Scientists explored the life around asphalt volcanoes in the Santa Barbara Gorge, a natural feature where oil vents breach the seabed near the California coast. These vents, opening along the Santa Barbara Strait, pose challenges for beachgoers because tar can stain sand and rock, yet they also carve out a distinctive underwater habitat that remains poorly understood by researchers. This paradox—coastal disruption paired with ecological mystery—drove a focused investigation into the resident fish communities and the ecological rules they follow in this unusual setting. [Citation: University of California Santa Barbara]
The study aimed to map which fish species occupied which zones around the vents and to uncover the reasons behind those patterns. To achieve this, researchers deployed a remotely operated underwater vehicle, enabling extended, precise observations without disturbing the animals. Over an eight hour period, the team collected thousands of images and videos, producing a rich dataset that revealed both the breadth and the depth of life around the asphalt features. In total, observations logged 1,836 individual fish, representing at least 43 species, with a surprising emphasis on the regionally important groupers. The researchers noted that the high, fairly smooth rocky reefs surrounding the vents supported a robust presence of these dominant predators, a pattern consistent with what ecologists observe in similar reef structures elsewhere. [Citation: University of California Santa Barbara]
Several fish showed a preference for the vented slopes, where perches and other rock-dwelling species with distinctive green markings congregated on the textured surfaces. These species included various sebastes forms, noted for their resilience in disturbed habitats. Around the vents, the muddy seabed hosted a different set of inhabitants, including marine chanterelles and flounder that thrived in the soft, silty substrates that frame the underwater dunes. An intriguing and unexpected observation was the presence of narrow halos of tar-free water around the vents, creating small, tar-free windows where certain flatfish and other taxa were absent. This separation suggests that the tar residue itself might influence microhabitat choice and feeding opportunities for nearby communities. The researchers hypothesized that any fish approaching too closely could be impeded by the sticky surface, effectively altering their risk-reward calculations and driving them to stay at safer distances. [Citation: University of California Santa Barbara]
The study documented movements of several fish groups between the silty regions and the tar-rich zones, including greens, green band groupers, and American hydrolagoons. The authors emphasize that even modest amounts of asphalt visible in the imagery correlated with notable shifts in species composition. In particular, fish adapted to the soft seafloor tended to avoid hard tar surfaces, altering the expected distribution and density of individuals across the habitat mosaic. These findings highlight the nuanced ways in which a single environmental feature can shape community structure, succession dynamics, and species interactions on a localized scale. [Citation: University of California Santa Barbara]