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Succession in a Humboldt Bay Marine Fouling uccession in a Humboldt Bay Marine Fouling SCommunity: The Role of Exotic Species, Larval Settlement and Winter Storms Michael Boyle1, Dean Janiak2 and Sean Craig3 Image credits (Above) PEER, UC Berkeley; (pp. 222 and 230) ©2006 California Academy of Science; p. XXX Sean Craig. 1Kewalo Marine Laboratory, University of Hawaii, 41 Ahui Street, Honolulu, Hawaii 96813. 2Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, Connecticut 06340. 3Department of Biological Science, Humboldt State University, 1 Harpst Street, Arcata California 95521. Proceedings of the 2004 Humboldt Bay Symposium … 215 Abstract The initiation and pattern of succession in a marine “fouling” community was observed on a set of 20 black plastic panels suspended horizontally underneath the docks at Woodley Island Marina, Humboldt Bay, California from August 2001 to May 2003. The role of recruitment in the develop- ment of this community was examined using a second set of 20 panels which were scraped clean each month to allow new larvae to settle. Each month, both “undisturbed” and “settlement” panels were digitally photographed, and the percent cover of all species occupying at least 2% cover on each photo was recorded. Approximately 54 species of motile and sessile organisms were identified from these photos, of which roughly 35% were exotic species. The “undisturbed” fouling community was characterized by seasonal pulses of fast-growing, short-lived species (e.g., colonial tunicates) combined with the persistent accumulation of longer- lived, slower-growing species (e.g., mussels, sponges and tubiculous amphipods). The initial phases of development were dominated by colonial and solitary ascidians, bryozoans and hydroids, almost all of which were introduced to Humboldt Bay. Rainstorms, which brought fresh water and heavy sediment loads into the bay each winter, appeared to lead to the sudden disappearance of many of these suspension feeders. Over time mussels, sponges and tubiculous amphipods gradually increased in their abundance, perhaps due to their tolerance to heavy sediment loads. In conclusion, the “fouling” community in Humboldt Bay is heavily influenced by non-native taxa, many of which disappear following repeated winter storms, leading to sudden increases in free space. Concurrent increases in sedimentation after winter storms appear to select for slow-growing, tolerant species (e.g., mussels) that may form a “climax” community over a longer temporal scale. Myxicola infundibulum 216 … Boyle et al. Introduction In this study we report on preliminary The intentional or accidental introduction of data from an ongoing effort to monitor the “exotic” species by humans is one of the lead- settlement, growth and subsequent establish- ing causes of the biodiversity crisis (Wilcove et ment of “fouling” communities under the al. 1998). The release of larvae from the hulls Woodley Island Marina in Humboldt Bay, and ballast tanks of ships from distant ports, California. Because of Humboldt Bay’s loca- the dumping of algal “packing material” (with tion between San Francisco Bay and Coos Bay, associated species) when shipping live organ- Oregon, it receives substantial shipping traffic isms for human consumption, and the deliber- from fishing vessels traveling up and down the ate introduction of non-native shellfish species U.S. West Coast as well as larger, ocean-going for aquaculture have all contributed to an ac- vessels traveling from ports as far away as Japan. celerated homogenization of species in coastal A study by Boyd et al. (2002) has shown that marine habitats. As a result, estuarine habitats a substantial number (97) of exotic species such as San Francisco Bay (Carlton 1979) are currently reside within Humboldt Bay. These among the most threatened ecosystems in the exotics represent several major phyla ranging world (Carlton and Geller 1993). Further from vascular plants to fish. The largest num- knowledge of the mechanisms used by exotic bers of invasive species, however, are from vari- species to invade new locales, and whether par- ous invertebrate taxa including polychaetes (24 ticular types of communities repel or facilitate species), amphipods (20 species) and bryozoans their arrival, is clearly needed. (8 species). Some of the invasive species identi- The functional role that successful in- fied by Boyd et al. (2002) were likely to have vaders have on future ecosystem function in been introduced long ago, from dry ballast or marine habitats has been largely unexplored. “shingle” on wooden ships in the mid-1800s. Invasive species can potentially out-compete The most abundant salt marsh cordgrass, native populations and drive them to local ex- Spartina densiflora, was probably introduced in tinction. This may in turn affect higher trophic this way to Humboldt Bay from South America levels (e.g., commercial or sport fisheries), as sometime in the 1860s. Since its introduction, witnessed by the collapse of the anchovy fishery S. densiflora has become the dominant cordgrass in the Black Sea from the introduction of an species within Humboldt Bay. exotic comb jelly (Kideys 2002). Likewise, For the majority of introduced marine sessile marine invertebrates attached to ship species living in Humboldt Bay, little is known hulls, docks and other man-made structures about their natural role within the bay eco- often feed on suspended plankton during both system. Our work represents one of the first their larval and adult phases, and therefore attempts to record the presence of native and their growth and/or survivorship may reflect exotic species under docks in Humboldt Bay, changes in planktonic communities within a and to investigate their relative ecological role bay. Benthic-pelagic coupling of communities within fouling communities on man-made could have implications for commercial opera- structures within the bay. tions, such as the rearing of oysters for human Man-made structures are increasingly consumption. A baseline study of marine “foul- common elements along the shoreline of bays ing” communities, for example, might establish and estuaries and may even represent novel important biological indicators of early changes habitats for marine invertebrates (Connell in the “health” of a bay or estuary. 2000). Many of them, including pier pilings Proceedings of the 2004 Humboldt Bay Symposium … 217 and floating docks, have a luxuriant growth of nine (30–70 ft) floating docks oriented per- marine invertebrates on them. These systems pendicular to the shoreline. These large docks are relatively easy to study because of their extend into North Bay channel, one of two ease of access, and deployment of experiments channels connecting North Bay and Eureka and data-gathering methods do not require Slough with the entrance channel into Hum- SCUBA gear. Field experiments can address the boldt Bay. ongoing debate concerning factors governing Site Characteristics time-dependent patterns of succession, such as whether succession leads to alternative stable Precipitation patterns within Humboldt Bay states or “climax” communities (Sutherland are highly seasonal and rainfall amounts vary 1974; Petraitis and Dudgeon 2004). More from year-to-year (Figure 1). Water temperature applied concerns, including whether exotic spe- within the bay varies daily with tidal flow and cies affect local fisheries and other commercial cloud cover, and both seasonal and annual pat- activities, can be examined. terns are detectable with mean low values ~ 9.0 Specifically, the goals of this study are to: °C and mean highs ~ 18.0 °C. Intermittent sa- (1) describe the pattern of settlement and suc- linity measurements taken at panel-depth along cession in invertebrate “fouling” communities the dock ranged from a low of 19 ‰ during within Humboldt Bay, (2) evaluate the relative periods of high rainfall, to a high of ~ 34 ‰ importance of native and exotic species as space during high tides (data not shown). North Bay occupiers within this system, and (3) determine water surrounding Woodley Island was visibly the variability in community structure through turbid from sediment loading following periods time. of high rainfall, and often remained turbid for Long term goals include (1) identification days at a time, despite tidal flushing. of water-column factors that might influence Fouling panels community structure and perhaps reflect the Two sets of artificial fouling panels were de- “health” of the bay, (2) establish methods for ployed on rectangular frames constructed of the early detection of exotic species introduc- 1-in.-diameter polyvinyl chloride pipe (PVC). tions, and (3) field test recently developed Each frame measured 150 x 50 cm, and held theory on the mechanisms of succession in 20 (15 x 10 x 0.65 cm) ABS black plastic sheets epifaunal marine communities. (panels), individually engraved for identifica- Methods tion and attached with stainless steel bolts and wing nuts. The panel replicates were evenly Site spaced on each frame and randomly reattached Recruitment and community development of to the alternate frame after each sampling. fouling invertebrates were observed on artifi- A vertical section of the frame was affixed to cial plastic panels suspended below the south the dock side with galvanized pipe brackets breakwater dock at Woodley Island Marina, and screws; panels were oriented horizontally, Humboldt Bay, California. Because this marina face-down, and submerged directly beneath the receives heavy traffic from commercial
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