Non-Indigenous Marine Species of Humboldt Bay, California

Executive Summary
During this survey, we collected and identified 95 species that are possibly nonindigenous marine species (NIS) in Humboldt Bay. There were representatives from most major groups of organisms, ranging from vascular plants to fish. The largest number of non-indigenous species is found in various invertebrate groups, including polychaetes (24 species), amphipods (20 species), and bryozoa (8 species). Previous studies in Humboldt Bay (Barnhart et al. 1992) were not focused on identification and enumeration of introduced species, but many of the nonindigenous species found in this study have been reported in that earlier work.

A number of introduced species have been in Humboldt Bay for a long time, in some cases going back to the first settlement of the region by Europeans in the mid-1800s. Almost immediately following initial settlement, maritime trade began, with shipping of lumber and lumber products to all parts of the world. It appears that sometime in the 1860s, the most abundant plant of Humboldt Bay salt marshes, Spartina densiflora, was brought into the bay from South America, probably as shingle or dry ballast (Barnhart et al. 1992).

Intentional introductions have also accounted for a number of species that are numerous in the bay. All along the California coast, efforts to introduce and grow oysters were pursued beginning in the 1890s (Bonnot 1935). Following attempts to grow eastern oysters and European oysters that failed, Japanese oysters were successfully introduced into Humboldt Bay. A significant commercial aquaculture activity continues around the planting, growth, and harvesting of Japanese oysters in the bay. The cultch (seed oysters) for this species is now produced in Puget Sound and shipped in bags to Humboldt Bay. These shipments provide continuing opportunities for introductions from Puget Sound. We identified one species of algae, previously unreported from Humboldt Bay, which has probably arrived from Puget Sound in this manner. Other examples of species that were introduced intentionally include the Eastern soft shell clam (Mya arenaria) and the Japanese cockle (Venerupis phillippinarum).

As intentional introductions took place, unintentional introductions also occurred. Early methods of transporting marine organisms from one area to another might take several days and packing in wet algae was a common way to retard desiccation. Numerous small juveniles of other species or species inconspicuous by their size might be concealed among the algae or attached to blades. In this manner, small polychaetes, species attached to algae blades, and small crustaceans were 3 inadvertently introduced into the bay as the packing material was disposed of by tossing it into bay waters.

We included in this study species that are clearly the result of introductions and those that have been characterized as cryptogenic (Cohen and Carlton 1995; Carlton 1996). Cryptogenic species are organisms that appear to be widespread in bays, ports, and estuaries of the world and cannot be identified as definitely native or exotic to a particular region. Carlton (1996) has proposed that many of these species are the result of maritime trade and other human activity that go back hundreds of years. Some cryptogenic species occurrences are the result of intentional or unintentional introductions that are lost in time and history. Others are of uncertain relationship to species that have a wide range of occurrence but may be genetically distinct in parts of their range. In yet others, their present day occurrence is merely an indication of their capacity to adapt to a wide range of environmental conditions. Of the 95 species that we identified as possible introductions to Humboldt Bay, 23 have been classified as cryptogenic.

We compared the occurrence of introduced species in Humboldt Bay to their occurrence mentioned in previous studies done along the Pacific coast of North America (Cohen and Carlton 1995; Ruiz et al. 2000). In particular, we compared the reported occurrence of species in San Francisco Bay to the south and in Coos Bay, Oregon to the north. Of the 95 species in Humboldt Bay, 31 have been reported from all three bays. There are 23 species that are found in San Francisco Bay and Humboldt Bay. There were no species that were found to co-occur only in Coos Bay and in Humboldt Bay. Twenty-seven of the introduced species we report are found only in Humboldt Bay. These data on co-occurrence suggest that San Francisco Bay could be an important source area for introductions to Humboldt Bay, a finding consistent with ship and small boat traffic moving between these two locations. The number of species that appear to be found only in Humboldt Bay (27) suggests that there may be factors in the nature of shipping or other human influences that are unique to the bay.

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