Northern Strait Research Articles

Understanding the invasion of the macroalga Rugulopteryx okamurae (Ochrophyta) in the northern Alboran Sea through the use of biogeographic models

Rugulopteryx okamurae is a brown alga native to the northwestern Pacific and invasive elsewhere. It was first sighted in the southern Strait of Gibraltar in 2015, expanded to the northern Strait of Gibraltar in 2016, and had covered most of the northern Alboran Sea by 2021. Understanding the factors that may explain its different phases of colonisation is crucial for developing mitigation and control measures. We modelled the yearly distribution of R. okamurae in the northern Alboran Sea from 2016 to 2021 using the favourability function, which produces commensurable biogeographic models despite variations in species prevalence across years. This function also allows the use of fuzzy logic operations to combine previous environmental models based on different explanatory factors, namely biotope, biocoenosis, coastal influence, accessibility through dispersion, and oceanographic characteristics. Significant environmental models were assembled, and their fuzzy intersection and union applied. This resulted in two final biogeographic models for each year, which were used to predict the distribution of the species in following years. The biogeographic models exhibited a high predictive capacity, as most years accurately predicted colonisation in the following year or even multiple years ahead. Accessibility through dispersion and oceanographic characteristics were critical during the initial years of establishment, while complete establishment depended on all five factors together. Expansion to the whole northern Alboran coast was explained by favourable conditions for any of the explanatory factors, while all factors except coastal influence explained the saturation of the invasion. We conclude that the biogeographic models prove valuable in understanding the factors that contributed to the spread of R. okamurae in the northern Alboran Sea. This approach could help prevent further colonisation and mitigate the ecosystem and commercial consequences of R. okamurae's invasion.

Spatial Distribution and Potential Impact of Drifted Thalli of the Invasive Alga Rugulopteryx okamurae in Circalittoral and Bathyal Habitats of the Northern Strait of Gibraltar and the Alboran Sea

The arrival of a new invasive alga, Rugulopteryx okamurae, in the Strait of Gibraltar (SoG) in 2015 marked an unprecedented milestone in the North African and, later, in the European marine ecosystems. Nowadays, it is colonising vast infralittoral areas and significantly modifying some habitats and associated communities of the southern Iberian Peninsula. In recent expeditions, a high amount of free drifted thalli of this alga has been detected in different circalittoral and bathyal habitats of the northern SoG and the Alboran Sea. The present study combines quantitative data of this alga obtained with the use of a remotely operated vehicle (ROV) and a bottom otter trawl. The coverage–entanglement level of the drifted thalli on circalittoral and bathyal benthic invertebrates (e.g., not covering, covering only the basal part, covering one-third of the invertebrate, etc.) was also annotated from picture frames taken in locations with abundant drifted thalli. In underwater images, drifted thalli were mainly detected in circalittoral and bathyal bottoms of the northern SoG and the north-western Alboran Sea, between 50 to ca. 450 m depth. Nevertheless, abundant drifted thalli were also detected in bottom otter trawl samples from circalittoral bottoms of the north-central and north-eastern Alboran Sea. Small benthic organisms (e.g., encrusting sponges, hydrozoans, etc.) generally displayed low coverage–entanglement levels of drifted thalli. Nevertheless, large sessile and colonial benthic organisms with a complex three-dimensional morphology (e.g., gorgonians, colonial scleractinians) reached high levels of R. okamurae thalli entangled in different parts of their colonies. The drifted R. okamurae thalli entangled in these colonial suspension feeding organisms may hinder their feeding capability in the long term, resulting in habitat deterioration in the near future.

Seasonal and spatial dynamics of the phytoplankton community in the Salish Sea, 2015–2019

A chemotaxonomic approach (HPLC) was used to determine the phytoplankton composition for the Salish Sea (coastal NE Pacific Ocean). The method was applied to 721 samples collected between 2015 and 2019. Microscopy was used to build then verify the CHEMTAX matrix and CHEMTAX outputs. Statistical methods were used to describe the patterns of phytoplankton composition over space and time. HPLC produced a more complete picture of the phytoplankton community than previous studies relying on microscopy. Nine taxonomic groups and four phytoplankton functional types were identified: (1) centric diatoms were present year round and were dominant during the spring bloom; (2) small flagellates (cryptophytes, haptophytes, prasinophytes) and pennate diatoms were ubiquitous but generally not bloom-forming; (3) large flagellates (dinoflagellates, dictyochophytes, raphidophytes) were mostly absent but with occasional very large blooms; and (4) cyanobacteria were rare. The pigment violaxanthin was diagnostic for Heterosigma akashiwo, which formed the largest bloom observed in our study (75 μg/L Tchl a). Cluster and network analyses identified three regions based on similarities in phytoplankton composition: (1) Juan de Fuca Strait and tidally mixed areas, (2) central Strait of Georgia, and (3) northern Strait of Georgia. Seasonally, significant differences in taxonomic composition occurred between winter and spring, and interannually between 2015 (a warmer year) and 2017 (a cooler year). Centric diatoms were associated with stronger vertical mixing, whereas haptophytes were associated with higher temperatures, reduced vertical mixing and lower nutrients. The CHEMTAX matrix we present is robust and useful for future studies in this area.

Patterns of winter occurrence of three sympatric killer whale populations off eastern Vancouver Island, Canada, based on passive acoustic monitoring

Understanding habitat use patterns of animal populations across space and time is fundamental to identifying ecological requirements, and informing threat mitigation and conservation strategies. Persistent data gaps tend to occur with cryptic species in difficult-to-access environments, where the use of appropriate monitoring tools is indispensable for detection. Three populations of threatened and endangered killer whales occur year-round in waters off British Columbia, Canada; however, their winter habitat use patterns are not well known. Here we quantify wintertime use of the northern Strait of Georgia by these sympatric killer whale populations, revealing the importance of this previously understudied region. Using a network of passive acoustic monitoring devices deployed over three winter periods, we examine site-specific and regional patterns of occurrence of Bigg’s, and Southern and Northern Resident killer whales. All three populations frequented these waters in nearly every month from November to April, and across all study years. Bigg’s killer whales were detected most frequently, followed by Southern Residents, then Northern Residents. Population-specific differences in site use was apparent, with Southern Resident detections occurring more often than expected off the southwest side of Texada Island, while Northern Residents appeared to favor the east side of Texada Island. Remarkably, the patterns of winter use we observe in this region by Resident killer whale populations have seemingly persisted for at least 50 years. Additionally, we evaluate and discuss the effect of using multiple simultaneous recorders to characterize habitat use patterns. Lastly, we present a data-driven approach for estimating acoustic residence time, describe inter-population differences in winter residency in the northern Strait of Georgia, and discuss implications for critical habitat designation. This study fills important knowledge gaps related to killer whale winter occurrence off western Canada, highlighting the significance of the northern Strait of Georgia for these at-risk populations.

Operational interactions between humans and Indo-Pacific Finless Porpoises, Neophocaena phocaenoides: An integrated spatial model in the northern Strait of Hormuz

The Indo-Pacific Finless Porpoise (Neophocaena phocaenoides) is a little-known cetacean under human pressure in the Persian Gulf and the Gulf of Oman. In Iran, most sightings have been reported from the northern coasts of the Strait of Hormuz. We invested the spatial overlap between finless porpoise habitats and human activities in the Harra Protected Area and Biosphere Reserve in the north of the Strait of Hormuz. Suitable porpoise habitats were modeled using the Maxent model, employing 112 presence points and an array of physical seascape variables. A detailed (30 m) Landsat 8-derived depth layer was found as the most important factor determining porpoise distribution. The multi-criteria evaluation procedure was calibrated using a set of pairwise weighted and fuzzified layers including ship routes, and distance from main boat routes, coastal and port cities, and fishing zones to determine the intensity of human sea use. Results showed a significant spatial overlap of over 3,500 ha (8.7% of the region) between highly suitable porpoise habitats and human sea use areas, covering the whole entrance of the estuary where high-speed boats sail between northern and southern cities. Since the porpoise population is found in the study area only within the borders of the Harra Protected Area, limited fishing activities and low-speed boat movement inside the zone of overlap are suggested to lower the human-porpoise interaction in the region.

Drastic Fluctuation in Water Exchange Between the Yellow Sea and Bohai Sea Caused by Typhoon Lekima in August 2019: A Numerical Study

AbstractConnecting the Bohai Sea (BS) and Yellow Sea (YS), the Bohai Strait is vital in controlling physical‐biogeochemical conditions in the East Asian marginal seas. In August 2019, Typhoon Lekima moved northward inland into eastern China and caused drastic water exchange through the Bohai Strait. The specific variation and underlying dynamics involved were investigated with observations and high‐resolution numerical simulations. Volume transport featured an intense inflow followed by an intense outflow, with a fluctuation magnitude of 1.88 Sv, which was much greater than the seasonal‐interannual variations. The corresponding current patterns presented three phases: strait‐wide inflow, strait‐wide outflow, and outflow in the south and inflow in the north. The strait‐wide inflow was driven by strong east‐northeasterly winds through local Ekman dynamics. The strait‐wide outflow resulted from the dynamic adjustment of ocean currents accompanying the rapid weakening of easterly winds. The third current pattern was part of a large‐scale cyclonic circulation in the BS and North YS and was governed by different factors in the southern and northern straits. Further comparisons indicated that transport caused by winter storms and other typhoons in the year had opposite phase variations to that caused by Lekima. The underlying dynamics mainly involved local Ekman dynamics and/or remote wind forcing via the propagation of coastal trapped waves but could differ greatly from events. Finally, we found that to a large extent, geostrophic transport derived from the sea surface height difference across the Bohai Strait could be used as actual transport during synoptic weather events.

Abundance and Distribution of Macro- and Mesoplastic Debris on Selected Beaches in the Northern Strait of Malacca

Plastics account for 60–80% of marine debris worldwide, and, in 2021, Malaysia was the 28th largest plastic polluter in the world. In light of this finding, the Malaysian government has launched the Roadmap Towards Zero Single-Use Plastics 2018–2030 and the Plastics Sustainability Roadmap 2021–2030 to reduce plastic pollution and implement a circular economy for Malaysia. A comprehensive database of the status of plastic pollution in Malaysia is needed to achieve this target. This study aims to record the presence of macro- (>2.5 cm) and mesoplastic (0.5–2.5 cm) debris at selected beaches in the northern Strait of Malacca. All study sites are publicly accessible beaches (Pulau Songsong, Teluk Aling, and Pulau Gazumbo) except Pulau Lembu, which is in a Marine Protected Area (MPA). The debris was collected from predetermined transects on the beach and categorised according to its form and economic market segments in Malaysia. Most of the macro- (53–75% of total mass) and mesoplastics (52–80% of the total number) were accumulated in the backshore area. Public beaches such as Pulau Gazumbo and Pulau Songsong recorded the highest abundance of macroplastics, with 7.32 g/m2 and 9.77 g/m2, respectively. Teluk Aling recorded the lowest abundance of macroplastics (3.58 g/m2) but the highest in mesoplastics (0.55 items/m2). Most of the macroplastics found were packaging plastics such as plastic bottles, containers, and polystyrene foam debris. Although Pulau Lembu is an MPA, the amount of macroplastics found was considerably high (7.17 g/m2). Based on the beach cleanliness index, Pulau Gazumbo (−3.99) was the dirtiest site, followed by Pulau Lembu (−2.92) and Pulau Songsong (−2.85), while Teluk Aling (−1.63) was the cleanest site, which can explain the amount of macroplastic debris found. However, all the study sites’ cleanliness may not be ideal, as the indexes were less than zero due to the low availability of waste bins and insufficient frequency of beach cleaning. This may not be able to curb the effects of high anthropogenic activities conducted in addition to uncontrollable natural factors.

Estimation of the Spring Tide Bedload Transport at the Eastern Entrance of the Qiongzhou Strait

Marine sediment deposits near the Qiongzhou Strait have great potential as sources for beach nourishment and infrastructure industry aggregates. Estimation of bedload transport during the spring tide improves the understanding of the sediment movement characteristic under dynamic conditions, which would further favor the assessment and mining of marine sand resources. To study the bedload transport at the eastern entrance of the Qiongzhou Strait, the surficial sediment distributions were obtained through hundreds of sediment samples from field work. A semi-implicit cross-scale hydrological science integrated system model was adopted and validated to simulate the tidal currents in the Qiongzhou Strait. With field observation and simulated data, we estimated the spring tide bedload transport in the study area using the Bagnold Model. The transport rate in the study area was found to have large temporal and spatial variation. The net transport direction during the spring tide cycle was eastward in the southern parts of the strait and westward in the northern strait. Our research has important implications for regional engineering and marine resources management.

A clustering approach to determine biophysical provinces and physical drivers of productivity dynamics in a complex coastal sea

Abstract. The balance between ocean mixing and stratification influences primary productivity through light limitation and nutrient supply in the euphotic ocean. Here, we apply a hierarchical clustering algorithm (Ward's method) to four factors relating to stratification (wind energy, freshwater index, water-column-averaged vertical eddy diffusivity, and halocline depth), as well as to depth-integrated phytoplankton biomass, extracted from a biophysical ocean model of the Salish Sea. Running the clustering algorithm on 4 years of model output, we identify distinct regions of the model domain that exhibit contrasting wind and freshwater input dynamics, as well as regions of varying water-column-averaged vertical eddy diffusivity and halocline depth regimes. The spatial regionalizations in physical variables are similar in all 4 analyzed years. We also find distinct interannually consistent biological zones. In the northern Strait of Georgia and Juan de Fuca Strait, a deeper winter halocline and episodic summer mixing coincide with higher summer diatom abundance, while in the Fraser River stratified central Strait of Georgia, shallower haloclines and stronger summer stratification coincide with summer flagellate abundance. Cluster-based model results and evaluation suggest that the Juan de Fuca Strait supports more biomass than previously thought. Our approach elucidates probable physical mechanisms controlling phytoplankton abundance and composition. It also demonstrates a simple, powerful technique for finding structure in large datasets and determining boundaries of biophysical provinces.

Where do recruits come from? Backward Lagrangian simulation for the deep water rose shrimps in the Central Mediterranean Sea

AbstractBackward‐in‐time Lagrangian dispersion models can efficiently reconstruct drifters trajectories by linking known arrival positions to potential sources. This approach was applied to the deep water rose shrimp (Parapenaeus longirostris) in the Strait of Sicily (central Mediterranean Sea). The objective was to identify the potential spawning areas of the larvae that settle in the known nursery grounds of the northern sector of the Strait of Sicily, thus quantifying the extent of the potential contribution to recruitment from the surrounding regions. Numerical simulations were performed over 11 years (2005–2015) and for two different periods (spring/summer and autumn/winter) corresponding to the species' spawning peaks in the region. The persistence over time of potential spawning areas was identified through a Hotspot analysis of the backward trajectories end‐points, filtered to meet a suitable depth range for spawners. The results confirmed the expected downstream connectivity between spawning and nursery grounds along the Sicilian–Maltese shelf and, notably, indicated that these spawning grounds contribute to the high productivity and resilience of deep water rose shrimp fisheries in the northern Strait of Sicily more than the spawning grounds in surrounding regions. A minor and time‐varying contribution is due to potential spawning areas identified on the African shelf. These results are important to adequately define the geographical scale for the assessment and management of this important fishery resource in the Strait of Sicily. In particular, the assumption of a single stock that does not consider the spatial structure of the population should be revised for the purpose of fisheries management.

Dynamic coastal pelagic habitat drives rapid changes in growth and condition of juvenile sockeye salmon (Oncorhynchus nerka) during early marine migration

Migrating marine taxa encounter diverse habitats that differ environmentally and in foraging conditions over a range of spatial scales. We examined body (RNA/DNA, length-weight residuals) and nutritional (fatty acid composition) condition of juvenile sockeye salmon ( Oncorhynchus nerka) in British Columbia, while migrating through oceanographically variable waters. Fish were sampled in the stratified northern Strait of Georgia (NSoG); the highly mixed Johnstone Strait (JS); and the transitional zone of Queen Charlotte Strait (QCS). In 2015, body and nutritional condition were high in the NSoG but rapidly declined to reach lowest levels in JS where prey availability was low, before showing signs of compensatory growth in QCS. In 2016, juvenile salmon had significantly lower condition in the NSoG than in 2015, although zooplankton biomass was similar, condition remained low in JS, and no compensatory growth was observed in QCS. We provide evidence that differences in juvenile salmon condition between the two years were due to changes in the food quality available to juvenile fish. We propose that existing hypotheses about fish survival need to be extended to incorporate food quality in addition to quantity to understand changes in fish condition and survival between years.

Description of the first acoustic recording of spinner dolphins (Stenella longirostris) from the northern straits of Malacca, Malaysia (L).

Relatively little is known about spinner dolphins in Malaysian waters and the wider Southeast Asian region. This note represents the first known acoustic recording of the species sighted opportunistically in the northern Straits of Malacca. Over a brief 20 min sighting, 46 whistles were recorded and four tonal types were detected, with 54.4% being upsweep whistles. The whistle duration ranged from 36 to 977 ms and the frequency ranged from 6.6 to 23.8 kHz. Fifty-seven click trains with a mean interclick interval of 41.5 ± 19.3 ms were detected. These findings provide a baseline for future regional acoustic research on this species.

Studi Karakteristik Suhu Permukaan Laut (SPL) Di Perairan Selat Lombok Menggunakan Citra Satelit EOS Aqua MODIS

The Lombok Strait is a strait located between Lombok Island and Bali Island which connects the waters of the Bali Sea to the Indian Ocean, whose SST conditions vary with oceanographic-atmospheric conditions in the Indian Ocean and the Pacific Ocean. This research aims to determine the temporal and spatial SST in the North and South Lombok Strait. Therefore, this study divides the Lombok Strait area into two because of the influence of the Pacific Ocean and the Indian Ocean. The method used in this research is descriptive and statistical analysis. The highest average monthly SST in the northern and southern Lombok Strait occurred in April at 29.11 °C and the lowest in August at 26.82°C. For the average seasonal SST, the highest occurred at transition I of 28.86°C, and the lowest occurred in the eastern season at 27.39°C. The highest average annual SST occurred in 2010 at 28.83°C and the lowest occurred in 2018 at 27.69°C. The northern SST anomaly has the same fluctuation as ENSO with inversely proportional IOD. Southern SST anomaly has fluctuation which is inversely proportional to ENSO and IOD. The correlation between SST anomaly in the north and ENSO correlates 0.90 (very strong), while with IOD it correlates 0.12 (very low). The correlation between SST anomaly in the southern part and ENSO correlates -0.11 (very low), while with IOD it correlates -0.73 (strong)

In situ photosynthetic performance of Porites lutea inhabiting contrasting habitats of the Northern Straits of Malacca (NSoM), Malaysia

ABSTRACT Coral reefs in the Northern Straits of Malacca (NSoM), Malaysia, are frequently exposed to high concentrations of total suspended solids (TSS), thus reducing the light availability for photosynthesis. This study describes the photosynthetic performances of Porites lutea inhabiting contrasting habitats of Pulau Kendi, Pulau Songsong, and Pulau Payar in the NSoM. The light attenuation (Kd (PAR)) was significantly different between all sites, whereby highly turbid water of Pulau Kendi has the highest Kd (PAR) (m−1) = 0.8 ± 0.0 and TSS (mg/L) = 95.7 ± 2.5 in comparison to the protected reef in Pulau Payar, Kd (PAR) (m−1) = 0.5 ± 0.0 and TSS (mg/L) = 36.7 ± 0.4. Here, Pulse-Amplitude-Modulated fluorometry (PAM) and Rapid Light Curves (RLCs) indicate that P. lutea exhibits a different trend of photosynthetic performances to cope with in situ light availability. Turbid waters of Pulau Kendi were observed to provide some protection from light-induced photoinhibition whereby the maximum photosynthetic yield (F v /F m = 0.8 ± 0.0) was significantly higher than those in Pulau Payar and Pulau Songsong. This observation suggested that they could survive near darkness with low light availability for photosynthesis, but a significant reduction in photosynthetic capacity (rETRmax = 77.5 ± 7.4) was also observed. In contrast, greater photosynthetic capacities were observed in P. lutea inhabiting the high-light environment of Pulau Payar. This study emphasized that P. lutea can photoacclimate by maximizing light availability for photosynthesis to ensure survival in turbid nearshore environments.

The Invasive Macroalga Rugulopteryx okamurae: Substrata Plasticity and Spatial Colonization Pressure on Resident Macroalgae

The present study constitutes the first evaluation of the space colonization strategies performed by Rugulopteryx okamurae when co-occurring with the resident macroalgal community in the introduced areas. Since the first apparition of the nonindigenous macroalga in the Strait of Gibraltar, its high propagation capacity together with its colonization ability has enhanced the establishment success of the species in detriment of the resident biota. In this study, we carried out observational surveys during 2017–2020 in order to assess the coverage levels of R. okamurae on different lighting conditions, surface orientations, and substrata types (artificial and natural). Results revealed that, beyond the high percent coverages already reported at illuminated and semi-illuminated natural rocky habitats, R. okamurae is able to settle on a wide variety of artificial substrata. The settlement performance of the species was also investigated and different mechanisms underlying the space colonization were proposed. Thus, R. okamurae was observed interacting with 43 resident macroalgal species at generally illuminated rocky habitats of the northern Strait coasts. Six colonization mechanisms were proposed for spatial growth scenarios. Overall, results pointed out that, in most of the cases where the invasive species co-occur with the resident community, R. okamurae would be favored as regards spatial growth success. Competitive interactions and environmental factors which influence results obtained must be addressed in order to fully predict impacts on resident communities. Moreover, together with previous scientific works, overall data provided in this study highlight the need to urgent implement management measures focused on habitats susceptible to be invaded, as well as studies on the ecology and dispersal vectors of R. okamurae in the Strait of Gibraltar and adjacent areas.

Biometric Relationship of Tegillarca granosa (Bivalvia: Arcidae) from the Northern Region of the Strait of Malacca

This study on the growth pattern of the blood cockle Tegillarca granosa focused on the aspects of biometric prints on the shell, which aimed to predict the growth of the T. granosa population in the northern region of Malacca Strait. The local sample populations of the cockle were collected in three different intertidal areas called Lhokseumawe and Banda Aceh in Indonesia and Pulau Pinang in Malaysia. The biometric analysis showed that the length–weight relationship model of T. granosa populations in this region indicated that the cockle population generally had a negative allometric growth pattern (b < 3) or that shell length is more dominant compared to shell weight. Therefore, the result showed that the growth performance of T. granosa was not ideal, and the highest b value (the coefficient of biometric relationship) was recorded in Lhokseumawe, followed by Banda Aceh and Pulau Pinang. The value of the coefficient b could be affected by various factors such as environmental conditions, adaptation, and dietary patterns. Cluster analysis revealed that the population of T. granosa from the northern region of the Strait of Malacca was divided into two clusters, which were T. granosa from the northern Strait of Malacca (Banda Aceh and Lhokseumawe in Indonesia) and T. granosa from the Western Strait of Malacca (Pulau Pinang in Malaysia). The factors that might cause the differences in the biometric component of both clusters were at the geographical level on the source of population and local environmental parameters.

The Occurrence and Distribution of Benthic Foraminifera in Tropical Waters Along the Strait of Malacca

Foraminifera are shelled single-celled protists that are found in all marine environments. Benthic foraminifera either live in sediments or attach to surfaces on the seafloor. Understanding the distribution and ecological response of benthic foraminifera is crucial, as they can indicate past and current ocean conditions. However, the benthic foraminifera distribution along the busy Strait of Malacca, which connects the Indian Ocean (north) to the Java Sea (south), is undersampled. In this study, we collected 24 surface samples from the northern Strait of Malacca to understand the distribution of foraminifera assemblages in shallow tropical waters. A total of 49 species of benthic foraminifera were identified. Calcareous hyaline species dominated the assemblages, with an extremely low occurrence of calcareous porcelaneous species. The common calcareous hyaline taxa were Asterorotalia pulchella, Pseudorotalia schroeteriana, Discorbinella bertheloti, Ammonia tepida, and Heterolepa praecincta. Cluster analysis categorised the foraminiferal assemblages into three major groups. The first cluster (Group A) consisted of a more diverse assemblage of hyaline and agglutinated species that inhabited a mean water depth of 45 m. The second cluster represented a population that inhabited deeper water environments (average water depth of 59 m). Finally, the third cluster (Group C) consisted of a foraminifera assemblage that inhabited shallow coastal environments (average depth of 22 m) with higher organic matter enrichment. The multivariate canonical correspondence analysis (CCA) showed that the foraminiferal assemblages reflected the shallow to deep water transition in the Malacca Strait. Water depth, which defines the depositional environment, had a greater influence on foraminifera distribution here than organic matter and salinity.

Zooplankton variability in the Strait of Georgia, Canada, and relationships with the marine survivals of Chinook and Coho salmon.

The Strait of Georgia, Canada, has complex interactions among natural and human pressures that confound understanding of changes in this system. We report on the interannual variability in biomass of 12 zooplankton taxonomic groups in the deep (bottom depths greater than 50 m) central and northern Strait of Georgia from 1996 to 2018, and their relationships with 10 physical variables. Total zooplankton biomass was dominated (76%) by large-sized crustaceans (euphausiids, large and medium size calanoid copepods, amphipods). The annual anomaly of total zooplankton biomass was highest in the late 1990s, lowest in the mid-2000s, and generally above its climatological (1996-2010) average after 2011, although many individual groups had different patterns. Two latent trends (derived from dynamic factor analyses) described the variability of annual biomass anomalies underlying all zooplankton groups: a U-shaped trend with its minimum in the mid-2000s, and a declining trend from 2001 to 2011. Two latent trends also described the physical variables. The variability represented by these four latent trends clustered into two periods: 1996-2006, with generally declining zooplankton biomass and increasing salinities, and 2007-2018, with increasing zooplankton biomass and decreasing salinities. ARIMA modelling showed sea surface salinity at Entrance Island in the middle Strait of Georgia, the Pacific Decadal Oscillation, and the peak date of the spring phytoplankton bloom were significantly related to the two latent zooplankton trends. ARIMA models comparing zooplankton and physical variables with the marine survivals of four salmon populations which enter the Strait as juveniles (Chinook: Cowichan River, Puntledge River, Harrison River; Coho: Big Qualicum River) all included zooplankton groups consistent with known salmon prey; prominent among the physical variables were sea surface salinity and variables representing the flow from the Fraser River. These regressions explained (adjR2) 38 to 85% of the annual variability in marine survival rates of these salmon populations over the study time period. Although sea temperature was important in some relationships between zooplankton biomass and salmon marine survival, salinity was a more frequent and more important variable, consistent with its influence on the hydrodynamics of the Strait of Georgia system.

Phytoplankton Composition and Environmental Drivers in the Northern Strait of Georgia (Salish Sea), British Columbia, Canada

A 4-year (2015–2018) weekly to bi-weekly time series of phytoplankton biomass and composition derived from high-performance liquid chromatography (HPLC) phytoplankton pigments and Chemtax analysis is presented and used to investigate phytoplankton community dynamics at a station in the northern Strait of Georgia (NSoG). Through the time series, blooms were largely dominated by diatoms, which formed the bulk of annual biomass. Spring diatom bloom timing and magnitude varied widely and appears to have been driven by complex interactions of solar radiation, wind, stratification, and grazing. In turn, post-spring diatom blooms were mostly associated with nutrient renewal to the surface layer as suggested by redundancy analysis (RDA), which showed inverse relationships between diatoms and temperature and stratification. A single non-diatom bloom in July 2016, dominated by the silicoflagellate, Dictyocha sp., was the time series maximum biomass and occurred under warm, stratified conditions and a freshening of the surface layer: The Chemtax dictyochophyte group was positively linked to temperature and stratification through RDA. Outside of bloom conditions, diverse communities emerged with prasinophytes and cryptophytes showing persistent contributions and their highest biomass during summer. Uniquely, these groups often persisted through nutrient renewal and drawdown events typically associated with diatom blooms and suggestive of high grazing pressure and nutrient regeneration. The prevalence of these groups through diverse conditions likely precluded statistical links with environmental drivers. This time series is the first of its kind for the NSoG, creates a baseline for future analyses, and highlights the contributions by small species, particularly prasinophytes, to regional phytoplankton communities.

Assessment of Nutrient Supply by a Tidal Jet in the Northern Strait of Georgia Based on a Biogeochemical Model

AbstractWe present a coupled three‐dimensional biological‐physical model for the Salish Sea and evaluate it by comparison to nitrate, silicate, and chlorophyll observations. It accurately reproduces nitrate concentrations with Willmott skill scores, root‐mean‐square error, and bias ranging from 0.84–0.95, 4.02–6.5 μM, and −2.33–1.84 μM, respectively, compared to three independent discrete sample data sets. A prominent feature of the model output is a tidal jet emanating from Discovery Passage producing a downstream plume of elevated surface nitrate. The signal is present from April to September, when surface nitrate is otherwise drawn down. It has a weak but statistically significant correlation to Discovery Passage tidal velocity (R=0.37, p&lt;0.01). Within the turbulent jet and associated plume, the average rate of vertical nitrate supply due to mixing and advection across a depth of roughly 6 m is 0.46 μmol m−2 s−1 between 15 May and 20 August 2015, compared to 0.10 μmol m−2 s−1 for the northern Strait of Georgia as a whole. Close to Discovery Passage, where velocities and shear are strongest, the majority of the vertical nitrate flux is due to mixing. As velocities weaken downstream, vertical advection becomes more important relative to mixing, but vertical velocities also decrease. The tidal pulses out of Discovery Passage drive waves that contribute net upward nitrate flux as far south as Cape Lazo, 40 km away. The nitrate supply drives new production, consistent with existing observations. Similar dynamics have been described in many other tidally influenced coastal systems.