Introduction

Background & Rational

Holoplanktonic gastropods are mollusks that have evolved to complete their life cycle in the pelagic zone (Lalli & Gilmer, 1989). To these belong the subclasses Prosobranchia and Opisthobranchia. Especially the shell containing families, Heteropoda and the shelled and unshelled Pteropoda, have generated recent research interest due to their sensitive response to ocean acidity and great potential as bioindicators (Comeau, 2010; Bednaršek, 2012). However, their application is currently limited by knowledge gaps about their taxonomy, genetic diversity, ecology, and distribution patterns. 

Pelagic gastropods are an important component of the marine plankton and marine food webs, both as consumers of phytoplankton and other zooplankton, and as prey of carnivorous zooplankton, commercially exploited fishes, marine mammals, and sea birds. It has been estimated that they have a global biomass of 5x104 gC (Lalli and Gilmer, 1989 ; Hunt et al., 2008; Bednaršek et al., 2012). These gastropods also play an important role in ocean carbon flux, generating at least 12% of the total carbon flux worldwide (Berner and Honjo, 1981). The shell of these organisms is composed of aragonite (Figure 1) (Mucci, 1983; Kroeker et al., 2013), which makes them particularly vulnerable to ocean acidification and global warming, directly affecting their larval development, growth and reproduction (Bednaršek et al., 2016; Manno et al., 2017). This characteristic makes them considered as candidates to indicate the presence and absence of meteorological phenomena, ocean warming and anthropogenic ocean acidification (Comeau et al., 2010; Lischka and Riebesell, 2012).

Climate change and anthropogenic ocean acidification have severe consequences on many marine organisms (Byrne, 2011; Bednaršek et al., 2016). Ocean acidification has a major impact on calcifying plankton, particularly for bivalves and gastropods in which shell development becomes more energetically costly due to increasing in ocean pCO2 levels (Gazeau et al., 2013). Studies have confirmed negative effects on survival, calcification, growth, development, and abundance on diverse marine planktonic taxa (Kroeker et al., 2013; Bednarsek et al., 2019). Organisms under low pH, in combination with elevated temperatures may not be an optimal food source for many fish species, forcing them to rely more heavily on other new sources, potentially changing trophic interactions and the marine food web, which may significantly impact commercial species, ecosystems diversity and resilience (Bakun et al., 2015; Bednaršek et al., 2018). 

Research objectives 

These holoplanktonic gastropods are known for their cosmopolitan distribution (Van Der Spoel, 1972; Lalli and Gilmer, 1989), most species are found in warmer waters. However, research focused on this taxonomic group for the waters of the Eastern Tropical Pacific are scarce (Cruz, 1980; Moreno-Alcántara et al., 2017). Very little is known about how diversity and abundance of pelagic gastropods related to environmental conditions in coastal environments, and especially in the tropics. Therefore, in this study we described the community composition of the planktonic gastropods in the Bay of Panama (Figure 2) and we determined if there are direct correlations between their density and the environmental conditions to determine if there is an effect of the upwelling in the community of plankton and if so, can we distinguish which aspects of the upwelling drive these changes?

To asses this question, our main objectives are:

1. To characterize the spatiotemporal distribution patterns of pteropod communities across different sites in Panama Bay.

2. Quantify species composition and abundance across different sites (Las Perlas, Bay of Panama, Taboguilla).

3. Quantify the influence of environmental parameters (water temperature, pH, salinity, and dissolved oxygen) on the community structure and species distribution of pteropods across multiple coastal sites, and to identify the primary environmental drivers shaping these communities.