Spatial and temporal changes in reef fish assemblages on disturbed coral reefs, north Pacific coast of Costa Rica

Abstract

Benthic structure of coral reefs determines the availability of refuges and food sources. Therefore, structural changes caused by natural and anthropogenic disturbances can have negative impacts on reef‐associated communities. During the 1990s, coral reefs from Bahía Culebra were considered among the most diverse ecosystems along the Pacific coast of Costa Rica; however, recently they have undergone severe deterioration as consequence of chronic stressors such as El Niño‐Southern Oscillation and harmful algal blooms. Reef fish populations in this area have also been intensely exploited. This study compared reef fish assemblages during two periods (1995–1996 and 2014–2016), to determine whether they have experienced changes as a result of natural and anthropogenic disturbances. For both periods, benthic composition and reef fish abundance were recorded using underwater visual censuses. Live coral cover (LCC) decreased from 43.09 ± 18.65% in 1995–1996 to 1.25 ± 2.42% in 2014–2016 (U = 36, p < 0.05). Macroalgal cover (%) in 2014–2016 was sixfold higher than mean values reported for the Eastern Tropical Pacific region. Mean (±SD) fish species richness in 1995–1996 (36.67 ± 14.20) was higher than in 2014–2016 (23.00 ± 9.14; U = 20, p < 0.05). Over 40% of reef fish orders observed in 1995–1996 were not detected in the 2014–2016 surveys, including large‐bodied predators. Reduction in abundance of fish predators such as sharks, grunts, and snappers is likely attributed to changes in habitat structure. Herbivorous such as parrotfishes and pufferfishes increased their abundance at sites with low LCC, probably in response to predators decline and increased algal cover. These findings revealed significant degradation and drastic loss of structural complexity in coral reefs from Bahía Culebra, which now are dominated by macroalgae. The large reduction in structural complexity of coral reefs has resulted in the loss of diversity and key ecological roles (e.g., predation and herbivory), thus potentially reducing the resilience of the entire ecosystem.

Drivers of reef fish assemblages in an upwelling region from the Eastern Tropical Pacific Ocean

“…(2019) reported 94 species from 37 families, whereas Arias‐Godínez et al . (2019) found 56 species from 24 families in the Gulf of Papagayo (North Pacific of Costa Rica). UVC from the present study alone detected more species (122 species from 42 families) than these two studies; nevertheless, this number was likely because of differences in sampling effort, temporal variability and severe habitat degradation reported in some areas (Arias‐Godínez et al ., 2019; Beita‐Jiménez et al ., 2019).…”

“…The Thermal Dome is located in the North Pacific of Costa Rica, and this seasonal upwelling is known to modify the structure and dynamics of marine communities, speeding up coral growth rates, algae dominance and the settlement of sessile invertebrate (Fernández‐García et al ., 2012; Jiménez and Cortés, 2003; Roth et al ., 2015). Recent studies in the North Pacific of Costa Rica have provided important information on how fish assemblages are influenced by the state of the reef (Arias‐Godínez et al ., 2019) and habitat protection (Beita‐Jiménez et al ., 2019). Nevertheless, it is still unclear whether seasonal upwelling events are also a major driver of reef fish assemblages in this region.…”

Monitoring elasmobranch assemblages in a data-poor country from the Eastern Tropical Pacific using baited remote underwater video stations

“…nursery, reproductive and/or feeding grounds) for threatened species 36,66,67 . In Costa Rica, rapid coastal development and changes in land use practices are already impacting the health of coral reefs and reef fish communities in some areas 68,69 . However, despite their close proximity to human centers and limited resources for surveillance, Caño and Murciélago islands are still two of the healthiest and most productive areas in Costa Rica, and provide numerous ecosystem services for coastal communities 48,70,71 .…”

“…All open-fishing sites included in this study (Loros Island, Bajo Rojo and Santa Elena Bay) were located in the North Pacific of Costa Rica, an area that has been historically exposed to strong pressure from semi-industrial and artisanal fisheries 28 , 76 . Declining shark populations since the 1990s have likely resulted in changes in fish community structure and composition, as well as less productive and more degraded habitats 69 , 70 . Furthermore, anecdotal information from local stakeholders indicate that apex predators (e.g.…”

“…Urobatis halleri and Hypanus longus ) and the BRUVS at open-fishing sites. Although there is some evidence that the absence or decline of top predators from coastal habitats in Costa Rica may result in shifts in community structure and function 69 , more studies are still needed to further elucidate major drivers influencing these patterns. Increasing the number of BRUVS deployed in no-take and open-fishing sites from the Central and South Pacific regions may help clarify whether fishing and/or other drivers are responsible of the shifts in predator abundance.…”