Background information and definitions
Many populations of marine subtidal benthic invertebrate species have declined or been depleted due to the multiple threats they are under, such as habitat loss (Airoldi et al. 2008). To improve animals’ survival or recolonization success, some assistance can be provided in the form of artificial shelters that mimic the natural shelters usually found in the marine environment, such as ‘casitas’ used for lobsters (Gutzler et al. 2015). These shelters can provide refugia and potentially help animals avoid predation (Arce et al. 1997).
Airoldi L., Balata D. & Beck M.W. (2008) The gray zone: relationships between habitat loss and marine diversity and their applications in conservation. Journal of Experimental Marine Biology and Ecology, 366, 8–15.
Arce A.M., Aguilar-Dávila W., Sosa-Cordero E. & Caddy J.F. (1997) Artificial shelters (casitas) as habitats for juvenile spiny lobsters Panulirus argus in the Mexican Caribbean. Marine Ecology Progress Series, 158, 217–224.
Gutzler B.C. Butler M.J. & Behringer D.C. (2015) Casitas: A location-dependent ecological trap for juvenile Caribbean spiny lobsters, Panulirus argus. ICES Journal of Marine Science, 72, 177–184.
Supporting evidence from individual studies
A replicated, controlled, before-and-after study in 1997–1999 of nine plots in a reef lagoon with seagrass meadows in the Caribbean Sea, Mexico (Briones-Fourzàn & Lozano-Álvarez 2001 – same experimental setup as Lozano-Álvarez et al. 2009) found that during one year after deploying artificial shelters (‘casitas’), abundance of Caribbean spiny lobsters Panulirus argus increased in plots with artificial shelters but not in plots without, regardless of whether the plots had lobsters or not before deployment. Lobster abundance increased over time in plots with shelters (before deployment: 0–30; after: 7–104 lobsters/ha) while it did not increase in plots without (before: 0–24; after: 0–32 lobsters/ha). After a year, plots with artificial shelters had bigger lobsters (average 25 mm) than sites without (22 mm). Ten ‘casitas’ (1.1 m2, 3.8 cm diameter entrance) were deployed in each of five plots (1 ha) (≤5 m depth) in July 1998. On 13 occasions before (February 1997–July 1998) and every two months for a year after deployment, divers counted and visually estimated the carapace length of all lobsters across each ‘casitas’ plots and at four plots without casitas. Before deployment, three ‘casitas’ plots and two plots without ‘casitas’ had zero lobsters. No fishing is reported to occur in the study area because all lobsters present are typically undersize juveniles.Study and other actions tested
A replicated, controlled study in 1993–1995 in four sites across two areas of seagrass in the Everglades National Park, Florida Bay, USA (Nizinski 2007) found that providing artificial shelters had varied effects on Caribbean spiny lobster Panulirus argus abundance (shelter occupancy) depending on shelter designs, but all designs had similar abundance of their molluscan prey. Lobster abundance was greater in full-roof artificial shelters (13 lobsters/shelter) than mesh-roof shelters (6 lobsters/shelter), and more lobsters were found in these two designs than in either artificial shelter frames (1 lobster/shelter) or plots without artificial shelters (0 lobster/plot). Abundance was not significantly different in shelter frames and plots without shelters. Abundance data for molluscs in each treatment were not shown. Four treatments (three shelter designs and no shelter) were tested; 1) an artificial shelter frame without a roof, 2) an artificial shelter frame covered with a 3.8 cm diamond mesh roof, 3) an artificial shelter frame covered with an aluminium sheet and 4) delimited empty plot of similar size as an artificial shelter. In July 1993, at two sites (1 km apart) in each of two areas (12 km apart), artificial shelters were deployed (4 replicates/treatment/site). Quarterly in 1993–1994 and twice in 1995, divers counted and measured lobsters >20 mm, and using a suction sampler identified and counted molluscs >1 mm sampled (1 replicate/treatment/sampling time; 0.05 m2 samples) in all treatments.Study and other actions tested
A replicated study in 1998–2002 of nine plots in a reef lagoon with seagrass meadows in the Caribbean Sea, Mexico (Lozano-Álvarez et al. 2009) found that over the 2.5 years after their deployment, artificial shelters (‘casitas’) were occupied by more and bigger Caribbean spiny lobsters Panulirus argus than natural shelters (crevices). More lobsters were found occupying artificial shelters (3.5–5.5 on average; 3,707 in total) than crevices (1–1.6 on average; 200 in total). In addition, artificial shelters hosted larger lobsters (30–32 mm carapace length) than crevices (17–18 mm). Ten ‘casitas’ (1.1 m2, 3.8 cm diameter entrance) were deployed in each of five plots (1 ha) (≤5 m depth) in July 1998. On 22 occasions after deployment (September 1998–November 2002), divers counted and visually estimated the carapace length of all lobsters inside all artificial shelters and inside all naturally occurring shelters (crevices) in each plot.Study and other actions tested
A replicated, controlled, before-and-after study in 1997–2002 of nine plots in a reef lagoon with seagrass meadows in the Caribbean Sea, Mexico (Lozano-Álvarez et al. 2010 – same experimental setup as Briones-Fourzàn & Lozano-Álvarez 2001) found that over the 2.5 years after deploying artificial shelters (‘casitas’), abundance of Caribbean spiny lobsters Panulirus argus increased in all plots but more so in plots with artificial shelters than those without, and that lobsters in plots with artificial shelters were bigger. Before deployment, all plots had similar lobster abundance (1.5–8 lobsters/ha). After deployment, abundance increased approximately four times more in plots with artificial shelters (17–83 lobsters/ha) than plots without (5–21 lobsters/ha). Plots with artificial shelters had bigger lobsters (31 mm) than sites without (24 mm). Ten ‘casitas’ (1.1 m2, 3.8 cm diameter entrance) were deployed in each of five plots (1 ha) (≤5 m depth) in July 1998. On six occasions before (December 1997–July 1998) and 22 occasions after (September 1998–November 2002) deployment, divers counted all lobsters across each ‘casitas’ plots and at four plots without casitas. For the ‘after’ surveys only, the carapace length of lobsters was also visually estimated.Study and other actions tested
A replicated, controlled study in summer 2012–2013 of multiple sites in two areas of either rocky, sandy or seagrass bed in the Florida Keys, USA (Gutzler et al. 2015) found that the effects of artificial shelters (‘casitas’) on the nutritional condition of Caribbean spiny lobsters Panulirus argus varied with location, and that lobsters occupying them had similar sex ratio and typically similar survival, compared to lobsters in natural shelters, but lobsters in the artificial shelters were larger. The nutritional condition of lobsters (data presented as an index) differed between the two areas, but within each area lobsters inside artificial shelters had greater nutritional condition than lobsters in crevices. In addition, artificial shelters hosted larger lobsters (average 66 mm) than crevices (52 mm). Each artificial shelter was on averaged occupied by 22–41 lobsters. In three of four comparisons, lobster survival following predation experiment was similar in artificial (59–97% survival) and natural shelters (57–93% survival). In one comparison (of lobsters <35 mm), survival was lower in artificial (56% survival), compared to natural shelters (82% survival). The ‘casitas’ (4 m2) were flat rectangular structures with at least two open sides. In one area, ’casitas’ (number unspecified) had been deployed in 1990 (at 2–3 m depth). In the other area, 16 were deployed (at 10 m depth). In May–August 2012–2013, divers counted lobsters occupying 16 of the ‘casitas’, and collected lobsters using hand nets and tail snares found inside artificial and natural shelters at all sites. All lobsters were measured (carapace length), their sex recorded, and a subset was used to assess nutritional condition based on the weight of their lobster’s digestive gland. Divers also experimentally assessed lobster mortality from predation inside artificial and natural shelters (using a tethering method).Study and other actions tested
Referenced paperLozano-Álvarez E., Briones-Fourzán P., Álvarez-Filip L., Weiss H., Negrete-Soto F. & Barradas-Ortiz C. (2010) Influence of shelter availability on interactions between Caribbean spiny lobsters and moray eels: implications for artificial lobster enhancement. Marine Ecology Progress Series, 400, 175-185.