Jessica Rodgers
Species distributions in a kelp forest in Monterey Bay, California
Introduction
Knowing the distribution and abundance of species in a kelp forest community may help explain the many levels of interaction between species and the environment they live in. Distributions may explain the relationships between, and effects of many biotic and abiotic factors including but not limited to intraspecific and interspecific competition, resource availability and partitioning, predation, disturbances, etc. (Hallacher & Roberts 1985). The abundance of available resources, such as sunlight, proper nutrients and space may contribute to species distributions and density. The amount of sunlight available for primary producers may impact their depth distributions. The abundance of organisms consumed as prey may effect the distribution of their predators and visa versa (Hallacher & Roberts 1985). Large-scale disturbances such as the El Nino Southern Oscillation may have visible effects on species distribution such as the movement or death of cold-water species and replacement with warm water tolerant species (Edwards, 2003). Seasonal changes in upwelling affect the recruitment of mid-water fish (swept out in surface currents, return to recruit in deep currents) and benthic fish (swept in and out on surface currents) to kelp forest communities. Knowledge of the distribution and abundance of species is helpful in understanding community dynamics.
Species distributions were determined using a qualitative sampling method in the field in order to estimate the abundance of selected fish, algae and invertebrate species in a Monterey bay kelp forest. The qualitative method is advantageous because it is a quick and efficient way to conduct an ecological assessment of abundance. However, cons associated with the qualitative method include overlooking species that hide amongst rocks or algae (such as some species of rockfish and invertebrates such as snails), and mobile species that hide in various places (such as some rockfish). As opposed to the qualitative method, the quantitative method yields accurate counts of abundance, distribution and dispersion. Cons of the quantitative method include subjectivity towards more frequent or easily seen species and away from rare species or species in hiding(such as counting cup corals and ignoring abalone), completely missing some organisms due to being preoccupied and the efficiency at which the sampling can be done. An important question to ask when determining which sampling method is better to use is which method will yield more reliable data?
The qualitative method was chosen over the quantitative method because it is more efficient for estimating the distribution of multiple species on a single dive. The distribution data this study collected is important to scientists so they can better understand the dynamics behind community interactions including biotic and abiotic factors that influence community structure.
Methods
Study system and species
This survey was conducted using SCUBA at Hopkins Marine Reserve in Monterey Bay, California. Hopkins is a rocky reef with a fringing M. pyrifera kelp forest. A cable runs along the bottom roughly north to south (fig. 6). Fourteen buddy pairs did one dive to qualify species distributions and were assigned a meter mark along the cable. Meter marks were assigned 5 meters apart, from the 80m to 145m marks in order to determine if species abundance varies with distance along the cable.Each buddy pair sampled a 30m distance for both their deep and shallow transects, within a depth range from 5-15mto determine if species abundance varies with depth.
This survey measured abundances for six species of algae, nine species of fish and thirteen species of invertebrates. The species of algae included Cystoseiraosmundacea, Chondracanthuscorymbiferous, Dictyoneurumcalifornicum, Macrocystispyrifera, Dictyoneurumreticulatumand Phyllospadix spp. The species of fish included Oxylebiuspictus, Hexagrammosdecagrammus, Sebastesmystinus, Sebastescarnatus, Sebasteschrysomelas, Sebastesatrovirens, Embiotocajacksoni, Embiotocalateralis, andDamalichthysvacca. The species of invertebrates includedPatiriaminiata, Pycnopodiahelianthoides, Pisasterbrevispinus, Pisastergiganteus, Urticinapiscivora, Urticinalofotensis, Pachycerianthusfimbriatus, Balanophylliaelegans, Tethyaaurantia, Calliostomaligatum, Loxorhynchusgrandis, Haliotisrufescens, and Strongylocentrotusfranciscanus.
Questions
Variability in observed abundances raises the question, what qualifies a species as a good or poor candidate for qualitative sampling? Good candidates for qualitative sampling would likely be well known and have distinct characteristics that make them easy to spot and identify. Good candidates would also be evenly distributed on both sides of the meter tape and common enough so both buddies see them. A simple body plan without camouflage, and no “look-alike” species would prevent mix-ups in identification. Poor candidates would likely have the opposite characteristics; good camouflage and close resemblance to other species and uneven or clumped distributions. Differences in diver knowledge of where to look for species may cause that species to be a poor candidate, such as one buddy knowing to look on the blades of brown algae for ring topped snails and the other buddy unaware of the snails’ algal residence.
The objective of our qualitative survey was to examine the distribution of selected species in a Macrocystispyrifera kelp forest. To address this objective we asked the following questions: (1) what are the sources of variance and how do they affect distribution data? (2) Are there any obvious patterns of species abundance that vary with depth or distance along the meter tape? (3) Is there such a difference between buddies that the reliability of the data is compromised?
Specific methods
We measured species distributions with the qualitative method because it is more efficient for measuring abundance of twenty-eight species in one dive.
In order to qualitatively estimate abundance we used visibility as our sampling distance for observing the two 30m transects.Each of the species was individually rated in one of 5 categories of abundance; 1: absent, 2: rare, 3: present, 4: common, 5: abundant.Each buddy pair also recorded the depth at their meter mark, at the end of leg 1 and the end of leg 3 to see if there was a significant change in depth, and if so how that affects species distribution.To determine the reliability of our qualitative estimates we comparedabundance ratings for each species between both individuals that sampled the same transect.
Statistical analyses
Transect data were collected from all divers and analyzed for percent of variance between depth (on each side of the meter line), buddy pairs, and distance along the meter line (fig. 1). The percent variance between the three above sources was also measured by taxa to determine which sources supplied the most variance between taxa (fig. 2). The mean abundance for all species was calculated to determine which species are more abundant than others (fig. 3). The relative difference between the buddies was calculated for each of the species in order to determine which species may or may not be a good candidate for qualitative sampling methods (fig. 4). Finally, the mean value of each level of abundance was calculated along with the relative difference between buddies (fig. 5). This is significant because it shows the range of ratings that had the most variability between buddies.
Results
You were supposed to include figures in your word document. AND figures require legends…always.
Sources of variance
Use active tense. (we identified three sources of variation….)There were found to be three sources of variance in this observational study consisting of depth, distance along the meter line, and between buddies (fig. 1). The smallest portion of variance within the data came from depth, measured at 23%. The next largest source of variance came from between buddies, at 37%, with the most variance coming from distance along the meter line, at 40%.
Variance by taxa
Variance from the three sources was measured for each taxa included in the study (fig. 2). For all species of algae, the lowest amount of variance was by depth, found to be roughly 10%. The next greatest contribution to variance was from the buddy groups, at 40%, followed by the variance along the meter line, found to be over 50%.
For all species of fish, the lowest amount of variance occurred between buddy pairs, at 15%, followed by about 20% variance by depth. The largest source of variance within the fish taxon was along the meter line, measured at 80%.
In contrast to fish and algae, invertebrates showed almost no variance along the meter line, followed by equal variance between depth and within buddy pairs, measured at 50% respectively (fig. 2).
Mean abundance of all species
The mean abundance of each species for all buddy pairs was graphed in order to examine overall distributions of species throughout the site at Hopkins (fig. 3). The error bars associated with figures 3 and 4 were calculated with the standard error equation; standard deviation divided by the square root of the sample size.
The mean abundances of all nine fish species were classified as rare with relatively small error associated with the data.
Out of the six species of algae, Phyllospadix spp. was the least common, with an abundance rating between absent and rare. This abundance rating in between two distinct levels is the result of taking the average of all group data; some buddy pairs may have observed Phyllospadix spp. and some may have not. Three of the species of algae were classified as rare, includingChondracanthuscorymbifera, DictyoneurumcalifornicumandDictyoneurumreticulatum. The most abundant species of algae included CystoseiraosmundaceaandMacrocystispyrifera, classified as common.
The thirteen species of invertebrates displayed the most variety of abundance levels out of the three taxa observed, ranging from absent to common. The species marked as absent included Haliotisrufescens, StrongylocentrotusfranciscanusandUrticinalofotensis. The species with a mean abundance rating between absent and rare consisted of Loxorhynchusgrandis, Pisasterbrevespinus, PycnopodiahelianthoidesandUrticinapiscivora. Species measured as present included Balanophylliaelegans, Calliostomaligatum, Pisastergiganteus, PachycerianthusfimbriatusandTethyaaurantia. The most abundant species of invertebrate observed was Patiriaminiata (fig. 3).
Relative difference between buddies
The relative difference between buddies was determined for each species in order to compare measures of variance with mean abundance values.
All fish species showed 25-40% variation except for Sebasteschrysomelas, which showed only 10% variance between buddies.
The species of algae that had the most variance between buddies were DictyoneurumreticulatumandDictyoneurumcalifornicum. Both Dictyoneurum spp. showed 50% variance between buddies, where the four other species only showed 25-30% variance.
Invertebrates displayed the largest range of relative difference between buddies, ranging from 10-60%. On the low end of the relative differences lie Haliotisrufescens, Urticinalofotensis and Strongylocentrotusfranciscanus, with 10% differences between buddies. Species that showed 20-40% of relative difference between buddies includes Loxarhynchusgrandis, Patiriaminiata, Pisasterbrevespinus, PycnopodiahelianthoidesandUrticinapiscivora. Species that showed 50-60% relative difference between buddies includes Balanophylliaelegans, Calliostomaligatum, Pachycerianthusfimbriatus, PisastergiganteusandTethyaaurantia (fig. 4).
Our last graph depicts the relative difference between buddy pairs as a function of mean abundance of species (fig 5.). This graph shows that our least reliable data are in the abundance scoring range from 1.5-3, where the relative difference between buddies is over 50%. This graph also shows that our most reliable data is that of the ratings absent, common and abundant because the relative difference between buddies is less than 25%.
Discussion
Sources of variance
The three sources of variance within our data help us understand species distributions along with differences between buddies. The scale of these variations provide us with knowledge of the variation in species abundance with changing depths and distance along the meter line, along with knowledge of the degree to which we can rely on the data due to buddy variance. (???)
The low amount of variance in the depth category suggests that there is not much variation in species abundance and distribution between the deep and shallow transects. Hopkins is a relatively shallow site, with the depths changing gradually along the meter line and never more than 10m for any buddy pair. Good
Variation between buddies is a very important source to consider when analyzing this data because high variance between buddies means less reliable data. Such high variance within buddy pairs may be the result of lack of communication prior to the dive, where buddy pairs should have conversed about what measures they think would count as abundant for each species, and the differences between the levels of scoring for each species (such as what determines the difference between present and common for B. elegans). Another cause of the variation between buddy pairs could be a significant difference in diving in temperate kelp forests between buddies. More experienced divers may have a more accurate idea of how many individuals of a certain species is common to see on a dive, rather than the inexperienced diver who may think observing twenty cup corals is considered abundant, and seeing five rockfish considers them rare.No specification in sampling distance from the meter tape other than vision, and differences in the focal points of individuals (ex. Looking in cracks vs. scanning the landscape) can yield differences in species observed. Other sources of buddy variability include each side of the meter tape containing different substratum and abundances of species, mobile fish being unequally seen by both individuals, and small invertebrates being overlooked or unequally dispersed.
The largest source of variance in this survey comes from distance along the main cable, which runs north to south. This result shows that Hopkins is highly variable along the cable. This may be because of the patchy distribution of sand and rocky reef outcrops that allow for variable distributions and abundances of species. The underwater environment found here consists of sand, rocky substrate covered in corallines, red, and brown algae that compose the canopy, sub canopy and understory layers of foliage. Amongst the rocky outcrops there are plentiful surfaces for invertebrates, including both horizontal surfaces and vertical surfaces. Cracks and crevices provide shelter for fish, as well as invertebrates, and a quality hiding place from any predators and offer protection from the surge.
Variance by taxa
The high variance along the meter line combined with low variance in depth for species of algae supports our finding that Hopkins is a highly variable environment with gradual sloping and a capacity for multiple species of algae to coexist while competing for resources (fig. 2). However, the moderate amount of variance between buddies suggests that this data is not completely reliable. The variability between buddies is likely a result of each individual having a different idea of abundance for each species, or paying differing amounts of attention to algae abundance, and more attention to fish or invertebrates. What qualities of the taxa lend themselves to poor or good sampling by this method?
Spatial distribution of fish varied more along the meter mark than depth, possibly because fish are territorial and competitive, which leads to resource partitioning and competitive exclusion with some and coexistence with other species who do not use the same resources to survive. The highly variable environment at Hopkins provides abundant habitats for the multiple fish species observed. Buddies accounted for the least amount of variability within the fish taxon, possibly because there are fewer fish than inverts and algae, or because fish mobility or tendencies for them to be out in the open give them a better chance to be seen by both buddies, and thus equally scored. Buddies may also have a more equal picture in mind of fish abundance in terms of distribution.
Invertebrates displayed only two sources of variance; there was virtually no variance by meter mark. The variance between buddies might be a result of the highly varied abundance and distribution of invertebrates throughout Hopkins. Invertebrates are usually the most frequent taxa of organisms inhabiting the kelp forest, as well as the most varied taxa. The high variability and abundance of invertebrates may lead to buddies observing only a portion of what is actually in their transect. Such high variance between buddies jeopardizes the reliability of our data, and obscures the significance of other important variables. The high variance of invertebrates by depth may be a result of respective predator/ prey distributions. Organisms trying to escape predation are going to seek out a range where their predator either cannot survive, or cannot see them. One possibility to investigate is if there is a certain depth range at Hopkins that provides invertebrates with more protection or places to hide (such as algae cover, crevices).
Mean abundance of all species
The mean abundance of species was calculated to provide us with an idea of overall species abundance throughout the site at Hopkins. The average abundance of species may provide researchers with valuable knowledge of trophic interactions, and if these data are collected over time, could tell us the effects predation has on prey populations, and populations associated with the prey species.