Invasion History

First Non-native North American Tidal Record: 2006
First Non-native West Coast Tidal Record: 2006
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Conopeum chesapeakensis was described by Banta et al. (1995) from the Rhode River, Maryland, Chesapeake Bay, from specimens collected in 1993. This bryozoan was collected earlier, as Membranipora membranacea by Osburn (1944), from Annapolis to the mouth of the Potomac, found on seagrass Ruppia maritima and as an unidentified Membranipora sp. in the Potomac and James Rivers (Dudley 1973).

The extent of its range on the East Coast is not known, but it has been collected in Tampa Bay, the St. Johns River, Florida, and Great Bay, New Hampshire (Ruiz et al., unpublished data). On the West Coast, it was found on the hulls of obsolete cargo ships stored in brackish waters in the San Francisco estuary. In 2006, two of these ships were towed to Brownsville, Texas, for dismantling, a voyage of 5,000 nautical miles through the Panama Canal. Conopeum chesapeakensis remained abundant and alive on the hulls of the ships (Davidson et al. 2008a).

North American Invasion History:

Invasion History on the West Coast:

In 2006, Conopeum chesapeakensis, as Membranipora chesapeakensis, was found to cover large areas of the hulls of two obsolete cargo ships of the US Ready Reserve Fleet, moored in Suisun Bay, in the inner San Francisco Estuary. The ships had been moored for more than 10 years, in low-salinity water (0-22 PSU) to minimize fouling and corrosion. The date of establishment of C. chesapeakensis in San Francisco Bay is not known. Confusion with other species of Membranipora and Conopeum make it likely that this species has been previously overlooked. It was found to be a common fouling organism on recreational boats at several marinas in San Francisco Bay, including the low-salinity harbor of Benicia (Davidson et al. 2010). Conopeum chesapeakensis is abundant in low-salinity habitats in the San Francisco estuary (Jimenez et al. 2018). In 2015, it was collected from Chinook, Washington on the Columbia River (Ruiz et al, unpublished data(.


The colonies of Conopeum chesapeakensis are tan-colored, erect, branching, tubular structures, with the branches widening into flat ribbons near their tips. Branches of the colony are cylindrical, comprised of four or more rows of zooids, and arise from flat fronds comprised of two layers. The cylindrical portion expands along its length, becoming a two-layered ribbon or frond, with 20 or more rows of zooids. The colony is composed of autozooids, with no specialized forms. The colony is lightly calcified. Autozooids are arranged in quincunxes (patterns like the five in dice), with the zooids in each row offset from its neighbors to the side. The zooids of the two layers share their basal cuticle and develop in unison, but are also offset, so that the lateral wall between two zooids in a row on one side of the colony lies adjacent to the midpoint of a zooid on the opposite side. There are no spines, ovicells, or avicularia. The polypide has 14 tentacles. This bryozoan is characteristic of hard substrates and seagrasses in brackish water (description from: Banta et al. 1995; Winston and Hayward 2012).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Bryozoa
Class:   Gymnolaemata
Order:   Cheilostomata
Suborder:   Anasca
Family:   Membraniporidae
Genus:   Conopeum
Species:   chesapeakensis


Membranipora chesapeakensis (Winston and Hayward 2012, )

Potentially Misidentified Species

Membranipora membranacea
Conopeum chesapeakensis was originally identified as this species (Osburn 1944; Dudley 1973).



Life History- Conopeum chesapeakensis is an erect, lightly calcified bryozoan, composed of many individual zooids. The zooids feed by extending the ciliated tentacles of the lophophore as a funnel, creating a current, and driving food particles into their mouths. The food is guided along the tentacles and through the pharynx by the cilia. Larger food particles can be moved or captured by flicking or contracting the tentacles (Barnes 1983). Larvae of C. chesapeakensis are planktotrophic, and probably have a long planktonic period (Banta et al. 1995). Larvae settle on a substrate and metamorphose into the first zooid of a colony, an ancestrula (Barnes 1983).

Ecology-Conopeum chesapeakensis is known from seagrass beds, oyster beds, pilings, oyster shells and ship hulls (Osburn 1944; Dudley 1973; Banta et al. 1995; Davidson et al. 2008a). It appears to be most abundant in brackish water (Banta et al. 1995).


Phytplankton, detritus

Trophic Status:

Suspension Feeder



General HabitatCoarse Woody DebrisNone
General HabitatGrass BedNone
General HabitatOyster ReefNone
General HabitatVessel HullNone
General HabitatMarinas & DocksNone
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Life History

Tolerances and Life History Parameters

Minimum Salinity (‰)4Field salinity (Banta et al. 1995)
Maximum Salinity (‰)37Field salinity, surviving on ships towed to Brownsville, Texas
Broad Temperature RangeNonecold-temperate-Subtropical
Broad Salinity RangeNoneOligohaline-Mesohaline

General Impacts

Conopeum chesapeakensis formed the bulk of a dense fouling matrix on the hulls of obsolete ships stored in Suisun Bay, California (Davidson et al. 2008a). Attempts have been made to reduce the transport of fouling organisms by underwater cleaning of the hulls of obsolete ships stored in the James River, Virginia. Some colonies of C. chesapeakensis survived the cleaning (Davidson et al. 2008b). Conopeum chesapeakensis also occurred on the hulls of recreational boats in San Francisco Bay (Davidson et al. 2008a; Davidson et al. 2010). However, the extent to which it affects recreational boating and commercial shipping is unknown.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NA-ET3 Cape Cod to Cape Hatteras 1993 Native Estab
NEP-V Northern California to Mid Channel Islands 2006 Def Estab
CAR-VII Cape Hatteras to Mid-East Florida 0 Native Estab
P090 San Francisco Bay 2006 Def Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 0 Native Estab
NA-ET2 Bay of Fundy to Cape Cod 0 Native Estab
P260 Columbia River 2015 Def Estab
NEP-IV Puget Sound to Northern California 2015 Def Estab
B-X None 2024 Def Estab
B-IX None 2024 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
767840 Ruiz et al., 2015 2011 2011-09-16 Loch Lomond Marina, San Francisco Bay, CA, California, USA Def 37.9724 -122.4796
767894 Ruiz et al., 2015 2011 2011-09-27 Vallejo Marina, San Francisco Bay, CA, California, USA Def 38.1086 -122.2694
767942 Ruiz et al., 2015 2011 2011-09-28 Glen Cove Marina, San Francisco Bay, CA, California, USA Def 38.0663 -122.2130
767956 Ruiz et al., 2015 2011 2011-09-28 Benicia Marina, San Francisco Bay, CA, California, USA Def 38.0453 -122.1561
768214 Ruiz et al., 2015 2012 2012-09-10 Pittsburg Marina, San Francisco Bay, CA, California, USA Def 38.0346 -121.8829


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Davidson, Ian C.; McCann, Linda D.; Sytsma, Mark D; Ruiz, Gregory M. (2008b) Interrupting a multi-species bioinvasion vector: The efficacy of in-water cleaning for removing biofouling on obsolete vessels., Marine Pollution Bulletin 56: 1538-1544

Davidson, Ian C.; McCann, Linda D.; Fofonoff, Paul W.; Sytsma, Mark D.; Ruiz, Gregory M. (2008a) The potential for hull-mediated species transfers by obsolete ships on their final voyages., Diversity and Distributions 14(3): 518 -529

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