Heceta Bank
The unique bathymetric features and seasonal circulation within the bank provides habitat for a diversity of economically-important fish species.
During the last glacial low stand, approximately 15,000–20,000 years ago, prehistoric humans migrated from northeastern Asia into North America.
The presence of these old rocks, as well as a series of folds and faults underneath the banks, provide evidence for this subduction and uplift phenomenon.
[2] The bank consists of a north and south crest, which are shoals where the bathymetry is distinctly shallower than the surrounding seafloor (Fig.
In shallow depths (<100 m), the bank is composed primarily of rock and boulder outcrops, which are separated by small valley-like features.
[5] Furthermore, the irregularity in topography, caused by movement due to crustal uplift and transform faults, also allows for the release of methane gas from the sediment, which occurs from <100 to 600 m depth.
As explored below, the topographic variations unique to Heceta Bank significantly influence how these wind-driven seasonal changes affect this region.
Relatively less dense water on the outer southern part of Heceta Bank is also present in the bottom density field.
[8] Here, approximately 0.5 Sverdrup of the cold upwelled water is exported out into the deep ocean as the jet cannot follow the continental shelf's abrupt turn back towards the coastline.
[12][16] The amount of materials lost into the deep ocean depends on the velocity of the jet, which is largely determined by the strength of the wind-driven currents.
[14] There is much room for future research as current understanding of oceanographic dynamics associated with Heceta Bank is growing, but limited.
[17] The Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) program has also collected data through moorings and played a large role in expanding knowledge of the Oregon upwelling system of the inner shelf.
[21] Microbial mats are generally inhabited by chemosynthetic organisms, Beggiatoa and Thiothrix filamentous bacteria, and Methanogen, a group of anaerobic archaea.
[6] The origin of these aragonite crystals is supported by the isotopic composition of 13C measured at various locations around the Heceta Bank which show a negative delta value.
[24] The occurrence of hypoxia in open coast upwelling systems reflects ocean conditions that control the delivery of O2-deficient and nutrient-rich deep water onto continental shelves.
[25] The mid-shelf location in the sheltered region of the Heceta Bank complex is especially vulnerable to O2-deficient events due to the large shelf width, as well as weak currents and high productivity.
[27] Since 2002, seasonal hypoxia has been observed annually to extend over an area >820 km2 along the Oregon coastal shelf region in the summer months.
Samples of dissolved oxygen (DO) point to the fact that in the summer months, bottom waters at Heceta Head line (44.0 N, respectively)[25] were consistently hypoxic, or falling between 43–64 micromolar (μM) of O2.
[26] In August 2006, surveys along the central Oregon coast transect lines revealed the complete absence of all fish from rocky reefs.
[30] In addition to increased primary production, respiration can further exacerbate O2 deficits as bottom boundary water transits shoreward over the shelf.
[31] In July 2003, high (Chl-a) values of 43 mg/L were directly sampled from an inshore shelf station on the Heceta Head line.
[33] Denitrification appears to be particularly important in shelf sediments in the California current system, due to the seasonally hypoxic bottom waters[28] that typically emerge during summer upwelling.
Further, denitrification in the Heceta Bank region by bacteria frees up O2 to be utilized by other organisms like rockfish and other demersal fish species.
Citharichthys sordidus Merluccius productus Glyptocephalus zachirus Eopsetta jordani Sebastes elongatus Microstomus pacificus Sebastes crameri Radulinus asprellus Lyopsetta exilis Bathyagonus pentacanthus Sebastes diploproa Lycodopsis pacificus Poroclinus rothrocki Engraulis mordax Xeneretmus latifrons Thaleichthys pacificus Eptatretus stoutii Cymatogaster aggregata Allosmerus elongatus Microgadus proximus Parophrys vetulus Icelinus borealis Citharichthys stigmaeus The most abundant species in shallower areas is the Pacific sanddab, while in deeper areas the slender sole is the most abundant.
Moreover, the Shannon diversity index (H) varies between 0.7 and 2.5, showing the same pattern as the number of species along different depths (higher in deeper areas).
Moreover, models have shown that larvae have higher survival rates if they are released into this region, which highlights the importance of Heceta Bank for the successful recruitment of fish populations.
[45] Heceta Bank is considered a persistent biological hotspot, in terms of biomass and nekton species diversity, in the northern California Current.
[46] The most important environmental parameters provoking this feature are sea-surface temperature, salinity, and density, indicating that the mechanisms of the hotspot are related to the flow through the region and differing patterns of circulation.
This last point means that associations between species and their functional redundancy are important factors in the high biomass and nekton diversity in this area.
[49] On other side, studies have shown that jellyfish have negative effects on nekton species due to competition and predation on fish larvae.
