Retention and dispersion of virtual fish larvae in the Mesoamerican Reef

Highlights

• Retention in the Gulf of Honduras increases with depth.

• During November and December, the retention time increases in the Gulf of Honduras.

• Belize, Chinchorro channel and Cozumel channel could function as dispersal corridors.

• Retention in the Chinchorro channel can potentially promote self-recruitment.

Abstract

Retention and dispersion of virtual fish larvae were compared in four regions of the Mesoamerican Barrier Reef System: Gulf of Honduras, Turneffe Atoll, southern coast of Mexico (Xcalak/Chinchorro channel) and northern Chinchorro Bank. The results indicated that in the Gulf of Honduras, 20 % of the surface particles can be retained for up to 40 days, this retention was longer at 50 m depth. The area of Turneffe Atoll showed southward dispersion during November and December; whilst between Chinchorro Bank and Turneffe Atoll, it passes 70% of the released particles of the system. In Xcalak/Chinchorro channel countercurrent area, particles can be retained at the surface and at 50 m depth from September through December, and at 100 m throughout the year. In the northern system, which includes the northern Chinchorro Bank and Cozumel Island, the Yucatan Current rapidly dispersed the particles towards the Gulf of Mexico. These results were partially in agreement with previous studies of connectivity and dispersion. Our results suggest that the retention of particles in the Gulf of Honduras and Xcalak/Chinchorro channel could be higher than it was previously estimated, and that the self-recruitment rates of these two regions could be underestimated with potential population repercussions for species with a planktonic life cycle.

Introduction

A considerable number of marine resources of social, ecological and economical relevance present a planktonic stage that follows a distribution pattern according to the oceanic circulation (Fernández-Álamo and Färber-Lorda, 2006, Cowen et al., 2007). Dispersion and retention processes due to physical factors play an important role in population dynamics, since larvae dispersion allows to colonize new habitats or connects subpopulations with one another, while larval retention enhances local populations ability to maintain their own larval supply (self-recruitment) (Paris and Cowen, 2004, Cowen, 2006). Additionally, it has been determined that cyclonic eddies can function as retention structures of particles. They can also function as a temporary habitat that supplies food, so they can potentially increase the survival rate of several fish larvae (Danell-Jiménez et al., 2009, Apango-Figueroa et al., 2015, Shulzitski et al., 2015). In contrast, regions with intense velocity fields promote dispersion and therefore the geographical expansion of populations (Cowen et al., 2000, Holstein et al., 2014). Thus, dispersal processes could reduce self-recruitment, and populations will depend on the larvae supply from upstream (Hinrichsen et al., 2001, Cowen, 2006, Holstein et al., 2014). Moreover, regions with intense dispersion create connectivity routes between remote regions. The conceptualization of connectivity highways that unite a system through the exchange of biological material, allows us to create a conceptual scheme in which we can organize and classify the ecological system according to local processes and unite them from the dispersion or connectivity routes. Recently, a study of potential connectivity of virtual fish larvae in the Mesoamerican Barrier Reef System (MBRS), highlighted the relevance of oceanographic processes in the establishment of network connections between Marine Protected Areas. In the MBRS, the circulation pattern is defined by the Cayman Current, which is part of the Caribbean circulation system. When the Cayman Current impinges upon the Yucatan Peninsula, part of this current re-organizes as a northward flow that becomes the Yucatan Current (reaching speeds up to 2.5 ms⁻¹) (Carrillo et al., 2015). However, in the southern MBRS the currents are more variable and weaker than in the northern region; moreover, in the Gulf of Honduras, there is a mesoscale gyre known as the Honduras gyre (Fig. 1) (Ezer et al., 2004, Ezer et al., 2012, Soto et al., 2009, Carrillo et al., 2015). Furthermore, in the southern region of the system, the presence of cyclonic eddies near the reefs intensify a current that moves southward; however, when an anticyclone eddy is near the reef, the flow that predominates has a westward direction (Ezer et al., 2004, Sheng and Tang, 2004). Also, a countercurrent has been detected along the channel between mainland and Chinchorro Bank (Fig. 1) (Ezer et al., 2004, Carrillo et al., 2015, Carrillo et al., 2017). Based on several connectivity indexes and the associated circulation patterns Martínez et al. (2019) suggested a regionalization of four zones in the MBRS. The first zone was the Gulf of Honduras where the Honduras gyre dominates, a second zone was Belizean reefs with relatively high self-recruitment rates and with ecological relevance as source of fish larvae and as a bridge between the southern and northern MBRS. A third zone was characterized by a low larval arrival rate and the occurrence of a countercurrent, and finally a fourth zone that was influenced by the intense Yucatan Current (Fig. 1, Fig. 2) (Martínez et al., 2019). However, in Martínez et al. (2019), only the surface circulation (10 m depth) was used in the dispersion of virtual fish larvae to study connectivity and the role of the retention mechanisms was not completely explored. If the velocity of the current varies with depth then the dispersion/retention of particles could be enhanced or reduced with depth. For instance, if the velocity of currents reduces in deeper layers, species of fish larvae with vertical migrations could potentially be retained for a longer time in a given region (Haury et al., 1990, Denman and Garnet, 1995, Pineda, 1999, Paris and Cowen, 2004, Paris et al., 2007, Metaxas, 2011, Butler IV et al., 2011).

In this manuscript, we investigated the dispersion/retention of the virtual larvae (particles) in the MBRS at different depths. In particular, the southern MBRS showed weak and variable currents (compared with the well-defined Yucatan current with speeds up to 2.5 ms⁻¹, (Carrillo et al., 2015). It is expected that oceanographic features such as gyres (Honduras gyre) and countercurrents (Xcalak/Chichorro Channel) played a relevant role in the retention time of virtual larvae or particles. A series of numerical experiments of dispersion of passive particles were performed by implementation of a particle tracking model, considering the circulation pattern along the MBRS of daily surface currents from Global HYCOM outputs for the years 2010–2012 with 1/12°resolution. Dispersion of particles released at 10, 50 and 100 m depth was analyzed in four areas of the MBRS: (1) the gyre of the Gulf of Honduras, (2) the countercurrent area in the Xcalak/Chichorro channel, (3) the Turneffe Atoll, and (4) the northern of Chinchorro Bank.

The rest of the manuscript is organized as follows: Section 2 describes the particle dispersal simulations, Section 3 provides the results of the retention times, dispersal distance of particles and some basic statistics for the different sites and depths, Section 4 gives a discussion of the main results and gives the potential implications of retention and dispersion of larvae in the MBRS, and finally Section 5 presents the conclusions.