Managing an invasive corallimorph at Palmyra Atoll National Wildlife Refuge, Line Islands, Central Pacific

Biol Invasions https://doi.org/10.1007/s10530-018-1696-1 ORIGINAL PAPER Managing an invasive corallimorph at Palmyra Atoll National Wildlife Refuge, Line Islands, Central Pacific Thierry M. Work . Greta S. Aeby . Benjamin P. Neal . Nichole N. Price . Eric Conklin . Amanda Pollock Received: 29 September 2017 / Accepted: 26 February 2018 Ó The Author(s) 2018. This article is an open access publication Abstract In 2007, a phase shift from corals to corallimorpharians (CM) centered around a shipwreck was documented at Palmyra Atoll, Line Islands. Subsequent surveys revealed CM to be overgrowing the reef benthos, including corals and coralline algae, potentially placing coral ecosystems in the atoll at risk. This prompted the U.S. Fish and Wildlife Service, the lead management agency of the atoll, to remove the shipwreck. Subsequent surveys showed reductions in CM around the ship impact site. We explain patterns of spread of the CM in terms of both life history and local currents and show with a pilot study that T. M. Work (&) US Geological Survey, National Wildlife Health Center, Honolulu Field Station, PO Box 50187, Honolulu, HI 96850, USA e-mail: G. S. Aeby Hawaii Institute of Marine Biology, 46-007 Lilipuna Rd, Kaneohe, HI 96744, USA B. P. Neal
N. N. Price Bigelow Laboratory for Ocean Sciences, 60 Bigelow Dr, East Boothbay, ME 04544, USA E. Conklin The Nature Conservancy-Hawaii, 923 Nuuanu Ave, Honolulu, HI 96817, USA A. Pollock US Fish and Wildlife Service, Refuges, PO Box 50167, Honolulu, HI 96850, USA pulverized bleach may be an effective tool to eradicate CM on a local scale. If applied strategically, particularly in heavily infested ([ 66% cover) areas, active intervention such as this could be an effective management tool to reduce CM impact on localized areas and decrease colonization rate of remaining reefs. This is the first documentation of the response of an invasive cnidarian to shipwreck removal. While this was a singular event in Palmyra, the spatial and temporal patterns of this invasion and the eradications lessons described herein, are useful for anticipating and controlling similar situations elsewhere. Keywords Corralimorpharian
Invasive species
Shipwreck disturbance
Invasion dynamics
Coral reefs
Control
Management
Phase shifts Introduction Coral reefs are subject to damage from both natural and anthropogenic causes, including large scale storm events, temperature anomalies and subsequent bleaching events, disease outbreaks on foundational species, overfishing, and ship groundings. The resultant disruption from these events can facilitate colonization or expansion by invasive organisms that can result in phase shifts (Chadwick and Morrow 2011; Hughes et al. 2010). Phase shifts are defined here as ‘‘extensive decreases in coral cover coinciding with substantial 123 T. M. Work et al. increases in some alternative benthic organism, due to a pulse or press disturbance, that have persisted [ 5 year’’ (Norström et al. 2009). For example, mass mortality of the sea urchin, Diadema antillarum, throughout the Caribbean from an apparent disease outbreak contributed to a phase-shift from coral- to algal-dominated communities (Lessios 2016). In the Indo-Pacific, similar phase-shifts have occurred in response to shipwrecks where coral dominated communities change to those dominated by opportunist benthic organisms. On Rose Atoll in American Samoa where a fishing vessel wrecked on the reef, the percent cover of turf/cyanobacteria was an order of magnitude higher (40%) in areas surrounding the wreck as compared with reference sites on the same island (Schroeder et al. 2008). In the Line Islands, iron enrichment from shipwrecks fueled growth of invasive cyanobacteria and turf algae (Kelly et al. 2012). Once established, invasive organisms are difficult to control, with failures mostly due to late detection resulting in sufficient time elapsing for invasives to occupy areas too large for eradication to be practical (Hewitt and Campbell 2007). However, in the rare attempts that have been made to manage marine invasives, successes do exist; for instance the complete elimination of the invasive algae, Caulerpa racemosa near San Diego, California. This effort was successful because the algae were detected early, were within a welldefined area, and were eradicated before they spread over a large scale (Anderson 2005). In 2007, a corallimorpharian (CM), Rhodactis howesii, was discovered smothering coral reefs at Palmyra Atoll National Wildlife Refuge (Palmyra), a remote atoll within the Line Islands ca. 5° north of the Equator (Work et al. 2008). The CM invasion encompassed a well-defined 1 km2 area with a predominant NW to SE orientation surrounding a longline vessel that had wrecked on the atoll in 1991. The distribution of the CM around the shipwreck and around mooring buoys fastened by iron chains suggested that substances leaching from metals, possibly iron, might in part be driving the spread of the infestation on the reef (Work et al. 2008). In response, the US Fish and Wildlife Service (FWS) in collaboration with The Nature Conservancy switched out existing iron mooring chains with stainless steel in 2010. Another conjecture to explain the spread is that CM are an opportunistic, weedy species, competitively superior to other cnidarians such as corals, and 123 capable of year-round reproduction via sexual (pelagic spawning) or asexual clonal replication (ChadwickFurman and Spiegel 2000; Chen et al. 1995). Some species of CM can rapidly replicate with a polyp doubling time in as little as 2 months (Chadwick and Adams 1991). R. howesii is considered native to Palmyra based on observations of its presence around the atoll prior to the outbreak (Work et al. 2008). Perhaps life history characteristics of the CM population around the shipwreck contributed to the observed rapid spread on the atoll. The increased presence of CM around the ship would be analogous to an outbreaks of other native species such as the crown of thorns seastars on coral reefs (Pratchett et al. 2014). In 2013, the FWS secured funding to disassemble and remove the shipwreck at Palmyra Atoll NWR with all the metal shipped back to the mainland U.S. for scrap. Our objectives were to (1) document the distribution of CM at Palmyra before and after shipwreck removal, (2) examine the life history of CM and the oceanographic conditions that could help explain the observed patterns of spread, and (3) test methods for control CM. Methods Surveys In 2011 and 2016, surveys of CM infestation were conducted following protocols described previously (Work et al. 2008). Briefly, a snorkeler was towed at an approximate speed of ca. 50 m/min over benthic transects that originated from the shipwreck site towards the 8 major points of the compass (N, NE, E, SE, S, SW, W, NW). Every minute (ca. 50 m), the towboat stopped, and the snorkeler subjectively integrated benthic cover during the to (...truncated)