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. 2016 Mar 31;11(3):e0152261.
doi: 10.1371/journal.pone.0152261. eCollection 2016.

The Effects of Anthropogenic Structures on Habitat Connectivity and the Potential Spread of Non-Native Invertebrate Species in the Offshore Environment

Rachel D Simons  1 , Henry M Page  2 , Susan Zaleski  3 , Robert Miller  2 , Jenifer E Dugan  2 , Donna M Schroeder  3 , Brandon Doheny  2
Affiliations

The Effects of Anthropogenic Structures on Habitat Connectivity and the Potential Spread of Non-Native Invertebrate Species in the Offshore Environment

Rachel D Simons et al. PLoS One. .

Abstract

Offshore structures provide habitat that could facilitate species range expansions and the introduction of non-native species into new geographic areas. Surveys of assemblages of seven offshore oil and gas platforms in the Santa Barbara Channel revealed a change in distribution of the non-native sessile invertebrate Watersipora subtorquata, a bryozoan with a planktonic larval duration (PLD) of 24 hours or less, from one platform in 2001 to four platforms in 2013. We use a three-dimensional biophysical model to assess whether larval dispersal via currents from harbors to platforms and among platforms is a plausible mechanism to explain the change in distribution of Watersipora and to predict potential spread to other platforms in the future. Hull fouling is another possible mechanism to explain the change in distribution of Watersipora. We find that larval dispersal via currents could account for the increase in distribution of Watersipora from one to four platforms and that Watersipora is unlikely to spread from these four platforms to additional platforms through larval dispersal. Our results also suggest that larvae with PLDs of 24 hours or less released from offshore platforms can attain much greater dispersal distances than larvae with PLDs of 24 hours or less released from nearshore habitat. We hypothesize that the enhanced dispersal distance of larvae released from offshore platforms is driven by a combination of the offshore hydrodynamic environment, larval behavior, and larval release above the seafloor.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Southern California Bight and model domain.
The study area, shown by the red box, is located in the eastern Santa Barbara Channel.
Fig 2
Fig 2. Locations of oil and gas platforms (circles) and harbors (squares).
Red symbols identify the locations where Watersipora was assumed present or observed in 2001 and 2013. Blue symbols identify the locations where Watersipora was present in 2013, but not in 2001. Green symbols identify the locations where Watersipora was not present in 2001 or 2013. SBH = Santa Barbara Harbor, VH = Ventura Harbor, CIH = Channel Islands Harbor, and PHH = Port Hueneme Harbor. Bathymetry contours in meters are shown by the black lines.
Fig 3
Fig 3. Percent cover of Watersipora at depths of 6 m, 12 m, and 18 m on platform Gilda in 2001 and 2013 and on platforms Gail, Gina, and Grace in 2013.
Watersipora was absent from platforms Gail, Gina, and Grace in 2001. The percent cover is displayed as mean values ± one standard error.
Fig 4
Fig 4. (a) PDDs averaged over 12 years for scenario 1. (b) PDDs averaged over 12 years for scenario 2.
White circles and squares identify the platforms and harbors respectively that are source sites, where particles are released. Black circles identify the platforms that are used only as destination sites.
Fig 5
Fig 5. Average dispersal distance of particles (km) versus PLD (hr) for platforms Gilda, Grace, Gina, and Gail.
PLD equates to the travel time of the particles.
Fig 6
Fig 6. Photographs of the same sample plot on platform Gail (a) in 2001 with plot dominated by barnacles and (b) in 2013 with plot dominated by Watersipora.
Sample plot was located on a conductor pipe at 9 m depth and measured 41 x 62 cm internal diameter (0.25 m2).
See this image and copyright information in PMC

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