0034-77440034-7744S0034-77442012000800020USACosta RicaAlaska001120120011201260303319Characterization of deepwater invertebrates at Isla del Coco National Park and Las Gemelas Seamount, Costa Rica
Richard M. Starr1*, Jorge Cortés2*, Cheryl L. Barnes1, Kristen Green3* & Odalisca Breedy2
The deepwater faunas of oceanic islands and seamounts of the Eastern Tropical Pacific are poorly known. From 11-22 September 2009, we conducted an exploration of the deepwater areas around Isla del Coco National Park and Las Gemelas Seamount, located about 50km southwest of Isla del Coco, Costa Rica using a manned submersible to survey the seafloor habitats. The goal of the exploration was to characterize the habitats and biota, and conduct quantitative surveys of the deepwater portions of Isla del Coco National Park and Las Gemelas. We completed a total of 22 successful submersible dives, spanning more than 80hr underwater, and collected a total of 36hr of video. With respect to invertebrates, our objectives were to gather quantitative information on species composition, density, distribution and habitat associations as well as to compare the invertebrate communities between the two sites. A total of 7 172 invertebrates were counted from analysis of the video collected on this project. Larger organisms were counted and placed into 27 taxonomic groups to characterize the deepwater invertebrate fauna of Las Gemelas Seamount and Isla del Coco National Park. The Shannon-Weiner Index for biodiversity (H’) was calculated to be 0.14 ± 0.02 for Isla del Coco and 0.07 ± 0.03 for Las Gemelas surveys. Although richness was fairly equal between the two sites, evenness was greater at Isla del Coco (J = 0.04 ± 0.006) when compared to Las Gemelas (J = 0.02 ± 0.01). This lower level of evenness in the community at Las Gemelas was a result of high densities of a few dominant species groups, specifically sea urchins and black corals. We also evaluated invertebrate percent cover at both Isla del Coco and Las Gemelas Seamount with respect to habitat type, slope and rugosity. Results indicated that highly rugose habitats contained the highest frequencies of all invertebrates at both sites, with the exception of glass sponges and polychaetes at Isla del Coco, which were found in greater quantities at intermediate levels of rugosity. Information obtained from these submersible surveys indicate that seamounts in the tropical eastern Pacific Ocean may be an important source of biodiversity and that more quantitative surveys are needed to characterize the fauna of the region.
La fauna de aguas profundas de islas oceánicas y de montes submarinos del Pacífico Tropical Oriental son muy poco conocidas. Para caracterizar las faunas de aguas profundas del Parque Nacional Isla del Coco y el Monte Submarino Las Gemelas, Costa Rica, llevamos a cabo un estudio cuantitativo de los hábitats y su fauna. Se tomaron videos de transectos desde un sumergible entre 50 y 402m de profundidad del 11 al 22 de setiembre 2009. Se recolectó información cuantitativa de la composición de especies de invertebrados, densidad, distribución y hábitats asociados en ambas localidades y se comparó. Se contaron 7,172 invertebrados en los videos analizados, y se ubicaron en 27 categorías taxonómicas. El Índice de Shannon-Weiner (H’) fue de 0.14 ± 0.02 para la Isla del Coco y 0.07 ± 0.03 para Las Gemelas. La riqueza fue parecida en ambos sitios pero la equitabilidad fue mayor en la Isla del Coco (J = 0.04 ± 0.006) comparado con Las Gemelas (J = 0.02 ± 0.01). Este menor nivel de equitabilidad en Las gemelas de debió a la alta densidad de unos pocos grupos dominantes, específicamente erizos de mar y coral negro. También evaluamos el porcentaje de cobertura de los invertebrados con respecto a tipo de hábitat, pendiente y rugosidad del sustrato. Los resultados indican que hábitats con alta rugosidad contiene más invertebrados en ambos sitios, excepto la esponjas silíceas y los poliquetos en la Isla del Coco, que se encontraron en mayor cantidad en niveles intermedios de rugosidad. La información obtenida con este estudio indican que los montes submarinos en el Pacífico Tropical Oriental pueden ser una fuente importante de biodiversidad y que se necesitan más estudios cuantitativos para caracterizar la fauna de la región.
Palabras clave: Encuestas sobre diversidad, montes marinos, invertebrados en aguas profundas, observaciones en sumergible, biodiversidad.
Isla del Coco, also ]]>
DeepSee submersible started operations (Cortés & Blum 2008). Since then more than 1,500 dives have been logged at Isla del Coco.
In 2007, a conservation gap ]]>
et al. 2012) and invertebrates, conduct observational surveys of macroplankton, collect images of habitats and species, and collect octocorals (Octocorallia), black corals (Antipatharia), echinoderms ]]>
Methods
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From 11-22 September 2009, scientists from the US National Geographic Society, University of Costa Rica, Moss Landing Marine Laboratories, Monterey Bay Aquarium Research Institute, Ocean Research & Conservation Association, and the University of California conducted an exploration of the deepwater areas around Isla del Coco National Park (5°33’N, 87°02’W) and Las Gemelas Seamount (4°59’N, 87°38’W, Lizano 2012). We used the Undersea Hunter Group’s DeepSee ]]>
At Las Gemelas Seamount we surveyed a general area that was suggested to us by commercial fishermen. When we arrived in the general vicinity of the seamount, we conducted bathymetric surveys of the region using the support vessel’s echosounder to locate the shallowest ]]>
DeepSee submersible to survey two of the shallow peaks. At Isla del Coco National Park most submersible dives occurred at dive locations along the drop-off at the northern edge of the island in areas normally visited by the DeepSee during its regular trips with commercial passengers. At all dive sites observers usually spent 30-60min exploring the area. After getting a sense of the habitat types associated with the dive site, observers haphazardly chose starting depths and directions for quantitative ]]>
Submersible transects were patterned after strip transect surveys that have been commonly used to evaluate invertebrates in temperate environments (Yoklavich & O’Connell 2008, Tissot et al. 2007, Starr & Yoklavich 2008). During these quantitative transects, observers looked forward and downward through the submersible dome, for a set time period (usually 10 ]]>
In order to compare invertebrate communities at Las Gemelas Seamount and Isla del Coco National Park, we used only data from submersible dives that occurred at similar depths and covered similar habitats at each site. The ]]>
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To evaluate taxa composition, we estimated taxa richness (defined as the number of discrete taxa identified) and diversity (Shannon-Wiener Index, Zar (1999)) at each site – using those macroinvertebrates that we could identify and count individually (generally invertebrates >5cm in size). We then calculated density of each taxonomic group for each dive by summing the number of macroinvertebrates observed on transects and dividing that number by the total transect area of that dive (i.e., transect lengths x 1m width). Invertebrate densities for ]]>
In addition to ]]>
Stylaster spp. To document percent cover we selected a random starting point within the first minute of the transect and then analyzed individual video frames every 20 seconds of the transect. For each of ]]>
Habitats were defined by a ]]>
et al. (1999) and Tissot et al. (2007). We used seven primary substrate codes: boulder (B), cobble (C), gravel (G), pebble (P), bedrock or rock outcrop (R), sand (S), and a code for a vertical pinnacle (T). We defined bottom type as a two-letter code representing the approximate percent cover of the two most prevalent substrata in a particular habitat patch. The first character of the code represents the substratum that ]]>
Results
Submersible dives and transects: We completed a total of 22 submersible dives. Rough weather limited our ]]>
Table 1). Four of these dives occurred at Las ]]>
2. At Isla del Coco National Park, we conducted 25 quantitative transects on 12 dives, and surveyed 1999m2. At Las Gemelas Seamount, we completed 13 video transects on four dives, and surveyed 1004m2. We collected 36hr ]]>
Quantification of Individual Organisms: A total of 7 172 individual invertebrates were counted from analysis of the video collected on this project. These macroinvertebrate species were counted and placed into 27 taxonomic groups to characterize the deepwater invertebrate fauna of Las Gemelas ]]>
Table 2). Invertebrate species richness was slightly greater at Las Gemelas Seamount than at Isla del Coco. We encountered 21 taxonomic groups on quantitative transects around Las Gemelas, whereas only 20 taxonomic groups were observed at Isla del Coco. Because we encountered several invertebrates that have not yet been reported in the scientific literature, we grouped species into higher taxonomic levels for our analyses (Table 2). Octocorals (Genus Anthomastus), ]]>
Table 3).
The Shannon-Weiner Index for biodiversity (H’) was calculated to be 0.14 ± 0.02 for Isla del Coco and 0.07 ± 0.03 for Las Gemelas Seamount surveys. Although richness was fairly equal between the two sites, evenness was greater at Isla del Coco (J = 0.04 ± 0.006) when compared to Las Gemelas (J = 0.02 ± 0.01). This lower level of evenness in the community at Las Gemelas was a result of high densities of a few dominant species ]]>
Table 4).
Invertebrate Density: Bray-Curtis similarity indices demonstrated that the invertebrate taxa and densities at Las Gemelas Seamount are different than at Isla del Coco. A cluster analysis of square-root transformed density data (Fig. 1) ]]>
Fig. 2). The combined density of all invertebrate groups was 4.9 times higher at Las Gemelas (568 invertebrates/100m2) than at Isla del Coco (115 invertebrates/100m2). This large difference in overall ]]>
Table 4). These invertebrates were distributed throughout all transects, as evidenced by the 100% occurrence on all dives. Also, Anthomastus spp. were present at both sites, but exhibited substantially higher densities around Las Gemelas Seamount ]]>
We examined invertebrate densities at both Isla del Coco and Las Gemelas Seamount with respect to habitat type, slope, and rugosity. Whereas invertebrate densities were highest in sand, rock, and boulder habitats at Las Gemelas, invertebrates at Isla del Coco were denser in pinnacle, rock, mixed areas of sand and rock, pebble, and ]]>
Fig. 3). When comparing density with slope, we found that invertebrate densities at Isla del Coco increased with increasing slope, whereas invertebrate densities at Las Gemelas were highest in moderate slopes of 30° to 60° (Fig. 4). A comparison of invertebrate densities by rugosity category indicated that medium to high rugosity habitats contained the highest invertebrate densities at both sites (
Fig. 5).
Habitat types: We encountered a total of 14 combinations of the seven substratum codes. At Isla del Coco, 58% of the habitats surveyed were comprised primarily of rock and 34% were primarily sand, whereas at Las Gemelas, 73% of the transects covered rocky habitats and 25% covered sandy habitats (Table 5). Transects at Las Gemelas Seamount occurred over somewhat more rugose habitats. At Isla del Coco, 39.9%, 28.5%, and 31.6% of the habitat area surveyed was high, medium, and low rugosity, respectively. At Las Gemelas Seamount, 46.8%, 34.3%, and 18.9% of the habitat area surveyed was high, medium, and low rugosity, respectively. Similarly, transects at Las Gemelas more typically occurred on higher slopes. At Las Gemelas Seamount, 30%, 56%, and 14% of slops in the hábitat area surveyed were <30°, 30–60°, and >60°, respectively. At Isla del Coco, 48%, 35%, and 17% of the slopes in the habitat area surveyed were <30°, 30–60°, and >60°, respectively.
Quantification of Percent Cover: All six taxonomic groups used in the quantification of percent invertebrate cover were present at both Isla del Coco and Las Gemelas Seamount (Table 6). Brachiopods, glass sponges and polychaetes were more prevalent at Isla del Coco, whereas encrusting sponges, polyps/soft corals and Stylaster spp. were found in higher frequencies at Las Gemelas (Fig. 6). Encrusting sponges were the most commonly encountered taxonomic group at both sites. We evaluated invertebrate percent cover at both Isla del Coco and Las Gemelas Seamount with respect to habitat type, slope and rugosity. Whereas encrusting sponges and Stylaster spp. dominated every habitat type at Las Gemelas, percent cover of encrusting sponges and Stylaster spp. at Isla del Coco were greater in rock, pinnacle, and mixed areas of sand and rock or pebble habitats only (Fig. 7). Glass sponges dominated habitats consisting primarily of boulders at Isla del Coco. When evaluating percent cover with slope, we found that all invertebrate groups were more prevalent in areas with intermediate (30° to 60°) or steep (> 60°) slopes (Fig. 8). A comparison of percent cover and rugosity indicated that high rugosity habitats contained the highest frequencies of all invertebrates at both sites, with the exception of glass sponges and polychaetes at Isla del Coco, which were found in greater quantities at intermediate levels of rugosity (g. 9).
Discussion
In September 2009, ]]>
Seamounts are ]]>
et al. 2010, ]]>
et al. 2010b), and are very fragile (Koslow et al. 2001). Although Samadi et al. (2006) and Thoma et al. (2009) indicated that genetic studies might refute the concept of increased endemism on seamounts, they did agree with the hypothesis that seamounts are diversity hotspots, possessing benthic assemblages with particularly high species richness. ]]>
Habitats surveyed at Las Gemelas contained rich, dense assemblages of invertebrates. Some of the prominent benthic invertebrates included sea urchins, black corals, sponges, anemones, corals, gorgonians, echinoderms, and crustaceans. Two taxonomic groups (sea urchins and black corals) accounted for more than 70% of the total combined invertebrate density at Las Gemelas. These very prevalent taxa were found at higher frequencies in areas of rock and/or sand, intermediate slopes (30° to 60°), and medium ]]>
et al. (2004) for intertidal invertebrates. They showed that significant differences in community structure were found between vertical and horizontal samples in different locations. Also, differences in structure were much greater between localities than among replicates within each locality. Rowden et al. (2010a) analyzed more than 5000 sea-floor images on ]]>
The difference in invertebrate densities between the two sites may also be attributed to habitat heterogeneity. At Isla del Coco, 74% of habitats were either all rock or some mixture of rock and ]]>
et al. (2010) showed that deep, steep underwater slopes as prime habitats for many decapod crustaceans and suggested that these ]]>
]]>
One important qualitative observation is that we saw a larger number of encrusting and structure-forming invertebrates at Las Gemelas Seamount than at Isla del Coco. This habitat complexity further indicates that habitats at Las Gemelas may be able to harbor a greater diversity and biomass of both invertebrate and fish species than at Isla del Coco. O’Hara et al. (2008) reported that the large biogenic structures formed by colonial cold-water scleractinian corals ]]>
Given the diverse and rich assemblages of invertebrates carpeting the bottom habitats at Las Gemelas Seamount, as well as the fact that the area contains numerous species which have not yet been described in the ]]>
et al. (2001) discussed concerns about the vulnerability of seamount communities to human impacts, especially with the development of large-scale bottom trawl fisheries in the deep sea. They reported that 24 to 43% of the invertebrate species they recovered from experimental trawling were new to science, and between 16 and 33% appeared to be ]]>
et al. (2001) is that seamount invertebrate communities are fragile. O’Hara et al. (2008) believe that the slow growth rate of seamount corals that recovery of damaged cold-water coral assemblages will be a long-term process. The high densities of invertebrates in the area around Isla del Coco National Park and Las Gemelas seamount signifies the need for increased protection and study of these areas, because of the paucity of information related to the distribution and relative ]]>
Acknowledgments
We thank Shmulik Blum, Sylvia Earle, Avi Klapfer, Bruce ]]>
Argo for safe submersible operations and help with observations of fishes and macroinvertebrates. Katie Schmidt helped excerpt information from video and Dan Malone provided the MDS plots. Fund- ing was provided by the National Geographic Society, California Sea Grant Program, Moss Landing Marine Labs, and the Universidad de Costa Rica.
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*Correspondencia a: Richard M. Starr. University of California Sea Grant Program and Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, California 95039, USA; starr@mlml.calstate.edu Jorge Cortés. Centro de Investigación en Ciencias del Mar y Limnología (CIMAR), Ciudad de la Investigación, Universidad de Costa Rica, San Pedro, 11501-2060 San José, Costa Rica; jorge.cortes@ucr.ac.cr ]]>
Cheryl L. Barnes. University of California Sea Grant Program and Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, California 95039, USA. Kristen Green. Alaska Department of Fish and Game, 304 Lake Street, Room 103, Sitka, Alaska, 99835; kristen.green@alaska.gov Odalisca Breedy. Centro de Investigación en Ciencias del Mar y Limnología (CIMAR), Ciudad de la Investigación, Universidad de Costa Rica, San Pedro, 11501-2060 San José, Costa Rica
1. University of California Sea Grant Program and Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, California 95039, USA; starr@mlml.calstate.edu 2. Centro de Investigación en Ciencias del Mar y Limnología (CIMAR), Ciudad de la Investigación, Universidad de Costa Rica, San Pedro, 11501-2060 San José, Costa Rica; jorge.cortes@ucr.ac.cr 3. Alaska Department of Fish and Game, 304 Lake Street, Room 103, Sitka, Alaska, 99835; kristen.green@alaska.gov
Received 05-III-2012. Corrected 06-IX-2012. Accepted 24-IX-2012.