Caprellid Amphipods Return to Docks

Caprella mutica back in Provincetown after Hurricane Irene

After Hurricane Irene passed through New England in late August, 2011, much of the growth on the docks at MacMillan Wharf was washed away, particularly delicate algae and invertebrates. One species that I failed to see in the following days and month was the amphipod Caprella mutica, also called the Japanese skeleton shrimp, which was observed fairly commonly on the docks earlier in 2011.  In 2012, Caprella had not re-established itself during my summer monitoring, but this year, groups of Caprella were found during July and August at several locations on the docks.   Most of the caprellids were attached to bushy hydroids and were not commonly observed on other filamentous (e.g., algae) or bushy species (e.g., bryozoa).   

My observations motivated a visit to the CZM MORIS website where species maps can be created for MIS species in previous years.  Confirming my previous observations, sighting of Caprella mutica decreased at different moriting sites from Narragansett Bay to Wells, Maine.   

 Groups of Caprella mutica living on branched hydroids

 

Populations of Caprella attached by their hind legs crawl over branched hydroids. Larger males and a few smaller females with mid-body brooding pouches can be identified. 

  

Caprella mutica MIMIC sightings in 2011 and 2012     

MORIS website-generated map of the locations where populations of Caprella mutica were found during invasive species monitoring in 2011 (top) and 2012 (bottom).  Caprella sightings decreased by about one-third.   No reports were made in 2012 in Narragansett Bay, Buzzards Bay, or Cape Cod Bay, and fewer sightings were reported in Salem Sound.  Website: MORIS: CZM’s Online Mapping Tool.  Credit: "Massachusetts Office of Coastal Zone Management (CZM), Executive Office of Energy and Environmental Affairs."

 

LINKS:

Harbor Watch:  Coastwatch 2012

"Caprella mutica (Caprellid amphipod a.k.a. skeleton shrimp) - Very common living on algae and bryozoa. These small amphipods look and act like miniature preying mantis.  They hold tight to surfaces and do not "swim around" like typical amphipods and shrimp." 

Pappal, A, Pederson, J, and Smith JP. Marine Invaders in the Northeast. Rapid Assessment Survey of Non-native and Native Marine Species of Floating Dock Communities.
Massachusetts Office of Coastal Zone Management (CZM): Home page
CZM - Aquatic Invasive Species (AIS) Program

MORIS: CZM’s Online Mapping Tool
WILD Shores of Singapore: Workshop on Bryozoans and Hydroids: 29 April- 4 May, 2013.  "Tiny skeleton shrimps are commonly seen on some hydroids!"