Species Distribution in the Rocky Intertidal Zone La Bonte Species distribution of the rocky intertidal zone o rganisms at La Islita in Cuajiniquil, Costa Rica John La Bonte Department of Ecology and Evolutionary Biology University of California, Santa Cruz EAP Tropical Biology and Conservation, Fall 2017 15 December 2017 Abstract The rocky intertidal zone is an area of the seashore between the high and low tide marks with a hard substrate for organisms to move on. The organisms in this habitat face biotic and abiotic factors that determine their distribution and abundance through a biological mechanism called vertical zonation. I studied the rocky intertidal zone of La Islita near Cuajiniquil, Costa Rica in an effort to find the species that are present in this habitat and their relative abundance throughout the zone. I surveyed fiv e transects that spanned the majority of La Islita to find where and in what abundance each species is present. There are a total of 28 species that I found, with most showing distinct distributional patterns of where they live in the rocky intertidal zone I divided my results into the class's bivalvia, gastropoda, and anthozoa and also looked at the distributions of two species: Dia dema mexicanum, and Chthamalus anisop oma Species within each class all showed different distribution s even though these spec ies have very similar physical characteristics. Microhabitats created by the terrain in different littoral zones allows species to expand into other littoral areas they would normally be excluded from due to abiotic factors. This densely populated habitat shows the prominence that biotic and abiotic factors play in influenci ng species distributions. DistribuciÂ—n de especies en la zona intermareal rocosa en La Islita, Cuajiniquil, Costa Rica Resumen La zona intermareal rocosa es el Â‡rea entre los lÂ’mites de marea alta y marea baja, que provee un sustrato para diferentes orga nismos. Los organismos en este hÂ‡bitat se enfrentan a factores biÂ—ticos y abiÂ—ticos extremos que determinan su distribuciÂ—n y abundancia a travÂŽs de un mecanismo biolÂ—gico llamado zonificaciÂ—n vertical. EstudiÂŽ la zona intermareal rocosa en La Islita, cerc a de Cuajiniquil, Costa Rica. Para encontrar las especies que estÂ‡n presentes en este hÂ‡bitat y su abundancia relativa en toda la zona, inspeccionÂŽ cinco transectos que abarcaron la mayorÂ’a de La Islita. DeterminÂŽ la ubicaciÂ—n y abundancia de cada especie presente. EncontrÂŽ un total de 28 especies, y la mayorÂ’a muestran patrones de distribuciÂ—n distintos en la zona intermareal rocosa. DividÂ’ mis resultados en las clases a las que pertenecen: bivalvos, gastropodos y anthozoos y tambiÂŽn analicÂŽ las distribuci ones de dos especies: Diadema mexicanum y Chthamalus anisopoma Las especies dentro de cada clase mostraron una distribuciÂ—n diferente a pesar de que tienen caracterÂ’sticas fÂ’sicas muy similares. Los microhÂ‡bitats creados por el terreno en diferentes zonas de La Islita permiten que las especies se muevan a otras Â‡reas cercanas que normalmente serÂ’an excluidas debido a factores abiÂ—ticos. Este hÂ‡bitat densamente poblado muestra la influencia de factores biÂ—ticos y abiÂ—ticos en la distribuciÂ—n de especies.
Species Distribution in the Rocky Intertidal Zone La Bonte Introduction The Intertidal Zone of Costa Rica is an environment that has been poorly studied compared to other ecosystems in the country The last ice age was 120,000 years ago, but for only 20,000 years have the shorelines been increasing in size and in species richness. In geological terms, the shoreline is a young habitat ( Intertidal Zones ) The intertidal zone is very unique and special environment where many species have adapted to the special circumstances that arise there The intertidal zone is an area of the seashore that is covered during the high tide and exposed during low tide Chan ging abiotic factors shape organisms that live in this ever changing environment The rocky intertidal zone is an area of the seashore where there is a solid subs trate that some groups of organisms can live on These areas are sites of intense competition for resources such as shade, water, and nutrition. Patterns of species distributions along the rocky intertidal zone have been described by Joseph H. Connell and the patterns are key to understanding why certain organisms occupy the zones they do in the rocky intertidal zone (Conne l l, 1972). Species d istribution s in rock y intertidal zones are affected by three main factors: vertical zonation, horizontal zonation, and small scale patches (Connel l 1972) Vertical zonation refers to the correlation between the higher degree of exposure to air from low to high tide levels. The e ffect of air creates a pattern in the narrow horizontal zones from low to high tide. In the upper limits of the intertidal zone, the tide is the main factor that determines species composition. Tide creates different physical patterns that include wave action, and ocean spray which keep the surface wet. In the upper limits of the intertidal zone there is increased desiccation, high temperatures, and stronger solar radiation that affect organisms Biological interactions in the lower limits of the intertidal zone play the most important part in the species composition and distribution because abiotic factors such as water and temperature become less of a factor The importance of biological interactions as a limit for where species can be found has been shown through field manipulations where species of algae, barnacles, and mussels we re settled lower down the intertidal zone and survived where physical stresses are different (Conne l l, 1972) Horizontal distribution is determined by water movement along a shore. Waves and the water level affect how species survive as the tide level in creases and decreases throughout the day. Wave action creates a rough environment n ear the shore line, which only some organisms can thrive in Wave action in the lower intertidal zone affects predation by terrestrial predators because some organisms may o nly be visible or accessible at small intervals throughout the day. Air exposure by the movement of the tide will also affect where organisms can survive. Lastly, small scale patches in the intertidal zone create different environments, even at the same ho rizontal latitude of the same zone. These patches are due to the direct action of the physical environment and can create great variation s in slope s and the orientation of rocks. These patches create resources that are used by organisms up and down the zon e that may not be common in that particular horizontal band to create heterogeneity (Connel l 1972) Heterogeneity in this aspect refers to species being found throughout the zone in areas where their distribution is not common. Surveys of the Costa Rican c oast have started to be gathered and organized in the last 20 years. Willis (2001) compiled a list of the mollusks present in Manuel Antonio National Park, which is in the central Pacific area of Costa Rica He compiled this list by looking through past papers, photographs, and by studying transects of the rocky intertidal zone. They found 74
Species Distribution in the Rocky Intertidal Zone La Bonte # species of mollusks, with more than half being found at one site and many only being found in very low densities. They concurred with Paine's (1966) fi nding "that tropical rocky intertidal areas do not exhibit high diversities, but a few species are present in high densities." The class anthozoa or sea anemones, has been widely underreported for both coasts of Costa Rica and a study by AcuÂ–a (2013) fou nd 16 total species, with six of them being from the Pacific coast. Only one of those anemone species is adapted to live in the intertidal zone. There are three zones in the intertidal zone: the lower littoral zone, the mid littoral zone, and the upper l ittoral zone. The low littoral zone is always covered expect at low tide, the mid littoral zone is covered and unconverted twice a day, and the upper littoral zone is normally uncovered, expect at high tides ( Marine Animals ) All three of these zones are p resent in the rocky intertidal zone of La Islita La Islita is a small peninsula off a beach that is about 2 kilometers nor th of Cuajiniquil, Costa Rica The rocky intertidal zone there is comprised of multiple species that demonstrate the effect that inte rspecific interactions and abiotic factors have on the occurrence of organisms present in the different zones From my observations at La Islita I want to answer the question s what organisms are present in the rocky intertidal zone and what is there dist ribution throughout the zone ? Methods and Materials Site Description The Intertidal zone of La Islita occurs on the west side where the wind is blocked from the land mass known as "La Islita" ( Appendix A : Photo 1, 2 ) The wave action is severely dampened on th is side of La Islita due to the protection it provides and creates a more regular wave pattern for the shoreline There are multiple species present on the west side of La Islita while on the east side there are mainly only crabs and barnacl es which is indicative of the type of abiotic factors they can survive The intertidal zone leads into the water that has a variety of fish and other life on a reef that must be covered in water at all times to survive. Through observation, I noticed that there are f ew species that are found in both the intertidal zone and in the underwater reefs directly off the intertidal zone La Islita is about 70 meters long and the terrain from the low to upper littoral zone changes. The l ow littoral zone is characterized by holes carved in the rocks that sea urchins have created over time and has a pink algae or sponge that grows o n top. The mid littoral zone has tide pools of varying sizes and depths. There is an increase in the slope in the northern section of the mid littoral zone. The main characteristic of the upper littoral zone is a smooth flat surface with grooves where water can form puddle s There are two valleys that run through the intertidal zone. The largest and widest runs diagonally from the no rthern most point of La Islita into the ocean in the middle of the intertidal zone. The second valley starts from the the upper littoral zone and gradually continues east to the ocean where it opens up and becomes apparent in transect 4 In the mid and upp er littoral zone, the valley is about 10 cm deep and about 20 cm wide. Methods I surveyed organism s along the intertidal zone in five one meter wide transects tha t were perpendicular to La I slita (Diagram 1) The transect s describe the vertical zonation of organisms. The five transects were separated north to south by 10 meters (0 1 m, 10 11 m, 20 21 m, 30 31, & 40 41 m) The transects were measured from the rock face of La Islita to the the waters edge at low tide. Transects 1 through 4 were betwee n 25 30 meters long and Transect 5 was 25 meters long. Eac h one meter wide transect was divided into five meter long plots that started from the low tide mark up until the rock face. The plots describe the horizontal zonation of organism s
Species Distribution in the Rocky Intertidal Zone La Bonte $ Transects 1 thr ough 4 were divided into six five meter plots and Transect 5 was divided into f ive five meter plots. Diagram 1: The spatial layout of the rocky intertidal zone of La Islita. This also shows the layout of my survey with the 5 transects and the 5x1 m plots that were made in each. The transects were surveyed 18 November 2017 through 23 November 2017 Depending on the tide, the survey would either start at the low or upper littoral zone. This was done to ensure that species at the lowest plot could be survey ed at low tide. The transects were surveyed in or der from the northernmost transect to the southernmost transect, with the north transect being 1 and the southern transect being 5. Each plot was secti oned off with flagged rocks to create a 5x1 meter area. The flagged rocks were moved up the transect after each plot was finished bein g surveyed. Any rock or tide pool within the lines of my plot would be surveyed entirely. So even if there was only a quarter of a rock in between the lines of my plot, it was treated as if it was entirely within my plot. Plots 1 and 2 represent the low littoral zone, Plot 3 and 4 represent the mid littoral zone, and Plots 5 and 6 represent the upper littoral zone. A p icture was taken for each plot and a layou t of the plot was drawn on a notebook. On the drawing in the notebook, I drew symbols for all the organisms present that could be seen. Each organism had its own symbol and the amount of symbols present was indicative of the species abundance Each organis m was given an approximate abundance for each plot in the form of a logarithmic scale: 0, 1, 10, 100 or 1000 based on my observations. Notes were taken for each plot which included more specific details of the amount of each spe cies present, their location and details of the plot itself such as algae and water presence. Each plot was categorized based of f the most prevalent terrain type: holey, valley, tide pool, or bare rock ( Appendix A : Photos 3 6 ) I gave all the organisms I found a key name based of f their morphology or behavior. All seven morphotypes of s ea anemones were classified as one species because at low tide most were closed and in distinguishable from one another The morphotypes can be see in ( Appendix A : Photos 7 13)
Species Distribution in the Rocky Intertidal Zone La Bonte % Results A total of 2 8 species (Table 1) was found throughout the intertidal zone. The maximum number of species found in a transect was 25 ( Fig. 1 ). Figure 1 is the total number of species found for each transect and shows that the species distribution between all transe cts is fairly heterogeneous. Two species were only found once in separate transects, an unidentified sea slug and a group of sea cucumbers When comparing the total number of species found in each transect by plot, it can be seen that the most species were found in Plot 1 and the least number of species were found in Plot 6 (Fig. 2). It is of importance to note that there is no Plot 6 for Transect 5 in any of the figures. The correlation between the amount of total species for all transects and the increasi ng tide zone has an R 2 = 0.679 The terrain type for each plot can be seen in Diagram 2 and is colored according to the most prevalent terrain type. Phylum Class/ Key Name Species Name Appendix A Mollusca Bivalvia Large Clams Photo 14 Purple Clams Photo 15 Black Clams Photo 16 Gastropoda Large Snails Photo 17 Polka Snails Photo 18 Twirl Snails Littorina sp. Tide Snails Nerita scabricosta Photo 19 Sesame Seeds Granigyra piona Photo 20 Pink Limpet Keyhole Limpet Photo 21 Star Limpet Photo 22 Unknown Sea Hare Photo 23 Jennay's Slug Dolaborifera dolabrifera Photo 24 Polyplacophora Chiton Chiton virgulatus Unknown Siphon Photo 25 Cnidaria Anthozoa Anemones Photos 7 13 Arthropoda Malacostraca Hermit Crabs
Species Distribution in the Rocky Intertidal Zone La Bonte & Crab Hexanauplia Volcano Barnacles Tetraclita stalactifera Maxillopoda Acorn Barnacles Chthamalus anisopoma Photo 26 Echinodermata Diadematoida Black Urchin Diadema mexicanum Photo 27 Pencil Urchin Stelleroidea Black Spiny Brittlestar Ophiocoma aethiops Holothuroidea Sea Cucumber Photo 28 Annelida Unknown White Annelid Chordata Actinopterygii Tidepool sculpin Oligocottus maculosus Photo 29 Unknown Fish 1 Fish 3 Table 1 : The list of species that are present in the Intertidal Zone of La Islita Figure 1 : T he total number of species found in each transect and in each plot '( %( !'( !%( "'( "%( #'( %( $( #( "( !( !"#$%#&'()*+#,'' -,./$0'
Species Distribution in the Rocky Intertidal Zone La Bonte ) F igure 2 : The total number of species found in each plot for all transects. Shows the species presence in each horizontal zone. Transect Plot 1 (0 5m) Plot 2 (5 10m) Plot 3 (10 15m) Plot 4 (15 20m) Plot 5 (20 25m) Plot 6 (25 30m) 1 2 3 4 5 XXX XXX Diagram 2: The most prevalent terrain type described by plot There are three classes of organisms that are very prevalent throughout the intertid al zone and showed distinct distribution patterns : a nthozoa (sea anemones), bivalvia (clams), and gastropoda (snails) Two other species Diadema mexicanum the black urchin, and Chthamalus anisopoma acorn barnacles also show interesting distribution patterns Anthozoa (Sea Anemones ) Anemones are mainly found in aggregations along shaded ridges or in tide pools Anemones in the mid littoral zone are smal ler and in aggregations, while anemones in the lower and upper littoral zones tend to be larger and solitary. Anemone distribution follows a bell shaped curve when looking at the total number of species found in each transect by plot (Fig. 3 (a)). Anemones were all present at an equal abundance in Plot 3 Figure 3 (b) shows the distribution and abundance of anemones in the rocky intertidal zone of La Islita. The z axis shows each individual transect the x axis shows each plot, and the y axis is the measure of the '( !'( "'( #'( $'( %'( &'( *+,-(!(./0( *+,-("( *+,-(#(( *+,-($( *+,-(%( *+,-(&(1231( 4**(5( 6789:;<-(!( 6789:;<-(("( 6789:;<-((#( 6789:;<-(($( 6789:;<-(%( 1#2#/3' 4565, 1,+;=( ( ( ( >8++;=( ( ( ( 6?@;(*,,+( ( ( ( A87;(B,
Species Distribution in the Rocky Intertidal Zone La Bonte D abundance. All together this graph shows the abundance of each species in each plot for each transect as a 3 D representation of La Islita as a whole. Anemone distribution in Transect 1 and 2 follows the bell shaped curved pattern, while the distribution in other transects varies. No transects have an abundance of one Figure 3(a): The summed distribution for all seven morphotypes of sea anemones in each transect by plot Figure 3(b): The distribution and abundance patterns for all seven morphotypes of sea anemones Bivalvia (Clams) There are three species of bi valves that a re found in the intertidal zone: large c lams p urple clams, and b lack clams Each clam has a different distribution and abundance pattern. Large clams (Fig. 4(a)) are mostly found in the low littoral zone, purple clams (Fig. 4(b)) are the most abundant in the mid littoral zone, and black clams (Fig. 4(c)) are found in only the uppe r littoral zone of the transects and only in the mid littoral zone of Transect 5. '( !''( "''( #''( $''( %''( &''( *+,-(!( *+,-("( *+,-(#( *+,-($( *+,-(%( *+,-(&( 7+)/3.$/#''' 8650' 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "'( $'( &'( D'( !''( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( 7+)/3.$#' 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%(
Species Distribution in the Rocky Intertidal Zone La Bonte E Figure 4(a): The distribution and abundance pattern for "Large clams" in La Islita Figure 4(b): The distribution and abundance patterns for "Purple clam" in La Islita 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "'( $'( &'( D'( !''( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( 7+)/3./$#' 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "'( $'( &'( D'( !''( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( FGH9@89<;( 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%(
Species Distribution in the Rocky Intertidal Zone La Bonte !' Figure 4(c): The distribution and abundance patterns for "Black clams" in La Islita Gastropoda (Snails) The re are four species of gastropods with spherical shells that I found: l arge snails, polka snails, Littorina sp. ( twirl snails ) and Nerita scabricosta (tide snails) Large snails (Fig. 5(a)) are only found in the first five meters of the zone Polka snails (Fig. 5(b)) have a max abundance of 10 and are found in the first plot for four of the transects and can also be found in the mid littoral zone. They are found up to Plot 5 in Transect 2. Twirl snails Littorina sp., (Fig. 5(c)) are found starting in the mid littoral zone up to the high tide mark and have max abundances in both the mid and upper littoral zone s Tide snails N. scabricosta, (Fig. 5(d)) have the largest abundance for gastropods and are found largely in the upper littoral zone. It was found by Garrity (1984) that N scabricosta aggregate in multilayer clumps of up to 1000 individuals in crevices. 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "''( $''( &''( D''( !'''( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( 7+)/3./$#' 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "( $( &( D( !'( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( 7+)/3.$#' 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%(
Species Distribution in the Rocky Intertidal Zone La Bonte !! Figure 5 (a) : The distribution and abundance patterns for "Large Snails" in La Islita Figure 5(b): The distribution and abundance patterns for "Polka snails" at La Islita Figure 5(c): The distribution and abundance patterns for Littorina sp." at La Islita 6789:;<-(!( 6789:;<-"(( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "( $( &( D( !'( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( 7+)/3./$#' 6789:;<-(!( 6789:;<-"(( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "'( $'( &'( D'( !''( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( 7+)/3./$#' 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%(
Species Distribution in the Rocky Intertidal Zone La Bonte !" Figure 5(d): The distribution and abundance patterns of N. scabricosta at La Islita Diadema mexicanum (Black Urchin) and Chthamalus anisopoma (Acorn Barnacles) The black sea urchi ns in the low littoral zone are juveniles, while the larger adult black urchins are in the reef below La Islita. They ranged in size from a one centimeter to ab out ten. All black urchins were found in Plot 1 with only one black urchin, about five centimeters, being found in Plot 3 of Transect 4 in a large tide pool (Fig. 6). The acorn barnacles C. anisopoma, were expansive and by far the must abundant species present in the rocky intertidal zone. They covered the surface from Plot 2 on in all transects (Fig. 7). I noticed that barnacles were not found far into tide pools and they would tend to stop at the water line of the tide pools. Figure 6: The distribution and abundance patterns of Diadema mexicanum at La Islita 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "''( $''( &''( D''( !'''( !"''( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( 7+)/3./$#' 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "'( $'( &'( D'( !''( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( 7+)/3./$#' 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%(
Species Distribution in the Rocky Intertidal Zone La Bonte !# Figure 7: The distribution and abundance patterns of Chthamalus anisopoma at La Islita Discussion Diversity across the rocky intertidal zone is variable depending on the specie s that is being accessed. However, the diversity of organisms in the low li ttoral zone is greater than in the upper littoral zone at La Islita When comparing the different tra nsects, there is no apparent pattern in the location of the transect and the amount of species present Species diversity in La Islita is determined by the d istance from the low tide mark. B iological interactions are the main factor in determining the composition of the low littoral zone (Connell, 1972) and at La Islita it happens to be the most species rich. Sea anemone distribution in the intertidal zone follows a bell shaped curve when looking at the plots of all transects. They are the most abundant in Plot 3 (10 15 m ) in which there are tide pools and valleys. In the tide poo ls anemones line the crevices and are found in little holes within the larger pool. These crevices tend to be covered and more protected by the sun. In valleys the anemones are found to be aggregated in colonies along the steep slope, but not on the floor because gastropods and hermit crabs roam everywhere Anemones aggregate into colonies with each colony being genetic clones of one another. Colonies that are different genetically however are separated by a distance of a fraction of a cm to five cm (Fran cis, 1973) This fact creates groups of anemones in one pool that can be distinguished from one another The distribution of anemones su ggests that they are the dominant species in the mid littoral zone and exclude other organisms such as gastropods and bi valves from settling in ideal habitats that are protected from the sun and predators Anemones may be the dominant species in the mid littoral zone because they are able to defend themselves from predators, outcompete others for valuable microhabitats, an d are able to defend themselves against the abiotic factors at low tide. Anemones can defend themselves by using sticky bumps on the side of their body to collect shells which they cover themselves with for camouflage and to prevent themselves from drying out (Aggregating Anemone) Each species of bivalvia present at La Islita had different abundance s and distributional patterns. The large clam had the greatest abundance in the lower littoral zone and the distribution seemed to end in the mid littoral zone. Plot 5 in Transect 2 did show a presence of this species 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%( '( "''( $''( &''( D''( !'''( *+,-(!( *+,-("( *+,-(#( *+,-($(( *+,-(%( *+,-(&(( 7+)/3.$/#'' 6789:;<-(!( 6789:;<-("( 6789:;<-(#( 6789:;<-($( 6789:;<-(%(
Species Distribution in the Rocky Intertidal Zone La Bonte !$ which is due to the presence of a tide pool being a source of constant water. This distribution suggests that this clam is limited by abiotic factors such as sunlight. Purple clams ar e found in individual groups that consist of about 20 individuals and occupy plots in greater abundance where anemone abundance is at 10 o r zero It is clear that purple clams are not present in any of the first two plots and only increase to their greates t abundance of 100 in the mid and upper littoral zones. This suggests that purple bi valves are preyed on in the low littoral zone and are intolerant to the abiotic factors of the upper littoral zone (Willis, 2001). Black clams are only about 5 mm long and live lined up along crevice s where water is present They are found in three transects in the upper littoral zone at an abundance of 100. Only in Transect 5 are they found at their greatest abundance of 1000 in the mid littoral zone. This may be because t his bare rock terrain is free from the great abundance of N. scabricosta that is found in Plot 6 of Transect 1 and 2. The distributions of bivalvia here show that the larger species are closer to the low tide mark and the smaller species are distributed cl oser to the high tide mark. Gastropoda species follow the same pattern that bi valves do in regards to size and distribution at La Islita. Large snails are exclusively found in the first plot which could be due to its intolerance to the abiotic conditions above that zone or the fact that it is a good competitor in this plot. They are largest of all the snails and are found to be solitary. Polka snails have a max abundance of 10 and are fo und in the low littoral zone of all transects Their abundance in the higher plots of Transect 2 can be explained by the microhabitats that are created by the terrain present there, a valley and tide pools. The Littorina sp. do not aggregate and have an av erage height of 10 13mm Their distribution starts in the mid littoral zone and they are found in the upper littoral zone of all transects. They were mainly found in pools of water such as in the tide pools of Plot 4 for Transects 1 and 3 but could also b e found on exposed rock. They are generally found where N. scabricosta are also found with the exception of one plot. I believe that the decreased wave action of the mid and upper littoral zones play s a major role in their distribution because of their sm all size (Connell, 1972) N. scabricosta are always found aggregated in the shade or along crevices in the upper littoral zone Th is species can be seen moving as a group down the intertidal zone as the tide changes from high to low. This behavior suggests that N. sca bicosta is not suited to long term exposure of water and e xplain s their preference for the upper littoral zone D. mexicanum, the black sea urchin, is the most abundant species in the first plot and follows a distribution that is very similar to Large snails. This distribution suggests that these urchins need to be covered in water and prefer habitats where they can be protected. The holey terrain of Plot 1 provides protection from wave action. C. anisopoma i s the most dominant species throughout the whole rocky intertidal zone of La Islita and is found in every plot and in every transect. They are only found once in Plot 1 at an abundance of 100 in Transect 2. Acorn barnacles do not seem to not have a suitabl e habitat on holey terrain. This is suggested by their relatively low abundance in Plot 1 compared to the large abundance in every other plot. In Plot 2 of Transect 1, which has a holey terrain, there is an abundance of 100 whereas P lot 2 of the other tra nsects have an abundance of 1000 and are not characterized by holey terrain s The distribution of C. anisopoma can be explained by it outcompeting other organisms on the rocky surface due to its durable shell and its ability to protect itself against the a biotic factors that affect the upper littoral zone. The rocky intertidal zone is a habitat that illustrates how organisms are distributed when faced with biotic and abiotic factors. These factors determine the distribution of individual species in this h abitat. Organisms in the rocky intertidal zone of La Islita show vertical zonation
Species Distribution in the Rocky Intertidal Zone La Bonte !% patterns, with the greatest abundances of a species being found in the same littoral zone or very close near by. Exceptions to this pattern can be explained by microhabitats that are created by the terrain. There are many specialized niches that can be occupied in this zone and that is demonstrated through the 28 species that I found. There is so much more to learn from the rocky intertidal zone of La Islita. There are a tota l of seven morphotypes of sea anemones that I found, but none matched pictures of th e six species that are said to be found in the Pacific coast Costa Rica (AcuÂ–a 2013) Connell (1977) found that species distribution changes throughout the year due to chan ges in tide level S eeing how species change throughout the year could give insightful information on what factors truly drive each organism at La Islita Distribution in the rocky intertidal zone is not arbitrary, but rather is a result of complex interac tions between other organisms, tide, and the sun. Acknowledgments This project has opened my eyes to the diversity and complex interactions that are present in the ocean. I implore everyone to stop and take an hour to look carefully in tide pools becaus e what you find may surprise you. This project could not be done without the help of my advisors Frank Joyce and Emilia Triana. They have given me endless support and feedback to enhance my findings. Thank you to the Vega family for accepting me into their home and making Cua jiniquil a place I will hold dearly in my heart because of them. Also a huge thank you to all my other marine researchers (Stephanie, Rebecca, Nate, Zac, Eric, Brooke and Eliot) who helped me power through the endless days, especially J ennay who loves La Islita as much as I do and will always be wanting to go back to have one more lunch on a tropical beach. Literature Cited AcuÂ–a, FabiÂ‡n H., et al. "New records of sea anemones (Cnidaria: Anthozoa) from Costa Rica." Revista de biologÂ’a marina y oceanografÂ’a 48.1 (2013). "Aggregating Anemone." Monterey Bay Aquarium Monterey Bay Aquarium www.montereybayaquarium.org/animal guide/invertebrates/aggregating anem one. Connell, Joseph H. "Community interactions on marine rocky intertidal shores." Annual Review of Ecology and Systematics 3.1 (1972): 169 192. Francis, Lisbeth. "CLONE SPECIFIC SEGREGATION IN THE SEA ANEMONE ANTHOPLEURA ELEGANTISSIMA." The Biological Bulletin 144.1 (1973): 64 72. Garrity, Stephen D. 1984. Some adaptations of gastropods to physical stress on a tropical rocky shore. Ecology 65(2): 559 574 "Intertidal Zones." Intertidal Zonations Clark University 2002, www2.clarku.edu/departments/biology/biol201/2002/JLagliva/IntertidalZone.html. "Marine Animals of the Rocky Intertidal Zone." Olympic Coast National Marine Sanctuary marinedebris.noaa.gov/sites/default/files/Intertidal%20Zone%20Animals%20Field%20G uide%201.pdf.
Species Distribution in the Rocky Intertidal Zone La Bonte !& Paine, R.T. 1966. Food web complexity and species diversity. Amer. Nat. 100: 65 75. Willis, Samuel, and Jorge CortÂŽs. "Mollusks of Manuel Antonio National Park, Pacific Costa Rica." Rev. Biol. Trop 49.Suppl 2 (2001): 25 36. Appendix A Photo 1 Photo 2 Photo 3 Photo 4
Species Distribution in the Rocky Intertidal Zone La Bonte !) Photo 5 Photo 6 Photo 7 Photo 8 Photo
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Species Distribution in the Rocky Intertidal Zone La Bonte "! Photo 27 Photo 29