Rapid Assessment of Nonindigenous Marine Species on Coral Reefs in the Main Hawaiian Islands1

Rapid Assessment of Nonindigenous Marine Species on Coral Reefs in the Main Hawaiian Islands1 S. L. Coles,2 F. L. M. Kandel,3,4 P. A. Reath,4 K. Longenecker,2 and L. G. Eldredge2 Abstract: Coral reefs at Kaua‘i, O‘ahu, Moloka‘i, Maui, and Hawai‘i were surveyed using a rapid assessment method for marine nonindigenous and cryptogenic species commonly found in Hawaiian harbors and embayments with restricted circulation. In 41 sites surveyed by rapid assessment 26 nonindigenous and cryptogenic species (three algae, 19 invertebrates, and four fishes) were recorded from a total of 486 total taxa identified, and 17 of the nonindigenous and cryptogenic species occurred at only one or two sites. No more than six nonindigenous and cryptogenic species were recorded at any one site, and 21 of the 41 sites had fewer than three. By comparison, laboratory identification of sam- ples collected from seven of the sites closest to harbors found 6–23 nonindigenous and cryptogenic species per site. Values for nonindigenous and cryptogenic species from rapid assessment were compared with factors potentially influenc- ing spread and proliferation of introduced marine species. These factors included distances from harbors, boat-launching ramps, stream mouths, and shorelines; degree of shoreline urbanization; quantity of artificial surfaces in the water; reef condition and isolation from the open ocean; and native species richness. A best subsets regression model explained over 65% of the variance in nonindigenous and cryptogenic species from two predictor variables and their interaction: isolation from the open ocean and number of native taxa, with most of the variance explained by a highly significant relationship of nonindigenous and cryptogenic species with isolation from open-ocean conditions. Introductions of nonindigenous (intro- Sommer 1995, Daehler and Strong 1996, duced) marine species are considered to have Greenberg et al. 1996, Ruiz et al. 1997, 2000, escalated in the last 30 yr (e.g., Carlton 1985, Bax et al. 2001), sometimes with serious neg- Carlton et al. 1990, Carlton and Geller 1993, ative consequences when introduced species Cohen et al. 1995, Gosliner 1995, Mills and become invasive (i.e., compete with native species to the point that they alter the struc- ture or function of the invaded ecosystem). 1 This project was conducted with the financial sup- Marine species invasions have been ranked port of the Hawai‘i Coral Reef Initiative and National among the most serious potential perturba- Oceanic and Atmospheric Administration grant no. tions of marine ecosystems (Carlton 1994), NA03NOS4260044. This is contribution number HBS 2006-001 from the Hawai‘i Biological Survey and contri- and alteration of habitats and food webs by bution 1224 from the Hawai‘i Institute of Marine Biol- invasive species has been proposed as a poten- ogy. Manuscript accepted 30 December 2005. tial major factor contributing to degradation 2 Department of Natural Sciences, Bishop Museum, of coral reefs (Birkeland 2004). 1525 Bernice Street, Honolulu, Hawai‘i 96817 (e-mail: In Hawai‘i there is a substantial pool of [email protected]). 3 Department of Zoology, University of Hawai‘i at potentially invasive marine organisms that Ma¯noa, Honolulu, Hawai‘i 96822. have reached the Islands over at least the last 4 Hawai‘i Institute of Marine Biology, P.O. Box 1346, century. Eldredge and Carlton (2002) desig- Ka¯ne‘ohe, Hawai‘i 96744. nated 343 Hawaiian marine or brackish-water species as introduced or cryptogenic (i.e., of Pacific Science (2006), vol. 60, no. 4:483–507 uncertain geographic origin sensu Chapman : 2006 by University of Hawai‘i Press and Carlton [1991] and Carlton [1996]). A All rights reserved number of comprehensive surveys for marine 483 484 PACIFIC SCIENCE . October 2006 introduced species have been completed in the likely to occur, (2) oligotrophic open-ocean Hawaiian Islands (Coles et al. 1997, 1998, reef environments may not provide sufficient 1999a,b, 2002a,b, 2004a,b, DeFelice et al. food to support the filter-feeding inverte- 1998, 2002), Johnston Atoll (Coles et al. brates that prevail among nonindigenous 2001), American Samoa (Coles et al. 2003), organisms, (3) generally higher native species Guam (Paulay et al. 2002), and port areas of richness on ocean-exposed coral reefs may act northern Australia (e.g., Hewitt et al. 1998, to limit introduced species that proliferate in Hoedt et al. 2000, 2001a,b, Russell and Hew- the less-diverse communities of harbors or itt 2000, Neil et al. 2001). Most of these estuaries. Few introduced species have been studies have focused on harbors or disturbed noted in higher-diversity tropical regions for areas with limited oceanic circulation. ports in northern Australia (Hewitt et al. Invasive introduced algae have monopo- 1998, Hoedt et al. 2000, 2001a,b, Russell and lized nearshore reefs (Rodgers and Cox 1999, Hewitt 2000, Neil et al. 2001), Guam (Paulay Woo et al. 1999, Smith et al. 2002) through- et al. 2002), and at American Samoa (Coles out the main Hawaiian Islands. An invasive et al. 2003), where native species richness is octocoral was recently found overgrowing substantially higher than in Hawai‘i. Hawaiian deep-water black corals (Grigg In this study we compared the occurrence 2003, 2004), and an abundant introduced of introduced species among 41 coral reef sponge may be similarly impacting shallow- sites in various environmental conditions and water reef corals in southern Ka¯ne‘ohe Bay distances from harbors, piers, and boat ramps (Coles and Bolick 2006). An introduced, ag- throughout the main Hawaiian Islands. We gressive mantis shrimp has displaced native evaluated the results in terms of important mantis shrimp species from coral rubble hab- factors that may influence the occurrence of itats in Hawai‘i (Kinzie 1968, 1984), and reef introduced species at the reef sites. fishes purposely introduced to Hawai‘i in the 1950s are common to abundant on reefs throughout the Hawaiian archipelago (Ran- materials and methods dall and Kanayama 1972, Randall 1987). Field Techniques However, despite the potential importance of invasive introduced species on coral reefs, A total of 41 coral reef sites distributed across little is known about the occurrence or im- five islands was surveyed using a rapid assess- pact of most marine introductions in Hawai‘i ment technique. Sites were selected to include or elsewhere in the tropical Pacific (Coles and a variety of environmental characteristics that Eldredge 2002). Further, there has been no might influence the establishment of intro- evaluation of the factors that may influence duced species, such as proximity to harbors the establishment and proliferation of intro- and boat ramps, distance from shore or duced species on coral reefs. streams, presence of artificial structures in We used a standardized rapid assessment the water or degree of shoreline develop- technique to determine the presence of intro- ment, reef condition, and exposure to the duced marine species on coral reefs for the open ocean. Selection criteria also included five largest Hawaiian Islands and evaluated utilization of sites established by ongoing factors that may influence introduced species reef-monitoring programs that could provide occurrence. Previous findings (Coles et al. historical and future data on reef commu- 1997, 1998, 1999a,b, 2001, 2002a,b, 2003, nities. Twenty-four of the 41 rapid assessment DeFelice et al. 1998, 2002) suggested that sites coincided with Hawai‘i Coral Reef As- three principal factors may influence the dis- sessment and Monitoring Program (CRAMP) tribution and proliferation of most nonindig- sites ( Jokiel 2002, Brown et al. 2004), and enous species in Hawai‘i and other tropical eight of the 10 surveys on Hawai‘i were areas: (1) isolation may limit recruitment made at West Hawai‘i Aquarium Project from likely sources such as harbors and (WHAP) sites (Tissot et al. 2001). boat landings where introductions are mostly Anticipating that introduced species were Nonindigenous Marine Species on Hawaiian Coral Reefs . Coles et al. 485 Figure 1. Kaua‘i coral reef stations. likely to be low in frequency and abun- and F.L.M.K.) swam in tandem for 15 min dance, we utilized a replicable methodology along the perimeter of the triangle, recording to examine large reef areas within no- the first occurrence of all invertebrates, fishes, decompression time limits for up to three and identifiable macroalgae along a swath up scuba dives per day at 10–20 m. Locations of to 2 m on either side. For the next 15 min we the 41 sites surveyed are shown in Figures recorded organisms that occurred within the 1–5, and their station numbers, locations, 312-m2 triangular area. Finally, we spent 15 depth ranges, and coordinates are listed in min searching outside the triangle recording Table 1. Our timed search approach provided all taxa not previously observed. In addition a standardized and sufficiently large search to the observations made by these two ob- area to assure that most macrobiota at the servers, a third diver (P.A.R.) searched sub- site were observed. We recorded the location habitats known to support nonindigenous and of each reef site using Global Positioning cryptogenic species (i.e., overhangs, crevices, System and deployed a 50-m transect line dead coral heads, coral rubble, algal turf and parallel to the shore for 25 m, then turned tufts) at 28 sites on Kaua‘i, Moloka‘i, Maui, the line at a right angle for the remaining 25 and Hawai‘i (Table 1) and recorded cryptic m, with the resulting triangular observation organisms. We recorded all field-identifiable area established by the hypotenuse thus ap- organisms on underwater paper, and we col- proximating 312 m2. Two observers (S.L.C. lected species suspected to be introduced and 486 PACIFIC SCIENCE . October 2006 Figure 2.

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