Lobster Settlement Research Articles

Bridging the spawner-recruit disconnect II: Revealing basin-scale correlations between zooplankton and lobster settlement dynamics in the Gulf of Maine

In recent decades, recruitment of young-of-year lobsters to benthic nursery habitats in the Gulf of Maine was regionally synchronized and exhibited correlative links with changes in the abundance of the copepod Calanus finmarchicus, a foundational zooplankton species of the pelagic food web. The spatial scale at which recruitment dynamics were correlated indicated that recruitment processes were not as strongly coupled to trends in spawner abundance as might be expected, but, rather, were influenced by common, ecosystem-scale processes. Here we explored how local- and basin-scale zooplankton dynamics and oceanographic indicators in the Gulf of Maine correlated with lobster settlement indices and each other since the late 1980s. Our analysis indicates that lobster settlement trends in southwestern Gulf of Maine study areas, from Midcoast Maine to Cape Cod Bay, tend to be significantly correlated with basin-wide C. finmarchicus dynamics and the composition of waters entering the Gulf of Maine through the Northeast Channel. In contrast, lobster settlement in the northeastern Gulf, from Penobscot Bay to the Bay of Fundy, tended to correlate more strongly to C. finmarchicus variability in the Bay of Fundy region, which was distinct in earlier years but converged with the broader basin-scale processes in the latter years. Our results are consistent with the hypothesis that the combined effect of climate-related declines in abundance and phenological shifts of C. finmarchicus have contributed to declines in lobster settlement over the past decade, and justify further research into the mechanisms of this interaction. These changes also align with the weakening influence of cold Labrador Slope Water and strengthening effects of warm Gulf Stream waters that precipitated an ecosystem-wide regime shift in the Gulf of Maine over the past decade and may have greater implications for lobster recruitment than previously suspected.

Larval presence and settlement of the American lobster (Homarus americanus) in a changing southern New England estuary

During the late 1980s and early 1990s, the American lobster (Homarus americanus) fishery boomed in southern New England, but starting in the early 2000s lobsters declined in the nearshore regions and the fishery retracted. While previous research has focused on the causes for the declining numbers of adult lobsters in the region as well as lobster settlement, lobster larvae were not sampled in Rhode Island waters. Additionally research was mixed on the origin of lobster larvae found inshore. To examine larval presence in coastal Rhode Island, weekly net tows were conducted at the mouth of Narragansett Bay during summer from 2019 to 2021, and light traps were deployed in 2020 and 2021. Time series segmentation and generalized linear models assessed trends and connections between lobsters caught in trawl surveys, commercial landings data, lobster settlement data, bottom water temperatures, and climate indices. Larval supply to Narragansett Bay is very low and mostly concentrated in the East Passage where ocean water flows into the bay, suggesting that a failure in larval supply from offshore sources is harming local population levels. Time series segmentation and models indicate that declines in lobster settlement followed the decline in adult lobsters in coastal Rhode Island, not Narragansett Bay. Altogether, the data suggest that larval lobster are transported inshore from spawning stock outside the bay. Present circulation patterns combined with the movement of lobsters into deeper waters has made the transport of larvae to Narragansett Bay unlikely.

Recruitment of Psostlarval Spiny Lobster, Stone Crabs, and Larval Fish to Back-Reef Nursery Habitats in the Florida Keys, USA

Back reef areas contain a mosaic of relatively shallow habitats that serve as a key nursery for reef species. Expansive back reef habitats in the lower Florida Keys, USA border the Atlantic Ocean and the Gulf of Mexico. A combination of floating, artificial settlement substrates and plankton nets moored in channels connecting coastal waters and back reef habitats quantified spiny lobster (Panulirus argus) and stone crab (Menippe sp.) settlement, and larval fish ingress, respectively, during 1999 and 2002–2003. The key finding was that channels connecting coastal waters with back reef areas serve as conduits for ingressing larval spiny lobster, stone crabs, and fishes. The results highlight the important role of Atlantic Ocean sources of spiny lobster pueruli and lutjanid fish larvae in this back reef system, and Gulf sources of stone crabs. Spiny lobster settlement generally peaked in August and September and occurred on the Atlantic Ocean side of this back reef system; settlement of stone crabs peaked at the same time as spiny lobster yet occurred predominantly on the Gulf side. Recruitment of larval fish was higher on the Atlantic than the Gulf side, with 37% of fish species collected nearly exclusively on the Atlantic side and about 25% collected nearly exclusively on the Gulf side. Channel habitats appear critical to supporting the nursery role of back reef habitats and should receive special consideration in future ecosystem studies, as well as during spatial planning and evaluations of essential fish habitat.

The American Lobster Settlement Index: History, lessons, and future of a long-term, transboundary monitoring collaborative

Understanding the processes that influence recruitment variability in marine populations has been a long-standing challenge for resource management. Quantifying abundance at early life stages for marine fish and invertebrates with complex life histories can be difficult and require unconventional sampling approaches. However, the benefit of developing appropriate tools to sample early life stages is that, together with associated demographic and environmental information, the data can provide insights into the causes and consequences of recruitment variability, allowing prediction of older life stage abundance. Before the 1980s, the earliest benthic life stages of the American lobster (Homarus americanus) eluded quantitative field surveys. With the development of diver-based and vessel-deployed sampling methods over the past three decades, the American Lobster Settlement Index (ALSI) program has expanded into a regional, transboundary commitment to better understand lobster settlement processes and forecast future fishery trends for what has become the most valuable single-species fishery in North America. In this context, “settlement” is a shorthand for the annual recruitment of young-of-year lobster to coastal nurseries, as postlarvae settle to the seabed at the end of larval development. Here, we review the development and products of the ALSI program, first outlining the goals, methods, and data products of the program. We then highlight how the program has advanced the scientific knowledge on pre- and post-settlement processes that influence the fate of a cohort from egg hatch to harvest, which provides insight into the spawner-recruit relationship. Lastly, we provide guidance for future research recommendations building on the ALSI science to-date, some major elements of the program that have allowed for its success, and considerations for maintaining the ALSI program. By highlighting the uniqueness and contributions of the ALSI program, we hope it serves as a model for other scientists, managers, and industry collaborators aiming to understand recruitment processes for species over a broad geographic area.

Identifying the Environmental Factors Affecting Puerulus Settlement of the Spiny Lobster, Panulirus homarus in Awang Bay, Lombok Island

This research aims to observe the settlement of puerulus lobster larvae in the waters of Awang Bay in relation to the spatial and temporal fluctuations in aquatic environmental conditions. This research was conducted from August to October 2020 in the waters of Awang Bay, Lombok Island. The main data collected in this study is puerulus settlement,while the supporting data are physical, chemical and biological parameters of the waters. Observations of the aquatic environment are carried out in-situ, namely direct measurements in the field and analysis of satellite images. The collected data were analyzed by multiple regression analysis. The results showed that the distribution of sea surface temperature and chlorophyll-a in the waters of Awang Bay and its surroundings based on satellite imagery during August to October ranged from 25-32 °C and 0.1370 - 2.3532 mg/m3 respectively. Warm temperatures and chlorophyll-a are concentrated in coastal areas and are decreasing towards the offshore direction. The nine environmental parameters studied contained two parameters that significantly influenced individually on puerulus lobster settlement, namely the abundance of plankton and temperature. Meanwhile, brightness, current velocity, dissolved oxygen, salinity, pH, phosphate and nitrate had no significant effect. The significant relationship between plankton abundance and temperature and puerulus lobster settlement was due to plankton being the main food for larvae, and the sea water temperature was still relatively stable so that lobster seeds still survived and could support puerulus lobster settlement.

Incorporating spatial heterogeneity and environmental impacts into stock-recruitment relationships for Gulf of Maine lobster

ABSTRACT Functional stock-recruitment relationships (SRRs) are often difficult to quantify and can differ over space. Additionally, climate change adds to the complexity of recruitment dynamics. This paper's aim was to incorporate spatial heterogeneity and environmental effects on productivity in SRRs with American lobster in the Gulf of Maine (GOM) as a case study. GOM lobster recruitment has substantially increased since the mid-2000s, due to improved survival rates of pre-recruits and increased spawning stock biomass (SSB). GOM bottom water temperatures have increased at a rate of 0.2ºC per decade, which caused lobster settlement area to expand and improved survival rates. We first estimated local SSB using bottom trawl survey data and a geostatistical model. Using estimated SSB, recruitment data from a ventless trap survey, and an interpolated bottom water temperature field, we developed modified Ricker stock-recruitment models accounting for spatial heterogeneity and temperature impacts with varying coefficient generalized additive models. Results showed that temperature significantly impacted recruitment. Changes in temperature mediated productivity differed between the eastern and western GOM. Our study demonstrated that the incorporation of spatial heterogeneity and environmental effects impacts our understanding of SRRs. These methods can be applied to other species to understand recruitment dynamics influenced by climate change.

The brighter side of climate change: How local oceanography amplified a lobster boom in the Gulf of Maine

Ocean warming can drive poleward shifts of commercially important species with potentially significant economic impacts. Nowhere are those impacts greater than in the Gulf of Maine where North America's most valuable marine species, the American lobster (Homarus americanus Milne Edwards), has thrived for decades. However, there are growing concerns that regional maritime economies will suffer as monitored shallow water young‐of‐year lobsters decline and landings shift to the northeast. We examine how the interplay of ocean warming, tidal mixing, and larval behavior results in a brighter side of climate change. Since the 1980s lobster stocks have increased fivefold. We suggest that this increase resulted from a complex interplay between lobster larvae settlement behavior, climate change, and local oceanographic conditions. Specifically, postlarval sounding behavior is confined to a thermal envelope above 12°C and below 20°C. Summer thermally stratified surface waters in southwestern regions have historically been well within the settlement thermal envelope. Although surface layers are warming fastest in this region, the steep depth‐wise temperature gradient caused thermally suitable areas for larval settlement to expand only modestly. This contrasts with the northeast where strong tidal mixing prevents thermal stratification and recent ocean warming has made an expansive area of seabed more favorable for larval settlement. Recent declines in lobster settlement densities observed at shallow monitoring sites correlate with the expanded area of thermally suitable habitat associated with warmer summers. This leads us to hypothesize that the expanded area of suitable habitat may help explain strong lobster population increases in this region over the last decade and offset potential future declines. It also suggests that the fate of fisheries in a changing climate requires understanding local interaction between life stage‐specific biological thresholds and finer scale oceanographic processes.

Mesoscale circulation determines broad spatio-temporal settlement patterns of lobster.

The influence of physical oceanographic processes on the dispersal of larvae is critical for understanding the ecology of species and for anticipating settlement into fisheries to aid long-term sustainable harvest. This study examines the mechanisms by which ocean currents shape larval dispersal and supply to the continental shelf-break, and the extent to which circulation determines settlement patterns using Sagmariasus verreauxi (Eastern Rock Lobster, ERL) as a model species. Despite the large range of factors that can impact larval dispersal, we show that within a Western Boundary Current system, mesoscale circulation explains broad spatio-temporal patterns of observed settlement including inter-annual and decadal variability along 500 km of coastline. To discern links between ocean circulation and settlement, we correlate a unique 21- year dataset of observed lobster settlement (i.e., early juvenile & pueruli abundance), with simulated larval settlement. Simulations use outputs of an eddy-resolving, data-assimilated, hydrodynamic model, incorporating ERL spawning strategy and larval duration. The latitude where the East Australian Current (EAC) deflects east and separates from the continent determines the limit between regions of low and high ERL settlement. We found that years with a persistent EAC flow have low settlement while years when mesoscale eddies prevail have high settlement; in fact, mesoscale eddies facilitate the transport of larvae to the continental shelf-break from offshore. Proxies for settlement based on circulation features observed with satellites could therefore be useful in predicting broadscale patterns of settlement orders of magnitudes to guide harvest limits.

Spatial surface temperature correlates of American lobster (Homarus americanus) settlement in the Gulf of Maine and southern New England shelf

American lobster, Homarus americanus H. Milne-Edwards, 1837, populations along the east coast of North America are geographically distributed over some of the steepest latitudinal ocean temperature gradients in the world. A disconnect between spawner biomass and postlarval settlement, i.e., young-of-year (YoY) recruitment, to the sea bed at the end of the larval season highlights the role of external environmental factors. To understand the spatial dimension of sea surface temperature correlates of settlement, we compared over two decades of inter-annual variation in lobster settlement at three oceanographically contrasting areas: the Bay of Fundy, coastal Gulf of Maine, and southern New England, with satellite-derived sea surface temperature anomaly (SSTa) patterns over the coastal regions and shelf waters. Correlations were performed between the settlement time series and monthly SSTa maps at time lags relevant to larval hatching, development, transport, and settlement. Settlement was significantly and positively correlated with SSTa in southern New England, showing associations with upstream areas over Georges Bank and southern Nova Scotia during months when larvae are expected in the water column (July–August). The Gulf of Maine site was correlated with SSTa in the immediate vicinity of the settlement site, and only in the month of settlement sampling. Settlement at the Bay of Fundy site was not correlated to SSTa patterns. The observed associations are consistent with larval advection by residual oceanic flow structure in the region, and are further supported by studies on lobster larval supply and genetic connectivity reported in the literature.

Evaluation of Effectiveness of Fixed‐Station Sampling for Monitoring American Lobster Settlement

AbstractThe American lobster Homarus americanus supports one of the most valuable fisheries in the USA. One of the important monitoring programs is for benthically settled lobsters, which closely relates to recruitment. The lobster settlement sampling program follows a fixed‐station design. However, the performance of this design has not been evaluated, and we are unclear if the design can capture the temporal dynamics of settlers, in particular in response to changes in spatial distribution of lobster in the last 2 decades. In this study, we compared the fixed‐station design with a random sampling design for the mid‐coast region of the Gulf of Maine. We developed a generalized additive model (GAM) to quantify the relationship between habitat variables and density of early benthic phase and older juvenile lobsters by using the data from inshore trawl surveys from 1989 to 2012. The GAM model was then used to simulate putative true populations using the habitat variables. The two different sampling designs were applied to sample the simulated true populations. The fixed‐station sampling design tended to underestimate the true density but could capture the temporal trends in settler density. A persistence index analysis suggests that the fixed‐station design could identify interannual change of the lobster settler density. This study suggests that fixed‐station sampling design is effective in monitoring temporal changes in settler density but could not be used for the estimation of absolute density of settlers.Received December 16, 2014; accepted July 9, 2015

Settlement and early survival of southern rock lobster, Jasus edwardsii, under climate-driven decline of kelp habitats

Abstract Kelp habitats provide food, refuge, and enhance the recruitment of commercially important marine invertebrates. The southern rock lobster, Jasus edwardsii, supports valuable fisheries in southern Australia and New Zealand. Kelp habitats once covered large areas of inshore reef around Tasmania, Australia, but coverage has reduced over the last few decades due to climate change, especially off the eastern coast of the island. We investigated whether the kelp influences the settlement of lobster post-larvae to artificial collectors and how the presence of kelp affected the overnight predation on the early benthic phase (EBP). Settlement of lobster was tracked over 6 months using crevice collectors that had either natural or artificial giant kelp, Macrocystis pyrifera attached, or nothing attached (control). Collectors with natural kelp had higher catches than those with artificial kelp or controls (p = 0.003), which suggested enhanced settlement through chemical attraction. Additionally, we measured overnight predation of the EBP in barren and kelp habitats individually tethered to artificial shelters. The kelp habitat was dominated by brown macroalgal species of Ecklonia radiata, Phyllospora comosa, and M. pyrifera, while the barren was devoid of macroalgae. Survival of the EBP was higher (∼40%) in the kelp habitat than in the barren habitat (∼10%) due to differences in predation (p = 0.016). These results suggest that the kelp habitat improves the recruitment of J. edwardsii and that decline in this habitat may affect local lobster productivity along the east coast of Tasmania.

Predation by green crab and sand shrimp on settling and recently settled American lobster postlarvae

Very little is known about predation on early life stages of the American lobster, Homarus americanus Milne Edwards, 1837, including the identity of predators and the threat they represent. In this laboratory experiment, we investigated the predatory threat that green crabs, Carcinus maenas (Linnaeus, 1758), and sand shrimp, Crangon septemspinosa Say, 1818, represent to settling and recently-settled lobster postlarvae. Lobster survival within 48 hours varied between 80-100% in control aquaria. In contrast, survival was only 40-60% in the presence of sand shrimp and 0-20% in the presence of green crab. Some sand shrimp were observed successfully catching and preying upon lobster as they were exploring the substrate for settlement, whereas green crab seem to have captured lobsters after they had adopted a benthic mode of existence. Since both of these predators commonly inhabit shallow cobble-bottom habitat where lobster settlement occurs, they could be important predators of young lobsters. Given these findings, we believe that future research should undertake the challenging task of confirming predation by green crab and sand shrimp on young lobsters in nature, and we suggest that molecular analysis of predator gut contents is the most promising approach to this question.

Large‐scale coherence in New England lobster (Homarus americanus), settlement and associations with regional atmospheric conditions

AbstractTime series of American lobster (Homarus americanus) postlarval settlement from southern New England to Atlantic Canada exhibit many common features, and a cluster analysis indicates a block of regions extending from Massachusetts to Maine that have coherent interannual variations. The spatial scale of this block suggests that variability in settlement is related to large‐scale, rather than local, processes. We examined the association between settlement at six reference regions and monthly mean atmospheric conditions (temperature, geopotential height, westerly and southerly wind components, and wind curl) from the North American Regional Reanalysis. We first extracted the dominant modes of variability in monthly averaged geopotential height, temperature, and wind curl. The leading mode from September, which represents high geopotential height, warm temperatures, and negative wind curl throughout the study area, was strongly correlated with settlement at most of the regions. The third mode from August, which represents enhanced southwesterly winds, was correlated with settlement in Rhode Island. Correlations between local atmospheric conditions and lobster settlement confirm the principal component results. Settlement was correlated to varying degrees with geopotential height (positive), temperature (positive) and wind curl (negative) with lobster settlement at the northern sites, with temperature being a stronger indicator in the north and curl a stronger indicator in the south. Rhode Island settlement was strongly correlated with August westerly winds. The correlation between settlement and atmospheric conditions could improve our understanding of stock‐recruit relationships for lobster populations and provides one mechanism for how climate change could impact lobsters.

Near-bottom hydrodynamic effects on postlarval settlement in the American lobster Homarus americanus

Following a planktonic larval phase, American lobster Homarus americanus postlarvae seek out appropriate habitat in which to settle and develop through a shelter-restricted juvenile phase. Previous studies have shown that lobster postlarvae exhibit strong directional swimming ability, distinct bottom-searching behaviours, and clear responses to physical and chemical cues at settlement. However, most laboratory experiments have been conducted in still water and little is known about how hydrodynamics affect lobster settlement. We conducted flume experiments with different sizes of cobble to investigate the effect of moderate flow (~7.5 cm s–1 free stream velocity) on postlarval swimming behaviour and settlement. In 1 h trials, significantly more postlarvae settled in flow than in still water. Postlarvae in flow were more likely to encounter bottom substrate than postlarvae in still water. Cobble size had no significant effect on settlement. Behavioural observations indicated that postlarval behaviour is modified by flow. In contrast to still water, postlarvae in flow appeared to deliberately sink and were entrained by bottom turbulence, thereby contributing to higher substrate encounter and settlement rates. Postlarvae in flow performed significantly fewer dives and exhibited fewer bottom searching behaviours than postlarvae in still water. Bottom flow therefore affects settlement frequency by influencing encounter rates through an interaction between passive and active processes. These results suggest that lobster settlement behaviour may be affected by spatial and temporal differences in flow and should therefore be considered when examining and predicting settlement patterns.

Connectivity of lobster (Homarus americanus) populations in the coastal Gulf of Maine: part II. Coupled biophysical dynamics

AbstractWe used a coupled biophysical model to investigate larval transport and connectivity patterns in the Gulf of Maine lobster (Homarus americanus) population. Biological ‘particles’ were released at over 21 000 locations every 10 days over a 4‐month hatching period, and were followed from hatching through late postlarval stage. In addition to circulation and dispersion, model calculations included spatial patterns of egg production, temporal patterns of hatching, temperature‐dependent development, vertical distribution and mortality. We ran the model for three larval production seasons using the same hatching patterns and individual‐based modeling parameters but different flow patterns in the coastal current system. Model results gave distribution and abundance patterns of competent postlarvae that closely resembled observed, alongshore patterns of lobster settlement density. We evaluated the relative contribution of all source regions to the total number of competent postlarvae in a series of medium‐size zones along the coastal shelf, many of which are used in lobster management. Connectivity depended on many factors, including patterns of egg production and transport, and the location and size of the receiving zones. Self recruitment ranged from a few percent to >90% of competent postlarvae. Although it was common for postlarvae to come from many, often distant, sources, most of the competent postlarvae in a zone originated within one to two zones in the prevailing ‘up‐stream’ direction, forming shorter connections along the coast than the energetic currents might otherwise suggest. Inshore migrations during summer hatching may contribute to these shorter patterns of connectivity. Transport in the prevailing ‘upstream’ direction was also indicated.

Lipid nutrition and settlement behaviour in American lobster Homarus americanus

This study examines the effects of varying dietary lipids on growth, survival, lipid com- position and behaviour in lobster Homarus americanus (Milne Edwards, 1837) postlarvae. Lobsters were fed one of 3 diets during their early ontogeny: (1) Artemac, a widely used Artemia replacement; (2) a ternary mixture consisting of Artemac, frozen Artemia adults and Artemia flakes; or (3) a mix- ture of live A. salina nauplii and adults. We evaluated the olfactory capacity (response to predator odour plume) and cryptic behaviour (ability to hide during settlement) of lobster postlarvae as a function of these diets and the lipid and the fatty acid composition of lobsters. Growth and survival of lobster postlarvae were highest in those fed live Artemia, followed by the ternary mix, then Artemac. The low performance of lobster postlarvae fed Artemac may be attributable to dietary deficiencies in phospholipids (PLs) or 20:4n-6 and coincided with low levels of endogenous triacylglycerols (TAG). Those lobsters fed live Artemia showed low levels of 22:6n-3 and 20:5n-3 compared to levels occur- ring in wild animals. Here we report the selective incorporation of 20:4n-6, 20:5n-3 and 22:6n-3 to polar lipids and, to a lesser extent, to neutral lipids in lobsters. Finally, lobster postlarvae fed the 3 experimental diets responded to a predator odour plume by reducing their activity levels and increas- ing the time spent swimming downstream. However, lobster settlement behaviour varied as a func- tion of the diet: low-performing lobsters fed Artemac were less active than those fed the other diets, presumably due to low levels of endogenous TAG or changes in dietary long-chain PUFA.