Black Rockfish S. Melanops, While Spatially-Mapped and Observed in Some of the Same Schools and Locations As Blue Rockfish, Were
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Part One: Survey of Punta Gorda Ecological Reserve Black rockfish S. melanops, while spatially-mapped and observed in some of the same schools and locations as blue rockfish, were more widely distrib- uted in areas also occupied by kelp greenling H. decagrammus and canary rockfish S. pinniger (Figure 26a–c). Cluster analyses by habitat and relief suggest that these three species are more closely associated to each other than to blue rockfish S. mystinus (Figures 22, 23, 24, and 25). While they do cluster together, each has a unique habitat preference. All three were found over Rocksand1 and Rocksand3 substrates, however kelp greenling showed a preference for low-relief habitats common to canary rockfish (“boulderlow” and “rocklow”), differing from black rockfish, which shares blue rockfish’s preference for “rockhigh” habitat. Given these differences, spatial distribution patterns reveal that low-relief “generalists” common to areas with both sand and rock, such as kelp greenling, are more pervasive at PGER than canary rockfish, which were found in “rock-sand” interface areas. Our visual observa- tions and orientation analysis, which indicate that canary rockfish are in contact with or near sand substrate adjacent to reefs, validates the results from both cluster analysis and mapped distributions. Macroinvertebrates PGER is dominated by filtering organisms that are able to withstand a high particulate load and a strong, current-dominated environment. Colonial suspension feeders such as cnidarians, sponges, and tunicates were the most numerous organisms on hard substrates. Other organisms observed in moder- ate numbers at PGER include predatory and filter-feeding sea stars and the deposit-feeding sea cucumber. These organisms must respond to a variety of abiotic and biotic environmental influences in order to endure in this harsh environment. Abiotic factors may include water flow (Harris 1991), seston flux (Lesser, et al 1994), and sand inundation (McQuaid and Dower 1990, Antonio 1986). Biotic factors may include predation (Duggins 1983), prey availability (Annett and Pierotti 1984), competition (Chadwick 1991), and community composition (Anthony 1997). Psammophilic macroinvertabrates: Greater than 50% (22/42) of the species observed was found at least once on sand. This indicates that most of the species present at PGER were tolerant of sand (e.g., sessile species—the sponge, P. pachymastia) or would move over sand (e.g., motile species—the sea star, H. leviuscula). However, several sessile species had much higher densities in areas of strong sand movement and could be considered psammophilic. These species include the sponges P. pachymastia and T. aurantia. Cnidarians included the unidentified gorgonian and the urticina, U. piscivora, and chordates such as the tunicates P. planum and S. montereyensis. Sandy sites may serve as refuges that protect these species from potential competitors or predators (Antonio 1986). The sea cucumber P. californicus, and the leather star D. imbricata, were found on sand ranging from 9–28% of Karpov 48 Part One: Survey of Punta Gorda Ecological Reserve the time. Comparatively, the urchin S. franciscanus was never seen on sand (0%) and Stimpson’s sunstar Solaster stimpsonii was only seen twice on sand (2 observations). The few invertebrates that were found out on the sand habitat were in close proximity to areas of rocky reef (Figures 35b, c and 36b). This associa- tion between sand epifauna and reef is likely due to the increased sand stabil- ity created by the rocks’ deflection of ocean currents and waves. In addition, areas of sand which had ripples <10 cm high had higher densities of inverte- brate species than area with sand ripples >10 cm. For example, the sea pen Pstilosarcus gurneyi, which occurred in very low densities, was only found in sand habitat with small ripples and in areas of sand-impacted bedrock that had high sand cover. Large volumes of sand have apparently moved through PGER’s deeper waters, impacting the boundaries of the rocky reef. Only high-relief rock outcroppings and boulders remained exposed and unworn. Within areas of higher-relief rock, fine sand and detritus filled the cracks, crevices, and depres- sions. Low-relief rock < 1m high dominates most of the central reef at PGER. The outer boundaries of this reef area were often covered by sand; only the tops of the rocks and boulders lacked some degree of coverage. Organisms living on these rock tops were inundated by sand. Examples of commonly- identified organisms in this habitat were the sponge P. pachymastia and the unidentified gorgonian. Moderate-relief rock from 1 to 3 m high was some- what to very sparsely covered by sand and represented the second most abundant deep-water habitat type within the reserve. Commonly identified species found in this habitat included the following: sponges A. erathacus, C. arb, Halichondria sp., and T. aurantia; the hydroids Aglaophenia sp., G. annulata, and Plumularia sp.; the anthozoans C. californica, E. scotinus, and U. piscivora; the scallop C. giganteum; the barnacle B. nubilus; the asteroids D. imbricata, H. leviuscula, Mediaster aequalis, P. brevispinus, and Pycnopodia helianthoides; and the tunicates Aplidium sp., Cystodytes lobatus, and P. planum. High-relief rock represented the smallest proportion of deep-water habitat within PGER, but it contained some of the most diverse invertebrate assem- blages. These habitats were most common within the boundaries of the rocky reef, and consisted of rocky outcroppings that were greater than 3 m high. Commonly-identified species included the above mentioned species found in the exposed low-relief Bedrock and Boulder habitat with the following addi- tions: the hydrocorals S. californicus and Stylantheca porphyra; the anemone M. giganteum; the sea cucumber, P. californicus; and the sea stars S. stimpsonii and O. koehleri. Karpov 49 Part One: Survey of Punta Gorda Ecological Reserve Comparison Few published studies pertain to the subtidal ecology of Northern California. of PGER with Those that do are in areas far to the north and south of PGER. To the north, Previously the only published reports are Areas of Special Biological Significance (ASBS) Examined reports on the Kelp Beds at Trinidad Bay ASBS (Anonymous 1979c) and Areas of Redwood National Park ASBS (Anonymous 1981b). To the south, published ASBS descriptions of the Pygmy Forest Ecological Staircase ASBS (Anony- Special mous 1981a), the Kelp Beds at Saunders Reef ASBS (Anonymous 1980), Biological Gerstle Cove ASBS (Anonymous 1979a), and Bodega Marine Life Refuge Significance ASBS (Anonymous 1979a) are representative of the few subtidal descriptions (ASBS) in south of Punta Gorda. These ASBS reports are predominantly anecdotal, with Sonoma, varying detail and little temporal information. Waters deeper than 12m were Mendocino, not described in much detail, if at all. The lack of well-described subtidal Humboldt and habitats makes comparisons between ASBS sites difficult and subject to Del Norte interpretation. Therefore, we cannot make comparisons between the deep subtidal areas of PGER and the Areas listed above. The following compari- Counties sons of ASBS reports and PGER focus on descriptions of the habitat types observed and similarities in the biota found in waters shallower than 18 m (Table 25). Differences are examined based on species of management impor- tance. Kelp beds at Trinidad Bay ASBS To the north, Trinidad Head is the only major headland between Cape Mendocino and Point St. George (Figure 1). The sheltering effects of Trinidad Head place Trinidad Bay proper in the lee of northwesterly swell, which continues throughout most of the year. Due to the sheltering effects of the headland, the bay proper is distinctly different from most sites studied in Northern California. Invertebrates found within Trinidad Bay are apparently representative of the types of species found in deeper waters with higher rates of deposition (Table 25). The western section of Trinidad Head is highly exposed to northwesterly swell, as are other Northern California ASBS sites. The subtidal waters are strongly influenced by local rivers to the south, which discharge large amounts of fresh water and eroded materials. Waves from the south, along with local currents, trap much of the depositional material in the bay, reducing the photic zone throughout the area. The photic zone extends to a depth of about 6 m as indicated by algal species such as the bull kelp N. luetkeana, which is common in protected areas on rock tops that ascend into the photic zone. Subtidal biota are highly influenced by wave exposure and sediment deposition. The wave-protected areas of the bay proper are composed of a sand/silt bottom with sheer-faced sea stacks and boulder piles. Wave energy is reduced to a moderate surge that scours the bases of rocky oucroppings. The rocky habitats are highly depositional and contain many invertebrate species not found in the more exposed areas of the bay. Examples of invertebrates include the brachiopod Terebratalia transversa and the tunicate Chelyosoma productum. Karpov 50 Part One: Survey of Punta Gorda Ecological Reserve Wave exposed areas of Trinidad Bay are composed of sand bottom with sheer- faced sea stacks, which rise nearly to or above the surface of the water, and boulder piles near the base of the sea stacks. The sand habitat is reported to be highly turbid with a mixture of infaunal and epifaunal species. Epifaunal species were associated with areas of semi-stable sand and included the olive snail Olivella biplicata, the Dungeness crab Cancer magister, and the sand dollar Dendraster excentricus. The rocky substrate was dominated by filter feeding invertebrates such as the hydroid Aglaophenia sp., the sea strawberry G. rubiformis, the anemone M. senile, the barnacle B. crenatus, and the sea cucum- ber Eupentacta quinquessemita which formed large aggregations on the lee side of sheer-faced rocks. Few urchins or abalone were found in Trinidad Bay. Redwood National Park ASBS Moving farther north, Redwood National Park is located in northern Humboldt county and southern Del Norte county (Figure 1).