Invasive Species

Invasion of the Indo-Pacific Red Lionfish (Pterois volitans)

The first Indo-Pacific lionfish reported in USVI waters was found in 2009 on the west end of St. Croix under the Frederiksted pier. The invasive species had been rapidly spreading throughout the Caribbean from the believed introduction point of Florida, and was already common in the Bahamas, Jamaica and Hispanola. Several more of the fish were seen over the next few weeks; however, it was not until early 2010 that the first lionfish was reported in St. Thomas. By early 2011, divers and fishermen from around the territory were finding lionfish commonly, and although a concerted effort was made by to eradicate the fish, reports escalated. Today the invader is quite prevalent throughout the territory and Caribbean region. It is estimated around 30,000 lionfish were taken by St. Thomas fishermen in traps in 2011 (Olsen, unpub. data), and fishermen say lionfish numbers are now higher than ever (Berry, commercial fisherman, pers. com.).

The lionfish invasion is particularly important because of the ability of lionfish to consume large quantities of native reef fish. Lionfish are gape-limited stalking predators capable of consuming prey that are almost half their total length, yet lionfish are themselves largely protected from predation by venomous fin spines (Morris and Whitfield 2009). Lionfish have rapidly spread over more than 4,000,000 km² of marine habitat across the Western Atlantic, Caribbean and Gulf of Mexico, and are now undergoing exponential increases in abundance at many locations (Betancur-R et al. 2011; Foundation 2012). Invasive lionfish occupy a range of habitat types and depths, where they consume an array native fishes and crustaceans at very high rates (Schofield 2009; Green et al. 2011). There is growing concern that predation by lionfish will nullify efforts to protect vulnerable fish populations from anthropogenic threats in the region.

In the TCRMP, lionfish were first observed on roving dives at only two sites in 2010, Lang Bank and Kings Corner, both located off St. Croix. By 2011, seven sites out of 32 held lionfish, including four sites off St. Thomas. Fish were recorded in transects as well as roving dive surveys. One year later lionfish were recorded on transects at over 50% of monitoring sites. On roving dives, they were observed on 20 out of 32 sites (data not shown). Lionfish were more abundant overall on TCRMP sites off St. Thomas/St. John in 2013, however the number was down on sites off St. Croix. The number of sites they were observed on was down on both island shelves. A total of 58 lionfish were observed on transects off St. Thomas/St. John in 2013, and 9 on transects conducted off St. Croix. As in the previous year the mesophotic sites off St. Thomas had higher abundances than other sites. This includes the deep (64m) Ginsburgs Fringe site, where large and small lionfish were very abundant around the permanent transects, but were not quantified. Lionfish were observed during roving dives on seven out of 14 sites off St. Croix, and eight out of 18 on St Thomas. On roving dives as well as transects, more lionfish were seen on St. Thomas/St. John sites than on St. Croix sites. Lionfish across the territory ranged in size from 6 to 40 cm TL but the majority of fish were in the 20-30 cm size bin (~50%). Twelve lionfish (18%) were recorded over 30 cm TL in 2013.

Little data has been collected and analyzed regarding preferential habitat for lionfish in the western Atlantic; however, based on the TCRMP data and many other dives conducted across the USVI shelves by the authors, it appears that the species likes a variety of habitats, and basically anything with structure. They are common on hard bottom areas (generally attached to the largest rock /coral around) as well as coral reefs, and are found to be particularly fond of submerged man-made structures. They may be somewhat limited from turbulent or high current environments by their large fins. It is unknown if their high densities on mesophotic reefs represent a preference for deepwater habitats, or a reduced fishing pressure. The Grammanik Bank and Red Hind Bank are marine reserves where bottom fishing is prohibited and large snappers, groupers and sharks are observed regularly. Predation by large piscivores does not appear to control the recruitment or growth of lionfish in and around these sites.

A project conducted by the U.S. Food and Drug Administration, the University of the Virgin Islands and collaborators was the first to document the presence of toxins responsible for Ciguatera Fish Poisoning in the flesh of lionfish harvested from USVI waters (Robertson et al. 2013). This indicates a potential human health threat from the consumption of lionfish that needs to be addressed in any management plan that considers harvesting lionfish for food. The research suggests that lionfish toxicity rates above FDA guidelines (0.1 μg/kg C-CTX-1 equivalents) were roughly 12%. The rates of toxicity are comparable to the schoolmaster snapper (Lutjanus apodus), a fish that is eaten in the USVI, with precautions taken on area caught. Typically the south side of St. Thomas-St. John is considered more toxic than the north bank of the Puerto Rican Shelf and St. Croix and many species, including schoolmaster snapper, are avoided here. Similar precautions could be applied to lionfish. A market has developed for lionfish in the USVI and no poisonings have been reported to which we are aware. This suggests that typical prophylactic procedures of commercial and recreational fishermen are working to limit the risk of Ciguatera Fish Poisoning for lionfish consumption.

Normally the TCRMP wound provide management recommendations for the lionfish, but in this case defer the recently published USVI Lionfish Management Plan for recommendations. Instead, the information here is presented as a documentation of the invasion and current progress towards management in the territory.

UPDATED: Invasion of the Indo-Pacific Red Lionfish (Pterois volitans)

The first Indo-Pacific lionfish reported in USVI waters was found in 2009 on the west end of St. Croix under the Frederiksted pier. The invasive species had been rapidly spreading throughout the Caribbean from the believed introduction point of Florida, and was already common in the Bahamas, Jamaica, and Hispanola. Several more of the fish were seen over the next few weeks; however, it was not until early 2010 that the first lionfish was reported in St. Thomas. By early 2011, divers and fishermen from around the territory were finding lionfish commonly, and although a concerted effort was made to eradicate the fish, at least initially, reports escalated. Today, the invader is quite prevalent throughout the territory and Caribbean region; however, both divers and fishermen say they are seeing fewer fish than 2011-2013, and they are smaller in general.

There continues to be an effort to control the lionfish through fishing, and a growing market for the species as a food fish exists on all three islands. Ciguatoxin is present in many individuals (Robertson et al. 2013), but poisonings are not known.

The lionfish invasion is particularly important because of the ability of lionfish to consume large quantities of native reef fish. Lionfish are gape-limited stalking predators capable of consuming prey that are almost half their total length, yet lionfish are themselves largely protected from predation by venomous fin spines (Morris and Whitfield 2009). Lionfish have rapidly spread over more than 4,000,000 km2 of marine habitat across the Western Atlantic, Caribbean and Gulf of Mexico, and are now undergoing exponential increases in abundance at many locations (Betancur-R et al. 2011; REEF 2012). Invasive lionfish occupy a range of habitat types and depths, where they consume an array native fishes and crustaceans at very high rates (Schofield 2009; Green et al. 2011). There is growing concern that predation by lionfish will nullify efforts to protect vulnerable fish populations from anthropogenic threats in the region.

In the TCRMP data, lionfish were first observed on roving dives at only two sites in 2010, Lang Bank and Kings Corner, both located off St. Croix. By 2011, seven sites out of 32 held lionfish, including four sites off St. Thomas. Fish were recorded in transects as well as roving dive surveys. One year later, lionfish were recorded on transects at over half of all monitoring sites. On roving dives, they were observed on 20 out of 32 sites (data not shown). In the latest year of sampling (2015) lionfish were observed during roving dives on twelve out of 14 sites off St. Croix, and eight out of 18 on St Thomas. Lionfish encounters in 2015 were higher overall than in 2014 around the northern USVI (112 in 2015 and 81 in 2014); however, this was primarily due to a very large number observed on the mesophotic Hind Bank FSA and Ginsburgs Fringe sites. Around St. Croix numbers observed on transects were nearly the same in the last two years of monitoring (20 in 2015 and 18 in 2014).Mesophotic sites off St. Thomas continue to have the highest abundances of lionfish, and two of these sites (Hind Bank FSA and Ginsburgs Fringe) had large increases in 2015. The Grammanik Bank had a notable decrease in lionfish in 2015, possibly due to the spawning aggregations of large piscivorous fish that use the reef. Lionfish across the territory ranged in estimated size from 6 to 40cm TL and the majority (~45%) of fish were between 11 and 20cm TL. In 2014, the majority of fish (41%) were estimated to be between 20 and 30cm TL. Only seventeen lionfish (13%) were recorded over 30 cm TL in 2015. This number was down 7% from 2014 data.

Little data has been collected and analyzed regarding preferential habitat for lionfish in the western Atlantic; however, based on the TCRMP data and many other dives conducted across the USVI shelves by the authors, it appears that the species utilizes a variety of habitats and use any available structure within the area. They are common on hard bottom areas (generally associated with the largest rock /coral around) as well as coral reefs, and are found to be particularly abundant on submerged man-made structures. They may be somewhat limited from turbulent or high current environments by their large fins. It is unknown if their high densities on mesophotic reefs represent a preference for deepwater habitats, or a reduced fishing pressure. The Grammanik Bank and Hind Bank are marine reserves where bottom fishing is prohibited and large snappers, groupers, and sharks are observed regularly. Predation by large piscivores could partially control the recruitment or growth of lionfish at the Grammanik Bank, but the data is equivocal.

Emergence of the Invasive Red Algae Ramicrusta spp.

Many nearshore coral reefs throughout the Caribbean region have been experiencing increases in macroalgae cover. This increase in macroalgae has been linked with negative impacts to living stony corals through abrasion, shading, and chemical release. While the majority of macroalgae cover at TCRMP locations is dominated by Dictyota spp. and Lobophora spp., several have experienced relatively rapid increases in an encrusting red algae Ramicrusta spp (hereafter Ramicrusta). The genus Ramicrusta is present in multiple locations in the Pacific Ocean (Dixon and Saunders 2013), but was not reported in the Caribbean until 2009 at Discovery Bay, Jamaica (Pueschel and Saunders 2009). The genus has since been documented in Bonaire (Eckrich and Engel 2013) and Puerto Rico (Ballantine David et al. 2016). At present, three Ramicrusta species have been identified: Ramicrusta textilis (Pueschel and Saunders 2009) in Jamaica and Puerto Rico, Ramicrusta bonairensis (Ballantine, Ruiz, Lozada-Troche & Norris 2016) in Bonaire, and Ramicrusta monensis (Ballantine, Ruiz, Lozada-Troche & Norris 2016) in Puerto Rico. The TCRMP believes this genus has now become established in the USVI but exact ID is pending judgment of specialists. Until then this summary assumes the species is/are of the genus Ramicrusta. There is very little known about the biology of Ramicrusta and the environmental factors that determine its presence.

Ramicrusta ranges in color from red to brown and primarily forms thin crusts, though frondose edges may be present. Ramicrusta appears to be a strong competitor relative to most other benthic organisms, rapidly colonizing and expanding on open substrate. It has been observed overgrowing live coral tissue, sponges, gorgonians, zoanthids, and other kinds of macroalgae. Interactions with live coral colonies appear to be indiscriminate, and often cause bleaching and partial, if not complete, colony mortality. Successful recruitment of coral larvae or other benthic organisms has not been recorded on Ramicrusta substrate with the exceptions of occasional short fronds of Dictyota spp. (Ennis, pers. obs. 8 Dec 2016). This combination of factors has the potential to be particularly devastating to reef ecosystems that are already under stress from other environmental conditions.

Further analysis of benthic cover at Savana, which is an offshore site with little apparent human impacts, has shown that Ramicrusta has been present at low cover since the location’s first sampling in 2003. Ramicrusta cover at Savana was less than 10% until the 2005 bleaching event, after which cover increased nearly five-fold by 2008 and is currently about 60% of the total benthic cover. The increase in Ramicrusta cover after the 2005 bleaching suggests a tipping point was reached when coral cover declined from 20% to 10%. Ramicrusta initially took over this space by 2006, but has since increased linearly and by 2016 occupied 60% of the substrate, depressing all other benthic categories. Corals are in high contact with the algae and are being overgrown on the margins. Ramicrusta is likely driving the decline in coral cover since 2010.

Although the change in Ramicrusta benthic cover at Savana is an extreme case relative to all other TCRMP locations, it demonstrates the need for continued monitoring of changes in the cover of this algae. This is especially relevant given the potential devastation of overgrowth and the general lack of information regarding the life history of the genus in the Caribbean. Further examination of the long-term TCRMP dataset could provide valuable insight into the factors driving or controlling Ramicrusta sp. abundance. Future work by TCRMP and UVI will attempt to experimentally determine the mechanisms of impacts on corals and factors controlling the growth of Ramicrusta, such as productivity and impacts of herbivores. It is not clear if Ramicrusta was introduced to the Atlantic Ocean or has always been present in low abundance. However, it is clear that Ramicrusta is rapidly increasing in abundance at the expense of stony corals.