1. Long-term Colonization Of A Subarctic Artificial Reef System In Whittier, Alaska
Charlotte Levy1 & Eloise Brown2
1 Oregon State University, Department of Fisheries and Wildlife
2 Alaska Pacific University, Department of Environmental Science
Background
Increased coastal development poses a potential threat to the nearshore habitats. Artificial reefs (AR) are becoming increasingly popular for mitigating habitat loss. Although well studied in tropical and temperate locations, less is known about AR efficacy in high latitude locations. Since AR’s are heavily influenced by ecological factors specific to their environment, these studies may not apply to sites in subarctic Alaska. An AR was deployed in Whittier in 2006 as part of a mitigation settlement for Alaska Marine Lines facility expansion. Surveys conducted the following year suggested the artificial reef assemblages resembled those of adjacent natural reefs, however, long-term surveying of community composition is necessary to allow for the establishment of a climax community. This research is part of an ongoing survey of the AR in Whittier to assess how the demersal fish and macroalgae assemblages have changed since Preliminary results are presented here from summer surveys conducted in June-August 2016.
Figure 1. Map of study location in Smitty’s Cove showing the 6 different survey plots labeled by structure type and the location of Whittier within Prince William Sound.
Objectives
Demersal fish and macroalgae assemblages were quantified at two types of artificial reef (AR) structures: Fish Havens (FH) and Reef Balls (RB) in Whittier and compared to former assemblages present in 2007 at both AR and natural reef (NR) sites.
Research Questions
How have artificial reef fish and macroalgae assemblages changed from 2007 to 2016?
How do these assemblages compare to natural reef assemblages from 2007?
Are there any significant differences in these assemblages between the two types of structures?
Methods
Study Location
Smitty’s Cove, Whittier, Prince William Sound (Figure 1).
N=6 plots containing AR 30 structures each, for a total of 180 structures.
2 reef types (n=3 Fish Havens and n=3 Reef Balls) for a total of 90 of each type (FH and RB).
Sampling Design
Bi-weekly dive surveys June-November 2016.
Demersal fish density was calculated from abundance estimated in-situ via 30 m transects (60 m2; n=1 per plot)
Macroalgae percent cover was estimated in-situ with 0.25 m2 quadrats (n≥6 per plot)
Species richness was calculated as the number of species normalized per unit area.
Sampling is still in progress for 2016.
Statistical Analysis
Means and standard deviations were averaged across n=6 and n=3 reef-types in 2016 and compared to data from Reynolds (2007).
Future multivariate analysis will further quantify changes in community composition and address environmental variables such as temperature, depth and visibility that may explain variability in the model (MANOVA across periods, reef types and years). Power analyses will determine the model’s ability to detect errors (Zar).
Figure 2. Comparison of macroalgae % cover between artificial reefs in 2007, artificial reefs in and natural reefs in 2007.
Table 1. Species and common names.
Figure 3. Comparison of fish density between artificial reefs in 2007, artificial reefs in and natural reefs in 2007.
Preliminary Results
There is an increase of Sebastes spp. species present, an absence of P. laeta and M. proximus, the addition of S. punctatus, a change in greenling from H. stelleri to H. decagrammus, and a change in sculpin from H. hemilepidotus to M. polyacanthocephalus (Figure 2).
Preliminary results appear to indicate a change in the dominant macroalgae from Laminaria to Agarum. (Figure 3).
There is an increase in macroalgae species present, with all species being new additions except Saccharina spp.
Initial results from summer sampling (June-August 2016) indicate no significant difference between reef structure types for both fish (Figure 3) and macroalgae (Figure 4) richness.
Conclusions
The artificial reef as a whole not only resembles the natural reefs in 2007 but have surpassed them in terms of species composition and habitat complexity .
There is a change in the dominant macroalgae from Laminaria saccharina to Agarum clathratum similar to adjacent natural reefs.
Fish Havens have a higher fish species richness than reef balls despite increased habitat complexity at reef balls. This could indicate these species have a preference of the high-relief provided by the height of Reef Havens over macroalgae.
Figure 4. Comparison of fish density and macroalgae species richness by reef structure type.
Acknowledgements
Funding support for this project came from At-Sea Processors’ Association Pollock Conservation Consortium , E.R. Jackman Scholarship
Support Award, Izma Bailey Conser Memorial Scholarship and NOAA Fisheries. I would also like to thank Erika Ammann (NOAA) and Selina
Heppell (OSU) for their guidance, and my dive team for the countless hours of assistance with field work.