The deep freeze...and then came the thaw

By Quinn Whitesall, Habitat Restoration Technician, American Littoral Society

​The deep freeze that took place in Delaware Bay this month created some of the harshest conditions our oyster reefs have ever experienced. For over a week, solid ice covered portions of the Bay and the shoreline, and in some places the ice was over three feet thick. We wanted to know how the ice and tide would impact our intertidal reefs and one of the best spots to assess these effects was at Veterans Reef located slightly offshore Reeds Beach. Shane, the Delaware Bay Habitat Restoration Coordinator pictured in the photo below, and I, arrived at Reeds Beach where we were greeted by a landscape that was more reminiscent of the treeless Arctic tundra rather than that of the open water of the Delaware Bay. We were shocked that the reef was not visible at all and feared the worst for our oysters and the reef itself. We decided we would need to come back at low tide after the thaw and assess any damage to this very important ecological community.

Shane attempting to locate the reef under a thick blanket of ice.

Once temperatures rose and the ice melted away into memory, I once again took a trip to Veterans Reef to re-assess possible damage from the ice. Overall, the reef structure was intact which further provided evidence on the heightened resiliency of whelk shell when used as a foundation for intertidal reefs and the importance of interstitial space and the shape of the shell, not just for providing habitat or species refugia, but to possibly combat impact of ice with its asymmetrical surface. Condition of the reef and the health of the oyster community appeared to relatively unaffected by the ice and current observations were similar to those of our last visual inspection from the fall. A few reef segments appeared to be unaffected at all. 

Intact reef block, completely unaffected by ice movement.

Out of 23 reef segments at Veterans Reef, only one seemed to have been impacted. Quite a few bags had come loose, were dislodged, and were shifted forward, most likely a result of large ice blocks moving with the tide.

Shifted and displaced shell bags, likely a result of ice movement with tides.

​This was easily repairable. The outer reef was completely intact with no shell bag movement most likely because it was never exposed due to depth of water versus depth of ice.

Along some segments of the reef, gapers, dead, open oysters with tissue inside, were spotted. We have identified gapers on the reefs in the past, but none were present during our fall observation. Some oysters, which were more exposed to the ice and located on the outer surface of the whelk foundation, were completely crushed, likely a result of shifting ice. However, oysters that were more sheltered between shell bags were not affected at all. Overall, it would appear that oyster mortality was rather low and intertidal oyster reefs in Delaware Bay can combat and tolerate impacts associated with ice. There will be some loss but that is understandable. This was evident with other sessile reef inhabitants, like the ribbed mussel and barnacle.

Intact ribbed mussels sheltered under oysters.

Barnacles exposed to the elements, unaffected by the ice.

Species that were more sheltered by the reef or whelk shell, were not affected, however those same species that were more exposed to the elements, like the thin-shelled ribbed mussel, were crushed by ice movement. Oddly enough, the barnacles faired well and did not seem affected at all regardless of where they were on the reef which again, like the whelk, could be a function of their asymmetrical shape. Another visual assessment will take place this spring, stay tuned!