Cerithidea

Abstract: We conducted a Before-After-Control-Impact (BACI) study using larval digeneans infecting the California horn snail, Cerithidea californica, to evaluate the success of an ecological restoration project at Carpinteria Salt Marsh in California, USA. Digenean trematodes are parasites with complex life cycles requiring birds and other vertebrates as final hosts. We tested two hypotheses for prevalence and species richness of larval trematodes in C. californica: (1) prior to the restoration, sites to be restored would have lower trematode prevalence and species richness relative to unimpacted control sites, and (2) that these differences would diminish after restoration. The sites to be restored were initially degraded for trematode species. They had a mean trematode prevalence (12%) and species richness (4.5 species) that were lower than control sites (28% trematode prevalence and 7 species). Despite the differences in prevalence, the proportional representation of each trematode species in the total community...

Abstract: Experimental field and laboratory studies indicate that Cerithidea californica, a native mud snail, is restricted to only a portion of its normal habitat range in San Francisco Bay as a result of direct interactions with an introduced ecological equivalent, Ilyanassa obsoleta. The native snail typically inhabits marsh pans, tidal creeks and mudflats in estuaries along the Pacific coast. However, in San Francisco Bay it is confined to pans for most of the year, while the non-native snail inhabits the creeks and mudflats. Experiments and field monitoring demonstrate that this abnormal distribution pattern is caused by 1) interference competition for space in the form of an adult-adult behavioral avoidance by C. californica in the presence of invading I. obsoleta, and 2) predation by I. obsoleta on the eggs and juveniles of C. californica. The competitive exclusion of C. californica by I. obsoleta has not led to the extinction of the native snail because of the existence of a refuge for C. californica in pan habitats, beyond the physiological tolerances of I. obsoleta. As a consequence of the seasonal migrations of both species and changes in abiotic factors along the habitat gradient, repeated competitive displacements, rather than a one-time competitive exclusion, are observed between these two species. This is the first documented case of the competitive displacement of an endemic marine intertidal species by an introduced ecological equivalent.

Abstract: Historical or recent extinctions (here called neoextinctions) are rarely reported among marine and estuarine invertebrates. Four case histories of neoextinctions, using gastropod mollusks (snails) as examples, are reviewed: the periwinkle Littoraria flammea (last collected < 1840 in China), the rocky shore limpet “Colliselld” edmitchelli (1861/3 in southern California), the eelgrass limpet Lottia alveus (1929 in Maine), and the marsh horn snail Cerithidea fuscata (1935, southern California) are all probably extinct. The central element in the demise of all four species may have been a vulnerable, extinguishable habitat. Three considerations suggest that neoextinctions among marine invertebrates have been generally overlooked: 1), hundreds of taxa have not been reported since the 18th and 19th centuries (these are treated by systematists as either unrecognizable, rare, or synonyms of known species); 2), species may have become extinct prior to their description; and 3), there has been a precipitous decline in systematics, biogeography, and natural history at the end of the 20th century—leaving too few workers to tell the story of neoextinction in the ocean. Searches in the literature and museums for overlooked neoextinctions would fruitfully focus on species reported from highly impacted, urbanized coastal habitats—saltmarshes, estuaries, lagoons, seagrass communities, and supralittoral (maritime) zones—habitats now largely obliterated on most coastal margins of the world.