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New and Unusual Marine Invertebrates Discovered at the California Channel Islands during the 1997-1998 El Nino.

John M. Engle (1)

Daniel V. Richards (2)

Abstract.--The occurrence of new and unusual subtropical invertebrates at the Channel Islands was documented for the exceptional 1997-1998 El Nino and subsequent 1998-2000 La Nina during periodic shallow subtidal surveys. Six species (Chloeia viridis, Stenorhynchus debilis, Pleurobranchus areolatus, Chromodoris galexorum, Polycera alabe, and Holothuria impatiens) were new to California. Six others (Bunodeopsis sp., Hemisquilla ensigera californiensis, Dromidia larraurei, Pteria sterna, Arbacia incisa, and Centrostephanus coronatus) represented new records at one or more islands. Most new records occurred at the southernmost and easternmost islands (Santa Catalina, San Clemente, and Anacapa). Repeated sightings of progressively larger size classes provided recruitment, growth, and survivorship information for five species. Increased sightings of subtropical species in California likely are due to northward shifts of biogeographic provinces that occurred during more than two decades of above average seawater te mperatures.

The California Channel Islands support a great diversity of nearshore marine life, due primarily to their location within the Southern California Bight, astride the transition between warm subtropical waters of the Californian Province to the south and cold temperate waters of the Oregonian Province to the north. The complex mixing of warm and cold water masses results in unique oceanographic conditions influencing each of the eight islands (Fig. 1), which in turn affect the distribution of plant, invertebrate, fish, bird, and mammal species. Overall, there is an obvious southeast (i.e., Santa Catalina Island) to northwest (i.e., San Miguel Island) trend of decreasing sea surface temperatures among the islands that correlates well with differences in the composition of species assemblages (Engle 1993, 1994). Individual species distributions may shift northwesterly or southeasterly over time at the islands, depending on the magnitude and duration of warm-water (e.g., El Nino) or cold-water (e.g., La Nina) regi mes. New sightings of subtropical species typically are associated with major El Nino events (e.g., Radovich 1961; Strachan et al. 1968).

Southern California waters have experienced a long-term warming trend that began in 1976, including major El Nino events in 1983-1984, 1986-1987, 1992-1993, and 1997-1998. Of these, the 1983-1984 and 1997-1998 E1 Nino were two of the strongest on record with some of the highest temperature anomalies ever recorded (McPhaden 1999). During the recent E1 Nino, the Southern California Bight experienced above normal sea temperatures for 1.5 yr, from May 1997 to August 1998 (CoastWatch Bulletins 1997-2000). By September 1998, the El Nino abruptly switched to La Nina, which caused cooler temperatures also for 1.5 yr, from September 1998 to March 2000 (CoastWatch Bulletins 1997-2000).

This paper presents new distributional records for shallow-water subtropical invertebrates at the California Channel Islands during and after the 1997-1998 El Nino. New and unusual fish records at the Channel Islands are reported in a companion paper by Richards and Engle (this volume). Post-El Nino records are important because some species that recruit during the warm-water period are slow-growing and only become evident after attaining larger sizes. Periodic surveys allow determination of growth and survivorship of these exotic species. The invertebrate observations we report here include six subtropical species seen for the first time in California waters as well as six other species that have newly appeared (or have notably increased abundances) at one or more of the eight Channel Islands (Table 1). We have noted some southern California mainland sightings, but have not attempted to include all new mainland records for these species.

Methods

The eight Channel Islands off the southern California coast have been surveyed periodically since 1980 in cooperative studies by the Tatman Foundation's Channel Islands Research Program (CIRP) and Channel Islands National Park (CINP) Kelp Forest Monitoring Program. CINP divers regularly survey 16 fixed sites at five islands to monitor population dynamics of key algal, invertebrate, and fish species. Invertebrates are quantified using random point contact, quadrat, and transect techniques (Davis et al. 1999). CIRP divers conduct qualitative reconnaissance surveys at a broader spectrum of locations at all eight islands to provide an overview of island marine assemblages. Both programs include general search methods to note unusual species at each survey site. Voucher collections and photographs or videographs maintained at CJRP and California museums (primarily the Natural History Museum of Los Angeles County (NHMLAC)) are utilized to additionally document new sightings whenever possible. Latitude/longitude coo rdinates are provided for island sites not named on National Oceanic and Atmospheric Administration nautical charts.

First Occurrences in California

Phylum Annelida Class Polychaeta Order Amphinomida Family Amphinomidae Chloeia viridis Schmarda 1861 Ornate fireworm (Fig. 2A)

Previous reported range.--Throughout the Gulf of California to Panama, and the entire Caribbean; intertidal and subtidal to at least 91 m (Hartman 1940; Brusca 1980; Kerstich 1989).

First Channel Islands records.--Over 70 fireworms observed on stable sand habitats at Santa Catalina Island during October 1998 to May 2000. Sites: Willow Cove (>60 specimens) at 9-21 m depths (10/98, 5/99, 6/99, 10/99); Empire Landing (>10 specimens) at 12-20 m depths (5/00). Vouchers: photographs (E. Erikson) and specimens (NHMLAC).

Remarks.--Chloeia viridis is a distinctive polychaete with long venomous setae. Though common throughout the Gulf of California (Brusca 1980), there are no records from the Pacific Coast of Baja California (L. Harris, pers. comm.). One of us (Engle) has surveyed mantis shrimp (Hemisquilla ensigera californiensis) at least annually since 1984 at Willow Cove, yet Chloeia was not found prior to 10/98. No specimens have been reported elsewhere in California. C. viridis was observed crawling on the surface of sheltered-shore, silty-sand substrates and entering tubes of the parchment worm Chaetopterus variopedatus. On several occasions, fireworms appeared to be feeding on bat ray (Myliobatis californica) feces, and in two instances, an individual was seen consuming the sea slug Navanax inermis.

Phylum Arthropoda Class Malacostraca Order Decapoda Family Majidae Stenorhynchus debilis (Smith 1871) Panamic arrow crab (Fig. 2B)

Previous reported range.--Guadalupe Island (Baja California) (M. Wicksten

pers. comm.) and Gulf of California to Chile and the Galapagos Islands; intertidal and subtidal to 61 m (Brusca 1980; Kerstich 1989; Gotshall 1998).

First Channel Islands records.--Several hundred arrow crabs observed at 3-23 m depths on rocky substrata at three islands during March to October 1998. Santa Catalina Island: Pebbly Beach, Casino Point, and Ripper's Cove (>100 specimens, E. Erikson, 3/98); Bird Rock, Lion's Head, and Blue Cavern Point (L. Roberson, 3-7/98); and West End (9 specimens, 10/98). San Clemente Island: Mosquito Cove (1 specimen, 5/98); E. Pyramid Cove (2 specimens, 5/98); Pyramid Head (>100 specimens, 5/98, 9/98); Purse Seine Rock (1 specimen, 5/98); and Seal Cove (1 specimen, 9/98). Anacapa Island: Frenchy's Cove (1 specimen, 8/98). Vouchers: photographs (E. Erikson, R. Herrmann) and specimens (NHMLAC).

Remarks.--Stenorhynchus debilis was observed by various scuba divers at Santa Catalina and San Clemente Islands and along the southern California mainland from Mission Bay to Redondo Beach in spring/summer 1998 (C. Gramlich & D. Cadien pers. comm.). Also, it was collected in trawling surveys around Santa Catalina Island (7/98) and off Huntington Beach (8/99) (see Montagne & Cadien this volume). This short-lived crab is seasonal in the Gulf of California, attaining maximum sizes in May to July (Kerstich 1989). We observed peak abundances in spring (few small crabs; most moderated-sized) and summer 1998 (most large), with only a few heavily-fouled individuals seen in fall 1998 (all large), and none thereafter. Two spring-collected specimens survived in aquaria until fall 1998. S. debilis mostly occurred in small crevices or under the spine canopy of the coronado sea urchin Centrostephanus coronatus (29 of 667 C. coronatus surveyed had a sheltering arrow crab at Pyramid Head on 5/18/98). Some crabs were found un der rocks or mooring blocks in sheltered silty coves (E. Erikson pers. comm.).

Phylum Mollusca Class Gastropoda Order Notaspidea Family Pleurobranchidae Pleurobranchus areolatus Morch 1863 Warty sea slug (Fig. 2C)

Previous reported range.--San Benitos and Cedros Islands (Baja California) (D. Behrens pers. comm.), Gulf of California to Ecuador, throughout the Caribbean and tropical west Africa; intertidal and subtidal to 31 m (Keen 1971; Kerstich 1989).

First Channel Islands records.--Seven individuals found at 5-22 m depths on rocky reefs at three islands during June 1998 to June 1999. Santa Catalina Island: Casino Point (1 specimen, E. Erikson, 6/98) and West End (1 specimen, 10/98). San Clemente Island: Pyramid Head (2 specimens, 9/98) and Purse Seine Rock (32[degrees] 52.48' N, 118[degrees] 24.94' W) (2 specimens, 6/99). Anacapa Island: Frenchy's Cove (1 specimen, 8/98). Vouchers: photographs (E. Erikson, R. Herrmann, D. Richards) and specimens (D. Behrens). Also, P. Haaker and M. Tegner (pers. comm.) collected two specimens at San Clemente Island in August 1998.

Remarks.--Pleurobranchus areolatus is a large ([sim]10-15 cm) distinctive opisthobranch, whose dorsal surface is covered with warty orange and reddish-brown tubercles. Variations in color patterns and tubercle morphology among the specimens raise suspicions that some individuals represent an undescribed Pleurobranchus (D. Behrens, pers. comm.); however, these variations may be within the range of characters exhibited by P. areolatus. Several specimens were collected during the same period on the mainland at La Jolla (D. Behrens, pers. comm.).

Phylum Mollusca Class Gastropoda Order Nudibranchia Family Chromodorididae

Chromodoris galexorum (Bertsch 1978) Galactic sea slug (Fig. 2D)

Previous reported range.--Guadalupe and Cedros Islands (Baja California) to the Gulf of California; subtidal 3-45 m (Bertsch 1978; Bertsch and Kerstich 1984; Kerstich 1989).

First Channel Islands records.--Five galactic nudibranchs found on rocky reefs along north side of Santa Catalina Island at 10-18 m depths during October 1998 to May 2000. Sites: Ship Rock (1 specimen, 10/98); Blue Cavern Point (1 specimen, 5/00); and Long Point (3 specimens, E. Erikson, 5/00). Vouchers: photographs (E. Erikson, D. Richards) and specimens (D. Behrens).

Remarks.--Chromodoris galexorum is a colorful nudibranch, with red rhinophores and gills and yellow-ringed reddish spots on a creamy white background. The previous northern limit at Guadalupe Island was considered an anomaly due to El Nino conditions (Kerstich 1989). The live specimen from Big Fisherman Cove was 83 mm long, more than double the reported size range of 19-38 mm (Kerstich 1989).

Phylum Mollusca Class Gastropoda Order Nudibranchia Family Polyceratidae Polycera alabe Collier & Farmer 1964 Inkstain nudibranch (Fig. 2E)

Previous reported range.--Cedros Island (Baja California) to the Gulf of California; intertidal and subtidal (Keen 1971; Behrens 1991; Kerstich 1989).

First Channel Islands records.--Three inkstain nudibranchs observed at 8-15 m depths on rocky reefs at three islands from June to September 1998. Santa Catalina Island: Italian Gardens (33[degrees] 24.64' N, 118[degrees] 22.75' W) (1 specimen, E. Erikson, 6/98). Santa Barbara Island: Arch Point (1 specimen; 9/98). Anacapa Island: Cathedral Cove (34[degrees] 00.71' N, 119[degrees] 22.29' W) (1 specimen; 8/98). Vouchers include photographs (E. Erikson) and video (D. Kushner).

Remarks.--Polycera alabe is a small, blue-black, orange-spotted nudibranch that feeds on bryozoans (Kerstich 1989).

Phylum Echinodermata Class Holothuroidea Order Aspidochirotida Family Holothuriidae

Holothuria impatiens (Forskal 1775) Brown spotted sea cucumber (Fig. 2F)

Previous reported range.--Rosario Bay (Baja California) and throughout the Gulf of California to Ecuador and the Galapagos Islands, circumtropical; intertidal and subtidal to 46 m. (Brusca 1980; Kerstich 1989; Hendler et al. 1995; Gotshall 1998).

First Channel Islands records.--Three individuals were found at 5-8 m depths under rocks at Pebbly Beach, Santa Catalina Island during November 1998 (E. Erikson, 1 juvenile and 1 adult 25 cm long) and May 2000 (1 adult ~21 cm long). Vouchers: photographs (E. Erikson) and specimens (NHMLAC).

Remarks.--Holothuria impatiens adults were golden-brown with numerous papillae. The juvenile was a lighter cream color. All individuals eviscerated when handled out of water.

New Records at One or More Channel Islands

Phylum Cnidaria Class Anthozoa Order Actiniaria Family Boloceroididae Bunodeopsis sp. Stinging sea anemone

Previous reported range.--Mission Bay (San Diego) and Puerto Escondido (Baja California); shallow subtidal (J. Ljubenkov 1995).

New Channel Islands records.--Bunodeopsis were found as locally abundant epibionts on eelgrass (Zostera marina), surfgrass (Phyllospadix spp.), and various brown algae at 3-15 m depths on sheltered sand and rock habitats at two islands from May 1996 to August 2000. Santa Catalina Island: Big Fisherman Cove (hundreds on Zostera, 9/97); Catalina Harbor (few on Zostera, 4/98); and Isthmus Cove (L. Roberson, locally common on Macrocystis pyrifera, Eisenia arborea, Cystoseira neglecta and other brown algae, 9/98). San Clemente Island: Purse Seine Rock (hundreds on Zostera, 5/96, 9/98, 8/00) and Pyramid Head (abundant on Phyllospadix, Sargassum palmeri, Zonaria farlowii, and miscellaneous brown algae, 9/98). Vouchers: photographs (R. Herrmann, L. Roberson).

Remarks.--Bunodeopsis is a tiny translucent white sea anemone that was discovered on eelgrass in Mission Bay (San Diego) in 1995, where its extensive cover contributed to a decline in Zostera populations (Sewell & Williams 1995). This little-known representative of a subtropical/tropical genus is thought to be an undescribed species (Ljubenkov 1995). The anemone is capable of autotomizing tentacles, drifting with currents, and stinging exposed skin of divers (Ljubenkov 1995).

Phylum Arthropoda Class Malacostraca Order Stomatopoda Family Hemisquillidae

Hemisquilla ensigera californiensis (Stephenson 1967) Mantis shrimp

Previous reported range.--Point Conception (Santa Barbara County) to the Gulf of California and Panama; subtidal to 91m (Brusca 1980; Morris et al. 1980; Kerstich 1989; Gotshall 1994; Jensen 1995).

New Channel Islands records.--Hemisquilla have been present or common at 8-21 m depths in stable sand habitats at Santa Catalina and San Clemente Islands, but rare at Anacapa and Santa Cruz Islands (Basch and Engle 1993; J. Engle unpub. data.). During the 1997-1998 El Nino, recruitment was evident and abundances increased at surveyed island sites. Santa Catalina Island: Cherry Cove (common: 9/97, 4/98); Big Fisherman Cove (common: 9/97, 4/98); Willow Cove (adults common, juveniles abundant: 9/97, 10/98) (adults present, juveniles rare: 5/99, 6/99, 10/99); Big Geiger Cove (33[degrees] 27.58' N, 118[degrees] 31.04' W) (common: 4/98, 4/99); Catalina Harbor (common: 4/98); Parson's Landing (present: 4/98); East End (common: 9/98), Arrow Point (present: 4/99); and Empire Landing (present: 5/00). San Clemente Island: Purse Seine Rock (common: 5/98, 9/98, 8/00). Anacapa Island: Frenchy's Cove (present: 6/98, 8/98, 7/99, 6/00) and Cathedral Cove (present: 6/98). Santa Cruz Island: Scorpion Cove (present: 8/98, 8/99); Prisoner's Cove (present: 8/98); Potato Harbor (present: 8/99); Twin Harbor (present: 8/99); Smuggler's Cove (present: 6/00); and Hazard's Anchorage (present: 8/99). The sightings at Prisoner's Harbor, Twin Harbor, and Hazards Anchorage represent new northwestern island records.

Remarks.--Hemisquilla ensigera californiensis is a large but cryptic mantis shrimp that inhabits burrows in sheltered sand habitats. This species typically closes its burrow entrance with a plug of sand during bright midday hours (Basch and Engle 1989); therefore, abundances likely were underestimated except at Willow Cove where population dynamics have been monitored since 1984 (Engle unpub. data). Also Hemisquila can occur at depths to 70 m (Basch and Engle 1993), but our surveys were limited to 21 m depths. Stomatopod burrow densities increased nearly ten-fold at Willow Cove during 1996-1998 (0.01/[m.sup.2] (1995), 0.1/[m.sup.2] (1996), 0.06/[m.sup.2] (1997), 0.1/[m.sup.2] (1998), 0.01/[m.sup.2] (1999)), with 80% of the increase due to additional small (<20 mm diameter) burrows.

Order Decapoda Family Dromiidae

Dromidia larraburei Rathbun 1910 Sponge crab

Previous reported range.--Monterey Bay and Long Beach to Magdalena Bay (Baja California), the Gulf of California, Peru and the Galapagos Islands; intertidal and subtidal to at least 18 m (Schmitt 1921; Brusca 1980; Kerstich 1989).

New Channel Islands records.--Three individuals were found on a stable sand slope at Frenchy's Cove, Anacapa Island in June 1998 (paired male and female) and July 1999 (1 female) in 6-7 m depths. Vouchers: photographs (J. Carroll, E. Erikson) and specimens (NHMLAC).

Remarks.--Dromidia larraburei is a small, cryptic anomuran crab known for using its modified fifth leg to hold a sponge on its back (Kerstich 1989); however, the 6/98 male and 7/99 female at Anacapa Island were holding brown bubble kelp (Colpomenia sinuosa) over their bodies. The freshly-molted 6/98 female held by the male was soft and pink. Dromidia settled in large numbers on Mission Bay Reef (San Diego) in spring 1998, were still abundant in early 1999, then disappeared by August 1999 (C. Gramlich pers. comm.).

Phylum Mollusca Class Bivalvia Order Pterioida Family Pteriidae

Pteria sterna (Gould 1851) Pacific wing-oyster

Previous reported range.--Venice (Los Angeles County) and Santa Barbara Island to Morro Santo Domingo (Baja California), throughout the Gulf of California to Peru and the Galapagos Islands; subtidal 1-25 m (Keen 1971; Brusca 1980; Coan et al. 2000).

New Channel Islands records.--Pteria commonly observed attached to gorgonians at 6-23 m depths at numerous sites around all Channel Islands except San Nicolas and San Miguel during the period September 1998 to August 2000. Santa Catalina Island: Church Rock (9/98); Salta Verde Point (9/98); Ship Rock (10/98, 4/99, 10/99, 5/00); West End (10/98); Willow Cove (on buoy lines: 10/98, 5/99, 10/99); Blue Cavern Point (4/99); Bird Rock (8/98 (L. Roberson), 4/99, 5/00); Arrow Point (4/99); Long Point (10/99, 5/00); Eagle Reef (5/00); and Hen Rock (5/00). San Clemente Island: Dune Point (33[degrees] 01.58' N, 118[degrees] 33.80' W) (9/98); Northwest Harbor (9/98); Pyramid Head (9/98, 8/00); and W Pyramid Cove (9/99, 8/00). Santa Barbara Island: Southeast Sea Lion (33[degrees] 27.45' N, 119[degrees] 01.52' W) (10/98, 7/99, 6/00); South End (9/99); Arch Point (9/99); Sutil Island (8/00); and Landing Cove (8/00). Anacapa Island: Landing Cove (34[degrees] 00.70' N, 119[degrees] 21.71' W) (10/98); Admiral's Reef (34[degree s] 00.33' N, 119[degrees] 25.86' W) (7/99); Cathedral Cove (7/99); Cat Rock (8/99); Survey Rock (34[degrees] 00.66' N, 119[degrees] 22.28' W) (6/00); and West End (6/00). Santa Cruz Island: Potato Rock (8/99); Cavern Point (8/99); Twin Harbor (8/99); Hazards Anchorage (34[degrees] 03.61' N, 119[degrees] 49.73' W) (8/99); Forney Cove (8/99); Gull Island (8/99); Blue Banks Anchorage (8/99); and San Pedro Point (8/99). Santa Rosa Island: Johnson's Lee (7/99). Vouchers: photographs (E. Erikson, R. Herrmann, D. Richards) and specimens (J. Engle).

Remarks.--Pteria sterna have appeared in southern California during previous warm-water periods, but have not established permanent populations (Coan et al. 2000, Engle unpub. data). Prior distributional records for these "pearl" oysters at the Channel Islands have been sparse, and their association with sea fans (Order Gorgonacea) not well documented (Keen 1971, Brusca 1980, Coan et al. 2000). Except for several wing-oysters found attached to subsurface float lines at Willow Cove, all Pteria encountered were attached to shallow-water gorgonians, including Muricea californica, M. fruticosa, Lophogorgia chilensis, and Eugorgia rubens. Smaller individuals (5-9 cm) predominated in 1998 (shell length variability mainly was due to size differences in the anterior spike-like wing). Most Pteria were large in 1999 and 2000 (10-15 cm). Largest individuals exceeded the published size limits of 10 cm (Keen 1971, Brusca 1980, Coan et al. 2000). At Willow Cove, three Pteria on float lines grew on average from 6.5 to 12 cm in one year (10/98 to 10/99). Increased numbers of empty shells were observed at many sites in 2000.

Arbacia incisa (Agassiz 1863) Arbacia sea urchin

Phylum Echinodermata Class Echinoidea Order Arbacioida Family Arbaciidae

Previous reported range.--Newport Bay (Orange County) and Gulf of California to Peru, and the Galapagos Islands; intertidal and subtidal to 90m (H. L. Clark 1948; Brusca 1980; Morris et al. 1980; Gotshall 1998).

New Channel Islands records.--Several dozen Arbacia found in rocky crevices and artificial recruitment modules (ARM's) (Kushner et al. 1999) at 5-18 m depths at five islands during May 1998 to September 2000. Santa Catalina Island: Pebbly Beach (1 juvenile, E. Erikson, 10/98). San Clemente Island: Purse Seine Rock (1 juvenile, 5/98). Santa Barbara Island: Southeast Sea Lion (2 found in twenty-four 0.25 [m.sup.2] quadrats in 9/98; 6 in 6/99, 3 in 6/00). Anacapa Island: Admiral's Reef (ARM: 1 each in 8/98 (10 mm), 8/99, and 8/00 (35 mm)); Landing Cove (ARM: 1 juvenile in 8/98); and Cathedral Cove (ARM: 1 each in 7/98 (12 mm), 7/99, and 9/00 (32 mm)). Santa Cruz Island: Gull Island (ARM: 1 each in 7/98 (7 mm) and 9/99). Vouchers: photographs (E. Erikson) and specimens (NHMLAC).

Remarks.--Arbacia incisa was not previously known from the Channel Islands. Most individuals (8-10 mm diameter recruits in 1998 and larger individuals in 1999 and 2000) were found in concrete recruitment modules surveyed by Channel Islands National Park. Three juveniles raised in aquaria grew from 8-10 mm in spring 1998 to 27-33 mm in spring 2000 to 29-36 mm in fall 2000. Arbacia also were found in San Diego (C. Gramlich, Mission Bay in 4/97 and 1/99).

Order Diadematoida Family Diadematidae

Centrostephanus coronatus (Verrill 1867) Coronado sea urchin

Previous reported range.--California Channel Islands to the Gulf of California to Peru, and the Galapagos Islands; intertidal to 125m (Brusca 1980; Morris et al. 1980; Gotshall 1994; Kerstich 1989).

New Channel Islands records.--In prior years, Centrostephanus coronatus has been common/abundant at San Clemente and Santa Catalina Islands, uncommon/rare at Santa Barbara, San Nicolas, Anacapa, and Santa Cruz Islands, and absent at Santa Rosa and San Miguel Islands (J. Engle, unpub. data). Large-scale recruitment of 5-25 mm (test diameter) Centrostephanus was documented during surveys and in ARM's (Kushner et al. 1999) at numerous island sites during spring to fall 1998 (and in some ARM's in summer 1999). Santa Catalina Island: Indian Rock (4/98); Blue Cavern Point (4/98); Bird Rock (4/98); Church Rock (9/98); Ship Rock (10/98); West End (10/98); and Torqua Springs (10/98). San Clemente Island: Northwest Harbor (5/98); Dune Point (5/98, 9/98); Pyramid Cove (5/98, 9/98); Pyramid Head (5/98, 9/98); and Seal Cove (9/98). Santa Barbara Island: Southeast Sea Lion (9/98: most recruits ever); Arch Point (9/98: most recruits ever); and Cat Canyon (33[degrees] 27.24' N, 119[degrees] 02.47' W) (9/98). Anacapa Island: Survey Rock (6/98); Frenchy's Cove (6/98); Landing Cove (8/98: most recruits ever (4.1/ARM)), 8/99 (2.3/ARM); Cathedral Cove (7/98: most recruits ever (1.8/ARM)), 7/99 (0.5/ARM); and Admiral's Reef (8/98: most recruits ever (4.4/ARM)), 8/99 (2.5/ARM). Santa Cruz Island: Gull Island (8/98: first recruits ever (0.7/ARM), 9/99 (1.0/ARM); Fry's Harbor (7/98: most recruits ever (0.6/ARM), 8/99 (0.4/ARM); Pelican Bay (8/98: most recruits ever (2.7/ARM), 8/99 (0.2/ARM); Scorpion Cove (8/98 (0.17/ARM)); Yellowbanks (9/98: first recruits ever (0.9/ARM), 7/99 (1.9/ARM); and Potato Rock (8/98). No Centrostephanus <20 mm were found in ARMs in 2000. Two coronado urchins (7/99 (25 mm), 8/00) found on a transect at Rodes Reef became the first record of this species at Santa Rosa Island.

Remarks.--The huge settlement of Centrostephanus in late 1997/early 1998 also was observed in San Diego (Mission Bay Reef); numbers of tiny urchins dropped substantially by late 1998 (C. Gramlich pers. comm.).

Discussion

Six species of subtropical nearshore invertebrates were documented for the first time in California. New northern geographic range limits based on records at the Channel Islands include the following: 1) Chloeia viridis: extended from Gulf of California to Santa Catalina Island; 2) Stenorhynchus debilis: extended from Guadalupe Island to Anacapa Island; 3) Pleurobranchus areolatus: extended from San Benitos Islands to Anacapa Island; 4) Chromodoris galexorum: extended from Guadalupe Island to Santa Catalina Island; 5) Polycera alabe: extended from Cedros Island to Anacapa Island; and 6) Holothuria impatiens: extended from Rosario Bay to Santa Catalina Island.

Six additional species of subtropical invertebrates, though occurring within or near their known geographic range limits, were documented for the first time at one or more of the Channel Islands during or after the 1997-1998 El Nino period. New island records include: 1) Bunodactis sp.: previously reported at Mission Bay, now known at San Clemente and Santa Catalina Islands; 2) Hemisquilla ensigera californiensis: increased abundances at four islands and newly appeared near the west end of Santa Cruz Island; 3) Dromidia larraburei: first island record at Anacapa Island; 4) Pteria sterna: newly found at three northern islands; 5) Arbacia incisa: previously reported from Newport Bay, now known at five islands; and 6) Centrostephanus coronatus: increased recruitment at six islands and newly appeared at Santa Rosa Island.

The conspicuousness of most of the above invertebrates coupled with extensive CIRP and CINP surveys dating back to 1980 make it unlikely that these warm-water species would have occurred at the newly-recorded island locations prior to the 1997-1998 El Nino without being noticed. The observed temporal pattern of predominantly smaller individuals during El Nino followed by larger sizes during La Nina for Stenorhynchus, Hemisquilla, Pteria, Arbacia, and Centrostephanus is consistent with the hypothesis that their larvae settled out from El Nino-associated currents flowing north from Baja California (see Hickey 1993). Previous northern limits for some of these species (e.g., Stenorhynchus, Pleurobranchus, Chromodoris, and Polycera) were established after El Nino events of the 1980's. Such progressive extensions of northern range limits are likely a result of the extended warm-water regime in place since 1976 (Engle 1994).

Long-term sea surface temperature patterns show consistent differences among the eight Channel Islands (Fig. 1). Santa Catalina, the warmest island, had the most records of subtropical invertebrates (Table 1), as well as subtropical fishes (see Richards and Engle this volume). Another warm-water island, San Clemente, and a transitional island, Anacapa, also had many southern species records. Though more northern, Anacapa Island is close to the mainland where it is influenced by northerly-flowing warm-water currents. The few subtropical species records at Santa Barbara Island may be due to its paucity of sheltered habitats (where at least 5 of the species were found) and because this island was surveyed less often than Santa Catalina, San Clemente, and Anacapa. Remote, military-controlled San Nicolas Island was only surveyed at two locations in September 1999. The northern islands within Channel Islands National Park were visited regularly. Only two minor occurrences of subtropical species were noted at Santa Rosa Island and none at San Miguel, the coldest-water island.

Repeated sightings provided growth and survivorship information for five species. Short-lived Stenorhynchus was found only during an eight-month period in 1998. Aquarium-held individuals also died by fall 1998. In contrast, Arbacia, found as 8-10 mm juveniles in spring 1998, continued to be found as adults in 1999 and 2000. All three aquarium-held Arbacia survived for over two years (as of 9/2000), having grown from an average of 9 mm to 32 mm test diameter. Pteria was found in progressively larger sizes at many sites over the two-year period from fall 1998 to fall 2000, with many empty shells evident in 2000. The lack of small Stenorhynchus, Arbacia, or Pteria in the two years following the 1997/1998 settlement indicates that these populations are not likely self-sustaining. As has often been observed in populations at their northern limits (e.g., Reaka 1986), these species (as well as Chloeia, Pleurobranchus, and Chromodoris) attained or exceeded maximum recorded sizes. Hemisquilla and Centrostephanus also experienced El Nino recruitment peaks. Their established populations on southern islands may make it easier for further recruitment to northern islands.

The 1997-1998 El Nino influenced the composition of Channel Islands shallow-water species assemblages in many other ways besides the enhancement of subtropical species (see Tegner and Dayton 1987 for 1983-1984 El Nino effects). For example, certain herbivores, planktivores, and seastars, incurred high mortality apparently due to thermal stress, reduced food availability, and disease (J.

Eagle and D. Richards, unpub. data). Deterioration of kelp forests reduced habitat, shelter, and food for many species. Low oceanographic productivity resulted in less food for suspension-feeders. Seastars and other echinoderms experienced extensive mortality from a warm-water wasting disease (Eckert et al. 2000). The rapid switch from El Nina to La Nina conditions in fall 1998 reversed thermal stress, low productivity, and echinoderm disease influences. Also, La Nina apparently halted further recruitment of subtropical forms, but did not appear to affect the survival of the subtropical species we monitored. It remains to be seen whether this La Nina signals the start of an oceanographic regime shift toward cooler conditions or is a temporary deviation in the long-term warming trend. If warm-water conditions resume, we can expect further appearances of subtropical species at the Channel Islands as biogeographic provinces shift northward.

Acknowledgments

Many individuals participated in the surveys that provided new records for subtropical invertebrates at the Channel Islands. We thank the Channel Islands Research Program and Channel Islands National Park research vessel crews and divers for their assistance, especially David Kushner for directing the CLNP Kelp Forest Monitoring Program surveys. We thank Erik Erikson, Constance Gramlich, Pete Haaker, and Loretta Roberson for providing additional records of unusual invertebrates. We greatly appreciate the underwater photographic talents of Jay Carroll, Erik Erikson, Richard Herrmann, and Loretta Roberson. Valuable taxonomic and biogeographic expertise were provided by Dave Behrens, Don Cadien, Henry Chaney, Dan Gotshall, Leslie Harris, Gordon Headier, John Ljubenkov, Paul Valentich Scott, and Mary Wicksten. The surveys were sponsored by the Tatman Foundation (CIRP) and National Park Service (CINP).

(1.) Tatman Foundation and Marine Science Institute, University of California, Santa Barbara, California 93106 Phone: 805-893-8547 Fax: 805-893-8062 Email: j_engle@lifesci.ucsb.edu

(2.) Channel Islands National Park, 1901 Spinnaker Drive, Ventura, California 93001

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Accepted for publication 22 December 2000.

[Graph omitted]
Table 1. Previous and new (1997--1998 El Nino) records for 12 species of
subtropical marine invertebrates at the eight California Channel
Islands. Abbreviations: Islands: SCL = San Clemente, SCA = Santa
Catalina, SBA = Santa Barbara, SNI = San Nicolas, ANA = Anacapa, SCR =
Santa Cruz, SRO = Santa Rosa, and SMI = San Miguel; Records: P =
previous and N = new (1997--1998 El Nino).

 California Channel Island
 Phylum Species SCA

Cnidaria Bunodeopsis sp. N
Annelida Chloeia viridis N
Arthropoda Dromidia larraburei
 Hemisqulla ensigera P
 Stenorhynchus debilis N
Mollusca Chromodoris galexorum N
 Pleurobranchus areolatus N
 Polycera alabe N
 Pteria sterna P
Echinodermata Arbacia incisa N
 Centrostephanus coronatus P
 Holothuria impatiens N

 California Channel Island
 Phylum Species SCL SBA SNI

Cnidaria Bunodeopsis sp. N
Annelida Chloeia viridis
Arthropoda Dromidia larraburei
 Hemisqulla ensigera P
 Stenorhynchus debilis N
Mollusca Chromodoris galexorum
 Pleurobranchus areolatus N
 Polycera alabe N
 Pteria sterna P P
Echinodermata Arbacia incisa N N
 Centrostephanus coronatus P P P
 Holothuria impatiens

 California Channel Island
 Phylum Species ANA SCR SRO

Cnidaria Bunodeopsis sp.
Annelida Chloeia viridis
Arthropoda Dromidia larraburei N
 Hemisqulla ensigera P P
 Stenorhynchus debilis N
Mollusca Chromodoris galexorum
 Pleurobranchus areolatus N
 Polycera alabe N
 Pteria sterna N N N
Echinodermata Arbacia incisa N N
 Centrostephanus coronatus P P N
 Holothuria impatiens

 California
 Channel
 Island
 Phylum Species SMI

Cnidaria Bunodeopsis sp.
Annelida Chloeia viridis
Arthropoda Dromidia larraburei
 Hemisqulla ensigera
 Stenorhynchus debilis
Mollusca Chromodoris galexorum
 Pleurobranchus areolatus
 Polycera alabe
 Pteria sterna
Echinodermata Arbacia incisa
 Centrostephanus coronatus
 Holothuria impatiens
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Author:Engle, John M.; Richards, Daniel V.
Publication:Bulletin (Southern California Academy of Sciences)
Geographic Code:1U9CA
Date:Dec 1, 2001
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Previous Article:New and Unusual Reef Fish Discovered at the California Channel Islands During the 1997-1998 El Nino.
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