this together into a more coherent paragraph with a strong main point and make sure all your sentences make sense]]

Our class looked at whether select kelp forest fish are associated with biological and physical habitats in varying abundance and composition at Hopkins Marine Station in Pacific Grove, California. The diversity of species and habitat features in addition to its accessibility make it a perfect system to study. Our data can provide ecologists with knowledge that aids kelp ecosystem upkeep by helping: 1. construct marine reserves to protect specific species 2. assess and identify critical habitats for endangered species and 3. manage marine ecosystems [[these implications should come lower down, get to the questions first]]. We attempted to answer three questions: 1. Do fish species differ in relative abundance from zone to zone (shallow and deep)? 2. Does fish species composition vary from zone to zone? 3. Do the zones differ in biological(M. Pyrifera, C.osmundacea)/physical (substrate/relief) characteristics? Answering these will give us a general idea of how certain fish species are spread throughout a kelp forest and analysis can help understand why.

MATERIALS/METHODS: [[13/18]]

Approach/Study System: To answer these you should probably reiterate the questions briefly because they’re in a different section]] questions we used SCUBA to compile data on the relative abundances and compositions of benthic kelp forest fish species in relation to ecological zones (depth and habitat attributes.) Our Kelp Forest Ecology class conducted field observations in May of 2012 at Hopkins Marine Station in Pacific Grove, California (Lat: 36.37 Long: -121.54)(Fig 1): [[strange way to use a colon]]a protected marine reserve located in central California, commonly used for scientific research on temperate kelp forest ecosystems. Hopkins has a variety of substrate and relief, but the reef is primarily comprised of granite, a good substrate for Macrocystis pyrifera and Cystoseira osmundacea to attach. This provides habitat for a wide diversity of fish, invertebrates, and other algae. The range of substrate types and relief categories along with depth variation make this an ideal system for observing whether fish species are related to ecological zones. To sample Hopkins, we used two common observational methods: Swath and UPC.

Uniform Point Contacts were used to estimate percent cover of physical and biological attributes like substrate (sand, cobble, boulder, bedrock) and relief type (flat, shallow, medium, high) associated within each marked zone: shallow and deep. UPC's are a good method to estimate sample species and terrain that is too abundant to count individually. Swaths of both primary brown algae (M. pyrifera/C.osmundacea) and select fish helped in understanding abundance and composition patterns within each zone by giving us an estimate of the number of individuals per area. Comparing UPC and Swath surveys on the same transect allowed us to see patterns of association between species and habitat type. Graphs were created to depict percent associations of relief and substrate type as well as C. osmundacea and M. pyrifera abundances within each zone. In addition, two graphs were created with chi-square analysis to depict the relative abundance and composition of species in each zone.

Study Design:

Fish species differ in relative abundances as a function of zone: To test this hypothesis we input our fish swath data into a Pearson Chi-Square analysis with a 95% confidence interval to compare fish density graphs as a function of zone. This gave us a visual representation of the varying densities of fish in relation to “Deep” and “Shallow” zones. (Fig 2)

Species composition varies as a function of zone: We took our fish swath data and created a graph comparing the relative composition of each species in relation to their zone. This allowed us to see patterns in fish composition: whether fish species were evenly distributed throughout a zone, how great a specific species differed in composition between each zone, etc. (Fig 3).

Zones differ in biological/physical characteristics: We used our algal swath data and relief/substrate UPC's to create graphs depicting their percent associations to each zone. This allowed us to visualize the differences between zones for each category of relief and substrate type as well as C. osmundacea and M. pyrifera abundance and composition. (Figs 4, 5, 6)

Data Collection:

Transects occurred along the main cable at Hopkins between 90-135 meter markers in 5m increments (Fig 1).

UPC: Ten buddy pairs conducted Uniform Point Contacts (UPC's) at specified distances along the main cable, allowing for the greatest spatial coverage of benthic terrain to be sampled (Fig 1). Each buddy pair did a deep (270 degrees) and shallow (90 degrees) dive, where they laid out a 30m transect and obtained one sample every half meter on the tape. This created a total of 1200 points sampled within 2700 m^2 of terrain. At each point, (directly under the meter tape) the diver marked substrate type, relief estimate, species type and whether drift algae or juvenile Laminaria were present. Substrate: Marked directly under the tape (sand, cobble, boulder, bedrock). Relief: The greatest relief of the substrate within .5 m of either side of the point and .25 m ahead and behind. Categories: 0-10 cm (flat), 10-1m (shallow), 1-2m (moderate), >2m (high). Inverts/Algae: Every half meter the sessile algae or invertebrate directly under meter tape was noted. If drift algae or juvenile Laminaria were present, this was noted along with the algae or invert beneath. Only one species was marked per uniform point. (Invertebrate data was not used in our analysis)

UPC's gave us an estimation of the general benthic layout for each zone.

BROWN ALGAE SWATH: Each buddy pair conducted a brown algae swath on/offshore on the same transect they did their UPC. Each group laid out a 30m transect perpendicular to the main cable and marked C. osmundacea counts and M. pyrifera stipe counts within 1m of each side of the meter tape. Data was recorded in five meter sections, six sections per transect. This totaled 120 sections or 1,200 m^2 of observed area. This allowed us to compare brown algae abundance and composition between the shallow and deep zones

FISH SWATH: Commonly seen kelp forest fish were counted using fish swaths along 30m on/offshore transects every five meters along the main cable. Buddies counted/noted all benthic fish that were found in a two meter wide by two meter high estimated box in five meter increments along each transect. This gave us an estimation of the varying fish densities and compositions between the shallow and deep zones.

RESULTS: [[13/16 – your general results are a bit weak]]

Our study suggests fish species prefer different areas of the kelp forest [[you can’t actually say anything about preferences, because who knows what a rockfish WANTS]]. In addition, the physical and biological habitat slightly changes with depth at Hopkins Reef. Rhacochilus vacca, Sebastes chrysomelas, Rhinogobiops nicholsii, Embiotocidae jacksoni, Sebastes mystinus, Sebastes atrovirens, and Embiotocidae lateralis were the species with the greatest variation between zones. Reasons for these variations will be analyzed in the discussion section.

Fish species differ in relative abundance as a function of zones in a kelp forest (Fig 2):

The p-value suggests that fish densities differed between each zone significantly. (X^2 = 66.04, df = 18, p-val = <.000001) (Table 1). Our analysis showed that the “deep” zone had a greater relative abundance of fishes than the “shallow” zone in almost every instance. Only S. chrysomelas and R. nicholsii abundances were greater in the shallow zone. Additionally, more species were found in the deep zone: all fish found in the shallow zone were seen in the deep zone, but S. caurnatus, S. caurinus, S. marmoratus, B. frenatus, and C.r aggregata were only seen in the “deep” zone.

Fish species composition varies as a function of zone (Fig 3):

There was an apparent difference in species composition between both zones. Species composition was more evenly distributed in the shallow zone, but there was less variety and abundance. Generally a species had a larger percent composition with one zone than the other. For example: Rhacochilus vacca comprised over 30% of the deep zone composition but less than 5% of shallow. Rhinogobiops nicholsii made up around 10% of the shallow zone and less than 1% of deep. There were some species whose composition was relatively the same for each zone: S. mystinus for example.

Zones differ in biological (M. Pyrifera, C.osmundacea) and physical (substrate/relief) characteristics (Figs 4, 5, 6):

Both shallow and deep zones had different levels of biological and physical characteristics. Substrate: The shallow zone was primarily made of “bed rock” (~40 %) while the deep was primarily “sand” (~50%) (Fig 4). Relief : Both zones were primarily composed of flat and shallow relief, but the deep zone had a greater percentage of flat, while shallow had a greater percentage of shallow relief (Fig 5). Brown Algae: C. osmundacea and M. pyrifera were both more abundant in the shallow zone (Fig 6).

DISCUSSION: [[18/22 – if you’re going the way of hypothesis-specific headings, follow it through]]

Fish species appear to inhabit a variety of areas in the Hopkins kelp forest suggesting that niche diversification occurs and helps explain how diversity is maintained. It was also observed that habitat composition changes with depth. I believe the change in species abundance and composition at varying depths is due to predation influences, habitat choice, reproductive methods and species competition. Since this study showed patterns of variance in fish accumulation between areas of a kelp forest, it could be used to inform services that manage and conserve marine ecosystems. More in depth studies should be conducted to reinforce these observations.

Species and habitat abundance and composition variations as a function of zone:

The deep zone had more fish species and greater abundances than the shallow for what appear to be obvious reasons. I believe the largest contributor to the abundance and variety of fish species in the deep zone is simply that it has a greater volume, so there is more space for fish to occupy [[but you surveyed exactly the same volume, this doesn’t explain greater densities of fish]]. There are other factors like prey choice and inter-species competition that influence where fishes are found, but the greater volume found in the deep zone is an easy explanation for the larger abundances. Additionally, species composition differed between zones likely because less species occupied the shallow region and habitat composition was different. Fewer species variety in the shallow zone can explain why their composition was more evenly distributed. It is also possible that the overwhelming abundance of R. vacca in the deep zone drastically altered the compositions we observed.

Variations in habitat composition were apparent but not drastic. C. osmundacea and M. pyrifera were slightly more abundant in the shallower regions of the kelp forest likely because both require light to grow. It makes sense that shallower depths would house a larger abundance of algae because more light penetration occurs. Although substrate and relief varied between zones, sand and bedrock were the primary substrates. Sand was largely the primary substrate for the deep zone, explaining why flat relief was abundant. Reversely, bedrock was the primary substrate in the shallow zone so variations in its relief were generally greater. The greater amount of bedrock in the shallow zone is another reason why algae was more abundant, since both algae types require a hard substrate for settlement and anchorage. It can be deduced that variations in substrate affect relief and depth variation can help drive algae abundance.